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Starting factor


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#1 Lewis

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Posted 14 February 2003 - 09:54 AM

Hello everyone,

I need to estimate the starting current for 3 phase induction motor.
What should the starting current be for :
1)DOL
2)Star-Delta
3)ACVV
4)auto-transformer
,if the motor is 37kw;380v;50Hz.
And assume efficiency of the motor is 80%, power factor is 0.85.

Does it have any "starting factor" for different starting method?

#2 marke

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Posted 14 February 2003 - 07:15 PM

Hello Lewis

Firstly, there is no "correct" answer to your questions because there are too many parameters and variables that affect the answer. Please have a good look at http://www.lmphotonics.com/m_control.htm[/url] and http://www.lmphotonics.com/m_start.htm
To summarize, there are very large differences between the starting characteristics of induction motors. The DOL start current can vary from as low as 550% to over 900% of the rated current of the motor. The DOL start torque can vary from less than 100% to greater than 300% of rated torque.
The current in star is one third of the current in delta and the torque is one third of the torque in delta. If there is sufficient torque in star to accelerate tha driven load to full speed, then the current for a star / delta start is one third of DOL. The minimum start torque requirement is determined by the driven load.

If you can give some details of the driven load and the LRT and LRC of the actual motor you are considering, we can give you more meaningfull answers.
Best regards,




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