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#130191 - 02/22/06 04:49 PM Sizing Power factor caps?
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
How would size these if the PF changes from .62-.78 depending upon the load?

The highest reading I took during a 3hr test was .84. Would you calculate it at the highest reading or average it out?


Dnk...

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#130192 - 02/22/06 07:42 PM Re: Sizing Power factor caps?
Bob Offline
Member

Registered: 02/05/02
Posts: 182
Loc: Mobile, AL, USA
Is the customer being bill for a KVA demand?
You would size the caps based on the max demand and PF. Suggest you contact the utiltiy and get the max demand from them.If the PF is 0.84 I would try to improve it to
0.98 or something close depending on the size of the caps rrequired.

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#130193 - 02/23/06 09:34 AM Re: Sizing Power factor caps?
Radar Offline
Member

Registered: 04/30/04
Posts: 349
Loc: Los Angeles, CA
Dnk - Rather than calculating based on min, max or average, I think I'd try to figure out what the nominal PF is, I mean what is the prevailing PF reading most of the time. It might be dificult to ascertain, but it seems to me that if you correct for that level, then the amount of time of over correction and under correction will be minimized, and the amount of time of 'just right' correction will be maximized.

Radar
_________________________
There are 10 types of people. Those who know binary, and those who don't.

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#130194 - 02/23/06 09:57 AM Re: Sizing Power factor caps?
Bob Offline
Member

Registered: 02/05/02
Posts: 182
Loc: Mobile, AL, USA
Radar
Thats one way of doing it. However if you are being billed for the max KVA demand that method will cost you money.

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#130195 - 02/23/06 12:36 PM Re: Sizing Power factor caps?
Radar Offline
Member

Registered: 04/30/04
Posts: 349
Loc: Los Angeles, CA
OK - I can see that. That being the case, should we figure out what the PF is while at max KVA demand and correct for that?

Radar
_________________________
There are 10 types of people. Those who know binary, and those who don't.

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#130196 - 02/23/06 04:38 PM Re: Sizing Power factor caps?
Bob Offline
Member

Registered: 02/05/02
Posts: 182
Loc: Mobile, AL, USA
Radar
That is correct. The utility can tell you what the KVA demand and PF is. You can then caculate the required capacitors to correct the PF to say 0.98 or 0.99.

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#130197 - 02/23/06 05:14 PM Re: Sizing Power factor caps?
Radar Offline
Member

Registered: 04/30/04
Posts: 349
Loc: Los Angeles, CA
OK Bob - let me ask another question here (I feel like we're leaving Dnk outta this). Your first question was whether the customer is being billed for KVA demand. What if they weren't, would we then be back to what I said earlier about figuring out the PF that takes the largest amount of time and correct for that, recognizing we'd be over correcting or under correcting at other times? Hopefully we'd be covering a major portion of the day with close to 1 correction.

Or would we still figure the hishest KVA demand and correct for that? Or would we simply forget the whole thing altogether if the poco is not billing for KVA demand?

Radar
_________________________
There are 10 types of people. Those who know binary, and those who don't.

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#130198 - 02/23/06 06:06 PM Re: Sizing Power factor caps?
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
Radar, you're not leaving me out of anything....

I am reading everything you guys say, and learning. I have more input, but I am waiting to hear responses to kinda formulate my next post...

I agree to what Bob is saying, however my readings were taken off a subpanel, @ 250' away from the service. Somehow I think I need to contact the power company, and do a whole plant survey with readings from the service to each subpanel, draw a line diagram and possibly correct in different areas rather than a bulk correction at the service entrance....

The sub panel is a 400A 480v panel. The customer is a huge machine shop.

What is your guys take on this idea?

Dnk..

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#130199 - 02/23/06 07:39 PM Re: Sizing Power factor caps?
Bob Offline
Member

Registered: 02/05/02
Posts: 182
Loc: Mobile, AL, USA
If the customer is being billed on a KW demand then there is no need to install the caps. They won't reduce the demand charge.

Dnk
If the main is only a 400 amp I doubt that there is a KVA demand. Probably a KW demand.
If there is a KVA demand charge, I think installing the caps at the main will be a cheaper installation. How did you measure the PF at the panels?

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#130200 - 02/24/06 03:34 AM Re: Sizing Power factor caps?
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
Bob, service is 1200A 480V. That was just a subpanel reading.

Would correcting PF reduce line losses?

Fluke 434B (3) phase analyzer..

Dnk..

[This message has been edited by Dnkldorf (edited 02-24-2006).]

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