Question

Where will speed-torque characteristics will lie when armature reaction is considered?

(a) Below the speed-torque characteristics when armature reaction is not considered

(b) Above the speed-torque characteristics when armature reaction is not considered

(c) On the speed-torque characteristics when armature reaction is not considered

(d) Can be anywhere with the speed-torque characteristics when armature reaction is not considered

The question was posed to me in unit test.

My question is based upon Speed Control Using Field Control of Shunt Motor in portion DC Motors of DC Machines

Answer 1

Right answer is (b) Above the speed-torque characteristics when armature reaction is not considered

Explanation: The speed-torque characteristic which has a small linear drop due to the second term (Ra effect) and translates upwards as the field is weakened due to the armature reaction. The demagnetizing effect of the armature reaction causes the characteristics to somewhat bend upwards with increasing torque (increasing load current).