Test: Operating Characteristics Of DC Motors - Electrical Engineering (EE) MCQ

If the dc motor has compensating winding, flux will remain constant regardless of load.

Torque = Power/(speed in rev/s)
= 5000/(2*pi*1000/60)
= 47.76 N.

The flux and induced emf are non linear function of its mmf.

If the torque is zero in dc series motor then the speed will be infinite causing the damage of the machine permanently.

Shunt machine has almost constant speed while the series varies as inverse relation with torque.

This is basically an unstable scenario which makes the machine unable to be used.

 It is so because of the unstable speed and torque characteristics. At starting, armature current and series field current are high. Since the series flux subtracts from shunt flux, series flux actually reverses the magnetic polarity.This motor will typically be still or turn slowly in wrong direction while burning up because of excessive current.

At starting , the flux should be rated so that there is no abnormal situation arise.

At no load, armature current is zero, so the internal generated voltage is 250 V. So 5 A will be the shunt field current at no load.

As the starter is placed very rapidly from off to on the resistance seen by the machine will be very less and it will draw a large starting current.