Electronic Engineering (Maths)

Question

The voltage equation for a motor is – 

V = E + Ia*Ra

where, Ia = Armature Current, Ra = Armature Resistance and E = Induced  EMF

A 240 V DC motor has an armature resistance of 2.5 Ω. If the full load armature current is 13A, find the induced EMF.

Answer 1

V=240V Applied Voltage

I_a=13A Full Load Armature Current

R_a=2.5Ω Armature Resistance

E=V-I_aR_a=240V-13A*2.5Ω=207.5V Induced Emf

E=207.5V

This assumes that the motor is a Shunt Wound DC Motor which is typically used in constant speed applications such as lathe, drills, boring mills, spinning and weaving mills etc.

The equation provided is not appropriate for Series Wound or Compound Wound DC Motors which have different formulas.