Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 8th Sem Old 180904 Electrical Machine Design Ii Previous Question Paper
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VIII (OLD) EXAMINATION ? WINTER 2018
Subject Code: 180904 Date: 03/12/2018
Subject Name: Electrical Machine Design -II
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 the factors affecting the selection of Air gap of three phase Induction
Motor.
07
(b) Explain factors affecting specific electric loading and specific magnetic
loading of3 phase IM.
07
Q.2 (a) Explain the effect of skewing the rotor slots in a squirrel cage induction motor. 07
(b) Estimate the stator core dimensions, number of stator slots and number of stator
conductors per slot for a 100KW, 3300V, 50 Hz, 12 pole star connected slip
ring induction motor. Assume Bav=0.4wb/m
2
, ac=25000 A/m, Efficiency=0.9,
power factor=0.9 and winding factor =0.96. Choose main dimensions to give
best power factor. The slot loading should not exceed 500 ampere conductors.
07
OR
(b) Draw and explain briefly the current distribution wave form spreaded over one
pole pitch in bars and end rings squirrel cage induction motor.
07
Q.3 (a) What is dispersion coefficient? Show its effect on maximum power factor and
overload capacity of three phases Induction Motor.
07
(b) Find the current in the bars and end rings of a 11KW, 6 pole, 50 Hz , 3 phase
star connected induction motor having 54 stator slots with 9 conductors in each
slot. The number of rotor bars is 64. The machine has an efficiency of 0.86 and
a power factor of 0.85. The rotor mmf may be assumed as 85 % of stator mmf.
Also find the suitable size of the cage bars and end rings if the current density
is 5 A/mm
2
.
07
OR
Q.3 (a) Explain methods of Improving starting torque of Induction Motor. 07
(b) Draw flow chart and write algorithm steps for design of submersible motors. 07
Q.4 (a) Explain steps of design of field winding of alternator. 07
(b) The field coil of a salient pole alternator are wound with a single layer winding
of bare copper strip 30 mm deep with separating insulation 0f 0.15mm thick.
Determine a suitable winding length, number of turns and thickness of
conductor to develop mmf of 12000 A with a potential difference of 5 V per
coil and with a loss of 1200W/m2 of total coil surface. The mean length of turn
is 1.2 m. The resistivity of copper is 0.021ohm/m and mm
2
07
OR
Q.4 (a) Define SCR of a synchronous machine. Discuss the importance of SCR in the
design of synchronous machine.
07
(b) For the same h.p. output compare the relative sizes of a 3-phase induction
motor to 1-phase induction motor (split phase capacitor start). Assume same
loadings, same number of poles, same power factor and efficiency.
07
Q.5 (a) What is the role of damper winding in (i) synchronous generator and (ii)
synchronous motor? Derive the equation of MMF of damper winding.
07
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Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VIII (OLD) EXAMINATION ? WINTER 2018
Subject Code: 180904 Date: 03/12/2018
Subject Name: Electrical Machine Design -II
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 the factors affecting the selection of Air gap of three phase Induction
Motor.
07
(b) Explain factors affecting specific electric loading and specific magnetic
loading of3 phase IM.
07
Q.2 (a) Explain the effect of skewing the rotor slots in a squirrel cage induction motor. 07
(b) Estimate the stator core dimensions, number of stator slots and number of stator
conductors per slot for a 100KW, 3300V, 50 Hz, 12 pole star connected slip
ring induction motor. Assume Bav=0.4wb/m
2
, ac=25000 A/m, Efficiency=0.9,
power factor=0.9 and winding factor =0.96. Choose main dimensions to give
best power factor. The slot loading should not exceed 500 ampere conductors.
07
OR
(b) Draw and explain briefly the current distribution wave form spreaded over one
pole pitch in bars and end rings squirrel cage induction motor.
07
Q.3 (a) What is dispersion coefficient? Show its effect on maximum power factor and
overload capacity of three phases Induction Motor.
07
(b) Find the current in the bars and end rings of a 11KW, 6 pole, 50 Hz , 3 phase
star connected induction motor having 54 stator slots with 9 conductors in each
slot. The number of rotor bars is 64. The machine has an efficiency of 0.86 and
a power factor of 0.85. The rotor mmf may be assumed as 85 % of stator mmf.
Also find the suitable size of the cage bars and end rings if the current density
is 5 A/mm
2
.
07
OR
Q.3 (a) Explain methods of Improving starting torque of Induction Motor. 07
(b) Draw flow chart and write algorithm steps for design of submersible motors. 07
Q.4 (a) Explain steps of design of field winding of alternator. 07
(b) The field coil of a salient pole alternator are wound with a single layer winding
of bare copper strip 30 mm deep with separating insulation 0f 0.15mm thick.
Determine a suitable winding length, number of turns and thickness of
conductor to develop mmf of 12000 A with a potential difference of 5 V per
coil and with a loss of 1200W/m2 of total coil surface. The mean length of turn
is 1.2 m. The resistivity of copper is 0.021ohm/m and mm
2
07
OR
Q.4 (a) Define SCR of a synchronous machine. Discuss the importance of SCR in the
design of synchronous machine.
07
(b) For the same h.p. output compare the relative sizes of a 3-phase induction
motor to 1-phase induction motor (split phase capacitor start). Assume same
loadings, same number of poles, same power factor and efficiency.
07
Q.5 (a) What is the role of damper winding in (i) synchronous generator and (ii)
synchronous motor? Derive the equation of MMF of damper winding.
07
2
(b) Explain the designing of capacitance value for maximum starting torque in
case of capacitor start single phase induction motor.
07
OR
Q.5 (a) Explain evaluation of Direct and Quadrature axis reactance of Alternator 07
(b) Explain the terms ?critical speed? and ?run away speed? with reference to
synchronous machine.
07
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This post was last modified on 20 February 2020