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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
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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
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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
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/
/
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
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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
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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.
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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
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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
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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)
IEE PROCEEDINGS, Vol. 133, Pt. A, No. 8, NOVEMBER 1986
Fig. 30 500
kV im pulse test laboratory H)
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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.
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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