See figure attached.

They give us details of the no load conditions for this shunt DC machine and I assume that's how you are supposed to find the rotational losses but I can't seem to figure it out.

How do you obtain the rotational losses using the information provided from the no load conditions?

Thanks again!

 

At no load the motor presumably draws 5A at a set terminal voltage of 230 V.

The shunt field would take 2A, so the armature has the remaining 3A. The armature resistance drop is 0.3V so the armature emf = 229.7V. The no-load power input is therefore found from the 3A current and 229.7V armature emf - which would correspond to the rotational loss.

 

At no load the motor presumably draws 5A at a set terminal voltage of 230 V.

The shunt field would take 2A, so the armature has the remaining 3A. The armature resistance drop is 0.3V so the armature emf = 229.7V. The no-load power input is therefore found from the 3A current and 229.7V armature emf - which would correspond to the rotational loss.

Thank you very much.

It wasn't clear to me from the question that the no load condition was indeed at a terminal voltage of 230V.