1. International Symposium on Standards for UHV Transmission 1 3.1 System Impacts on UHV Substation Equipment On behalf of CIGRE WG A3.22 29-30 January 2009, New Delhi, India Hiroki Ito Mitsubishi Electric Covenor, CIGRE WG A3.22 Scope: Review the state-of-the-art of project specific and national technical specifications for all substation equipment within the scope of CIGRE Study Committee A3 at voltages exceeding 800 kV. Recommend future specifications and standardizations of 1100 kV and 1200 kV equipment and provide technical backgrounds on the collected information to IEC TC17.

2. Publications of CIGRE WG A3.22 2007 Technical paper presented at IEC-CIGRE UHV symposium in Beijing 2-4-1 “Technical requirements for UHV substation equipments” 2008 First Technical Brochure submitted to CIGRE CO in February & published in December TB 362 “Technical requirements for substation equipments exceeding 800 kV” CIGRE Session paper presented at 2008 CIGRE session in Paris A3-211 “Technical requirements for UHV substation equipments” Recommendations submitted to IEC TC17 in November “Summary of technical backgrounds of UHV equipment specifications” 2009 Technical paper presented at IEC-CIGRE UHV symposium in New Delhi 3-1 “System impacts on UHV substation equipment” 4-1 “CIGRE state of the art & prospects for equipment” Second Technical Brochure will be submitted to A3 chairman in March “Background of technical specifications of substation equipment exceeding 800 kV” 2

3. 3 Specific issues for UHV AC systems The applications of multi sub-conductor bundles with large diameter as well as large capacity transformers affect the technical requirements for UHV substation equipment, those will not be simply extrapolated from the existing standards up to 800 kV.

4. Chapter 2: System requirements 2.1 Insulation levels (LIWV / SIWV) 2.2 Temporary Overvoltage (TOV) 2.3 Secondary arc extinction 2.4 Out-of-phase 2.5 DC time constant 2.6 MOSA impacts on equipment Chapter 3: Equipment requirements (GCB) 3.1 Terminal faults 3.2 Transformer limited faults 3.3 Long-line faults 3.4 Short-line faults 3.5 Capacitive current switching 3.6 Requirements for auxiliary equipment of CB 4 Scope of CIGRE WG A3.22 (Contents of second Technical Brochure) Chapter 4: System requirements (DS,ES) 4.1 Capacitive current switching by DS 4.2 Bus-transfer switching by DS 4.3 Requirements for resistor-fitted DS 4.4 Induced current switching by ES Chapter 5: Equipment requirements (MOSA) Chapter 6: Equipment requirements (VT,CT) Chapter 7: Factory &Lab. Testing experience Chapter 8: Field testing experience WG A3.22 will provide the scientific backgrounds on the collected technical specifications to IEC TC17 based on precise predictions with digital simulation techniques

5. LIWV>1.25 x LIPL, providing LIPL with the residual voltage of MOSA at 20 kA. LIWV requirements for transformers in Italy, Russia, India and China are comparable. LIWV requirements for other equipment are fairly close. Japan studies the insulation levels in UHV systems using the EMTP analysis with a lightning current of 200kA-1  s/70  s WG A3.22 is investigating a limited survey on utilities’ policies on the insulation level. 5 Insulation level: LIWV and LIPL

6. SIWV>1.07 x SIPL, providing SIPL with the residual voltage of MOSA at 2 kA. SIWV requirements for 1200 kV in Russia and India have the same values. SIWV requirements for 1100 kV in China and Japan are slightly different. The applications of new technologies such as MOSA with higher performance, CB with opening/closing resistors, DS with switching resistor can effectively suppress the switching surges, which is a predominant factor to reduce the construction cost of UHV transmission. 6 Insulation level: SIWV and SIPL

7. WG A3.22 will investigate how the secondary arc current can be effectively extinguished in UHV systems with double circuits and also provide advantages and disadvantages for HSGS and Four legged shunt reactor more in depth. Secondary Arc Extinction 7 Secondary arc can be extinguished less than one second if the current does not exceed 60 A. 4-legged shunt reactor can reduce the secondary arc current by a half.

8. Surveys on DC time constants in fault currents Tower and conductor designs Calculations predict a large DC time constants in fault current in UHV transmission systems due to usage of multi sub-conductor bundles and the existence of large capacity power transformers. Influences of the high DC component on test-duty T100a does not show any significant difference when the constant exceeds around 120ms. Therefore, it is recommended to use a special case time constant of 120 ms for rated voltages higher than 800 kV. 8

9. Further investigations: WG A3.22 will try to provide scientific explanations for these proposals. Verification of MOSA clipping level and comparison with the analytical TRV Long-term reliability of high-performance MOSA 9 MOSA clipping levels on TRV Proposals and recommendations from A3.22 members 1) 1460 kV (1.63 p.u.) for the SIPL value of 1100 kV MOSA 2) 1526 kV (1.70 p.u.) based on the maximum switching surge level of 1100kV system 3) 1615 kV (1.80 p.u.) provided with 10% margin to the SIPL level 4) 1715 kV (1.91 p.u.) considered with additional 10% design margin

10. Bus-charging current switching by DS The length of the busbar in the Jindognan substation (China pilot) is 96.2 m at the first stage, which corresponds to 4200pF of load side capacitance and provides the bus-charging current of 0.84 A. The substation is planned to be expanded with the busbar up to 420 m at maximum in the future, which corresponds to 19300pF of load side capacitance and provides the bus-charging current of 3.9 A. 10

11. Bus-transfer current switching by DS The existing IEC standard recommended 80-100 % of the rated normal currents. However, the value was introduced in 1980’s when the maximum rated normal current was 2000 A. According to the WG survey, the value of 80% stipulated in the existing IEC standard seems to be rather conservative and the value of 60 % could be more realistic. Since the maximum rated current is now increased up to 3150A and 4000A in the EHV systems and 8000 A in the UHV system, the bus-transfer current should be revised by reflecting the rated current specified for the UHV systems. 11

12. Induced current switching by ES Induced current interruptions duty can be easily evaluated with configurations of transmission line, line length and rated current. Requirements for UHV ES is expected to exceed the extrapolation of the existing standards. Japanese UHV systems Maximum Line length: 200km, Rated current: 8000A, Double circuit transmission line - Electromagnetic coupling : 810A-65k,162V/  s - Electrostatic coupling : 31.8A-45.4kV 12

13. IEC SC17A requests for CIGRE on UHV standardizations IEC TC17 requested CIGRE WG A3.22 to investigate the technical backgrounds of UHV substation equipment in accordance with the following IEC standards. WG A3.22 will continuously provide technical backgrounds to support the standardization works within IEC TC17. IEC 62271-1 Ed.1.0, HV Switchgear & Controlgear-Part 1: Common specifications IEC 62271-100 Ed.2.0, HV Switchgear & Controlgear-Part 100: Circuit Breaker IEC 62271-101 Ed.1.0, HV Switchgear & Controlgear-Part 101: Sythetic testing IEC 62271-102 Ed.1.0, HV Switchgear & Controlgear-Part 102: A.C. DS and ES IEC 62271-110 Ed.1.0, HV Switchgear & Controlgear-Part 110: Inductive load switching Application Guide to IEC 62271-100 and IEC 62271-1: Opening resistor New project : High-Speed Grounding Switches 13

14. Summary and Considerations Insulation levels Suppressing switching overvoltage as much as possible is a predominant factor to reduce the height of transmission towers and the dimension of open-air parts in substations. Such technologies as MOSA with higher performance, CB with opening/closing resistors, DS with switching resistor can effectively suppress the switching surges less than 1.6pu for substation equipment and 1.7pu for OH-lines. Secondary arc 4-legged shunt reactor can reduce the secondary arc current by a half. Secondary arc can be extinguished less than 1 sec. if the current does not exceed 60 A. First-pole-to-clear factor (FPCF) Use of a large capacity power transformer reduces FPCF (1.1 for Japan, 1.2 for India) DC time constant / Line surge impedance Multi sub-conductors bundles with large diameter can increase the time constants (150 ms for Japan, 120 ms for China) and reduce the line surge impedance around 350 ohm. TRV MOSAs reduce the TRV peaks for terminal faults below the SIPL for in UHV systems. TRV for TLF appears severe RRRV only in a special case. 14 29-30 January 2009, New Delhi, India