3 March 2018

Compare Natural Commutation and Forced Commutation

Natural commutation

  •  It is also called as Phase commutation, line commutation or AC commutation.
  •  The natural commutation is only possible in the AC circuit. 
  • No extra circuit is necessary in order to turn off the SCR. 
  • The SCR turns off automatically during negative half cycle of alternating supply when reverse voltage applied across SCR for sufficient time. 
  • The time period of the negative half cycle should be more than the turn off time of the SCR. 
  • There is no power loss in the circuit because no commutation circuit. 
  • Class F is example of natural commutation.

Forced commutation 

  • It is possible only in the DC circuit. 
  • As there is no natural zero current in the DC circuit, extra commutation circuit ( which include L and C ) requires in order to turn off the SCR. 
  • The forced commutation may be voltage commutation or current commutation.
  • Class A, Class B, Class C, Class D and Class E are example of forced commutation. 
  • Some power loss takes place in the commutation circuit.
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