1. 1 Progress of, and prospects for, commercial applications of UHV 1100kV Transmission System in TEPCO 2 nd International Symposium on International Standards for Ultra High Voltage, New Delhi, January 29-30, 2009 Hiroshi OKAMOTO TEPCO

2. 2 UHV Transmission Lines in TEPCO 〈 North-South Route 〉 [1993] Minami-Nigata Line: 49km ×2cct (Total Length: 111km) (Total Length: 111km) Nishi-Gunma Line: 138km ×2cct 〈 East-West Route 〉 [1999] Minami-Iwaki Line: 194km ×2cct Higashi-Gunma Line: 44km ×2cct 〈 North-South Route 〉 [1993] Minami-Nigata Line: 49km ×2cct (Total Length: 111km) (Total Length: 111km) Nishi-Gunma Line: 138km ×2cct 〈 East-West Route 〉 [1999] Minami-Iwaki Line: 194km ×2cct Higashi-Gunma Line: 44km ×2cct

3. 3 UHV System Design Secondary arc extinction for fast reclosing, etc. Size reduction of UHV transmission tower Electric and Magnetic field, corona noise, wind noise Rationalization of insulation coordination Transmission line design Insulation design Solution for network problem peculiar to UHV system Size reduction of substation equipment Development of highly reliable equipment Substation design High Speed Grounding Switch(HSGS) MOSA, CB with resistor

4. 4 Issues to be addressed in voltage upgrade To reduce annual capital expenditure below a certain rational level, To ensure flexibility under uncertainty in the development of power plants, To reduce a risk of degradation of reliability during the construction period for upgrading, and To shorten the planned outage of transmission lines during the construction.

5. 5 Schematic diagram of UHV designed transmission lines

6. 6 Option 1 Only single circuit will be operated at 1100kV and the other circuit at 550kV in the very first stage of the upgrading.

7. 7 Studied Issues a. switching overvoltage induced in 1100kV and 550kV circuits, b. lightning overvoltage in the substations, c. short circuit phenomena between 1100kV and 550kV circuits, d. necessity of HSGS in the 550kV circuit to extinguish secondary arc current after the fault in the circuit, e. operation and maintenance considering outage of equipment, f. protection, g. TRV and h. voltage deviation due to energization and de- energization

8. 8 Option 2 Simplified bus configuration may be applied as a cost- effective solution for line U1-U5 only if the subsequent upgrade is not expected over the long term.

9. 9 Switching Overvoltage Analysis simplified bus configurationdouble-bus-bar four-bus-tie configuration U1 U5 U1 U5

10. 10 Option 3 Double T connection at U2 S/S, instead of double  connection, can reduce the installation cost.

11. 11 Concluding Remarks TEPCO is now studying the issues for upgrading the operating voltage of the constructed UHV transmission lines from 550kV to 1100kV. We will finalize technical specification of substation equipment shortly so as to be able to respond quickly and flexibly to future generation developments. In this context, standardization of the UHV technology is urgently needed.