Department of Electrical Engineering
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Pre-University
Test : 15/04/2017
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8EE2A:
Electric Drives and their Control
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Attempt all questions.
Internal options are given in each question. All questions have been asked in
previous years- RTU Papers
1
a)
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Explain the classifications of Load Torques.
Discuss their nature.
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8
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b)
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Explain Load Equalization in Drives with
necessary diagrams and derivatives.
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8
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OR
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1
a)
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A motor equipped with a flywheel is to supply a
load torque of 1000 N-m for 10 second followed by a light load period of 200
N-m long enough for the flywheel to regain its steady state speed. It is
desired to limit the motor torque to 700 N-m. What should be moment of
inertia of flywheel? Motor has the inertia of 10 Kg-m2. Its no
load speed is 500 rpm and slip at a torque of 500 N-m is 5%. Assume speed
torque characteristic of motor to be a straight line in the region of
interest.
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8
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b)
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What do you understand by Steady State Stability?
Discuss its main assumptions.
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8
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2
a)
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Explain the various methods of speed control of
DC Motors.
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8
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b)
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What are different types of braking methods used
in DC Motor? Discuss the differences
between each type of braking
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8
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OR
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2
a)
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A 200 Volts, 200 Amps, 800 rpm DC separately
excited motor has an armature resistance of 0.06 Ohms. The motor armature is
fed from variable voltage source with an internal resistance of 0.04 Ohms.
Calculate internal voltage of the variable voltage when the motor is
operating in regenerative braking at 80% of the rated motor torque and 600
rpm
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8
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b)
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A 200 Volts, 10.5 Amps, 2000 rpm Shunt motor has
the armature and field resistance of 0.5 Ohm and 400 Ohms resp. It drives a
load whose torque is constant at rated motor torque. Calculate speed if
source voltage drops to 175 Volts.
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8
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3
a)
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Discuss the A.C. Dynamic braking of Induction
motor drives
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8
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b)
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Discuss the various starting methods of three
phase Induction motors.
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8
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OR
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3
a)
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Discuss the voltage source inverter fed induction
motor drive operated in stepped wave inverter mode
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8
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b)
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A 400 Volts, star connected, 3 ph, 6 poles, 50 Hz
Induction motor has following parameter referred to stator: RS= R’r= 1
Ohm, Xs= X’r = 2 Ohms. For regenerative
operation of this motor, determine over-hauling torque it can hold and range
of speed for safe operation.
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8
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4
a)
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Explain the static Kramer’s drive for Induction
motor. Give its circuit diagram and
derivations.
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8
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b)
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Explain the Frequency control method of Induction
motor. How frequency can be controlled by power electronics devices
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8
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OR
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4
a)
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Explain the slip power recovery scheme with
static scherbius drive. Give the circuit diagram and derivation
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8
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b)
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Discuss the voltage source inverter control of
Induction motor
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8
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5
a)
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Explain the dynamic braking of synchronous motor
with VSI.
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8
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b)
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Discuss the operation of VSI fed self controlled
Synchronous motor drive
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8
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OR
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5
a)
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Explain the braking of Synchronous motor with
VSI. Draw the Speed-Torque characteristics of Regenerative braking
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8
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b)
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Explain the control of Synchronous motor with CSI
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8
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