Power circuit of DC circuit breaker
The basic circuit for DC circuit breaker is shown in the figure A. The principal of DC circuit breaker is Class C commutation. The SCR 1 is main SCR. When it is necessary to break load current, the SCR 1 is turned off. There is no control circuit given in this figure for simplification.
Working of DC circuit breaker
SCR 1 Switched ON
When the SCR 1
is turned on, the load voltage becomes equal to supply voltage and charging
of capacitor is
done through path (+) Vdc – R1 – (+) C – C (-) – SCR 1
– Vdc (-). The polarity of capacitor charging
voltage is shown in the figure A.
SCR 2 Switched ON
When it is require breaking load
current, the SCR 2
is turned on. As soon as the SCR 2 is turned on, the SCR 1
is turned off due to reverse voltage across it. The capacitor once again charges
with reverse polarity through path (+) Vdc – LOAD – (+) C – C
(-) – SCR 2 due to turned off of the SCR 1. When voltage across capacitor reaches
up to supply voltage, the load current becomes zero resulting SCR 2 is turned
off. The current passes through load resistance R1 becomes less than
the holding
current of the SCR 2.
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