Compressed gas circuit breaker for large generator protection - uses fault limiting resistor across main contacts and fusible link across resistor to divert high fault currents

摘要

The compressed qas circuit breaker protects large ac generators against overcurrents. The main breaker contacts have across them a series combination of a smaller circuit breaker and a low value resistance. A contactor in series with a parallel qroup of fusible links, is connected across the resistance. The fusible links and the resistance are arranged to minimise their inductance. When an overcurrent is detected, the level is discriminated and if it exceeds approximately 200kA the contactor connects the fusible link in parallel with the resistance at the same time as the main contacts are opened. As the main arc weakens the fusible link diverts some of the fault current, assisting arc extinction until the fusible link melts. As the fusible link approached failure the current is increasingly carried by the resistance which limits the fault current before it is completely eliminated by the breaker contacts in series with the resistance. The appts. has a high rupture capacity.