Tähtikolmiokäynnistys

Tähtikolmiokäynnistys, also known as a wye-delta starter, is a method used to reduce the starting voltage applied to a three-phase induction motor. This reduction in voltage leads to a lower starting current, which can be beneficial for several reasons.

The principle behind a wye-delta starter is to initially connect the motor windings in a wye (or star) configuration. In this configuration, the voltage across each winding is reduced by a factor of the square root of three (approximately 58%) compared to a direct delta connection. This lower voltage results in a significantly reduced starting torque and, more importantly, a lower starting current. After the motor reaches a certain speed, the connections are switched to a delta configuration, allowing the motor to run at its full rated voltage and power.

This method is particularly useful for larger motors where direct online starting would draw excessive current from the power supply, potentially causing voltage dips or tripping protective devices. By using a wye-delta starter, the inrush current can be reduced to about one-third of that of a direct online start.

The switching from wye to delta is typically done automatically by a timer or manually by an operator. While effective, wye-delta starting does produce a momentary interruption in power during the transition, which may not be suitable for all applications. The starting torque is also reduced, so this method is best suited for loads that do not require a very high starting torque.