Electrical Engineering ⇒ Topic : Capacitor start-cum-run motor method

Capacitor start-cum-run motor method

The capacitor start motor employs capacitance to split the phase, rather than resistance. The use of capacitance has many advantages. The fluxes in the two phases can be made to have a phase difference of practically 90⁰, so that the motor becomes essentially a two-phase motor. Figure (a) shows the connection diagram.

                                     figure (a) Capacitor start-cum-run motor method.

Since the currents I_m and I_a differ by almost 90⁰, the starting torque is considerably greater than with the usual split-phase motor of the same rating. The capacitance may remain in the circuit continuously so that the power factor of the motor is very nearly unity. The starting torque can be further increased by increasing the capacitor rating.