Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 7th Sem New 2170909 Design Of Ac Machines Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VII (NEW) EXAMINATION ? WINTER 2018
Subject Code: 2170909 Date: 29/11/2018
Subject Name: Design of AC Machines
Time: 10:30 AM TO 01:30 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) Explain direct axis and quadrature axis synchronous reactance in synchronous
machine.
03
(b) State important design difference between turbo alternators and hydro
generators.
04
(c) What do you mean by specific electric loading and specific magnetic loading
applied to electric machines? State the factors on which the choice of these
loadings depends.
07
Q.2 (a) Explain harmonic induction and harmonic synchronous torques produced in
induction motor.
03
(b) Explain the terms ?critical speed? and ?run away speed? with reference to
synchronous machine.
04
(c) Explain the term SCR and its effects on synchronous machine performance 07
OR
(c) Explain steps for design of field winding of synchronous machine. 07
Q.3 (a) What are the design criteria that should be taken care while design of
submersible motors?
03
(b) Explain which combinations of number of stator and rotor slots should be
avoided in the induction motor design ? why?
04
(c) Write a note on computer aided design of Induction motor. Explain algorithm
steps to find main dimensions.
07
OR
Q.3 (a) What is done to reduce tooth pulsation losses in an induction motor? 03
(b) Discuss the Finite Element Method for design of electrical machine 04
(c) State the rules for the selection of rotor slots. Describe the methods for
reducing the effect of harmonics torque.
07
Q.4 (a) Explain estimation of full load field mmf in synchronous machine. 03
(b) Draw and explain briefly the current distribution wave form speeded over one
pole pitch in bars and end rings squirrel cage induction motor
04
(c) Estimate the main dimensions, air gap length, no of stator slots, stator turns
per phase and cross sectional area of stator conductors for a 3 phase, 20 h.p.,
400V, 6 poles, 50 Hz, 970 rpm, induction motor, suitable for a star delta
starting. Assume magnetic and electric specific loadings as 0.45 wb/m
2
, and
23000 ac/m respectively, current density = 4 A/mm
2
, ratio of core length to
pole pitch is 0.85, full load efficiency 0.88 and power factor 0.89.
07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VII (NEW) EXAMINATION ? WINTER 2018
Subject Code: 2170909 Date: 29/11/2018
Subject Name: Design of AC Machines
Time: 10:30 AM TO 01:30 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) Explain direct axis and quadrature axis synchronous reactance in synchronous
machine.
03
(b) State important design difference between turbo alternators and hydro
generators.
04
(c) What do you mean by specific electric loading and specific magnetic loading
applied to electric machines? State the factors on which the choice of these
loadings depends.
07
Q.2 (a) Explain harmonic induction and harmonic synchronous torques produced in
induction motor.
03
(b) Explain the terms ?critical speed? and ?run away speed? with reference to
synchronous machine.
04
(c) Explain the term SCR and its effects on synchronous machine performance 07
OR
(c) Explain steps for design of field winding of synchronous machine. 07
Q.3 (a) What are the design criteria that should be taken care while design of
submersible motors?
03
(b) Explain which combinations of number of stator and rotor slots should be
avoided in the induction motor design ? why?
04
(c) Write a note on computer aided design of Induction motor. Explain algorithm
steps to find main dimensions.
07
OR
Q.3 (a) What is done to reduce tooth pulsation losses in an induction motor? 03
(b) Discuss the Finite Element Method for design of electrical machine 04
(c) State the rules for the selection of rotor slots. Describe the methods for
reducing the effect of harmonics torque.
07
Q.4 (a) Explain estimation of full load field mmf in synchronous machine. 03
(b) Draw and explain briefly the current distribution wave form speeded over one
pole pitch in bars and end rings squirrel cage induction motor
04
(c) Estimate the main dimensions, air gap length, no of stator slots, stator turns
per phase and cross sectional area of stator conductors for a 3 phase, 20 h.p.,
400V, 6 poles, 50 Hz, 970 rpm, induction motor, suitable for a star delta
starting. Assume magnetic and electric specific loadings as 0.45 wb/m
2
, and
23000 ac/m respectively, current density = 4 A/mm
2
, ratio of core length to
pole pitch is 0.85, full load efficiency 0.88 and power factor 0.89.
07
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2
OR
Q.4 (a) Why closed types slots are often used for small induction motors? 03
(b) In single phase induction explain design of auxiliary winding for capacitor
start motor.
04
(c) What is Dispersion coefficient? Explain the effect of Dispersion coefficient on
maximum output power factor.
07
Q.5 (a) Explain how length of air gap is estimated in synchronous machine. 03
(b) Explain how mmf is calculated for magnetic circuit in synchronous machine. 04
(c) Determine the main dimensions of a 12 MVA, 13.8KV, 50Hz, 1500 rpm, 3
star connected synchronous generator. The additional data is given as: Bav=
0.6wb/m
2
, ac=42000 ac/m and peripheral speed= 80m/sec. Find also the
maximum flux, the number of stator slots if one conductor per slot is used, and
the number of turns per phase.
07
OR
Q.5 (a) Discuss the effect of ?skewing? on the performance of three phase induction
motor.
03
(b) Explain design considerations to eliminate harmonics in synchronous
machines..
04
(c) Briefly discuss factors affecting determining air gap length in induction motor
design.
07
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This post was last modified on 20 February 2020