Calculating Of Currents In Dol And Star-delta?

[dinesh]

What are the formulae to calculate Line currents in DOL and star -delta starters?

How can we say that in star-delta starter the currents through the windings are 1/root3 of line current?

Please explain.

[kana]

Upon reaching rated speed, line current of motors using both direct online starter and star delta starter are the same.

 

I = P / sqrt(3) x U x cos a

 

I is the line current of the motor.

P is the input power to the motor. (Usually stated on the motor nameplate)

U is the line to line voltage.

cos a is the power factor of the motor. (Usually stated on the motor nameplate)

 

 

 

As for the star delta starter, during start

 

 

 

The line current is 1/sqrt(3) because the voltage is reduced by 1/sqrt(3) as the motor winding is in star configuration.

 

 

 

Regards,

 

Kana

 

 

[marke]

Hello dinesh

 

have a look at http://www.lmphotonics.com/m_start.htm and http://www.lmphotonics.com/m_control.htm

 

Best regards,

Mark.