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Placement Of Pf Correction


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#1 hmcparadise

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Posted 06 August 2008 - 01:27 AM

Hello all

We have high voltage supply where our meter is. Between the high voltage supply and
low voltage loads there is a stepdown transformer.

If we correct the Pf at the low voltage side of the transformer, at the loads, from
a cost point of view, can we expect to see an improvment in our bills?

#2 jraef

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Posted 07 August 2008 - 07:41 PM

You need to define "our bills" a little more.

If you are referring to your overall energy usage and associated tariffs, the answer is no, not really. There will be ever so slightly less heating in the transformer because it no longer has to supply the VARs for the motor loads, but that's it. If you buy the power in bulk, metered at the HV side of that transformer, then the transformer losses are part of your costs. So you may see a very very slight drop in the bill, probably not enough to pay for the capacitors in under 10 years.

If on the other hand your utility is assessing a penalty for having poor power factor at the HV side, then you could very well see a drop in the penalties by correcting the pf, and money is money!
"He's not dead, he's just pinin' for the fjords!"

#3 hmcparadise

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Posted 07 August 2008 - 08:15 PM

Hi jraef

Thank you for your reply.

The utility company does have a demand meter and consumption meter at the HV service entry on to the property.
They do charge a penelty based on maximum demand, I belive the demend meter is required to be reset once every
6 months.

Just to clarify, knowing from other PFC installations that the utility company has a typical 0.65Pf lagging, and we
do the correction at the HV service entry. If this is accurate and we target the correction to say .95-.98 lag then
the savings could potentially be about the 30%? Our demand and apparent consumption should drop a good bit, isnt
this correct?

If in addition to this we also did PFC at the low voltage side of the transformers which belong to us, the transofrmers
would work a bit less hard and the benifits would be to the lines and loads therafter.

#4 marke

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Posted 09 August 2008 - 09:40 AM

Hello hmcparadise

If you are looking to gain maximum reduction in transmission losses, then the closer to the load that you connect the capacitors, the greater will be the loss reduction. Connecting the correction on the secondary side of the transformer will reduce the reactive current flowing in the transformer and thus will increase the potential loading that can be applied to that transformer and will reduce the copper loses in the transformer.

I would not expect to see a significant difference in the maximum demand charge for correction connected on the input side, or the output side of the transformer.

Best regards,
Mark.




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