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Rating Of Ac3 Contactors For Auto Transformer Motor Starting


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#1 saheer

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Posted 09 December 2009 - 05:54 PM

can any one help me to solve my problem

This is my problem
I have to start 90KW air blower motor using auto transformer Having 50%, 65%, 80% taping. I use 5 contactors for controlling start operation. 1 for 65%tapping, 1 for 80% tapping, 1 for disconnecting transformer after completing startring operation, 1 for tr. star connecting and last one is main line contactor. How calculate contactor rating for this type starting.

kks

#2 yuri

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Posted 11 December 2009 - 05:27 PM

QUOTE (saheer @ Dec 9 2009, 05:54 PM) <{POST_SNAPBACK}>
can any one help me to solve my problem

This is my problem
I have to start 90KW air blower motor using auto transformer Having 50%, 65%, 80% taping. I use 5 contactors for controlling start operation. 1 for 65%tapping, 1 for 80% tapping, 1 for disconnecting transformer after completing startring operation, 1 for tr. star connecting and last one is main line contactor. How calculate contactor rating for this type starting.

kks


Hello.
Why do not you want to use just one variable speed drive for your air blower motor?

#3 TonyS

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Posted 05 November 2010 - 09:20 AM

Use Google and look up Korndorffer autotransformer starter. You will see you only need 3 contactors. The rating of the contactors needs to match the line requirements, it’s cost effective to use the same rating for the others.



#4 marke

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Posted 06 November 2010 - 09:11 PM

Hello saheer

The rating of the contactors is esssentially thermal.
All contactors are subjected to a high start current and need to be rated accordingly.
I would recommend just using the AC3 rating at the rated current of the motor of the motor for reliable operation. Some would suggest smaller contactors for the 50% tap as the start current will be lower, but you will shorten the life of the contactor.

I assume that you are using a complex timing arangement to control the contactors to ensure that there is a closed transition at each step.
Open transition switching should be avoided.

Best regards,
Mark




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