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Design and operation perspective o f a

British UHV laboratory

Prof. H.M. Ryan. B.Sc, Ph.D., C.Eng., F.I.E.E., F.lnst.P.,

and J. Wh iskard, B.Sc. Eng .), C.Eng., M.I.E.E.

Indexing terms: Design, Instrumentation and measuring science, Reviews of progress

Abstract: The authors have, in the past, been directly involved in the design, planning and supervision of the

construction, of a new ultra-high-voltage laboratory. The main purpose of the laboratory was to provide a

major facility in the UK for the development of switchgear rated up to 765 kV and in the dielectric research

required for such an undertaking. Following the opening of the laboratory in 1970, the authors have in recent

years been closely connected in the development of new ranges of open terminal and metalclad SF

6

switchgear

rated up to 525 kV and for fault currents up to 63 kA. These activities have been supported by extensive

dielectric research studies, which have enabled the major factors influencing the insulation integrity of practical

equipment to be determined. First, this paper outlines the criteria used in designing the laboratory and presents

a critical appraisal of the facilities during the first 15 years of operation. Secondly, consideration is given to

illustrating some significant laboratory activities. Examples are given of various switchgear and nonswitchgear

components for systems =765 kV, which have been subjected to rigorous dielectric proving tests in the main

test hall. The use of specific high-voltage test procedures (e.g. climatic, artificial rainfall, mixed voltage testing)

are described, and important technical factors which have influenced the dielectric design of apparatus are

considered.

1 Introduction

In the 1920s, switchgear manufacturers were mainly

engaged in exploring the problem of protecting oil-

immersed switchgear by means of surge arresters, for

which the impulse generators and the test cages then avail-

able were adequate for the purpo se.

The problem of damage to station equipment due to

lightning strokes was, however, becoming an important

issue during the 1930s, and the necessity to learn more

about the behaviour of dielectric materials and electrical

equipment when subjected to lightning voltages, was

becoming urgent. The outcome of these requirements was

the establishment of a whole generation of high-voltage

laboratories in this country and abroad. These labor-

atories provided a major factor in the development of

switchgear rated up to 400 kV, and the accumulation of

knowledge in the related problems of high-voltage impulse

wave behaviour.

The laboratories established in the late 1930s continued

to prove their usefulness even though additions in testing

equipment, increases in test area and even in the height of

the laboratories, were required from time to time. This

state of affairs continued until the early 1960s, during

which time the establishment of the British National Super

Grid, and the use of air-blast circuit breakers were taking

place.

It was becoming evident by this time (early 1960s) that

with the foreseeable development of transmission voltages

in excess of 400 kV, much more knowledge in the behav-

iour of impulse and switching voltage waves was required

for the development of higher voltage rated air-blast gear

and the rapidly developing technology of pressurised gases

(SF

6

).

A new generation of ultra-high-voltage laboratories was

initiated in the UK and abroad, particularly in Italy,

France, Germany, USA, Canada and Ja pan.

Paper 4889A

(S3),first

eceived 19th July

1985

and in revised form 7th April 1986

The authors were formerly with NEI Reyrolle Ltd. Professor Ryan is now at the

Department of Electrical, Electronic and Control Engineering, Sunderland Poly-

technic, Edinburgh Building, Chester Road, Sunderland SRI 3SD, United

Kingdom. Mr. Whiskard is now retired and can be contacted at 28 Briardene Drive,

Gateshead, Tyne and Wear NE10 8AN, United Kingdom

As a major switchgear manufacturer in this country, it

was imperative to develop our own ultra-high-voltage

facilities. The possibility however, had not been ignored of

sending equipment for tests to already existing laboratories

abroad, but the cost of testing and of transportation of

large and heavy equipment, the lengthy processing of test

results and data at considerable distance from the parent

company, all proved a major drawback to this course of

action. The decision was taken towards the end of the

1960s period to go ahead in the design and construction of

the laboratory which is the subject of the present paper.

This paper describes the criteria used in designing the

new UHV laboratory, outlines the finalised design and

provides an app raisal of

i)

the effectiveness of major labor-

atory test equipment and (ii) the salient work carried out

in the laboratory during the past 15 years. In this

appraisal, particular attention is given to problems

encountered with the test equipment and ways in which

some of them were overcome are considered. Difficulties in

the test work are also described and some of the many

successes achieved are highlighted. Where appropriate, the

paper will 'position' the UK state of the art, by describing

laboratory achievements and activities of this industrial

laboratory complex and comparing with related work

carried out elsewhere particularly at three other UHV

test laboratories in the UK, France and Canada operated

by national supply utilities.

2 Criteria used in designing the labora tory

As usual in engineering design, the criteria used are a

mixture of technical reasoning, economic considerations

and time scales. Preliminary considerations started about

the middle of 1963 regarding the feasibility of such a

project an d b roadly covered the following g rou nds :

(a) Enlarging existing high-voltage laboratory building

and uprating existing test equipment such as AC trans-

former, impulse generator, high-voltage measuring devices

etc.

b) Survey of available land with the possible purpose of

creating a new high-voltage test site.

(c) Determination of maximum rating of switchgear to

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be developed and therefore tested in the foreseeable future

with a test voltage margin above this for future develop-

ment and research. Evaluation of the probable physical

size of future switchgear at the maximum rating con-

sidered.

d) Evaluation of the size of the test hall based on the

maximum foreseeable size of test piece and on clearances

derived from switching impulse data associated with point-

to-plane airgaps.

e) Con sidera tion was given to the following alterna-

tives

:

(i) test area completely outdoors, with or without

some protection for main test equipment

(ii) test area indoors, to maximum ideal dimensions,

with all major test equipment in fixed positions

(iii) test area indoors, but with additional facility for

outdoor testing

(iv) test hall of reduced dimensions (economical size),

but with major test equipment mobile.

3 Finalised labo rator y design

In 1963, when the projected design of the laboratory was

first under review and its potential role was being con-

sidered the natural steps of circuit-breaker ratings

beyon d the 420 kV level already o perating in the UK , were

750-765 kV and 1100-1200 kV. Although serious doubts

remained that any progress upwards towards transmis-

sion systems >420 kV would be made in the home

market within the next twenty to thirty years, there were

definite indications that overseas the rating in certain pro-

jects e.g. Ontario/Quebec Hydro (Canada), El-Chocon

(Argentina) etc., would reach 765 kV and, in the foresee-

able future, 1200 kV was likely. This prediction would

obviously identify and quantify the laboratory test volt-

ages and air clearances which would be necessary to

undertake dielectric research, development and ultimately

type tests associated with any new switchgear.

The other prediction was to evaluate what form future

switchgear designs would take. On the one hand, it was

logical to think that the principle of air-blast interruption

(see Fig. 1) and comp ressed-air insulation would prevail

and all that would be required was to scale up the known

parameters, at the existing statutory ratings, while at the

same time anticipating future EHV dielectric test specifi-

cations, customer requirements etc. On the other hand,

there was a general realisation that circuit breakers using

sulphurhexafluoride gas (SF

6

) for interruption and dielec-

tric duties represented an alternative possibility at

EHV/UHV levels in which case, fewer series interrupter

breaks per phase might be possible and any future trend

towards 'compact' SF

6

metalclad switchgear installations

would obviously result in a significantly reduced labor-

atory test hall dimensional requirement. In general terms,

if a 275 kV air-blast circuit breaker was associated with a

test object of length 5.2 m in the test hall, 420 kV with

about 11.3 m, for 1.1-1.2 MV rated gear, a length of about

18.3 m would be a reasonable assumption.

Since the most onerous test condition is imposed by the

application of the positive-polarity switching impulse

F i g . 1

Earlier designs of 420 kV air-blast circuit breakers

c

Recent labo ratory tests have involved UHV system co-ordination studies

a

Single phase of

afirst-generation

breaker (12 breaks/phase)

b

Single phase of

a

second-generation breaker

6

breaks/phase)

502

Part schematic diagram of

b

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15.2 m

door height

18 9

m

width 5.7m

Mr

heig ht 18.9m

w id th 11.7m

48.8 m

B C

c

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D A

Fig.

2 UHVlaboratory layout

a Plan

bElevation

c

External view looking north

d

View of test hall and equipment

A

2 MV

AC

transformer, overall height 18.3 m

B

4 MV impulse generator, overall height 13.2

m

C 4 MV capacitor divider, overall height 14.7 m

D Test specimens

E Mobile oil-filled test tank

Internal diameter 5.5 m

Depth 5.5 m

Additional supplementary facilities were located

within the original laboratory building following

reorganisation in 1980. They are illustrated in

Figs. 25-31 and their locations identified by

letters F-L

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waves, it was necessary to establish the minimum air clear-

ance for this test plus a comfortable margin above this

level for research and to take into account the unpredict-

ability of switching impulses and proximity effects with

large practical air gaps, when values of 1.8 MV peak are

reached and exceeded.

Studies at the time in other laboratories gave extreme

examples of flashover paths of (i) 8.75 m for 1.4 MV peak

positive switching impulse SI wet with a clearance of

7 m to the building, (ii) broken paths equivalent in one

case to 8.78 m for 1.9 MV positive SI dry and, in another

example, to 9.28 m for 1.9 MV peak positive SI dry. For

1.1-1.2 MV rated gear, switching impulse voltages of up to

2.3 MV could be required for insulation coordination

evaluation, for which a laboratory clearance of 15.3 m was

estimated.

The dimensions of the labora tory, denned as the work-

ing clearance, were then estimated to be 33.5 m (110 feet)

wide x 32 m (105 feet) high x 82.3 m (270 feet) long.

However, since the cost of building is roughly propo rtional

to the volume, a worthwhile economy could be effected by

reducing the length of the building and, in compensation,

ensuring that all test equipment would be mobile.

The resultant laboratory length selected was a reduction

from 82.3 m (270 feet) to 48.8 m (160 feet), but an outdoor

test pad was provided which could be serviced readily

because of the mobility of test equipment, so as to mini-

mise the disadvantage of reduced internal space. The

general layout of the labo ratory is illustrated in Fig. 2. The

main items of test equipment are shown in Figs. 2 and 3

and described elsewhere [1 , 2] . They include:

(i) 2 MV RM S 50 Hz test transformer (Figs.Id and 3a)

(ii) 4 MV lightning impulse 2.8 MV switching surge gen-

erator (Figs.

2d

and 3b)

(iii) 4 MV potential divider (Figs.2dand 3c)

(iv) artificial rain equipment capable of continuous rain

oper ation (Fig. 5)

(v) two large oil tanks (Figs. 3c and 5c)

(vi) various high-voltage measuring devices other than

(iii) abo ve.

A full list of equipment with technical data is given in

Appendix 10.2.

Historically, it should be recalled that the laboratory

was officially opened on 15th May 1970, by the then Min-

ister of Technology, the Rt. Hon. Anthony Wedgwood

Benn and was named, the Clothier Laboratory to honour

an earlier eminent engineer Henry William Clothier, 1872

1938,

remembered for his pioneer work in furthering the

expansion of the electricity supply industry. From the

outset, it was intended to make these laboratory facilities

available to the supply industry and to manufacturers, uni-

versities, polytechnics and HEI for high-voltage research

and development.

4 Critical operational appraisal of facilities

4.1 Rating ofequipment tested

Prior to the completion of the new facility in May 1970,

laboratory facilities existed in an old EHV laboratory,

located in the Hebburn main works area, suitable for high-

voltage type testing of switchgear of up to 420 kV rating

with certain clearance restrictions. The original design

philosophy was a new UHV test facility to cater mainly for

transmission switchgear equipment etc. rated 765 kV and

above with adequate provision for increasing the test

capacity to levels appropriate to 1.1 MV transmission

systems. Moreover, the new facility would enable overvol-

tage insulation co ordination studies to be made o n 420 kV

switchgear at impulse test voltages >

2

MV.

Contrary to expectations however, during its first 15

years of operation the extent of UHV laboratory testing

devoted to gear rated at 765 kV, and above, was mainly

concerned with bushings with only one sample at 1.1

MV, and with in-depth testing of tower-window per-

formance for 765 kV ratings. The majority of work has

involved testing equipment rated at 420 or 525 kV (see

Figs.1, 6-14, 17-20, 23, 24 and 31).

The prediction that air-blast gear would develop to

higher rating s than 420 kV was not fulfilled and the labo r-

atory was involved in research work and development of

the alternative range of SF

6

insulated open-type and

metalclad switchgear and in proving tests for this type of

gear at levels of = 525 kV as illustrated in Figs. 17-20.

In general, this change in technical development from

pressurised-air to SF

6

insulation meant that the laboratory

area was more than adequate (i.e. there was a surplus of

floor area), because of the smaller size of SF

6

equipment

compared to air-blast gear and this resulted in a consider-

able saving of time which would have been spent in

moving the major test equipment. For example, the 2 MV

transformer was kept in one position most of the time (see

Figs.Id and 17).

For economic reasons, it was decided in 1980 to close

down all the dielectric laboratories in the old works. A

careful appraisal was made of the test equipment most of

which was scrapped and only items in very good condition

were retained. By making full use of this equipment, it was

possible to establish three test areas within the main hall of

the UHV laboratory, without effectively reducing the effi-

ciency and usefulness of the main area (see Appendix 10.1,

Figs.25, 28 and 30). At the same time, the usefulness of the

erection bay was reconsidered since little effective use had

been made of it. A multipurpose mechanical/thermal/

dielectric area was therefore established in the erection bay

(Figs.

29 and 31a), thus considerably enlarging the scope of

the laboratory. The dielectric area included facilities for

research into insulation materials, including endurance

and accelerated frequency testing (see Appendix 10.1, Figs.

26

and 27).

4.2 EffectivenessofUHV laboratory equipment

4.2.1 2 MV RMS-50 Hz test transformer see Fig. 3c):

This has been electrically satisfactory with a constant

partial-discharge performance of about 5 pC at 1 MV

Fig . 3 Major items of laboratory equipment

a 2

MV transformer positioned for outdoor use

b4 MV impulse generator

c

Standard laboratory setup for power factor and partial internal discharge testing

of bushings. 950 kV bushing (courtesy Bushing Co. Ltd.)

d

View of

2

M spheregaps, control room and galleries

eMain control room

/Screened room

Clothier Laboratory:

Dimensions of test hall for electrical clearance: length 49 m, width 33.5 m, height

32 m

Size of outdoor test pad : width

15.3

m, length 24.4 m

Size of

main

access door to test pad: width 11.7 m clear, height

19

m clear

Impulse generator for outdoor and indoor use: maximum nominal voltage 4 MV

peak, maximum nominal energy

150

kJ, height

13

m

test transformer for outdoor and indoor use: maximum nominal voltage 2 MV

RMS,

primary input 2.7 kV RMS, nominal rating 3.2 MVA, high-voltage maximum

current rating 1.6 A, maximum kVA demand on supply system 750 kVA, height

18.3 m

Capacitive voltage divider: maximum voltage for impulse waves 4 MV peak, for

switching surges 2.8 MV peak, for 50 Hz 2.8 MV peak, height 15 m

Oil test tank: Internal diameter 5.5 m, internal height 5.5 m, suitable for vacuum

impregnation with 0.133 Pa l/s maximum leakage rate, number of inspection ports

12,maximum weight of test piece on top cover 10.2 tonnes, mobile by means of air

cushion

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Fig. 4

Shielding and earthing details

[ /]

a

Interconnecting copp er straps

dPlan view of earthing box, earth rod and water hole

b

Copper earth rod

e

Earthing connection

c Earthing box with to p cover

/Co ppe r mesh and copper tapes

RMS. Mechanically, however, the considerable weight of

the transformer (203 tonnes) borne by railway type wheels

travelling on rails, resulted in appreciable wear and distor-

tion of the wheels which had to be replaced with a better

grade of steel.

4.2.2 4 MV impulse generator see Fig. 2d):

This in

general was satisfactory, but the following experiences

were noted:

(a) The maximum charge voltage of 200 kV DC per

stage was not achievable due to interstage flashover gener-

ated by corona (at about 180 kV DC). One of the main

reasons for this problem was the substantial mechanical

reinforcing incorporated into the finalised design to make

the generator suitable for outdoor use, even under severe

wind conditions. In compensation, two additional stages

were added (bringing the total to 22 stages).

b) Irregularities were experienced in firing the generator

and to counter these it was found necessary to circulate

dry air through the 'polytron' gaps 24 hours a day. To

improve performance of the gaps and reduce maintenance,

all original gaps were modified gradually with graphite

tips.

(c) The generator was fitted with front and tail resistors

to provide nominal standard waves of 1.2/50microseconds

and 250/2500 microseconds. It has been recognised that

additional resistor sets should be obtained for greater ver-

satility. Nevertheless, by careful arrangement of the exist-

ing resistors, it was still possible to obtain nonstandard

waves such as 1/40, 20/1600 microseconds and others for

certain co-ordination work on 420 kV live-tank

SF

6

-insulated circuit breakers etc.

4.2.3 Capacitor-resistive potential divider see Fig. 2d):

This has given excellent service. The divider is calibrated

routinely at intervals of six months against a pure resistive

divider, and checked for impulse waves with uniform field

gaps,

and for power-frequency voltages against a 1 MV

standard capacitor of 109.09 pF (shown in foreground of

Fig.3c).

506

This divider is normally used for all tests which require

voltage measurements and recording. The two-metre

sphere gaps (Fig.

3d )

which are available in the laboratory

are not used for accurate voltage measurements, due to

flashover inconsistencies which can introduce errors of up

to 10%.

4.2.4 WOO pF capacitor: For RIV and partial discharge

testing, a capacitor C (see Fig. 17), of approximately

1000 pF, was built by stacking in vertical construction

existing capacitor units taken from surplus 400 kV CV

transformers. Adequate anticorona buns and shields were

incorporated into the design, the whole structure being

made fully mobile. It is capable of operating up to 1 MV

RMS.

4.2.5 Double-beam type 72 Haefely transient recorders-

Three recorders are available (see Fig. 3e). These instru-

ments, which are calibrated at regular intervals, have been

fairly reliable. Records are taken with 35 mm cameras with

automatic frame advance operation, which facilitates the

enormous output required in statistical research studies.

Special table projectors with enlargement up to

254 x 203 mm (10 x 8 inches) of the 35 mm records aid

accurate measurements and observation of anomalies in

the wave shapes.

4.2.6 Screening: Although the laboratory control room is

screened from the test hall, the screening is not adequate

when operating equipment for the observation of flashover

phenomena and image enhancing. A completely screened

room was designed and manufactured for this purpose. It

can be deposited at any convenient location within the test

hall on an insulated sheet, so that one-point earthing can

be applied (Fig. 3/). So far, some difficulties with electrical

interference have not been completely resolved.

4.3 Earthing system

The earthing system is based on an underfloor copper

mesh linking a multirod arrangement in the subsoil, access

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being obtained by screwing in connectors at the head of

the rods. The earth system is tied to the metal walls of the

building [1-3] forming a gigantic Faraday cage. Some of

the details of copper mesh, rod connections, intercon-

nections to the building walls etc. are shown in Fig. 4 and

discussed in Reference 1.

It has been found that with flashover in SF

6

-insulated

gear, due to the steep collapse of voltage (

x 1

MV//is)

multisparkover of the earthed points has been consistently

experienced. This has led to problems in laboratory pro-

tective circuits. Because of the variety of test objects to be

handled in the test hall, it was not thought practical to

obviate these sparkover phenomena by mounting all

equipment on large thick aluminium plates.

4.4 Outdoo r test facility

An outdoor test pad was provided outside the main door

opposite the control room for the following reas ons:

(a) additional electrical clearance not obtainable within

the building for testing at higher ratings than 765 kV

{b) additional test area facility when the main hall was

engaged in long-term testing

(c) its close proximity to adjacent high-power short-

circuit test facilities.

Earlier prevailing weather studies had indicated the fea-

sability of outdoor testing. In the first few years, this

facility has only been used infrequently since the internal

laboratory clearances have been more than adequate for

the work undertaken with particular reference to metalclad

SF

6

equipment. Its usefulness, however, for the future

remains for possible application to ultra-high-voltage

transmission-line hardware and experimental lengths of

transmission line for which there is adequate room to

accommodate up to 150 m. Further application is possible

to special situations when the combined facilities of the

short-circuit station and ultra-high-voltage laboratory may

be deployed.

The outdoor test facility has been used extensively

during the past five years for combined mechanical/

electrical operational proving tests on 420 kV metalclad

switchgear. This is clearly illustrated in Appen dix 10.1 by

the example presented in Fig.

3

Id and

e .

4.5 Artificial-rainequipment

4.5.1 Fixed standard equipment: To date , the design

philosophy of the rain-water equipment has been fully jus-

tified. The design incorporated:

Fig . 5 General view of wet-testing assemblies

Improved nozzle assembly

b

View of artificial rain catchment area: for circuit breaker, surge arrester or discon- area

nect isolator tests [2]

Set up for bushing wet tests showing oil-tank wet-test assembly and catchment

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(i) automatic mixing of the tap water and deionised

water to provide any requ ired resistivity

(ii) possibility of storing water with two different values

of resistivity separately in the storage vessels, for alterna-

tive imme diate use

(iii) collection of the rain water from the test piece and

return at high pressure and high speed to the pressurised

storage vessels via an intermediate open vessel.

The nozzles comply with IEC 60-1 regulations regard-

ing the mandatory dimensions. The rear chamber of the

nozzle assembly has been designed to give a better water

flow; restriction has been imposed on the angular move-

ment of the stem to prevent cutoff and obstruction of the

water flow. The frames supporting the nozzle assemblies

allow each row of nozzles to be rotated by up to 90 (see

Fig. 5a).

The catchment basin at the base of the test pieces is

built up with sheets of polythene for each test programme

since the floor cannot be used for this purpose, as it was

kept flat for air-cushion transportation. This disadvantage

was pa rtly justified by the flexibility afforded by this tech-

nique in placing the test objects anywhere in the test hall

(see Fig.5band c).

4.5.2 Special rain equipment: The rain equipme nt just

described forms the fixed installation, and is located o n the

wall opposite the control room. There are occasions when

such a standard installation is unsuitable, and special

arrangements have been devised. In the case of bushings,

mounted in the oil tanks, a nozzle frame has been mounted

on a mobile 'beanstalk', where the height is controlled

hydraulically. The frame is ideally dimensioned to produce

the required rainfall on such a narrow and long test piece

as a bushing (see Fig. 5c). In the case of a tower window, a

frame was built along the top of the tower with nozzles

pointing upwards so that the required even rainfall could

be produced (see Figs.15band15d).

4.6 Oil test

equipment

The oil system, which comprises underground storage

tanks (127 m

3

(28000 gallons)), pumping station, stream-

line purifier and conditioner, and delivery pipes to outlets

in the centre of the laboratory floor area, has been satisfac-

tory.

There are two test tanks, mainly used for testing bush-

ings. The first one is of 127 m

3

(28000 gallons) capacity

(Fig. 3c) and can be sealed for vacuum impregnation (if

required); it is mobile with skirted air cushion. The second

tank (Fig. 5c) has been acquired in recent years and

although smaller than the first, can be used for bushings

up to 765 kV rating. The advantage of this tank is that in

the case of transformer bushings, the smaller test tank

reproduced more accurately the stresses existing in actual

power transformers.

4.7 General movemento fobjectsand cranage

All the floors in the test hall, erection bay and on the

outside test pad, were constructed flat to close tolerances,

so that objects, test pieces etc., could be moved about

using air-cushion-skirt principles (see Fig. 3c). In practice,

when moving objects, the following difficulties were experi-

enced

:

instability of large or high structures causing oscil-

lations of the air pads, failure of the air cushion and

bottoming of the load onto the floor.

The crane is of

7

ton capacity and runs the whole length

of the test hall with a beam equal to the width of the hall

at a height just below the

roof.

The crane is adequate for

the work required but suffers from pendulum oscillations

due to the 30.5 m drop of the crane hook, and is normally

supplemented with mobile cranes.

5 Scope and range of dielectric activities

While the modern UHV laboratory facilities outlined in

this paper are mainly devoted to switchgear product

research, development, quality control and certification,

many of the experimental techniques involved are equally

applicable to testing equipment for commercial operations

Fig . 6

Transportable metaldad switchgear assemblies prior to routine

dielectric testing

a

Assembly mounted on trailer

b

Circuit breaker assembly, with temporary 800 kVfibre-glass est bushing, being

moved into works test area using multipalette systems

508

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not connected with switchgear. The laboratory and test

facilities, including consultancy services and an extensive

library of electrostatic field and power-system computer

programs have been made available to outside clients on a

confidential contractual basis for many years.

An indication of the scope of dielectric activities under-

taken within the present integrated UHV complex during

the past 15 years can be seen from the following group-

ings:

(i) barrier flashover characteristics [8, 13]

(ii) GIS site installation, quality and testing procedures

[9, 10]

(iii) particle-initiated breakdown [11, 13]

(iv) insulation coordination [14-1 8]

(v) laboratory testing techniques [1,2, 19-21]

(vi) GIS backparts and interrupter developments

[23-28]

(vii) general contractual testing [22, 29-32]

(viii) insulation materials evaluation [33-37]

(ix) gas breakdown characteristics for large practical

electrode systems [4-7].

Extensive use was made of established field analysis and

breakdown estimation techniques [26]. Technical details

relating to most of these aspects are fully covered in the

original reference publications and only a brief general

appraisal of some salient work carried out in the UHV

laboratory area is given in Section 6.

6 Appraisal of salient examples of UHV laboratory

utilisation

6.1 Dielectric properties of pressurised SF

6

As illustrated in Section 5, the insulation group of

researchers in the authors company have been actively

involved in many aspects of dielectric research and devel-

opment work during the past 20 years. The emphasis has

been on determining the breakdown and flashover charac-

teristics of gas gaps and support insulation, the work being

directly relevant to the design of gas insulated switchgear

equipment (GIS). The laboratory work, which involved the

use of large test rigs (e.g. Figs. 6-9), had five main objec-

tives :

(a) Before the first 300/420 kV GIS equipment was pro-

duced in the UK it was vital to establish reliable clear-

ances. Consequently, it was necessary to embark on

research programmes to provide comprehensive design

da ta; reproduced in Figs. 10-12 [7, 13].

b)It was also important to carry out a considerable

amount of testing, using video techniques, to gain an

appreciation of the influence of particulate contamination

Fig. 7

General view of 2.6 MV test rig and SF,,gas recovery plant

[7 ]

Fig. 8 400/525 kV development rig for SF

6

metalclad switchgear

on the attainable withstand capabilities of GIS (see Fig.

12).

(c) In addition, to carrying out short-term studies it was

necessary to determine projected in-service or long-term

characteristics ofGIS.

Fig . 9 Typical schematic of a 420/525 kV GIS

IEE PROCEEDINGS, Vol. 133,Pt. A, No. 8, NOVEMBER 1986

509


10/21

d) The b roa d q uestion of insulation coordina tion for

GIS had also to be resolved by studying the interrela-

tionship between GIS voltage/time [13, 15-18] character-

istics and those of line gaps and surge arresters (see Fig.

13).

e)Fin ally, effective factory quality control, work s and

site erection testing procedures had to be established. Elec-

trically, each GIS subassembly unit was subjected to a

2.0

0.1 0.2 0.3 0 .4 0.5

p r e s s u r e , M P a

0 . 6

F i g . 1 0

Lightning and switching impulse V

50

levels in SF

6

for perturbed

cylinder configuration

0.1 0.6

.2 0.3 0.4 0.5

a pressure,MPa

b

F i g . 1 1 A Withstand characteristics of epoxy resin support insulator in

Fig . 11 B

Surface flashover marks on a 400/525 kV cast-resin insulator

after extensive laboratory testing

1000

600

1600

>

400

20 0

SF

6

0.55 MPa

420 kV

-phas.e

system

vol tage

44

1

jclean withstandfl min)J

630KV works test level

520 kV routine test level

, ^ 4 2 0 ^

site test level

typical particle 1

lift off voltage

0 2 4 6 8 10 12

part icle size,mm

F i g . 1 2

50 Hz flashover characteristics of epoxy resin conical spacers

under varying degree of metallic contamination [ / i ]

high-voltage test of one minute duration in the works,

before despatch to site; this test was repeated on site prior

to commissioning. Extensive laboratory studies have been

.2.1 m gap

.2.5m gap

0.1

1 10 100

t ime, us

Fig . 13

Insulation co-ordination diagram

[ / J ]

A

Typical V/t characteristics of

420

kV GIS

BRepresentative characteristics of

396

kV ZnO arrester

C

Lower limit curve of

a

line gap for specific gap settings

(i) upper limit 40

kA

amplitude

(ii) lower limit 3 kA am plitude

carried out by the authors to evaluate the effectiveness of

various site-commissioning test procedures for large GIS

installations [9]. In addition, various on-line monitoring

techniques have been under development in recent years

which should result in still further improvements in service

reliability in SF

6

-insulated switchgear.f

One on-line monitoring technique examined in the

laboratory by the authors recently [10], related to a

chemical SO

2

detection method. If flashover occurs during

any test in SF

6

-insulated GIS, it is important to be able to

distinguish between a nonself-restoring surface flashover

of the cast-resin support barriers and self-restoring flash-

over across gas gaps. Examples of experimental tests based

on this chemical approach are shown in Fig. I4a-e.

Preliminary 50 Hz studies involved full-scale laboratory

experiments which were established on GIS assemblies

(Fig. 14a-/) to assess the comparative sensitivity of this

SO

2

detection technique. These tests, without absorbent,

indicated the possibility of clearly differentiating between

gas-gap and insulator gas-to-surface flashover, with an

SO

2

concentration differing by a factor

x

1000 (e.g. Fig.

14a).

Using an SF

6

test volume of 350

1

at 0.55 MPa, with

molecular sieves fitted, a family of curves was produced

(Fig.

He)

giving the time taken to obtain readings of SO

2

concentrations against time elapsed after flashover [10]. It

was noted that even after 14 hours had elapsed following a

single 50 Hz spacer flashover, significant concentrations of

SO

2

were detectable.

Three controlled-energy impulse studies were also

reported using different energies and chamber volumes.

For purposes of direct comparison, results from these

impulse studies are shown in Fig. 14/, curves 2, 3 and 4

respectively, together with the 50 Hz results reproduced in

curve 1. All results refer to SO

2

detection reading of 15.

These curves clearly demonstrate the relationship of gas

volume, arc energy and disposition of the arc relative to

the gas sampling points, in the presence of a molecular

sieve absorbent, against elapsed time following flashover

event [10]. These controlled-energy impulse tests sup-

ported by TNA studies provided a useful means of assess-

ing the sensitivity of the simple SO

2

detection method. The

f B.F. Hampton (CERL ) is currently at the forefront of novel developments relating

to site testing of GIS

51 0

IEE PROCEE DINGS, Vol. 133, Pt. A, No. 8, NOVEMBER 1986


11/21

experiments demonstrated that the technique is clearly

able to differentiate between a gas-gap or spacer flashover

in GIS assemblies. The authors point out that further

work is necessary to confirm the effectiveness of this test

technique when referred and applied to larger GIS gas

zones under site conditions [10 ],

Special purpose-built large test rigs and associated

bushings were designed to be used for much of the above

studies [7]; these, together with digital programs to facili-

tate correlation of test data and gas handling equipment

(Fig. 7) enabled essential technical information to be

acquired. The recent introduction of video library and

recording techniques, to augment standard and high-speed

cameras, has provided a valuable new diagnostic monitor-

ing capability which can be used to study in detail the

influence of particles in GIS and correlate particle position

with partial discharge level etc. [13].

6.2 Switchingimpulse strengthof 765 kVtower

window

For the tower-window study (Fig. 15), sponsored by the

combined efforts of ERA UK Manu facturers/Con-

sultants [30], it was necessary to build a structure 19.5 m

high with a window width of 15 m (18 m width overall).

The corresponding laboratory height and width dimen-

sions are 32 and 34 m, showing that there were no diffi-

culties in accommodating such structures. The frame

sections were preassembled elsewhere, so that the time of

erection in the test hall could be minimised, effectively

reducing costs because of the high charges of occupation.

To increase stability of the structure, which could not be

bolted to the laboratory floor, (a precaution used to pre-

serve the integrity of the underlying earth mat), ties to the

building stanchions were used.

An additional moveable box trusss was added to vary

2 S 10 IS 202 5 30

F i g . 1 4

Results from a recent S0

2

detection study [Iff]

a

Gastec SO

2

detector tube

(i) after repeated gas gap flashovers

(ii) after o ne flashover across solid insulation

b, c,dLaboratory GIS test arranagements (SF

6

al 0.55 MPa)

B bauxite spacer

SP sampling point

O observation port

M molecular sieve containe r

Sg position of

Al

spike gas breakdown

Ss position ofAlspikes spacer flashover

Relationship between time and SO

2

concentration O (arbitrary scale)

4

epoxy/alumina spacer, vol. 650

I,

energy 712 J, impulse

I

5

0

tim

( 5 ) @ @ (20) (25) (30

- -

- * -

,30)

tubeG

60 120

tube C

tube B

tube A

8 12 16 20

e required to obtain reading,minutes

10 15 20

time after f lashover, h ours


511


12/21

/

/

S

S.

\

\

\2

/\/\/\/\/\/\/\

1 5 m

\

S ,

S

3

MV)

bduring preapplied pollution tests using sail/clay mixture (voltage 250 kV RMS)

much better 'feel' for the complex arc-interruption pheno-

mena [27] in the SF

6

interrupter units, ably assisted by the

adoption of effective dielectric principles using analytical

field analysis and breakdown estimation techniques. Con-

siderable progress has been made in both arc-interruption

and dielectric modelling techniques in recent years as more

reliable experim ental d ata beco mes available [7, 13, 27,

28].

F i g . 1 9 View of 420 kV SP D 2 break) metalclad circuit breaker

assembled in main UHV hall for type testing

Two vertically mounted porcelain inlet bushings and horizontal connecting busbar

are also shown which enables complete type and conjunctive bias testing to be

carried out on this vertically-mounted metalclad switchgear assembly. The pho-

tograph indicates the size of main hall which provides adequate air clearances for

more than one test object to be assembled at the same time so minimising erec-

tion delays.

51 4

Recent changes in dielectric specifications have resulted

in the need for more sophisticated test procedures such as

phase-phase and bias-testing techniques.

Laboratory staff have participated in IEC (TC28) and

BSI deliberations on revision to relevant specifications.

6-break 4-break 3-break 2-break

1-break

(1976) (end 1976) (1979) (1981) (1985)

Fig . 20

Stages in the evolution of a 420 kV dead-lank circuit breaker

1281

For bias testing, simultaneous application of power-

frequency and lightning impulse voltage to circuit breakers

or gas-insulated substation equipment (GIS) is required. A

typical circuit for bias testing is shown in Fig. 21. Here

again, the generous clearances available in the test hall,

together with the mobility of test equipment (e.g. 2 MV

transformer and 4 MV impulse generator) have enabled

these tests to be performed effectively. Obviously, special

care is required to ensure adequate protection of test

transformer from impulse test voltages.

impulse

generator

DC

charger

ha

test object X

differential voltmeter

protective

T

transformer.

point-on-

wave

selector tran sien t recorder

50 Hz

sample voltage

Fig. 21 Test circuit for bias testing GIS

1EE PROCEEDINGS, Vol. 133, Pt. A, No. 8, NOVEMBER 1986


15/21

6.5 Impulse -voltage measuring system

6.5.1 Analysis:

With the increasing amount ofdevelop-

ment and basic research work being undertake n at all

transmission voltages from UHV downwards, the require-

ments ofthe impulse-voltage measuring systems usedare

becoming necessarily more stringent.

In

order

to

obtain

maximum information about the impulse wave,theaccu-

racy limitations of themeasuring system must first be

established andunderstood. Some general points can be

made first:

(a) Measuring tasks may vary from the relatively simple

on e of recording with lowerror a full or tail-chopped

1.2/50fi simpulse wave (see Fig. 22a, waveforms (i), (ii))to

the more difficult problems involving a front-chopped

impulse or onehaving partial (layer) break dow n of the

solid insulation under test, usually about thepeak ofthe

impulse (waveforms (iii), (iv)).

b)A further difficult measurem ent tobe mad e,is ofthe

extent and magnitude of any oscillations occurring at the

test object. The occurrence of these voltage wave shapes

in

high-voltage development work is quite common, espe-

cially

the

full

and

tail-chopped waves. Fro nt-chopp ed

waves down

to

chopping times

of

about only

0.4[is are

often met, particularly when testing equipment per-

formance for insulation coordination.

(c) Partial breakdown ofinsulation unde r test (Fig. 22a

waveform (iv))canoccur ontest objects having multiple-

layer insulation (e.g. bushings, current transformers, capac-

itors etc.).

d) Almost all impulse waves recorded exhibit oscil-

lations whose significance must be analysed with regardto

compliance with the relevant specification anderrorsin

peak voltage and waveshape measurements.

e) Particular problems can beencountered with UH V

impulse measuring systems, suitablefor themeasurement

of fast transients, due to the large dimensions involved.

(/) 'Response time' and step responseofany measuring

system are two major criteria

in

determining its suitability

for fast-transient measurement [38-41].

During thepast 20years, authoritative work on UHV

divider response have been undertaken elsewhere by Creed

and Collins and also Zaengl. However, for the purposes of

the present paper it isadequate to highlight someofthe

early work undertaken by Richardson.

Richardson and Ryan [21] reported on the general con-

struction and described the testing techniquetoassess the

step response ofthe 4 MV impulse measuring systemin

the authors' UHV laboratory. An equivalent circuit, repro-

duced inFig.22b,was evolved, upon which the analytical

method was based and comp utational aspects of the

digital technique were briefly discussed. Although

the

influence of several circuit parameters were consideredit is

sufficient topickouttwo aspectsatpresent; the effectsof

(i) high-voltage lead damping resistor R

D

and (ii)high-

voltage lead length / and surge impedance Z

o

on step

response. Atypical set of response curves for Z

o

=300,

/

= 9 m and a

terminating capacitance

C

p

=

7.5

pF are

shown inFig. 22c.It can be seen thatit isprincipallythe

area of the first overshoot

T

2

,

which determines the

response time T where,asillustratedin the insert to Fig.

22c

100 200 300 400 0 100 200 300

d ns ns

0 100 200 300 400 0 100 200 300

F i g .

22 Study of response of impulse voltage measuring system [ 2 / ]

a Typical voltage shapes to be measu red

b Equivalent circuit of impulse measuring system

c Effect ofHV lead damping res i s to r onstep respo nse

Z

o

= 300 n, C

p

= 7.5

p F ,

/ = 9 m

T = T,

-

T

2

+

T

3

- T

4

d Effect of HV lead strength on step response RJZ

0

= 0.5)

Z

o

= 300 n, C , = 250 pF

init ial response referred to 3 mlead

(, Response parame ters ,ns

metres

T, T

2

T

3

39.5 3.5 36.0

6 40.6 8.4 32.2

9 42.7 10.9 31.8

e Effect of HV lead lengtho n step response R

D

/Z

0

=0.167)

Z

o

= 300fi C

r

= 250 pF

init ial response referred to 3 mlead

I , Response parame ters ,

n s

metres

3 23.2 24.1 6.35

6 27.9 34.3 11.25

9 34.0 42.5

/Effect ofHV lead surge impedance on step response (S

D

/Z

0

= 1.0)

/= 9 m, C, = 7.5 pF

Z

o

,

1 Response time

T,ns

30 0 24.3

50 0 25.4

58 0

26.5

g Effect ofHV lead su rge impedanc eo n step response (R

o

/ Z

0

= 0.5)

/ = 9 m, C

p

= 7.5 pF

Z

o

, n Response t ime T,ns

30 0 9.2

50 0 17.8

58 0 19.2



16/21

Briefly, with fast-response voltage dividers, the response

time can be significantly affected by R

D

.

Fig. 22d, e and /, g, respectively, illustrate interesting

results obtained by Richardson due to (i) effects of HV lead

length on step response for different values of damping

resistor R

D

)and (ii) effects of HV lead surge impedance on

the step response for different values of damping resistor.

The results of this computer-aided analysis [21] were vali-

dated by laboratory testing and such characteristics were

subsequently well documented in laboratory test manuals

for future reference.

6.5.2 Practical considerations:

Hav ing mad e a full

appraisal of the theoretical measuring system and the pre-

ferred layout of measurement equipment, it is important to

determine the long-term reliability and accuracy of one sel-

ected measuring system to avoid the necessity of frequent

and even daily repeated calibrations, which would inter-

rupt a series of tests or even cause postponement of them,

a procedure very costly in time and money.

The particular measuring system selected always com-

prises a combination of the ASEA 4 MV-capacitor-

resistive divider in conjunction with denned low-voltage

arm(s),

coaxial cable and Haefely CR O.

Other methods of measurement in the laboratory

included 2-metre sphere gaps for checking and measuring

high-voltage peak values, but du e to erra tic fiashover char-

acteristics up to 10% errors were experienced. Very little

improvement was obtained by UV ionising procedures.

Eventually, uniform field gaps of 4 feet diameter were

installed with which an accuracy of better than 1% was

achieved. A pure resistance divider (Haefely) with capac-

itance grading is used for calibrating the ASEA divider,

which is supplemented by cross referencing to the uniform

field gaps.

Finally, it must be stressed that theoretical consider-

ations cannot be divorced from the practical reality of long

leads connecting the impulse generator with the test piece

and the potential divider. Also, the practical problem exists

of reducing the inductive effects of loops whilst retaining

adequate clearances and dealing with physically large test

components and test pieces which occupy considerable

areas of the UHV laboratory floor.

6.6 General and contractual H V testing

In addition to extended investigations of the types

described in Sections 6.1-6.4, there has been considerable

activity in type testing, proving tests and routine pro-

duction testing. In the case of routine testing, either the

work could not be done in the works' extensive high-

voltage test facilities, due to technical reasons or during

periods of high production.

The regular practice of routine testing in the UHV

laboratory cannot be fully defended on economic grounds,

but when necessary, the costs can be considerably reduced

by erecting a number of similar test pieces contemporan-

eously (for which there is ample floor space and electrical

clearance) and testing them in quick succession.

Another advantage of the available floorspace was the

fact that providing operating voltages are not too high

tests could be interrupted on one particular test piece,

and work continued on another which had been suitably

erected on the floor. Fig. 19 shows, in fact an arrangement

for testing a 420 kV dead-tank SF

6

circuit breaker, whilst

phases of a live-tank 420 kV circuit breaker, placed else-

where, were awaiting tests. At the same time, a rig was also

erected on the floor for routine testing of cast-resin

support barriers.

With regard to contractual work, a considerable

amount of type and routine testing has been carried out on

500 kV and 765 kV bushings, and in particular trans-

former bushings. For the latter, test requirements for the

oil are stringent (less than 10 parts in 10

6

of moisture,

usually 4 parts in 10

6

and test-cell breakdown in excess of

60 kV) and can be more readily achieved by using the

smaller of the two oil test tanks available (Fig. 5c). The

smaller tank could be sealed more effectively against mois-

ture ingress durin g the artificial rain tests.

Although the laboratory was designed specifically for

testing power-engineering equipment, it has been used

because of its lightning voltage capability for the con-

tractual testing with electrogeometric models of aircraft

(Fig. 23). After proving the validity of the scale techniques,

and contributing to a better understanding of the physics

Fig . 23

Aircraft lightning studies using simplified models

[29]

Fig . 24 BAC Nimrod lightning strike studies laboratory impulse tests on front radome

Laboratory tests on aircraft to evaluate the probability of lightning strike have underlined the importance of

multicamera operation to obtain a three dimensional picture of the exact point of strike. Similar techniques

have also been used in assessing voltage coordination in GIS and live-tank circuit breakers, line gaps etc.

51 6

1EEPROCEEDINGS,

Vol.

133,

Pt.A,

N o.

8,NOVEMBER

1986


17/21

of long sparks and lightning discharges [29]. Later work

was carried out on full-size aircraft radomes as fitted fore

and aft to AEW Nimrods (UKAEA Culham being the

main project contractor) to evaluate lightning protection

(see Fig. 24). Further studies have recently been reported

[31,32].

For the economic accountability of an UHV laboratory,

it is necessary to operate test programmes with very tight

schedules leaving only very limited opportunity for investi-

gating new testing techniques or carrying out maintenance.

Preferably the latter should be carried out outside normal

working hours. Nevertheless, new techniques must be

regularly explored to keep the facilities competitive.

For this reason, considerable laboratory time has been

set aside recently for conjunctive impulse and power-

frequency testing. After designing the necessary equipment

for point-on-wave operation the following cases have been

successfully studied:

(a) AC and impulse applied to the same pole as for

bushing CTs etc.

b)

AC and impulse applied to oppo site poles as with

open breaks of a circuit breaker.

7 Final comments and conclusions

In recent years, the major emphasis in research and devel-

opment has shifted from air blast to SF

6

-insulated live-

tank and metalclad switchgear. This has been illustrated

by the more fundamental work carried out during this

period of SF

6

breakdown phenomena and on particulate

initiated breakdown in SF

6

/solid insulation systems [7, 13,

27, 28]. In addition, preparatory to new designs, extensive

insulation co-ordination studies have been undertaken

within this UHV laboratory and in collaboration with

power-systems specialists.

Because of the trend towards compact SF

6

switchgear,

the electrical clearances available within the laboratory

have been more than adequate. Consequently, it has

proved possible to introduce additional dielectric facilities

within the UHV laboratory complex for research,

distribution equipment testing, insulation material evalu-

ation with necessary ancillary mechanical/thermal proving

capabilities [25, 36, 37]. This change from the original

UHV laboratory design philosophy has resulted in estab-

lishing a complete dielectric complex on one site, covering

all ratings from distribution up to UHV transmission

levels. These supplementary test facilities are illustrated in

Appendix 10.1 with app ropriate explanatory captions.

As discussed in Section 4, numerous technical problems

have been encountered with laboratory test equipment,

but the difficulties experienced have been of a minor

nature rather than of fundamental importance. Moreover,

the effectiveness of the laboratory has to be judged in rela-

tion to what has been accomplished in the first 15 years

approximately of its life, and the following achievements

are here sum marised.

(a) A major contribution to the fundamental develop-

ment of 300, 420 and 525 kV SF

6

-rated switchgear by the

dielectric evaluation of representative electrode arrange-

ments of practical GIS.

b)

Type and proving tests on air-blast and SF

6

switch-

gear, bushings etc. by extensive test programmes. Investi-

gations into particulate contamination and potential

causes of breakdown in SF

6

GIS.

(c) Evaluation, backed up by computer techniques, of

the high-voltage measurements carried out in the labor-

atory. This work was necessary for establishing confidence

in the high-voltage work undertaken and in the results

obtained.

d) Development of test equipment and test methods for

RIV and partial discharge investigations and testing at

very high voltages up to

1

MV RMS.

e) Experimental techniques: design and fabrication of

nozzles, support frames, automatic mixing plant for artifi-

cial rain testing which can operate under continuous

testing conditions and diversified test objects and develop-

ment of conjunctive-impulse/power-frequency test pro -

cedures and techniques.

(/) Considerable diversification in the extensive work

undertaken for outside customers has included:

(i) tests on transmission-line hardware

(ii) tower window for 765 kV transm ission lines

(iii) performance of porcelain bushings etc. (inclined

at various angles to the vertical) typical of outdoor

transformers, subjected to rain and washing pro-

grammes (or preapplied pollution)

(iv) Lightning-strike studies on simulated scaled air-

craft models followed by studies on full-scale radomes,

as fitted to aircraft.

In conclusion, the laboratory has been a very effective

'tool' in the research, development and routine testing

undertaken. The design of the laboratory layout has made

it possible, in the last few years, to make useful additions

to the facilities thus considerably increasing and extending

the testing potential of the laboratory complex.

From a national point of view, it is to be noted that this

laboratory, and that at CERL Leatherhead represent in

1986 the only UHV testing facilities available in the UK.

This disappointing state of affairs, with consequential

reduction in personnel expertise, compares very unfavour-

ably with the testing and manpower resources available

especially in Japan, Canada, France, Italy, Germany and

the USSR.

8 Acknowledgments

The authors wish to thank the Directors of NEI Reyrolle

Ltd., for permission to publish this paper. Thanks are also

due to their former colleagues for their continued support

and assistance over the years. The au tho rs gratefully

acknowledge permission to reproduce extensively from

laboratory contractual research studies undertaken for

various organisations over the years and fully acknowl-

edged in the original publication sources.

9 References

1 LEGG, D., RYAN, H.M., and WHISKARD, J. : 'A new Bri t ish ul t ra-

high voltage laboratory'. Presented at IEEE Winter Power Meeting,

New York, 1972, Paper C72 224-9. Also reviewed in

Reyrolle Parsons

Rev., summer 1971,1,(1), pp. 11-16

2 R YAN, H.M., and WH ISKA RD , J. : 'Recent studies in the Clothier

Labora tory ' , Reyrolle Parsons Rev.,winter 1974/75, 2, (2), pp. 2 4-28

3 KARADY, G., HYLTEN-CAVALLIUS, N.: 'Electromagnet ic shield-

ing of high voltage laboratories'. IEEE Trans. Paper 70 TP 604-PWR

(1970).

4 RYAN, H.M., and W ATS ON, W.L.: 'Electr ical breakd own and

voltage-time characteristics in SF

6

at high pressures'. Presented at

IEEE PES Summer Power Meet ing, Por t land Oregon, 1976, Paper

F76 390-5. Based on paper presented at the Internatio nal High

Voltage Symposium, Zurich, September 1975, pp. 12-18 (Annexe).

Also reviewed in Reyrolle Parsons Rev., winter 1975/76, 2, (4), pp.

24-28

5 RYAN, H.M., WA TSO N, W.L., DAL E, S.J., TE DF OR D , D.J. ,

KU RIM OT O, A., BAN FORD , H.M., and HA MP TO N, B.F.:

'Factors affecting the insulation strength of SF

6

filled systems'.

CIG RE , 1976, Pap er 15.02

6 WAT SON , W.L., and RY AN, H.M.: 'Breakdown and vol tage- t ime


517


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character ist ics in SF

6

for voltages in the range 0.62M V , IEE Conf.

Publ. 143,

1976, pp. 153-156

7 RYAN, H.M., and WATSON, W.L.: ' Impulse breakdown character-

istics in SF

6

for non-uniform field gaps'. CIGRE, 1978, Paper 15.01

8 RYAN, H.M., and WATSON, W.L.: 'Breakdown character ist ics in

S F

6

for non-uniform field gaps and support insulation for voltages in

the range 0.8-2 M V . Presented at 1976 IEEE Conference on Com mu-

nicat ion and Power , M ontreal , October 1976, pp. 501-504

9 RYAN, H.M., and MILNE, D.: 'Dielectr ic test ing of GIS: Review of

test procedures and evaluat ion of test resul ts ' . CIGRE Colloquium,

Edinburgh, 1983,

SC33,

Paper 33-83

10 R YAN, H.M., M ILN E, D., and P OW EL L, C.W.: 'Si te testing and the

evaluation of a technique to differentiate between a gas or spacer

flashover in SF

6

GIS'. Presented at Symposium on Gas Insulated

Substat ion Tech nology and Pract ice, Toro nto, Can ada, Septembe r

1985,

Paper K2

11 RYAN, H.M., and MILNE, D.: 'Breakdown performance studies in

S F

6

under clean and contaminated condi t ions' ,

4th Int. Symp. HV

Eng.,

Athens , 1983, Pap er 34-12

12 RYAN, H.M., ALI, S.M.G., and POWELL, C.W.: 'Field computat ion

relating to switchgear design',

Ibid.,

Pape r 12-12

13 RYAN , H.M., LIGH TL E, D., and M ILN E, D.: 'Factors influencing

dielectric performance of SF

6

insulated GIS', IEEE Trans., 1985,

PAS-104 (6), pp. 1527-1535

14 RYAN , H.M., and PO WE LL , C.W.: '50 Hz breakdown character-

istics of long air gaps'.

IEE Conf. Publ. 90,

1972, pp. 30-32

15 RYAN, H.M. , WATSO N, W.L. , HO GG , W.D. , and RITC HIE, W .M.:

'Effects of system overvoltages on insulation coordination require-

ments for EHV open type and metalclad installations'. Presented at

Internat ional Conference on the Design and Appl icat ion of EHV Sub-

stat ions, London, 22-24th November 1977

16 WATSON, W. , HOWIE, R.B. , RYAN, H.M. , IRWIN, T . , HOGG,

W.D., and PETTY, H.C.: ' Insulat ion coordinat ion of a 420 kV SF

6

insulated substat ion in the UK'. CIGRE, 1984, Paper 33.05

17 RYAN, H.M., FLYNN, A, and WATSON, W.: 'Vol tage- t ime charac-

teristics of long air-gaps'. Presented at 8th International GDC,

Oxford, Septemb er 1985, pp. 368-373

18 W AT SON , W., FL YN N, A., IRW IN, T., and RYAN , H.M .: 'Determi-

nation of the voltage/time characteristics of rod gaps etc.'. CIGRE,

1986,

Pa pe r 15.05

19 RYAN, H.M., and MATT1NGLEY, J.M.: 'Salt-fog artificial pollution

val idat ion studies' , Proc. IEE, 1970, 117 (7), pp. 1389-1392

20 ELLIS, N.S. , LU GT ON , W.T., POWEL L, C.W. , and RYAN , H.M. :

'Special spark-gap switches for use in synthetic test circuits'. Presented

at IEEE Winter Power Meet ing, New York, 1972, Paper T72 051-6.

Subsequent ly publ ished in

IEEE Trans.,

1972,PAS-91 pp. 2020-2025

21 RIC HA RD SO N, A.V., and RYA N, H.M .: 'Comp uter aided analysis

of an impulse voltage measuring system'. Presented at International

Sym posiu m: High Vol tage Technology, Munich, March 1972, pp.

245-251. Also presented at IEEE PES Summer Meet ing, Vancouver ,

Canada, 1973, Paper C73 345-6

22 RYA N, H.M., EL LIS, N.S., and B ELL, W.R.: 'Case for a UK co l labo-

rative research strategy using major industrial laboratory facilities'.

Presented at 17th Universities Power Engineering Conference,

UMIST, Manchester , 30th March 1982-1 Apri l 1982

23 RYAN, H.M. : 'SF

6

switchgear further developments', Reyrolle

Parsons Rev.,

sum mer 1977, 3, (1), pp. 1-8

24 BALL, E.H., RICHARDSON, A.V., and RYAN, H.M.: 'Terminat ions

used in EHV metalclad substations'. Presented at IEE International

Conference on the Design and Application of EHV Substations,

Londo n, 22-24 th Novem ber 1977, pp. 134-139

25 RYAN, H.M., LIGH TLE , D., HEA DLE Y, P. , and K ELSE Y, T.:

'Engineering considerations relating to EHV metalclad switchgear for

currents up to 63 kA'. CIGRE, 1980, Paper 13.02

26 RYAN, H.M.: 'Applications of gaseous insulants'. Presented at IEE

Summer School on Electrical insulation-measurements design and

materials for power engineering, University of Salford,

5-8th

Septem-

ber 1983, Chap. 6. Also in B RAD WE LL , A. (Ed.): 'Electrical insula -

tion'(Peter Peregrinus Ltd., UK, 1983)

27 ALI, S.M.G., RYAN, H .M., LIG HT LE , D., SHIM MIN , D.,

TAYLOR, S., and JONES, G.R.: 'High power short circuit studies on

a commercial 420 kV, 60 kA puffer circuit breaker',

IEEE Trans.,

1985,PAS-104 (2), pp. 459-* 68

28 RYAN, H.M., and JONES, G.R.: IEE Review on SF

6

Switchgear

(Paper in preparation, commissioned by IEE)

29 PH ILL POT T, J. , LITTLE , P. , WHIT E, E.L., RYAN, H .M.,

POWELL, C.W., DALE, S.J. , AKED, A., TEDFORD, D.J. , and

WATERS, R.T.: 'Lightning strike point location studies on scale

models'. Presented at International Lightning and Static Electricity

Conference, Culham Laboratory, United Kingdom, April 1975

30 POWELL, C.W., and RYAN, H.M.: 'Switching impulse strength of a

765 kV simulated tow er window with V-string insulators under artifi-

cial rain'. Presented at 3rd International Symposium on High Voltage

Engineering, Milan, August 1979, Paper 52.11

31 BISHO P, J. , AK ED , A., PO WE LL , C.W., and RYAN, H.M.: 'Aspects

of lightning protection schemes for radomes'. Presented to Interna-

tional Aerospace and Group Conference on Lightning and Static

Electricity, Paris, Franc e, 1 0-1 lth J une 1985, pp. 499-507

32 AKED, A., POWELL, C.W., RYAN, H.M., and BISHOP, J. : 'Aspects

of lightning protection schemes for radomes'. Presented at 8th Inter-

national GD C, Oxford, Septemb er 1985, pp. 372-375

33 GREENWAY, R., and RYAN, H.M.: 'Modern developments in the

insulation of switchgear components'.

IEE Conf. Publ. 83,

(I), pp. 122-

127.Also D iscussion (2), pp . 54 -55

34 RYAN, H.M., WAUGH, R.A., and GREENWAY, R.: 'An appraisal

of realistic discharge levels for high voltage switchgear'. Presented

at BEAMA 2nd International Electrical Insulation Conference,

Brighton, May 1974, pp. 271 -280

35 RYAN, H.M., GREENWAY, R., and POWELL, C.W.: 'Inst rument

transformers for modern EHV substations'. Presented at BEAMA 3rd

International Conference, Brighton, Ma y 1978, pp. 170-180

36 POWELL, C.W., MILNE, D., and RYAN, H.M.: 'The appl icat ion of

RBGF and solid dielectric materials in modern switchgear'. Presented

at BEAMA Insulation Conference, Brighton, May 10th-13th 1982

37 MILNE, D., and RYAN, H.M.: 'The evaluation of solid dielectric

systems for use in high voltage switchgear',

IEE Conf. Publ. 239,

1984,

pp .76-79

38 ZAENGL, W.: The impulse voltage divider with h.t. lead', Bull. ASE,

1970,61, (12), pp. 1003-1017

39 ZAENGL, W., and FESER, K.: 'Contr ibut ion to the calculat ion of

the transmission behaviour of impulse voltage dividers',

ibid.,

1964, 55,

(25),p . 1249

40 ZAENGL, W.: 'A new divider for steep impulse voltages',

ibid.,

1965,

56 ,p . 23 2

41 Working Group

33.03:

'Record of performance of voltage and current

measuring systems',

Electro,

1981, 78, pp. 35-69

F i g . 2 5 Views of insulation research test facilities installed in main XJHV hall south wall F )

518



19/21

Fig . 27

View of insulation materials evaluation laboratory showing

ovens and samples prior to test G)

Fig . 26

Endurance/accelerated frequency test area

(/)

Fig . 28

Views of 250 kV discharge test area K)

Fig . 29

Mechanical and thermal test area

(L)


Fig. 30 500

kV im pulse test laboratory H)

519


20/21

10 Appendix

10.1

Supplementary

test facilities

Following laboratory reorganisation in 1980 three addi-

tional test areas were established within the main hall of

the UHV laboratory, without effectively reducing the effi-

ciency and usefulness of the main area. In addition, a

multipurpose mechanical/thermal/dielectric area was

established in the erection bay; insulation material

research areas, suitable for endurance and accelerated fre-

quency testing, were also established within the UHV

laboratory precinct. Examples of these supplementary

facilities are given in Figs.2531.Identification letters F -L

refer to Fig.2a .

10.2

High voltage

facilities

a t

NEI

Reyrolle Hebburn

10.2.1 Laboratory dimensions and facility data: Th e

main test plant and equipment are detailed below and

illustrated in Figs. 2, 3, 5-8, 17 -19.

Fig. 31 Examples of thermal, mechanical and dielectric testing

a View of SF

6

insulated mctalclad switchgear assembled for thermal testing (L).

Close proximity of main UHV hall makes it very convenient to carry out dielectric

tests on the thermal test arrangement if required.

b

Modern 420 kV SPD (4 break) metalclad circuit breaker set up in mechanical/

electrical test hall for mechanical endurance type testing. Vertically mounted por-

celain inlet bushing and voltage transformer are shown connected to the circuit

breaker for these tests.

c 420 kV SPD (2 break) circuit breaker inside an environmental test chamber with

range 40 to 50C (L). Studies also included power-frequency dielectric testing

and video filming

for particulate count.

d, e Views of 420 kV (2 break) dead-tank circuit-breaker assembly (mounted for

outdoor mechanical type testing) (2000 operations). Studies also included power-

frequency dielectric testing and video filming

for particulate count.



21/21

JO.2.1.1

Indoor laboratory:

(i) Maximum internal clearance 48.7 m x 33.5 m x 32

m (high) (provision/space to extend southern facing wall by

at least 24.4 m)

(ii) do or openin g 11.7 m x 18.9 m (high)

(iii) overhead cran e 7.1 tonnes (7 tons)

(iv) mobile cra nes

(v) floor loading 21.9 tonnes/m

2

(2 ton/sq. ft.)

(vi) Maximum tension for overhead line and insulator

tests 10.1 tonnes

(vii) Underground oil storage tanks (136 m

3

(30000

gallons)), pumping station, streamline purifier and condi-

tioner

(viii) main oil test tank (127 m

3

(28000 gallons)) suit-

able for oil impregnation and testing of transformer insula-

tion and for complete bushings, testing up to 765 kV

rating

(ix) wet test equipment. Testing in accordance with IEC

60 etc. on complete assemblies of 420/525 kV open termin-

al and metalclad switchgear, disconnectors, transformer

bushings transmission towers/lines and hardware etc. (e.g.

Figs.

5,15)

(x) compressed air supplies

(xi) SF

6

handling equipment

(xii) various compressed-gas test vessels for GIS studies

at voltages 2.8 MV and pressures up to 8 x 10

5

N /m

2

(gauge).

10.2.1.2 Erectionbay:(Figs. 2, 29, 31a)

(i) maximum internal clearance 10.5 m x 15 ra x 15.6 m

(high)

(ii) various transformers for thermal testing switchgear

panels, GIS or for cables etc. for AC and DC type testing

(iii) mechanical/thermal test capability in this area with

ready access to HV supplies from main test hall.

10.2.1.3 Outdoor laboratory:(see Figs. 2, 3a, 3Id,e)

(i) concrete are a 15.3 m x 24.4 m.

(ii) Flat grass/concrete area adjacent to both high-

voltage and short-circu it facilities 150 m x 60 m

approx imately (see Figs. 2c, 31c).

10.2.2

High

voltage

equipment:

10.2.2.1 Directvoltage tests:

(i)

1

MV generator

(ii) 2 MV generator capability produced from exist-

ing 4 MV impulse generator

(iii)

1

MV wire-wound resistor divider

(iv) electrometers for low current measurements etc.

10.2.2.2 Power-frequency

tests:

(i) 2 MV, 3.2 MVA transformers (see Figs.

2d,

3)

(ii) 2 x 0.5 MV, 500 kVA transformer (cascaded units)

(iii) 250 kV, 100 kVA transformer

(iv) 200 kV, 20 kVA transformer

(v) various shielded gas capacitors up to 1.2 M V

(vi) compensated capacitor divider up to 2.0 MV

(vii) various Schering bridges (up to 200 kV)

(viii) RIV test set

(ix) partial discharge detectors.

10.2.2.3Impulsevoltagetests:

(i) 4 MV, 150 kJ generator (see Figs. 2d , 3) (could be

extended to 5.6 MV)

(ii) 800 kV, 9.5 kJ generator

(iii) 600 kV, 4.2 kJ generator

(iv) bias (impulse/AC) test con trols

(v) 4 MV compensated capacitor divider with series-

distributed resistors (see Figs.Id ,3c)

(vi) 1.2 MV capacitive graded resistor divider

(vii) impulse oscilloscopes

(viii) digital transien t recorders

(ix) various uniform field and sphere gaps

(x) pressurised measuring spark gaps

(xi) specialised screened room, suitable for detailed gas

prebreakdown studies

(xii) Digital support: programs for statistical analysis of

test results, for electric field evaluation of test objects, and

for step response evaluation of laboratory test circuits.

Also a suite of power-system analysis programs available

for analysing laboratory switching studies involving surge

arresters, switchgear etc.

1EE PROCEEDINGS Vol. 133 Pt. A No. 8 NO VEMBER 1986

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