Question { Bhel, 21624 }

why motor starting current is High ?

Answer

Dear Mr. Gajanan, as you are dealing with more machineries,
i want to stress some points:
During starting of motor:

the armature(rotor) is stationary, and it does not having
any magnetic property to resist the applied rotational
frequency at that time.

so it will act as a conductor fixed at rotating magnetic
field and produce some eddy current loss, and with in short
period of time, it will develope some anti rotional effect
to resist the rotational field, ie: rotating with same
direction to reduce the eddy curent.Thats why after
starting current reduces.

inertia of the rotor also having some major role on the
starting current. The gap between rotor and stator having
role on the starting current and initial power factor.

Question { Bhel, 14966 }

a 3 phase motor was running with delta connected, suddenly
one phase winding got burnt off, what will be the effect ?

Answer

delta connected winding, one winding burnt off means, its
open circuited. So the motor will work as open delta system
and run normaly with non uniform torque.
The max. load that can carry will be reduced to 57.7% of
full load.
If the motor is connected through a phase faliure relay,
the relay will trip the total ckt.

Question { Reliance, 7861 }

why ELCB's are not useful for operation theater equipments ?

Answer

Operation theatre using life saving equipments,and even if
there is small leakage, the circuit will trips off and if
it happends during a major operation, it should not be happen.

Question { 9546 }

Fire pumps are not used with ELCB control, why ?

Answer

Fire pumps are emergency equipment, and even if there is
earth leakage, it should work uninterrupted.
So ELCB's are not used with fire pumps as per NFPA norms

Question { Indian Military Services, 13338 }

How can you justify a fully carged battery by physical
checkup ?

Answer

By touching the battery, we can sense the temperature. if
there is enough temperature, we can assue its fully charged.

also check the metal body temperature of the equipment, if
both battery and equipment are at same temp. our assumption
is wrong