Second IEC-CIGRE UHV Symposium, 29-30 January 2009, New Delhi 3-2 Insulation Coordination for UHV AC Systems based on Surge Arrester Application (CIGRE C4.306) Eiichi Zaima Tokyo Electric Power Claus Neumann RWE TSO Strom January 29, 2009 Eiichi Zaima Convenor, CIGRE WG C4.306 Second IEC-CIGRE UHV Symposium, 29-30 January 2009, New Delhi

Introduction Different countries in the world, such as China, India and Japan, are planning and realizing UHV AC systems with the highest voltage of 1100kV and 1200kV. The research activities for UHV transmission within previous CIGRE SC33 has provided a good basis on the basic design for them. In the recent practice of UHV system, insulation coordination throughout substation and transmission line are generally based on metal oxide surge arresters and gas insulated switchgears (GIS, MTS). My presentation will cover the recent practice on insulation coordination for UHV AC systems from system aspects, the approved CDV (28/195/CDV) and the future work of CIGRE WG C4.306 (Insulation coordination for UHV AC systems)

Recent Practice of Insulation Coordination for UHV AC Transmission System

UHV Insulation Coordination Concept Insulation coordination throughout substation and transmission line Reduction of insulation levels to a reasonable level by sophisticated technologies. Practical application of high performance metal oxide surge arrester Reliable circuit breaker with closing and/or opening resistor Rational Insulation Specification Switching Overvoltage Insulation Design Level (Transmission Line) LIWV (Substation) SIWV (Substation)

Overvoltages specific to UHV System (1) [TOV] Load rejection at a heavily loaded long line of UHV system produces TOV whose amplitude is 1.3-1.5 p.u.. [Slow-front overvoltage] Closing, opening, and ground fault overvoltages are of particular importance for UHV systems because they are the predominant factor of transmission tower size. [Fast-front overvoltage] Lightning overvoltages within UHV substation are greatly suppressed because they are the predominant factor of substation equipment size. [Very fast transient overvoltage (VFTO)] Disconnector switching overvoltages in UHV GIS are likely to exceed the lightning overvoltage if no measures are taken to control them.

Overvoltages specific to UHV System (2) Precise digital analyses Example of switching overvoltage calculation by EMTP and its measuring results in Japan’s 1100 kV project Excellent agreement Accurate result of analyses

Switching Overvoltage Level and Suppression Measures Surge arresters and closing resistor have been basically used to suppress switching overvoltage on transmission line below switching overvoltage insulation design level. Open resistors have been adopted in Italy and Japan.

Application of High Performance Surge Arresters and LIWV High performance surge arrester can be applied in order to determine rational LIWV.

Standard Withstand Voltage for UHV Substation Equipment

LIWV and SIWV for UHV Substation Equipment Approved CDV(28/195/CDV) for amendment for IEC 60071-1 Notes (4) This value is only applicable to the phase to earth insulation of single phase equipment not expose to air. (5) Presently in the IEC 60038 edition 6.2/2007-07, Um=1200 kV is a standard value but in a proposed CDV submitted nowadays for vote the status is only under consideration. In the final version of this amendment, the final status of Um=1200 kV will be the one finally adopted in the revision or confirmation of IEC standard 60038 under the responsibility of TC 8.

Procedure of Insulation Coordination Flowchart for insulation coordination in IEC 60071-1 Insulation coordination Safety factor Standardization

Example of Selection of Insulation Level for UHV Equipment and Transmission Line

Japan’s 1100 kV Project (1) Switching overvoltage design level of transmission line Measures for overvoltage reduction Size reduction for tower Switching Overvoltages are effectively reduced to 1.6-1.7pu by the application of closing/opening resistor (700) and high performance surge arrester at substation. Tower Height: 143m  110m Switching Overvoltage: 2pu  1.6 - 1.7pu

Japan’s 1100 kV Project (2) LIWV: 1950 kV for transformer and 2250 kV for GIS (kV) Layout of Surge Arrester Transformer 1950 1950 1950 1950 1950 1950 LIWV GIS 2900 2900 2900 2700 2550 2250 LIWV Cost 102 % 105 % 109 % 103 % 103 % 100 % Economically Most Favorable Layouts of Surge Arresters

Japan’s 1100 kV Project (3) Lightning overvoltage at severe and normal substation condition Overvoltage distribution I, II, III: severe circuit condition IV: normal circuit condition Transformer GIS Severe condition 1896 kV 2208 kV Normal condition 1850 kV 2047 kV

Maximum switching overvoltage Japan’s 1100 kV Project (4) SIWV for substation equipment From the system requirements, Transformer GIS Maximum switching overvoltage 1309 kV (1.46 p.u.) 1400 kV (1.56 p.u.) Frequent overvoltage 1250 kV (1.39 p.u.) SIWV 1425 kV 1550 kV * * Atmospheric correction of attitude 1000m (1.06) is considered.

Japan’s 1100 kV Project (5) Power Frequency Test Voltage for Substation Equipment It is a combination of “the short-duration section to confirm dielectric strength against temporary overvoltage” and “the long-duration section to confirm long-term dielectric strength against operating voltage”, based on the systematically accumulated data. 1.5 p.u.  1h + 3 p.u.  5min + 1.5 p.u.  1h

China’s 1100 kV Project (1) Switching overvoltage design level of transmission line Switching Overvoltages are effectively reduced to 1.7pu by the application of closing resistor (600) and high performance surge arrester at substation.

Maximum lighting overvoltage China’s 1100 kV Project (2) LIWV with the consideration of safety factor LIWV  Maximum lightning overvoltage  Safety factor (1.15 for internal insulation) Transformer Other equipment Maximum lighting overvoltage 1796 kV 2040 kV Safety factor 1.15 LIWV 2250 kV 2400 kV

(Residual voltage of 2kA) China’s 1100 kV Project (3) SIWV with the consideration of SPIL SIWV  SPIL (V2kA)  Safety factor (1.15) Transformer Other equipment SPIL (Residual voltage of 2kA) 1460 kV Safety factor 1.15 SIWV 1800 kV

Future Plan by CIGRE C4.306

CIGRE New WG C4. 306 (1) Title of WG: “Insulation coordination for UHV AC systems” Recent practice of UHV insulation coordination Collaboration with A3.22 and B3.22 CDV(28/195/CDV) for amendment for 60071-1 Study items 1. Recent practice on insulation coordination for UHV system Insulation coordination throughout substation and transmission line Reduction of insulation levels by application of high performance surge arresters and other overvoltage suppression measures Continued

CIGRE New WG C4. 306 (2) Study items 2. Overvoltage in UHV range (especially focused on peculiarity to UHV AC system) Determination of stresses (TOV, switching overvoltage, lightning overvoltage and VFTO) by simulation tools and verification by measuring results TOV due to load rejection and ground fault Switching overvoltages caused by closing and opening with ground fault overvoltage Lightning overvoltage caused by back-flashover and direct lightning, VFTO stress in GIS due to disconnector switching (ref to CIGRE brochure "Monograph on GIS Very Fast Transients 1989) Continued

CIGRE New WG C4. 306 (3) Study items 3. Review on insulation coordination of air gaps in the UHV range Phase-to-phase insulation 4. Selection of insulation levels Coordination withstand voltages and safety factors for equipment Selection of insulation levels for equipment and transmission lines Proposal of recommendation for application guide IEC 60071-2 (1996) by the end of 2010

CIGRE New WG C4. 306 (4) Membership National Committee Member Name Company / University Japan Eiichi Zaima Tokyo Electric Power Company Convenor Japan Takayuki Kobayashi Tokyo Electric Power Company Secretary Japan Jun Takami Tokyo Electric Power Company Asistant Secretary Brazil Paulo Cesar Fernandez FURNAS Centrals Electricas cM Canada David Peelo DF Peelo & Associates Ltd. RM Canada Que Bui-Van Hydro Quebec TranEnergie cM China Zehong Liu State Grid Corporation of China to be invited France Alain Sabot EDF RM France Francois Gallon Areva T&D to be invited Germany Edelhard Kynast Siemens RM India Ashok Pal Powergrid RM Italy Stefano Malgarotti CESI RM Japan Tokio Yamagiwa Japan AE Power System RM Korea Eungbo Shim Korea Electric Power Company RM Russia Andrey Lokhanin Electrotechnical Research Institute to be invited South Africa Asiff Amod ESKOM to be invited Switzerland Urs Krusi ABB Switzerland RM Switzerland Bernhard Richter ABB Switzerland cM, A3.17 Convenor The United States Albert J. F. Keri American Electric Power RM Japan Hiroki Ito Mitsubishi Electric RM, A3.22 Convenor Japan Takeshi Yokota Toshiba Corporation RM, B3.22 Convenor RM=regular Member, cM=corresponding Member

Conclusion

Conclusion Sophisticated insulation coordination is necessary for UHV system and should be technical-economically optimized throughout the UHV transmission line and substation. Reasonable insulation levels have been specified on the effective reduction of lightning and switching overvoltages by the application of high performance surge arresters and other measures, such as closing and/or opening resistors.. A new CIGRE WG C4.306 “Insulation coordination for UHV AC system” will review and discuss the recent practice of UHV insulation coordination based on the approved CDV (28/195/CDV) and will investigate the safety factor. Finally, the WG will propose the recommendation for 60071-2 “Application Guide”.

Thank you !