Objective Questions on AC Three Phase Motor for Electrician Trade
| Sr. No. | Questions with options |
| 1 | How the voltage is received in the rotor of induction motor?
(a) Direct connection from stator (b) Due to back emf produced in stator (c) Direct connection to rotor from supply (d) By the transformer action of stator and rotor Ans – (d) |
| 2 | Which method is applied to control the speed of 3 phase squirrel cage induction motor from its motor side?
(a) Cascade operation (b) Changing applied voltage (c) Changing applied frequency (d) Changing the number of poles Ans – (a) |
| 3 | Which loss of 3 phase induction motor is determined by blocked rotor test?
(a) Copper loss (b) Friction loss (c) Hysteresis loss (d) Eddy current loss Ans – (a) |
| 4 | Why pre heating is necessary for motors before varnishing in rewinding process?
(a) To dry the varnish quickly in winding (b) To easy flow of varnish in the winding (c) To increase the insulation resistance value (d) To drive out the moisture in between winding layers Ans –(d) |
| 5 | Which type of test is conducted using internal growler in AC motor winding?
(a) Ground test (b) Polarity test (c) Continuity test (d) Short circuit test Ans – (d) |
| 6 | Which device is used to test startor winding short and open fault?
(a) Tong tester (b) Internal growler (c) External growler (d) Digital multi meter Ans –(b) |
| 7 | What is the purpose of using thermal cutout in addition to fuse in A.C motor circuit?
(a) Protect from heavy load (b) Protect against high voltage (c) Allow for continuous over loading (d) Protect against dead short circuit Ans –(c) |
| 8 | Which type of motor is used to provide high starting torque at variable speed?
(a) Universal motor (b) Permanent capacitor motor (c) 3 phase slip ring induction motor (d) Three phase single squirrel cage induction motor Ans – (c) |
| 9 | What is the relation between torque and slip in an A.C induction motor?
(a) Slip increases torque decreases (b) Slip increases torque increases (c) Slip decreases torque increases (d) Slip decreases torque decreases Ans – (b) |
| 10 | What is effect of A.C induction motor if rotor bar is in open circuit?
(a) Vibration of shaft (b) Motor will not start (c) Runs n slow speed (d) Over heating of motor Ans – (d) |
| 11 | Which type of wire is used for rewinding of AC 3 phase motors?
(a) Super enamlled copper wire (b) PVC covered copper winding wire (c) Single cotton covered copper wire (d) Double cotton covered copper wire Ans – (a) |
| 12 | Which material is used as wedges in winding process?
(a) Empire (b) Cotton (c) Bamboo (d) Terylene Ans – (c) |
| 13 | Which test in winding is essential before giving supply?
(a) Ground test (b) Polarity test (c) Open circuit test (d) Short circuit test Ans – (b) |
| 14 | Why the rotor bars are mounted in a slightly skewed position in 3 phase motor?
(a) Generate maximum flux (b) Reduce the stray losses (c) Maintain the rotor speed consultant (d) Produce more uniform rotor field and torque Ans –(d) |
| 15 | Which loss is determined by no load test of 3 phase induction motor?
(a) Iron loss (b) Copper loss (c) Friction loss (d) Windage loss Ans-(a) |
| Data Collected By – Rashmi | |
| Published On – 29th May 2022 | |
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