APPLICATIONS OF HIGH TEMPERATURE SUPERCONDUCTOR AND

ITS BENEFITS IN POWER SYSTEM TRANSMISSION

A MINI PROJECT

PRESENTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE COURSE EEE492

IN

DEPARTMENT OF ELECTRICAL ENGINEERING, FACULTY OF ENGINEERING, UNIVERSITY OF NIGERIA NSUKKA

BY

NWOKOLO, ERIC ONYEKACHI2008/158226

OCTOBER, 2012

CERTIFICATION PAGE

This is to certify that I am responsible for the work submitted in this mini

project, and the original work submitted therein has not been submitted to this

department for the course EEE 492

NWOKOLO, ERIC ONYEKACHI

2008/158226

DATE: -------------------------------------

APPROVAL PAGE

This mini project has been approved by the Department of Electrical

Engineering, faculty of Engineering, University of Nigeria, Nsukka.

BY

---------------------------------- --------------------------------Engr. M. J. MBUNWE Date(Project supervisor)

---------------------------------- --------------------------------Engr. C. A. NWOSU Date

(Mini Project Co-ordinator)

……………………………… …………………………. ENGR. DR. B.O. ANYAKA Date (Head of Department)

TITLE PAGE

APPLICATIONS OF HIGH TEMPERATURE SUPERCONDUCTOR AND

ITS BENEFITS IN POWER SYSTEM TRANSMISSION

DEDICATION

This work is dedicated to the almighty God that gives me the strength to

write this work and the inspiration he endowed on me in the course of writing

this mini project. Also it is dedicated to the entire family of Mr. and Mrs.

Nwokolo B.I. for their immense support in the course of writing this work both

financially and otherwise. More so, it is dedicated to my friends, well wishers

who have in one way or the other helped me in organizing and making this work

successful.

ACKNOWLEGMENTS

First of all I recognize the strength and wisdom God has bestowed on me

to see this work (mini project) come to reality. A work of this nature cannot be

complete without the supports receive from people of good will. I owe a lot to

those noble men and women. Among them is my project supervisor, Engr M.J.

Mbunwe, a highly principled somebody. Gratitude is a debt we owe and remains

one that must be settled. My gratitude also goes to scholars I made reference to

their work.

I also thank my father, Mr. Nwokolo B.I. and my mother, Mrs. Nwokolo

R., my elder sister Mrs. Ozor N.V., onyinye, chidera, udoka (my sisters) and

ikechukwu (my younger brother) for their understanding and patience in neglect

of family affairs during this research. Thanks a million times.

ABSTRACT

An aging and inadequate power grid is now widely seen as among the greatest

obstacles to efforts to restructure power system markets. In light of new and

intensifying pressures on the nation’s power infrastructure, industry and policy

leaders are looking to new technology solutions to increase the capacity and

flexibility of the grid without further raising system voltages. High Temperature

Superconductor (HTS) cable is regarded as one of the most promising new

technologies to address these issues. Among HTS cable designs, one in particular

– shielded cold dielectric cable – offers performance advantages particularly well

suited to today’s siting, reliability and performance challenges. Shielded cold

dielectric HTS transmission cables feature very close spacing between the

conductor and shield layers of wire in a coaxial cable. This close spacing result in

several advantages: lower electrical losses; the virtual elimination of stray EMF;

and significantly lower impedance than conventional cables and lines. Cables

suited for distribution-voltage, high-current applications exhibit similar benefits;

including the HTS cables design which make it possible to control power flows

over HTS circuits .

TABLE OF CONTENTS

Certification page…………………………………………………….. ii

Approval page………………………………………………………… iii

Title page……………………………………………………………….. iv

Dedication……………………………………………………………… v

Acknowledgement……………………………………………………… vi

Abstract………………………………………………………………….. vii

Table of contents……………………………………………………… viii

CHAPTER ONE:

1.0Introduction…………………………………………………………. 1

1.1Purpose of the study………………………………………………… 3

1.2Statement of the problem…………………………………………… 3

1.3Limitation of the study……………………………………………. 4

CHAPTER TWO:

2.0 Literature review…………………………………………………… 5

2.1Superconductor material……………………………………………… 8

2.2 Special Properties of super conductor ………………………………. 9

2.3 High temperature super conductor cable architectures……………… 10

2.4Comparison between Superconductor and Other Conductors……….. 12

CHAPTER THREE:

3.0 Methodology……………………………………………………… 13

3.1 Area of study……………………………………………………… 13

3.2 Instrument for data collection…………………………………….. 13

3.3 Methods of data collection……………………………………….. 13

3.4 Methods of data analysis…………………………………………. 14

3.5Applications of high temperature superconductor in power system…… 14

3.6Benefits of superconductors in power system…………………………. 22

CHAPTER FOUR

4.0 Discussion…………………………………………………………..... 28

4.1 Outcome of case studies……………………………………………… 29

4.2 Analysis of the research………………………………………………. 33

4.3 Cost of the research …………………………………………………. 37

CHAPTER FIVE

5.1 Conclusions…………………………………………………………… 39

5.2 Recommendations …………………………………………………… 40

REFERENCES.

APPENDIXES.

CHAPTER ONE1.0 INTRODUCTION

Superconductivity is a unique and powerful phenomenon of nature. Nearly

a century after its first discovery, its full commercial potential is just beginning to

be exploited. It is widely regarded as one of the great scientific discoveries of the

20th Century. This miraculous property causes certain materials, at low

temperatures, to lose nearly all resistance to the flow of electricity [1]. This state

of approximately zero loss enables a range of innovative technology applications.

At the dawn of the 21st century, superconductivity forms the basis for new

commercial products that are transforming our economy and daily life.

Superconductor-based products are extremely environmentally friendly compared

to their conventional counterparts [1]. They generate no greenhouse gases and are

cooled by non-flammable liquid nitrogen (nitrogen comprises 80% of our

atmosphere) as opposed to conventional oil coolants that are both flammable and

toxic. They are also typically at least 50% smaller and lighter than equivalent

conventional units which translate into economic incentives. These benefits have

given rise to the ongoing development of many new applications in the electric

power system sector.

However, superconductors enable a variety of applications to aid our aging

and heavily burdened electric power infrastructure - for example, in generators,

transformers, underground cables, synchronous condensers and fault current

limiters. The high power density and electrical efficiency of superconductor wire

results in highly compact, powerful devices and systems that are more reliable,

efficient, and environmentally harmless [1].

More so, an aging and inadequate power grid is now widely seen among

the greatest obstacles to restructure power markets. Utilities and users face

several converging pressures, including steady load growth, unplanned additions

of new distribution capacity, rising reliability requirements, and stringent barriers

to sitting new facilities, particularly extra-high voltage (EHV) equipment [2]. In

light of persistent challenges to proposals for conventional grid expansion, and

the recognition that industry reforms cannot succeed without renewed grid

investment, new technologies that can increase the attention are now becoming in

view. Interest in new, low-profile technologies to solve grid reliability problems

intensified as a result of frequent blackout in the nation which highlighted the

importance of power system reliability and the extent to which the margin for

error in this critical system has been eroded by falling investment and other

factors [2].

Moreover, one of the technologies with the greatest promise to address the

problem of power system is the high capacity, high-temperature superconductor

(HTS) cable which is capable of serving very large power requirements at

medium and high-voltage ratings. Over the past decade, several HTS cable

designs have been developed and demonstrated. All of these cables have a much

higher power density than copper-based cables or other convectional conductor.

Hence, because they are actively cooled and thermally independent of the

surrounding environment, they can be fit into more compact installations than

conventional copper cables, without concern for spacing or special backfill

materials to assure dissipation of heat. This advantage reduces environmental

impacts and enables compact cable installations with three to five times more

enough than conventional circuits at the same or lower voltage [3]. In addition,

HTS cables exhibit much lower resistive losses (approximately zero) than occur

with conventional copper or aluminum conductors. Despite these similarities,

important distinctions do exist among the various HTS cable designs.

1.1 PURPOSE OF THE STUDY

There are many applications of high temperature superconductor which

include: electric power, transportation, medicine, industry, communication, and

Scientific Research. In this work, the purpose or goal of this study is to find out

application of high temperature superconductors and its benefits in power system

transmission.

1.2 STATEMENT OF THE PROBLEM

An aging and inadequate power grid is now widely seen among the

greatest obstacles in efforts to restructure power system markets. In light of new

and intensifying pressures on the nation’s power infrastructure, industry and

policy leaders are looking to new technology solutions to increase the capacity

and flexibility of the grid. Thus, the need to know the applications of High

Temperature Superconductor (HTS) cable since it is regarded as one of the most

promising new technologies to address these issues in power system

transmission. These problems of power system include: overloading of the

cables, problem of siting new lines, issue of moving power safely and

efficiently, carbon free electric power, instability of power, unacceptably high

power surges.

1.3 LIMITATION OF THE STUDY

There are many applications of high temperature superconductor and their

benefits in different fields as a result of its unique characteristics. In electronic,

the low microwave losses of HTS thin films enables the coupling of an

unprecedentedly large number of resonators to microwave filter devices with

much sharper frequency characteristics than conventional compact filters, in

military, in aircraft electronics, for better rejection of interference noise in aircraft

radar systems, in mobile phone communication systems, HTS microwave filter

subsystems are already a commercially available solution for problematic radio

reception situations, as in sensors, magnets, Power applications [1]. Hence, our

study here will be limited on the application of high temperature superconductor

and their benefits in power system transmission.

CHAPTER TWO

2.0 LITERATURE REVIEW

In 1911, H. K. Onnes, a Dutch physicist, discovered superconductivity by

cooling mercury metal to extremely low temperature and observing that the metal

exhibited approximately zero resistance to electric current. Prior to 1973 many

other metals and metal alloys were found to be superconductors at temperatures

below -249.8oC [1]. These became known as Low Temperature Superconductor

(LTS) materials. Since the 1960s a Niobium-Titanium (Ni-Ti) alloy has been the

material of choice for commercial superconducting magnets. More recently, a

brittle Niobium-Tin inter-metallic material emerged as an excellent alternative to

achieve even higher magnetic field strength. In 1986, J. G. Bednorz and K. A.

Muller discovered oxide based ceramic materials that demonstrated

superconducting properties as high as -238oC. This was quickly followed in early

1997 by the announcement by C. W. Chu of a cuprate superconductor

functioning above -196oC the boiling point of liquid nitrogen. Since then,

extensive research worldwide has uncovered many more oxide based

superconductors with potential manufacturability benefits and critical

temperatures as high as -1380C.

Hence, a superconducting material with a critical temperature above

-249.8oC is known as a High Temperature Superconductor (HTS), despite the

continuing need for cryogenic refrigeration for any application. High-temperature

superconducting (HTS) cable, characterized by high current density and low

Fig 1: Transition in Superconductor Discoveries [1]

transmission loss, shows promise as a compact large-capacity power cable that

exhibits several environmental advantages such as energy and resource

conservations as well as no external electromagnetic fields [1]. It must be noted

that the “approximate zero resistance” ascribed to HTS material applies to the

transmission of direct current (DC) power, while there is some electricity loss

involved in AC transmission. HTS DC cable takes maximum advantage of the

characteristics of superconductivity [4].

However, there are absent of those problems unique to AC applications, HTS

DC cables are expected to outpace HTS AC cables, in line with future

performance enhancement and price reduction of converters. However, the

diagram above shows the transition in superconductor discoveries starting from

1911 through 2010 [1].

However, there are some challenges that are often encountered in the use of

superconductor in power system which include:

Cost

Refrigeration

Reliability

Acceptance

More so, many years of development and commercialization of applications

involving LTS materials have demonstrated that a superconductor approach

works best when; it represents a unique solution to the need. Alternatively, as the

cost of the superconductor will always be substantially higher than that of a

conventional conductor in the field of power system, it must bring overwhelming

cost effectiveness to the system. The advent of HTS has changed the dynamic of

refrigeration by permitting smaller and more efficient system cooling for some

applications [1].

Moreover, design, integration of superconducting and cryogenic

technologies(at very low temperature) demonstration of systems cost benefits and

long term reliability must be met before superconductivity delivers on its current

promise of major societal benefits and makes substantial commercial inroads into

new applications. It is widely regarded as one of the great scientific discoveries

of the 20th Century. This miraculous property causes certain materials, at low

temperatures, to lose all resistance to the flow of electricity. This state of

approximately zero loss enables a range of innovative technology applications.

At the dawn of the 21st century, superconductivity forms the basis for new

commercial products that are transforming our economy and daily life. However,

Current Commercial applications of superconductors include the following [1]:

Magnetic Resonance Imaging (MRI)

Nuclear Magnetic Resonance (NMR)

High-energy physics accelerators

Plasma fusion reactors

Industrial magnetic separation of kaolin clay

Hence the major commercial applications of superconductivity in the medical

diagnostic, science and industrial processing fields listed above all involve LTS

materials and relatively high field magnets. Indeed, without superconducting

technology most of these applications would not be viable. Several smaller

applications utilizing LTS materials have also been commercialized, example,

research magnets and Magneto-Electroencephalography (MEG); the latter is

based on Superconducting Quantum Interference Device (SQUID) technology

which detects and measures the weak magnetic fields generated by the brain. The

only substantive commercial products incorporating HTS materials are electronic

filters used in wireless base stations. About 10,000 units have been installed in

wireless networks worldwide to date [1].

2.1 SUPERCONDUCTOR MATERIAL

A Superconductor material differs fundamentally in quantum physics

behavior from conventional materials in the manner by which electrons or

electric current move through the material. It is these differences that give rise to

the special properties and performance benefits that differentiate superconductors

from all other known conductors [1]. A superconductor is an element or metallic

alloy which, when cooled to near absolute zero, dramatically lose all electrical

resistance. In principle, superconductors can allow electrical current to flow

without any energy loss (although, in practice, an ideal superconductor is very

hard to produce). In addition, superconductors exhibit the Meissner effect in

which they cancel all magnetic flux inside, becoming perfectly diamagnetic

(discovered in 1933). In this case, the magnetic field lines actually travel around

the cooled superconductor. It is this property of superconductors which is

frequently used in magnetic levitation experiments.

2.2 SPECIAL PROPERTIES OF SUPERCONDUCTOR MATERIALS

Approximately zero resistance and high current density have a major impact

on electric power transmission and also enable much smaller or more powerful

magnets for motors, generators, energy storage, medical equipment and industrial

separations. Low resistance at high frequencies and extremely low signal

dispersion are key aspects in microwave components, communications

technology and several military applications [1]. Low resistance at higher

frequencies also reduces substantially the challenges inherent to miniaturization

brought about by resistivity. The high sensitivity of superconductors to magnetic

field provides a unique sensing capability, in many cases 100 percent superior to

today’s best conventional measurement technology. Magnetic field exclusion is

important in multi-layer electronic component miniaturization, provides a

mechanism for magnetic levitation and enables magnetic field containment of

charged particles. The final two properties form the basis for digital electronics

and high speed computing well beyond the theoretical limits projected for

semiconductors. All of these materials properties have been extensively

demonstrated throughout the world. These properties of superconductor can be

summarized under the following points [1]:

Zero resistance to direct current

Extremely high current carrying density

Extremely low resistance at high frequencies

Extremely low signal dispersion

High sensitivity to magnetic field

Exclusion of externally applied magnetic field

Rapid single flux quantum transfer

Close to speed of light signal transmission.

2.3 HIGH TEMPERATURE SUPERCONDUCTOR

CABLE ARCHITECTURES

Interest in the field of superconducting power cable dates to the 1960’s, but

because conventional metallic superconductors required cooling with liquid

helium, these cable system designs were excessively complex and cost-

prohibitive. Interest in the field was renewed following the discovery of

ceramics-based high-temperature superconductors in the late 1980’s, which

enabled the use of liquid nitrogen as a cooling medium. Liquid nitrogen is widely

used in a variety of industrial applications and is recognized as a cheap, abundant

and environmentally harmless coolant [2].

Over the past several decades, a variety of cable designs were prototyped

and developed to take advantage of the efficiency and operational benefits of

superconductivity, while minimizing the additional capital and operating costs

that result from the requirement that HTS cables be refrigerated. Variations in

cable architecture have important implications in terms of efficiency, stray

electromagnetic field (EMF) generation, and reactive power (Volt Ampere

Reactive or VAR) characteristics. At present there are two principal types of HTS

cable. The simpler design is based on a single conductor, consisting of HTS wires

stranded around a flexible core in a channel filled with liquid nitrogen coolant

[2]. This cable design employs an outer dielectric insulation layer at room

temperature, and is commonly referred to as a "warm dielectric" design. It offers

high power density and uses the least amount of HTS wire for a given level of

power transfer. Drawbacks of this design relative to other superconductor cable

designs include higher electrical losses (and therefore a requirement for cooling

stations at closer intervals), higher inductance, required phase separation to limit

the effects of eddy current heating and control the production of stray

electromagnetic fields (EMF) in the vicinity of the cable. Most of the HTS cable

demonstrations undertaken to date have been based on the warm dielectric

design.

An alternative design employs concentric layer(s) of HTS wire and a cold

electrical insulation system. Liquid nitrogen coolant flows over and between

both layers of wire, providing both cooling and dielectric insulation between the

center conductor layer and the outer shield layer. This is commonly referred to as

a coaxial, "cold dielectric" design. Cold dielectric HTS cable offers several

important advantages, including higher current carrying capacity; reduced AC

losses; low inductance; and the complete suppression of stray electromagnetic

fields (EMF) outside of the cable assembly. The reduction of AC losses enables

wider spacing of cooling stations and the auxiliary power equipment required to

assure their reliable operation [2].

2.4 COMPARISM BETWEEN SUPERCONDUCTOR AND OTHER CONDUCTORS

Normal conductors have resistance which restricts the flow of electricity

and wastes some of the energy as heat. The resistance increases with the length of

the conductor. Superconductors have close to zero or zero resistance and a few

other properties, but the resistance is the most important one because it means

electricity can flow more efficiently through it. The drawback is that all the

superconductors we know of today have to be cooled down to extremely low

temperatures to achieve superconductivity [5].

Figure 1. Single-phase warm-dielectric cable Figure 2. Single-phase cold-dielectric cable

CHAPTER THREE

3.0 METHODOLOGY

This chapter describes the procedures or steps adopted while carrying out

the study. It is discussed under the following points: area of study, instrument for

data collection, method of data collection and method of data analysis.

3.1 AREA OF STUDY

The area of study of this work has been chosen to be United States power

system grid. A superconductor application is still a young technology and has not

been practiced in Nigeria.

3.2 INSTRUMENT FOR DATA COLLECTION

The researcher has chosen to consult the works of other scholars mainly.

This was taken due to lack of time and necessary materials for experimentation.

The option of structured questionnaire was avoided because the researcher could

not tour all round the area chosen due to logistic constraints. Also this instrument

will be easy in terms of data collection.

3.3 METHODS OF DATA COLLECTION

The researcher collected data for this study through visiting the internet

and works of scholars online, visiting the library to read books written by well

know writers. Data were also sourced using computer software like Encarta

premium. The writer did not relent to have discussion with colleagues in order to

verify facts.

3.4 METHOD OF DATA ANALYSIS

The method the researcher used in analyzing data is data comparison. The

researcher gets information from different authors, compares them and uses the

results to draw out conclusion.

3.5 APPLICATIONS OF HIGH TEMPERATURE SUPERCONDUCTOR

IN POWER TRANSMISSION

Today’s power grid operators face complex challenges that threaten

their ability to provide reliable service; steady demand growth; aging

infrastructure; mounting obstacles to sitting new plants and lines; and new

uncertainties brought on by structural and regulatory reforms. Advances in high

temperature superconductivity (HTS) over the past two decades are yielding a

new set of technology tools to renew this critical infrastructure, and to enhance

the capacity, reliability and efficiency, of the nation’s power system. Power

industry experts in the United States have widely agreed that today’s aging power

grid must be strengthened and modernized. Utilities must cope with a growth in

the underlying level of demand driven by our expanding, high technology-

intensive economy [1].

Consumers in the digital age have rising expectations and requirements for

grid reliability and power quality. Competitive reforms have brought about new

patterns of power flows. EPRI (The Electric Power Research Institute) has

estimated that huge amount of resources must be spent over the next ten years to

achieve and maintain acceptable levels of electric reliability. At the same time,

utility shareholders are insisting on strong financial performance and more

intensive use of existing utility assets.

Moreover, gaining approval to site new infrastructure - both generating

plants as well as transmission lines - has become extremely difficult in the face of

landowner and community opposition and the NIMBY (“not in my back yard”)

phenomenon. This is especially the case in urbanized areas where power needs

are concentrated. As a result, utilities face lengthy and uncertain planning

horizons, as well as a rising risk of costly blackouts and other reliability

problems. The existing grid is also becoming increasingly regionalized with more

generation located remotely to be close to its particular source of fuel. The grid

will therefore have to mitigate increasing inter-regional fault current transfers and

the increasing number of parallel transmission paths that will be required to allow

lowest cost electricity to flow to where it is needed and to allow a smarter grid to

quickly respond to disruptions of sources, transmission or local generation paths

[1].

Distributed generation can help but is not always available when needed, and

also must be redesigned, possibly with the help of fault current limiters, to ride

through local fault and remain available. Solving this complex set of problems

will require a combination of new policies and technologies. Regulatory reforms

are needed to foster stronger incentives for grid investment and to overcome the

fragmentation that has impeded utilities ability to raise the required investment

capital.

Beyond all this new rules, however, the physical nature of the challenge

requires the adoption of advanced grid technologies, including those based on

HTS. These new HTS technologies have undergone rapid development in the

comparatively short time of two decades. The first HTS compounds were

synthesized in research laboratories in the late 1980s. Today, the HTS industry

has advanced to full-scale power equipment prototypes and demonstration

projects that are undergoing the rigors of in-grid evaluation. As these new

technologies are incorporated into the existing power system, they will offer

utilities new tools to ease the pressures that limit the performance and capacity of

their systems – with much lower space and land use impacts and with major

environmental benefits that are available using traditional grid upgrade solutions

[1].

3.5.1 HIGH TEMPERATURE SUPERCONDUCTOR WIRE

The foundation of these applications is a new generation of wire capable of

carrying vastly (on the order of 100 percent times) higher currents than

conventional copper wires of the same dimension, with approximately zero or

negligible resistive losses. Today’s prototype and demonstration technologies

have made use of a proven, readily available and high-performance first

generation HTS wire that is multi-filamentary in composition. Second generation

(2G) HTS wire, using coated conductor architecture and a variety of thin film

manufacturing processes, is rapidly making its way to market. 2G wire will

greatly broaden the addressable market for existing HTS devices because of its

predicted lower cost. It will also enable altogether new types of HTS applications

due to its superior performance characteristics in certain modes of operation. 2G

wire has been commercially available since 2006. HTS wire, in short, brings the

promise of a revolution in the way electricity is generated, delivered and

consumed - much as the introduction of optical fiber led to a technological leap

forward in the telecommunications industry. Among the power system

applications of HTS wire enables are the following:

3.5.2 HIGH TEMPERATURE SUPERCONDUCTOR POWER CABLES

Today’s conventional power lines and cables are being operated closer to their

thermal limits, and new lines are becoming hard to site. Compact, high-capacity

underground HTS cables offer an important new tool for boosting grid capacity.

Today’s advanced HTS cable designs enable controllable power flows and the

complete suppression of stray EMF.HTS power cables transmit 3-5 times more

power than conventional copper cables of equivalent cross section, enabling more

effective use of limited and costly rights-of-way. Significant progress toward the

commercialization of HTS cable is underway. Three major in-grid

demonstrations have been completed in the US including the world’s first HTS

power transmission cable system in a commercial power grid which is capable of

transmitting up to 574 megawatts (MW) of electricity, enough to power 300,000

homes. Two more demonstrations are in the planning stage in the US and another

dozen projects are active around the world [1].

3.5.3 HIGH TEMPERATURES TRANSFORMERS

Grid operators face a major challenge in moving power safely and efficiently,

from generators to consumers, through several stages of voltage transformation.

At each stage, valuable energy is lost in the form of waste heat. Moreover, while

demands are continually rising, space for transformers and substations -

especially in dense urban areas - is severely limited. Conventional oil-cooled

transformers also pose a fire and environmental hazard. Compact, efficient HTS

transformers, by contrast, are cooled by safe, abundant and environmentally

harmless liquid nitrogen. As an additional benefit, these actively-cooled devices

will offer the capability of operating in overload, to twice the nameplate rating,

without any loss of life to meet occasional utility peak load demands [1].

3.5.4 HIGH TEMPERATURE SUPERCONDUCTOR TRANSFORMERS

FOR WIND ENERGY

The increasing demand for clean, carbon free electric power, coupled with the

global warming crisis, has fueled tremendous interest in and development of

renewable energy technologies such as wind power. To break through the

economic barrier and ensure the future of this vast and critically important green

energy source, new technologies are needed offering lower weight, higher

efficiency, and significantly improved reliability. Direct drive wind generators

are utilizing a new high-efficiency stator design and replacing copper with HTS

wire on the rotor. Estimates are that a 10 MW drive utilizing HTS technology

would weigh about one third the weight of a conventional direct drive generator

with the same power rating. This reduction in weight would also allow an

increase in blade size and greater power output. The net effect is expected to

double the power system capacity of conventional systems and lower the cost of

wind generated energy [1].

3.5.5 ENERGY STORAGE

With power lines increasingly congested and prone to instability, strategic

injection of brief bursts of real power can play a crucial role in maintaining grid

reliability. Small-scale Superconducting Magnetic Energy Storage (SMES)

systems, based on low-temperature superconductor, have been in use for many

years. These have been applied to enhance the capacity and reliability of

stability-constrained utility grids, as well as by large industrial user sites with

sensitive, high-speed processes, to improve reliability and power quality. Larger

systems, and systems employing HTS, are a focus of development. Flywheels,

based on frictionless superconductor bearings, can transform electric energy into

kinetic energy, store the energy in a rotating flywheel, and use the rotational

kinetic energy to regenerate electricity as needed. Using bulk HTS self centering

bearings allows levitation and rotation in a vacuum, thereby reducing friction

losses. Conventional flywheels suffer energy losses of 3-5 percent per hour,

whereas HTS based flywheels operate at <0.1 percent loss per hour. Large and

small demonstration units are in operation and development [1].

3.5.6 HIGH TEMPERATURE SUPERCONDUCTOR FAULT CURRENT

LIMITERS

As new generators are added to the network, many local grids face a rising risk

of unacceptably high power surges that result from “faults” or short circuits.

These occasional surges are induced by adverse weather, falling tree limbs,

traffic accidents, animal interference and other random events. As fault current

levels rise, they pose a mounting risk that such surges will exceed the rating of

existing conventional circuit breakers, switchgear, bus, distribution transformers

and other equipment and expose grids to much more costly damage. HTS

technology enables a new solution: compact, “smart” fault current limiters

(FCLs) that operate passively and automatically, as power “safety valves” to

ensure system reliability when individual circuits are disrupted. Taking advantage

of the inherent properties of superconductors, they sense such dangerous over

currents and reduce them to safe levels by changing state instantaneously, from

“super” conductors to resistors. Several demonstrations of this breakthrough

technology are now underway, with an expected commercial horizon of 2010 [1].

3.5.7 AN ENABLER OF THE ELECTRICITY REVOLUTION

The advent of HTS technology offers the opportunity for grid operators to move

to a new level of power system performance. Since the dawn of the utility

industry in the late 19th century, power system networks have been based almost

exclusively on components made of conventional materials such as copper,

aluminum and iron. The performance and capacity of the grid has been improved

and expanded over time. Yet grid performance is ultimately limited by the

inherent properties and limitations of these materials. HTS-based technology

removes many of these operational and space constraints. It offers grid operators

a new set of tools and strategies to improve the performance, reliability, safety,

land use and environmental characteristics of a power system. The need for such

new solutions is becoming acute with the relentless electrification of energy use -

a trend that makes our aging, heavily burdened grid more critical than ever to the

functioning of modern society. However, in many ways, the electric power

industry is at a crossroads. Within the past few years, electric power industry

structural reform efforts have stalled perceptibly. The current gridlock in policy

reforms and power flows is largely due to the mounting difficulty of expanding

the power delivery network. Without a way to expand the “superhighway

system” that supports power flows, recent competitive market reforms simply

cannot succeed. HTS technology can play an important role in “breaking the

gridlock” of power flows and policy reforms that threaten the power industry and

our overall economy.

However, before HTS technology solutions can enjoy broad acceptance,

they must undergo field trials. Such demonstrations play a crucial role in

establishing a record of reliability and working out grid integration issues.

Despite the acute needs facing the power system sectors, it is widely observed

that investor-owned utilities have taken a cautious and conservative approach to

adopting new technology solutions in recent years. This has resulted from several

factors including: a perception of asymmetric regulatory risks; disallowances

resulting from past technology failures; and the loss of sites where experimental

technologies can be tested without potentially adverse consequences for

customers. Industry restructuring efforts underway since the early 1990’s

moreover have had the unfortunate effect of undermining investment in jointly-

funded industry R&D [1].

3.6 BENEFITS OF HIGH TEMPERATURE SUPERCONDUCTORS IN

POWER TRANSMISSION

Using high temperature superconductor in power transmission can translate into

significant cost savings. The factors that lead to lower costs on an installed

system basis may be summarized as follows:

3.6.1 SHORTER LENGTHS

Short, strategic insertions of HTS cable could achieve the same power flow

benefit as lengthier circuits of overhead line. HTS cable need not be cost-

competitive with conventional cable or overhead line technology on a stand-alone

basis for it to offer a lower total cost solution. For example, with HTS cable

utilities may solve power flow problems with shorter circuit lengths, e.g.,

connecting to the more pervasive 11/33/66 Kv system rather than tying back to

the more distant EHV backbone transmission system [3].

3.6.2 LOWER VOLTAGES

Because of the higher capacity of HTS cable (approximately three to five times

higher than conventional circuits), utilities may employ lower-voltage equipment,

avoiding both the electrical (I²R) losses typical of high-current operation and the

capital costs of step-up and step-down transformers (as well as the no-load losses

within the transformers themselves). High-current HTS cables at 33 kV or even

11 kV may solve problems that would ordinarily require a 132 kV or 330 kV

conventional solution. The ability to operate at lower voltages translates into

lower costs for cable dielectric/insulating equipment, reduced hazards, as well as

lower cable and ancillary costs, which are driven by the voltage level of the

selected solution. In the long run, HTS may make unnecessary the much higher

system costs (e.g., transformer and breaker replacement) associated with wide-

area voltage up-ratings [3].

3.6.3 GREATER CONTROLLABILITY

HTS cable offers the ability to control power flows with conventional series

reactors, yielding market and reliability benefits typically associated with other

"controllable" forms of transmission e.g., FACTS (Flexible AC Transmission

Systems) or DC transmission. Yet this control at the terminal of a line would be

achieved with much less expense and complexity than is typically required using

conventional technologies (e.g., large, inflexible DC converter stations or the

large-scale power electronic devices often associated with conventional FACTS

devices). Whereas DC lines are limited to point-to-point flows, HTS cable

systems could be expanded to provide controllability to many points in a

network. This inherent controllability has important regulatory implications. For

example, HTS could form the basis for private, at-risk investment in merchant

transmission projects with assignable property rights in transmission capacity,

outside of the rate base framework, in situations where DC and conventional

FACTS solutions are not cost-competitive. The cost of DC systems is highly

impacted by the cost of converter stations. For short runs of DC transmission,

system costs are dominated by the cost of converter stations; HTS cables face no

such penalty [3].

3.6.4 LIFE EXTENSION AND IMPROVED ASSET UTILIZATION

HTS cable represents a new weapon to attack the principal enemy of congested

urban transmission systems: heat. Over time, thermal overload ages and degrades

cable insulation. By drawing flow away from overtaxed cables and lines,

strategic insertions of HTS cable can "take the heat off" urban power delivery

networks that are increasingly prone to overheating, the inevitable result of

increased loadings and acute siting difficulties associated with siting

conventional (copper or aluminum-based) system expansions. Reducing the

burden on existing electrical pathways will extend the life of conventional system

elements. This approach also improves overall asset utilization, and defers the

need for the large-scale capital investment required for the replacement of aging

and worn-out grid infrastructure [3].

3.6.5 EXPANDED GENERATOR SITING OPTIONS

Because it greatly reduces voltage drop, HTS cable has the ability to "shrink

electrical distance". This means that new generators could be located at greater

distance from urban loads (where land, labor and other costs are lower), while

providing the same degree of voltage support as if they were located in or

adjacent to the city center. Thus, HTS transmission lines could be deployed as

"virtual generators" to solve both power supply and reactive power problems [3].

3.6.6 REDUCED ELECTRICAL LOSSES

In specially optimized designs, cable can result in lower net energy losses than

occur in either conventional lines and cables or unshielded HTS cables with a

single conductor per phase, offering a transmission path with high electrical

efficiency. Because HTS circuits tend to attract power flow, they will naturally

operate at a high capacity factor, reducing the losses on other circuits and further

magnifying their efficiency advantage [3].

3.6.7 INDIRECT AND NON-MONETARY SAVINGS

In addition to these "hard cost" savings, HTS cable may result in other "soft

cost" savings. For example, time to install may be shortened because of reduced

siting obstacles associated with compact underground installations and less

burdensome siting requirements for lower-voltage facilities. HTS cables might be

routed through existing, retired underground gas, oil or water pipes, through

existing (active or inactive) electrical conduit, along highway or railway rights-

of-way, or through other existing corridors. While HTS cables “off-the-shelf” are

likely to cost more than conventional cables, the net cost of a fully installed cable

system may be lower because of the smaller space requirements associated with

HTS cables, and the ability to make adaptive reuse of existing infrastructure

where it exists, or the ability to use guided boring machines instead of costlier

and more disruptive trenching where such infrastructure does not exist. The

expansion of siting options would reduce the need for costly and controversial

expropriation proceedings. Indirect impacts on property values resulting from

overhead line construction would also be avoided. Communities that host HTS

projects would gain the benefit of higher property valuations, e.g., higher

property tax receipts and broader development options [3].

3.6.8 REDUCED REGIONAL CONGESTION COSTS

Finally, and perhaps most significantly, the ability to complete grid upgrade

projects more quickly will translate into the earlier elimination or relaxation of

grid bottlenecks. Solving physical bottleneck problems will sharply reduce the

grid congestion costs that, in today's unsettled, imperfectly competitive

marketplace, can impose huge penalties on consumers and the economy at large

[3].

3.7 ENVIRONMENTAL BENEFITS

Beyond the cost advantages outlined above, HTS cable will yield several

environmental advantages over conventional technology. Some of these

advantages are due to the very same characteristics of HTS cable that result in

lower-cost installed solutions. For example [3]:

Underground placement: The underground placement of HTS cable will

eliminate the visual impact of overhead lines.

Shorter cable lengths: Solving power flow problems with shorter lengths

of cable in more compact rights-of-way will reduce the disruptive effects

of construction.

Reduced losses: The reduced losses in HTS circuits, as well as reduced

I²R losses on adjacent, conventional circuits that are offloaded due to the

"current hogging" effects of HTS cable, will translate into reduced fuel

consumption for generation.

Environmentally harmless dielectric: Liquid nitrogen, the

coolant/dielectric of choice for HTS cables, is inexpensive, abundant and

environmentally compatible [3].

CHAPTER FOUR

4.0 DISCUSSIONS

The system study “Applications of High Temperature Superconductivity

(HTS) and its benefits in power system transmission”, lists the applications;

technical and economical benefits in power system generation, transmission and

distribution systems, and using components build up with HTS material

considering the state of the art in knowledge on superconductivity.

Besides minimal transmission losses, the ability to carry large current

densities is an important criterion for superconducting materials to create

favorable conditions for applications using this new technology. The current

densities of known HTS materials are about 100A/mmsq, which is at least 10

times larger compared to the current densities in conventional aluminum or

copper conductors.

Another interesting feature is the use of the transition from the

superconductor to the non superconducting state of the material. This property is

used for current limiting in power system. The advantages of the low energy

losses compared with the actual cost of investment and maintenance do not

justify an economical application of most superconducting components in power

system today. Therefore, additional benefits seem to be required in order to

guarantee a successful implementation of superconductor in the field of electric

power applications. An example of such benefit is the integration of the current

limiter and the superconducting transformer. This solution combines the two

element superconducting transformer with low energy losses and current limiter

in an advantageous manner. The current limiter permits then a decrease of the

transformer short circuit impedance, which one hand leads to a larger

transmission capacity and on the other hand allows for an improved voltage

stability at the secondary side of the transformer .These synergies lead to a

reduction of the investment cost, to more economical applications due to

integration as well as to an increase of energy efficiency in the transmission and

distribution system.

4.1 OUT COME OF CASE STUDIES

Detailed research activities are necessary to show the potential of using

high temperature superconductivity in the field of power system. Hence a set of

case studies have been investigated:

Increase of transmission capacity by reducing impedances

Increase of mesh of power system

Increase of quality and availability of power system

Re-dimensioning of elements used in power system

Reduction of energy losses

Reduction of environmental impacts

Increase of the dynamic stability

Integration of power production plants

Development of new switchgear concepts

Application of DC network in power system

The result of the system study is categorized as discussed below (ideas, solution

approaches and economical solutions).

I. IDEAS

The transmission capacity of a network can be increased due to the

realization of a network with low ohmic, coaxial or concentrically constructed,

superconducting cables and transformers. The high current capability of the HTS-

cable gives in selected cases the possibility to exchange the 380kv voltage level

by one of 110kv. Another possibility is to keep the 380kv level for the European

power system and to transform the power directly from 380kv to powerful

superconducting backbone-lines in the distribution network.

II. VISION

If government requirements change concerning environmental impacts for

the realization of overhead lines, it might be impossible to build new overhead

lines and it might be mandatory to replace existing overhead lines by

underground cables. HTS- cables could in such a situation, be the solution to

economically transmit the increasing need of energy in the major centers with a

low environmental impact. Possible scenarios are superconducting connections

through road or railway tunnels in mountain areas with the aim to reduce the

number of the overhead lines and to decrease transmission losses as well as a

backbone solution for the transit of energy.

III. ECONOMICAL SOLUTIONS

The result of case studies concerning the integration of current limiters in

power system show the great potential using these elements in a technically

efficient manner independent of the nominal power in all voltage levels of power

system. The actual production costs are difficult to calculate in detail. It must be

assumed that the cost lie in a range affordable. An investment cost at the upper

end of this range allows an economical use, especially in regional distribution

and industrial power system. An important advantage resulting from the

introduction of current limiters in distribution system is the use of load breakers

instead of the expensive short circuit breakers as switching devices.

The main benefits of the superconducting transformers are the low energy

losses, the decrease in weight and volume as well as the reduction of

environmental impacts. Due to it’s the behaviors of the superconducting

transformers at restart, its first economical applications are seen in urban cable

networks and as blocks transformers in power plants. The integration of the

current limiting function in transformers will increase number of economically

advantageous applications.

IV. SOLUTION APPROACHES

The replacement of conventional copper cables by HTS-cables in existing

ducts result in the simultaneous effect that in the same space more power with

less electrical losses can be transmitted. Due to the larger current densities

compared to conventional cables, superconducting cables must be constructed in

a new manner.

Besides the coaxial construction principle, a concentric construction

principle might also be possible. With these two construction variations, the

electromagnetic influence outside of the cable can be eliminated. This will be a

requirement considering the expected applications of large current density. With

the mentioned constructions principles, it would for instance be possible to

manufacture 110kv HTS-cables with similar physical parameters and

transmission capacity as 380kv conventional overhead lines. The use of

superconducting cables is most promising for direct current networks. Large

current applications imply the possibility to eliminate some voltage levels of an

electrical network.

Due to this effect, the DC superconducting cables may cost about 4 times

as much as the conventional cables. Moreover, the following conclusions are

important from a technical point of view:

Superconducting cables with nominal voltages higher than 20kv can be realized

in a technical efficient manner both for AC and DC system;

The use of HTS-DC cables is economically more attractive than the application

of HTS-AC-cables. The essential advantages are the effect of no losses in the

duct and no dielectric losses as well as the very compact design.

The application of the high temperature superconducting magnetic energy

storage devices (SMES) is not economical compared with the flywheel. Reasons

are the physical parameters of existing BISSCO HTS-materials. These materials

have a large decrease of the critical current density in a relatively small magnetic

field. If in future the HTS-material YBCO will be available, the comparison has

to be repeated because the stability of the magnetic field of this material is much

better.

4.2 ANALYSIS OF THE RESARCH

4.2.1 ANALYISI ON TRANSFORMER APPLICATION

The basic design process for the HTS transformers is similar to that of

conventional transformers. A good design is a function of the optimal use of

active materials such an iron-core, HTS material and cryogenic cooling system.

Below are a few analyses that are significant impact on the size, weight, cost and

performance of HTS transformer.

a) AC losses in HTS winding: CTC is used in the design analysis in order to

minimize the AC losses in the winding. The AC losses could represent a

significant portion of the total thermal load on the refrigeration system, but no

reliable analysis is available for estimating these losses while a CTC carries the

AC and experiences the external AC field.IRL and others are in process of

developing AC loss analysis formulations. Due to unavailability of good analysis

basis, AC losses have not been estimated for the windings.

b) Size and weight: Voltage per turn is a measure of core limbs cross section.

A larger core cross section may lower HTS consumption at the expense of larger

weight and size. The larger core will also require bigger diameter coils. However,

a manufacturer may prefer winding diameter no larger than what their existing

machinery can handle. Thus, by keeping the core diameter similar to that of

conventional transformers, it is possible to reduce the overall size and weight of

HTS transformers of similar rating. In other words a transformer manufacture

could produce HTS transformers of twice the rating within the capabilities of

their existing winding and handling equipment and facility space. However, some

customers may not mind the larger weight caused by the larger diameter core,

provided that the product price is lower .selection between the two approaches is

better made by discussion between a customer and a manufacturer.

c) Operating temperature: A conventional oil-cooled transformer designed

for 100 degrees Celsius operation can be operated at 50 percent overload by

circulating oil in the tank and at 100 percent overload by providing additional

cooling fans. Similar ratings are also possible with HTS transformers. For

example if an HTS transformer is designed for operation at 77k ,then it is

possible to overload it by 50 percent and 100 percent by operating it at 70k and

64k, respectively. Lower temperature operation will require additional cryogenic

cooling capacity.

d) Operational constraints: Since HTS winding are more compact than

copper winding of a conventional transformer, the leakage reactance of HTS

transformers can be designed to be low. A low leakage reactance result in lower

output voltage variations between no –load and rated load conditions. It might

also be possible to eliminate use of tap changers typically employed to correct

output voltage as a function of load. However, lower leakage reactance generates

higher through fault current and forces during a short circuit event experienced

by a transformer. Thus a compromise is needed between lower leakage reactance

and acceptable fault current.

4.2.2 ANALYSIS ON FAULT CURRENT LIMITERS APPLICATION

High temperature superconductor technology permits a modern solution to

eliminate surge in power system transmission. This is as a result of its compact

and simplicity in any system incorporated. It allows the passive and automatically

operated circuit as power safety valves. Also because of its transition from

superconductor to resistor when a high current density passed through the

material, this particular application was able to achieve.

4.2.3 ANALYSIS ON HTS POWER CABLE AND WIRE APPLICATION

The basis of these particular applications is a new technology of wire

capable of carrying more than 100 percent higher currents than conventional

cables/wire of the same dimension, with approximately zero or negligible

resistive losses. Looking at Nigeria power grid, characterized by aluminum or

copper cable/wire it has being marked with low voltage as a result of its radial

network. In which if this HTS cable is used in the network will account for less

loss in the network and deliver equal voltage in the sending end of the power

system

4.2.4 ANALYSIS ON ENERGY STORAGE APPLICATION

Power system is often marked by instability of supply. Superconducting

Magnetic Energy Storage system can solve this issue based on low temperature

superconductor. These can been apply to enhance the capacity and reliability of

stability-constrained utility grids; For example Flywheels, based on frictionless

superconductor bearings, can transform electric energy into kinetic energy, store

the energy in a rotating flywheel, and use the rotational kinetic energy to

regenerate electricity as needed. And this will ensure continuity in the system.

Generally, the integration of high temperature superconductor in power

system transmission is as a result of its following features which in include:

environmentally harmless dielectric, reduced loss, shorter cable lengths, highly

efficient in underground placement, indirect and non-monetary savings, reduced

regional congestion costs, expanded generator siting options, life extension and

improved asset utilization, greater controllability, lower voltages as the author

has highlighted above.

4.3 COST OF RESEARCH

This research work is relatively expensive to the author. This is so because

the researcher lacks the necessary material to carry out the work effectively.

Hence, he relents on online material by browsing through a subscription made to

GLO/MTN network using modem, thus this subscription make the work

expensive.

4.4 PROBLEMS ENCOUNTERED IN THE CAUSE OF WRITING

THIS RESEARCH WORK

As a result of carrying out this research work the author encountered many

problems which include:

a. The use of high temperature superconductor is not used in Nigeria where the

author is leaving, thus he could not get some information required to carry out the

research work effectively.

b. The usual problems of power failure also pose a great obstacle during the

research work.

c. The author also encountered the problem of analyzing the online material and

other material collected in the cause of writing this work and putting it in a

simple language that can be generally understand by anybody.

d. Also the author lacks some statistical material and equipment to carry out the

experimental study.

CHAPTER FIVE

CONCLUSIONS AND RECOMMEDATION

5.0 CONCLUSION

Given today's acute level of concern about power system reliability and

new competitive pressures, it brings to our notice that strategies to control and

redirect transmission flows have greater value than ever before. As power

transmission problems have intensified across the nation's grid over the past few

years, the need for new technology solutions has become apparent. HTS cables

constitute new tools to develop these strategies. By taking advantage of their

outstanding features, utilities and regional transmission operators will find new

and less expensive ways to tackle grid congestion problems, reduce grid security

violations, improve overall asset utilization and extend the life of their existing

systems.

Also, the widespread commercial adoption of these superconducting devices for

power networks has great potential to generate a range of economic,

environmental and reliability benefits, many of which are discussed herein.

Yet, as is often the case with many “breakthrough” technologies that are initially

high-cost, early developers, and users face high risks. These risks are

compounded by the very uncertainties and regulatory complications that VLI

cable could ultimately help to resolve. It is important, therefore, to undertake all

appropriate steps to speed the commercialization of this promising technology.

5.1 RECOMMENDATION

Generally series of demonstration projects to illustrate the power flow attributes

of HTS cables, to develop a reliability record for the technology, and to resolve

system integration and other issues should be a top priority of public officials

responsible for power system related policy.

As in the case where the author is residing the new technology is not in practice

at all. Thus he urges utilities, experts and the federal government to embark on

the use of the new technology as integration in power system components so as to

reduce the problems of power system in the country in which it can address as

seen from this study. Which include in high temperature superconductor wire,

high temperature superconductor power cables, energy storage, high temperatures

transformers and high temperature superconductor fault current limiters etc.

REFERENCE

[1] IEEE CSC council on superconductivity, Superconductivity its present and future application.

[2] John Howe, Very low impedance superconductor cables, concepts, operational implications and financial benefits.

[3] Pascale Strubel, A cost-effective way to upgrade urban power networks while protecting the environment.

[4] High-Temperature Superconducting Wind Turbine Generators Wenping Cao

Newcastle University upon Tyne United Kingdom

[5] Wikipedia- what is the difference between superconductor and other convectional conductor.

[6] B. R. Oswald, Technical and Economical Benefits of Superconducting Fault Current Limiters in Power Systems

[7] Dr.G Schnyder, Application of high temperature superconductor in power system