For the starting of Motors, on-line starting is a simple and inexpensive means. While it provides maximum starting torque andacceleration, it has two important limitations:
Various types reduced voltage starting are used, mainly on motors 25 HP or larger, to overcome this limitation.
The major advantages of this method of starting motors are:
Autotransformer – Starting uses an Autotransformer to reduce the line voltage during the starting period. The Autotransformer Voltage taps provide choice of three different starting currents and torques, depending on the load requirements. In this system, the first step is connected one of the reduced voltage taps which results in a reduced starting current and torque. After a pre-set time delay, the second step applies full rated voltage to the motor for normal operation. For the same value of line current drawn during the starting period, motors with Autotransformers type starters deliver the maximum starting torque when compared to other type of starters.
Specifications: In order to completely specify the auto-transformer, the following information is required.