1. Trupti Kumar
Member

i have a small doubt regarding dc macines…
suppose a shunt dc motor is loaded and running in stable condition and suddenly i have turned off the power suppply to its field winding then would its speed increase as speed is inversely proportional to flux or would the speed decrease as the net power input to the machine(not armaature alone) is decreased but the load torque is same,if possibble please give me information about what would be its effect on back emf.

1. P = W * T (W = 2 * pi * f) f=freq, T = torque

as field = 0, and as its inversely proportional to speed, speed becomes infinite.

Hence T = P/(infinite),
Torque becomes zero and motor comes to an eventual stop. As there is not field generated hence no Back Emf.

NOT SURE ABOUT THE ANSWER’S Correctness…I’m good at A/C machines lost complete touch with DC…Please correct me if i’m wrong

1. Santhosh
Member

when the motor is loaded and field is opened the total mech torque is acting opposite to electromagnetic torque( ELEC TORQUE which is equal yo ZERO))
so motor will stop..