1.
In dc machines by increasing the number of poles, all of the following reduce except:
A
Weight of copper
B
Weight of iron parts
C
Frequency of flux reversals
D
Overall size of the machine
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In dc machines by increasing the number of poles, all of the following reduce except:
Weight of copper
Weight of iron parts
Frequency of flux reversals
Overall size of the machine
In dc machines the number of poles is generally decided by
Frequency of flux reversals
Weight of iron parts
Weight of copper
all of the above
The effect of harmonics in rotating machines can be minimized by
Use of longer air gap
Skewing the poles
Use of distributed winding
all of the above
The harmonics in rotating machines are generated due to
Non-sinusoidal field form
Slotting of the stator core
Both (A) and (B) above
None of the above
Skewing of rotor slots helps in
Improving beat transfer
Reducing noise
Suppressing undesirable harmonics
all of the above
The dimensions of a dc machine primarily depend on
kW output
Work done per revolution
Exposed surface
None of the above
The output of a rotating electrical machine is limited by
Size of the machine
Peripheral velocity
Temperature rise
None of the above
DC motor yoke is generally made of
Wood
Copper
Aluminum
Steel
Inter poles in DC machines are provided to reduce
Sparking
Armature reaction
Iron loss
Efficiency
An electric machine will have high efficiency when
input/output ratio is low
Reactive power is more
kWh consumption is low
losses are low
Which DC motors has approximately constant speed?
Series motor
Shunt motor
Cumulatively compound motor
All of the above.
In a DC series motor increase in load current results in
Decrease in speed
Increase in speed
Better commutation
Increase in the back emf
The starting winding of a single-phase motor is placed in
Rotor
Stator
Armature
Field
Which of the following motors has a high starting torque?
AC series motor
DC series motor
Induction motor
Synchronous motor
Damper windings are provided in synchronous machines to
Damp out rotor oscillations
Reduce the over-voltages under abnormal conditions
Facilitate starting
All of the above
A synchronous machine having large length of the air gap will have
Higher noise level
Smaller unbalanced magnetic pull
Lower limit of stability
Higher value of inherent regulation
In squirrel cage motors, skin effect occurs in
Stator winding
Rotor winding
Both (A) and (B) above
None of the above
In induction motor if the number of rotor slots is equal to the stator slots then
The motor will run smoothly
The motor will mil at zero slip
The noise level will be low
The motor may refuse to start
The use of double squirrel cage winding on the rotor provides
Low noise
Reduced starting torque
A large starting torque
Higher efficiency
Induction motor which of the following depends on the leakage reactance?
Starting torque
Maximum torque
Starting current
All of the above