Significance of Counter EMF

Ia = (Vln –CEMF)/Ra.

Ia = armature current
Vln = line voltage to the motor
Ra = armature resistance
CEMF = voltage generated within the motor

Equation tells us that the armature current is a function of the applied voltage minus the CEMF. Because CEMF increases with motor speed, the faster the motor runs, the less current the motor will draw, and consequently its torque will diminish. This explains why most DC motors have a finite maximum speed; eventually, if the motor keeps going faster, the CEMF will nearly cancel out the line voltage, and the armature current will approach zero.

Speed regulation is the ability of a motor to maintain its speed when the load is applied. The basis of this self-regulation is the CEMF. When the motor’s load is increased, the speed tends to decrease, but the lower speed reduces the CEMF, which allows more current into the armature. The increased current results in increased torque, which prevents the motor from slowing further.
Courtesy : eblogbd.com