Gujarat Technological University 2011-6th Sem B.E , 160901 - Electrical Machine - III on - Question Paper
GUJARAT TECHNOLOGICAL UNIVERSITY
B E Sem-VI exam May 2011
Subject code: 160901
Subject Name: Electrical Machine - III
Date:16/05/2011 Time: 10.30 am – 01.00 pm
Total Marks: 70
Seat No. Enrolment No.
GUJARAT TECHNOLOGICAL UNIVERSITY
B E Sem-VI Examination May 2011
Subject code: 160901 Subject Name: Electrical Machine - III Date:16/05/2011 Time: 10.30 am - 01.00 pm
Total Marks: 70
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) Explain Hopkinsons test for determination of efficiency of DC shunt 07 machine.
(b) What are the advantages of connecting alternators in parallel? Explain with 07 diagram three dark lamp method of synchronizing two three phase alternators.
Q.2 (a) Describe the construction and working principle of a reluctance motor. 07
(b) A 3-phase, 8-pole, 750 rpm star-connected alternator has 72 slots on the 07 armature. Each slot has 12 conductors and winding is short chorded by 2 slots. Find the induced emf between lines, given the flux per pole is 0.06 Wb.
OR
(b) Explain coil span factor and distribution factor of an alternator. 07
Q.3 (a) Write short note on Field test for DC series machines. 07
(b) Explain construction and working principle of hysteresis motor. 07
OR
Q.3 (a) Two identical DC machines when tested by Hopkinsons test gave the 07 following test results:
Field currents are 2.5 A and 2 A. Line voltage is 220 V. Line current including both the field currents is 10 A. Motor armature current is 73 A.
The armature resistance of each machine is 0.05 ohm. Calculate the efficiency of both machines.
(b) Write short note on AC servo motor. 07
Q.4 (a) Briefly explain the ZPF method of finding the voltage regulation of 07 Alternator.
(b) What is armature reaction? Explain the effect of armature reaction on the 07 terminal voltage of an alternator.
OR
Q.4 (a) What are the causes of harmonics in the voltage waveform of an alternator? 07 How can these be minimized?
(b) Explain the two reaction theory of salient pole synchronous machine. 07
Q.5 (a) Explain an experimental method of determining V curves for a 07 synchronous motor.
(b) Briefly explain the principles of operation of DC servo motor and PM 07 synchronous motor.
OR
Q.5 (a) Explain circle diagram of auto synchronous motor. 07
(ii) Draw experimental setup diagram of Brake test for DC motor and write 03 down its efficiency equation.
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