Two DC machines are mechanically coupled. One is operating as a motor and the other as generator. The iron and frictional losses of the machines will be identical when:
- A. Their speeds are identical
- B. Their speeds and excitation are identical
- C. Their speeds are equal and back emfs are half of the supply voltage
- D. Their armature sizes are identical
Answer: B. Their speeds and excitation are identical
Explanation: Excluded from evaluation by ISRO. Iron losses depend on flux (excitation) and frequency (speed); mechanical friction and windage losses depend on speed. Hence both are identical when speeds and excitations are identical.