Three Phase Induction Motor Starters

Why am I the first to give you a GA? Now that is a REAL mystery....

Very well described to my mind!! If the OP does not understand, then its his problem!!

The motor is first started by connecting its stator winding in a star configuration. The phase voltage in the star configuration is 1/√3 of the phase to phase or line voltage. Thus the voltage applied to the stator winding is about 58 % of the line voltage. The starting stator current reduces to 1/√3 of the full load current when the motor is started on star winding configuration. However, with a reduction of the starting current, the starting torque delivering capacity of the motor get also adversely affected. The Torque of Induction motor is proportional to the square of the applied voltage.

T= Slip* V^{2 ----------(1)}

^{At starting, slip=1} Tst= K* V^{2 ---------------(2)}

Tst= K* (1/√3)2 Tst= K*1/3 ---------------(3)

The torque delivering capacity of the motor becomes 33 % of the full torque capacity of the motor during the running of the motor in a star configuration. Therefore, the star delta starter can be used for starting loads that require less starting torque.

Read More:https://sdvelectrical.blogspot.com/2019/03/star-delta-starter.html

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REPORTED TO ADMINS

A1) The question is abstruse. That is the reason for selecting a star-delta starter.

A2) Some options:

• Ask lyn via CR4 personal messaging system.
• Attend Electrical Technician training locally.
• Ask for a local Mentor that can explain it.

Looks like Lyn has done his homework.

Note to self
get eyesight checked

But it looks like the OP is trying to get someone else to do his.

The answer is:

What will be the first two questions on the test today?

My apologies Lyn

At it's most basic a 3-phase motor or transformer has 3 coils/windings.

Trace the circuit.

in delta, one coil will be connected across 2 phases at full line voltage.

In star, 2 coils will be connected in series across 2 phases at full line voltage thus the voltage across each coil will be reduced.

Root 3 comes form the triangle of phase vectors - as others have explained.