The type of single-phase induction motor, expected to have the maximum power factor during steady state running condition, is

The correct answer is capacitor start, capacitor run.

Let's analyze the characteristics of different single-phase induction motors to understand why the capacitor-start capacitor-run motor has the maximum power factor during steady-state running conditions:

1. Split-phase (Resistance start) Motor:
This motor uses an auxiliary winding with high resistance and low reactance, and a main winding with low resistance and high reactance. During running, the auxiliary winding is disconnected by a centrifugal switch. The motor runs only on the main winding, which is highly inductive, resulting in a relatively low running power factor (typically 0.55 to 0.65).

2. Shaded-pole Motor:
This motor has extremely low efficiency and a very poor power factor (typically 0.3 to 0.5) due to high copper losses and the nature of the shading coil lagging magnetic field mechanism.

3. Capacitor-start Motor:
This motor uses a capacitor in series with the starting (auxiliary) winding to get a high starting torque. However, once the motor reaches about 75% to 80% of synchronous speed, a centrifugal switch disconnects the auxiliary winding and the capacitor. During steady-state running, it operates just like a split-phase motor on the main winding alone, resulting in a low running power factor.

4. Capacitor-start, Capacitor-run (Two-value Capacitor) Motor:
This motor utilizes two capacitors: a high-value capacitor for starting and a low-value capacitor for running. The running capacitor remains in series with the auxiliary winding during normal steady-state operation. The presence of this running capacitor continuously counteracts the inductive reactance of the motor windings, which significantly improves the phase angle between the voltage and current. Consequently, it achieves the highest power factor under steady-state running conditions (often close to 0.85 to 0.90 or higher).