The starting torque of the resistance start motor is about 1.5 times the full load torque. Here, n 0 is the point at which the centrifugal switch operates. The Torque Speed Characteristic of the Split Phase motor is shown below: This phase difference is enough to produce a rotating magnetic field. The time phase difference ϕ is not 90 degrees, but of the order of 30 degrees. Thus, there exists a time difference between the currents of the two windings. The current in the auxiliary winding I A is approximately in phase with the line voltage. The current in the main winding (I M) lags behind the supply voltage V almost by the 90-degree angle. The phasor diagram of the Split Phase Induction Motor is shown below: Therefore, the relay opens and disconnects the auxiliary winding from the supply, making the motor runs on the main winding only. Thus, the starting winding is in the circuit, and as the motor attains the predetermined speed, the current in the relay starts decreasing. In the starting, the heavy current flows in the circuit, and the contact of the relay gets closed.
Motor winding resistance chart series#
If the motors are rated about 100 Watt or more, a centrifugal switch is used to disconnect the starting winding and for the smaller rating motors relay is used for the disconnecting of the winding.Ī relay is connected in series with the main winding.
At the starting of the motor both the windings are connected in parallel.Īs soon as the motor reaches the speed of about 70 to 80 % of the synchronous speed the starting winding is disconnected automatically from the supply mains. Hence, the starting torque is small, of the order of 1.5 to 2 times the stated running torque. The current in the two windings is not equal as a result, the rotating field is not uniform. A resistor is connected in series with the auxiliary winding.
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