ONLINE ELECTRICAL ENGINEERING will contain ELECTRICAL ENGINEERING QUESTIONS & ANSWERS,ELECTRICAL INTERVIEW QUESTION & ANSWERS and important topics from ELECTRICAL MACHINES, POWER SYSTEMS ,POWER ELECTRONICS AND DRIVES and other ELECTRICAL ENGINEERING SUBJECTS.Objective tests will be conducted periodically which would be useful for exams like POWERGRID , NTPC ,NHPC ,ENGINEERING SERVICES ,IES ,ETC..FEEL FREE TO ASK YOUR DOUBTS REGARDING ELECTRICAL SUBJECTS.
Thursday, October 24, 2013
ONLINE ELECTRICAL ENGINEERING TEST - 3
Hi all.Please take up the Electrical Engineering Test-3.The test contains the questions which were asked in some competitive exams.Though the questions are theoretical it would be helpful in understanding the basic concepts.We have been preparing questions ourselves, so that it is useful for all Electrical Engineers.Online Electrical Engineering team has been taking efforts to satisfy the readers with the best they can...Your valuable comments are welcome to improve the quality of the tests. Cheers !!
1. A 3-phase, 4 pole , 50-Hz induction motor runs at a speed of 1440 rpm.The rotating field produced by the rotor rotates at a speed of ....... rpm with respect to the rotor.
A) 1440
B) 1500
C) 0
D) 60
ANSWER :
D) 60
EXPLANATION :
Ns = (120*f)/p = (120*50)/4 = 1500
Rotating field rotates at the speed with respect to rotor = Ns - N = 1500 -1440 = 60
2. In 3-phase IM, the rotor field rotates at synchronous speed with respect to ?
A) Stator flux
B) Rotor
C) Stator
D) None of the above
ANSWER :
C) Stator.
3. Thrust developed by a linear induction motor depends on
A) Number of poles
B) Rotor input
C) Synchronous speed
D) Both B) and C)
ANSWER :
D) Both B) and C)
4. Which statement is false with regards to the skewing of motor bars in squirrel cage IM ?
A) it reduces motor 'hum' during its operation
B) it prevents cogging
C) it produces more uniform torque
D) it increases starting torque
ANSWER :
D) it increases starting torque
5. The efficiency and power factor of a squirrel cage IM increases in proportion to its
A) Mechanical load
B) Speed
C) Rotor torque
D) Voltage
ANSWER :
A) Mechanical load
6. The power factor of a squirrel-cage induction motor is
A) low at heavy loads only
B) low at light loads only
C) low at rated load only
D) low at heavy & light loads
ANSWER :
B) low at light loads only
7. The efficiency of a 3-phase induction motor is approximately proportional to
A) s
B) N
C) (1-s)
D) Ns
ANSWER :
C) (1-s)
8. What are the advantages of a double squirrel cage induction motor over squirrel cage induction motor ?
A) High efficiency under running conditions
B) Speed regulation under normal operating conditions
C) Starting torque
D) All the above
ANSWER :
D) All the above
9. The capacitor in a capacitor-start induction-run ac motor is connected in deries with ...... winding.
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