Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 5th Sem Old 150901 Electrical Machine Ii Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?V (OLD) EXAMINATION ? WINTER 2018
Subject Code:150901 Date: 04/12/2018
Subject Name: Electrical Machine - II
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) Draw connection diagrams, phasor diagrams and clock representations for Dy1
and Yd11 connections of three phase transformer.
07
(b) Explain Scott connection in detail also explain how we can obtain a balanced two
phase supply from a balanced three phase supply by using this connection.
07
Q.2 (a) State and explain the essential and desirable conditions for parallel operation of
two three phase transformers.
07
(b) Explain the open delta connection (V-V connection) in details. 07
OR
(b) 120 KVA, 3-phase, 50 Hz, 6600/400-V transformer is delta connected on H.V.
side and star connected on L.V. side. The resistance of HV winding is 4.5
ohm/phase and of LV winding is 0.04 ohm/phase. If it ?s full load efficiency is
95% at 0.85 p.f. (lag), Calculate (i) Iron losses & copper losses at full load. (ii)
Efficiency of transformer at half load and 0.8 p.f. (lead)
07
Q.3 (a) A 20 hp, 400 V , 50 Hz, three phase star connected induction motor has the
following test data:
No-load test: 400 V, 11 A , p.f = 0.2
Blocked rotor test: 100 V, 25 A, p.f = 0.4.
The stator and rotor copper losses are equal at standstill. Draw the circle diagram
and find out the line current, speed, efficiency and p.f at full load.
07
(b) Why induction motor is taking a large current at starting? Give the list of various
starters used for induction motors and also explain any one of them in detail.
07
OR
Q.3 (a) Derive the expression of torque developed by a three phase induction motor. Also
obtain the condition for maximum torque.
07
(b) Derive the equivalent circuit of a three phase induction motor step by step. 07
Q.4 (a) Give the list of various methods of controlling the speed of three phase induction
motor. Explain any one method in detail.
07
(b) Explain in detail about the terms crawling and cogging in three phase induction
motor.
07
OR
Q.4 (a) With the help of double revolving field theory explain why the single phase
induction motor is not a self starting.
07
(b) Explain the construction and working principle of double cage induction motor. 07
Q.5 (a) Explain the construction and operating principle of Schrage motor. 07
(b) Draw the constructional features and operating characteristics of shaded pole
induction motor. Also state its application.
07
OR
Q.5 (a) Explain the operating principle, construction and applications of induction
generator.
07
(b) Explain the effect of unbalanced supply voltage and variation in frequency on the
operation of three phase induction motor.
07
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This post was last modified on 20 February 2020