Why is star delta running used?

Answer 1

Star delta starting is used to reduce the dip in voltage which can feed back to the primary line which makes other customers unhappy when their lights dim each time a high HP motor is started on the same circuit they are connected to. By starting in a wye connection there is less disruption of voltage on the system that the motor is connected to, by starting the motor at a lower voltage and hence lower inrush current. Some utility companies will not allow across the line starting on motors above 30 HP.

This type of motor starting circuit is used less and less, now that VFDs and Soft Starters are becoming cheaper to purchase and more readily available in lower HP ratings

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Answer 2

A connection is one or the other, star or delta in a three-phase system. Delta has the three loads connected between the live lines, while star has the loads connected from the live wires to a neutral point.

In the power supply industry delta connections are normally used at high voltage because the circuits are three-phase 3-wire, with equal currents in all three phases.

At low voltage (below 1000 v) the circuits are usually three-phase 4-wire using a star-connected transformer secondary, which allows a lot of separate single-phase loads to be supplied, each one between one of the live lines and the 4th neutral wire.

That is how power is supplied to a group of houses.

Answer 3

In a 3 phase motor connection initial current will be 5times of the normal current drown at the load for few seconds so it may get damage your motor winding or unless drow more current so..