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Star-Delta Motor Starting Mathematical Expansion

Motor Starting Ways

Asynchronous motors draw up to 3-4 times their nominal current at the time of the first start. Although these values ​​do not have much effect on the electrical installation in small motors, they can cause some negative situations in large powerful motors.

When a large powerful asynchronous motor draws 3-4 times the nominal current in the direct start, these high currents can damage the windings of the motor. Another effect of the high current drawn is that it causes voltage drop.

Asynchronous motors, various starting methods are applied to the motors against these adverse effects that may arise at the time of take-off. One of the cheapest and easiest methods of these methods is the star-delta starting method.

Asynchronous motors can be safely taken off with the star-delta starting circuit that can be installed with three contactors and a time relay.

The star-delta starting method, where the inrush current drops around 30% and the inrush torque drops around 25%, can be used safely in applications that do not take off with full load.

The motor must be suitable for this method in order to apply the star-delta starting method. If star-delta starting values ​​are shown in motor plate values, star-delta starting can be given to the motor.

In addition, since the starting torque is low in star-delta starting method, this method cannot be used in systems that will take off with heavy loads.

The triangle outline current is 3 times the star outline current. However, since the star operation takes place at the time of development, the star working currents are also high due to the moment of development + load moment. Practitioners know this difference between this theoretical knowledge (let’s say plain logic, let’s not say theoretical knowledge) and practice. The vast majority of the reasons for star contactors to fail are due to this.