Electrical Engineering Mcqs

A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because

(A) speed of the motor is reduced
(B) power factor is decreased
(C) Eb (back e.m.f.) becomes less than V (applied voltage)
(D) Er (net resultant voltage) in armature is increased
(E) none of the above

Submitted By :Ali Uppal

If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor

(A) will become more
(B) will become less
(C) will remain unchanged
(D) none of the abov

Submitted By :Ali Uppal

Stability of a synchronous machine:

(A) decreases with increase in its excitation
(B) increases with increase in its excitation
(C) remains unaffected with increase in excitation
(D) any of the above

Submitted By :Ali Uppal

If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to____________?

(A) increase in both armature current and power factor angle
(B) increase in back e.m.f. but decrease in armature current
(C) increase in both armature current and power factor which is lagging
(D) increase in torque angle but decrease in back
(E) m.f.

Submitted By :Ali Uppal

While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by_____________?

(A) induction motor torque in field winding
(B) induction motor torque in damper winding
(C) eddy current and hysteresis torque in pole faces
(D) reHetance motor torque due to saliency of the rotor
(E) all of the above methods

Submitted By :Ali Uppal

A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will___________?

(A) remain same
(B) go down
(C) improve
(D) none of the above

Submitted By :Ali Uppal

Power factor of a synchronous motor is unity when_____________?

(A) the armature current is maximum
(B) the armature current is minimum
(C) the armature current is zero
(D) none of the above

Submitted By :Ali Uppal

In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be____________?

(A) 3000 r.p.m.
(B) 1500 r.p.m.
(C) 750 r.p.m.
(D) none of the above

Submitted By :Ali Uppal

In a synchronous motor, V-curves represent relation between____________?

(A) armature current and field current
(B) power factor and speed
(C) field current and speed
(D) field current and power factor

Submitted By :Ali Uppal

By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?

(A) By changing the supply frequency
(B) By interchanging any two phases
(C) By changing the applied voltage
(D) By changing the load

Submitted By :Ali Uppal

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