Evaluation of Gas Insulated Lines

(GIL) for Long Distance HVAC

Power Transfer

A thesis submitted to Cardiff University

in candidature for the degree of

Doctor of Philosophy

By

Khalifa Elnaddab

School of Engineering

Cardiff University

December 2014

DECLARATION

This work has not previously been accepted in substance for any degree and is not

concurrently submitted in candidature for any degree.

Signed.. (Candidate) Date.

STATEMENT 1

This thesis is being submitted in partial fulfilment of the requirements for the

degree of PhD.

Signed.. (Candidate) Date.

STATEMENT 2

This thesis is the result of my own independent work/investigation, except where

otherwise stated. Other sources are acknowledged by explicit references.

Signed.. (Candidate) Date.

STATEMENT 3

I hereby give consent for my thesis, if accepted, to be available for photocopying

and for inter-library loan, and for the title and summary to be made available to

outside organisations.

Signed.. (Candidate) Date.

STATEMENT 4

I hereby give consent for my thesis, if accepted, to be available for photocopying

and for inter-library loans after expiry of a bar on access previously approved by

the Graduate Development Committee.

Signed.. (Candidate) Date.

In the name of Allah, the Most Gracious, the Most Merciful

Peace and blessings be upon our Prophet Muhammad

and upon his family and companions

ACKNOWLEDGEMENTS

First and foremost, I would like to thank the Almighty Allah for enabling me to

complete this work; peace and blessings be upon our Prophet Muhammad and

upon his family and companions.

I would like to express my extreme appreciation and sincere gratitude to my

supervisor, Professor Manu Haddad. His guidance, encouragement and advice

were essential in helping me to finish this work.

My sincere appreciation also goes to my second supervisor, Dr Huw Griffiths, for

his valuable advice and constructive criticism during our weekly meetings and

annual progress assessment.

I would also like to thank the following for their contributions:

Professor Abdelhafid BAYADI from Ferhat ABBAS University of Setif, Algeria

for his extensive knowledge and help in the EMTP simulation program

All the members of the academic and administrative staff of School of

Engineering, Cardiff University

Dr Alex Bogias, Dr Maurizio Albano, Dr David Clark, Fabian Moore, Dr

Muhammad Saufi Kamarudin, Philip Widger, Tony Chen, for valuable

discussions and for their friendship

And my special thanks to my wife, my daughter, and my parents for the selfless

patience and endless support which they have shown throughout the period of my

studies.

Lastly, I would like to thank my older brother Abu Baker for his financial support

during my PhD studies.

PUBLICATIONS

i. K. H. Elnaddab, A. Haddad, H. Griffiths, "The transmission

characteristics of gas insulated lines (GIL) over long distance,"

Universities Power Engineering Conference (UPEC), 2012 47th

International, vol., no., p.1,5, 4-7 Sept. 2012 doi:

10.1109/UPEC.2012.6398633

ii. K. H. Elnaddab, A. Haddad, H. Griffiths, Future Gas Insulation Lines

for Transmission Networks, Fifth Universities High Voltage Network

(UHVNet), 18-19 January 2012, Leicester, UK

iii. K. H. Elnaddab, L. Chen, M.S. Kamarudin, A. Haddad, and H.

Griffiths, Gas Insulated Transmission Lines Using CF3I, Sixth

Universities High Voltage Network (UHVNet), 16-17 January 2013,

Glasgow, UK

iv. M. S. Kamarudin, P. Widger, L. Chen, K. H. Elnaddab, A. Haddad, H.

Griffiths, CF3I and Its Mixtures: Potential for Electrical Insulation,

International Council on Large Electric Systems (CIGRE) Session 45,

D1-309_2014, Paris, France

SUMMARY

Offshore wind power is a key element in EU policies to reduce the greenhouse

effect and secure energy sources. In order to accomplish the EUs target of a 20%

share of energy from renewable sources by 2020, some of the planned projects

have to be placed far away from the shoreline to benefit from the high wind

speeds in the open sea area.

However, a traditional transmission system for offshore wind farms based on a

High Voltage Alternating Current (HVAC) utilizing conventional cables is not

appropriate for long distances. In contrast, a High Voltage Direct Current

(HVDC) can transmit electrical power over such distances, but the complicated

concept of converting the HVAC offshore generated power into DC and then

converting the DC power at the onshore grid back to AC requires sophisticated

and expensive converter stations at both ends.

Therefore, developing a new infrastructure solution based on HVAC transmission

technology, which has been in operation for more than a century and which runs

almost entire electrical systems, to support and advance the development of

offshore wind energy is a highly desirable outcome.

This research work was conducted to examine and determine the suitability of

using an HVAC gas-insulated transmission line (GIL) as a long-distance

transmission system for offshore wind farms in terms of technical and economic

costs.

A computer model of GIL has been built using the Electromagnetic Transient

Program (EMTP) to assess the suitability of GIL and quantify the voltage, current

and power transfer characteristics of the GIL under different steady state

conditions. Furthermore, a suitable model has been developed for the simulation

of the switching transient during energisation of the GIL transmission system and

various wind farm components.

The development concept of GIL as a submarine Power Transmission Pipeline

(PTP) is described, and the practical side of installing the PTP technology and the

special design requirements of the offshore wind farms were illustrated. The PTP

components, the maximum transmission capacity of the PTP system and the

layout options were addressed. In addition, the challenges facing this technology

were discussed.

An economic comparison of the total cost for both HVAC-GIL and HVDC-VSC

transmission systems is made, including annual costs (operation, maintenance,

and losses) during the lifetime of the projects. The initial investment costs are

added to the annual costs in order to obtain the total cost for the assumed project.

Furthermore, the Power Transmission Cost (PTC) is calculated for each MVA-km

being delivered to the receiving end of the GIL transmission line.

Table of Contents

DECLARATION ........................................................................................................ ii

ACKNOWLEDGEMENTS ....................................................................................... ii

PUBLICATIONS ....................................................................................................... iii

SUMMARY ................................................................................................................ iv

CHAPTER 1: INTRODUCTION .......................................................................... 1-1

1.1 Introduction ........................................................................................... 1-1

1.2 Transmission System for Offshore Wind Frames ................................ 1-3

1.3 Research Objectives .............................................................................. 1-7

1.4 Contribution of Thesis .......................................................................... 1-8

1.5 The Structure of the Thesis ................................................................... 1-9

CHAPTER 2: OVERVIEW OF GAS-INSULATED TRANSMISSION LINE

(GIL) ......................................................................................................................... 2-1

2.1. Introduction ........................................................................................... 2-1

2.2. Definition and Description of GIL ....................................................... 2-2

2.3. History of Development ....................................................................... 2-3

2.3.1. First Generation of GIL ................................................................. 2-3

2.3.2. Second Generation of GIL ............................................................ 2-6

2.3.3. Alternative Gas to SF6 ................................................................... 2-9

2.4. GIL Design Criteria ............................................................................ 2-12

2.4.1. Dielectric Dimensioning .............................................................. 2-13

2.4.2. Thermal Dimensioning ................................................................ 2-14

2.4.3. Gas Pressure Dimensioning ......................................................... 2-14

2.4.4. High Voltage Tests Design .......................................................... 2-15

2.4.5. Short Circuit Rating Design .....................................