Maximum Efficiency Condition

Correct Answer

D — Armature copper losses are equal to constant losses

Explanation

For a DC machine operated with essentially constant flux, maximum efficiency occurs when the variable copper loss equals the constant losses. In a motor this is commonly expressed as armature copper loss equal to constant losses.

Key Concept

Maximum Efficiency Condition

Formula

I_a²R_a = constant losses

Exam Point

Maximum efficiency: variable loss = constant loss.