1
GATE EE 2014 Set 2
+1
-0.3
In a constant V/f control of induction motor, the ratio V/f is maintained constant from 0 to base frequency, where V is the voltage applied to the motor at fundamental frequency f. Which of the following statements relating to low frequency operation of the motor is TRUE?
A
At low frequency, the stator flux increases from its rated value.
B
At low frequency, the stator flux decreases from its rated value.
C
At low frequency, the motor saturates.
D
At low frequency, the stator flux remains unchanged at its rated value.
2
GATE EE 2014 Set 2
+1
-0.3
A three-phase, 4-pole, self excited induction generator is feeding power to a load at a frequency $$f_1$$. If the load is partially removed, the frequency becomes $$f_2$$. If the speed of the generator is maintained at 1500 rpm in both the cases, then
A
$$f_1,f_2$$ > 50Hz and $$f_1$$ > $$f_2$$
B
$$f_1$$ < 50Hz and $$f_2$$ > 50Hz
C
$$f_1,f_2$$ < 50Hz and $$f_2$$ > $$f_1$$
D
$$f_1$$ > 50Hz and $$f_2$$ < 50Hz
3
GATE EE 2014 Set 2
+2
-0.6
A three-phase slip-ring induction motor, provided with a commutator winding, is shown in the figure. The motor rotates in clockwise direction when the rotor windings are closed. If the rotor winding is open circuited and the system is made to run at rotational speed fr with the help of prime-mover in anti-clockwise direction, then the frequency of voltage across slip rings is f1 and frequency of voltage across commutator brushes is f2. The values of f1 and f2 respectively are
A
f + fr and f
B
f - fr and f
C
f - fr and f + fr
D
f + fr and f - fr
4
GATE EE 2014 Set 2
+2
-0.6
A $$20$$-pole alternator is having $$180$$ identical stator slots with $$6$$ conductors in each slot. All the coils of a phase are in series. If the coils are connected to realize single-phase winding, the generated voltage is $${V_1}.$$ If the coils are reconnected to realize three-phase star-connected winding, the generated phase voltage is $${V_ 2}.$$ Assuming full pitch, single-layer winding, the ratio $${V_1}/{V_2}$$ is
A
$${1 \over {\sqrt 3 }}$$
B
$${1 \over 2}$$
C
$${\sqrt 3 }$$
D
$$2$$
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