A thorough comparison among impact of different ... · A thorough comparison among impact of...

18th Power Systems Computation Conference Wroclaw, Poland – August 18-22, 2014

A thorough comparison among impact of different

technologies on power system reactive planning

Cristian Bovo, Luca Radaelli, Alberto Berizzi

Politecnico di Milano

Department of Energy

[email protected]

Andrea Mansoldo, Mark Norton

EirGrid plc. Grid Development and Commercial (GDC)

[email protected]

Abstract—The Irish transmission network is quickly

changing its basic features from many points of view, and the

consequent potential scenarios increase uncertainty in planning

future network. In particular, the importance of wind power

generation has risen in the last years so much as to be considered

among the most important and affordable Renewable Energy

Sources (RES), with a growing rate faster than other

technologies. This requires new criteria to set out the appropriate

architecture for future grids, in terms of topology, technology

and control structures. This paper describes how to use a var

planning methodology to identify reactive needs for future mixed

meshed AC/DC system, taking into account different

transmission technologies.

Keywords—ORPF, reactive planning, operational planning,

RES, wind power.

I. INTRODUCTION

The importance of wind power generation has risen in recent years so much as to be considered among the most important and affordable Renewable Energy Sources with a growing rate faster than other technologies. Today, wind developers are looking at offshore installations, due to both the lack of land resources and the environmentalist opposition. This requires new criteria to set out the appropriate architecture for future offshore grids, in terms of topology, technology and control structures and their integration in existing grids [1].

To face the above-mentioned new challenges, some optimization procedures have been recently set up, related mainly to the planning framework, by EirGrid and Politecnico di Milano. In particular, the var planning issue has been investigated and the new model built has been presented in [2][3], where the mixed AC/DC feature of the grid and the simultaneous presence of overhead lines and a significant amount of submarine cables are taken into account.

The above procedure is composed of two steps: a Var PLanning Assessment (VPLA), which solves an optimization problem where the total cost is minimized, and a Voltage Collapse Margin Assessment (VCMA). The objective function takes into account both the investment and operational costs (essentially re-dispatching and reactive power usage costs) and allows, by means of some penalties, to deal with numerical problems or infeasibility problems (monitored by Wind Curtailment Costs, Generation Shedding Costs, Load Shedding Costs). The review of the use of these penalties in the optimisation process makes it possible to

identify weak nodes in the power system. VCMA takes into account voltage collapse risks and contingencies, thus resulting in a var allocation able to face main security issues.

The above methodology can be used for planning purposes, but also to assess the economic impact of different technologies currently under investigation to reinforce AC/DC meshed transmission systems via a cost-benefit analysis process.

In this paper, the var planning procedure proposed in [3] has been used to carry out a thorough comparison of the system cost in the planning horizon, identifying critical corridors in the Irish system (due to the high penetration of wind and tidal power) and comparing the impact, in terms of overall costs, of different technologies applied to these corridors. In particular, the following technologies have been considered for comparison: HVDC and related DC cables, both VSC and LCC technology, AC cables, and Gas Insulated Lines (GIL). The comparison makes it possible to assess the relative costs of long-term solutions in the planning horizon.

A second procedure presented in the paper is relevant to the use of a model derived from the VPLA able to cope with operational planning framework. In this framework, the impact of a particular technology improvement has been assessed: the Real-Time Thermal Rating (RTTR) of cables has been considered and advantages at operation stage evaluated applied to a test system.

II. VPLA MATHEMATICAL MODEL

The var planning procedure is carried out by means of a modified Optimal Reactive Power Flow (ORPF) problem. Traditionally, ORPF procedures aim at allocating var sources, either shunt capacitors or shunt reactors, at the system buses to provide reactive power support to the grid; in this case, the same procedure also makes it possible to accommodate RES deployment with the minimal overall costs. A multi-Objective Function (OF) considers the main grid costs and its minimization is the goal of the optimization process:

𝑂𝐹 = 𝐼𝐶 + 𝐸𝐼𝐶 + 𝑅𝐷𝐶 + 𝑅𝑈𝐶 + 𝐺𝑆𝐶 + 𝑊𝐶𝐶 + 𝐿𝑆𝐶 [𝑘€

𝑦𝑒𝑎𝑟]

The first two terms of the OF formulation refer to the option of installing var sources: the Investment Costs (ICs) are the cost of new reactive sources, whereas the Extra Investment Costs (EIC) help the convergence of the algorithm if reactive support is needed at a specific bus more than what has been


deemed technically possible. Re-Dispaching Costs (RDCs) take into account the incremental generation re-dispatching with respect to a fixed base-case operating condition, which is an input of the algorithm. Reactive Usage Costs (RUCs) are the costs of the reactive power, included to model a possible reactive power market. Generation Shedding Costs (GSCs), Wind Curtailment Costs (WCCs) and Load Shedding Costs (LSCs) are penalty factors modelling the opportunity to disconnect some generation (conventional or wind generation) or some load, if necessary. These terms help the convergence of the algorithm in the same way as EICs.

Each term is assigned a suitable cost, based on EirGrid experience. The OF is subjected to equality (i.e. AC and DC power flow equations, AC and DC bus equations, etc.) and inequality constraints (i.e., power limits, independent variable boundaries, etc.). In addition, modelling of tap-changing and phase-shifting transformers provides a detailed representation of the grid components. Generator angle is limited according to EirGrid Operating Security Standards [4], allowing the deployment of only a restricted area of the generators capability curve:

14.76 14.76

The OF is estimated on a yearly basis, making use of multiple Load/Generation scenarios for the evaluation of operational costs and annualising var investments.

A. VPLA and VCMA

The above model is the basis of the VPLA, providing a complete var allocation, including both the N and the (N-1) security concepts. At first, a var planning optimization problem is solved in the N case, i.e., in case of intact grid. Second, a pre-defined list of all possible contingencies is used to update the solution according to the (N-1) security criterion, aiming at providing an optimized reactive support strategy when a contingency occurs. Due to computational limits, considering all contingencies at the same time in a unique ORPF problem is not feasible. Therefore, two different methods have been implemented:

- Single contingency method: it is the easiest approach as contingencies are taken into account one by one;

- Grouping method: pre-defined sets of contingencies are considered at the same time, dividing the complete set of contingencies into smaller groups of about 2-3 contingencies each. The aim is to find possible synergies among different contingencies, for a better reactive allocation.

Finally, the var planning outcome results from the envelope of the solutions of the ORPF problems.

A Voltage Collapse Margin Assessment (VCMA) is implemented as well [3]. In this case, the margin from the point of voltage collapse is investigated through the “loadability” concept, i.e., the extra load the system can accommodate before reaching the voltage collapse. The VCMA aims at assessing system voltage security considering more severe conditions, i.e., in the (N-1-g) case where also the loss of a generator is considered. Details are provided in [3].

B. Operational planning module

The ORPF-based algorithm described above is also used to set up an operational module to estimate the system operational performance over a chosen time span (e.g., 24 hours); it is expected to define the optimal use of the existing

resources, without allocating any extra var support with respect to VPLA. The main features of the operational module are listed in the following:

the operational scenario is defined, updating the load demand and the wind generation, and a sequential approach is adopted that carries out an ORPF for each of the next 24 hours (Figure 1);

the objective function adopted (Operational Cost, OC) does not include investment costs and it is on an hourly basis:

𝑂𝐶 = 𝐸𝐼𝐶 + 𝑅𝐷𝐶 + 𝑅𝑈𝐶 + 𝐺𝑆𝐶 + 𝑊𝐶𝐶 + 𝐿𝑆𝐶 [𝑘€

ℎ]

no installation of new var support is allowed (the term IC is included in OC), except for EIC, when feasibility is not obtained with the currently installed reactive sources.

The procedure can be applied according to N-1 security criterion, as well as for and multiple contingencies involving both branches and generators.

Fig.1 - Sequential analysis

C. Real-Time Thermal Rating model

The operational module makes it possible to assess the performances of a dynamic rating system. A Real-Time Thermal Rating (RTTR) model of AC cables was set up: the cable is modelled with a two-loop thermal equivalent circuit, considering the cable being formed by the conductor, the insulation and the sheath. Dielectric losses, important for high voltage AC cables, are taken into account considering their impact on steady-state temperature rise of the conductor.

Sheath losses modelled by means of the sheath loss factor s and are included in the conductor losses Wc [5]. A general expression for the temperature rise caused by losses is a sum of exponential terms [5], [6]:

𝜃𝑖(𝑡) = 𝑊𝐶 ∑ 𝑇𝑖𝑗

𝑛

𝑗=1

(1 − 𝑒𝑃𝑗𝑡)

where:

( )i t is conductor temperature;

Wc is the heat generated by Joule losses;

Tij and Pj are parameters that depend on cable geometrical characteristics and installation conditions.

Initial solution

Starting point

Adjustment of

load and wind

generation

Grid state check

(Contingency case)

Hour zero

Time interval

ORPF

Solution

T(h) T(h+1)


Based on the actual temperature of the conductor, the algorithm calculates the temperature margin for the next hour, i.e., the difference between the maximum allowable temperature (for example, 90 °C) and the actual conductor temperature, considering also the temperature decrease due to the natural heat dissipation. Then, the cable capacity margin for a user-defined number of consecutive hours is computed and the rating is updated for next hour. Therefore, with reference the continuous rating, the cable equipped with RTTR can be overloaded as long as its temperature is kept below the limits enforced by insulating materials. Based on the load and wind forecast, the algorithm can use the short-term overload capability of the cable in real-time, without violating the thermal design constraints.

III. THE IRISH NETWORK

The Irish Transmission System (ITS), represented in Figure 2, is an interesting case of study due to its topology and the great variety of technologies existing or foreseen in the future. The island is interconnected with UK by means of two HVDC links, one based on LCC technology and the other one based on VSC technology. Moreover, further HVDC interconnections between the island and UK and/or France are currently under investigation. Ireland has set the target at 40% of energy produced by RES by 2020. This quite aggressive strategy envisages an exponential growth in wind production thanks to the great availability of wind resources, in particular off-shore. At present, the growth is limited by technical constraints and non-synchronous generation cannot exceed 50% of the power consumption. In the future, with storage devices and large investments on the power system, EirGrid is expected to move the limit to 75% [15].

Fig.2 - The Irish network

IV. PLANNING PROCESS AND COST BENEFIT ANALYSIS

Since late 2008, a long-term development grid plan has been delivered by EirGrid, following results on an all-island basis, which have been used to provide EU with achievable targets in term of RES penetration and CO2 emissions. About 22 B€ were envisaged in the Electricity Sector, with 4 B€ directly related to HV transmission system [7].

A planning process procedure has been set-up in order to be as transparent as possible and gain public acceptance on infrastructure developments [8]. For any large project, a transmission technology review has been performed in order for the EirGrid planner to have a wider range of perspective options and to the select the most appropriate. The ultimate goal is to provide the most economic, efficient and reliable solution for the ITS, which is part of the EirGrid licence agreement to operate, maintain and develop the transmission grid. Cost-benefit analysis assessment plays an important role in a technical/economic ranking of planning solutions; it is necessary to justify the most suitable option when presenting the power system planning schedule to the National Authorities.

In addition to the investment costs of each technology, EirGrid has undertaken a thorough investigation into the operational costs associated with each technology. In this paper, a comprehensive AC optimisation tool is applied to estimate the impact on system operating cost of different transmission technologies. It is worth mentioning that further analysis may dictate that a technology solution may not be feasible in some scenarios following for example, electromagnetic transients analysis and temporary overvoltages incurrence [9] as they are neglected at this stage.

V. TRANSMISSION TECHNOLOGY ANALYSIS

The following technologies are currently considered in EirGrid Planning process.

A. Overhead Lines (OHL)

EirGrid considers the OHL technology as the first option when designing a new reinforcement. However, opposition has intensified against OHLs and some of the strategic projects are encountering difficulties and delays to get construction permissions. To mitigate the need for new OHL, EirGrid has investigated additional solutions such as re-conductoring techniques using High Temperature Low Sag conductors or transforming a 220 kV to a 400 kV using same towers and right-of ways [10]. These allow the reduction of the investment costs.

B. AC Cables, land and submarine

Depending on the project, both underground and submarine cables could be part of the available options, changing completely the reactive behaviour of the grid. In this case, length and compensation play an important role in terms of the impact: significant compensation and additional substation might be required for lengths more than 30-50 km.

Additionally, another cable technology can be provided by a RTTR [11], which may allow dynamic rating and increased system performance, in particular emergence situations, without violating equipment capabilities.

C. Gas Insulated Lines (GIL)

GIL technology has been around since the 1990s; however, so far, high investment costs and lack of experience about its reliability have driven TSOs to only try them in short lengths and in specific circumstances, to build up operational experience. Furthermore, GIL may be initially developed using tunnels left over at the end of some transportation infrastructure projects, i.e. railways [12]; the capital offset of this part of the civil works make the technology more


competitive. For offshore grid purposes, this technology concept has recently been extended to submarine applications [13].

D. HVDC

HVDC technology has gained recent popularity both to enhance RES grid integration and to conceive offshore transmission grids. In particular, attention is drawn to the new Voltage Source Converter (VSC) technology which, compared to the mature Line Commutated Converter (LCC) technology, mitigates the impact on the AC grid with lower filtering and reactive compensation requirements.

Further to the high investment costs with the addition of AC/DC converters, the technology offers several system advantages:

upgrading of existing AC reinforcements with an increased transfer capacity [15];

power flow control capability, increasing system flexibility and security.

They are both of paramount importance, the first to ease additional infrastructure projects and gain acceptance from locals; the second to mitigate volatility in power flow scenarios with high RES penetration. In fact, it is more and more difficult to find a single AC solution able to cope with the yearly system behaviour efficiently, whereas a controllable link may easily adapt to multiple power flow patterns. This technology may be used with both OHL and Under Ground Cables, UGC (onshore and submarine types).

Figure 3 - Test grid

VI. TEST GRID

Figure 3 shows the structure of the test system adopted. It is made up of 58 busses, divided into four areas (A, B, C, D) where loads (red squares), converters (dashed circles), and generators (empty circles) are connected through OHL and/or UGC. The system is a meshed AC/DC grid where HVDC converters are assumed VSC technology. Area D is interconnected with neighbouring areas by means of submarine cables, and West and East areas model wheeling power flows, kept fixed in the considered analysis. Nine conventional (fossil fuel) generators supply the load. Data of the generation and load demand are shown in Table I.

TABLE I – LOAD AND GENERATION BY AREAS FOR TEXT GRID

Area Load [MW] Generation [MW]

A 6000 5576,07

C 1200 1223.93

D 2800 3200

West 0 0

East 0 0

Total 10000 10000

A. Comparison of different technologies

The methodology explained above can be used to compare the impact of different transmission technologies on the power system operation. Different technical solutions are installed on one grid circuit (link) and the analysis is carried out by considering the objective function of the operational module that does not include the IC term.

In particular, the procedure is applied on the submarine cable circuit SM2A-COOD (about 87 km long) interconnecting area A with area D. Its rated voltage is 220 kV and its rated power is 450 MVA.

Feasible technological solutions for this type of circuit are an AC submarine cable, GIL and HVDC submarine cable solutions with either LCC or VSC converters. Table II summarizes the main electrical data for the different technologies.

TABLE II–TECHNICAL DATA OF THE DIFFERENT TECHNOLOGIES

Resistance

[Ω/km] Reactance

[Ω/km] Capacitance

[nF/km]

AC cable 0.04 0.056 210

GIL 0.0015 0.07 65

HVDC LCC 0.035 - -

HVDC VSC 0.153 - -

Changing the transmission technology solution implies a different impedance of the circuit, which affects the entire grid behaviour. Therefore, a VPLA has to be carried out for each technology considered as a different var allocation might result. The VPLA is run considering five different scenarios which represent different grid conditions over the year: scenarios 1 and 2 represent winter and summer load peaks respectively; scenario 3 is the minimum load peak and scenarios 4 and 5 take into account a wheeling power flow of 2000 MW from West to East and from East to West, respectively. The above-mentioned five scenarios represent suitably the operation of one year, if they are weighed by proper weighing coefficients, as represented in table III, according to the TSO experience.

TABLE III - LOAD AND WEIGHT FOR EACH VPLA SCENARIO

Scenario Weight [h] Load [MW]

1 1060 10000

2 4700 10000

3 1000 5000

4 1000 9500

5 1000 9500

N-1 security criterion case is considered, adopting the grouping method described in [2][3].

Considering the capital cost of a var shunt equal to 80 k€/Mvar and a return of investment lifetime of 43 years at a discount rate of 5.63%, VPLA results are shown in Table IV, where total grid capacitive and reactive requirements are shown, as well as their cost IC.


TABLE IV - REACTIVE ALLOCATION FOR EACH TECHNOLOGY

Capacitors [Mvar]

Reactors [Mvar]

Investment var

cost IC

[M€/year]

AC cable 2100 520 13.1

GIL 2020 280 11.5

HVDC LCC 2120 340 12.3

HVDC VSC 2120 40 10.8

For what capacitive reactive power is concerned, capacitors are installed close to loads and the total amount is quite similar in all four cases. Significant differences are present from the inductive reactive power point of view. In general, reactors are located close to submarine AC cables, which require significant amount of inductive power at both ends to compensate the reactive power generated by cables at low load. GIL, instead, does not need a great deal of reactive compensation, thus reducing the reactors needed. The HVDC solution with LCC converters needs capacitive reactive power for the conversion process, which is generated by both capacitors allocated by the VPLA assessment and by the adjacent AC cable. The inductive reactive requirement is due to particular unloading conditions of the HVDC that can only be handled by installing 260 Mvar of reactors at bus COOD. The HVDC solution with VSC converters minimizes the need for further shunt compensation, especially where several AC cables are present in the network close to the VSC converter location, for example for offshore grids.

Once the planning stage has been defined, the var allocation is kept fixed, and the operational module allows the comparison of technologies at the operational stage, making use of known load and generation profiles (Figure 4).

Figure 4 – Load profiles in pu

In the presented case, four different daily demand profiles have been selected for the analysis, each one occurring for a certain number of days during the year (table V).

TABLE V – WEIGHT OF THE DIFFERENT DAILY DEMAND PROFILES

Demand profile Weight [days/year]

Summer Weekday 130.5

Summer Weekend 52

Winter Weekday 130.5

Weekend Weekend 52

For each technology considered, a VPLA has been carried out and the relevant yearly var planning costs ICs are evaluated. Then, the operational module is run and the operation costs OC are computed for each hour; based on the operational module, the yearly operational cost is evaluated

based on the load profiles in Figure 4 and the weight in Table V.

Table VI shows the results of the analysis applied to the choice of the technology for a given link. The first row depicts the change of the yearly operation costs with respect to a reference operation costs reference peak hour conditions and in the presence of the AC cable. As the load is generally lower than in reference conditions, the change of operation costs is always negative. The total yearly cost is obtained by summing up the yearly OC and IC.

According to Table VI, the AC cable produces a very large amount of reactive power, which has to be compensated by shunt reactors: this impacts on IC. The GIL solution offers the overall best performances, thanks to both a low IC and a reduction in system losses. Generally, HVDC solutions have generally a worse overall performance at the operational stage. Losses in LCC converters are lower than in VSC converters, but the total reduction of losses in the grid does not compensate the higher reactive investments needed; on the contrary, the VSC four quadrant control allows the minimization of reactive investments.

TABLE VI - COMPARISON OF THE OBJECTIVE FUNCTIONS FOR THE DIFFERENT

TRANSMISSION TECHNOLOGIES

AC cable GIL HVDC

LCC

HVDC

VSC

Total change of

yearly operation costs OC

[M€/year]

-1202.3 -1202.4 -1200.5 -1200.4

var investment costs IC

[M€/year]

13.1 11.5 12.3 10.8

Total yearly cost

[M€/year] -1189.2 -1190.9 -1188.2 -1189.6

Benefit

[M€/year] 0 -1.7 1.0 -0.4

B. RTTR impact

The operational analysis enables the implementation of advanced technology systems like the Real Time Monitoring System (RTMS) associated with a cable. In the example, a comparison is performed between the reference case and the case where the cable SM2A-COOD is equipped with RTMS technology. Additional data is necessary in the assessment, see table VII, to model the thermal behaviour of the cable.

TABLE VII - TECHNICAL DATA OF A 3X220 KV XLPE SUBMARINE CABLE

Conductor radius 23.6 mm

Insulation radius 59 mm

Sheath radius 64 mm

Burial depth 1.5 m

Cable configuration Trefoil formation

Initial conductor temperature 55 ℃

Four cases have been investigated: a cable without RTTR and cable equipped with RTTR considering different time periods for the calculation of the expected Interconnection Transmission Capacity (ITC). RTTR k hours means that the cable rating is such that the corresponding current, assumed constant, will drive the cable temperature to the maximum allowed in k hours. The time periods considered in this paper are 1, 3 and 10 hours.


An additional reserve generator has been placed in area D. An (N-1-g) situation is considered: a contingency on the generator G4 located in area D and on the cable SM2A-GEOD, linking area D with area A. This determines a critical overload situation or the activation of the expensive reserve unit, depending on the available ITC on the remaining connections. Table VIII depicts the change in total operating cost over 24 hours of a selected day (winter weekday, see Figure 4) with respect to the reference conditions.

The RTTR allows better exploitation of the capacity of the cable (Fig. 4). In facts, in spite of the continuous rated capacity of 450 MVA, initially the cable can carry a higher power, giving rise to a remarkable temperature increase (Fig.5), that is however kept within the design values of 90°C. After the initial peak in allowed cable rating, temperature start rising until hour 7 and correspondingly the rating decreases; after hour 7, the cable rating can increase again, thanks to the decrease in load that makes temperature to be kept within the limits.

Figure 5 - Dynamic rating of the cable.

Figure 6 - Conductor temperature

In particular, it is worth noting that when re-calculating the ITC over short time-periods ahead (i.e., 1 hr), economic advantages are provided to the system (about 15 k€/day). If the assessment was carried out with longer re-calculation period, for example 10 hrs overload capability rating, the benefit would be reduced and performances would be close to those obtained with a fixed rating (Table VIII).

TABLE VIII – RTTR IMPACT ON THE TEST GRID

No RTTR

RTTR 1hour

RTTR 3hours

RTTR 10hours

Change of daily

operation cost OC

[k€/day]

-297.1 -315.5 -311.4 -302.0

Notwithstanding the local increase of losses, an overall grid optimization is achieved, as more active power can be

produced by cheap generation, thus minimising the need to use expensive reserve units.

VII. IRELAND TRANSMISSION SYSTEM TEST

The procedure above described has been applied to the Irish Transmission System (ITS).

A. Comparison of different technologies

According to the same methodology, the impact of different transmission technologies on a critical corridor has been evaluated.

The circuit considered is a new 400 kV circuit, which is part of the Grid Development Strategy, GRID25. In this analysis, the assessment does not include the capital cost of building the circuit with each technology type, but only of var compensation. In any case, the comparison will need to take into account further engineering considerations that might include or rule out some particular technologies.

The new link will be operated at 400 kV and will facilitate the power wheeling through the Isle of Ireland, in particular the wind generation in the northern and western part of the island. The technologies considered for the analysis are OHL, UGC, GIL, HVDC LCC and HVDC VSC. Table IX shows the main parameters of the transmission technologies.

TABLE IX- ELECTRICAL PARAMETERS OF DIFFERENT TECHNOLOGIES

Resistance

[Ω/km] Reactance

[Ω/km] Capacitance

[Ω/km]

OHL 0.03 0.32 11.1

UGC 1xCu 0.011 0.23 240

UGC 2xAl 0.031 0.22 180

GIL 0.020 0.07 65

HVDC LCC 0.018 - -

HVDC VSC 0.009 - -

TABLE X - COMPARISON OF OBJECTIVE FUNCTIONS FOR THE DIFFERENT

TECHNOLOGIES ON THE ITS.

OHL UGC

1xCu

UGC

2xAl

GIL HVDC

LCC

HVDC

VSC

Change of total

daily cost OC

[k€/day]

-6980.4 -6982.5 -6982.0 -6982.6 -6969.1 -6920.9

Table X shows the total daily operating cost change with respect to the cost of the flat profile in reference conditions. Although differences are very small (due to the large size and therefore to the large operating costs of the system considered), the results show that the GIL still offers overall marginal better performances. In this case, the system benefits from its low impedance path compared to OHL solution. In addition, an UGC solution provides a similar effect but with higher Reactive Compensation Costs.

HVDC solutions show significant overall costs, mainly due to the losses at the converters: they represent the main limit for the technology. In the case of a VSC solution, the reactive support provided by the converters does not compensate the higher active power losses. The control capability is not beneficial in this case.


VIII. CONCLUSIONS

An optimisation algorithm has been described with the purpose of both planning the var resources and assess the operational system performances. To fulfil the large variety of transmission technology expected to be available in the next future, the tool has been designed to cope with all possible grid structure and transmission equipment.

An operational module has been set-up in order to provide information and comparison among the impact of different transmission technologies. An example have been shown on the Irish Transmission Grid model, by estimating the system costs within a Cost Benefit Analysis assessment.

At this stage, a thermo-electric model has been also set up aiming at reproducing the operational optimisation of RTTR technology. This has been verified in a test system where economic advantages of a better exploitation of available transmission capacity, without violating the design parameters of the component as well as the system reliability criteria, are shown.

IX. REFERENCES

[1] M. Norton, A. Mansoldo, A. Rivera, “Offshore grid Study: Analysis of

the appropriate Architecture of an Irish Offshore Network”, 2011, http://www.EirGrid.com/media/2257_Offshore_Grid_Study_FA.pdf.

[2] C. Bovo, A. Mansoldo, M. Soranno, A. Berizzi, “Expansion Var

planning model in a meshed/mixed AC/DC network”, IEEE Power &

Energy Society General Meeting 2012, 22–26 July 2012, San Diego, California, USA.

[3] A. Berizzi, C. Bovo, S. Cuni, R. Zuelli, A. Mansoldo, M. Norton: “Var

Planning Assessment in a meshed AC/DC System: The future Irish

Transmission System”. 2013 IREP Symposium-Bulk Power System

Dynamics and Control –IX (IREP), August 25-30, 2013, Rethymnon,

Greece. [4] EirGrid,“Operating Security Standards”, December 2011,

http://www.EirGrid.com/aboutus/publications

[5] G. J. Anders, Rating of Electic Power Cables, Ampacity Computations for Transmission, Distribution and Industrial Applications, IEEE

Press, McGraw Hill, New York, 1997.

[6] M. E. VanValkenburg, “Network Analysis and Synthesis”, John Wiley, 1999.

[7] http://www.EirGrid.com/transmission/investinginthefuture-grid25/ [8] Document “Approach to the Development of Electricity Transmission

Lines”, EirGrid Report July 2012, available at

http://www.EirGrid.com/media/EirGrid%20Roadmap%20Brochure%20July%202012.pdf

[9] http://www.EirGrid.com/media/Tepco%20Report%20North%20Sout

h.pdf` [10] S. Murray, S. Temtem et al.,“Voltage uprate studies of the Irish 220

kV network to 400 kV”, submitted to CIGRE 2014 Paris.

[11] L. Goehlich, F. Donazzi, R. Gaspari, “Monitoring of HV Cables Offers Improved Reliability and Economy by means of ‘Power Sensors’”,

Power Engineering Journal 2002.

[12] R. Benato, E. M. Carlini et al., “GIL in Railway Galleries”, 2003 IEEE Bologna Power Tech, 23-26 June 2003, Bologna, Italy.

[13] Offshore Wind Parks, feasibility of Power Transmission

Pipelines(PTP), Siemens,Forwind, ILF 2010 report. [14] http://www.EirGrid.com/renewables/facilitationofrenewables/ EirGrid

website 2009.

[15] Offshore Grids: A technology challenge: The case of Ireland “. A.Mansoldo, M.Norton, E.Zaccone, V.Barry. Accepted to CIGRE

Symposium Bologna 2011“.

http://www.eirgrid.com/aboutus/publications/

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