By the end of 2004, the State Grid Corporation had a total of 157,858 isolators operating at voltage levels ranging from 72.5kV to 550kV. Among these, there were 3,235 units at 550kV, 1,276 at 363kV, 40,191 at 252kV, 96,146 at 126kV, and 17,010 at 72.5kV. The majority of the installed isolators were at 126kV and 252kV levels.
Domestic isolator models include GW4, GW5, GW6, GW7, GW10, GW11, GW16, and GW17, among others. On the other hand, imported and joint-venture products are mainly represented by models such as PR, KR, CR, and DR from Hangzhou Siemens; SPO/SPOL, SPV/SPVL, S3CD, and S2DA from Areva (formerly Alstom); and SSP, SP, OH, and SRT from EG1C (formerly MG) in France.
In the centralized bidding process of the State Grid Corporation, six major domestic manufacturers—XK, PGC, SHG, CZG, TKG, and RGH—were actively involved. According to the 2005 annual review of the high-voltage switch industry, the national production of isolators rated from 72.5kV to 550kV reached 28,640 sets in 2004. Of this total, the six manufacturers accounted for 22,380 sets, representing 78.1% of the overall production. Specifically, they produced 100% of the 550kV and 363kV isolators, 90.3% of the 252kV ones, 75.1% of the 126kV units, and 57.5% of the 72.5kV models. All six manufacturers provided improved products in the 2005 bidding.
In the State Grid’s large-scale procurement, isolators at 252kV to 550kV are categorized into single-column, double-column, and triple-column types, and structurally include single-column single-arm telescopic, single-column double-arm vertical telescopic, double-column horizontal telescopic, double-column horizontal middle-opening, and triple-column two-break horizontal opening configurations.
According to a survey conducted by the High-Voltage Switch Research Institute of the China Electric Power Research Institute, isolators commissioned before 2004 had poor operational performance, with common issues including porcelain insulator fractures, operation failures, overheating in the conductive circuit, and corrosion. Although the newly commissioned improved isolators in 2004 performed well, some unresolved problems still existed. In comparison, imported and joint-venture isolators demonstrated higher manufacturing quality and operational reliability than their domestic counterparts.
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