Why the Rotor of Slip Ring Induction Motor always Star Connected?

You may think why the rotor of the slip ring induction motor always stars connected, what will be the problem if it is Delta connected. There are some very simple reasons which are explained in this article.

Reason 1: Insulation Problem

The first and main important reason is the Insulation problem. We know that in a star connection, the phase voltage is root three times lesser than the line voltage, so if the rotor winding is connected in a delta connection the voltage across each winding will be high, therefore more insulation arrangement is required which is not economical.

Reason 2: High Current

If the rotor winding is delta connected, the voltage across each winding will be high. In this case, if we connect the rheostat to reduce the voltage of the rotor, a very high current will flow because here the voltage is high. This high current will cause sparking on slip rings and may damage the slip rings and rotor windings. So the conclusion is to operate at low voltage star connection is used.

Reason 3: Zero Speed

There is a closed loop in the delta connection, so the zero sequence current will flow through the windings which also creates a magnetic flux. So using the rotor resistance starter, the induction motor may not be started at zero speed. After giving the power supply, the induction motor will be started even without the rotor resistance starter.

Reason 4: Motor Size

To connect the rotor winding in the Delta connection, all six terminals should be brought out outside. This is only possible by using six slip rings instead of three slip rings which are not economical and also the size of the motor will be increased.

Reason 5: Rotor Resistance

We know there is one type of starter that is known Rotor Resistance starter, sometimes used for the starting. It is easy to connect resistors with the rotor windings in the star configuration than in the Delta configuration.

Read Also:

• Why Induction Motor cannot run at Synchronous Speed | Slip Phenomenon
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