Star-Delta Induction Motor Starter

 

Star-Delta Starter

In this post, we will discuss about Star-Delta Induction Motor Starter. Basically, the star-delta starter is used to start huge induction motors of higher rating that is, above 5 horse power rating induction motors. 

So, why do we need motor starters at all?

The answer is, when we start an induction motor, it draws a huge amount of current known as starting current which is almost 5 to 6 times normal running current. This huge inrush current initially drawn is due to the fact that when the motor rotor is at rest, the rotating magnetic field of stator cuts the rotor bars at a higher rate and hence drawing more current. This inrush current gradually decreases as the rotor starts to gain speed because the rotor is no longer at rest rather it is now rotating.

After all, due to inrush current, a voltage dip occurs causing other devices or machines to malfunction.

How does Star-Delta Starter helps start an induction motor smoothly?

The Star-Delta name tells us that initially we drive the motor in Star or Wye connection. In this type of connection, the voltage is divided into two set of windings at a time and hence less voltage across windings than the voltages in Delta connection. In delta connection, the full voltage goes to a single winding at a time and hence more current. 

Therefore, the motor is connected in star or wye connection using a dedicated contactor and when the rotor achieves a considerable speed, full voltage is applied using DELTA connection and hence the motor runs at full speed. This way, the inrush current is minimized.

Watch the video of a home-made Star-Delta Starter below: