Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 6th Semester (Sixth Semester) 2017-2018 NEN014 Special Electrical Machine Question Paper
Paper Id: 121616 Roll No:
Sub CodezNEN014
B.TECH
(SEM VI) THEORY EXAMINATION 2017-18
SPECIAL ELECTRICAL MACHINE
Time: 3 Hours Total Marks: 100
Note: 1. Attempt all Sections. 1f require any missing data; then choose suitably.
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2. Any special paper specific instruction.
SECTION A
Attempt all questions in brief. 2 x10 = 20
Why low speed machine are preferable when frequent starting and stopping is
required?
Explain how the operation of 3 phase induction motor is effected when single phasing
occurs.
Explain the function of two stator winding in a single phase induction motor.
What are the advantages of having low rotor inertia for a 2 phase servo motor?
What is slew range of stepping motor?
Discuss the single mode working of VRM.
Write the application of PMDC motor.
Explain single phase hysteresis motor.
A 200 volt 50 hz single phase series motor has a total reactance of 15 ohm and motor
current of 3.1 amp . Calculate the power factor.
Explain graphically the torque speed characteristic of repulsion motor.
SECTION B
Attempt any three of the following: 10 x 3 = 30
A slip power converter is directly connected to a 3? phase 50 hz wound rotor
induction motor having 6 pole. Induction motor is used to control the speed of a load
requiring torque proportional to the cube of its speed. if the speed is vary between 60
to 600 rpm and load needs a power of 5KW at 600 rpm then determine the power
handled by the slip power converter in terms of slip when slip power returned to the
supply. Also determine the value of slip power and motor in put at 60 and 600 rpm
and amount of maximum power that the slip power convertor can carry. Neglect
losses.
Derive the equivalent circuit of a single phase induction motor with the help of double
revolving field theory.
Describe with appropriate sketch, a 2phase 8/4 pole permanent magnet stepping
motor. For this motor determine the step angle and the excitation sequence of the 2
phase winding for clockwise an anticlockwise rotation of the rotor.
Explain a three pulse three phase brushless dc motor. Discuss how torque is
developed in this motor.
A 220 volt 50 hz, 400 W , 2500 rpm ,single phase series motor has total resistance of
15 ohm . For a stray power loss of 30 W find current and power factor when machine
works under rated conditions.
3.
SECTION C
Attempt any one part of the following: 10 x 1 = 10
(a) Explain static slip power recovery scheme for the speed control of a wound
rotor induction motor. Why it is more popular for adjustable speed drive?
(b) Explain equivalent circuit of double cage induction motor. A 3 phase,8 pole 50
hz, 440 volt induction motor develop maximum torque at a slip of 8 %. In a
particular application, it runs at 3% slip at rated voltage, driving a load to stop
demand is proportional to square of speed. What is the maximum value to
which the supply voltage can drop, if the speed of the motor is not to decrease
below 950 rpm? Neglect stator impedance drop.
Attempt any one part of the following: 10 x 1 = 10
(a) Why single phase motor is not self start? Explain capacitor start capacitor run
motor with its torque slip characteristic in detail. Which capacitor has higher
value, the start or run capacitor ? give reason.
(b) Explain construction and working of 2 phase AC servomotor, and draw its
torque slip characteristic with different rotor resistance. Also give its
advantages.
Attempt any one part of the following: 10 x 1 = 10
(a) Enumerate the features that the drive circuit for a stepping motor should posses
for optimum torque output. also describe the drive circuit used for VR and
hybrid stepping motors.
(b) Describe the inverter drive circuit used for switched reluctance motors A three phase
6/8 VRM is running at a speed of 1000 rpm Calculate the time between pulses
required to excite the phase winding.
Attempt any one part of the following: 10 x 1 = 10
(a) Explain construction and principle of operation of a PMAC motor.
(b) Explain in detail construction and working principle of reluctance motor. Also
show its characteristic.
Attempt any one part of the following: 10 x 1 = 10
(a) Explain construction and working of linear induction motor brie?y with its
applications.
(b) A universal series motor operates on 200 volts d.c. , draws a current of 10 amp
and runs at 1440 rpm. Find the new speed and power factor when machine
connected to 200 volt 25 hz supply . The motor has a resistance of 1 ohm and
total inductance of 0.1 H.
This post was last modified on 29 January 2020