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This set of Electrical and Electronics Engineering Multiple Choice Questions & Answers (MCQs) focuses on Electrical And Electronics Engineering Set 11
Q1 | When three phase induction motor is started with star-delta starter, during starting stator is connected
- in star
- in delta
- in star or delta
- none of these
Q2 | When three phase induction motor is started with star-delta starter, during normal running condition, stator is connected
- in star
- in delta
- in star or delta
- none of these
Q3 | The torque developed by three phase induction motor is approximately proportional to
- square of applied voltage
- applied voltage
- half of applied voltage
- double of appled voltage
Q4 | The rotor of an induction motor can't run at synchronous speed, if it did so then
- rotor emf would be zero
- rotor current would be zero
- rotor torque would be zero
- all of these
Q5 | A 3-phase , 50 Hz , 4-pole squirrel cage induction motor has its stator rewound for 6 poles without any alternations in the rotor. The motor would now run at a speed
- less than 1000 rpm
- less than 1500 rpm
- less than 3000 rpm
- zero rpm
Q6 | If the input voltage and the frequency of supply is halved, to the 3-phase induction motor
- the maximum torque is halved
- the maximum torque remains the same
- the air-gap flux is halved
- none of these
Q7 | The speed of the slip ring induction motor can be easily controlled by
- changing supply frequency
- changing number of poles
- changing the resistance of the rotor winding
- all of these
Q8 | A 440V, 20HP, 3phase motor operates at full load, 88% efficiency and 0.65 power factor lagging, the current drawn by motor is
- 59.28a
- 0.0458a
- 34.22 a
- 26.50a
Q9 | A6 pole 3 phase 50Hz induction motor develops mechanical power of 40Hp and has mechanical losses of 1500W at a speed of 960rpm when connected to 500V. The output available at the shaft is (Take 1HP=746W)
- 27kw
- 31340w
- 29840w
- 28340w
Q10 | DOL starter is used for 3 phase I.M. motor having rating of
- ≤5 h.p.
- > 5 h.p.
- 5 to 10 h.p.
- >10h.p.
Q11 | Thermal relays are used in DOL starter of Three Phase I.M. to
- protect the motor from high temperature
- protect the motor from overloading
- protect the motor from short circuit
- none of the above
Q12 | No. of contacts used in a contactor of DOL starter
- 2
- 3
- 4
- 1
Q13 | Q. In DOL starter NO(Normally open) contact is used as
- start push button
- stop push button
- a and b
- none of the above
Q14 | In DOL starter NC(Normally closed) contact is used as
- start push button
- stop push button
- a and b
- none of the above
Q15 | The advantage of Autotransformer starter over stator resistance starter is
- produces more torque
- produces less losses
- smooth variation of speed
- none of the above
Q16 | The rotor speed of a 6 pole 50Hz induction motor is 960 r.p.m. The percentage slip is ____.
- 0.03
- 0.04
- 0.05
- 0.02
Q17 | A 3 phase induction motor connected from a 3 pjhase, 50Hz AC supply runs at 720rpm and has slip 4%. The number of poles in motor are _____.
- 4
- 6
- 8
- 16
Q18 | The torque developed in an induction motor is nearly proportional to
- 1/v
- v
- v^2
- none of these
Q19 | The air gap between the stator and rotor of a 3 phase induction motor ranges from
- 2 cm to 4 cm
- 0.4mm to 4mm
- 1cm to 2cm
- 4cm to 6cm
Q20 | An induction motor under full load has slip of about____.
- 0.03
- 0.1
- 0.3
- zero
Q21 | A 4 pole, 440V, 50Hz induction motor is running at a slip of 4%. The speed of motor is ____.
- 1260 rpm
- 1440rpm
- 1500rpm
- 1560rpm
Q22 | A 4 pole, 50Hz induction motor runs at a speed of 1440rpm. The frequency of the rotor induced emf is _____.
- 3hz
- 2.5hz
- 2hz
- 1hz
Q23 | The value of slip is ___ at start.
- zero
- infinite
- 100
- 1
Q24 | Slip rings are usually made up of ___.
- copper
- iron
- carbon
- phosphor-bronze
Q25 | The rotor standstill resistance and reactance of an induction motor are 0.5Ω and 2.5Ω hence the rotor impedance at 5% slip is____.
- 0.5Ω
- 0.025Ω
- 0.5154Ω
- 0.125Ω