Quiz: Electrical Engineering 16 May 2020

Quiz: Electrical Engineering
Exam: NLC
Topic: Single phase induction motor

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. In comparison with to three phase induction motor, single phase induction motor has
a)Lower efficiency
b)Lower power factor
c)Poor speed regulation
d)All of the above

Q2. The power factor at which single phase induction motor usually operate is
a)0.7 lag
b)0.8 lag
c)0.7 lead
d)Unity

Q3. Which of following tests are performed on single-phase ac motors?
a)Stator winding resistance test
b)Blocked rotor test
c)No Load test
d)All of the above

Q4. The torque speed characteristic of two-phase induction motor is largely affected by
a) Voltage
b) Speed
c) X/R Ratio
d) Supply frequency

Q5. Capacitor start Capacitor-run induction motors are used in
a)Hoists
b)Rolling mills
c)Mining
d)Refrigerator

Q6. In a shaded pole motor, the rotating field is developed by
a)Salient poles
b)A capacitor
c)Shading coils
d)Damping winding

Q7. In an induction motor, what is the ratio of rotor copper loss and rotor input?
a) 1/S
b)S
c)(1-S)
d)S/(1-S)

Q8. For an induction motor, operating at slip s, the ratio of gross power output to air gap power is equal to
a) (1-S)^2
b) (1-s)
c) √((1-S) )
d) (1-√S)

Q9. The rotor power output of a 3-phase induction motor is 15 kW. The rotor coppers losses at slip of 4% will be
a)600 W
b)625 W
c)825 W
d)900 W

Q10. A 3-phase induction motor operating at a slip of 5% develop 20kW rotor power output. What is the corresponding rotor copper loss in this operating condition?
a)705 W
b)1052 W
c)1250 W
d)1350 W

Solution

Sol 1. (d)
All of the above

Sol 2. (a)
single phase induction motor usually operate is 0.7 lag.

Sol 3. (a)
All of the above-mentioned test is performed on single phase induction motor.

Sol 4. (c)
The torque speed characteristic of two-phase induction motor is largely affected by X/R Ratio.

Sol 5. (d)
Capacitor start Capacitor-run induction motors are used in refrigerator.

Sol 6. (c)
In a shaded pole motor, the rotating field is developed by shading coil.

Sol 7. (b)
In an induction motor, what is the ratio of rotor copper loss and rotor input is S.

Sol 8. (b)
For an induction motor, operating at slip s, (1-s) is the ratio of gross power output to air gap power.

Sol 9. (b)
Rotor power output,
Pmech = 15 kW
Rotor copper loss at 4% slip,
= S/(1-S)× Pmech
= .04/(1-.04) ×15 ×1000
=625 W

Sol 10. (b)
Power developed,
Pmech = 20 kW
Slip, S= .05
Rotor copper loss,
= S/(1-S)× Pmech
=.05/(1-.05) ×20 ×1000
= 1052.6 W

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