MCQs on Electrical Machines

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01․ Slip rings of an induction motors are made of
carbon.
stainless steel.
aluminium.
phosphor bronze.

Under construction.
02․ Which type of bearing is provided in small induction motors to support the rotor shaft?
Ball bearings.
Bush bearings.
Cast iron bearings.
None of the above.

Under construction.
03․ In 3 - Φ induction motor some times copper bars are placed deep in the rotor to
reduce copper loss.
improve starting torque.
improve power factor.
improve efficiency.

Under construction.
04․ The rotor slots are slightly skewed in squirrel cage induction motor to
economize on the copper to be used.
provide ease of fabrication.
reduce magnetic hum and locking tendency of rotor.
increase of the strength of rotor bars.

Under construction.
05․ The induction motor shaft is made of
mild steel.
cast iron.
aluminium.
stainless steel.

Under construction.
06․ The shaft of induction motor may be unbalanced due to
uneven air gap.
poor lubrication.
overheating of winding.
overload.

Under construction.
07․ Motors for fans and pumps are selected in the rpm range
375 to 500.
500 to 720.
720 to 920.
1440 to 2880.

Under construction.
08․ Induction motors provided with open slots have
more breakdown torque.
less breakdown torque.
higher efficiency.
leading power factor.

Under construction.
09․ If any two leads from slip rings are interchanged in a 3 - Φ induction motor, the motor will
not run.
continue running in the same direction as before.
run in a direction opposite to previous one.
get damaged.

Under construction.
10․ The 3 - Φ induction motors are, by a very considerable margin, the most widely used AC motors as
they are capable of operation under range of leading and lagging pf.
these are cheaper in cost, simple and rugged in construction.
they have very good speed regulation.
they have maximum efficiency and maximum starting torque.

Under construction.
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