Power PE 56

[yaoyaodes]

The answer is A, not really understanding why. Can someone help?

 

[akyip]

This is the question about the SCR/thyristor, right? So basically, a couple of fundamentals about the SCR/thyristor:

-They act similarly to a diode (current flows only in one direction), BUT they do not conduct until there is a voltage or current pulsed on the SCR's or thyristor's gate terminal.
-Once the SCR or thyristor conducts, it will continue to conduct current until the voltage/current between the cathode and anode reaches zero.
-After the SCR or thyristor stops conducting, it will need a current on the gate signal to start conducting again.

 

[akyip]

So in this problem, the gate current signal first appears at alpha. The thyristor therefore first conducts anode current at alpha. Anode current is zero before alpha, but then it follows a sine wave curve until the anode current hits zero again at pi. The thyristor only conducts anode current when it is forward-biased, which is from zero to pi. It does not conduct any anode current when it is reverse-biased, which is from pi to 2 x pi.

 

[yaoyaodes]

Thanks for the explanation. That's really helpful.