If resistance is deliberately connected across the circuit breaker contacts to improve the arc interruption process, then it is called resistance switching. Resistance switching is employed to decrease the peak value of restriking voltage, RRRV, and severity of transient oscillations. It is mainly used in the air blast circuit breaker, as the post-zero resistance is very high.
The connection diagram of the shunt resistance R is shown in the below figure, in which L and C are inductance and capacitance of the system up to the location of the circuit breaker.
When fault "F" occurs, the Circuit Breaker (CB) opens its contacts and an arc appears in the gap. When a resistance R is connected across the breaker contacts, a part of the current flowing through the arc will be diverted through R. So, the arc current reduces, and therefore, the rate of deionization of the arc path increases. This further increases the arc path resistance. So, more amount of current will flow through R.
This rise of current through R continues until the arc current reaches a value near zero and finally, it will not be able to maintain the arc. As the current through shunt resistance is limited by the value of R, it can be easily interrupted.
Hence, resistance switching reduces the possibilities of restriking of arc. It is due to this fact that it helps in damping the oscillatory restriking voltage as shown below.
By connecting a resistance across the circuit breaker reduces the frequency of oscillations of restriking voltage transients. It can be proved mathematically that the frequency of damped oscillation of the circuit shown above is given as,
