Experience with large-scale power factor correction?

C

careful

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USA
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Engineer
I mainly design renovations for large commercial buildings and I've been asked a number of times about worsening power factor. In your experience, what has been the best way to deal with this?

So far my leading theory is underloaded transformers, based off of similarities in these buildings with a low PF. Any advice appreciated.
 
First is finding out why the PF is getting worse and whether that is really a problem. And how does a PF worsen? Much modern equipment is PF-corrected, so I'd expect the general PF of a building to get better over time as things like magnetic florescent ballasts are replaced and HVAC is updated with new motors or VFDs. That said, if what had been a 700kva load is now 250, maybe disconnecting some transformers and rerouting feeders might he appropriate, but then it might not.

FWIW, I hardly ever see commercial buildings with PF correction, but maybe in industrial settings.
 
zbang said:
First is finding out why the PF is getting worse and whether that is really a problem. And how does a PF worsen? Much modern equipment is PF-corrected, so I'd expect the general PF of a building to get better over time as things like magnetic florescent ballasts are replaced and HVAC is updated with new motors or VFDs. That said, if what had been a 700kva load is now 250, maybe disconnecting some transformers and rerouting feeders might he appropriate, but then it might not.

FWIW, I hardly ever see commercial buildings with PF correction, but maybe in industrial settings.
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I see varying opinions on this forum and internet on if LEDs are better or worse for harmonic distortion. In places where lighting used to be a large portion of the total load, but have been greatly reduced by LEDs, the system doesn't get re-worked. You might see a 1000A feeder just for lighting that now has a mere 100A load after LED conversion.
 
careful said:
So far my leading theory is underloaded transformers, based off of similarities in these buildings with a low PF. Any advice appreciated.
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Are the buildings typically instrumented with metering that measures and tracks power quality and PF over time? Or are customers complaining based on utility bill numbers? Starting by understanding the issue and then devising the solution is the best approach. If there is no data, consider adding a service to your offering to install temporary metering and analysis before or at the beginning of the renovation.
 
solarken said:
Are the buildings typically instrumented with metering that measures and tracks power quality and PF over time? Or are customers complaining based on utility bill numbers? Starting by understanding the issue and then devising the solution is the best approach. If there is no data, consider adding a service to your offering to install temporary metering and analysis before or at the beginning of the renovation.
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They are not, all info is from the utility company.
 
careful said:
I mainly design renovations for large commercial buildings and I've been asked a number of times about worsening power factor. In your experience, what has been the best way to deal with this?

So far my leading theory is underloaded transformers, based off of similarities in these buildings with a low PF. Any advice appreciated.
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Underloaded transformer will have a lower power factor, but also has low true power. Unless the utility is penalizing you most will ignore this. Though there is some real power losses involved as well, the heat those transformers give off is real power.
 
Worsening PF..... what sort of numbers are we talking about? a couple of points or 15 points? Larger changes pretty much have to correlate with a substantial change in the load, that needs to be identified before determining whether it needs to be corrected and how.
 
winnie said:
Keep in mind that power factor because of inductive loads (displacement power factor) is a different beast than power factor because of harmonic loads (distortion power factor).
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Can you even do powerfactor correction for harmonic loads?
The only thing I have ever seen done is pull a full size neutral.
In the past triplen harmonics were a issue in office buildings I am not sure what changed to make it go away (if it did), but again I think the only thing we did was pull a full size neutral and use fewer MWBC.
 
tortuga said:
Can you even do powerfactor correction for harmonic loads?
The only thing I have ever seen done is pull a full size neutral.
In the past triplen harmonics were a issue in office buildings I am not sure what changed to make it go away (if it did), but again I think the only thing we did was pull a full size neutral and use fewer MWBC.
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I don't know if there are things on the market, but I recall research projects to create inverters or active front ends for drives that would do harmonic compensation.
 
I would be skeptical that there is much of a problem with power factor in a commercial building. First step would be to look at the power bill to see if they are being assessed a power factor penalty. If not, the only other issues are freeing up transformer or service capacity for more load or a voltage drop issue. The additional current created by reactive current increases cable losses by a small amount, but hard to justify remediation because of that.

We used to see comments like this after someone paid for a "power quality" analysis, and the report made a big deal out of power factor.

With the increased use of AFDs for HVAC loads, power factors have generally been increasing, not decreasing.

Unloaded transformer will have a poor power factor, but consume very few VARS in comparison with other loads.

If this is some kind of server farm, then there could be some more reason for concern.
 
Assuming they do have documented low power factor, I’m not a fan of large scale PFC systems. One mistake and you start damaging expensive electronics on a mass scale. I favor what’s called “at load” PFC, where you identify the low PF loads (generally AC induction motors that are not on VFDs) and add capacitors to the load side of the motor starters so that they are ONLY on-line when the motor is running. That reduces the possibility of ending up with a leading PF.
 
Brown-outing can create low PF. Is the building using heavy motor/compressor HVAC loads? This would cause a concern for low PF. Low PF can equate to high demand charges. I have installed the Blackhawk POWERHOUSE device and I believe in it. Capacitive banks with filters. DM me and I can try to size it for you per application.
 
Small, isolated PFC systems work best and have better results. I agree, fix the issue on a local level, not some huge cap bank at the main service. Thank you zbang.

1. Address each subpanel or motor load. Zero in on the low PF loads. Apply the "bucket" cap bank concept on each load.

2. Understand that voltage drop from an inductive motor load is the direct equivalent to the change in PF. Take the time to understand the quadrant lead/lag demand charge billing system from smart meters. Use VFDs as soft starters to avoid these demand charges and changes in lead/lag issues. Study the quadrant billing system.

3. Modern smart meters are taking 256+ samples every second. They catch everything. They work just like your AEMC or Fluke data logger.
 
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