Two DC series machines are mechanically coupled. One machine is running as a motor and the other as a generator. The iron and friction loss 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 excitations are equal and back emfs are half of the supply voltage
Answer: B. Their speeds and excitation are identical
Explanation: Because they are mechanically coupled and identical series machines, their rotational speed is mechanically identical, and identical series armature-field currents ensure identical magnetic excitation.