stjärndeltastart

Stjärndeltastart, also known as wye-delta start or star-delta start, is a method used to reduce the starting current of three-phase induction motors. It is a common and economical way to limit the inrush current drawn by a motor when it is first switched on. Standard starting methods for three-phase motors can draw a very high current, typically five to eight times the motor's full-load current. This high current can cause voltage sags on the power supply, which can affect other equipment, and can also place mechanical stress on the motor and associated components.

The stjärndeltastart method works by initially connecting the motor windings in a star (wye) configuration. In this configuration, the voltage across each winding is reduced by a factor of sqrt(3), and consequently, the starting current is also reduced to approximately one-third of what it would be if connected in a delta configuration directly. After a predetermined time, or when the motor has reached a sufficient speed, the connections are switched to a delta configuration. In the delta configuration, the motor then operates at its rated voltage and delivers its full power. The transition from star to delta is typically done using a timer and a set of contactors. This method is effective for motors that are not heavily loaded during startup and are designed to run in a delta configuration at their rated voltage.