doubt in machines

- 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.
    
    May 27, 2012 at 7:12 am
- 1. Sriram Kasyap
    Member
    
    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
    
    Jun 02, 2012 at 5:54 pm
- 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..
    if my answer is wrong.. then please text me at
    
    http://www.facebook.com/pvskskumar
    
    Oct 05, 2012 at 2:19 pm
- 1. Santhosh
    Member
    
    flux zero implies back emf too zero
    
    http://www.facebook.com/pvskskumar
    
    Oct 05, 2012 at 2:22 pm