Download PTU (Punjab Technical University) B.Tech (Bachelor of Technology) / BE (Bachelor of Engineering) 2021 January EE 3rd Sem 72163 Asynchronous Machines Previous Question Paper
Total No. of Pages : 02
Total No. of Questions : 18
B.Tech. (EE) PT (Sem.?3)
ASYNCHRONOUS MACHINES
Subject Code : BTEE-401
M.Code : 72163
Time : 3 Hrs. Max. Marks : 60
INST RUCT ION TO CANDIDAT ES :
1 .
SECT ION-A is COMPULSORY cons is ting of TEN questions carrying TWO marks
each.
2 .
SECT ION-B c ontains F IVE questions c arrying FIVE marks eac h and s tud ents
have to atte mpt ANY FOUR questio ns.
3 .
SECT ION-C contains THREE questions carrying T EN marks e ach and s tudents
have to atte mpt ANY TWO questions .
SECTION-A
Answer briefly :
1)
Why does an induction motor never run on synchronous speed?
2)
What will the effect on torque developed by an induction motor if applied voltage is
reduced to half with frequency unchanged?
3)
Define Crawling in 3-phase Induction machines.
4)
Why single phase motor is not self-starting?
5)
Explain in brief the voltage build-up of an isolated induction generator.
6)
What is universal motor?
7)
A 3-phase slip ring induction motor runs at 290 r.p.m. at full load, when connected to
50 Hz supply. Calculate the number of poles, slip and slip frequency.
8)
How can we increase the starting torque of an induction motor?
9)
What is the need of excitation for induction generator?
10) Write two advantages of slip ring Induction motor over squirrel cage Induction Motor.
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SECTION-B
11) A 746 kW, three phase, 50 Hz, 16 poles IM has rotor impedance of (0.02 + 0.15j) at
standstill. Full load torque is obtained at 360 rpm. Calculate :
a) Ratio of maximum to full load torque.
b) The speed of maximum torque.
c) The rotor resistance to be added to get maximum starting torque.
12) Describe the constructional features and principle of operation of a linear induction motor.
13) Describe constructional features and operating characteristics of capacitor start motor.
14) Name various methods of speed control of 3-phase cage rotor and wound rotor induction
motor. Discuss any one of the method.
15) What is induction generator? Discuss its principle of operation. What are its limitations?
SECTION-C
16) a) A 4-pole, 50 Hz induction motor is to be used as a frequency changer. Find the motor
speed, so as to give an output frequency of (a) 5 Hz (b) 80 Hz.
b) The rotor resistance and standstill reactance/phase of a 3 phase slip ring induction
motor are 0.05 ohm and 0.2 ohm respectively. What should be the value of external
resistance per phase to be inserted in the rotor circuit to give maximum torque at
starting?
17) a) Explain characteristics of 3 phase self excited induction generator.
b) Prove that in 3-phase induction motor the ratio of maximum torque to starting torque is
(1 + k2)/2k, where k is the ratio of rotor resistance to rotor reactance. Neglect stator
impedance.
18) Write a technical notes on :
a) Double field revolving theory
b) Stepper Motor
NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any
page of Answer Sheet will lead to UMC against the Student.
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This post was last modified on 26 June 2021