550 KV GAS-INSULATED TRANSMISSION LINE FOR HIGH POWER RATINGIN THAILAND

摘要

The world's first Gas Insulated Transmission Line (GIL) with N_2 and SF_6 gas mixture at a voltage level of 550 kV has been in operation in Bangkok, Thailand since January, 2002. The high current rating of 4000 A makes this GIL to one of the strongest high power transmission systems worldwide with 3800 MVA power carrying capability.The GIL is operated under severe ambient conditions with high sun radiation and high ambient temperatures, respectively. The high thermal requirements made it necessary to use accurate thermal calculations. This was facilitated with two different thermal calculation tools, using analytical and finite element methods. The results have been verified with measurements on prototypes and existing GILs in service.The Electricity Generating Authority of Thailand (EGAT) has built a gas-insulated 550 kVswitchgear in the Sai Noi substation 8 line feeders and 2 connection bays to the existing GIS.The decision was made for GIS technology in spite of AIS because land acquisition wasexpected to become difficult.The existing and the new GIS equipment are installed in the same building. The new 550 kVGIS, the existing GIS and the overhead lines are connected by GIL and by air insulatedbuses.The 2nd generation GIL design is optimised for on-site assembly which results in minimum installation times. The experiences gained with the on-site assembly, the gas handling and the high voltage testing were very positive and the works could be carried out in a shorter time frame than planned. In addition to the description of the project this article emphasises also on some physical advantages of GIL.