28 March 2017

Static DC Circuit Breaker

  • The basic circuit for DC circuit breaker is shown in the figure A. 
  • 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. 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.
  • 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 charge 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.


static dc circuit breaker

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