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A 220-V DC machine has an armature resistance of 1 Ω. If the full-load current is 20 A, the difference between the induced voltage when the machine runs as motor and as a generator is:

A 220-V DC machine has an armature resistance of 1 Ω. If the full-load current is 20 A, the difference between the induced voltage when the machine runs as motor and as a generator is: Correct Answer 40 V

Concept:

Induced EMF in the generator is given by

Eg = V + Ia× Ra

Induced EMF in the motor is given by

Em = V – Ia × Ra

Where V = terminal voltage

Ia = armature current

Ra = armature resistance

Calculation:

Difference between induced EMF when machine act as a generator and as a motor = Eg - Em

= 2 IaRa = 2 × 20 × 1 = 40 V

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