Class F Commutation ( Line commutation or AC commutation )

Class F commutation

The class F commutation is also called as line or natural commutation because the SCR is turned off automatically during negative cycle of alternating supply. There are no commutating components used in this method therefore it is not called as forced commutation method.

Power circuit diagram of class F commutation

Working of class F commutation

The SCR is turned on during positive half cycle of alternating supply. The SCR is turned off during negative half cycle of alternating supply. The time duration for the negative half cycle must be greater than the SCR specific turned off time as per data sheet. Figure A shows the circuit for the Class F commutation. This method is applicable only for alternating supply. 

Waveform of class F commutation

Applications of class F commutation

This method is used in the line commutation of rectifiers, inverters and cyclo – converters.

CLASS F COMMUTATION DRAWING AND WAVEFORMS.PDF

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