Impact of Midpoint STATCOM on Generator Loss of Excitation Protection

This paper explores the impact of a transmission-line midpoint STATCOM on the performance of the generator loss-of-excitation (LOE) protection. In this context, investigations are conducted on a two-hydrogenerator power station for two LOE contingencies, namely, a complete LOE due to a field-winding short circuit and a partial LOE due to a sudden drop in the excitation voltage at different generator loadings. The results of these investigations show that the midpoint STATCOM has adverse impacts on the LOE distance relay in the form of delay time and/or underreach phenomenon. These adverse impacts vary with the generator loading and the LOE mode. The time-domain simulation studies are conducted using PSCAD/EMTDC software.