Quiz: Electrical Engineering

Exam: UPSSSC JE

Topic: Miscellaneous

Each question carries 1 mark.

Negative marking: 1/4 mark

Time: 10 Minute

Q1. In an induction motor, the torque T is related to the supply voltage V as

(a) T α V

(b) T α V²

(c) T α√V

(d) T α 1/V

Q2. As load angle is increased, degree of stability __________

a) reduces

b) increases

c) remains same

d) no change in stability

Q3. Synchronizing power is

a) transient in nature

b) steady state in nature

c) pulsating at small frequencies

d) constant for a machine

Q4. Which of the following is/are used in synchronous machines to maintain mechanical stability?

a) Damper winding

b) Interpole winding

c) Compensating winding

d) Equalizer rings

Q5. For a 4-pole 3 phase, 400V alternator has synchronizing power of 300 units. Then the synchronizing power per mechanical degree is

a) 300

b) 1200

c) 900

d) 600

Q6. The operation of a synchronous motor operating on constant excitation across infinite bus will not be stable if power angle δ

a) is less than θ

b) exceeds internal angle θ

c) is more than θ/2

d) is less than θ/2

Q7. Variation in the dc excitation of a synchronous motor causes variation in

a) speed

b) power factor

c) armature current

d) armature current and power factor

Q8. Which motor can conveniently operate at lagging as well as leading power factor?

a) Squirrel cage induction motor

b) Slip ring induction motor

c) Synchronous motor

d) Stepper motor

Q9. In a rotating electrical machine with 2 poles on the stator and 4 poles on the rotor, spaced equally, the net electromagnetic torque developed is ____________

a) maximum

b) zero or no torque is developed

c) minimum

d) none of the mentioned

Q10. The basic torque and EMF expression of rotating electrical machines are ____________

a) applicable to DC machines only

b) applicable to AC machines only

c) applicable to both AC and DC machines

d) none of the mentioned

Solution

Sol 1. (b)

Relation between torque and supply voltage of an induction motor

T α V²

Sol 2. (a)

Synchronizing power = EV×cosδ/X.

Sol 3. (a)

It is transient in nature and determines the stability while disturbances.

Sol 4. (a)

Damper windings are the dummy windings which help to stabilize the machine during transient instability.

Sol 5. (a)

P(sy,mech) = Poles* P(sy,ele)/2

P(sy,ele)=300 units.

Sol 6. (b)

Power angle should not exceed θ, to operate under normal conditions.

Sol 7. (d)

Armature current and power factor both will vary by varying the dc excitation.

Sol 8. (c)

It’s the synchronous motor which can favorably operate both at leading and lagging power factor.

Sol 9. (b)

In a machine with 2 stator poles and 4 rotor poles spaced equally, the force of attraction will be cancelled due to the force of repulsion, and hence the net electromagnetic torque will be zero.

Sol 10. (c)

Basic torque and EMF expressions are same for both AC and DC machines as the fundamental principles underlying the operation of AC and DC machines are same.