Powerfacor

[JdoubleU]

I know I have posted on this before, but I am not sure what to do. We are penalized on powerfactor and in some of our buildings it is very poor. Is there a product out there that will correct powerfactor.

 

[eric9822]

There is. Google Power Factor Correction.

 

[SG-1]

Before you can select a product to fix it and move on to the next problem you will have to identify why it is so poor.

If it is inductive loads then capacitors, sync motor, etc can solve the problem.

If it is harmonics then a more complex solution is necessary, like filters.

I knew of a case where a mill had a bad powerfactor. One of the mill workers was going to electrical school. He was a hero when he found a synchronous motor running with a .8 powerfactor.

 

[robbietan]

Before you can select a product to fix it and move on to the next problem you will have to identify why it is so poor.

If it is inductive loads then capacitors, sync motor, etc can solve the problem.

If it is harmonics then a more complex solution is necessary, like filters.

I knew of a case where a mill had a bad powerfactor. One of the mill workers was going to electrical school. He was a hero when he found a synchronous motor running with a .8 powerfactor.

I agree, a thorough review of all the loads can help you find the cause and the solution to the low power factor.

in the past, capacitors are installed automatically when a place is penalized for low power factor. however, there is the danger of resonance every time harmonics is present in the system and some capacitor installations were damaged as the presence of harmonics was not identified.

 

[PowerQualityDoctor]

I agree, a thorough review of all the loads can help you find the cause and the solution to the low power factor.

in the past, capacitors are installed automatically when a place is penalized for low power factor. however, there is the danger of resonance every time harmonics is present in the system and some capacitor installations were damaged as the presence of harmonics was not identified.

By adding the right reactors in series with the capacitors, not only that resonance cannot occur, but some harmonics can be filtered. Moreover, as many loads have internal capacitors, and these capacitors do not have reactors, correcting PF by analyzing the loads can increase harmonic level.

 

[robbietan]

"....Moreover, as many loads have internal capacitors, and these capacitors do not have reactors, correcting PF by analyzing the loads can increase harmonic level.

reactance is added in parallel to capacitance to filter out harmonics. at least, that how harmonic filters are constructed, from my experience. and just how can you correct pf by "analyzing the loads" ? I meant that by properly assessing the facility loads (harmonic or non-harmonic loads), you can identify the source of poor power factor and provide the necessary solution. solution in the form of caps for large motors, etc

some motors have internal capacitors installed to supply kVARs and ultimately, correct facility pf.

motors are naturally inductive, which is why caps are installed to supply some of the kVAR requirements of the motor. so how can harmonic levels increase in this situation?

 

[PowerQualityDoctor]

The following document explains why reactors in series to capacitors is the method to filter harmonics - http://www.elspec.biz/Support/Harmonics_Filtering_Elspec.pdf.

After you agree on this, capacitors on the motors (or other loads), as they usually do not have reactors, have negative effect on harmonics. If you replace them with others with reactors, you will improve your harmonic pollution. As TPF is reduced by harmonics, sometimes removing capacitors without reactors improve the TPF.

 

[StewG]

Power Factor/Peak Demand

Power Factor/Peak Demand

Are these items related in some way that would reflect on the electric billing. Our plant got a big hit (highest in 17 years) for peak demand. Jumped the bill up a bunch. We are fishing for how this demand could happen. If we turned on everything at once within the apparent 15 minute time period, would that be enough? We have had some power dips in the last couple of months, that make lights flicker and machining centers "pause", but not shut down entirely, compressor either. Any ideas from the real world?

 

[PowerQualityDoctor]

Are these items related in some way that would reflect on the electric billing. Our plant got a big hit (highest in 17 years) for peak demand. Jumped the bill up a bunch. We are fishing for how this demand could happen.

Some utilities charge peak demand based on kVA (or current) rather than kW. In this cases, power factor significantly affect peak demand.

If we turned on everything at once within the apparent 15 minute time period, would that be enough?

Yes, turning everything on for 15 minutes will create high peak demand.

We have had some power dips in the last couple of months, that make lights flicker and machining centers "pause", but not shut down entirely, compressor either. Any ideas from the real world?

I don't think that power dips or flicker cause peak demand. If this is new, and no other change in the facility, power factor can be the source. If the utility charges peak demand for current or kVA, and you have power factor capacitors that failed, you will have high peak demand.

I suggest to upload or send me a copy of the electricity bill and I can have a look.

 

[ptonsparky]

How is the PF correction handled in your plant? Each load or staged per demand?

 

[robbietan]

Are these items related in some way that would reflect on the electric billing. Our plant got a big hit (highest in 17 years) for peak demand. Jumped the bill up a bunch. We are fishing for how this demand could happen. If we turned on everything at once within the apparent 15 minute time period, would that be enough? We have had some power dips in the last couple of months, that make lights flicker and machining centers "pause", but not shut down entirely, compressor either. Any ideas from the real world?

there were some who argue that voltage dips, together with the rise in current, is the cause of a higher demand billing. a simple calculation will show why it is not the case.

max demand billing (for us here int he Philippines, anyway) is the maximum demand average that is captured during a 15 minute period. a voltage dips usually lasts less than a second - assuming that a voltage dip lasted one second where the current (or kVA) shot up 6 times. then average it over 900 seconds (15 minutes). so an average demand of 100 kVA for 15 minutes becomes 100.55 kVA when the dip is included. A 0.56% increase which is to say, not much.

 

[SG-1]

I worked with a young guy that had been a maintence helper in a mill. He was sent to start up a chiller. He was not told that you could only try to start it once every 15min. It started after the third time. The mill got hit for exceeding their demand. A search was launched to find & fire the " chiller starter ". He was never identified & remains on the loose even now.