Related Questions

In medium sized induction motors, the slip is generally around
A 0.04 %
B 0.4 %
C 4 %
D 14 %
Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors?
A Low cost
B Wide speed range
C Stability
D High starting torque
In squirrel cage induction motors which of the following methods of starting cannot be used?
A Resistance in rotor circuit
B Resistance in stator circuit
C Autotransformer starting
D Star-delta starting
Blocked rotor test on induction motors is used to find out
A Leakage reactance
B Power factor on short circuit
C Short-circuit current under rated voltage
D All of the above
For three-phase induction motors which of the following is the least efficient method of speed control?
A Cascade control
B Pole changing
C Rheostat control
D Combination of cascade and pole changing
Which type of bearing is provided in small induction motors to support the rotor shaft?
A Ball bearings
B Cast iron bearings
C Bush bearings
D None of the above
In induction motors, the length of air gap in kept as small as mechanically possible is order to have
A low power factor
B high power factor
C high over load capacity
D any of the above
In three-phase squirrel-cage induction motors
A Rotor conductor ends are short-circuited through slip rings
B Rotor conductors are short-circuited through end rings
C Rotor conductors are kept open
D Rotor conductors are connected to insulation
In three-phase induction motors sometimes copper bars are placed deep in the rotor to
A Improve starting torque
B Reduce copper losses
C Improve efficiency
D Improve power factor
In squirrel cage induction motors, the rotor slots are usually given slight skew in order to
A Reduce windage losses
B Reduce eddy currents
C Reduce accumulation of dirt and dust
D Reduce magnetic hum

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