Separately Excited DC Motor Speed Control

Correct Answer

A — 1, 2 and 3

Concept and Reasoning

For a separately excited DC motor, speed is approximately N∝(V−IaRa)/Φ. Therefore speed can be controlled by changing armature supply voltage V, field current (which changes flux Φ), or effective armature-circuit resistance. All three listed methods are valid, so option A.

Calculation / Key Relation

N∝(V−IaRa)/Φ

Exam Takeaway

DC motor speed has three main levers: armature voltage, field flux and armature resistance.

Common Mistake

Do not assume field control is the only speed-control method for a separately excited motor.