Page 329 - Solutions Manual to accompany Electric Machinery Fundamentals

S1-10. A series-capacitor forced commutation chopper circuit supplying a purely resistive load is shown in
Figure S1-5.
V DC  120 V R  20 k
I  8 mA R LOAD  250 
H
V BO  200 V C  150 
F
(a) When SCR is turned on, how long will it remain on? What causes it to turn off?
1
(b) When SCR turns off, how long will it be until the SCR can be turned on again? (Assume that three
1
time constants must pass before the capacitor is discharged.)
(c) What problem or problems do these calculations reveal about this simple series-capacitor forced
commutation chopper circuit?
(d) How can the problem(s) described in part (c) be eliminated?

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