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Power Factor Correction at Different Voltage Level


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#1 mdlafferty

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Posted 25 July 2006 - 10:34 PM

I have a 4160 volt MCC lineup with four 300HP soft starters running 2 belt conveyors. Can I use a load break switch in the 4160 volt MCC to feed a 4160-600 volt transformer and then do my power factor correction with capacitors at the 600 volt level?
I was thinking of automatically switching the capacitors in 2 equal banks with none, one or both banks energized depending on whether there were none, one or two conveyors running.
Thanks for help.
Mark

#2 mariomaggi

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Posted 26 July 2006 - 05:01 AM

Dear Mark,
you can make correction at 600 V level.
Pay attention to harmonics generated by thyristors during starting, capacitors must be in position to accept such harmonics without damages.

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Mario

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#3 marke

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Posted 26 July 2006 - 06:29 AM

Hello Mark

You can certainly apply low voltage capacitors to the output of a transformer and use that to correct the HT network, but you do need to be careful

One of the problems with adding power factor correction, is that you are creating a resonant circuit. If there is plenty of load in parallel with the capacitors, then the Q of the circuit will be low and there will not be any major issues. If the load is high, then you cna have major resonance problems.

In this instance, you will be applying power factor correction to the secondary of a transformer and if that is the only connection to the secondary, there will be some resonance issues that could become problematic.

Provided that the load on the circuit connected to the primary of the transformer is high and close to the transformer, you will have a reaonant circuit comprising the capacitors and the leakage reactance of the transformer. I would suggest that you design around having some reasonably high voltages appearing on the secondary when you do any switching. If you have a reasonable electrical load on the secondary of the transformer in addition to the capacitors, then ther problem will be reduced.

Best regards,

#4 mdlafferty

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Posted 26 July 2006 - 03:26 PM

Thank you for your advice.
Mark




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