Resistance switching is normally resorted in case of-

Resistance switching is normally resorted in the Air blast Circuit breaker.

Resistance switching:

Circuit diagram for the resistance switching of circuit breaker is shown below.

• Resistance Switching in Circuit Breaker refers to a method adopted for dampening the over voltage transients due to current chopping, capacitive current breaking etc.
• In this method, a shunt resistance is connected across the contacts of circuit breaker.
• The main role of shunt resistance R is to limit the growth of re-strike voltage and cause it to grow exponentially up to recovery voltage.
• R is so selected that the circuit becomes critically damped then re-strike voltage rises exponentially till recovery voltage is reached.
• The value of R for critical damping is \(R = 0.5\sqrt {\frac{L}{C}} \)
• Resistance Switching also reduces the oscillatory growth of Re-striking Voltage

• Voltage appearing across the electrodes of circuit breaker or switching voltage \( = i\sqrt {\frac{L}{C}} \)