Lab Quiz
EEE301: Electrical Machines Fundamentals, Spring-2013
Date: 17/04/2013
Times: 40 minutes
SET: 01
Answer the following multiple choice questions (Q.1-Q.20). Put tick (√) marks on your
answer.
1. Transformer core is laminated in order to minimizeA. Hysteresis loss
B. Eddy current loss
C. Copper loss
D. Leakage flux
2. Open circuit test provides us withA. Core-loss resistance
B. Magnetizing reactance
C. Core-loss
D. All of the above
3. Short circuit test provides us withA. Core-loss resistance
B. Magnetizing reactance
C. Winding resistance
D. None of the above
4. You need a transformer to convert 220 AC voltage to 110 V AC. What will be turns
ratio?
A. 10
B. 20
C. 2
D. 0.2
5. What happens if you operate a transformer beyond the rated voltage?
A. Saturation of transformer core
B. High magnetizing current
C. Possibility of burning out of transformer
D. All of the above
6. Voltage regulation of an ideal transformer isA. 0%
B. 100%
C. 50%
D. -50%
7. Figure-01 shows the transformer with two secondary coils. The two secondary coils are
connected as indicated. The turns ratios are 2:1 and 2:1.25 respectively. What will be the
voltmeter reading for a primary voltage of 220 V?
A. 65 volts
B. 75 volts C. 495 volts D. -65 volts
8. A 50 KVA transformer has a turn ratio of 20:1. What would be its power rating if it is
reconnected as an autotransformer?
A. 50 KVA
B. 1000 KVA
C. 1050 KVA
D. 2.38 KVA
9. Suppose you want to design an autotransformer from a 2-winding transformer. What will
be the turns ratio of the windings to get an output voltage of 296V ac from a fixed source
of 240V ac?
A. 0.81
B. 1.23
C. 0.233
D. 2.23
10. A 2-winding transformer has a rating of 55 KVA. The rated primary and secondary
voltages are 550V and 220V, respectively. What KVA load can be connected to the
secondary winding if the primary is connected to 500V ac?
A. 45.45 KVA
B. 50 KVA
C. 60.5 KVA
D. 66.55 KVA
11. At fully CW position, each rheostat of the 3-φ rheostat of the lab has a value ofA. 105 Ω
B. 75 Ω
C. 75 Ω
D. 50 Ω
12. Electro-Dynamo meter is used toA. Measure load torque
B. Give load torque
C. C. Measure starting torque
D. All of the above
13. An induction motor has a starting torque of 2 N-m. For which of the load torque below,
the motor will not start?
A. 1 N-m
B. 0.5 N-m
C. 3 N-m
D. 1.33 N-m
14. Tachometer is used toA. Measure current
B. Measure locked-rotor torque
C. Count rotation of motor
D. All of the above
15. Increasing the speed-control rheostat resistance of the wound-rotor motorA. Increases the starting torque
B. Decrease the starting torque
C. Does not have any effect on starting torque
D. Has an unpredictable effect
16. Starting an induction motor with a load torque larger than locked-rotor torqueA. Does not have any effect on motor
B. May burn out motor
C. Increases the rotor current resulting in heating D. B and C above
Answer the following questions (5×2=10)
1. Why open circuit test is performed at the low tension side?
2. What is the effect of transformer impedance on short-circuit current?
3. Write the advantages and disadvantages of wound-rotor motor in comparison to squirrelcage motor?
4. Sketch the connection diagram for DC test of Induction motor. What parameters of an
induction motor are measured from this test?
5. Draw the torque-speed characteristics of an induction motor and label the significant
torque positions.