How star delta starter reduce starting current?

How star delta starter reduce starting current: Answer: A Star-Delta Starter reduces the starting current of an induction motor by initially connecting the motor windings in star (Y) configuration and then switching them to delta (Δ) configuration after the motor reaches about 70–80% of its rated speed.

Let’s break it down clearly

Working Principle:

1. During Starting (Star Connection):
   • In the star (Y) configuration, the line voltage is divided by √3 (1.732) across each winding.
   • This means each phase winding gets only 58% (1/√3) of the full line voltage.
   • Since current is proportional to voltage, the starting current is also reduced to about 1/√3 (≈ 0.577) of what it would be in delta connection.
2. During Running (Delta Connection):
   • After the motor gains sufficient speed, the starter automatically switches the windings to delta (Δ).
   • Now, each winding gets full line voltage, allowing the motor to deliver its full torque and power.

Reduction in Starting Current:

Let’s compare it with a Direct-On-Line (DOL) starter:

So, the starting current reduces to about one-third of the DOL starting current.

In Simple Words:

The Star-Delta Starter reduces starting current by lowering the voltage applied to each winding to 58% of the line voltage, which cuts the starting current to one-third of what it would be under direct starting.