1
GATE EE 2000
+1
-0.3
A thyristorised three phase fully controlled converter feeds a $$dc$$ load that draws a constant current. Then the input $$ac$$ line current to the converter has
A
An $$r.m.s$$ value equal to the $$dc$$ load current
B
An average value equal to the $$dc$$ load current
C
A peak value equal to the $$dc$$ load current
D
A fundamental frequency component, whose $$r.m.s$$ value is equal to the $$dc$$ load current
2
GATE EE 2000
+2
-0.6
A step down chopper operates from a $$dc$$ voltage source $${V_s}$$ feeds a $$dc$$ motor armature with a back $$e.m.f$$ $$\,\,{E_b}.$$ From oscilloscope traces, it is found that the current increases for time $${t_r}$$ falls to zero over time $${t_f},$$ and remains zero for time $${t_0}$$ in every chopping cycle, then the average $$dc$$ voltage across the freewheeling diode is
A
$${{{V_s}\,{t_r}} \over {\left( {{t_r} + {t_f} + {t_0}} \right)}}$$
B
$${{\left( {{V_s}\,{t_r} + {E_b}\,{t_f}} \right)} \over {\left( {{t_r} + {t_f} + {t_0}} \right)}}$$
C
$${{\left( {{V_s}\,{t_r} + {E_b}\,{t_0}} \right)} \over {\left( {{t_r} + {t_f} + {t_0}} \right)}}$$
D
$${{{V_s}\,{t_r} + {E_b}\left[ {{t_f} + {t_0}} \right]} \over {\left( {{t_r} + {t_f} + {t_0}} \right)}}$$
3
GATE EE 2000
Subjective
+5
-0
A $$dc$$ motor with armature resistance $${R_a}$$ is fed from a step down chopper in the continuous mode, and operates at some known speed and known excitation current. The motor current rises from $${I_{\min }}\,\,$$ to $${I_{\max }}\,\,$$ in the $${T_{on}}$$ period Ton of the chopper; and drops from $${I_{\max }}\,\,$$ to $${I_{\min }}\,\,$$ in the $${T_{off}}$$ period Toff of the same circuit. Both the rise and fall of the current may be assumed to be approximately linear. What is the average power loss in the machine armature?
4
GATE EE 2000
MCQ (More than One Correct Answer)
+1
-0.3
Triangular $$PWM$$ control, when applied to a $$BJT$$ based three phase voltage source inverter, introduces.
A
low order harmonic voltages on the $$dc$$ side.
B
very high order harmonic voltage on the $$dc$$ side
C
low order harmonic voltage on the $$ac$$ side
D
very high order harmonic voltage on the $$ac$$ side
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