UHV air insulation: physical and engineering research
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Editorial UHV air insulation: physical and engineering research Indexing terms: Arcing, Breakdown and gas discharges, Load and voltage regulation, Overvoltages, Physical properties The authorship of the papers comprising this special issue of IEE Proceedings Part A on UHV air insulation research will confirm the long-established international collabo- ration in this subject, and will reflect the universality of the economic and technical problems which arise in high- voltage power transmission engineering. Papers which report scientific and technological advances in this area often appear in the proceedings of CIGRE, ICPIG, Gaseous Dielectrics, International Symposia on High- Voltage Engineering, Gas Discharges and their Applica- tions, IEEE-PAS and others. IEE activities are promoted by colloquia and discussion meetings organised by Pro- fessional Groups S3 (Phenomena in ionised gases and in vacuum) and P8 (Power cables and overhead lines), and by major conferences such as that on Lighting and Power Systems (IEE Conf. Publ. 236, 1984). The aim of the present special issue is to give, in a permanent form, some specialised summary papers and a wide-ranging selection of reports on recent research activities. The papers relate to the problems of overvoltages on external insulation of lines or of substations, to the design of test equipment and the choice of testing strategies to determine engineering or physical parameters of insulation failure, to the physical and statistical modelling of these parameters, and to appli- cations in insulation co-ordination. Economic and environmental advantages, arising from smaller phase-to- phase clearances, for example, with consequent narrower rights of way, cheaper construction and lower electric field at ground level, must be balanced against the paramount need for system reliability and the less onerous corona effects with larger clearances. The last two decades have seen a significant accumula- tion of field experience in power systems with operating voltages of up to 525 kV. The future expansion of demand, the changing pattern of generation, and ecological pri- orities will require optimisation of UHV design at 1 MV for 10 GW power lines. The uncertainties of scaling and extrapolation make such prospective planning heavily dependent on present-day studies at large research and development laboratories, such as those of EdF at Les Renardieres, IREQ at Varennes, Canada, BPA at Vancou- ver, USA, the Polytechnic Institute at Leningrad, NEERI at Pretoria, FGH at Mannheim, VEB at Dresden, CESI at Milan, ENEL at Suvereto, CERL at Leatherhead, and Reyrolle Ltd at Hebburn, all of which are represented here. In parallel with these large-scale tests, university labor- atories have a part to play in providing a scientific base and improving measurement and theoretical techniques. Despite the delayed implementation of UHV transmission, research has been stimulated by the problems introduced by switching surges which become significant even at present maximum operating voltages, and by the require- ments of developing countries with specific meteorological hazards and altitude requirements. Further impetus has been given by the application of digital techniques to tran- sient network analysis for the prediction of surge behav- IEE PROCEEDINGS, Vol. 133, Pt. A, No. 7, OCTOBER 1986 iour, to electrostatic field computation of mixed insulation, and to the acquisition and processing of test data. Together with the improved research tools of high-speed photography and electric field measurement, these have improved knowledge of both air insulation and CGIS. Specific advances have followed in understanding the role of space charges, the properties of corona streamers and spark leaders, and the statistics of breakdown. As the present papers illustrate, however, there remain many chal- lenging aspects in the effects of nonstandard surge shapes and of successive overvoltages on phase-to-ground and phase-to-phase insulation, in the evolution of improved test procedures and in the design of UHV test equipment. Part 1 of this special issue consists of a paper by the Les Renardieres Group which was formed in 1971 from research teams in the United Kingdom, France, Italy and West Germany. The method of collaboration has consisted of a two-month test programme with an emphasis on the physical behaviour of long-gap breakdown, followed by a two-year period of analysis, discussion and report. The present paper extends the study of long-spark development to nonstandard impulses and to phase-to-phase analogues. In Part 2 of this special issue the following papers appear: A.J. Eriksson et al. give a review of work done at the new UHV laboratory established in South Africa at an altitude of 1425 m. This work has been directed to examine air density and humidity effects on impulse and power frequency air breakdown, from which improved correction factor models are sought. Physical effects such as the effect of humidity on corona streamers are also studied. C.L. Nellis et al. summarise a test campaign carried out in 1977-1984 by the Bonneville Power Administration of the US Department of Energy to examine the feasibility of power transmission at 1100 kV. Two test lines each of about 2 km length were constructed in Oregon, and the UHV laboratory facilities in Washington State were extended. Extensive testing with switching (SI) and light- ning (LI) impulses was done on airgaps with and without insulators. The effects of insulation type, grading rings, corrosion and contamination are described. H.M. Ryan and J. Whiskard were closely associated with the design and use of an industrial UHV laboratory for the switchgear manufacturer NEI Reyrolle Ltd in England. An account of 15 years of research and develop- ment, with experience of the use of test procedures, is given with reference to both air-insulated systems and GIS. R. Malewski deals with an important problem associ- ated with large-scale UHV testing, relating to the response of large voltage dividers to fast signals such as front- chopped impulses. The paper discusses specifically UHV measurement at the IREQ Laboratory. H. Studinger and K.H. Week augment IEC 76-3 specifications for phase-to- phase and phase-to-earth transformer insulation, by giving positive SI data for dry and wet tests. G.N. Aleksandrov 393
Transcript of UHV air insulation: physical and engineering research
EditorialUHV air insulation: physical and engineeringresearch
Indexing terms: Arcing, Breakdown and gas discharges, Load and voltage regulation, Overvoltages, Physical properties
The authorship of the papers comprising this special issueof IEE Proceedings Part A on UHV air insulation researchwill confirm the long-established international collabo-ration in this subject, and will reflect the universality of theeconomic and technical problems which arise in high-voltage power transmission engineering. Papers whichreport scientific and technological advances in this areaoften appear in the proceedings of CIGRE, ICPIG,Gaseous Dielectrics, International Symposia on High-Voltage Engineering, Gas Discharges and their Applica-tions, IEEE-PAS and others. IEE activities are promotedby colloquia and discussion meetings organised by Pro-fessional Groups S3 (Phenomena in ionised gases and invacuum) and P8 (Power cables and overhead lines), and bymajor conferences such as that on Lighting and PowerSystems (IEE Conf. Publ. 236, 1984). The aim of thepresent special issue is to give, in a permanent form, somespecialised summary papers and a wide-ranging selectionof reports on recent research activities. The papers relateto the problems of overvoltages on external insulation oflines or of substations, to the design of test equipment andthe choice of testing strategies to determine engineering orphysical parameters of insulation failure, to the physicaland statistical modelling of these parameters, and to appli-cations in insulation co-ordination. Economic andenvironmental advantages, arising from smaller phase-to-phase clearances, for example, with consequent narrowerrights of way, cheaper construction and lower electric fieldat ground level, must be balanced against the paramountneed for system reliability and the less onerous coronaeffects with larger clearances.
The last two decades have seen a significant accumula-tion of field experience in power systems with operatingvoltages of up to 525 kV. The future expansion of demand,the changing pattern of generation, and ecological pri-orities will require optimisation of UHV design at 1 MVfor 10 GW power lines. The uncertainties of scaling andextrapolation make such prospective planning heavilydependent on present-day studies at large research anddevelopment laboratories, such as those of EdF at LesRenardieres, IREQ at Varennes, Canada, BPA at Vancou-ver, USA, the Polytechnic Institute at Leningrad, NEERIat Pretoria, FGH at Mannheim, VEB at Dresden, CESI atMilan, ENEL at Suvereto, CERL at Leatherhead, andReyrolle Ltd at Hebburn, all of which are represented here.In parallel with these large-scale tests, university labor-atories have a part to play in providing a scientific baseand improving measurement and theoretical techniques.Despite the delayed implementation of UHV transmission,research has been stimulated by the problems introducedby switching surges which become significant even atpresent maximum operating voltages, and by the require-ments of developing countries with specific meteorologicalhazards and altitude requirements. Further impetus hasbeen given by the application of digital techniques to tran-sient network analysis for the prediction of surge behav-
IEE PROCEEDINGS, Vol. 133, Pt. A, No. 7, OCTOBER 1986
iour, to electrostatic field computation of mixed insulation,and to the acquisition and processing of test data.Together with the improved research tools of high-speedphotography and electric field measurement, these haveimproved knowledge of both air insulation and CGIS.Specific advances have followed in understanding the roleof space charges, the properties of corona streamers andspark leaders, and the statistics of breakdown. As thepresent papers illustrate, however, there remain many chal-lenging aspects in the effects of nonstandard surge shapesand of successive overvoltages on phase-to-ground andphase-to-phase insulation, in the evolution of improvedtest procedures and in the design of UHV test equipment.
Part 1 of this special issue consists of a paper by the LesRenardieres Group which was formed in 1971 fromresearch teams in the United Kingdom, France, Italy andWest Germany. The method of collaboration has consistedof a two-month test programme with an emphasis on thephysical behaviour of long-gap breakdown, followed by atwo-year period of analysis, discussion and report. Thepresent paper extends the study of long-spark developmentto nonstandard impulses and to phase-to-phase analogues.
In Part 2 of this special issue the following papersappear:
A.J. Eriksson et al. give a review of work done at thenew UHV laboratory established in South Africa at analtitude of 1425 m. This work has been directed toexamine air density and humidity effects on impulse andpower frequency air breakdown, from which improvedcorrection factor models are sought. Physical effects suchas the effect of humidity on corona streamers are alsostudied.
C.L. Nellis et al. summarise a test campaign carried outin 1977-1984 by the Bonneville Power Administration ofthe US Department of Energy to examine the feasibility ofpower transmission at 1100 kV. Two test lines each ofabout 2 km length were constructed in Oregon, and theUHV laboratory facilities in Washington State wereextended. Extensive testing with switching (SI) and light-ning (LI) impulses was done on airgaps with and withoutinsulators. The effects of insulation type, grading rings,corrosion and contamination are described.
H.M. Ryan and J. Whiskard were closely associatedwith the design and use of an industrial UHV laboratoryfor the switchgear manufacturer NEI Reyrolle Ltd inEngland. An account of 15 years of research and develop-ment, with experience of the use of test procedures, is givenwith reference to both air-insulated systems and GIS.
R. Malewski deals with an important problem associ-ated with large-scale UHV testing, relating to the responseof large voltage dividers to fast signals such as front-chopped impulses. The paper discusses specifically UHVmeasurement at the IREQ Laboratory. H. Studinger andK.H. Week augment IEC 76-3 specifications for phase-to-phase and phase-to-earth transformer insulation, by givingpositive SI data for dry and wet tests. G.N. Aleksandrov
393
and Y.A. Gerasimov approach the problem of generalisingtest data for 3-phase insulation where not only the phase-to-phase and phase-to-earth clearances S and H may bechanged but also the positive and negative voltage com-ponents U+ and U~. The authors succeed in identifyingthe generalised functions/(H/S) and f{U~/U + ; S/H) forthree practical configurations.
Prof. W. Mosch et al. outline their work on the profilingof UHV terminal electrodes which, together with addi-tional control electrodes, can optimise the overall dimen-sions of UHV test equipment. Where electrode areas canexceed 100 m2 many electron avalanches may be initiated,but will die in their early stages in the weak applied field.Nevertheless, a critical avalanche leading to streamerinception may still be formed, the development of whichcan be estimated on stochastic principles, i.e. by calcu-lation of the probability functions which describe therandom nature of electron impact ionisation.
C. Gary et al. review the analytical representation oftransmission towers for lightning current transients, andcalculate overvoltage amplitudes for tower and groundwirestrokes. This predicts the extent of surge curtailment bybackflashover. Insulator tests for short-tail impulses arealso reported. N.L. Allen considers present evidence con-cerning the effect of humidity on the positive impulsestrength of large airgaps. Current international standardsindicate dependence of humidity correction factor kh ongap length but not impulse shape. Dr Allen shows thatrecent Japanese tests imply a minimum in the value of khas a function of time to crest Tcr, analogous to the break-
down voltage t/-curve. T.E. Allibone and J.C. Saundersonreport negative DC corona tests at up to 1 MV, and verifythe corona current square law for gap spacings of 1 m. Forinverted gaps the l/d dependence on distance does nothold. T. Kawamura et al. apply the recently developedPockels cell probe to measure electric field transients in a0-8 m gap with negative SI. Direct measurement of space-charge density and dissipation rates are obtained.
The authors of the papers in this special issue deserveour thanks for these papers. The Guest Editor expresseshis appreciation of the work of the referees and the IEEeditorial staff.
R.T. WATERS
Ronald T. Waters researched for a Ph.D.degree in the group of Professor F.Llewellyn-Jones at University College ofSwansea, and subsequently worked for nineyears at the AEI Research Laboratories,Aldermaston, where his interest in high-voltage engineering was kindled by theDirector Professor T.E. Allibone. His sub-sequent research work has been at the Uni-versity of Wales Institute of Science andTechnology, Cardiff, where he is a Pro-
fessor in the Department of Physics, Electronics and ElectricalEngineering. He is a member of the Les Renardieres Group andthe EEC Group on Electrical Discharges in Gases. He is a PastChairman of Professional Group S3, and a member of theScience, Education and Technology Divisional Board.
IEE PROCEEDINGS, Vol. 133, Pt. A, No. 7, OCTOBER 1986
