AC and DC Machines

A homopolar generator usually has

high voltage and high current

low voltage and low current

low voltage and high current

high voltage and low current

The teeth in the armature of a dc machine are something skewed.This is done to reduce

hysteresis loss.

eddy current loss.

copper loss.

vibrations.

Which of the following are the variable losses in a rotating machine?

copper and mechanical losses

core loss and stray load loss.

core loss and mechanical loss

copper loss and stray load loss.

In electromechanical energy conversion devices(e.g. generators and motors),a small air gap is left between the stator and the rotor ignored to

increase fiux density in the air gap.

permit mechanical clearance

avoid saturation of field

reduce the reluctance of the magnetic path.

Laminated yoke in dc motor can reduce

iron loss.

temperature rise.

sparking on load.

speed regulation

The commutator pitch for simplex lap winding is

average pitch

+1

-1

+1 or -1

In a dc machine armature windind,the number of commutator segments is equal to the number of armature

conductors

coils

turns

coils sides

Minimum number of coils for 400v,6-poles lap connected dc machine for a maximum voltage of 15v between adjacent commutator segments should be

80

400

299

160

The commutator pitch for simplex wave winding is equal to

half average pitch

average pitch

twice average pitch

+1 or -1

Armature of a dc machine is made of

insulating material.

silicon steel

conducting material

non-ferrous material