21

Describe the effect on starting torque
if the supply voltage is ( a ) Increases
by 5% ( b ) Decreases by 5%.

The starting torque in the induction motor is directly proportional
square of the supply voltage therefore
( a ) T_{st2 }/ T_{st1 }= ( V_{2 }/ V_{1 })^{2}
^{ }= ( 1.05 / 1.0 )^{2}
^{ }= 1.1025
T_{st2 }= 10.25% T_{st1}
If the supply voltage is increased by 5% then
starting torque is increased by 10.25%.
( b ) T_{st2 }/ T_{st1} = ( V_{2 }/ V_{1 })^{2}
^{ }= ( 1  0.05 / 1.0 )^{2}
^{ }= 0 .9025
T_{st2}
= 90.25% T_{st1}
If the supply voltage is decreased by 5% then
starting torque is decreased by 9.75%.


22

Which parameters greatly affect the
maximum torque in the three phase induction motor?

Factor affecting maximum torque


23

At which value of slip, stable
operation of the induction motor depends?

The stable operation of the induction motor depends for the value of
slip between s = 0 and slip corresponding to maximum
torque.


24

Define : Pull out torque

Pull out torque


25

What should be rated supply voltage if
the rated supply frequency is increased by 20% for stable operation of the
induction motor?

If the supply frequency is increased by 20%, the rated supply voltage
will be 1.2 times the name plate rating for stable operation of the induction
motor.


26

Which parameters greatly affect the
flux in the air gap?

Flux in the air – gap
B_{max }α ( V / f )


27

What is magnetizing current in the
induction motor?

Magnetizing current


28

At which speed the value of
magnetizing current becomes minimum?

Synchronous speed


29

Describe the effect on torque and
rotor current if the supply frequency decreases in the three phase induction
motor.

Effect of supply frequency on torque and rotor
current


30

On which parameter the active power of
the Induction generator above the synchronous speed depends?

Slip


31

Which parameter greatly depends upon
straight torque – speed curve of the three phase induction motor?

Rotor resistance


32

What is meaning of the plugging in the
induction motor?

Plugging in the induction motor


33

Why the speed of the rotor decreases
during plugging period in the induction motor?

Plugging


34

What is induction generator or
asynchronous generator?

Induction generator


35

What is direction of torque and speed
in the case of induction motor and induction generator?

Induction Generator


36

What is operating speed range when the
induction motor works as ( a ) Induction motor ( b ) Induction generator ( c )
Brake

The speed range for


37

How to measure rotor frequency by
using milli – voltmeter in the slip
ring induction motor?

Measurement of rotor frequency


38

How to measure rotor speed without
using techo – meter in the slip – ring induction motor?

The speed of the rotor in the slipring induction motor is measured by
following methods
( a ) By comparing stator and rotor frequency
( b )
Stroboscopic method.


39

Describe the different methods to
measure slip in the induction motor.

Slip measurement


40

Why rotor copper loss in the induction
motor is neglected under running condition?

Rotor copper loss

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