Stator Start with Autotransformer

STATOR START WITH AUTOTRANSFORMER

This type of starting is used when it is desired to reduce the transient starting and running current from the mains to lower levels than starting with stator resistors but with the same starting torque.

The motor is supplied via an autotransformer with a reduced voltage of approximately 70% from the rated operating voltage. This reduces the current to half the transient starting current under direct connection.

Operation
The figures show the circuits for this startup. Below we describe its mode of operation:

• Pressing the S1Q button connects the K4T timer and the coil of the K1A contactor, which connects the primary of the autotransformer to the network and the secondary, through the K3A contactor, connects it to the motor, so that it starts at reduced voltage.
• Once the timing period for K4T has elapsed, it disconnects K1A and connects K2M. Additionally, K2M disconnects K3A and the motor operates at normal full speed.
• A new start will only be possible if the S1Q push button is pressed or the F2F protection devices are triggered.

Applications

High-power or high-inertia machines in cases where the reduction of peak intensity is an important criterion.