Leading power factor on ATS

[27hillcrest]

During a walk through of a facility last week I notice leading power on the 1200amp ATS. The owner says it comes and goes throughout the day. My concern is what will happen when the generator is running? Will the Geneset be able to handle leading power factor? Does leading power factor increase the kw used and the customer will be paying move than they should? They have 2 large UPS system in the site. If memory serves me that they would have line side filter bank that might be adding to the leading power factor?? Any thoughts for course of action?

 

[ron]

Do you know if the UPS's are loaded to some reasonable %?

 

[coulter]

Cummins has a medium decent paper on leading power factors and generation

http://www.cumminspower.com/www/literature/technicalpapers/PT-6001-ImpactofPowerFactorLoads.pdf

carl

 

[coulter]

...what will happen when the generator is running? Will the Geneset be able to handle leading power factor? ...

Mostly depends on the generator capability, real power load, and the pf. It may not. Heavy real loads and leading pf are a stability issue. Light real power loads with a low leading pf are a regulator stability issue.

The cummins article is pretty pesimistic. The Cats I'm dealing with have a lot more capability on the leading side of the curve.

...Does leading power factor increase the kw used and the customer will be paying move than they should? ...

Nope. Kw is real power, such as a motor load - the part going out the shaft, or resistive - electric heat. The pf shows the portion that is reactive - current is 90deg out of phase with the voltage. Reactive load draws current, but is not real power. Picture reactive load as storing energy on part of the cycle and returning the stored energy to the gen on the other part of the cycle.

However, the utility could have charge for low pf. Although they rarely squawk about leading pf. It helps counteract all the rest of their industrial customers with lagging pf.

...They have 2 large UPS system in the site. If memory serves me that they would have line side filter bank that might be adding to the leading power factor?? ...

Yes. Cap banks provide leading vars.

...Any thoughts for course of action?...

Get hold of he generator mfg and get the alternator load curve (alternator capability curve). I've had good luck calling the the generator mfg and asking for it. Put a recorder on the line to see what the load is doing. You need to know the pf and real power. Plot the load on the load curve and see if it is within the stability limits.

If it is - Praise be.

If not, the loss of excitation relay will trip the gen or it will slip poles - bad

Let us know how this one turns out - should be interesting.

carl

 

[27hillcrest]

Thanks Carl and Ron,

Ron, there are two UPS's. 1-160kva that has a load of about 80kw. 1-225kva that has a load of about 35kw. So I gather that the Cap's on the 225 are putting more var's into the system? Would this be a true statement?

Carl, in your reply you mentioned, "Mostly depends on the generator capability, real power load, and the pf. It may not. Heavy real loads and leading pf are a stability issue. Light real power loads with a low leading pf are a regulator stability issue." The facility has a 750kva Cummins geneset and the total kw usage of 200kw. When you say heavy real loads are you meaning a fully load service or mostly motor loads? The reason I ask is that the customer has been adding Dell blade servers and with the new efficient power supplies seem to be adding to the leading pf.

 

[coulter]

27 -
I'm not sure I completely understand your question. Cause, I suspect you already know all of this, but just to recap:

The power to a motor comes is delivered in two parts:
1. Real power - windage, friction, winding I^2R, shaft hp. This is kw

2. imaginary power - motor inductance. This is lagging vars. I look at this as an inductive load sucks vars and the generator has to output vars to match.

As I understand switching power supplies (computer supplies) show a leading power factor - UPS's as well. They both are rich harmonic loads, the current is drawn in pulses. And larger UPS's sometimes have filter cap banks to mitigate the harmonics. And the caps put out vars.

Read the cummins paper and ask again. It is likely we just have a terminology issue.

carl

 

[robbietan]

the leading pf in the site may mean their pf meter is not calibrated or their capacitors are overcompensating.

the danger is when operating a genset, leading pf may cause the genset trouble. the normal practice would be to shut off pf capacitors during genset operation.

 

[beanland]

Danger and mis-reading

Danger and mis-reading

If you have 3-phase 4-wire service and install line-line loads, the power factor measured phase-neutral is gobble-d-gook. A 100% PF load will look like 86% on one leg and -86% on another.

Unless the UPS is rated for it, do not install capacitors on a UPS.

 

[27hillcrest]

I'm getting the leading power factor reading right off the ATS sw. Many of the loads down stream are 208 30amp single phase. (About 40 Dell Blade Servers) So you are saying that when line-line loads are on the system than the reading on the ATS could be wrong?

 

[beanland]

Screwy Power Factor

Screwy Power Factor

Yes. A 100% power factor line-line load will present itself as a poor power factor when measured line-neutral. If the ATS or UPS is measuring only one phase and is measuring phase-neutral