Type testing of the GTO valves for a novel STATCOM convertor

A relocatable static VAr compensator (SVC), rated 0 to +225 MVAr at 400 kV, has been supplied to the National Grid Company (NGC) for its East Claydon substation in Buckinghamshire, England. The SVC comprises a fixed filter of 23 MVAr, a conventional TSC of 127 MVAr and a GTO-based STATCOM of 75 MVAr. All are connected, to a LV bus, at nominally 15.1 kV, fed via, the secondary winding of the compensator transformer. The STATCOM is a voltage-sourced convertor (VSC), using the novel chain-circuit topology. In this, a valve comprises a number of individually switched, series-connected, single-phase bridges (links), each link having its own DC capacitor. For East Claydon, there are 16 links in series per phase, each link incorporating four 4.5 kV gate turn-off thyristors (GTOs), having 3000 A turn-off capability. In the absence of any directly applicable international testing standards for VSC valves, the testing was based on an adaptation of available test guidelines for related conventional SVC valves. This paper describes the tests which fall into two main categories: operational tests and dielectric tests.