CAPACITIVE SWITCHING OF VACUUM CIRCUIT BREAKERS

Suswar Ganu
Jayesh Easwaramony
Milind Diwanji
Sachin Joshi
Mayuresh Deorukhkar
(BE - Electrical - VJTI)

On the medium voltage level, Vacuum Circuit Breakers (VCB’ s) offer several advantages such as repeated operating duty, long life, on load switching duties and almost maintenance free operation. They are compact, self-contained and totally pollution free.

On the other hand, capacitor banks, which are used for reactive power control in a power system, present a difficult switching duty for the vacuum circuit breakers. The problem of ‘re-strikes’ and ‘re-ignition’ while opening capacitor banks and that of ‘pre-arcing’ while closing of capacitor banks has to be dealt with.

The synopsis is structured into two sections viz.

1. SWITCHING TRANSIENTS:

This section deals with the phenomena of switching operations in ideal R-C and R-L-C circuits with analysis of making and breaking process in a circuit breaker. The best instants for switching off and on respectively are determined for these ideal circuits.

2. VACUUM CIRCUIT BREAKER & RELATED PHENOMENON:

This section deals with the properties of vacuum, the factors affecting the dielectric strength of the vacuum gap and the various breakdown hypotheses explaining the breakdown in the vacuum gap.

It also deals with the construction of vacuum interrupter and the various types of contacts. The physics behind the formation of vacuum arc is explained by the different types of arc modes while the effect of magnetic field on current interruption and recovery process is also discussed. We attempt to find a solution to the problem of capacitive switching of VCB’ s using pre-defined models and try to analyze the effect of the above on the Vacuum Circuit Breaker.