Dynamical simulation of a Vacuum Switch with PSCAD

The switching behavior of vacuum switches (VS) is different to that of other circuit breakers. There are several effects which have to be taken into account, for example the current chopping, the dielectric strength of vacuum gap, the arc voltage, the quenching capability of high frequency currents, virtual current chopping and prestrikes. In some earlier investigations the characteristics of vacuum circuit breakers had been simulated in different ways by taking into account some of the effects mentioned above. There are mainly two different approaches for modeling vacuum circuit breaker: The first is to use an ideal circuit breaker which is switched on/off after different criteria have been checked. The second is to use a variable resistor whose value is changed continuously. The VS model discussed in this paper is modeled with PSCAD and takes into account chopping current, dielectric strength of vacuum gap, arc voltage and quenching capability. It is represented by a variable resistance and is used to simulate frequently switching of inductances and capacitances. The stress of VS is investigated and the energy conversion in the vacuum tube: As the current through a VS is flowing from moment of contact separation until next zero crossing, together with arc voltage, the energy conversion is very high, dependent on the moment of contact separation.