ECET EEE 2012-2

1. Which one of the following methods gives more accurated result for determination of voltage regulation of an alternator

A. MMF method
B. Synchronous impedance method
C. Potier triangle method
D. ASA method

Answer : C. Potier triangle method
Explanation:-

2. Hydrogen is used in large alternators mainly to

A. reduce distortion of waveform
B. cool the machine
C. strengthen the magnetic field
D. reduce eddy current losses

Answer : B. cool the machine
Explanation:-

3. The frequency of emf generated in an 8-pole alternator running at 900rpm is

A. 50 Hz
B. 120 Hz
C. 90 Hz
D. 60 Hz

Answer : D. 60 Hz
Explanation:-

4. The angle between synchronously rotating stator flux and rotor poles of a synchronous motor is called _____ angle

A. synchronising angle
B. Slip
C. Power factor
D. Torque

Answer : D. Torque
Explanation:-

5. If θe be the electrical angle and θm be the mechanical angle and P be the number of poles of a synchronous motor, then which one of the following relation is true?

A. θe = P x θm
B. θe = (P/2) x θm
C. θe = θm/P
D. θe = P/θm

Answer : B. θe = (P/2) x θm
Explanation:-

6. The essential condition for parallel operation of two single phase transformers is that they should have same

A. polarity
B. KVA rating
C. Voltage ratio
D. Percentage impedance

Answer : A. polarity
Explanation:-

7. The V-curve of a synchronous motor is a plot of

A. State current versus stator power factor
B. Stator current versus rotor current at all loads
C. Stator current versus rotor currents when power delivered is constant
D. Stator current versus power delivered

Answer : B. Stator current versus rotor current at all loads
Explanation:-

8. A wound rotor induction motor runs with a slip of 0.03 when developing full load torque. Its rotor resistance is 0.25 ohm per phase, If an external resistance 0.50 ohm per phase is connected across the slip rings, what is the slip for full load torque ?

A. 0.03
B. 0.06
C. 0.09
D. 0.1

Answer : C. 0.09
Explanation:- Slip is directly proportional to rotor resistance
S2/S1=(R2+RX)/R2
S2=((R2+RX)/R2) X S1
S2= (0.25+0.50)/0.25) X 0.03
S2= 3X0.03
S2= 0.09

9. The torque developed in a three phase induction motor depends on

A. Stator flux and rotor current
B. Stator flux and stator current
C. Stator current and rotor flux
D. rotor current and rotor flux

Answer : A. Stator flux and rotor current
Explanation:-

10. A single phase ac induction motor is not self starting because it has

A. No slip
B. rotor is short circuited
C. High inertia
D. absense of rotating magnetic field

Answer : D. absense of rotating magnetic field
Explanation:-