Final answer:
At rated speed, a small value of capacitance is left in the circuit, utilizing the oil-filled run capacitor for optimal efficiency and power factor.
Step-by-step explanation:
When running at rated speed, a small value of capacitance is left in the auxiliary winding circuit of a two-value capacitor single-phase motor. The auxiliary winding, energized by a capacitor during start-up, helps in creating a phase shift to produce the necessary starting torque for the motor. Once the motor reaches its operating speed, the electrolytic start capacitor with higher capacitance is usually removed from the circuit by a centrifugal switch or electronic relay, leaving the oil-filled run capacitor with a smaller value of capacitance in the circuit to optimize running efficiency and power factor. Oil filled capacitors are used for start-up and have a larger capacitance value, while electrolytic capacitors are used for continuous operation and have a smaller capacitance value. The leftover small capacitance in the auxiliary winding circuit helps in the motor's starting and running processes.