Consider the above diagram. It represents a DC electrical$$ machine with $18$ slots.$$ The machine is rotating$$ clockwise at constant speed and the diagram shows the rotor position at a particular instant.$$ Rated currents flow$$ in the field winding and in the armature winding.

The armature$$ teeth are labelled $"$t$".$The nine armature slots$$ on the left hand side are labelled $"$A$+"$ The nine armature slots on the right hand side are labelled $"$A$-".$ The slots$$ labelled $"$A$+"$ house conductors that carry current with direction$$ "into"$$ the screen or page. The slots$$ labelled $"$A$-"$ house conductors that carry current in the opposite direction.$$ All slots contain the same number of conductors and all conductor currents have the same magnitude.

The field winding cross sections are labelled $"$F$+"$ and $"$F$-".$ The sections labelled $"$F$+"$ are those where the field current flow$$ "into" the screen or page.$$The sections labelled $"$F$-"$ are those where the field current flow$$ "out of$"$ the screen or page.

Which$$ one is the correct statement?

Question $5$Answer

a$.$

The electromagnetic torque is acting anti$-$clockwise driving the rotor with the electrical machine in generating mode.

b$.$

All the other statements are incorrect.

c$.$

The electromagnetic torque$$ is acting clockwise on the rotor attempting to slow it down.

d$.$

The electromagnetic torque is acting anti$-$clockwise opposing the motion of the electrical machine which is in generating mode.