Static DC Circuit Breaker
Q. With neat diagram describe the working of static D.C. circuit breaker.
Circuit diagram of Static DC Circuit Breaker :
- The circuit configuration of a static DC circuit breaker is shown in Figure.
Operation of Static DC Circuit Breaker :
- As soon as the start push button is pressed, a gate triggering pulse is applied to SCR1 through R1 and SCR1 starts conducting to supply power to load.
- The capacitor will charge through R1 and SCR1 quickly with a polarity as shown in Figure.
- If we want to turn off the power delivered to the load, then the stop button is pressed momentarily. This will supply a gate current pulse to SCR2 through R2 and SCR2 will be turned on.
- As soon as SCR2 is turned on the voltage across C is applied across SCR1 to turn it off due to voltage commutation.
- Now the load current flows through load, C and SCR2 to charge C with its left plate positive.
- As soon as C charges fully to supply voltage VS the load current reduces to zero. The current through R4 and SCR2 is less than the holding current of SCR2. So SCR2 is turned off due to natural commutation.
- Thus by pressing the stop button, we can turn off the power delivered to load.
Overload Condition of Static DC Circuit Breaker :
- When there is an overload condition, the circuit of Figure can interrupt the operation automatically.
- Let SCR1 be on and carrying the load current. If the load current increases beyond a certain limit, then the voltage across R2 increases to such a value that it can forward bias the diodes D1, D2, D3, D4. as well as the gate-cathode junction of SCR , This will turn on SCR2.
- As soon as SCR2 is turned on it will turn off SCR2 immediately due to voltage commutation as explained earlier.
- Thus the load can be protected automatically under the overload condition.