GTU B.Tech 2020 Winter Question Papers || Gujarat Technological University
GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER-VIII (OLD) EXAMINATION — WINTER 2020
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Subject Code:180904 Date:30/01/2021
Subject Name:Electrical Machine Design -11
Time:02:00 PM TO 04:00 PM Total Marks: 56
Instructions:
- Attempt any FOUR questions out of EIGHT questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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- (a) Show that the output for single phase induction motor is 2/3 of the output of the 3-phase induction motor for the same diameter and length. (07)
- (b) Explain the effect of skewing the rotor slots in a squirrel cage induction motor. (07)
- (a) Explain with diagram current distribution in rotor bars and end rings for squirrel cage rotor. (07)
- (b) Explain the role of damper winding in (i) synchronous generator (ii) synchronous motor. (07)
- (a) Discuss the effect of air gap length on the performance of a 3-phase induction motor. (07)
- (b) 11 KW, 3 phase, 6pole, 50Hz, 220V, star connected induction motor has 54 stator slots, each with 9 conductors. Find out values of bar and end ring currents, if number of rotor bars is 64. The efficiency is 86% and pf of 0.85. Also find out bar & end ring cross sections, if current density is 5 A/mm?. (07)
- (a) Discuss the design differences of a salient pole and non-salient pole synchronous machines. (07)
- (b) Explain the procedure to calculate the value of the capacitor to obtain the maximum starting torque of a capacitor start single phase induction motor. (07)
- (a) Explain methods to reduce effect of harmonics on performance of I.M. (07)
- (b) Explain factors affecting selection of number of armature slots for synchronous machine. (07)
- (a) Define SCR. Write effect of SCR on synchronous machine performance. (07)
- (b) 500 KVA, 33KV, 50 Hz, 600 rpm, 3 phase salient pole alternator has 180 turns per phase. The mmf required for gap is 80% of no load field mmf. Calculate length of air gap if Bavg is 0.54 Tesla, ratio of pole arc to pole pitch 0.65, SCR 1.2, Gap contraction factor 1.15 and winding factor 0.955. (07)
- (a) Discuss the factors that governs the choice of average gap density for a synchronous machine. (07)
- (b) Explain evaluation of Direct and Quadrature axis reactance of Alternator. (07)
- (a) Explain the terms “critical speed” and “run-away speed” with reference to synchronous machine. (07)
- (b) Explain the importance of circle diagram in designing auxiliary winding of a single phase motor. (07)
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