Question

Why is the role of running capacitor in Ac induction motor? Why only 1 phase motor has a running capacitor and whereas 3 phase motor does not have?

Answer 1

The single phase induction motors are not self starting because the produced stator flux is alternating in nature , the starting the two components of this flux each other and hence ther is no net torque.

run capacitors are used to self start the single phase induction motor. Run capacitors are used in single phase induction motor to energize the second phase winding to create a rotating magnetic file while the motor is running.

Three phase induction motor is self starting so there is no use of run capacitor to make self start the motor