Page 338 - Solutions Manual to accompany Electric Machinery Fundamentals

It reaches a voltage of 40 V at a time of 4.8 ms. Since the frequency of the waveform is 60 Hz, the
waveform there are 360 in 1/60 s, and the firing angle  is
 360 
   4.8 ms   1/60 s   103.7 or 1.810 radians

Note: This problem could also have been solved using Laplace Transforms, if desired.
(b) The rms voltage applied to the load is

/

2
V rms  1  v () t 2 dt    V M 2 sin  dt
t
T  
V M  2 1 1   /
V rms    t   sin2 t    
4
2

V 2 1 1 
M
V rms         4   2  sin 2  sin  
 2
Since  = 1.180 radians, the rms voltage is

V rms  V M 0.1753  0.419 V  M 71.0 V

S1-14. Figure S1-9 shows a three-phase full-wave rectifier circuit supplying power to a dc load. The circuit uses
SCRs instead of diodes as the rectifying elements.
(a) What will the load voltage and ripple be if each SCR is triggered as soon as it becomes forward
biased? At what phase angle should the SCRs be triggered in order to operate this way? Sketch or
plot the output voltage for this case.

(b) What will the rms load voltage and ripple be if each SCR is triggered at a phase angle of 90 (that is,
half way through the half-cycle in which it is forward biased)? Sketch or plot the output voltage for
this case.

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