Question

A 5 hp, 230 V DC motor has a nominal armature current of 25 A. If the armature resistance is 0.2 ohms, calculate the following:

i.The value of the starting armature current of the motor
ii.The value of the counter EMF with full load applied at rated speed.

Answer 1

The starting armature current of the motor is 1150 A. The counter EMF with full load applied at rated speed is 225 V.

Step-by-step explanation:

In order to calculate the starting armature current of the motor, we can use the formula:

IAstart = (V - E) / RA

Where V is the voltage, E is the back EMF, and RA is the armature resistance.

Substituting the given values:

IAstart = (230 V - 0) / 0.2 Ω = 1150 A

To calculate the counter EMF with full load applied at rated speed, we can use the formula:

E = V - IAfull * RA

Where IAfull is the full load armature current.

Substituting the given values:

E = 230 V - 25 A * 0.2 Ω = 230 V - 5 A = 225 V