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Soft Starter Application For Motors With Pfc Capacitors


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#1 schow

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Posted 23 July 2010 - 11:12 AM

Dear all,

I am having a client. who would like to use soft starters to start his 22kW motors for machines. The thing is the 22kW motors terminals are connected with 3 x PFC capacitors to improve the PF of the motors (near motor terminals and not the the mains DB) and these capacitors connected directly to the motor terminals without any control magnetic contactor.

My problem is, I am not sure if I could use soft starters in this configuration as if I am not mistaken, the capacitors will act like short circuit at 0Hz, which I am afraid this may damage the soft starters since short circuit will draw huge current from the soft starter!?

Does anybody has experience in this type of configuration?

Please kindly advice!

Dunke!!!

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#2 jraef

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Posted 08 September 2010 - 12:25 AM

QUOTE (schow @ Jul 23 2010, 04:12 AM) <{POST_SNAPBACK}>
Dear all,

I am having a client. who would like to use soft starters to start his 22kW motors for machines. The thing is the 22kW motors terminals are connected with 3 x PFC capacitors to improve the PF of the motors (near motor terminals and not the the mains DB) and these capacitors connected directly to the motor terminals without any control magnetic contactor.

My problem is, I am not sure if I could use soft starters in this configuration as if I am not mistaken, the capacitors will act like short circuit at 0Hz, which I am afraid this may damage the soft starters since short circuit will draw huge current from the soft starter!?

Does anybody has experience in this type of configuration?

Please kindly advice!

Dunke!!!

cool.gif

Yes you are correct. Having the PFC capacitors on line downstream of the soft starter usually creates a race to see if the SCRs in the soft starter are damaged by the di/dt of charging the capacitors, or the capacitors fail due to the high harmonics from the phase angle firing of the SCRs during ramping. Either way, you lose.
"He's not dead, he's just pinin' for the fjords!"




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