Q1. What are the drawbacks associated with the operation of induction motor with unbalanced rotor impedance?
Sol: when an
induction motor operates with an unbalanced rotor impedance following problems
arise –
1.
Overall shaft torque is low.
2.
Extra current is required.
3.
Harmonic disturbance.
Q2. During plugging operation of a wound rotor induction motor usually an extra resistance is inserted in rotor circuit, why?
Sol: During plugging operation of a wound rotor
induction motor usually an extra resistance is inserted in rotor circuit to limit the high flowing current during
plugging to save the rotor winding from burning.
Q3. Define Slewing/ what is slewing for a machine?
Sol: It is the response of a machine to a
sudden large increase in input, especially one that causes the device to
respond/operate at its maximum rate is called slewing.
Q4. Why deep bar
cage rotor and double cage rotor are used in induction motor?
Sol: deep bar cage rotor and double cage rotor are used for
obtaining high starting torque at low current. This is why we use deep
bar cage rotor and double cage rotor induction motor.
Q5. Why low
speed machines are preferable when frequent starting and stopping is required?
Sol: low speed machines are preferred over high speed when frequent starting and
stopping is required since inertia is
easy to overcome in case of low speed machines while it will be difficult
to overcome inertia in case of high
speed rotating machines.
Q6. Explain how
the operation of a 3 phase induction motor is effected when single phasing
occurs.
OR
What is single phasing?
Sol: If an induction motor / three phase motor undergoes single
phasing follow things will take place –
1.
The motor will run with reduced speed.
2.
It will operate with an uneven torque and it will also produce a humming noise.
3.
It may also cause overloading of the generator.
Q7. What do you
understand by a double cage induction motor/ what is a double cage induction
motor?
Sol: In a double cage
induction motor there are two rotor
windings or cages are used. These two rotor winding or cages are used for obtaining high starting
torque at low starting current. The stator of double cage induction motor is
no different than the stator of an ordinary induction motor.
Sol: double cage
induction motors are widely used in the industries and other places due to
following reasons.
1.
A double cage rotor, induction
motor provides a high starting torque.
2.
A double cage rotor, induction
motor draws very low current at
starting and provides a high starting torque.
3.
A double cage rotor, induction
motor is more suitable for direct on line starting.
4.
The cost of A double cage
rotor, induction motor is low.
Q9. What is a
constant torque drive?
Sol: a constant torque drive is used for controlling of slip
and hence to provide a constant torque the
slip power sPg is either returned or taken from the supply
mains.
Q10. What is a
constant power drive?
Sol: A constant power drive is used for controlling of
slip, for obtaining a constant power drive, the slip is either taken or added
to the shaft output of the main induction motor.
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