# Reactive power, and capactior banks for power factor correction.



## tmessner (Apr 1, 2013)

Our poco charges a stiff penalty for poor pf. I have a customer that will not spend 100,000$ for pf correction, even after we show him a payback of 1.5 years in penalty. We are about ready to do the job for them in exchange for 5 years off avoided penalty as payment.
We also had another job that was overloading the service and tripping the main. the problem was poor power factor, like 60 to 70%. When we added up all of the load we were at about 300 amps on a 480 volt 400 amp service. When we amp clamped it we were well over 400 amps.


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## MDShunk (Jan 7, 2007)

Had a customer that was all hot to trot on doing some PF correction in the early 2000's based on some of their in-house measurements at large machinery and remote panelboards. Cool so far. My measurements at the service and the utility bills proved out that things balanced out by the time your worked yourself back to the service entrance. I'd have loved to sell them some stuff, but they didn't need anything, and it took some real convincing to prove it to them.


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## tmessner (Apr 1, 2013)

Takes a good and honest contractor to talk a customer out of an expensive job. the industry needs more of you.


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## MTW (Aug 28, 2013)

tmessner said:


> Takes a good and honest contractor to talk a customer out of an expensive job. the industry needs more of you.


MDShunk isn't actually a real person. He's a sophisticated hologram created by a top secret government program.


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## JRaef (Mar 23, 2009)

When the PoCo meter reads your energy consumption, it is reading the watts (and hours) but since watts includes the PF, you don't actually pay for poor PF in your bill. For example you use 100A at 480V at a PF of 1.0 for 1Hr, that's 48kWh. If the PF is .8, that's only 38.4kWH, so you actually paid LESS for having poor power factor.



BUT, the PoCo still has to PROVIDE that "unbillable" energy of 48kWh to you by virtue of the size and capacity of their equipment and conductors. That's the only reason why they will penalize a commercial or industrial user when the PF goes below some threshold (.95 or .9 in some areas). They are *indirectly *making you pay for the fact that you are making them up-size their gear for energy they can't actually bill you for. So adding Power Factor Correction can, in some circumstances, result in a lower BILL, but only because it reduces or eliminates the PF PENALTY, if any.



With residential customers, they don't penalize you via separate metering, because those meters and the time to read them would cost more than they would recoup. So the "penalty" is baked into the slightly higher rates paid by residential users. That's why the "power factor correctors" sold to residential users are a scam; sure, they (might) correct it somwhat, but that has no effect on what you pay.


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## Wire Tags (May 11, 2016)

so the industry standard is the cost of poor pf penalty per year x 5 will equal the cost you charge for doing pf correction?


tmessner said:


> Our poco charges a stiff penalty for poor pf. I have a customer that will not spend 100,000$ for pf correction, even after we show him a payback of 1.5 years in penalty. *We are about ready to do the job for them in exchange for 5 years off avoided penalty as payment.*


So when you say things balanced out at the service entrance, it means the phase angle between the total circuit current and the total circuit voltage
is very small?


MDShunk said:


> My measurements at the service and the utility bills proved out that *things balanced out by the time your worked yourself back to the service entrance.*


the energy that the PoCo cant bill you for is it because that energy is transfered back to the source(back to the PoCo).
So the PoCo charges you a penalty because you made them do work to create this energy that is essentially being wasted.



JRaef said:


> BUT, the PoCo still has to PROVIDE that *"unbillable" energy* of 48kWh to you by virtue of the size and capacity of their equipment and conductors. That's the only reason why they will penalize a commercial or industrial user when the PF goes below some threshold (.95 or .9 in some areas). They are *indirectly *making you pay for the fact that you are making them up-size their gear *for energy they can't actually bill you for.* So adding Power Factor Correction can, in some circumstances, result in a lower BILL, but only because it reduces or eliminates the PF PENALTY, if any.



If reactive power does not dissipate energy, it just transfers energy back and forth between load and source, and a meter only reads your energy consumption then does that mean a meter only reads the energy consumption of a purely resistive circuit?


JRaef said:


> *When the PoCo meter reads your energy consumption, it is reading the watts (and hours) but since watts includes the PF, you don't actually pay for poor PF in your bill.* For example you use 100A at 480V at a PF of 1.0 for 1Hr, that's 48kWh. If the PF is .8, that's only 38.4kWH, so you actually paid LESS for having poor power factor.


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## gpop (May 14, 2018)

The higher the voltage the smaller the capacitors required to correct the PF. We correct at the sub station at 25000v. These are commonly referred to as a bomb in a box.


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## tmessner (Apr 1, 2013)

Wire Tags said:


> so the industry standard is the cost of poor pf penalty per year x 5 will equal the cost you charge for doing pf correction?
> 
> Yes, I would collect 3 1/2 years of free money because 1 1/2 years will pay back the cost of cap bank.


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## Wire Tags (May 11, 2016)

so a smaller capacitor means a larger capacitive reactance, and if the ratio between capacitive reactance and resistance in an AC circuit increases, the phase angle between the total voltage and the total current will increase in magnitude. This will help to correct the PF of inductive loads operating at higher voltages, by bringing current that lags voltage more in line with the voltage which basicly turns it into a pure resistive circuit?



gpop said:


> The higher the voltage the smaller the capacitors required to correct the PF. We correct at the sub station at 25000v. These are commonly referred to as a bomb in a box.


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## MDShunk (Jan 7, 2007)

Wire Tags said:


> so when you say things balanced out at the service entrance, it means the phase angle between the total circuit current and the total circuit voltage
> is very small?


I guess what I'm saying is that the things they were measuring were highly inductive loads, but when you measured the total load at the service (which took into account all loads on the property; inductive and capacitive and unity) the power factor was neither remarkably leading or lagging.


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## MDShunk (Jan 7, 2007)

gpop said:


> The higher the voltage the smaller the capacitors required to correct the PF. We correct at the sub station at 25000v. These are commonly referred to as a bomb in a box.


I always thought PF correction cap banks would make a nice blowup, but I've never heard of any special issues. I'm not even sure what the testing procedure is for aged cap banks. Probably just a replacement PM interval for the actual caps. The only blowup I've ever seen was an automatic cap bank, and the blowup was from the contactors and not the caps. 480 cap banks use pretty big caps, but the ones I seen on poles are just the size of a car battery with two bushings.


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## MTW (Aug 28, 2013)

Years ago when I worked for a large commercial EC, we went around installing PF correction cap banks at various grocery chain stores in the area. I'm guessing the power company gave them a load profile and how much correction was needed to arrive at the proper correction value. I never heard how much money was saved as a result or if it was just snake oil being sold.


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## MDShunk (Jan 7, 2007)

MTW said:


> Years ago when I worked for a large commercial EC, we went around installing PF correction cap banks at various grocery chain stores in the area. I'm guessing the power company gave them a load profile and how much correction was needed to arrive at the proper correction value. I never heard how much money was saved as a result or if it was just snake oil being sold.


Commercial work is the only time they make sense. They're not snake oil if you're getting charged a penalty for poor PF. (The resi stuff is snake oil)

Where the trouble lies: Sizing. If the load isn't fairly consistent, the power factor can vary from minute to minute or hour to hour. Some places, like groceries, have big offenders like the refrigeration racks, and they might do PF correction only on the big offender that cycles off and on with that load. Office builds are somewhat consistent, so they might have a properly sized static cap bank at the service entrance. A place like a factory is super variable, and an automatic cap bank is really the only thing that makes sense with such a variable load profile. Some places try to average things out and put in a static cap bank that will handle most things most days, and it will at least limit the PF penalty on the bill.


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## MTW (Aug 28, 2013)

MDShunk said:


> Commercial work is the only time they make sense. They're not snake oil if you're getting charged a penalty for poor PF. (The resi stuff is snake oil)
> 
> Where the trouble lies: Sizing. If the load isn't fairly consistent, the power factor can vary from minute to minute or hour to hour. Some places, like groceries, have big offenders like the refrigeration racks, and they might do PF correction only on the big offender that cycles off and on with that load. Office builds are somewhat consistent, so they might have a properly sized static cap bank at the service entrance. A place like a factory is super variable, and an automatic cap bank is really the only thing that makes sense with such a variable load profile. Some places try to average things out and put in a static cap bank that will handle most things most days, and it will at least limit the PF penalty on the bill.


These particular cap banks were wired directly to a breaker at the main service, so not particular to the refrigeration or roof top stuff. They were static banks so I'm guessing it was just to limit the PF penalty. IIRC they were on a 200 amp, 480 volt circuit so they were fairly large. Required an night time shutdown to actually install the breaker and land the conductors.


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## MDShunk (Jan 7, 2007)

I dunno. Groceries might be a lot less variable than I think. I have zero history ever taking any recording measurements on supermarkets. Just day to day piddly service calls and such.


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## MTW (Aug 28, 2013)

MDShunk said:


> I dunno. Groceries might be a lot less variable than I think. I have zero history ever taking any recording measurements on supermarkets. Just day to day piddly service calls and such.


I'm rusty on all the details now. Too bad Iwire isn't here, he would know what was behind it all. But I can stay that the poco's around here incentivize all that stuff since they charge aka steal a monthly fee on all electric bills for "energy efficiency programs". It's basically socialism in action.


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## MDShunk (Jan 7, 2007)

MTW said:


> I'm rusty on all the details now. Too bad Iwire isn't here, he would know what was behind it all. But I can stay that the poco's around here incentivize all that stuff since they charge aka steal a monthly fee on all electric bills for "energy efficiency programs". It's basically socialism in action.


Yeah, pretty much the only reason so many people are doing solar. Get a little bit of that stolen money back from the gazillion dollar escrow.


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## gpop (May 14, 2018)

MDShunk said:


> I always thought PF correction cap banks would make a nice blowup, but I've never heard of any special issues. I'm not even sure what the testing procedure is for aged cap banks. Probably just a replacement PM interval for the actual caps. The only blowup I've ever seen was an automatic cap bank, and the blowup was from the contactors and not the caps. 480 cap banks use pretty big caps, but the ones I seen on poles are just the size of a car battery with two bushings.



Ours are automatic with 25kv switches and a fuse wire to dump them if they fail. Every few years one will blow hard enough to take out the vacuum breaker knocking out half the plant. They have a distinct smell when they blow. I can not detect it but the sub station tech from the poco we contract for sub station work can smell it from outside the fence. 

The scary part is automatic switching so there no warning that a cap is about to be brought on line. You can tell alot about the plant just by the sounds of the regulators and cap switch's opening and closing. 

I will still take that over having 4160 cap banks (linked to one motor) in the mcc. I know that the door is meant to be able to contain a failure but im not sure i want to be there if it happens.


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## tmessner (Apr 1, 2013)

The job we were working on was engineered by one of my suppliers to use switching cap banks at the substation that serves the dairy operation.


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## Wire Tags (May 11, 2016)

If the dielectric of a capacitor is exposed to too great of an electrical stress it will break down causing the dielectric to conduct electric current.
So now the capacitor essentially becomes a conductor, a conductor that is not rated to handle large amounts of current, which will cause it to get hot and blow up like a bomb?


gpop said:


> The higher the voltage the smaller the capacitors required to correct the PF. We correct at the sub station at 25000v. *These are commonly referred to as a bomb in a box*.


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## JRaef (Mar 23, 2009)

Wire Tags said:


> If the dielectric of a capacitor is exposed to too great of an electrical stress it will break down causing the dielectric to conduct electric current.
> So now the capacitor essentially becomes a conductor, a conductor that is not rated to handle large amounts of current, which will cause it to get hot and blow up like a bomb?


Essentially, yes. Technically the plates arc across one another, burning a hole straight through them and causes the electrolyte to vaporize almost instantly. Many caps have vents to attempt to release the pressure more safely, so most of the time they just spew their guts all over everything in the cabinet. But if the energy involved is really high, the vents can’t act fast enough and the case can explode in the time it takes the fuse to clear. 

A cautionary tale on this subject:
http://www.ecmweb.com/design/case-exploding-capacitor


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## Wire Tags (May 11, 2016)

are capacitor banks one giant bank or is it similar to a battery bank for a solar setup?

It seems that if a cap bank is often exposed to a lot of electrical stress, it would be wise to rotate the cap banks around this way not one group of capacitor is constantly being exposed to a lot of stress.

Or is that what periodic maintenance is for, rotating the capacitors in a cap bank around so not a single group of capacitor bank is being exposed to too much electrical stress?



JRaef said:


> A cautionary tale on this subject:
> http://www.ecmweb.com/design/case-exploding-capacitor


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## gpop (May 14, 2018)

Wire Tags said:


> are capacitor banks one giant bank or is it similar to a battery bank for a solar setup?
> 
> It seems that if a cap bank is often exposed to a lot of electrical stress, it would be wise to rotate the cap banks around this way not one group of capacitor is constantly being exposed to a lot of stress.
> 
> Or is that what periodic maintenance is for, rotating the capacitors in a cap bank around so not a single group of capacitor bank is being exposed to too much electrical stress?


Doesn't really matter as you run them till they pop in a sub station. Hopefully the fuse knocks a bad one off line with out causing a problem.
Every week we inspect for blown fuse wires and once we have a few the bank is taken off line and the caps are replaced. Due to the voltage we do not test the caps (the insulator could be the reason why the fuse failed). We just trade them in for replacements.
Its surprising when you first see a cap bank and realize that the aluminum frame is part of the circuit. You learn never to lean against anything.
I have a lot of respect for the lineworkers that do most of our sub station work. No way will you see me on a lift in a sub station.


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## Wire Tags (May 11, 2016)

So as an industrial electrician doing maintenance the bulk of your work is to check fuses? cause it seems like a fuse is the first line of defence/indicator that something has gone wrong or will go wrong. 


gpop said:


> Doesn't really matter as you run them till they pop in a sub station. Hopefully the fuse knocks a bad one off line with out causing a problem.
> *Every week we inspect for blown fuse wires* and once we have a few the bank is taken off line and the caps are replaced.


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## gpop (May 14, 2018)

Wire Tags said:


> So as an industrial electrician doing maintenance the bulk of your work is to check fuses? cause it seems like a fuse is the first line of defence/indicator that something has gone wrong or will go wrong.



We have to do a little more than that but most is a visual inspection.
Theres insulator leak checks, temperature checks, Gas pressure check, regulator checks, battery checks, ct, pt, knife switches, cable ends, pest control, weed control, IR, Ultrasound, grounding checks, cap fuse checks, flag check, load check, voltage check, etc 

As theres only 3 electrician (one per shift) of which im the only E,I&C and we do all our own construction and upgrading im happy as hell to leave the sub station work to contractors. I can make a phone call and with in 30 mins i have a sub station tech on site. (pays to be the largest power user in the area).


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## gpop (May 14, 2018)

JRaef said:


> Essentially, yes. Technically the plates arc across one another, burning a hole straight through them and causes the electrolyte to vaporize almost instantly. Many caps have vents to attempt to release the pressure more safely, so most of the time they just spew their guts all over everything in the cabinet. But if the energy involved is really high, the vents can’t act fast enough and the case can explode in the time it takes the fuse to clear.
> 
> A cautionary tale on this subject:
> http://www.ecmweb.com/design/case-exploding-capacitor


We took a lightning strike at a small facility thats linked to the main site. All (8) 40hp SqD drives had liquid dripping out of the cabinets from where the caps vented the fault code said "pre-charge fault". (funny only the 40hp failed the smaller and larger drives survived and are still running 8-9 years later).


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## MDShunk (Jan 7, 2007)

gpop said:


> We took a lightning strike at a small facility thats linked to the main site. All (8) 40hp SqD drives had liquid dripping out of the cabinets from where the caps vented the fault code said "pre-charge fault". (funny only the 40hp failed the smaller and larger drives survived and are still running 8-9 years later).


I've seen drives blow in a cabinet full of drives and take out the drive to the left and the right as well as above and below. I can only assume the ionized gas from the one that blew created a brief conductive cloud. It's become a pretty normal occurrence for me to find one drive visually failed in a spectacular way, and the drives surrounding it just "dead" with nothing especially remarkable, visually, wrong with them.


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## paulengr (Oct 8, 2017)

You could measure the arcing voltage (CIV) as a PM on a cap to find weak ones as the edges get weak but nobody does this. Just look for bad ones.

Our bigger 12.5 kV motor test stand blew up for the third time. This time the builder took a hint. The utility is around 25 MVA wye wye three wire fed straight to it. It’s a 12.5 kV soft start firing into a wye autotransformer ungrounded with none of the shields grounded either. It was their first 12.5 kV test stand. It has Toshiba oil filled filters (not just power factor correction) on both ends. They launch parts, oil mist, and it makes a nice fireball when it goes off. Ungrounded systems act like a voltage multiplier which is where the trouble is.

The second problem with cap banks is your current goes down so you have to adjust overloads if you put them on the load side of a starter.

The third problem is resonance and voltage boosting. Overcorrecting causes it to shred starters and motors as the inductance and capacitance oscillate back and forth. Read up on ferroresoance which blows up motors and transformers. Never correct past 1.0 even accidentally. Boosted voltage is good on long lines though.

Electrolytic caps are cheap but fail over time. Oil filled (not electrolytic) and especially metal film caps last almost forever but they are twice as expensive and three times larger so either put up with failures every 5-10 years or spend money to fix that.


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## paulengr (Oct 8, 2017)

I also look not just for the slightest leak but if they swell at all, time to change. Don’t wait until they look like a pregnant sow.


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## gpop (May 14, 2018)

MDShunk said:


> I've seen drives blow in a cabinet full of drives and take out the drive to the left and the right as well as above and below. I can only assume the ionized gas from the one that blew created a brief conductive cloud. It's become a pretty normal occurrence for me to find one drive visually failed in a spectacular way, and the drives surrounding it just "dead" with nothing especially remarkable, visually, wrong with them.


Had some odd ones but touch wood haven't seen that one yet. I really dislike the way drives, fuses and breakers can be stacked in a cabinet. I do not want to have my head in a cabinet when i throw the breaker in.


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## JRaef (Mar 23, 2009)

gpop said:


> We took a lightning strike at a small facility thats linked to the main site. All (8) 40hp SqD drives had liquid dripping out of the cabinets from where the caps vented the fault code said "pre-charge fault". (funny only the 40hp failed the smaller and larger drives survived and are still running 8-9 years later).


The other drives may have been running at the moment of the surge, giving the energy somewhere to go, but the 40HP drives were off, as in not in a Run state. 

I had that happen once where I added a new fish oil processing wing to a fish plant in Alaska. My part of the project had 60+ VFDs, plus they added (separate contract) an APFC system over my recommendations against it. The contractor that added the APFC panel programmed it wrong and when my new addition was connected and run for testing, the APFC caps all came on at once and over corrected the entire plant, causing a huge voltage surge. Every single one of the existing Toshiba VFDs and the 75kVA UPS in the old plant instantly blew their caps, but not one of my drives. I was made out to be the hero for having used AB drives, but really my drives were all running for the testing of course, the rest of the plant was shut down but still connected... Did I tell them? I have to admit, no, because they immediately asked me to go in and replace every one of the blown drives and the UPS. That was going to have to happen no matter what do I used my “hero” status to get that contract added on. Am I ashamed? Maybe a little, but I HAD warned them not to use an APFC system with so many VFDs in the plant and they had ignored my advice.


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