20.

21.

22.

23.

24.

098/23

The primary objective for making the coil span of a DC armature winding equal to a
pole pitch is to

A
B

) Ensure the addition of emf of consecutive turns

) Obtain a coil span of 180 degree electrical

C) Obtain a full pitch winding

D) Distribute the winding uniformly under different poles

The primary objective of commutating or reversing emf in DC machine is to
A) Neutralize the reactance voltage

B
0
0

)
) Neutralize the commutating resistance
) Reduce heat production

) Convert AC to DC

Under light load condition a series generator has rising voltage characteristics, but
at a high loads the voltage starts decreasing due to

A) Over heating of brushes
B
0

)
) Low cross magnetising effect

) Poor armature field resistance

D) Excessive demagnetising effects of armature reaction

A 250 V shunt motor with armature resistance of 0.5 Q runs at 600 rpm on full load
and takes an armature current of 20 A. If resistance of 1.0 Q is placed in the armature
circuit, then the speed at half-full load torque is

A) 587.5 rpm B) 600 rpm

C) 475.3 rpm D) 1200 rpm

In a retaration test on a separately excited motor, the induced emf in the armature fall
from 220 V to 190 V in 30 seconds on removing the armature from the supply. The
same fall take place in 20 seconds if immediately after disconnection the armature
is connected to a resistance which takes 10 A during this fall. Then the stray losses
of the motor is

A) 1950 W B) 2750 W C) 3500 W D) 4100 W