1. 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, January 2009, New Delhi

2. 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)

3. Recent Practice of Insulation Coordination for UHV AC Transmission System

4. 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)

5. Overvoltages specific to UHV System (1)
[TOV]
Load rejection at a heavily loaded long line of UHV system produces TOV whose amplitude is 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.

6. 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

7. 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.

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

9. Standard Withstand Voltage for UHV Substation Equipment

10. LIWV and SIWV for UHV Substation Equipment
Approved CDV(28/195/CDV) for amendment for IEC
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 edition 6.2/ , 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 under the responsibility of TC 8.

11. Procedure of Insulation Coordination
Flowchart for insulation coordination in IEC
Insulation coordination
Safety factor
Standardization

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

13. 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 pu by the application of closing/opening resistor (700) and high performance surge arrester at substation.
Tower Height:
143m  110m
Switching Overvoltage:
2pu  pu

14. 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

15. 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

16. 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.

17. 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 p.u.  1h

18. 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.

19. 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

20. (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

21. Future Plan by CIGRE C4.306

22. CIGRE New WG C (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
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

23. 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

24. 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 (1996) by the end of 2010

25. 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

26. Conclusion

27. 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 C “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 “Application Guide”.

28. Thank you !