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21, rue d’Artois, F-75008 PARIS UHV Colloquium, New Delhi 2013

http : //www.cigre.org

International Colloquium on Ultra High Voltage in association with CIGRE

3-4 Apr il 2013, New Delhi, India

SPECIAL REPORT FOR SESSIONS 2.1 and 2.2

Equipment

Hiroki Ito (Chairman and Reporter)

TBD (Co-chairman from India)

The rapid growth in electrical power demand, especially in China and India creates someurgency for the development and construction of Ultra High Voltage (UHV) transmissionsystem exceeding 800 kV and demands the international standardisation in the field of UHVtechnologies. Figure 1 indicates the highest voltage of AC transmission. Canada developedthe world’s first 735 kV transmission systems in 1965 and the United States installed 765 kVlines in 1969. Brazil and Korea started their 800 kV transmissions in 1982 and in 2002.

On January 6th, 2009, in China, the worldwide first 1100 kV AC system has successfully been put into service after on-site commissioning tests in 2008. Regarding UHV transmission, onehas to remember the 1200 kV system that has been operated in the former USSR (Russia)from 1984 until 1991, which is currently operating at 525 kV. Since then, enormous progresshas been made in the field of insulation coordination by the introduction of higher

performance surge arresters (with relatively lower voltage protection level), by the applicationof, for instance, pre-insertion (closing) resistors and opening resistors, and by the use ofsophisticated transient simulation tools that have led to reduced margins in safety factors.These technologies have been applied to a pilot plant in Japan, to the system in China and willalso be applied in other countries such as India.

Figure 1 Highest voltage of AC power transmission

Chairman and Reporter’s email: [email protected]

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It is most important for UHV development to give attention to test facilities for design anddevelopment purposes (corona cage) and to new facilities, such as erected at the 420 kV Binasubstation, for field tests. The latter consists of a short 1200 kV line, two 1200 kV bays andtwo transformer groups and has been put into operation.

In the Sessions 2.1 and 2.2, five papers deal with the development of UHV AC equipment;two of them are about surge arresters of different designs and manufactures (A3-07 and A3-9); one about UHV bushings (A3-10); one about digital instrument transformers that are verysuited for UHV applications (A3-11); and one about 1200 kV MTS equipment (A3-05). Two

papers describe the development of compact GIS equipment for 800 kV, but with theintention to further develop the equipment to UHV (A3-05, A3-12). In two papers theinvestigations and recommendations of CIGRE WG A3.22 and WG A3.28 are reported.Report A3-02 deals with a method to accurately measure the fault current during the arcingtime in order to estimate life consumption of arc contacts and nozzles.

Two Reports have been withdrawn (A3-04 and A3-08).

Table 1 Report list in the session 2.1 and 2.2 Number Title Authors Country

A3-01 Impact of UHV and EHV System Designon TRV Waveshapes

A.Janssen, D.Dufournet, H.Ito, H.Kajino,Y.Yamagata, M.Kosakada, S.Poirier,J.Fan, Z.Xiang, P.Fernandez

Netherlands, France,Japan, Canada,China, Brazil

A3-02 Accurate I2t Evaluation for UHV CircuitBreaker Contact Erosion

K.Naresh, R.Rahul, A.Talluri,A.Parapurath

India

A3-03 Transformer Limited Fault Duties forUHV and EHV

A.Janssen, D.Dufournet, H.Ito, H.Kajino,Y.Yamagata, M.Kosakada

Netherlands, France,Japan

A3-05 Development of a Gas InsulatedDisconnector for UHV Networks

T.Berteloot, A.Girodet, P.Vinson, M.Bernard

France

A3-06 Design and Development of MixedTechnology switchgear (MTS)

K.Chauhan, U.Riechert, R.Mohammedi,U.Parikh

India, Switzerland

A3-07 Metal-Oxide Surge Arresters for 1200kVAC Transmission Systems

R.Göhler, M.Schubert Germany

A3-09 Voltage Distribution Studies on Ultra-High Voltage Lightning Arrester

S.Selvaraj, N.Jha, D.Yesuraj India

A3-10 Design and qualification of UHV ACBushings

G.Testin, P.Cardano, L.Perego,M.Boutlendj, B. Brunelli, A. Pigini

India, Italy

A3-11 UHVAC Digital Instrument Transformers D.Chatrefou France

A3-12 Development of a new highly-compact800kV gas-insulated circuit breaker

A.Bertinato, M.Bernard, S.Souchal France

Report A3-01 deals with TRV requirements of UHV and EHV circuit breakers for variousswitching conditions as a partial result of WG A3.28 investigations. On one hand, UHV TRVrecommendation to IEC SC17A were based on TRV analysis for bus terminal fault (BTF) andon the other hand they were based on for long line fault (LLF) under 3LG conditions in the1100 kV transmission system in Japan. The report A3-01 presented TRV requirements withradial and meshed network models using different system and equipment parameters at therated voltages from 550 to 1200 kV. The influence of conductor height, earth resistivity,single or double circuit towers on TRV is confirmed to be negligible, while the influence ofline transposition, MOSA characteristics, meshed networks versus radial networks is positive,

but limited.

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Question A3-01: Could it be concluded from the TRV studies that TRV specified in IEC forrated voltages 420kV to 800 kV adequately cover present system values?

Which typical phenomena have been discovered, that have not been considered (in depth) inthe past? For example, UHV MOSA has a reducing impact on the TRV peak values. Aresimilar phenomena expected in the 420 / 550 /800 kV systems?

Report A3-02 deals with contact erosion due to the current flowing through the arc betweenthe circuit breaker contacts. The authors show a method to calculate exactly the RMS-value ofan interrupted current between the moment of contact separation and arc extinction; i.e. theso-called arc current. This value is an indication of loss of contact material and nozzleablation.

Question A3-02: Contact and nozzle erosion is assumed to be proportional to the square rootof current, but studies have shown that it is a rough estimation. Previous CIGRE studies with

SF6 circuit breakers showed that the exponent is usually largely higher than 2 for low short-circuit currents and closer to 1.8 for the highest short-circuit currents. Knowing that, what

precision is really necessary when determining the square root value of current? Or, putting itthe other way around: is the accurate calculation of arc currents used to investigate more

precisely the deterioration of contacts and nozzles due to current interruption and to come upwith new life assessment formulas?

Report A3-03 deals with TRV measurements for Transformer Limited Fault (TLF) conditionsusing large-capacity power transformer. Different transformer limited fault conditions forcircuit-breakers with a rated voltage of 100 kV and above, are given. Parameters as thevoltage drop across the transformer, the first-pole to clear factor, the amplitude factor and therate of rise of recovery voltage are addressed. The additional capacitance of the connections

between circuit-breaker and transformer may have a large influence and minimum valueshave been investigated.

Question A3-03: Some specifications (e.g. IEEE C37.06.1) are based on a voltage drop closeto 90% irrespective of the fault current, but to CIGRE WG A3.28 there is a strong relationship

between voltage drop and fault current. Should the voltage drop prescribed in the Standards be corrected when large fault currents close to 30% of rated short-circuit current are required?

The authors claim that an amplitude factor of 1.7 is a conservative value, covering the actualcases above 100 kV. Is it necessary to specify even more margin, since the IEEE Standardspecifies an amplitude factor of 1.8? Can examples or evidence of cases leading to largeramplitude factors than 1.7 be given?

Report A3-05 dealt with the development of UHV gas insulated disconnector (DS) based on800 kV DS design. The authors show two developments: the development of more advanceddesign tools and the development of more compact GIS disconnectors for the highest ratedvoltages, starting with 800 kV. They incorporate in their design specifications higher bus-transfer currents than presently defined in the IEC Standard 62271-102.

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Question A3-05: For readers with less design experience, can the author explain why inFigure 1 the right side solution is better? A lower speed leads to lower VFTO as the trappedcharge is far less 1.0 pu, this is in line with published results and is well explained here.Further an optimum asymmetrical voltage withstand (between positive and negative voltagewithstands) can lead to lower trapped charges, but how can this be implemented in a design?

The present test voltage for bus transfer is 40 V for 800kV and 130V for 1100/1200kV, howthe test voltage of 70 V was chosen? Is the bus transfer current of 2800 A representative for800 kV requirements?

Report A3-06 deals with the development of Mixed Technology Switchgear (MTS or HybridGIS) applied to 1200 kV national testing station in Bina. In the Report the extrapolation of anexisting 1100 kV MTS design towards a 1200 kV application is described. Despite thesomewhat higher dielectric requirements at 1200 kV, the authors claim that the design fulfillsthe users’ requirements. Based on recent results from CIGRE worldwide reliability surveysfor switchgear, the authors calculate the failure rates of several substation technologies (AIS,

GIS, MTS) for a 1.5 CB scheme and show the superior reliability of GIS/MTS technology.The test setup at the BINA 1200 kV test site is described.

Question A3-06: Can the authors explain how they manage to upgrade the 1100 kVequipment to 1200 kV (higher SF6-gas pressure, enough margin in the design, special userrequirements, etc.)? Can the authors explain how the switching duties performed at 1100 kVmay be applied for 1200 kV, taking into consideration that at T100s the time coordinate t2 seems to be too long and at T100a Uc seems to be too low compared to the recent IECrequirements? In the paper it has been mentioned that the disconnector is manually operated.What are the consequences of manually operation versus a motor driven operation: speed,

travel characteristic, VFTO, bus charging, bus-transfer and safety?

It is not so clear how the authors extrapolated the results of the CIGRE enquiries to thereliability of equipment with a rated voltage far above the voltage classes investigated by WGA3.06. Did they take four times the failure rates at the 300 kV class? How did theyextrapolate the results of the reliability of GIS circuit breakers, which are already far worse atthe voltage class above 700 kV? Is the circuit-breaker not the most important component ofthe whole MTS?

Report A3-07 deals with development and testing of 1200 kV Metal-Oxide Surge Arresters

(MOSA). Extremely low voltage protective levels of UHV MOSA lead to high specificstresses under continuous operation conditions resulting in higher operating temperatures aswell as excessive energy handling requirements. The authors have developed an arrester thatconsists of (i) five series connected polymer hollow insulators with each five parallel columnsof ZnO blocks. Alternative solutions would have been (ii) polymeric insulation directlymoulded to the active parts (cage design arresters) with five insulators in parallel and in series,or (iii) porcelain hollow insulators similar to the authors design, or (iv) gas-insulated design.Apart from solution (iv), the authors compare shortly the alternative technologies. Furtherthey pay attention to the voltage distribution and voltage stress across the arrester sections andthe temperature distribution. Report A3-09 also dealt with the Voltage Distribution Analysison voltage shield ring of UHV MOSA. The calculation shows that the voltage distributionratio (K factor) can be reduced from 2 to 1.13 with application of the optimal designed shield

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ring. The authors of Report A3-09 describe the design of type (ii) and address similar topicsas the authors of A3-07.

Question A3-07, 09: Can the authors and other experts highlight the advantages and dis-advantages of the alternative solutions? As nowadays UHV substations seem to be designedin GIS or MTS technology, what are the advantages or disadvantages of metal enclosedarresters, type (iv)?

Report A3-10 deals with the design and qualification of UHV AC bushings. Several designsof the very tall bushings required for UHV AC applications are described and dielectric,mechanical and thermal requirements are addressed. The authors break a lance for polymericinsulation, but some pictures seem to show porcelain insulators (figure 6, figure 11).

Question A3-10: Is the assumption about porcelain insulators correct? And, if so, what

influence does porcelain have on the simulation models? Altitude correction factor: based oninput from CIGRE SC D1 what distance can be expected e.g. for an altitude of 4000 m?How can large electrodes impair performance under rain conditions?Have calculations of seismic withstand been performed? What are the seismic requirements inIndia? How reliable are simulations of thermal behavior?

Report A3-11 deals with UHV AC Digital Instrument Transformers. Non conventionalinstrument transformers present obvious advantages for UHV applications due to reducedweight and SF6 content, better seismic withstand. One merging unit is capable to catch thesignals from current transformers and voltages transformers in three phases and offer the

digitalized signals in an internationally standardized way to other secondary equipment, likemetering or protection. Several field tests over the world are shortly described.

Question A3-11: Why does the author use the inline Sagnac interferometer technology for theCT? Are the field tests performed with secondary equipment of the same manufacturer orwith protection and measuring equipment from totally different manufacturers?

Report A3-12 dealt with the development of 800kV gas-insulated circuit breaker. New two- break circuit breaker can allow a compact design for a GIS circuit breaker, and a more

compact GIS bay. Various simulation tools were used to evaluate the performance for alltypes of demonstration tests.

Question A3-12: why a vertical arrangement of the interrupting chambers was used instead ofa design with horizontal chambers? Can the author explain the merits and demerits for bothdesigns? In Report A3-05 a disconnector of the same manufacturer has been described. Itseems to be the same design series of very compact 800 kV GIS.All design performance results shown are based on calculations and simulations and no typetest results are given. Does this mean that the design still has to be approved by type tests?

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Appendix

UHV standardisation work has been conducted in close cooperation between CIGRE and IEC.

Upon the request of IEC SC 17A, CIGRÉ established WG A3.22 “Technical Requirementsfor Substation Equipment exceeding 800 kV” in October 2006. Technical specifications and

service experience from all major UHV projects and demonstrations have been reviewed inconjunction with relevant data from a number of commercially operated 800 kV systems. Thereview has clarified a number of technical subjects, which are particularly challenging in theUHV range and that simple extrapolation of assumptions from lower voltages is notappropriate in many cases. Several distinctive phenomena that may have significant impact onthe substation equipment have been identified. The application of long lines, radial networkstructures, multi-conductor bundle with large-diameter as well as large-capacity powertransformer, lead to, for example, a prominent Ferranti effect, large DC time constants, severeTransient Recovery Voltage (TRV)s and slow front overvoltage, prolonged secondary arcextinction and reduced first-pole-to-clear factors.

CIGRÉ WG A3.22 recommended technical specifications for UHV substation equipment tosupport the revision of standards for high-voltage switchgear in December 2008, allowing thestandardization works to start in IEC SC17A in February 2009. The studies have been

published in two CIGRE technical Brochures 362 and 456 and cover recommendations for the parameters that define the TRV envelopes including conditions such as Transformer LimitedFault (TLF), Long Line Fault (LLF), out-of-phase, the voltage factor for capacitive currentswitching and the effect of opening resistors and MOSA on the switching requirements.

Table 2 shows TRV requirements for 1100 kV and 1200 kV systems. The first pole-to-clearfactor has been proposed as 1.2 based on detailed investigations in UHV systems. Amplitudefactors are proposed to keep the same amplitude factors as for the lower voltages even thoughless attenuation expected at UHV. However, the amplitude factor for T100 is recommended to

increase from 1.4 to 1.5 so the factor of K pp * K af keeps the same peak value with the existingIEC standards up to 800 kV. Another particularity is a reduction of time to the peak value t2 for T100 and for T60. For voltages up to and inclusing 800 kV, the existing IEC standarddefines t2 as 4 times and 6 times t1 respectively. Considering the minimum equivalent linelength of 200 km for present and foreseen UHV systems, a lower t2 to t1 ratio has been

proposed.

Table 2 UHV TRV requirements

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Today all relevant standards under the responsibility of IEC SC17A have been revised (IEC62271-100, -101, -102, -110) and in addition two new documents have been established: IEC62271-306 the application guide for the high-voltage circuit breaker standard and IEC 62271-112 for HSES. In almost all cases, IEC SC17A followed the recommendations of CIGRÉ WGA3.22, in particular the TRV requirements for circuit breakers 1100kV and 1200 kV. The

relevance of these TRV requirements has now been confirmed by the recent study made byCIGRE WG A3.28. The requirements introduced in the new IEC 62271-112 for HSES arealso based on a study made by CIGRÉ WGA3.22.

Upon another request of IEC SC 17A, investigations on remaining subjects to supportstandardization for UHV and lower rated voltages, have been continued by CIGRÉ WGA3.28. In addition, WG A3.28 has investigated the influence of different UHV networktopologies, policies and practices on the requirements based on UHV and EHV radial andmeshed network models using the system and equipment parameters of different national

projects, as former studies were mainly based on the investigations for the 1100 kV system inJapan. The influence of various system aspects and equipment parameters on TRV was also

investigated in detail. The result will be published in a future TB, to be published in the beginning of 2014.

Transformer limited fault (TLF) TRVs are introduced in the new edition of IEC 62271-100for UHV circuit breakers. On request from IEC SC17A, CIGRE WG A3.28 is studying TLFTRVs for circuit breakers with rated voltages from 100kV up to including 800kV. It isexpected that in the future this study will support the standardization of TLF for all high-voltage circuit breakers. Work is also in progress in CIGRE WG A3.28 on switching

phenomena for EHV disconnectors and earthing switches, the result of this work will supportthe future revision of IEC 62271-102.

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