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UEE401

This document is an examination paper for the BE Electrical Engineering (IV Semester) course at Thapar Institute of Engineering and Technology, focusing on Alternating Current Machines. It contains five questions related to three-phase induction motors, covering topics such as rotating magnetic fields, speed control methods, phasor diagrams, torque characteristics, and motor testing. The exam is scheduled for March 11, 2023, and is conducted by Dr. Prasenjit Basak.

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saksham sharma
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19 views1 page

UEE401

This document is an examination paper for the BE Electrical Engineering (IV Semester) course at Thapar Institute of Engineering and Technology, focusing on Alternating Current Machines. It contains five questions related to three-phase induction motors, covering topics such as rotating magnetic fields, speed control methods, phasor diagrams, torque characteristics, and motor testing. The exam is scheduled for March 11, 2023, and is conducted by Dr. Prasenjit Basak.

Uploaded by

saksham sharma
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Roll Number:

Thapar Institute of Engineering and Technology, Patiala


Department of Electrical and Instrumentation Engineering
BE- Electrical Engineering (IV Semester) MST UEE401: Alternating Current Machines
11 March 2023, 10-30 A.M.
Time: 2 Hours; MM: 50 (Weightage 25 out of 100) Name of Faculty: Dr. Prasenjit Basak

Note: Attempt all questions. Assume missing data, if any, appropriately.

Q.1 a) Analyze how a rotating magnetic field is generated in a three-phase induction motor [5+ 5]
with an appropriate diagram.
b) Compare the speed control of the induction motor between voltage control and rotor
resistance control methods showing relevant circuit diagrams in each case.

Q.2 a) Compare phasor diagrams of a three-phase induction motor between standstill and 15+51
running conditions.
b) A 3-phase, 4 pole, 1440 rpm, 50 Hz induction motor has star-connected rotor winding,
having a resistance of 0.3 n per phase and a standstill leakage reactance of 1.5 Q per phase.
When the stator is energized at rated voltage and frequency, the rotor-induced emf at a
standstill is 130 V per phase. Calculate the rotor current, power factor, and torque at
starting and full load conditions.

Q.3 A 15 kW, 415 V, 50 Hz, 6-pole delta-connected squirrel cage induction motor gave the 1101
following test results:
No-load test: 415 V, 8 A, 300 watts.
Blocked-rotor test: 100 V, 35 A, 1500 watts.
The d.c. resistance of the stator-winding per phase measured immediately after the blocked
rotor test is 0.6 Q. Calculate the machine parameters and show the same in an equivalent
circuit diagram of the above-mentioned induction motor.

Q.4 (a) Analyze Torque versus Slip Characteristics of a three-phase induction machine in [5+5J
motoring mode operation, justifying the effect of rotor resistance on maximum torque and
slip.
(b) A 20 kW, 415, 3-phase, 4 pole, 50 Hz slip ring induction motor develops rated output
at rated voltage and frequency with its slip-rings short-circuited. The maximum torque
equal to twice the full-load torque occurs at a slip of 15% with zero external resistance in
the rotor circuit. Stator resistance and rotational losses are neglected. Calculate the
following. a) slip at full-load torque, b) rotor ohmic loss at full-load, c) starting torque, d)
starting current, and e) full-load efficiency.

Q.5 a) Justify the function of a star-delta starter for a three-phase induction motor by [5+5]
comparing the starting current and starting torque if a Direct-on-line starter is used
to start the same motor.
b) Explain how friction and windage loss, and core loss can be separated for a three-
phase induction motor.

END

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