DOL Direct-on-line starting

 Direct-on-line starting

This method of starting in just what the name implies the motor is started by connecting it directly to 3-phase supply. 

The impedance of the motor at standstill is relatively low and when it is directly connected to the supply system. 

The starting current will be high (4 to 10 times the full- load current) and at a low power factor. 

Consequently, this method of starting is suitable for relatively small (up to 75 kW) machines.

Note that starting current is as large as five times the full-load current but starting torque is just equal to the full-load torque. 

Therefore, starting current is very high and the starting torque is comparatively low. 

If this large starting current flows for a long time, it may overheat the motor und damage the insulation