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Power Systems and High Voltage Laboratory

Annual Report

2003

eeh elektrische energieübertragungund hochspannungstechnik

Annual Report 2003

Issued by

Power Systems and High Voltage Laboratory (Institut für Elektrische Energieübertragung und Hochspannungstechnologie)

Swiss Federal Institute of Technology (ETH) Zürich

ETH Zentrum, Physikstrasse 3, CH-8092 Zürich

Power Systems Laboratory Phone: +41 – 1 –632 41 86 Fax: +41 – 1 –632 12 52 Email: [email protected]

High Voltage Laboratory Phone: +41 – 1 –632 27 77 Fax: +41 – 1 –632 12 02 Email: [email protected]

Front cover: Conceptual view of a power system with Wide Area Monitoring

and Control. See page 20 Back cover: Electrical field simulation in a two-dimensional representation of

the switching chamber of a generator circuit breaker. Field strength is depicted by color, where blue corresponds to low strength and red high strength. The simulation is designed to gather information relevant to the placement of electric field probes exterior to the breaker chamber.

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Preface

Dear Friends of the Laboratory, The size of the research staff has during the last year stabilized at a level of about 30 active researchers, among which around 25 are PhD students. This seems to be an appropriate size with regard to available resources in form of office space, senior researchers, and funding. As seen from the detailed descriptions of the research projects in this annual report, many of the projects are carried out in collaboration with or with support from industrial partners. We are grateful for the confidence in the work performed at the laboratory shown by our external sponsors. Members of the staff have also been very active in different international conferences, workshops, and seminars by presenting papers and results based on the research results from various projects. Many of the papers and reports can be found at our homepage, www.eeh.ee.ethz.ch, where the progress of the different research projects is continuously updated. We are particularly pleased that the project concerning Future Energy Networks has gained additional momentum. At the moment four PhD students, two from the power systems laboratory and two from the high voltage laboratory, are involved in the project, and two industrial partners, ABB and Areva (former Alstom), are sponsoring the project. Discussions are going on with additional external partners. We also hope that our colleagues from the power electronics laboratory and automatic control laboratory could join us with collaborators during the next year. It is our intention and hope that we through this project can contribute to improving the efficiency and sustainability of the energy supply in the future, which we believe will be one of the most important questions in the coming decades. More about this project can be found on page 85. The spin-off company Plexim, which was formed by two members of the power systems laboratory two years ago and has its office in direct connection with the power systems laboratory, has been successful in promoting its products. During the year a project involving Plexim, ABB, and the power systems laboratory, was approved by KTI, Swiss Federal Commission for Technology and Innovation. This new project aims at further developing the products offered by Plexim, see page 22. We wish the founders of Plexim, Drs J. Allmelling and W. Hammer, all the best with their company. During the year Frau B. Rutz retired as secretary of the high voltage group after many years in this capacity. We want to thank Frau Rutz for excellent services and her positive attitude, and we hope that she will enjoy her retirement. We also want to welcome Frau K. Sonderegger as new secretary in the group. It is our hope that she will find our laboratory a stimulating and interesting place to work. Least but last we want to thank all the personnel of the laboratory for their enthusiastic and excellent work performance. The most important asset of an

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academic institution is its staff, and thanks to the good ideas and hard work of all our collaborators we can conclude that 2003 was another successful year of the laboratory. G. Andersson K. Fröhlich

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Contents

PREFACE III

CONTENTS V

ACTIVITIES OF THE POWER SYSTEMS LABORATORY 1

1. Organisation...................................................................................................... 1 2. Teaching.............................................................................................................3 2.1 Lectures 3 2.2 Seminars 5 2.3 Student Projects 5 2.4 Diploma Projects 5 2.5 Excursions 6

3. Research Activities............................................................................................7 3.1 Completed PhD Theses 7 3.2 Current Projects 11 3.3 Spin-Off Activities 22

4. Publications and Reports...............................................................................23 4.1 Publications 23 4.2 Reports 24

5. Presentations ..................................................................................................25

6. Conferences and Visits ..................................................................................27 6.1 Conferences and Workshops 27 6.2 Visits 29 6.3 Awards 29

ACTIVITIES OF THE HIGH VOLTAGE LABORATORY 31

1. Organisation.................................................................................................... 31 2. Teaching...........................................................................................................33 2.1 Lectures 33 2.2 Student Projects 35 2.3 Diploma Projects 35 2.4 Excursions 36

3. Research Activities..........................................................................................37 3.1 Completed PhD Theses 37 3.2 Current projects 41 3.3 Services offered 74

4. Publications and Reports...............................................................................75 4.1 Publications 75

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5. Presentations ..................................................................................................77

6. Conferences and Visits ................................................................................. 79 6.1 Conferences and Workshops 79 6.2 Events 81 6.3 Visits 81

JOINT ACTIVITIES 83

1. Colloquia ......................................................................................................... 83

2. Vision 'Future Energy Networks'................................................................. 85

Activities of the Power Systems Laboratory

1. Organisation Head: Prof. Dr. Göran Andersson

Secretary: Rita Zerjeski

Scientific Staff: Dr. sc. techn. Jost Allmeling Dipl. El.-Ing. Martin Geidl from 1 July 2003 Dipl. El.-Ing. Wolfgang Hammer Dipl.-Ing. Andrei Karpatchev until 15 October 2003 Dipl. El.-Ing. ETH Gaudenz Koeppel Dipl. Wirtsch.-Ing. Thilo Krause Mirjana Milosevic, M.Sc. El.Eng Derek Poon, cand. B.El.Eng from 15 May 2003 Rusejla Sadikovic, M.Sc. El.Eng Dipl. El.-Ing. ETH Christian Schaffner Marek Zima, M.Sc. El.Eng

Scientific Associates: Prof. em. Dr. Hans Glavitsch

External Lecturers: Dr. Rainer Bacher, Bundesamt für Energie, Bern Dr. Dieter Reichelt, Technische Betriebe, Kreuzlingen Dr. Christian Rehtanz, ABB Power Technologies Management Ltd

1. ORGANISATION

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ACTIVITIES OF THE POWER SYSTEMS LABORATORY

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2. Teaching The lectures and laboratory classes listed in the following section are part of the curriculum of the Electrical Engineering Department and are conducted by the staff of the Power Systems Laboratory. Details of the entire electrical engineering curriculum can be provided on application (list of lectures, option proposals). 2.1 Lectures

5th semester 4G Electric Power Systems Andersson, G. Elektrische Energiesysteme Fröhlich, K.

Structure of electric power systems; symmetric three phase systems; modelling of power transformers, generators and transmission lines; analysis of symmetrical and unsymmetrical three phase systems; transient switching phenomena; basics of current interruption; principles and applications of distribution- and transmission switchgear; basics of insulation coordination.

6th semester 4G Modelling and Analysis of Power Networks Andersson, G. Modellierung und Analyse elektrischer Netze

The electrical power transmission system, the network control system, requirements for power transmission systems (supply, operation, economics), network planning and operation management, models of N-port components (transmission line, cable, shunt, transformer), data specification per unit (p.u.), Linear Modelling of networks, Linear und non-linear calculation (NewtonRaphson), non-linear load flow (specification and solution methods), threephase und generalized short circuit current calculation, further applications of load flow calculation. Introduction to dynamics and stability in power systems. Rotor angle and voltage stability. Equal area criterion. Control of power systems.

7th semester 4G Optimization of Liberalized Electric Power Systems Bacher, R. Optimierung liberalisierter elektrischer Energiesysteme

Mathematical optimization methods, Karush-Kuhn-Tucker optimality conditions, Equality constrained non-linear optimization, Linear Programming (LP) (Simplex, Interior Point), Quadratic Programming (QP) and applications; Non-linear optimization; Goals of a power exchange (PX), of the "independent system operator" (ISO), of the regulatory institutions, of the new electric power utilities; Principles of optimization of a power exchange: Offer-Bids; Optimal regulated network operation: Payments for network use, long- and medium term network optimization as goals; Handling of network security limitations by optimization methods; Optimization methods to determine the efficiency of networks; Optimization of ancillary services as part of the liberalized electric power system.

2. TEACHING

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7th semester 2G Portfolio and Risk Management in a Liberalized Market 1 D. Reichelt Portfolio und Risk Management im liberalisierten Strommarkt 1

Open power markets all over the world, market models of the European countries, Swiss electricity market today, pan-european power trading, management of the physical portfolio of power plants and delivery contracts, power market indices, hedging strategies using futures, case study (1): hedging strategie, European energy exchange (EEX), energy market risk (value at risk, profit at risk), options and structured products in the power market, enterprisewide risk management (Basel II), case study (2): Barings Bank, introduction of swaps and other derivatives on electricity prices.

8th semester 2G Portfolio and Risk Management in a Liberalized Market 2 D. Reichelt Portfolio und Risk Management im liberalisierten Strommarkt 2

Understand the worldwide liberalisation of electricity markets, the various markets models, pan-european power trading and the role of power exchanges. Financial products (derivatives) based on power prices, management of a portfolio containing physical production, contracts and derivatives, evaluation of trading and hedging strategies, methods and tools of risk management.

8th semester 4G Power System Dynamics and Control Andersson, G. Systemdynamik und Leittechnik in der el. Energieversorung Rehtanz, Ch.

Dynamic properties of electrical machines, networks, loads and interconnected systems. Models of power stations and turbines, control of turbines, load- and frequency control, power exchange between networks, model of the synchronous machine connected with the network, behaviour of the machine in case of disturbances, transient stability, equal area criterion, model for small disturbances, voltage control. Facts-Devices. SCADA/State Estimation. EMS-Implementations, Protection, Asset Management, Future Trends in IT for Power Systems.


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2.2 Seminars

1st-4th semester 4 PPS PPS: Economical and technical aspects of a sustainable energy supply G. Koeppel Wirtsch. und techn. Aspekte einer nachhaltigen Energieversorgung Th. Krause

In the past, electricity markets were characterized by vertically integrated utilities operating as regulated monopolies. However, the ongoing liberalisation process, the Kyoto-protocol as well as upcoming technologies are forcing a reorganisation and redirection of the electricity market. The offered seminar addresses several issues related to this reorganisation process. Main topics are distributed generation, particularly aspects of renewable energy sources (solar and wind power) as well as economical and ecological issues on liberalized markets. The students are writing and presenting a report covering single aspects, learning how to search for literature as well as how to write and present scientific reports. 2.3 Student Projects

To be admitted to the diploma examinations of the 7th and 8th semester, students of the electrical engineering department must carry out two projects. Each student can freely choose his subject area, but usually the two projects have to originate from different subject areas. According to the curriculum, two days of the week during the semester period are to be devoted to this work. In general, the subjects are derived from topical research and development tasks. As we have close collaboration with the FKH some of the student projects as well as diploma work (see the following section) are supervised by staff of the FKH. G. Glanzmann, Implementation of a Market Model in an Interactive Power M. von Siebenthal Flow Simulation Platform R. Wohlwend Beschleunigte Berechnung des stationären Zustandes leistungselektronischer Systeme" 2.4 Diploma Projects

Allocated time is four months. The majority of students devote their time to this work in the winter semester. The student has the option to carry it out either before or after the formal diploma examination (dates in spring and autumn). Michele Bernocchi Simulation of Transmission Pricing Methods for Liberalized Markets Thomas Tarnowski FACTS Devices Optimizing an Electrical Energy Market subject to Power Transmission Constraints

2. TEACHING

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2.5 Excursions

Credit Suisse First Boston, Zürich; 10 June 2003 Trading Floor visit and presentation about structured financial products

ETRANS, Laufenburg; 2 July 2003

NOK, Baden; 17 June 2003


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3. Research Activities 3.1 Completed PhD Theses

DYNAMIC MODELING OF LINE AND CAPACITOR COMMUTATED CONVERTERS FOR HVDC POWER TRANSMISSION Candidate: Dipl. Ing. Wolfgang Hammer Thesis: ETH No. 15269 Date of oral examination: 19 September 2003 Examiner: Prof. Dr. G. Andersson, ETH Zürich Co-examiner: Prof. Dr. A. Golé, University of Manitoba, Canada

Author's summary For more than one hundred years, the generation, transmission, distribution and utilization of electric energy has been based principally on alternating current. However, there are a number of special applications for which direct current transmission is the better if not only choice, even taking into account the cost of the equipment that is necessary to convert between ac and dc:

• Bulk power transmission on long overhead lines At very long distances, ac overhead lines consume large amounts of reactive power which are furthermore dependent on the amount of active power transfered. In addition to the additional losses caused by the reactive current, this also gives rise to stability problems. DC lines, on the other hand, do not consume reactive power.

• Power transmission via cable Due to its construction, a cable has a much higher capacitance per unit length than an overhead line. This means that even for a cable of moderate length (50 km), the reactive current can utilize a major part of the total current capability when transmitting ac power.

• Transmission between unsynchronized ac systems AC power transmission is physically only possible between synchronized systems. When two systems operate at different frequencies (such as 50 Hz and 60 Hz), the only practical way to transmit power between them is by means of a dc connection.

In addition to these more traditional applications concerning rather the stationary operation of networks, there is a fourth aspect of HVDC transmission which gains more and more importance with the growing global interconnection of transmission systems:

• Parallel ac and dc transmission In interconnected ac systems technical problems like transient instability or power oscillations can occur when an interconnection between two parts is relatively weak. In such a case, the fast controls of an additional HVDC link in parallel to the ac interconnection can be used to stabilize the system.

With today's power systems being operated closer to their stability limits, and particularly in view of this last aspect, there is an increasing need to understand the dynamic interactions between HVDC converters and the ac system. Convenient models

3. RESEARCH ACTIVITIES

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are needed that will both facilitate control design and allow fast and accurate transient simulations. However, the analysis of HVDC converter systems is challenging because of their hybrid nature, as they incorporate both continuous-time dynamics (associated with the voltages and currents of capacitors and inductors) and discrete events (due to the switching of the valves). Transient stability programs typically use power electronics device models that are based on quasi-static approximations. Such models rely on the assumption that the ac system is in sinusoidal steady-state and, in case of a current source HVDC converter, that the direct current is ripple-free and constant. Due to these assumptions, the models are strictly valid only in the steady state and lack accuracy when transient stability or other dynamic phenomena are of interest. This work presents a new dynamic modeling approach for two types of HVDC converters: the conventional Line Commutated Converter (LCC) and the Capacitor Commutated Converter (CCC). This approach takes into account the dynamics of a variable direct current and (for the CCC) of the series capacitor voltages. The investigations are restricted to phasor-based models for use with transient stability programs. The resulting dynamic converter models are natural extensions of the standard quasi-static models and are in fact identical in the steady state. Case studies demonstrate the impact of the new models on the study of control interactions between the pole controller of an HVDC converter and the ac system, an application normally considered outside the scope of phasor-based simulations. For the LCC, there is only a marginal difference between the quasi-static and the dynamic model. For the CCC, on the other hand, the simulations clearly reveal the superiority of the proposed dynamic model over the quasi-static model. Two cases are presented in which the static model leads to a wrong estimation of the system stability, whereas the response of the dynamic model matches a detailed simulation nearly perfectly.

Figure 1: Response to a current order step change from 1.8 kA to 2.0 kA at 0.02 s: (a) ac bus phase voltage,(b) direct current, (c) firing angle. Thin solid line: detailed simulation; heavy solid line: dynamic model; dashed line: standard model.


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INCREASED TRANSMISSION CAPACITY BY FORCED SYMMETRIZATION Candidate: Dipl. Ing. Andrei Karpatchev Thesis: ETH No. 15342 Date of oral examination: 5 December 2003 Examiner: Prof. Dr. G. Andersson, ETH Zürich Co-examiner: Prof. em. Dr. H. Glavitsch, ETH Zürich Prof. em. Dr. D. Povh, University of Ljubljana

Author's Summary The electrical power industry experiences nowadays a significant need in modern techniques for increasing the capability of power transmission systems. The reason for this lies in growing power flows, caused by rising power consumption, and in deregulation of the electrical market, where power flows should be more flexible. These factors demand more transmission capability from the existing networks. The conservative expansion of the high voltage grid is often not desirable or not possible, because the approval of new overhead transmission lines meets often strong opposition. Furthermore, it takes a long time and is generally a risky long-term financial investment. New technological solutions are sought to meet the capability needs under consideration of modern environmental requirements. The presented work considers possibilities for ensuring power transmission through a AC transmission line with a damaged phase conductor. The disturbance of the symmetrical pattern of currents and voltages in the surrounding network can be eliminated by active measures for symmetry. The utilization of two remaining healthy phases of a three-phase transmission line with a damaged phase in this way can be an economical way to enhance the system reliability. The present planning procedure of the high voltage networks mostly respects the (n-1) criterion. This means that the network should not be subject to any overload or voltage drop below a strictly given limit when any network element is disconnected. Based on statistics, single phase-to-ground faults are the most frequent faults in transmission systems, typically approximately 2/3 of all line faults at voltage level 220-380 kV. Present planning procedures are often based on single outages of three-phase circuits, which do not take into account the actual fault pattern. For the single-phase faults it is necessary to avoid unsymmetrical conditions or unsymmetrical currents in the network. The reason for this is that the currents in the zero sequence system mean earth currents, and those can be dangerous for people and cause adverse interactions with other systems. The currents and voltages in the negative-sequence system are of concern to rotating synchronous machines like generators and motors, but if no such machines are connected to a network part, the negative-sequence voltages can be tolerated in that part. Symmetrization means the suppression of both zero- and negative-sequence currents on the network side of both line circuit breakers so that the network does not experience any unsymmetrical conditions. This can be performed by the installation of special equipment as shunt or serial elements at the line terminals.


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Different arrangements and strategies are considered in this work. In order to be able to try all the different arrangements a special system simulator has been developed. It is based on power flow calculations with multiple symmetrical system representations and allows simulation of the symmetrization effect in a complex meshed network. The fault currents in the negative and zero sequence systems can be studied directly. Different symmetrization topologies, both concentrated and distributed, are investigated and discussed. Modern power electronics devices and measurement technology provide the hardware basis for the practical implementation of different modern symmetrization techniques. The present work considers impact on the whole grid, in case symmetrization techniques are applied. The achieved rest transmission capacity of the damaged line and other "system" characteristics are in focus of interest. Different methods of symmetrization are considered and compared. A possibility of distributed compensation is also one item of interest, which is very promising for the protection of several lines. Symmetrization methods, which are examined in this work, considerably increase the system reliability and can be seen as competitive solutions for an extensive grid expansion on the existing congestion routes. The installation of the necessary additional equipment can be done in shorter terms than the construction of a new transmission line. Environmental and aesthetic impact is then very small too. The modern power electronics devices, which are needed to achieve these advantages, introduce more operational flexibility and can be used also in non-disturbed operation of the network.


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3.2 Current Projects

PROTECTION AND CONTROL SCHEMES FOR NETWORKS WITH A LARGE CONTINGENT OF DISTRIBUTED GENERATION Martin Geidl

Introduction The global trends of reducing greenhouse gas emissions and liberalising utility industries lead to an increasing utilisation of small, often private owned and mostly renewable power sources, which are commonly identified as 'distributed', 'embedded' or 'decentralised' generation (DG). Beside various benefits, several technical, economical and regulatory questions come up when integrating these sources in existing networks. In terms of physical integration, protection is one of the major issues. Utility relaying often fails due to changed short circuit levels, line impedances, reverse power flow etc. Therefore new schemes for operating the grid in case of a failure have to be developed, whereas both protection and control have to response properly. An advanced system combines the functionality of protection (classical as well as wide area) and control, the border in between gets unclear resp. disappears. Modern information technology has to be used to comply with the ambitious communication requirements.

Goal of the project The aim of this project is to develop protection and control philosophies for future networks with a large contingent of distributed generation. Additionally, the communication requirements of an integrated protection and control system should be estimated. The developed strategies will be verified using typical grid topologies which are preliminarily defined. This research is performed within the framework of the project Vision Future Energy Networks (please refer to the section 'Joint Activities').

References: [1] Dugan, R. C.; McDermot, T. E.: "Operating Conflicts for Distributed Generation on

Distribution Systems", IEEE Rural Electric Power Conference, 2001. [2] Dondi, P. et al: "Network integration of distributed power generation", Journal of

Power Sources, 2002. [3] Wallace, A. R.: "Protection of embedded generation schemes", IEE Colloquium on

Protection and Connection of Renewable Energy Systems, 1999. [4] Böse, C. et al: "Protection System Coordination - Considering New Techniques by

Using Flexible Models", 14th Power Systems Computation Conference, 2002.

Partnerships: ABB Switzerland, Alstom France, ETH Zürich


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DEVELOPMENT OF METHODS FOR THE OPTIMAL SIZING AND POSITIONING OF STORAGE DEVICES Gaudenz Koeppel

Introduction The increasing number of small-scale generators, often producing electricity from renewable sources, embedded in the sub-transmission and distribution networks, leads to several new issues and effects in the infrastructure and behaviour of power supplies. There are e.g. increased power fluctuations on the grid due to the stochastic nature of renewably produced electricity or e.g. different protection requirements, because of limited fault-ride-through capabilities (a literature review of this topic is given in [3]). Furthermore some very large cities begin to be confronted with capacity bottlenecks during peak load times, having limited options for building more transmission lines. Storage devices could be a solution to some of these effects and it is the goal of this project to develop methods for the optimal sizing and positioning of a storage device for a given infrastructure. Depending on the grid topology possibly including local generation, the consumer structure and behaviour as well as requirements for availability, reliability and power quality, the optimal size (energy and power) and place for a storage device should be determined.

Figure 1: Symbolic illustration of the impact from a possible placement of a storage device (flywheel) for

given load profiles and local power generation (wind turbine and fuel cell)

Figure 1 shows a symbolic example of how the cumulated load profiles for a sample network could look like after inserting a storage device. As the figure implies, the storage device could basically be placed anywhere, e.g. either to momentarily balance the stochastic output of the wind turbine or to e.g. balance the day-night differences of a part of the investigated grid – it depends only on the existing requirements. This research is performed within the framework of the project Vision Future Energy Networks (please refer to the section 'Joint Activities') and contributes to this project by


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defining the requirements for storage in terms of energy and power over time. These requirements then serve as input to more technologically oriented research areas within the project.

Objective The intention is to scientifically contribute to the discussion on the needs of storage devices in future energy networks. This discussion ranges from views, implying that information technology allows to perfectly match production and consumption, thus turning storage redundant to views, suggesting that every stochastic generator needs to be combined with a storage device. The corresponding task is consequently to find out, where how much storage will be needed, to fulfil given supply security requirements.

References [1] Billinton, R., Allan, R.N.: "Reliability Evaluation of Power Systems", 2nd Edition,

Plenum Press, New York 1996 [2] Kerstin, W.H.: "Distribution System Modelling and Analysis", Electric Power

Engineering Series, CRC Press, Boca Raton 2002 [3] Koeppel, G.: "Distributed Generation - Literature Review and Outline of the Swiss

Situation", Technical Report, Zurich 2003; available online: http://e-collection.ethbib.ethz.ch/show?type=bericht&nr=312


IMPLEMENTING TRANSMISSION PRICING FOR A DEREGULATED MARKET SIMULATOR Thilo Krause

Introduction That a country’s electricity market has been liberalized is a common but likewise unspecific proposition. "Delivered power is a bundle of many services. These include transmission, distribution, frequency control and voltage support, as well as generation. [...] Each service requires a separate market, and some require several markets."[1] Whereas the theory for each single market is nowadays well developed, there is still a need for studying the interaction of the different sub-markets. This especially applies to the energy-, transmission- and ancillary services markets. Generators may bid on a pool (or spot) market or directly settle into bilateral contracts with particular customers. This energy trade results in a physical power flow through the transmission network, where the grid should be capable of transmitting the energy according to the agreed set of contracts. In order do so transmission pricing methodologies have to be developed to: "a) promote economic efficiency b) compensate grid companies fairly for providing the transmission service c) allocate transmission cost reasonably among all transmission users d) maintain the reliability of the grid."[2] Methodologies reach from embedded to marginal pricing schemes. For the ongoing project it is proposed to use embedded methods for cost recovery and marginal methods for setting incentives to promote the


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efficient use of the network in the short-run and to ensure reliability in the long-run. The computed transmission prices serve as additional input data for the energy market, influencing the strategic behaviour of generators and loads. Thus, demand and supply are a function of generation- as well as transmission and reliability constraints.

Objective A report evaluating different transmission pricing methodologies is available since November 2003[3]. The report serves as initial study for the overall project. The objective for the next research stage is to implement the studied methods for the Deregulated Market Simulator (DemSi). The modelling of the energy market is carried at the EPFL Lausanne. Both parts will be merged presumably in summer 2004 to form a first prototype of the simulator. The simulator will be extended stepwise and used for case studies in order to verify the chosen approach.

References [1] Stoft, S. (2002): "Power System Economics. Designing Markets for Electricity.",

Piscataway 2002. [2] Cannella, M.; Disher, E.; Gagliardi, R. (1996): "Beyond the Contract Path: A Realistic

Approach to Transmission Pricing", The Electricity Journal. 1996. pp. 26 – 31. [3] Krause, Th. (2003): "Evaluation of Transmission Pricing Methods for Liberalized

Markets - A Literature Survey", Technical Report, Zurich, 2003; available online: http://e-collection.ethbib.ethz.ch/show?type=bericht&nr=314

Partnerships: PSEL, ETH Zürich

ISOLATED RURAL DISTRIBUTION NETWORKS WITH A LARGE PENETRATION OF RENEWABLE SOURCES Mirjana Milosevic

Participating Institutions Chalmers University of Technology, Sweden MIT, Cambridge, MA, USA University of Tokyo, Japan Shanghai Jiao Tong University, China

Goal of the project The principal scientific aim of this project is the development of methods for assessing the performance of rural electricity distribution networks with a large penetration of renewable sources of energy (like wind, sun and flow-of-river). The research concentrates on the development of models for reliability analysis of the supply, but some of the models can also be used in voltage quality assessment studies. Additional results of the project are expected on the development of techniques for improving the performance and/or reducing the cost.

Abstract The integration of energy sources requires an interface to the electrical system. The interface usually consists of a converter system converting a DC voltage or an ac


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voltage of varying frequency to an ac voltage of system frequency. The requirements on the permissible deviation within 0.1 Hz, or even smaller values are accepted in power systems used in the industrialized countries. In smaller systems, like the ones studied in this project, much larger frequency deviations must probably be accepted for an economic operation. This requires higher demands on the converters between the energy sources and the network. Thus, it means that models for the interaction between the network side and the energy sides of the converters are needed. If several of these are present in proximity of each other, interactions between them could arise. One application of these models is the specification of the design criteria of the power electronic equipment and for determining the electrical conditions at the energy source. Another application is for studying the interaction among several converters in a network and determining the possible adverse condition that could arise. So far, studies of the interaction between hysteresis controlled voltage source inverters connected to the same power network are analyzed [1]. The coupling between the inverters results in an interdependence of their switching. The effects of various parameters of the inverters are analyzed. One of the aims of this project is to develop models for the applications above. The following activities of this project are: 1) Development of models of the interface between the energy sources and the network 2) Studies of the stresses on the power electric equipment in typical model networks

References [1] M. Milosevic, J. Allmeling, G. Andersson, "Interaction between Hysteresis

Controlled Inverters used in Distributed Generation Systems", submitted for presentation at IEEE Power Engineering Society General Meeting, June 2004, Denver

Partnerships: Alliance for Global Sustainability, AGS

CONTROL OF ADVANCED AC TRANSMISSION SYSTEMS Rusejla Sadikovic

Goal of the project The overall goal of this project is to develop an entire control system architecture, which avoids complete system redesign in order to enable a most effective system expansion in terms of new transmission capabilities and more effective network utilization. For the realization of such a controller design the following specifications are defined:

• No adverse interactions occur when the controllability is lost due to faults or changes in system topology.

• No adverse interactions occur in normal operation, and when normal changes in control set points are introduced.


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Abstract In the traditional expansion of a planning system, or the replacement of an existing main component, extensive studies and redesign of control and protection systems are needed to guarantee an acceptable systems behaviour concerning performance and reliability. The concept of Non Intrusive Control Systems (NISC) has been introduced to overcome this problem. The basic idea in this concept is to apply a control strategy that enables the operation of a controlled transmission path without affecting the rest of the system. That control architecture is called Non-Intrusive System Control (NISCTM). NISCTM avoids complete system redesign. It enables a most effective system expansion and more effective network utilization by considering the needed transmission functions first. The goal of the NISCTM architecture is to simplify the design process so that new controlled transmission paths can be designed without extensive system studies. For the operation of a new transmission path the NISCTM architecture avoids adverse control interactions within the entire system without causing a redesign of already implemented controllers. Therefore a high degree of robustness and an effective design procedure can be achieved. Additionally, the proposed architecture allows for a proper reaction on critical events and avoids insufficient and hence wrong operation after the power system state changes.

References: [1] "Non-intrusive control system architecture for ac power transmission", AC-DC

Power Transmission, 2001. Seventh International Conference on (Conf. Publ. No. 485), 2001.

Partnerships: ABB Switzerland

VALUE OF CONTROLLABLE DEVICES IN A LIBERALIZED ELECTRICITY MARKET Christian Schaffner

Abstract In a liberalized electricity market, the transmission capability of an electrical network is of economic value to the network operator, which usually is regarded as a natural monopoly, combined with the mission to maximize the benefit for its users while giving a reasonable profit to its owners. Due to physical constraints, lines are often only utilized at a fraction of their physical limits. To improve customer benefit one possibility would be to raise the economic value of the transmission lines by increasing the power transfer capability of these lines. Additionally, there will be a gain in overall market efficiency since more energy trading can take place between competing regions with different price structures. Flexible AC Transmission Systems (FACTS) devices also allow the increase of the overall utilization of an electrical power network by controlling the power flow. Since installations of FACTS devices require huge investments, with costs that could be similar to new transmission lines, it is very important to investigate all different aspects of such as a device: For example not only the increased transmission capacity, but also


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the fact that such a device can be built in such a way that it can be relocated due to seasonal differences in the power transfer between regions.

Objective In this PhD thesis it will be examined what additional economic value the increased transmission capability provided by controllable devices (such as FACTS) gives in a liberalized electrical power transmission system.

Outline To achieve the objectives described in the preceding paragraph several research areas in the field of electric power transmission and controllable devices in such systems are examined. The idea behind our model is that a complicated algorithm using optimal power flow (OPF) is often too complex for the purpose of valuating such projects: Input parameters such as expected future generation mix are often hard to guess and error prone. Therefore it is reasonable to use a simplified model of the underlying electricity system. This method is based on a model that uses area-constraints and aggregated generation in each area coupled with a double auction market model, based on the production costs of generators. To perform the actual valuation of the FACTS one needs to find a framework suitable for this special kind of project. Here a so-called Special Purpose Vehicle company (S.P.V) is used: This company is a separate legal entity from the power producer but is -- in our study -- fully owned by the power producer. This is necessary to comply with the regulation that generating companies need to be financially separated from companies working in the field of electricity transmission. The S.P.V borrows the full amount it needs to fund the project from the power producer. It then buys electric energy in the low price zone and re-sells it in the high price zone. The cash flow is in the opposite direction: it gets paid from the consumers in the high price zone and gives back the profit to the power producer company (see Figure 1).

Power Producer Ltd.

in low price zone

FACTS S.P.V.

100% owned by power producer

Customer

in high price zone

PaymentProfit

PowerSale

PowerRe-Sale

Figure 1: A Special Purpose Vehicle (SPV) is used as business model

In different case studies the influence of various parameters on the value of the controllable device is determined. Typical parameters are: Investment costs, running costs, relocatability etc. The impact of transmission congestions on electricity prices, consumer, producer and society profit is also studied. The valuations carried out show that even if there is limited impact on removing congestions by installing a controllable device, it has a significant monetary value for the owner. In addition to quantitative results, qualitative aspects will describe the most important factors when evaluating this value.

Partnerships: ETH Zürich


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FLOWDEMO.NET: INTERACTIVE, INTERNET-BASED TOOL TO VISUALIZE POWER FLOW IN AN ELECTRIC TRANSMISSION SYSTEM Martin Geidl, Christian Schaffner

Abstract Flowdemo.net is an interactive load flow visualization software for education in electrical engineering. What differentiates it from similar tools is that it can be run via any Internet browser or, alternatively, as a stand-alone application. Thus there is no special installation needed for the user. Lecturers can use it to visually demonstrate load flow in electric transmission systems in a convenient way: They access predefined examples stored in a database on the server. Afterwards students can access the same examples via an Internet browser to deepen the new knowledge.

Description Flowdemo.net gives a visual representation of a calculated power flow including the network topology, graphical representation of the load flowing through a line, numerical and graphical representation of bus voltages and angles, state of switches etc. The graphical user interface (GUI) of Flowdemo.net displays the network topology together with graphical and/or numerical representations of the load flowing through a line, of bus voltages and angles, state of switches etc.

Bus 1

Bus 2

Bus 3

Bus 4

Bus 5

Bus 6

38.29MW

-37.8MVar

G

22.0MW

-25.9MVarG

32.5MVar

-1.58MVar

21.7MW

12.7MVar

7.6MW

1.6MVar

11.2MW

7.5MVar

13.5MW

5.8MVar

0.0MW

-20.59MVar

5.71MW

-21.7MVar

0.93

Figure 1: A six bus network in Flowdemo.net: Voltages, angles and load flows are displayed either in

numbers or graphically


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The user can interact with the calculation by switching on or off lines and components, changing parameters such as the voltage of a regulating generator or the active and reactive power of a load. The GUI is programmed in Java. The calculation is carried out on a server that communicates with the java applet running inside the Internet browser of the client computer.

Applications in Education A typical application of Flowdemo.net is as following: The lecturer prepares demonstration networks and puts the according net lists on the server. During class he can explain theoretical principles using one of the prepared networks. All he needs is a computer with Internet access and a computer display projector. To strengthen the knowledge students will use the same simulations after class to work through written questions. New concepts or devices can be implemented directly by the lecturer, since the source code is available. Also, as Matlab is well known by most engineering people, no special programming knowledge is needed.

New Version During 2003 we brought online version 2.0 of Flowdemo.net which is a rewrite from the ground up. The final version is available since later summer. It brings the following improvements over version 1.0:

• A graphical network editor allows the user to design new networks or change existing ones.

• The networks are stored in a central database, which makes it easier for lecturers to publish new networks to students. This database has designated areas for each user (private and public) and for specific lectures.

• Flexible AC Transmission Systems (FACTS) such as SVC and TCSC can be added. • A simple Market Simulator using optimal power dispatch makes it possible to study

the price-building mechanisms in a network. Cost curves can be assigned to each generator and load and Flowdemo.net will calculate the amount and prices of the traded energy.

• There is now the possibility to store and load networks to/from the local disk through the internet browser.

• PDF-Printing makes it possible to add calculated networks into documentation • A new compatibility mode for users behind a firewall

Success in education Starting this winter semester Flowdemo.net was used successfully at different lectures: At KTH in Stockholm Flowdemo.net was used in an introductory lecture with more than 100 students, at ETH Zurich in the lecture "Elektrische Energiesysteme" to name a few. Flowdemo.net has proven to be a stable system that is easy to use for educational uses. Student evaluations are on-going.

References: [1] http://flowdemo.net

Partnerships: ETH Zürich


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EMERGENCY CONTROL OF POWER SYSTEMS, DESIGN OF SYSTEM PROTECTION SCHEME Marek Zima Deliberalization of the electricity market in many countries yields frequent changes of generation and transmission pattern. This together with the continuous grow of the load demand causes significant stresses of the power systems, often beyond their limits. This in turn results in more frequent contingencies leading to severe consequencies – risk of failures, blackouts and financial losses. Since the extensions of the transmission systems are kept to a minimum for various reasons (mainly environmental), better utilization of existing assets becomes necessary. Various means can be used for this purpose, ranging from on-line monitoring of available transmission capacity to improved control, especialy under emergency conditions. The later one is task of System Protection Schemes (SPS) [1]. Conventional/traditional SPSs designs are based on the predefined worst scenarios obtained by off-line simulations, which are used to define certain rules. These rules are applied on tuning of local relays (underfrequency, undervoltage etc.) that shall operate a way eliminating incipient instability. However, assumptions used for setting these rules are too conservative and often leave a significant unused transmission margin. Moreover, these schemes have more protection than control functionality and Above mentioned disadvantages can be overcome by an on-line scheme, which would take into account actual network conditions and provide high degree of coordination in control. Such a SPS could rely on the phasor measurement units placed throughout the network to be able to provide a wide area view, since majority of dangerous phenomena in power systems have such an origin (voltage, frequency, small-signal etc.). The goal of this research project is to determine constraints for physically feasible SPS application, investigate and design an algorithm mitigating one or more instability phenomena. In the year 2003 the project activities were as follows.

• The new algorithm for emergency control has been proposed and presented in [2] and [3]. The algorithm is a new concept introducing Model Predictive Control based on the Trajectory Sensitivities.

• The long-term consequences of the Wide Area Control have been studied in terms of the improved security of the power system.

• Assessment method for investment into a Wide Area Monitoring and Control systems has been studied in [4].

This project is done partly at ETH and partly at one industry partner (which is actually sponsoring the project) in order to take into consideration practical aspects of possible future implementation.


21

References: [1] Marek Zima: "Special Protection Schemes in Electric Power Systems – Literature

survey", Technical Report, Zurich 2002; available online: http://e-collection.ethbib.ethz.ch/cgi-bin/show.pl?type=bericht&nr=96

[2] Marek Zima, Göran Andersson, "Stability Assessment and Emergency Control Method Using Trajectory Sensitivities", presented at the 2003 IEEE Bologna PowerTech, June 23 - 26, Bologna, Italy, 2003.

[3] Marek Zima, Petr Korba and Göran Andersson, "Power Systems Voltage Emergency Control Approach Using Trajectory Sensitivities", presented at the IEEE Conference on Control Application, 23 - 25 June, Istanbul, Turkey, 2003.

[4] Marek Zima, Thilo Krause and Göran Andersson, "Evaluation of System Protection Schemes, Wide Area Monitoring and Control Systems", presented at the 6th APSCOM Conference, 11 - 14 November, Hong Kong, China, 2003.



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3.3 Spin-Off Activities

COMPANY PLEXIM Since june 2002 the Power Systems Laboratory hosts the ETH spin-off Plexim. The company was founded by Jost Allmeling and Wolfgang Hammer with the purpose of bringing to market the simulation software PLECS that they had developed in the course of their research. After having developed PLECS into a marketable product the company started selling the first licenses in November 2002. Today, the software has been sold to universities and industrial customers all over the world with a focus on European countries and the United States. PLECS is intensively used for research and education activities in technical universities, especially in Germany and Switzerland.

Software PLECS The initial reason for the development of PLECS was the lack of appropriate simulation tools for power electronic systems. Power electronic systems usually comprise both an electrical circuit with many semiconductor switches and sophisticated controls. For this type of system PLECS offers two major advantages compared with other simulation programs:

• PLECS embeds electrical circuits seamlessly into Simulink models. This facilitates system simulations that comprise the electrical part modeled in PLECS and the control structures modeled in Simulink. Thanks to the schematic editor of PLECS, entering electrical circuits is equally intuitive as modeling control structures with Simulink.

• PLECS uses ideal switches and accelerates the simulation of switched systems by a factor of 10 to 100 compared with common circuit simulation programs.

The innovation of PLECS is the use of ideal switches. Unimportant detail information is neglected in order to obtain a high simulation speed. The simulation accuracy of the entire system is not affected. A pleasant side effect is that the user is not confronted with the specification of often unknown parameters. Therefore the initial effort to set up a simulation model is low and even inexperienced students will be able to work with PLECS.

Future developments PLECS is continuously improved by enhancing the component libraries and adding new features. In December 2003, Plexim has launched a KTI project in cooperation with ETH Zurich and ABB to expand the simulation algorithm in the next major release. (KTI = Swiss Federal Commission for Technology and Innovation)

References: [1] http://www.plexim.com


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4. Publications and Reports1 4.1 Publications

N. Dizdarevic, M. Majstrovic and G. Andersson "FACTS-based Reactive Power Compensation of Wind Energy Conversion System", Proceedings of 2003 IEEE Bologna PowerTech, Paper no 251, Bologna, Italy, 23 - 26 June

M. Zima and G. Andersson "Stability Assessment and Emergency Control Method Using Trajectory Sensitivities", Proceedings of 2003 IEEE Bologna PowerTech, Paper no 195, Bologna, Italy, 23 - 26 June

Ch. Schaffner and G. Andersson "Determing the Value of Controllable Devices in a Liberalized Electricity Market: A New Approach", Proceedings of 2003 IEEE Bologna PowerTech, Paper no 276, Bologna, Italy, 23 - 26 June

M. Zima, G. Andersson and P. Korba "Power Systems Voltage Emergency Control Approach Using Trajectory Sensitivities", 2003 IEEE Conference on Applications, CCA 2003, Istanbul, Turkey, 23 - 25 June

J. Allmeling "Schnelle Kompensation von Harmonischen mit Aktivfiltern" Bulletin SEV/VSE July 2003, No. 15, pp.15-20

N. Dizdarevic, M. Majstrovic and G. Andersson "Longer Term Stabilisation of Wind Power Plant Voltage/Reactive Power Fluctuations by FACTS Solution" IASTED Power and Energy Conference, Marbella, Spain, September

M. Zima, Th. Krause and G. Andersson "Evaluation of System Protection Schemes, Wide Area Monitoring and Control Systems", Proceedings of APSCOM 2003, Hong Kong, China, 11 - 14 November

A. Karpatchev, H. Glavitsch, and G. Andersson "Forced Symmetrization Techniques for the High Voltage Grid" Proceedings of APSCOM 2003, Hong Kong, China, 11 - 14 November

R. Sadikovic and G. Andersson "Power Flow Control by Sensitivity Based FACTS Controllers" Proceedings of IPEC 2003, Singapore, 24 - 29 November

G. Andersson, T. Green, B. Pal and Ch. Rehtanz "Advanced FACTS control" ABB Review, 4 (2003), pp 21-26

1 Publications and Reports can be downloaded from http://www.eeh.ee.ethz.ch

4. PUBLICATIONS AND REPORTS

24

4.2 Reports

G. Koeppel "Distributed Generation - Literature Review and Outline of the Swiss Situation", Technical Report, Zurich 2003; available online: http://e-collection.ethbib.ethz.ch/show?type=bericht&nr=312

Th. Krause "Evaluation of Transmission Pricing Methods for Liberalized Markets - A Literature Survey", Technical Report, Zurich 2003; available online: http://e-collection.ethbib.ethz.ch/show?type=bericht&nr=314

M. Milosevic "Decoupling Control of d and q Current Components in Three-Phase Voltage Source Inverter", Technical Report, Zurich 2003


25

5. Presentations M. Zima "Stability Assessment and Emergency Control Method Using Trajectory Sensitivities", presented at the 2003 IEEE Bologna PowerTech Bologna, Italy June 23 - 26, 2003

Ch. Schaffner "Determing the Value of Controllable Devices in a Liberalized Electricity Market: A New Approach", presented at the 2003 IEEE Bologna PowerTech Bologna, Italy June 23 - 26, 2003

G. Andersson "Regelenergie" BKW-CEPE Workshop 03 Bern, Switzerland 4 July 2003

G. Andersson European Energy Venture Fair 2003 Rüschlikon, Switzerland 28 October 2003

Th. Krause "Evaluation of System Protection Schemes, Wide Area Monitoring and Control Systems", presented at the 6th APSCOM Conference Hong Kong, China 11-14 November 11 - 14, 2003

A. Karpatchev "Forced Symmetrization Techniques for the High Voltage Grid" presented at the 6th APSCOM Conference Hong Kong, China 11 - 14 November, 2003

R. Sadikovic "Power Flow Control by Sensitivity Based FACTS Controllers" presented at IPEC 2003 Singapore 24 - 29 November, 2003

5. PRESENTATIONS

26


27

6. Conferences and Visits 6.1 Conferences and Workshops

G. Andersson Flexiges workshop, Comillas Unversity, Madrid, Spain 14 January 2003

G. Andersson Cigre B4-41 Meeting Las Vegas 27 - 28 January 2003

G. Andersson The Hong Kong Polytechnic University, Department of Electrical Engineering Hung Hom, Kowloon Hong Kong, China 17 - 21 February 2003

G. Andersson ABB University Power Technologies Ludvika, Sweden 4 - 6 March 2003

G. Andersson PHD Exam Lund University, Sweden 24 -25 April 2003

G. Andersson IEEE PES Fellow Committee Minneapolis, USA 2 - 3 June 2003

G. Andersson, Ch. Schaffner, M. Zima 2003 IEEE Bologna PowerTech Conference Faculty of Engineering , University of Bologna Bologna, Italy 23 - 26 June 2003

G. Andersson IEEE Power Engineering Society (PES) General Meeting 2003 Toronto, Canada 13 - 17 July 2003

6. CONFERENCES AND VISITS

28

J. Allmeling, W. Hammer EPE 2003 Conference and Exhibition Toulouse, France 1 - 5 September 2003

G. Andersson 38th Meeting and Colloquium of CIGRE Study Committee B4 Nuremberg, Germany 21 - 26 September 2003

G. Andersson, M. Zima University of Liege Liege, Belgium 1 - 3 October 2003

G. Koeppel DIgSILENT Workshop: Wind Power Integration Gomaringen, Germany 6 - 7 October 2003

M. Geidl "Realität und Vision der ökologischen Stromversorgung" ETG/Electrosuisse, OGE/OVE, ETG/VDE Salzburg, Austria 5 - 6 November 2003

A. Karpatchev, Th. Krause 6th APSCOM Conference Hong Kong, China 11 - 14 November 2003

R. Sadikovic IPEC 2003 Singapore, China 24 - 29 November 2003

G. Andersson CLP Hong Kong 8 - 12 December 2003

G. Andersson PhD Exam NTNU, Trondheim, Norway 17 - 18 December 2003


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6.2 Visits

Prof. Math Bollen Chalmers , Sweden 30 June 2003

Prof. S. T. Choi Kyongju University, South Korea 29 July 2003

Prof. J.-B. Lee Wongkwang University, South Korea 29 July 2003

Prof. Ani M. Golé Dept. of Electrical and Computer Engineering, University of Manitoba 18 - 19 September 2003

Rajiv Kumar Uni. Karlsruhe 21 November 2003

BfE Meeting 9 May 2003

IEEE Swiss Power Engineering Chapter 12 June 2003

AGS Meeting 15 - 16 September 2003

Optimization enabled Transient Simulation 18 September 2003

6.3 Awards

M. Zima Best Student Paper Award, 2003 IEEE Bologna PowerTech Conference Bologna, Italy 23 - 26 June 2003


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31

Activities of the High Voltage Laboratory

1. Organisation Head: Prof. Dr.-techn. Klaus Fröhlich

Secretary: Karin Sonderegger from 1 May 2003 Barbara Rutz until 31 May 2003

Scientific Staff: Dipl.-Ing. Stefan Berger Dipl.-Ing. Andreas Bitschi from 1 May 2003 M.Sc.El.Eng. Mike Chapman Dipl. El.-Ing. ETH Patrick Favre-Perrod from 1 May 2003 Dipl.-Ing. Manfred Grader Dipl.-Ing. Martin Hinow from 1 May 2003 Dipl.-Ing. Wolfgang Hribernik Dipl.-Ing. Bernd Klöckl Dipl. El.-Ing. ETH Urs Krüsi Dipl. El.-Ing. Evgeny Murtola from 1 May 2003 Dipl. El.-Ing. ETH Stefan Neuhold Dipl. El.-Ing. ETH Diego Politano until 30 April 2003 Dott. Fis. Claudia Roero Dr. sc. nat. Micha Semmler from 1 July 2003 Dipl. Phys. Ulrich Straumann Dipl.-Ing. Ruben Vogelsang

Permanent Staff: El.-Ing. HTL Hans-Jürg Weber High Voltage Laboratory Charles Sigrist Electronics Group Heiko Vögeli Electronics Group Henry Kienast Workshop

Scientific Associates: Tit.-Prof. em. Dr. sc. techn. Habibo Brechna Dr. rer. nat. Timm H. Teich Prof. em. Dr. Ing. Walter Zaengl

Visiting Lecturers: Dr. Werner Hofbauer, ABB High Voltage Techn. Ltd.

1. ORGANISATION

32

ACTIVITIES OF THE HIGH VOLTAGE LABORATORY

33

2. Teaching The lectures and laboratory classes listed in the following section are part of the standard curriculum of the Electrical Engineering Department and are conducted by the staff of the High Voltage Laboratory. Details of the entire electrical engineering curriculum can be provided on application (list of lectures, option proposals). 2.1 Lectures

1st Semester 2V+2U Networks and Circuits I Fröhlich K. Netzwerke und Schaltungen

The electric current and voltage; linear and non-linear resistive circuit elements; theory of meshed linear circuits (time variant and invariant); electric energy and power; ideal amplifier circuits with controlled current sources. Non-linear resistive systems, transistor amplifier as a non-linear system. As in the first semester the mathematical basics are not yet fully developed, the lecture is limited to direct current circuits. The knowledge to be achieved will be intensified by through exercises.

5th semester 4G Electric Power Systems Andersson, G. Elektrische Energiesysteme Fröhlich, K.

Structure of electric power systems; symmetric three phase systems; modelling of power transformers and generators; analysis of plain and unsymmetrical three phase systems; transient switching phenomena; basics of current interruption; principles and applications of distribution- and transmission switchgear; basics of insulation coordination.

6th or 8th Semester 4G High Voltage Technology Fröhlich, K. Hochspannungstechnik

Basic phenomena related to gaseous, fluid and solid dielectrics; dielectric breakdown mechanisms; dimensioning of high voltage components by employment of theoretical considerations and computer modelling tools (small project); sources of overvoltages (switching and lightning); overvoltage protection; investigation of dielectric stresses by computer modelling (small project); insulation co-ordination.

7th Semester 4G Technology of Electrical Power Systems Fröhlich, K. Technologie elektrischer Energiesysteme

Basic physical aspects when conducting high current and high voltage for distribution and transmission of electrical power; emerging technology in distribution and

2. TEACHING

34

transmission systems (super conductivity, fault current limitation, energy storage, HVDC); electromagnetic compatibility for system and personnel; intelligence of power system equipment (control, model based diagnosis); decentralised, renewable energy sources; project work; excursion to a utility and to a manufacturer.

7th Semester 2V Engineers Work – Technique and Economics Hofbauer, W. Ingenieurarbeit - Technik und Wirtschaft

After a short introduction to purpose of an enterprise, its control and the role of the engineer will be explained by the example of surge arresters. By some examples the accounting principles will be presented focusing on the meaning and goal of the financial statement, the income statement and the balance sheet. The importance of the capital expenditure accounting is explained which considers besides product related cost factors like functionality, design and variety of variants, also process related cost factors like personnel, infrastructure and make or buy decisions. By specific consideration of the engineers’ work the importance of the Research and Development process and its impact on the success of an enterprise will be explained.

5th - 8th Semester 4G Computer Science Oriented Project Work Fröhlich, K. EDV-orientierte Projektarbeit and assistants

Using information technology tools, the students, operating in teams and with only limited supervision, have to find solutions to topical problems chosen from the research or teaching activities of the high voltage group. Depending on the tasks, existing programme packages may be applied or, if necessary, new programmes or programme subsections have to be compiled


35

2.2 Student Projects

To be admitted to the diploma examinations of the 7th and 8th semester, students of the electrical engineering department have to carry out two projects. Each student can freely choose his subject area, but usually the two projects have to originate from different subject areas. According to the curriculum, two days of the week during the semester period are to be devoted to this work. In general, the subjects are derived from topical research and development tasks. M. Bartholet Aufbau und Test eines Transformatorprüfstandes zur Ch. Zwyssig experimentellen Identifikation von Prozessmodellen für ein Diagnosesystem Th. Brügger Ausbreitung elektrischer Entladungen an geschädigten Glimmer- bändern V. Bürker Rechnergestütze Berechnung kritischer Designparameter zur Entwicklung von Löschkammern für Hochspannungsleistungs- schalter E. Gallone Water droplets on High Voltage Conductors under a 20kw/a Electric Field S. Guha Thakurta Calibration and modelling of oil humidity sensors for online- monitoring of power transformers M. Nibelle Demonstration of the suitability of electromagnetic emissions for the measurements of aring time in circuit breakers Ph. Simka Dimensionierung und Aufbau einer Hochstromversorgung zur Lichtbogenerzeugung 2.3 Diploma Projects

Allocated time is four months. The majority of students devote their time to this work in the winter semester. The student has the option to carry it out either before or after the formal diploma examination (dates in spring and autumn). M. Lombardi Bestimmung der Restfestigkeit sowie der Isolationsstruktur an L. Pedrini betriebs- und zeitgealterten Wicklungsstäben von rotierenden (EIF Fribourg) elektrischen Maschinen M. Wagner Determination of Life-Cycle Cost Savings due to On-Line M. Flubacher Monitoring of Circuit Breakers (Diploma Project in Brisbane/Australia) L. Walter Resonance characteristics of a 100MJ/100MW SMES coil experimental model verification

2. TEACHING

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2.4 Excursions

ATEL Olten, 20 January 2003 Visit of net control center (Netzleitzentrale) and trading floor

Nordostschweizerische Kraftwerke (NOK) in Thalwil, 29 January 2003 Visit of a 220kV GIS (Gasisolierte Schaltanlage)

ABB Hochspannungstechnik, Baden, Switzerland, 26 May 2003 Visit of a GIS (generator circuit breaker)

Energy Excursion 2003, 20 June – 22 June 2003 Visit of Nexans Suisse, Cable Fabrication, Cortaillod, Switzerland Visit of Power Station Grimsel, Grimsel, Switzerland

ABB Hochspannungstechnik, Baden, Switzerland, 23 June 2003 Visit of a MO, surge arrester (Ueberspannungsableiter)

ABB Hochleistungslabor, Baden, Switzerland 4 December 2003


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3. Research Activities 3.1 Completed PhD Theses

THE PARTIAL DISCHARGE BEHAVIOUR IN MICROVOIDS OF POLYMERIC INSULATION MATERIALS "DAS TEILENTLADUNGSVERHALTEN IN MIKROHOHLRÄUMEN POLYMERER ISOLIERMATERALIEN"

Candidate: H.-P. Burgener Thesis: ETH No. 15028 Date of oral examination: 26 Februar 2003 Examiner: Prof. Dr. K. Fröhlich, ETH Zürich Co-examiner: Prof. Dr. K. Feser, Universität Stuttgart

Author’s Summary Fibre-reinforced materials are widely used in the field of power engineering. Due to their outstanding mechanical and dielectric behaviour these materials find also high voltage applications. The dielectric properties of the fibre-reinforced insulation materials are strongly related to the manufacturing process. The continuous development of the process engineering suppresses the bigger gas-filled voids of the order of one millimetre and the related partial discharges (PD). Improved material properties lead automatically to designs employing increased stresses. Thus the PD behaviour of weak spots in the order of micrometres such as delaminations between fibre and matrix or cracks can be of importance in the future. However, such small voids could lead to very small partial discharge levels (< 1 pC), which could be hardly detectable under practical conditions due to ambient noise, but could nevertheless affect the insulation. The reasons stated above demand a closer investigation of the PD behaviour of microvoids. The literature available shows that so far a range of experiments and simulations have been accomplished to assess the PD behaviour as a function of the geometry of disc-shaped or spherical voids. However, the influence of the side walls on the discharges has not been taken into account within these investigations. In contrast, this work considers the restricting effect of the side walls on the discharge with narrow microvoids or cracks parallel to the electrical field. Such cavities can also appear within fibre-reinforced materials. Considering this aspect methods were established, which distinguish themselves by an improved sensitivity and which could support the conventional PD measurement in assessment or dimensioning of insulation materials in the future. The restricting influence of the side walls of longish voids parallel to the electrical field has been investigated by means of an experiment. To assess this, well-defined holes of constant length (300 µm) and various diameters (50 – 300 µm) were drilled into the epoxy resin of a resin-filled electrode system. For each diameter the partial discharges were measured electrically as well as optically. A considerable increase of the PD inception voltage and inception field strength was found towards smaller diameters (< 100 µm). This increase has its origin mainly in the diffusion-based interaction of the electrons with the side walls.


38

The experimental effort for the manufacturing of the samples was large and the investigations of the PD behaviour of even narrower voids (< 50 µm) of various lengths were restricted due to the methods available for the preparation of the defined holes. Considering that voids of smaller dimensions can not yet be assessed by experiment a model for the simulation of the PD inception in narrow, cylindrical voids has been provided. The model is based on the continuity equations, which were coupled via the charge densities in the discharge with the Poisson equation and the electrical field. The PD inception criterion is based on a photonic feedback, i.e. a Townsend mechanism. With the experimental fitting of a parameter, which is describing the interaction of the electron avalanche with the periphery of the cylindrical void, a good correlation between the calculated and the measured PD inception voltages could be obtained. For the application of the model presented as a tool for an electrical dimensioning, the materials-specific geometries of the voids must be known and modelling with a cylindrical geometry must be applicable. Thus the usefulness of the simulation was investigated with mechanically stressed polyester fabric reinforced epoxy tubes. The light microscopy served to assess the mechanically induced geometries of the cracks. By means of comparison of the calculated and optically measured lengths of the cracks the applicability of the simulation of the PD inception field strength could be shown. For a simulation of the apparent charge the existing model should be expanded. Thus a model presented in the literature [1] has been used. Optical investigations of voids specific to the material in combination with simulation tools offer the potential to consider critical field strengths as well as void geometries, in a range not accessible to the conventional PD measurement. Thus the methods presented could be very helpful to users and manufacturers of insulation materials for formulating their requirements/specifications. Further investigations showed the influence of the sequential as well as simultaneous mechanical and electrical stresses on glass fibre-reinforced epoxy tubes. The experiments revealed that the dielectric failure potential is higher with simultaneous mechanical stresses. The reason is the generation of charge carriers during the cracking of the barrier layer between fibre and matrix. These charge carriers combined with a high field strength could lead to an avalanche development and to the dielectric failure. In the mechanical dimensioning and specification of fibre-reinforced materials, which have to support high dielectric and mechanical stresses, it has thus to be taken into account that even small-scale delamination and cracking must be avoided.

Partnerships: ABB High Voltage Technologies Ltd, Zürich, Switzerland Cellpack Ldt., Wohlen, Switzerland Micafil Ltd., Zürich, Switzerland

Reference [1] G. C. Crichton, P. W. Karlsson and A. Pedersen, "Partial Discharges in Ellipsoidal and

Shperoidal Voids", IEEE Trans. on Electrical Insulation, Vol. 24, No. 2, Apr. 1989, pp. 335-342.


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STRESS DEPENDENT ECONOMIC ASSESSMENT OF INNOVATIONS IN POWER SUBSTATIONS Candidate: Diego Politano Thesis ETH No. 15183 Date of oral examination: 27 June 2003 Examiner: Prof. Dr. K. Fröhlich, ETH Zürich Co-examiner: Prof. Dr. D. Birtwhistle, Queensland University, Brisbane, Australia

Author’s Summary When a power utility considers the introduction of a new component in their substation, it is primarily faced with costs. Each proposed investment must be defended facing the management. In the simplest situation a new component with higher performance will just be substituted for an older one. In this case the existing methodologies are sufficient to assess the economic impact of the investment. In many cases a simple comparison is not possible because the new substituted component has very different properties or because the innovation is simply added to the substation, thereby increasing substation complexity. For these cases the costs caused by innovation must be justified by the overall benefits brought to the substation. A methodology for the evaluation and the calculation of the financial impact of a modification in power substations is presented in this work. The new idea compared to the conventional cost calculation methodologies is that the life-cycle costs of power apparatus are evaluated in dependence on the stresses effecting an apparatus. The overall economic impact of an innovation is calculated by investigating its implications on the various items of apparatus of the substation. When subjected to certain stress conditions during a period of time, the new apparatus may suffer slight damage. The consequence is that an increased probability of failure compared to the initial state is possible. Subjected again to new stresses, the apparatus condition gets even worse, with an increased risk of failure. If no maintenance is performed this process leads sooner or later to the end-of-life of the apparatus. A mathematical model for the description of such a life cycle is described in this work. The model is based on the identification of all possible condition-states of an apparatus, the calculation of the probability of the change of condition and the association of all of these condition-states to cost parameters. The analysis is subdivided into seven phases. First the apparatus is broken down into its vital subcomponents in order to identify all the condition-states leading to a failure in the apparatus assessed. This information gathering is carried out performing a Failure Modes and Effect Analysis (FMEA) and a Fault Tree Analysis (FTA) on the apparatus. In a next phase the designed life-cycle process of the apparatus represent a multistate system and is modelled with a Markov chain. The stresses acting on the apparatus are investigated and the correlated state-transition probabilities are inserted. The Markov process is solved. To define the costs related to the condition states of the apparatus a similar algorithm is applied. Every condition-state of a subcomponent is associated with costs. Finally, the cash flow stream related to the investigated investment is calculated and the final decision about the profitability of the investment can be taken on the basis of the LCC calculation made.


40

To prove the suitability of the algorithm, the methodology has been applied in the assessment of two case studies. In the first one the economics of controlled energization of power transformers is investigated. The second one deals with the financial impact of the monitoring and diagnosis of HVAC circuit breakers. The step-by-step application of the algorithm has improved the understanding of the technical and economic impact of both innovative technologies. The models for the life-cycle costs of a power transformer and a circuit breaker have been developed. In both case studies the methodology helped to give evidence of a financial benefit due to the introduction of the innovations. It has been concluded that:

• The uncertainty of many of the input parameters is a major weakness of the stress-dependent life-cycle costs methodology. In particular, the condition-state-transition probability can often only be estimated on the basis of limited historical data. Therefore it is necessary to create a worldwide database containing information about the condition state transition probabilities, the cost parameters and failure mode analysis of power components.

• In order to reduce the uncertainty of the input parameters the methodology should be primarily used in comparative studies.

• Sensitivity analysis and risk assessment procedures are helpful in dealing with the uncertainty related to the input parameters. In addition performing sensitivity analysis the assessment of the weight of each parameter over the total costs leads to the identification of those parameters on which it is worthwhile investing time and money to increase the exactness of their values.

Future development should focus on the investigation of the life-cycle processes of other apparatus in substations and on the application of the methodology for the investigation of different substation configurations.


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3.2 Current projects

GECKO - GEOTHERMAL ENERGY CONVERSION KEY OBJECTIVIES Andreas Bitschi

Goal of the project While the emphasis of geothermal research is on the rock characteristics and the development of the reservoirs, other problems under study are concerned with the practical use of geothermal heat. Apart from the well-known use in geothermal central heating installations the transformation of the warmth into electricity is a priority goal. In order to effect this different processes and plants are available. All those considered here comprise a turbine, which drives via a shaft a generator. The fluid issuing from the borehole serves either directly as working medium or it transfers the warmth in a heat exchanger to a secondary fluid (binary systems). As the geothermal energy from thermodynamic view represents low-temperature (~200°C) energy and thus contains a large portion of energy, which cannot be converted into technically useful energy, the Carnot-efficiency of the transformation is relatively limited. At this time Organic-Rankine-Cycles (ORC) and Kalina processes have the highest efficiencies. In the context of the project methods are to be investigated for the transformation of low-temperature warmth into electricity with relatively high efficiencies. For this in a first step the state of the art was checked, now we are looking for improvements and proceed with the development of new ideas. A next step is the combination of the different processes and the identification of synergies. The last step would be the integration in existing and new power systems. A further aspect of the task is the downhole principle. That means the energy transformation should happen in the borehole. Therefore a machine without any moving parts would be very advantageous because the chances of maintenance will be limited.

From thermoelectric to thermionic Heat exchangers incorporating thermoelectric modules offer one possibility to generate electrical power from geothermal sources. These devices convert a temperature difference into an electric current. (Seebeck-Effekt). Thermoelectric materials are expensive and there is not more than 5-8 % efficiency available under ideal conditions. This circumstance is caused by the thermal conduction through the semiconductor crystals. An application that reduces the heat transfer to thermal radiation is the thermionic converter. Here a vacuum gap between the electrodes eliminates the heat conduction and the current is generated by thermal emission of electrons. For these electrons the vacuum gap means a potential barrier, which they have to surmont. The required energy of the electrons would need temperatures > 1000 K. An additional problem ist the fact of space charge, which further increases the height of the potential barrier. According to the quantum mechanics it is also possible for the electrons to tunnel the barrier depending on the height and width of the barrier. For this a barrier thickness of


42

nm-scale is required. For the implementation of such small gaps, special fabrication methods and positioning systems are needed. A further way to influence the shape of the energy barrier is an electric field between the hot and the cold sides, respectively, of the electrodes. In this case the superpositioning of the potentials leads besides a decrease of the barrier-height also to a reduction of the width of the barrier, so that the electrons already can tunnel on the height of the Fermi level. For tunneling the required energy of the electrons is much lower than in the case of overcoming the barrier and so can be effected by a lower temperature source like a geothermal reservoir. Outlook 2004

• Research with partners in materials science • Analytic calculations and modelling • Numerical simulations of static converters

Partnerships: under negotiation

FUTURE ENERGY TRANSMISSION TECHNOLOGIES Patrick Favre-Perrod The project replaces the former FUEL project and is a part of the broader Vision 2020 project. The project aim is to formulate proposals on how to implement energy transmission in the envisioned future energy networks According to our analysis, an evolution in transmission technologies will be induced by several constraints:

• Due to their impact on the landscape and EMC issues, as well as the limited available rights of way, new overhead lines are unlikely to be built.

• The economical operation of distributed generators will need solutions for (low) power infeed into the transmission network. The implications on the grid hardware might be lower operating voltages, d.c. operation, etc.

• Future producers and consumers (microturbines, fuel cells, etc.) will not handle exclusively electrical energy. Technological solutions using synergies between different energy forms (heat, chemical energy, electricity, etc.) will eventually be useful.

A possible structure of the envisioned energy network is shown in Figure 2. Different consumers and producers might connect to "energy hubs", which will permit energy exchanges as well as storage of excess energy, e.g. in chemical form. It appears that this grid provides more flexibility if these "hubs" can exchange these energy forms over longer distances. To profit from possible synergies, a combined energy transmission "bus" for several energy forms might be useful. As a first theoretical approach an energy bus for thermal and electrical energy has been studied (Figure 2). A chemical energy carrier flows through a coaxial electrical


43

conductor. This energy carrier medium is heated up by the ohmic losses in the electrical conductor. The layout of this bus offers several degrees of freedom: among them the type of coolant (gaseous, liquid), the diameter of the inner conduit and the operating pressures.

Biogas

Electrical energy

Chemical energy

Heat flux

Figure 1: Future energy networks will connect traditional plants as well as new distributed producers to

consumers. The energy exchange is likely to be electrical, chemical and thermal.

As a first result, it has been established that liquid coolants • require lower operating pressures • allow for higher power densities • offer a cooling power which is proportional to the temperature rise of the coolant

whereas gaseous coolants

• enable a decoupling of the transmitted chemical power and the absorbed waste heat

• can absorb much loss energy at moderate outlet temperatures • enable a limited storage of chemical energy in the transmission infrastructure.

Figure 2: Principle layout of hybrid energy transmission device



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STORAGE IN STOCHASTICALLY FED ENERGY SYSTEMS Bernd Klöckl

Aim To find technology-dependent optimum energy storage sizing algorithms for future systems.

Description Linked to the "Vision 2020 (Vision of Future Energy Networks)"-project, this research work covers the technological storage aspects in stochastically fed energy systems. Energy storage integration is the obvious procedure of choice to overcome the inherent problems raised by stochastic sources in electric power systems. However, location as well as optimum sizing and technological implementation of storage devices has always lacked a systematic theoretical coverage. Recent publications about energy storage have proposed a new view on the problem by developing a correct (although simplified) dynamical model of different devices into normalised correlations between power density and energy density, which are the two most important parameters to assess storage technologies [1,2]. This simple and efficient idea helps to understand the applicability of a technology for a certain constant power application. This approach is being extended to a more general one, where power demand is a function of time. This situation applies particularly in energy nodes (hubs of electric and other forms of energy with power infeed, consumption and integrated storage capability) which are fed by stochastic sources. It has been found out that, not surprisingly, the achievable energy density of a storage device exhibits remarkable variation with different power demand functions. Currently, it is investigated what kind of functions the power signals would impose on a storage device located close to a stochastic source. The investigation procedure must therefore include the collection and correct interpretation of P(t)-functions of many different kinds of sources (note that in this generalised approach a stochastic sink is viewed as a negative stochastic source) and the development of average power calculation procedures.

Wdel @ P = const„Ragone plots“

Wdel @ P = P(t)

t/f – Analysis

Input: time-domain stochastic data of source or sink

probability analysisinformation on t lost!

DA

TAST

OR

AG

E

Output:Storage

„capacity“

conventional HVL approach

+ +

Transmission„capacity“

Figure 1: The HVL approach for the determination of optima in storage technology


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These two steps make it possible to calculate the power demand signal a storage device would face, analyse it and feed it into the physical models of single storage devices or cascaded configurations. Proceeding in this way, one can assess the exact storage demand for a certain situation, not only from the energetic point of view, but also from the peak power point of view. Figure 1 and 2 show the systematics.

380 390 400 410 420 430 440 450−100

0

100

200

300

400

500

time [h]

pow

er [k

W]

day night

Figure 2: The power curve of a large photovoltaic installation during three winter days1. The shaded areas

represent energy contents. The envelope curve is shifted vertically by the yearly average power of the system which has been computed by a trend analysis algorithm.

Figure 2 shows the contradicting requirements for storage technologies in stochastically fed energy systems. While during daytimes the storage is required to absorb very dynamic high power signals from the PV arrays, it has to re-inject almost constant power into the grid during night time if it is designed to produce constant baseload for an arbitrary system. Both of these exigencies can generally not be covered by only one storage technology since the general basic distinction can be made into only two principles: Potential and kinetic storage. The determination of the exact optimum physical implementation by analysis of such signals is the basis of this research.

Outlook for 2004 Time-frequency analysis of stochastic sources will be integrated into energy storage theory. Combinations of storage devices will be investigated with various power demand curves and optimum cascading algorithms will be developed. The result should imply requirements for future energy storage technologies, e.g. high energy transmission cables or optimised energy nodes. The correlation with future transmission technologies (see also figure 1) and the investigation of possible synergies will be in the focus and form the interlink to P. Favre-Perrod’s scientific work at the High Voltage Laboratory.

1 Data for these investigations was kindly provided by HTA Burgdorf. Internet: www.pvtest.ch


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Further activities In coordination with the work of A. Bitschi, a publication about a transverse flux linear generator design for geothermal power conversion was elaborated ([3]). Additionally, B. Klöckl extended his collaboration with the University of Leoben, which resulted in another publication about permanent magnet synchronous machines ([4]). During July 2003, the High Voltage Laboratory hosted the academic guest Prof. Jong-Beom Lee from Wonkwang University, South Korea, who was attended by B. Klöckl. As a result of this visit, a publication in the field of time-frequency analysis of transients in power systems is to be submitted to IEEE (preliminary working title see publication [5]).

References [1] T. Christen, M. W. Carlen: Theory of Ragone plots; Journal of Power Sources 91

(2000), 210-216 [2] T. Christen, C. Ohler; Optimizing energy storage devices using Ragone plots;

Journal of Power Sources 110 (2002), 107-116 [3] B. Klöckl, K. Fröhlich: Energiekonversion Downhole – eine Vision; presented at the

Electrosuisse PES meeting "Geothermal Energy Conversion", Brugg, Switzerland, 19/3/2003

[4] A. Thaler, B. Klöckl: Measurement results using the fictitious field current model for PMSM; presented at the European Power Electronics Conference, Toulouse, France, 2-4/9/2003

[5] K.-H. Kim, J.-B. Lee, B. Klöckl, K. Fröhlich: Wavelet and neuro-fuzzy based fault location for combined overhead/cable transmission lines (working title); to be submitted to IEEE Trans. Power Delivery


ECONOMIC ADVANTAGES OF INNOVATION IN POWER SYSTEMS Martin Hinow

Goal of the project The liberalization on the energy market forced the energy suppliers to optimize the costs in their system. The substation is one of the most cost sensitive points in a power network. The investigation of the project focuses therefore on the Life Cycle Cost of a substation. The cost evaluation deals not only with the components to be considered. Usually a modification in the substation layout or a replacement of a component has consequences for the overall expense. A simple comparison of cost is thus not possible. The substation has to be considered as a complex system. The goal of the project is to develop a methodology for LCC-calculation, which takes the substation complexity into account.

Stress dependent LCC The power transformer is one of the most important and most cost intensive items of equipment for electrical power transmission and distribution. If a fault in a transformer occurs, this causes not only an interruption of electrical power but also large economic losses. From failure experience on transformers it is widely suspected that inrush currents, occurring when energizing unloaded transformers, was the reason for


47

substantial damage. The investigation therefore centres on how the controlled switching technology avoids inrush currents and reduces the stress profile for the transformer. It is fair to ask the question in which application fields the additional investment cost for the switching technology is balanced by the extended lifetime of the transformer.

Maintenance strategies Power companies want to reduce their maintenance cost by eliminating any superfluous maintenance schedule. However, a lower maintenance frequency can lead to a higher failure rate of the components. In this case the penalty cost for the energy not delivered and higher investment cost for the earlier replacement of the component are to be taken into account. The questions to be asked is: what is the cost with the present day maintenance schedule and what is it with an optimized maintenance strategy and in which application fields it is useful to change the strategy to the condition-based maintenance?

Substation layout modification One very well known controversial subject is how much redundancy should there be in the optimized substation layout. Highly redundant structures have high investment and maintenance cost. The additional components (double bus bar in a GIS for example) have to be maintained. On the other hand, the higher availability reduces the possibility of incurring high penalties.

State of the art of the project A methodology to calculate the stress dependent life cycle cost for one component has been developed. It includes a Markov process which comprises four condition states. This model has been applied in the assessment of two case studies. One deals with the economic benefit of controlled energization of the power transformer, the other deals with the impact of the monitoring and diagnosis system of the circuit breaker. The result of both case studies was that the innovations were amortized within a few years.

Outlook for 2004 The next step is to enhance the model to handle configurations with more components. Therefore the methodology has to be combined with a sensitivity analysis. Furthermore there is a need to develop methodologies to model aging processes and different maintenance strategies. One possible methodology may be found in the determination of maintenance-dependent reliability characteristics.

Partnerships: ABB Switzerland, Alstom France, NGC England, RWE Germany


48

MODEL-BASED TRANSFORMER DIAGNOSIS Wolfgang Hribernik

Goal of the project Power transformers are one of the most expensive investments in an electric power system. The deregulation of the electricity market forces the power utilities to reduce maintenance costs. This leads to a lack of transformer specific knowledge inside a power utility and increases the risk of a transformer failure. Moreover, the changed market situation increases the demand for controlled transformer life-time management. In order to estimate the actual condition of a power transformer, diagnostic measurement techniques such as dielectric spectroscopy, frequency response analysis, partial discharge measurement, etc. are in use. For the interpretation of the results and based on that a decision what further action is called for requires knowledge about relations between the measured properties – a model. Sensors e.g. for transformer temperatures, oil humidity, gas in oil, etc. provide data reflecting the actual transformer condition online. However, intelligent procedures for data interpretation are needed in order to gain information about the transformer condition from the data sets delivered by the sensors. Combining models for offline and online measurement techniques provides synergies, either for the modelling process or for decision making.

Model structure for a model-based diagnosis system For the thermal and dielectric behaviour of a power transformer, a model structure providing diagnosis facilities has been developed (Fig. 1). The thermal subsystem calculates transformer temperatures from load and ambient conditions. A dielectric subsystem predicts the (nonlinear) diffusion process of water from transformer oil to transformer paper. Dielectric spectroscopy provides information about the initial moisture content of the transformer. The predicted values are compared with data obtained online by means of sensors. This redundancy gives the opportunity to distinguish between system changes, sensor faults and modelling errors.

ambient temperature To

Tpthermal

subsystem

dielectric subsystem

(online)

ho

hpdielectric

subsystem(offline)

resi

dual

gen

erat

or

decision

Tp

To

hp

cooler statusload

paper moistureoil temperature

diel. response functionpaper temperature

oil temperatureoil conductivity

Ta

f(t)

To

hp

cS

TpToγo

ambient temperature To

Tpthermal

subsystem

dielectric subsystem

(online)

ho

hpdielectric

subsystem(offline)

resi

dual

gen

erat

or

decision

Tp

To

hp

cooler statusload

paper moistureoil temperature

diel. response functionpaper temperature

oil temperatureoil conductivity

Ta

f(t)

To

hp

cS

TpToγo

Figure 1: Model structure for a model-based transformer diagnosis system. A residual generator compares measured and predicted values. Redundancy between some residuals provides the chance to

distinguish between transformer faults, sensor faults and modelling errors.


49

An experimental setup consisting of a 630 kVA distribution transformer equipped with a controllable loading setup provides the functionality for heat runs (see Fig. 2). Sensors for temperatures, load and oil humidity deliver signals that are recorded with a data logger. The setup is used to adapt the model with model verification procedures and furthermore to develop procedures for implementation of the diagnosis system at a power transformer in the field.

0 20 40 60 800

20

40

60

80

Time (hours)

oil t

empe

ratu

re (°

C)

0 20 40 60 800

5

10

time (hours)

oil h

umid

ity re

l. (%

)

Figure 2: Measured values of transformer oil temperature and relative oil humidity during a heat run

test.

Outlook for 2004 • Improved modelling of the diffusion process of water between transformer oil and

transformer pressboard. • Development of adaptive strategies for identification of the temperature

dependent diffusion coefficient. • Modelling of the static and dynamic behaviour of capacitive-type sensors for

relative oil humidity. • Validation of nonlinear models and self-learning systems using the subsystems of

the model-based diagnosis system.

Partnerships: PSEL EPF Lausanne Chalmers University of Technology Gothenburg, Sweden BPA Bonneville Power Administration, Portland OR, USA


50

NEW SWITCHGEAR TECHNOLOGY (NST) Manfred Grader, Stefan Berger

Goal of the project The fundamental design of today’s high-voltage circuit breakers has not changed for several decades, and it appears that the limits of improvement of this technology have almost been reached. The main points of the NST project are the concept and design of new, unconventional switching principles and the exploration of the physical and technical fundamentals of their elements. Particular attention is paid to the requirements of potential configurations of power networks of the future.


CIRCUIT BREAKER REALIZED BY A MATRIX OF SMALL CONTACTS Manfred Grader

Introduction Based on experiments with a small number of low current contacts connected in series and parallel, calculations have been made to estimate the requirement of numbers of contacts to implement circuit breakers with a high switching capacity. Thought has been given to the required space, the power losses and to the costs.

Number of contacts for successful switching The basic values of the contacts in the calculations are taken from the properties of relays [1] we have used for building up the matrix in the experimental setup. The parameters of the rated voltage, rated current and the short-circuit current are taken from standardized values of the medium voltage (MV) and high voltage (HV) domain. Figure 1 shows the required number of contacts connected in series and the number of parallel paths to build up a current-limiting circuit breaker. The number of required parallel paths m is given by the current, carried by the matrix. Given that the short-circuit current is limited by the breaker, the values of the rated current Ir result in the number of parallel paths in the MV and HV regime. The number of contacts n is defined by the fact that the short-circuit current is limited by the sum of the arc voltages (20 V) of the opening contacts connected in series. Calculations have also been made for a current-zero circuit breaker due to the fact that the boundary conditions are completely different. In this case the number of parallel paths is given by the ability to carry the short-circuit current for one half-wave and the number of contacts connected in series is influenced by the required withstand voltage of the breaker and the electrical strength of the gap of an open contact. Figure 2 lists the total number of contacts for a matrix implemented as a current-limiting circuit breaker and a current-zero circuit breaker. The dimensions of one elementary switching system (contact, drive and condenser) leads to the space required for the matrix.


51

n

m

4000 6000

500

1000

300

Ur = 12kV625

400

Ur = 72.5kV

Ir = 1250A

1250

1800 3600

Ir = 2500A

Ur = 245kVUr = 145kV

Ir = 800A

6100

MV

HV

Figure 1: Number of contacts connected in series (n) and the number of parallel paths (m) for a current-

limiting circuit breaker

Although the number of contacts is pretty high, the space required is not the problem. But considering that the costs for one elementary switch are in the range of 1 CHF, building up a matrix of such dimensions is not practicable.

current-zero breaker

current-limiting breaker

MV HV

number of contacts (x1000)

83.2 - 570

120 - 1125

1400 - 2930

2250 - 7625

volume (m3)

MV

0.12 m3

HV

0.63 m3

0.24 m3 1.6 m3

Figure 2: Total number of contacts and dimensions of the matrices

Also an analysis of power losses has been made. The calculations point to the fact that the losses are linearly dependent on the number of contacts connected in series. Furthermore, the losses of a current-limiting breaker are pretty high (some hundreds of kW), due to the fact that we have a low number of parallel paths and a high number of contacts connected in series.

Outlook for 2004 • Next step is now to define the necessary standards of an elementary switching

system for creating a practicable matrix out of these calculations. • Estimation of the possibility to implement a practicable matrix with other

technologies (e.g. nanotechnology).

References [1] AXICOM data sheets, FX2 Relay, http://relays.tycoelectronics.com/axicom/relays.stm


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FAST SWITCHES AND HYBRID COMBINATIONS Stefan Berger

Introduction Research on fast switches and their behaviour in hybrid switching systems has been followed up. Up to now adequate knowledge of the arc physics and electrical behaviour for contact separation speeds grater than 10 m/s seems to be absent from the literature. Measurements with fast switches in various circuit configurations were therefore performed, especially focused on the current commutation in hybrid systems. Besides the electrical characteristics of the arc during commutation, it is of particular interest, whether there exists a limit for arcless commutation and if so one wants to know its dependence on the circuit parameters and the contact separation speed. A new fast switch has been developed to reach higher velocities (50 m/s) of the moving contact. This switch has one breaking contact and a low impedance in the current path. It has been placed in a test arrangement for alternating currents up to 10 kA at voltages in the range of 50-1000 V.

Test arrangement A synthetic test circuit has been built to measure the current commutation behaviour at different contact speeds with variable parameters of the commutation path (Fig. 1) The total current has been measured with a current transformer, the current in the parallel path with a 1 m shunt. A differential probe has been used for the voltage measurement. The measurement arrangement has also been improved due to potential separation and lower current coupling resulting from the drive coil of the fast switch.

Ct Rfs

Lfs

RtLt

Rpar

Lpar

RshuntFast Switch

i_tot

u_fs

i_par

V

switched path (fs)

parallel path (par)

Figure 1: Schematic of the test circuit

Measurements Figure 2 shows typical waveforms during the commutation process for two different circuit configurations. One can identify a phase of sliding contacts between 90 µs and 590 µs after the beginning of the current flow in the drive coil as a result of the contact geometry. In this phase the arc is very short and the voltage drop is determined by the electrode falls. Thereafter an arc burns as optically detected, which is confirmed in the voltage and current waveforms. The commutation time is about one millisecond or


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lower even at relatively high circuit impedances in the commutation path. At contact velocities greater than 20 m/s the arc voltage increases almost linearly with time, which is in good agreement to a blackbox model after Ayrton.

Figure 2: Typical waveforms during in the commutation interval. Parameters: v = 23 m/s, Lt = 230 µH,

Ct = 43 mF, Rt = 32 mOhm; (a) Lpar = 3.2 µH, Rpar = 72 mOhm; ( b) Lpar = 1.7 µH, Rpar = 49 mOhm

By now the limit for arcless current commutation could not be detected. Theoretical considerations indicate that this limit is strongly dependent on the commutation circuit impedance rather than the opening speed. None the less the fast switch offers a commutation time of less than 500 µs.

Outlook for 2004 • Complete the measurements and data analysis of the commutation process • Investigate the influence of the contact material • Derive a physical model that suits the measured data as well as known theory • Modelling of the system behaviour of rapidly elongated arcs


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MATIC – MEASUREMENT OF ARCING TIME IN CIRCUIT BREAKERS Mike Chapman

Goal of the project In the context of condition-based monitoring, a circuit-breaker monitoring algorithm is being developed that provides an improved estimate of contact and nozzle damage. One critical parameter in this algorithm is the duration of the arc for each switching operation, that is, the time from contact separation to current extinction. The goal of project MATiC is to develop a reliable method for measuring the individual arcing times of high-power switching arcs in circuit breakers in a non-invasive manner. There is special interest in application of the monitoring algorithm to generator circuit breakers, which have a high profit potential from condition-based monitoring.

State of the art It is possible to provide the circuit-breaker monitoring algorithm with an estimate of arcing time. Given a measurement of the arcing-contact travel curve and the geometry of the arcing zone, an estimate of the arcing time can be calculated. However, this is an indirect method of estimating the arcing time, so a direct method of measurement is sought both in the light and electromagnetic signals proceeding from the arc. Solutions involving measurement of the light have been rejected because they require access inside the arcing chamber. The presence of electromagnetic energy in substations has been studied from the perspective of EMI. More recently, it has received attention in the design of fault-detection and monitoring systems. However, no acceptable solution has yet been presented concerning the direct measurement of arcing times. In previous work on this project, measurements with electrical antennas have indicated that such an approach is indeed feasible. In the last year the measurement methodology has been improved, and a solution has been found for measuring the arcing time of a single breaker chamber. Emphasis in the project has therefore been shifted to the problem of distinguishing between the arcing signals of a three-phase breaker.

Coupling of the arc signal A measured arcing signal is displayed in Figure 1, along with the breaker current and terminal voltage. The high-frequency signal has been filtered, amplified and demodulated before capture; in this way only the essential signal information is extracted. Previously, strong bursts of measured energy were observed at key events in the switching process, but the measured signal was weak between these events. The improved method of measurement has increased the coupled signal strength compared to the previous methods, so that a consistent difference in the signal energy can be observed throughout the entire arc duration. This important result implies a significant shift in the arcing time measurement algorithm. If the signal energy can be observed throughout the arc duration, the algorithm is greatly simplified. Inasmuch as the duration of an individual arc can be measured, the problem of three-phase measurements becomes one of measuring in a location where the signals are decoupled, or possibly of decoupling them by means of the measurement. This problem is being approached in the context of generator circuit breakers, wherein it is analagous to partial discharge and very fast transient studies in GIS and generators. Basic initial modelling of the generator circuit and existing knowledge indicate that


55

electrical phase decoupling in the switch and along the conductors is high, which reduces interference. However, damping in the line propagation is weak and capacitive coupling at bus bars is strong, so interference can be expected. Tests and modelling are being carried out to analyze how the arc signal of one phase arrives at the other measurement locations, its significance, and if necessary how this interference can be minimized or even decoupled.

Figure 1: Sample demodulated arc signal with breaker current Is and terminal voltage Us

Outlook for 2004 • Verify measurement results in high-power switching tests at ABB facilities • Develop a solution for three-phase measurement

Partnerships: ABB Switzerland, ABB Greensburg USA


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ARCHITECTURE OF ARTIFICIAL INTELLIGENCE FOR CIRCUIT BREAKERS Urs Krüsi

Goal of the project The overall goal of this project is to develop a circuit breaker incorporating some artificial intelligence. To determine what kind and how much artificial intelligence is required, and which tasks it should perform, are the questions to be answered. In the past year the efforts focused on two subjects:

• Comparison of the calculated restrike probability while de-energizing capacitor banks with laboratory measurements

• Identification of circuit breaker dependences on external parameters like temperature, drive energy, idle time and closing coil voltage for circuit breakers already installed.

Restrike probability while de-energizing capacitor banks In cooperation with Per Jonsson from ABB Sweden, it was possible to verify the theoretical calculation of the restrike probability. It could be shown that with the help of the proposed calculation method the predicted potential for up-rating – use of the breaker at higher voltages and/or frequencies – was in very good agreement with the measured characteristics. The results have been accepted for publication at the CIGRE Session 2004 [1].

P (bar)

∆t?

P (bar)

∆t

I (s)

∆t?

P (bar)

∆t

P (bar)

∆t?

P (bar)

∆t

I (s)

∆t?

P (bar)

∆t?

P (bar)

∆t

V (V)

∆t?

P (bar)

∆t

P (bar)

∆t?

P (bar)

∆t

V (V)

∆t? P (bar)

∆t?

P (bar)

∆t

P (bar)

∆t?

idle time

closing coilvoltage

drive pressureController

closing resistors

transients

P (bar)

∆t?

P (bar)

∆t

V (V)

∆t?

P (bar)

∆t

P (bar)

∆t?

P (bar)

∆t

T (°C)

∆t?

temperature

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∆t?

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∆t

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∆t

V (V)

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∆t

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∆t

V (V)

∆t? P (bar)

∆t?

P (bar)

∆t

P (bar)

∆t?

idle time

closing coilvoltage

drive pressureControllerController

closing resistors

transients

P (bar)

∆t

P (bar)

∆t?

P (bar)

∆t

V (V)

∆t?

P (bar)

∆t

P (bar)

∆t?

P (bar)

∆t

T (°C)

∆t?

temperature

Figure 1: Illustration of the project goal: After monitoring the normal operation of the circuit breaker the controller identifies the characteristics needed to compensate the variations in closing time due to idle

time, closing coil voltage, temperature and drive pressure for controlled switching


57

Identification of circuit breaker characteristics for controlled switching Circuit breakers show variations in closing time due to variations of temperature, idle time, drive energy and close coil voltage. The degree of the variation is design dependent. For new circuit breakers these characteristics were determined by specialised tests to adjust the closing time in order to ensure consistent performance with controlled switching. Such characteristics are usually unknown for circuit breakers that were installed more than 10 years ago. The goal is to monitor the operation of the circuit breaker during its normal operation and separate the influences of the temperature, closing coil voltage, idle time and drive pressure. Controlling the breaker without a compensation of these variations will usually not result in an acceptable performance. By the potential elimination of pre-insertion resistors controlled switching may significantly cut down maintenance costs [2]. Simulations imply that such identification on a circuit breaker is possible. Laboratory tests on a 145 kV SF6 circuit breaker were started to verify the methods.

Outlook for 2004 • Complete the laboratory tests of the identification and evaluate the results • Publish the methods for the identification of circuit breaker characteristics

References [1] U. Krüsi and P. Jonsson, Increased performance of capacitor bank circuit breaker

by controlled opening, accepted for publication at CIGRE Session 2004, Paris [2] CIGRE WG A3.07, Controlled Switching of HVAC Circuit-breakers Benefits of

Controlled Switching, to be published on www.cigre.org, 2004

Partnerships: ABB Switzerland, ABB Greensburg USA


58

LOW FREQUENCY ACOUSTIC NOISE FROM OVERHEAD HIGH VOLTAGE LINES (PROJECT CONOR) Micha Semmler, Claudia Roero, Ueli Straumann, Timm H. Teich, Hans-Jürg Weber

Overall aim To elucidate the mechanisms of tonal noise generation on high voltage lines after precipitation and to assess methods to reduce such noise emissions.

General introduction Some high voltage lines emit tonal noise, particularly at twice mains frequency (100 Hz), when they are wet. The noise levels occurring may be unacceptable in sensitive locations. 100 Hz oscillation of water droplets on model lines had been convincingly recorded in the laboratory but it has been shown (see subsequent text) that the mechanical motion on its own cannot quantitatively explain the 100 Hz emission. Nevertheless, water drop deformation in the electric field and associated Taylor instability can be instrumental in charge injection into the immediate surroundings of the conductors. This charge injection is subject to present investigations by electrical and optical means. Meteorological conditions – rain intensity and duration, drop sizes, fog or rime – have a bearing on sound emission levels. The relationships involved are in the process of being mapped and should be useful in noise level predictions for the utilities. A remedy against tonal emission after precipitation is seen in the reduction of the population of readily deformable water drops on the conductors by encouraging run-off and drying as well as attaining drop shapes less subject to deformation. A hydrophilic surface can provide these properties, and various surface preparations have so far been studied under laboratory conditions.

Partnerships: Buwal Switzerland EnBW Germany APG Austria Illwerke Austria PSEL Switzerland


59

SURFACE PROPERTIES AND DROP/NOISE BEHAVIOUR Claudia Roero

Introduction Accepting that water drop deformation in the electric field is involved in generating tonal emission from overhead high voltage lines, facilities have been set up for detailed optical investigation of the single drop deformation in DC and AC fields and have proved their capability to yield significant information on the parameter dependence of deformation. Previous studies showed that with a strongly hydrophilic conductor there is a rapid initial decay of acoustical emission on cessation of rain. For this reason one is still looking for a suitable coating which shows a rapid initial water run-off and drying of the conductors and thus accelerates the recovery of the quiet conditions. Moreover, a potentially good coating should display a satisfactory stability of its characteristics as regards exposure to sunlight, different temperatures, different atmospheric conditions, but above all with increasing age.

Deformation of single drops in a DC and an AC field To elucidate the process involved in the acoustic emission from overhead high voltage lines a DC study of single drops was carried out. This investigation provided details on the instability of a water drop in the electric field in dependence on drop size, surface condition and field strength. Instability controls the size of surviving drops on the conductor, which contribute to sound emission. A record of all stages of water drop instability development at up to 10000 frames per second was also done, aiming to catch step by step the ejection of a fine water jet which follows instability. To asses the resonance effect with a single water drop a quick demonstration AC investigation was done. In an AC field drop motion is found to be subject to different oscillation modes and resonances in the frequency range of particular interest (100 Hz) dependent on drop size and electrical field strength. Records of motion sequences for different size drops in an AC field demonstrated that the oscillation of drops of smaller size is rotationally symmetric, while that of the bigger drops is seesaw.

Characterization and measurements of different surfaces and coatings In order to find a coating which shows a hydrophilic behaviour for a reasonable length of time, a number of samples and coatings were obtained from different companies and institutions. One set of samples analysed was half coated with photoactive material, annealed at different temperatures. It was proved that exposure to sunlight of those titania surfaces reduces contact angle also near to zero, but the effect does not persist long enough to give a significant noise reduction for more than a few hours after exposure (see sequence in Fig.1). It was demonstrated that another coating not based on titania is much more effective, as the hydrophilic effect appears to persist for six months or more even without any exposition to ultraviolet light. This coating seems to be potentially a good material to cover high voltage transmission lines. However, additional studies of the properties of the coating have to be carried out with respect to temperatures, different atmospheric conditions (rain, fog, snow, ice), increasing age (contamination, corrosion), etc.


60

Before sunlight, θ = 57° 0 min after sunlight, θ ~ 0°

4 hours after sunlight, θ = 23° 16 hours after sunlight, θ = 40°

Figure 1: Behaviour of a 50 µl droplet before and after UV irradiation.

To assess dependence of acoustical emissions during and after rain on field strength and on surface properties, a series of surface preparations (untreated, hydrophilic coated, hydrophobic coated and sandblasted) on stainless steel and aluminium have been analyzed. As example the case of the 20 mm diameter Al tube is reported in Fig.2 to compare the effect of different treatments/coatings with respect to noise emissions. All the results refer to 4 minutes ‘mean rain’, a quantity which corresponds to 0.39 mm/min at the conductor centre. Another acoustical measurement of interest is that regarding the variation of the noise level with respect to different electric field strength values. As examples the case of the 20 mm diameter Al tube covered with the potentially good hydrophilic coating is shown (Fig. 3). With this coating it is clear that the decay is rather rapid for all the field strength values and that the immediate return to the baseline amounts typically to 5 dB/ min.

Outlook for 2004 It has been demonstrated that one of the hydrophilic preparations analyzed could be potentially a good coating for overhead high voltage transmission lines. This needs additional investigations with regard to the durability of such coating under different conditions. Facilities for automated recording of water drop populations have to be generated and to be applied to population changes by variation of conditions.


61

Al, mean rain, 100 kV

34

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@ 1

00 H

z [d

B]

untreated (1)

hydrophilic(2)

hydrophobic (3)

sandblasted (4)

Rain

1

2

3

4

Figure 2: Decay of sound level after cessation of rain at t = 8’ for an Al tube with different

coatings/treatments

Al with hydrophilic coating, mean rain

0.0

5.0

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el @

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]

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80 kV (2) 90 kV (3)100 kV (4)

Rain

1

2

3

4

Figure 3: Hydrophilic conductor with different electrical surface field strengths proportional to rms

voltages given (note the shorter time scale).


62

TONAL EMISSION AND PRECIPITATION Micha Semmler Overhead high voltage transmission lines are exposed to precipitation which loads conductors with a certain amount of water, ice or snow. Subject of this part of CONOR are tonal emissions during the period of precipitation. Currently the focus is on rainfall and possible differences rain and fog give rise to.

Droplet populations on model conductors The experimental setup includes model conductors that can be subjected to high voltage (up to 100 kV) and a sprinkler system with several well-characterized nozzles (mean droplet size, rainfall) that produce rain or fog. If one knows the droplet population (size distribution) on the surface of the cable and the tonal emission due to a single droplet one should be able to determine the tonal emission from the entire high voltage transmission line.

Droplet diameter

Dro

plet

cou

nts

/ siz

e cl

ass

hydrophilic hydrophobic

sessile

pend

ant

pendant + sessile

(a)

Figure 1: Size distributions. (a) Schematically for (solid line) hydrophobic surfaces and (dashed line)

hydrophilic surfaces. (b) Droplet population on a model conductor (stainless steel, polished) with high voltage (dashed line, field strength 20 kV/cm) and without any voltage (solid line)

at heavy rainfall. Lines indicate log-normal fits to sessile droplets. Inset: Size distributions of pendant droplets, fitted by normal distributions.

Droplet populations depend on several parameters from which the most important is probably the nature of the conductor’s surface. A hydrophilic surface leads to an aqueous film (50-100 µm thick) around the cable and large pendant drops on the underside. In contrast one observes a bimodal population if the surface is hydrophobic: numerous small sessile droplets on top and a second mode of larger sessile and pendant droplets (Figure 1a). The presence of an electric field yields an enhanced number of small droplets as compared to a population without electric field (Figure 1b). Changes in the precipitation produce nonuniform trends, investigations of which have to be continued.

Total amount of water and noise level Within the first 1000 s a model conductor or real cable is exposed to precipitation the total amount of water increases monotonously (Figure 2a) except for sandblasted surfaces, where some reduction in resident water is observed after about 300-500 s

0 1 2 3 4 5 6

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63

(not shown). The total amount of water is reduced by several parameters: a lower rainfall (Figure 2a), an increase in the electric field strength, and an increasing hydrophilicity. Differences we see between model conductors and real cables are attributed to an artifact from the measurement and have not been investigated in detail so far. When precipitation begins a distinct noise signal is detected in the 100 Hz third-octave band and its harmonics. Interestingly all these frequencies exhibit different dependencies with time as the rain continues. The noise level in the 100 Hz third-octave increases rapidly by several decibel right after the rain has started. It remains constant or even decreases slightly in heavy rain, while it continues to increase for lower rates of precipitation at a lower noise level (Figure 2b). The trend with regard to rainfall is non-uniform: the noise levels at moderate rain and dense fog are identical within error limits. Again, differences between model conductor and cable are likely to originate from experimental limitations.

0 200 400 600 800 10000

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moderate raindense fog

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Figure 2: Model conductor (full symbols) and real cable (open symbols), both having an oxidized

aluminium surface, with applied high voltage (field strength 20 kV/cm) and at different rainfall.(a) Total amount of water (expressed as equivalent film thickness a water film would have if the entire water

were distributed homogeneously all over the surface) and (b) noise level in the 100 Hz third-octave band as a function of time elapsed since precipitation has started.

Prospects for 2004 • Physical models that explain the observations have not yet been developed. So far

the investigations have been descriptive only. It is essential to derive a model that is able to predict the size distribution and the total amount of water from any rain for a given conductor, possibly with a modified surface. Furthermore it is of practical interest to find a threshold precipitation at which noise emissions become significant.


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ON THE GENERATION OF THE TONAL EMISSION Ueli Straumann The idea that the 100 Hz tonal emission from high voltage lines is entirely due to the membrane-like periodic deformation of the water drops, seems to be inadequate. Investigation of the sound level emitted that way from a single drop showed it to be too low. The physical cause of this is generally speaking the multipole nature of such a source, which is due to the incompressibility of water. Further investigations in the past year showed that a model conductor with mechanical fixed protrusions exposed to high voltage also produces a tonal emission of 100 Hz. The hypothesis of today suggests that the liquid water drops under high voltage are deformed to a more pointed shape. With this form, the enhanced electrical field leads to discharges, which provide the energy for the tonal emission with a yet unknown process. This hypothesis is backed up by the fact that the discharge current is relatively symmetrical and that the power input of the discharge is more than large enough to provide the energy needed for the acoustical emission.

Oscillation frequency of drops and acoustical emission Investigations were made of drops with rotational symmetry and a contact angle of 90°. The surface ( )θR of such drops may be expanded in spherical coordinates according to

( ) ( ) ( ) ( ) ,~1 21

⎟⎟⎠

⎞⎜⎜⎝

⎛+=+= ∑

∞

=θθδθ l

lloo PtbRRRR

where oR is the radius of the undeformed drop, ( )θlP2

~ are standardised Legendre polynomials and ( )tbl their coefficients. Following the ideas of [1] and demanding that ( )°90R does not change in time, this leads, by taking only the lowest terms as a rough approximation, to the oscillation frequencies shown in Fig. 1. According to Fig. 1, drops with a radius of 1.7 mm or a volume of 10 µl would have a resonance at 100 Hz. Experiments proved this resonance, but showed also that drops of the size of 40 µl (theoretically 50 Hz oscillation frequency) have relatively large oscillation amplitudes. Sound emission of such a source is presented in Fig. 1. The emission of this membrane-like, mechanically deformed drop seems to be too low: There would be several millions of such sources necessary to produce sound levels measured on the 1 m long model conductor.

Acoustical emission from protrusions The protrusions on the conductor consisted of solder points about 4 mm long. The number of points was about 54. The sound emission of this arrangement is shown in Fig. 2. Remarkable are the relatively strong tonal emissions of 100 Hz (> 20 dB above the background) and their higher harmonics (namely 200 and 400 Hz). Thus it seems that there must be an emitting process possible which does not require the periodic deformation of the drops as acoustical membranes. It seems to be likely that this process involves discharge currents.


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10-4 10-3 10-2100

101

102

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104

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Freq

uenc

y [H

z]

0 10 20 30-110

-100

-90

-80

-70

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Soun

d le

vel [

dB]

Figure 1: The oscillation frequency of sessile water drops against their radii (left side). Calculated sound

level against the distance from the source, which consists of the 40 l water drop with oscillation amplitude of 40% of its radius (right side).

As investigation of the discharge currents pointed out, the discharge current is relatively symmetric on both half-waves. Partial discharge measurement suggests that the current is composed of Trichel pulses in the negative half-wave and a current with low dynamics in the positive half-wave. Measurements of the photonic emission give reason to assume that this latter current is a glow discharge. Together with these discharge currents, there is also the assumption that there are swarms of ions living longer than one half-cycle in the air and contributing to the discharge current. This assumption is supported by the values of the transit time, which means the time needed by the heavy ions to cross the discharge gap (see [2]). Calculation of this time points out that the ions would not cross the entire gap within a half-wave-time. The energy of the discharge current would be large enough to produce the measured sound levels.

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und

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]

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Figure 2: The sound level measured with the model conductor with solder points.


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Outlook for 2004 Understanding of the discharge current and its link to acoustical emission Further modelling of the drop deformation and its influence on the discharge current

References [1] Lord Rayleigh, "On the Capillary Phenomena of Jets". Proc. Roy. Soc. London 29, No.

196, 1879. pp. 71-97. [2] W.L. Lama und C.F. Gallo "Systematic study of the electrical characteristics of the

‘Trichel’ current pulses from negative needle-to-plane coronas". Journal of Applied Physics, Vol. 45, No. 1, 1974. pp.103-113.

DISCHARGE BEHAVIOUR OF SESSILE WATER DROPS Timm H. Teich, Hans-Jürg Weber

Aim To assist efforts to elucidate the processes involved in the generation of tonal acoustic emissions from high voltage conductors

Experiment A small-scale setup has been used to expose single sessile water drops to globally homogeneous or moderately inhomogeneous DC electric fields. Discharge currents and light emission from the arrangement are measured with bandwidths from DC to > 100 MHz. In order to register the passage of small water droplets ejected from drops reaching instability, a flat band of UV-rich light is passed between the apex of the sessile drop and the (upper) counter electrode to which the ejected droplet will move on account of its charge. Water drops of defined volume (2….100 µl) were placed on the hydrophobic surface of a metallic hemisphere of 10 mm radius residing centrally on the lower flat electrode of a 30 mm spacing homogeneous field discharge gap. Voltage of either polarity is increased to first discharge inception. As inception is controlled by drop deformation/instability, the onset voltage is the same for either polarity or decreases with increasing drop size. With negative drops, discharge onset produces a sequence of "packets" of fairly regular Trichel pulse trains [1], each of which is evidently terminated by droplet ejection (Figure). The "packet" repetition frequency (ca. 20….110 Hz) depends strongly on drop volume and is interpreted here in terms of resonant oscillation of the deformed drops. At a voltage kept constant the sequence comes to an end when the drop volume has been sufficiently reduced so that the onset conditions are no longer fulfilled. The fast front of each current pulse representing the ionisation period is associated with UV emission, while the scattered light signal produced by the passage of the ejected droplet is – of course – not associated with any appreciable current as the charged droplet motion is too slow to produce a readily measurable current signal. With positive drop polarity, behaviour appears to be similar, with burst pulse corona in place of the far more regular but lower amplitude Trichel pulses.


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Conclusions Water drops reaching instability in the electric field are significant sources for charge injection to the surroundings. In the absence of other sharp protrusions, they will be the only sources at reasonable voltage levels. All ionisation phases of current pulses are associated with UV light emission, so that optical observation is a valid method to map all ionisation generating processes.

Figure 1: Light emission (top two traces) and current (lower two traces) of Trichel pulse "packets"

recorded at discharge inception on a negatively charged 50 µl drop. The "satellite" light pulses (↓ ) signify the passage of a charged droplet towards the anode. The middle two traces are synchronous x20

expansions made to show that no significant current is associated with those light signals.

Outlook for 2004 The validity of the observations presented has to be proved to be maintained in large systems. Single drop coupled discharge and mechanical behaviour has also to be observed under AC conditions.

References: [1] W.L. Lama and C.F. Gallo, "Systematic study of the electrical characteristics of the

‘Trichel’ current pulses from negative needle-to-plane corona", J.Appl.Phys. 45(1), 103-113


68

ACIM - AGING OF MICACIOUS INSULATION MATERIALS Ruben Vogelsang

Goal of the project The goal of the project is to determine the main factors that lead to reduction of lifetime in winding insulations of high voltage rotating machines. The results are used to focus further research on the main factors that reduce lifetime of the insulations in order to improve materials and manufacturing techniques. In the past year, the efforts were focused on determination of time to breakdown of winding insulations with:

• different quality of industrial manufacturing • mechanical vibrations between 0 Hz and 50 Hz vibration frequency

Lifetime of winding insulations at different quality of industrial manufacturing In previous investigations it has been shown that electrical treeing is the main electrical degradation mechanism of winding insulations [1]. Based on that finding, a new method has been developed to test winding insulations with far less material and effort. This method allowed in a short time to investigate different factors that may influence lifetime of high voltage rotating machines. In order to determine different quality of industrial manufacturing, the newly developed test arrangement has been used. This arrangement has been described in detail in [1] and [2]. For the tests, two different types of material were chosen. The winding insulations were all manufactured in an industrial plant. The bars were taken from the production line. For comparing the results, time to breakdown was also determined for bars of the same materials prepared in a reference process. The reference process is characterised by automatically taping in a special application laboratory. The tests were carried out at a voltage of 32 kV rms, with a constant insulation thickness of d = 2 mm and at room temperature. Figure 1 shows the 63% values of time to breakdown with the 95% confidence intervals of the tests with the reference materials and industrially manufactured materials. The results show that for tests with both types of manufacturing, time to breakdown is significantly lower than for the reference material. The reduction of time to breakdown for the 63%-values is by a factor of 500 for material 1 and by factor 23’000 for material 2! The dramatic difference in time to breakdown shows that the type of manufacturing has a significant influence on insulations lifetime, even before the winding insulation is installed in the machines. The reason for such a reduction lies in the different material structure. Figure 2 shows the material at reference production. In contrast, in Figure 3 the material at poor industrial production shows many voids and delaminations at the conductor and within the insulation itself. When the tapes are not applied tight enough or when the impregnation quality is poor, the binder resin cannot fill all the regions at the conductor or between the mica tapes well enough. This causes voids and delaminations in the material as seen in Figure 3. The voids at the conductor lead to immediate tree inception after voltage application. The delaminations and voids in the insulation lead to very fast tree propagation through the material. Both processes caused the very low time to breakdown, shown in Figure 1.


69

0.01

0.1

1

10

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R1 M1 R2 M2

Tim

e to

bre

akdo

wn

[h]

Material 1,reference

manufacturing

Material 1,industrial

manufacturing

Material 2,industrial

manufacturing

Material 2,reference

manufacturing

Lower by aFactor 500 !

Lower by aFactor 23‘300 !

95%-confidence intervals

Figure 1: Time to breakdown values for two different materials with different types of manufacturing

500 µm

500 µm

Voids Delaminationsof tape layers

Figure 2: Material 2 at reference manufacturing

Figure 3: Material 2 at poor industrial manufacturing

Out of the results it can be concluded that manufacturing is a main influence on time to breakdown that determines the potential lifetime of the machines, even before the stator bars are inserted into the machines. It shall be mentioned that material 1 and material 2 were chosen since they are typical materials. The same effect of manufacturing quality on time to breakdown and therefore lifetime may apply for other materials too. Since testing with the new electrode arrangement demands far less effort, it is recommended to survey the insulation quality in random tests on samples from the production line.

Influence of mechanical vibrations on lifetime of winding insulations For the influence of mechanical load on lifetime of winding insulations, so far only little is known in the literature. For reasons of limitations of test equipment, investigations were only made at high deflections and low vibration frequencies. In the slot of rotating machines, there are vibration frequencies of 100 Hz with rather low amplitude. In order to close that gap, a bending machine was developed that allows testing of the bars at higher vibration frequencies with deflections of ± 0.25 mm and ± 0.75 mm. Between the deflection of ± 0.25 mm and ± 0.75 mm no difference in time to breakdown values was found. Figure 4 shows time to breakdown for treeing


70

experiments at mechanical vibrations between 0 Hz and 50 Hz and its extrapolation to 100 Hz and 120 Hz vibrations.

Figure 4: Time to breakdown for 2 different materials at mechanical vibrations

The results in Figure 4 show that the vibration frequency has a strong influence on time to breakdown of the materials. The values are reduced significantly for both materials at vibrations of 50 Hz compared to no vibrations. The extrapolation of the results show that time to breakdown at 100 Hz vibrations are expected to be 2 h for material A and 0.1 h for material B. This means a reduction of factor 800 for material A and 850 for material B compared to no vibrations. It can be concluded that mechanical vibrations lead to a significant decrease of time to breakdown of the insulations at higher vibration frequencies. Such vibrations must therefore be prevented or reduced in the machines.

Outlook for 2004 Future studies will be focused to further describe the influence of different manufacturing types and the influence of temperature on time to breakdown. The intention is to determine the main factors that are responsible for the lifetime of winding insulations.

References [1] R. Vogelsang, R. Brütsch, K. Fröhlich: "Effect of electrical tree propagation on mica

insulations", 13th International Symposium on High Voltage Engineering, ISH 2003, Delft, The Netherlands, August 2003

[2] R. Vogelsang, B. Fruth, K. Fröhlich: "Detection of electrical tree propagation in generator bar insulations by partial discharge measurements", 7th International Conference on Properties and applications of dielectric materials, ICPADM 2003, Nagoya, Japan, pp. 281 – 285, June 2003

Partnerships: Gebrüder Meier AG, Regensdorf Ofima/Ofible Power Station AG, Locarno PD-Tech Power Engineering AG, Stetten Von Roll Isola AG, Breitenbach


71

PDT-COIL – POWER AND DATA TRANSMITTING COMPOSITE COILED TUBING Stefan Neuhold, Evgeny Murtola

Goal of the project (phase II, demonstration phase) Research, development and demonstration of an intelligent power and data transmitting composite coiled tubing for the exploration of hydrocarbons. In the past year the efforts focused on two subjects:

• Test of prototype conductors with two different insulation materials within the worst case environmental conditions.

• Computer modelling of the electrical system (frequency converter – PDT-Coil – drilling motor) with special focus on transient overvoltages and electric losses

Testing of a flat, solid shielded electrical conductor (with chemical protection layer) for integration into a tube wall Detailed descriptions of the applications of a flat, solid shielded electrical conductor for integration into a tube wall has been given in a previous report [1] and paper [2]. In PDT-COIL phase one, this electrical conductor for integration into a tube wall has been designed, applied for patenting and manufactured. Two prototype conductors have been produced with different electrical insulation material (1. mica/varnish insulation 2. kapton/teflon insulation). Within the period of this report, these prototype conductors have undergone various tests like:

• Dielectric breakdown tests at different rates of voltage increase • Dielectric loss measurements at 20°C, 155°C and 180°C • Liquid leak rate tests • Current capacity test of electrical shield • Mechanical fatigue life tests (extension and compression up to 2%)

These tests showed that a special focus on the mechanical fatigue life of the insulation system is necessary. The related stress in service is generated by coiling and uncoiling of the PDT-COIL tube on a transport reel with 4 metre diameter.

System simulation All the key system parameters, like conductor impedance or mutual inductance between different conductors in a COIL are frequency dependent. Along with it, converter voltage is expected to have broad harmonic content due to use of Pulse Width Modulation (PWM). In order to simulate such a system correctly, a model, based on the Fourier series expansion, has been built using the Matlab/Simulink package. The inverter is simulated by a sine-wave voltage source and its equivalent impedance; COIL – by 3 phase line with distributed parameters; motor – by its equivalent impedance and EMF source. Waveforms of the inverter and EMF of the motor are taken from practical experience and will be specified more precisely on the basis of data provided by equipment suppliers. During simulation, voltages and currents in the system were calculated independently for each frequency within the range of interest, taking into account actual magnitudes of parameters. By adding, one can get approximate signals in the time domain.


72

Simulations showed possibility of overvoltages and resonances in COIL, considerable current in the shielding conductor, high power losses.

Outlook for 2004 • Optimization of the electric insulation system and build-up of a scaled test model

with frequency converter – PDT-COIL – motor and electrical connectors. • System simulation: Integration of temperature dependence of parameters and

specific data from motor/converter supplier; transient simulation and experimental validation of the model.

Figure 1. Simulink model of system

References [1] R. Hug, S.Neuhold. PDT-COIL – Power and data transmitting composite coiled

tubing. Annual Report 2002; Power systems laboratory and high voltage laboratory; ETH Zürich, pp. 2/40 – 2/41, 2002.

[2] S. Neuhold, K. Fröhlich, D. Inaudi. "Bohrgestänge von der Rolle", SEV BULLETIN 15/2003, pp 32 – 36, 2003.

Partnerships: Airborne Development B.V., Netherlands Shell Global Solutions International B.V., Netherlands Aptec B.V., Netherlands Smartec SA, Switzerland Katholieke Universiteit Leuven, Belgium


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MODEL OF A MAGNETICALLY LEVITATED TRAIN Peter Kronenberg and Habibo Brechna Magnetically levitated train systems are expected to play a major role in future transportation systems. Actual installations have been built using metallic magnet coils, with the drawback of high ohmic losses. In this work the potential use a of high temperature superconducting (HTS) moving part has been investigated. An experimental setup (shown below) has been developed. It consists of a cryo-cooled copper stator winding and an HTS tablet as a mover. Permanent magnets are placed under the stator winding. The Meissner effect then causes the mover to levitate. The propulsion of the moving part is caused by the moving sinusoidal field in the air gap induced by the three phase winding. The stator current is controlled by a PWM converter and a three phase transformer. Several HTS materials have been compared for the moving part, with electrical frequencies ranging from 25 to 400 Hz, thus allowing for speed control. A model for the displacement of the moving part and the traction force has been established. The feasibility of a magnetically levitated HTS train system has been confirmed, although further improvements to the magnetic layout and the converter system will be required.

Figure: Setup of the magnetically levitated train model


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3.3 Services offered

Hans-Jürg Weber Our accredited laboratories provided a wide variety of services for several Swiss companies and institutions in 2003.

Accredited calibration laboratory (SCS 081) The primary tasks this year were again the calibration of complete Impulse, AC and DC high voltage measuring systems under operating conditions in the customer's laboratory. Additionally impulse peak voltmeters, standard capacitors, C-tanδ-bridges and calibrators for PD measuring systems have been calibrated

Accredited testing laboratory (STS 181) Our testing laboratory for tests of electrical properties of components of electrical energy supply performed once more a wide variety of tests according to international standards as well as following laboratory-developed test procedures.


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4. Publications and Reports 4.1 Publications

Invited Publications K. Fröhlich, A. Pöltl "A new Algorithm Enabling Controlled Short Circuit Interruption" IEEE Transactions on Power Delivery, Vol. 18, No. 3. July 2003

K. Fröhlich "High voltage AC and DC insulation systems – state of the art" Proceedings of XIII ISH, International Symposium on High Voltage Engineering, Delft, The Netherlands 26 August 2003, p 421

K. Fröhlich "Trends in Technology and Diagnosis of High Voltage Equipment" Proceedings of GCC Power 2003, Muscat, Oman 9 Dec 2003

Publications K. Fröhlich, M. Steurer, Walter Holaus, K. Kaltenegger "A novel hybrid current-limiting circuit breaker for medium voltage: principle and test results" IEEE Transactions on Power Delivery, Vol. 18, No. 2, April 2003, pp 460-467

K. Fröhlich, K. Kaltenegger "Elektrische Energienetze der Zukunft" ET Elektrotechnik, Nr 11/2003, pp. 53-56

M. Grader, U. Straumann "A New Approach to Realize Circuit Breakers with Numerious Series- and parallel-Connected Low-Current Contacts" CIGRE International Colloquium, Asset Management of Switching Equipment and New Trends in Switching Technologies, Sarajevo, Bosnia Herzegovina, 15 - 16 September, pp 112-117

S. Berger, W. Holaus "Arcing Contacts and Nozzle Condition Diagnostics by Means of Measure of Thermal Stresses" CIGRE Colloquium, Asset Management of Switching Equipment and New Trends in Switching Technologies, Sarajevo, Bosnia Herzegovina, 15 - 16 September, pp 118-123

4. PUBLICATIONS AND REPORTS

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B. Kloeckl, A. Thaler "Measurements results using the ficticious field current model for PMSM" EPE 2003, Toulouse, France, 1 - 5 September

B. Kloeckl "Energiekonversion Downhole – eine Vision" Electrosuisse PES meeting "Geothermal energy conversion", Aarau, Switzerland, 2003

R. Vogelsang, B. Fruth, K. Fröhlich "Detection of Electrical Tree Propagation in Generator Bar Insulations by Partial Discharge Measurements" Proceedings of the 7th International Conference on Properties and Application of Dielectric Materials, ICPADM 2003, Nagoya, Japan, 1 - 5 June, pp. 281 - 285

R. Vogelsang, R. Brütsch, K. Fröhlich "Effect of electrical tree propagation on breakdown in mica insulations" Proceedings of the XIII ISH, International Symposium on High Voltage Engineering, Delft, NL, 2003, pp. 375 - 378

R. Vogelsang, R. Brütsch, K. Fröhlich "How imperfections in mica insulations influence tree propagation and breakdown time" 2003 Annual Report, Conference on Electrical Insulation and Dielectric Phenomena, CEIDP 2003, Albuquerque, NM, USA, 19 - 22 October, pp. 657 - 660

W. Zaengl "Off-line-Isolationsdiagnostik an Transformatoren" SGB Transformator-Symposium in Switzerland, Zurich, Switzerland 8 May 2003

W. Hribernik "Modellbasierte Transformatordiagnose", PSEL Tätigkeitsbericht 2002

St. Neuhold, K. Fröhlich, D. Inaudi "Bohrgestänge von der Rolle – Integration der elektrischen Leitung in die Schlauchwandung" Bulletin SEV/VSE, 15/03, 2003

K.-H. Kim, J.-B. Lee, B. Klöckl, K. Fröhlich "Wavelet and neuro-fuzzy based fault location for combined overhead/cable transmission lines" (working title); to be submitted to IEEE Trans. Power Delivery


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5. Presentations Invited Lectures K. Fröhlich " Introduction to Controlled Switching" Presented at the CIGRE Workshop Controlled Switch Gear Committee St. Pete’s Beach, Florida, United States 8 May 2003

K. Fröhlich "A new Algorithm Enabling Controlled Short Circuit Interruption" Presented at the IEEE Power Engineering Society General Meeting Toronto, Canada 15 July 2003

K. Fröhlich "High voltage AC and DC insulation systems – State of the art" Presented at the XIIIth International Symposium on High Voltage Engineering Delft, The Netherlands 26 Aug 2003

K. Fröhlich "Trends in der Technologie von Hochspannungsapparaten und Komponenten" Presented at the CIGRE National Committee Bern, Switzerland 27 November 2003

K. Fröhlich "Trends in Technology and Diagnosis of High Voltage Equipment" Presented at the GCC Power 2003, Conference and Exhibition Muscat, Oman 9 December 2003

Other presentations B. Klöckl "Energiekonversion Downhole – eine Vision" Presented at the ETG Meeting, Brugg, Switzerland 19 March 2003

U. Krüsi "Controlled switching – suitability check for already installed HVAC circuit breakers" Presented at the CIGRE Workshop Controlled Switch Gear Committee St. Pete’s Beach, Florida, United States 8 May 2003

5. PRESENTATIONS

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M. Grader "A New Approach to Realize Circuit Breakers with numerous Series- and parallel-Connected Low-Current Contacts" Presented at the CIGRE Colloquium, Asset Management of Switching Equipment and New Trends in Switching Technologies Sarajevo, Bosnia Herzegovina 16 September 2003

S. Berger "Arcing Contacts and Nozzle Condition Diagnostics by Means of Measure of Thermal Stresses" Presented at the CIGRE Colloquium, Asset Management of Switching Equipment and New Trends in Switching Technologies Sarajevo, Bosnia Herzegovina 16 September 2003

R. Vogelsang "Effect of electrical tree propagation on breakdown in mica insulations" Presented at the XIII ISH, International Symposium on High Voltage Engineering Delft, The Netherlands 28 August 2003

W. Zaengl "Off-line-Isolationsdiagnostik an Transformatoren" Presented at the SGB Transformator-Symposium in Switzerland Zurich, Switzerland 8 May 2003


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6. Conferences and Visits 6.1 Conferences and Workshops

D. Politano, H.J. Weber ETG (Energietechnische Gesellschaft des SEV) Informationstagung "Spannungsfelder bei den Beschaffungsprozessen" Bern, Switzerland 30 January 2003

K. Fröhlich, U. Krüsi, W. Hribernik, St. Neuhold, B. Klöckl, D. Politano, M. Chapman, S. Berger, R. Vogelsang ETG (Energietechnische Gesellschaft) "Geothermische Energie-Erzeugung: Vision oder Realität?" Tagung Brugg, Switzerland 19 March 2003

K. Fröhlich CIGRE National Committee Lugano, Switzerland 11 April 2003

K. Fröhlich CIGRE Technical Committee Rio de Janeiro, Brasil 24 - 25 April 2003

K. Fröhlich, U. Krüsi CIGRE A03 Working Group Committee Meeting St. Pete’s Beach, Florida, United States 6 - 7 May 2003

K. Fröhlich, U.Krüsi CIGRE Workshop Controlled Switching, IEEE Switch Gear Committee St. Pete’s Beach, Florida, United States 8 May 2003

W. Hribernik, W. Zaengl SGB Transformator-Symposium in Switzerland Zurich, Switzerland 8 May 2003

H.J. Weber Highvolt-Kolloquium 2003 Dresden, Germany 22 - 23 May 2003


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K. Fröhlich EBL – Veranstaltung der Elektrik Basel Land zur geothermischen Energie Basel, Switzerland 17 June 2003

R. Vogelsang ISOTEC 2003 Berlin, Germany 16 - 18 June 2003

K. Fröhlich IEEE Power Engineering Society General Meeting Toronto, Canada 13 - 17 July 2003

K. Fröhlich XIII ISH, International Symposium on High Voltage Engineering Delft, The Netherlands 25 - 26 August 2003

R. Vogelsang XIII ISH, International Symposium on High Voltage Engineering Delft, The Netherlands 25 - 29 August 2003

K. Fröhlich, M. Grader, S. Berger CIGRE Study Committee A3, Chair Sarajevo, Bosnia Herzegovina 15 - 16 September 2003

K. Fröhlich CIGRE Colloquium, Asset Management of Switching Equipment and New Trends in Switching Technologies, Chair Sarajevo, Bosnia Herzegovina 17 - 18 September 2003

B. Klöckl "Energietechnik für die Zukunft", ETG Tagung 2003 Hamburg, Germany 7 - 8 Oct 2003

R. Vogelsang 2003 Conference on Electrical Insulation and Dielectric Phenomena, CEIDP 2003, Albuquerque, NM, USA 19 - 22 October 2003

H.J. Weber, M. Hinow, U. Krüsi FKH- / VSE-Fachtagung "Hochspannungsmesswandler" Brugg-Windisch, Switzerland 12 November 2003


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A. Bitschi 1. Fachkongress Geothermischer Strom Neustadt-Glewe, Germany 12 - 13 November 2003

H.J. Weber Metas "Seminar über die Messunsicherheit 2003" Bern, Switzerland 18 November 2003

K. Fröhlich, U. Krüsi, W. Hribernik, St. Neuhold, E. Murtola, P. Favre-Perrod, R. Vogelsang CIGRE, CIRED, Informationsnachmittag "Neue Trends und Nutzen" Bern, Switzerland 27 November 2003

K. Fröhlich CIGRE GCC Power 2003 Muscat, Oman 8 - 9 December 2003

6.2 Events

Besuch des EKZ und des VA TECH-Konzerns "Aktuelle Forschungsschwerpunkte der Fachgruppe Hochspannungstechnologie" Organisation: H.J. Weber 18 August 2003

Alumni Tagung 2003 "Elektrische Energiesysteme – Forschung und Visionen" Organisation: H.J. Weber / R. Vogelsang / D. Politano / B. Klöckl 9 Mai 2003

Mittelschülerinnentage "Forschung und Visionen in der Hochspannungstechnologie" Organisation: H.J. Weber, H. Kienast 3 and 4 June 2003

6.3 Visits

Prof. Jong-Beom Lee Wongkwang University, South Korea July 2003


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Joint Activities

1. Colloquia Topical Problems of Electric Power Engineering Aktuelle Probleme der Energietechnik

In collaboration with the "Energietechnische Gesellschaft ETG/SEV"

Modellierung von Preisbildungs-Mechanismen in Elektrizitäts- und CO2 - Märkten Dr. Jacob Bernasconi ABB Schweiz AG - Corporate Research, Baden-Dättwil, Schweiz 21 January 2003

Regelenergiemarkt in Deutschland Dr.-Ing. Michael Ritzau Büro für Energiewirtschaft und technische Planung GmbH, Aachen 17 June 2003

Voltage Dips - A Major Power-Quality Issue Prof. Dr. Math Bollen Chalmers University of Technology, Gothenburg, Sweden 1 July 2003

Fault Location in Combined Transmission Lines with Underground Power Cables and Reduction Methods for Sheath Circulating Currents Prof. Dr. Jong-Beom Lee Department of Electrical, Electronic & Information Engineering, Wonkwang University, South Korea 15 July 2003

IEC 61850 - Standardisierter Informationsaustausch in Schaltanlagen und darüber hinaus Dr. Klaus–Peter Brand Utility Automation Systems, ABB Schweiz AG 18 November 2003

Zuverlässigkeitsanalyse in der Planung elektrischer Energieübertragungsnetze Dr. Markus Leuzinger Busarello + Cott + Partner Inc., Erlenbach 25 November 2003

1. COLLOQUIA

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JOINT ACTIVITIES

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2. Vision 'Future Energy Networks' Patrick Favre-Perrod, Martin Geidl, Bernd Klöckl and Gaudenz Koeppel Recent developments and scenarios for the future energy supply of industrialised countries have shown that the actual grid structure needs to be improved. Our energy system is faced with several challenges:

• Environmental aspects are increasingly considered in the commissioning of new installations and therefore affect the design process and the technological development of energy equipment more and more. For electric energy, specific problems can be identified - To operate non-dispatchable, renewable energy sources economically, solutions

for energy storage are needed - As rights of way become harder to obtain and the environmental concern about

overhead lines grows, new solutions for underground energy transmission should be found.

• The needs of future grid participants (producers and consumers) will continue to change rapidly in the light of liberalisation processes and increasing demand for customised power quality

• Large scale use of distributed, dispatchable (small CHP, geothermal,...) and non-dispatchable generation (wind, solar,...) needs solutions for power infeed into distribution networks. Furthermore, small scale generators rarely are 50 Hz generators

• New components such as chemical storages, fuel cells, future transportation systems (e.g. hybrid vehicles), etc. may use chemical as well as electrical energy.

• The increasing energy demand, especially in very large agglomerations of the future ('mega-cities') can hardly be covered using actual distribution structures.

Considering the interdisciplinary nature of the above problems, a partnership among four ETH laboratories has been launched. According to the competences of the participants, four workpackages have been defined:

• Power systems laboratory (Prof. Dr. G. Andresson): System aspects including System implications of storage and protection, control and communication

• High voltage laboratory (Prof. Dr. K. Fröhlich): Technological aspects including energy storage technologies and energy transmission technologies in future networks.

• Power electronics laboratory (Prof. Dr. J. Kolar): Design of converters for storage devices, power generation and power transmission.

• Automatic control laboratory (Prof. Dr. M. Morari): Control of future energy networks.

In a first step, a greenfield approach has been chosen. For each subtopic, ideal solutions will be worked out regardless of today’s grid. In further steps, transition scenarios will of course be considered. The activities will include:

• The formulation of a model for energy flow simulations, implemented for rural, urban and mega-city structures including the consideration of available and foreseeable energy technologies.

2. VISION 'FUTURE ENERGY NETWORKS'

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• Studying the coherence between (stochastic) production, transmission and storage of energy.

• Identification of missing technological principles with highly desirable properties in the hypothetic system.

Figure 1 shows a proposal for a new network structure which will be used in the further project steps: The network consists of interlinked decentrally controlled, autonomous clusters or energy nodes. The interlinks are operated according to the needs of the participants, allowing for the transmission of electrical and chemical energy at customisable frequencies, voltages, pressures, etc. The emphasis is laid on the hybrid character which all energy systems already have today and that should be integrated in the technological functionality and the control strategies of future systems for the sake of economy and sustainability. The linkage between different forms of energy is illustrated in the figure. Several basic topology proposals will be assessed using a combination of technical, economical and environmental criteria.

Figure 1: Vision of a fully decentralised network structure consisting of independent energy nodes


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