1
GATE EE 2008
MCQ (Single Correct Answer)
+1
-0.3
In a stepper motor, the detent torque means
A
minimum of the static torque with phase winding excited.
B
maximum of the static torque with phase winding excited.
C
minimum of the static torque with phase winding unexcited
D
maximum of the static torque with the phase winding unexcited
2
GATE EE 2008
MCQ (Single Correct Answer)
+2
-0.6
A $$400$$ $$V,$$ $$50$$ $$Hz,$$ $$30$$ $$hp,$$ three-phase induction motor is drawing $$50$$ A current at $$0.8$$ power factor lagging. The stator and rotor copper losses are $$1.5kW$$ and $$900$$ $$W$$ respectively. The friction and windage losses are $$1050$$ $$W$$ and the core losses are $$1200$$ $$W.$$ The air-gap power of the motor will be
A
$$23.06$$ $$kW$$
B
$$24.11$$ $$kW$$
C
$$25.01$$ $$kW$$
D
$$26.21$$ $$kW$$
3
GATE EE 2008
MCQ (Single Correct Answer)
+2
-0.6
A $$400$$ $$V,$$ $$50$$ $$Hz$$, $$4$$ pole, $$1400$$ $$rpm$$, star connected squirrel cage induction motor has the following parameters referred to the stator:
$$R = 1.0\,\Omega ,{X_s} = X{'_r} = 1.5\,\Omega $$ Neglect stator resistance and core and rotational losses of the motor. The motor is controlled from a $$3$$-phase voltage source inverter with constant $$V/f$$ control. The stator line-to-line voltage $$(rms)$$ and frequency to obtain the maximum torque at starting will be:
A
$$20.6\,V,\,\,2.7\,Hz$$
B
$$133.3\,V,\,\,16.7\,Hz$$
C
$$266.6\,V,\,\,33.3\,Hz$$
D
$$323.3\,V,\,\,40.3\,Hz$$
4
GATE EE 2008
MCQ (Single Correct Answer)
+2
-0.6
A synchronous motor is connected to an infinite bus at $$1.0p.u$$ voltage and draws $$0.6$$ $$pu$$ at unity power factor. Its synchronous reactance is $$1.0$$ $$pu$$ and resistance is negligible.

Keeping the excitation voltage same, the load on the motor is increased such that the motor current increases by $$20\% $$. The operating power factor will become

A
$$0.995$$ lagging
B
$$0.995$$ leading
C
$$0.791$$ lagging
D
$$0.848$$ leading