Fault current due to asynchronous connection of the generator to the grid and impact on HV circuit breaker with gas SF6

Abstract

The description and analysis of phenomena that occur in case of disconnection of fault currents with generator circuit breakers after asynchronous connection of a generator and difficulties encountered during the process of disconnection are given in the paper. Generally, the biggest problems occur during the interruption of the fault when the direct current component (DC) is very high. DC component value depends on the type and conditions of the fault. For this purpose, a real study case with accidental asynchronous connection of generator via 400 kV circuit breaker is given from the Kosovo Power System which seriously damages the circuit breaker. For the purposes of this analysis, the real case situation has been also modelled with software such as: EMTP/ATP and PSS/E. It is important to emphasize that during using the high speed AC circuit breaker in power system it is not always the advantage to make successful disconnection of failures through High Voltage Circuit Breaker due to the presence of the high value DC component and the delay of passing of AC current through zero. For the generator the most important is detail analysis of behaviour of the generator in network in order to specify proper circuit breaker that can cover all circumstances that can happen in the system so to be able to protect the generator, step up transformer and other equipment.

Keywords

• AC component
• asynchronous connection
• DC component of fault current
• high voltage generator circuit breaker
• short circuit