Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 6th Sem Old 160901 Electrical Machine Iii Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI (OLD) EXAMINATION ? WINTER 2018
Subject Code:160901 Date: 07/12/2018
Subject Name: Electrical Machine - III
Time: 02:30 PM TO 05:00 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) Explain Hopkinson?s test for determination of efficiency of DC shunt machine 07
(b) A Field?s test on two mechanically coupled similar motors with their fields connected
in series and with one machine running as motor and the other as a generator gave the
following data:
Motor: Armature current 40A, armature voltage 200V, the drop across its field winding
15V.
Generator: Armature current 32A, armature voltage 160V, the drop across its field
winding 15V.
The resistance of each armature is 0.4 ?. Calculate the efficiency of each machine at
this load.
07
Q.2 (a) List different methods for finding voltage regulation of an alternator and explain Potier
method.
07
(b) Derive the equation of induced emf for a synchronous generator and explain pitch
factor as well as distribution factor.
07
OR
(b) Explain Armature reaction and its effects at different power factor in alternator. 07
Q.3 (a) Explain the two reaction theory of salient pole machine in detail with phasor diagram. 07
(b) A single phase 1500 r.p.m., 4 pole alternator has 8 conductors per slot with total of 24
slots. The winding is short pitched by 1/6 th of full pitch. Assume distributed winding
with flux per pole as 0.05 Wb. Calculate the induced e.m.f.
07
OR
Q.3 (a) Explain V and inverted V curve of synchronous motor 07
(b) A 3-phase salient pole synchronous generator is rated at 3.5 MVA, 6.6 kV. It?s direct
and quadrature axis reactances are 9.6 ? and 6 ? per phase. The winding is star
connected and resistance is negligible. If the generator is supplying 2.5 MW at rated
voltage and at 0.8 p.f. lagging to an infinite bus. Find the voltage regulation.
07
Q.4 (a) State the conditions necessary for paralleling alternators. Explain one dark and two
bright lamp method with necessary electrical circuit diagram
07
(b) Draw and explain the capability curve of a synchronous generator. 07
OR
Q.4 (a) Explain the effect of varying the excitation and torque of the prime-mover of
synchronous machine connected to infinite bus-bar
07
(b) Briefly describe the short circuit ratio and its significance 07
Q.5 (a) Write a short note on Switched Reluctance Motor 07
(b) Explain the construction and working of an induction regulator 07
OR
Q.5 (a) Explain construction, working & applications of SRM (Switched Reluctance Motor) 07
(b) Explain the operation of d.c servo motor 07
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This post was last modified on 20 February 2020