# Power Factor Correction Capacitors-Are they worth it?



## Cow (Jan 16, 2008)

We received the green light to redo the electrical for three irrigation pump stations this winter:

Station 1: 2300v 9700HP total

Station 2: 480v 1250HP total

Station 3: 480v 3600HP total

I spent a good length of time on the phone with one of the utility company engineers making sure we were on the right track with harmonics, power factor, etc. He mentioned the customer will pay for poor power factor below .97. That sounds high to me, but maybe it's normal?

We have included PFC's in our quote at the station with 2300v MV equipment. We have not included any PFC's in the 480v stations. All the stations will have 1-2 VFD's with everything else on softstarts.

From two different reputable gear reps, they tell us they never supply PFC's for the 480v equipment they sell. We see a fair amount of old PFC installations in our travels, but I can't say I've seen it installed on any new equipment that I remember.

So, despite hearing that, I was curious what others on the forum may do with their installs? 

Is it worth it or is the payback many years down the road? Electricity in this area is some of the cheapest in the nation due to the dams/wind farms nearby.

Thanks for the help.


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## joebanana (Dec 21, 2010)

I wouldn't worry about it. Maybe if you had a bunch of motors it may be worth the consideration.


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## telsa (May 22, 2015)

PF of .97 -- the dude is a jolly joker.

The standard rule of thumb is that PF of .90 is as high as a Poco can get away with demanding -- because they are regulated. At that PF they are not wasting that much on their transmission investments -- which is what this is all about.

Obviously, as the PF falls the Poco has to upsize their system to net the same amount of kWHrs.

Look at the power bill -- and contact the public utility commission for their tariff schedule. 

&&&&

BTW, cow, you were wrong on the Klixon. As pictured that Klixon is NOT an integral motor Over Load thermal protector. It's OUTSIDE -- in the panel -- just what I'd expected. 

My T-213 motors never had enough room in their peckerheads for a Klixon. Heck, they barely could accept the conductors.

The fact that a Klixon is one O/L instead of three -- as would be required in a standard NEMA 3 phase contactor -- Size #2 -- put to use for a single phase motor did not make me wrong.

BTW, if you want to get nasty -- use a PM.

You don't see me making a hax of things -- do you?


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## gpop (May 14, 2018)

lower voltage larger caps which is why its not that common on 480v. If cost to install is more than a 5 year pay back on increased utilities costs once you add in maintenance on the caps and surge protection it probably wouldn't make sense. With out have a study done by a engineer the best you can do is leave space for future cap installs later when you have numbers to work with.


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## glen1971 (Oct 10, 2012)

Cow said:


> We received the green light to redo the electrical for three irrigation pump stations this winter:
> 
> Station 1: 2300v 9700HP total
> 
> ...


We used to install PFCs on larger 480 volt motors, but haven't in years. Not sure on what the payback time frame is.. Maybe someone crunched the numbers and found it may not have been worth it..

FWIW.. I'm not sure what your power distribution is like in your neck of the woods, or what what size your VFD's and soft start are, but we just removed an across the line starter on a 5,000 hp motor, with it's capacitor bank, and went with a soft start. Well long story short, the soft start is coming out and a VFD is going in. The starting current and duration on the soft start was enough to cause a large fluctuation in the utility system and caused multiple issues in other areas. Perhaps a quick discussion with your utility to ensure you don't have any issues when you go to start, may not be a bad idea.


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## gpop (May 14, 2018)

glen1971 said:


> We used to install PFCs on larger 480 volt motors, but haven't in years. Not sure on what the payback time frame is.. Maybe someone crunched the numbers and found it may not have been worth it..
> 
> FWIW.. I'm not sure what your power distribution is like in your neck of the woods, or what what size your VFD's and soft start are, but we just removed an across the line starter on a 5,000 hp motor, with it's capacitor bank, and went with a soft start. Well long story short, the soft start is coming out and a VFD is going in. The starting current and duration on the soft start was enough to cause a large fluctuation in the utility system and caused multiple issues in other areas. Perhaps a quick discussion with your utility to ensure you don't have any issues when you go to start, may not be a bad idea.


Starting 5000hp on a soft start probably caused the local sub station to not only sense the voltage drop and PF but it lasted long enough for the sub to start making corrections. Occasionally our sub would get silly as the PF corrections caps and the regulators seemed to get in a running battle with each other.


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## Cow (Jan 16, 2008)

Appreciate the responses everyone.





telsa said:


> BTW, cow, you were wrong on the Klixon. As pictured that Klixon is NOT an integral motor Over Load thermal protector. It's OUTSIDE -- in the panel -- just what I'd expected.
> 
> My T-213 motors never had enough room in their peckerheads for a Klixon. Heck, they barely could accept the conductors.
> 
> ...



We'll agree to disagree.


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## HackWork (Oct 2, 2009)

telsa said:


> You don't see me making a hax of things -- do you?


Hey, I think I should be offended! :vs_mad::vs_mad:


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## glen1971 (Oct 10, 2012)

gpop said:


> Starting 5000hp on a soft start probably caused the local sub station to not only sense the voltage drop and PF but it lasted long enough for the sub to start making corrections. Occasionally our sub would get silly as the PF corrections caps and the regulators seemed to get in a running battle with each other.


The regulator adjacent to the site was trying to compensate, and I'm assuming the ones upstream were also working too.. I'm amazed that there was no issues in the sub. The current on site was around 1,200 amps (4,160 volts) for about 60 seconds, until it tripped (fail to start). I think the regulator was a 200 amp regulator and had 270 amps going through it. When the unit was trying to start, until it tripped the utility voltage was varying +/- 2,000 volts on a 13.8 line. All that they need is a capacitor bank installed on the utility line, which I heard was about 6 months away.


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## tates1882 (Sep 3, 2010)

I've used these when require, on carwashes with about 1000 total HP vast majority of motors being VFD driven. https://transcoil.com/products/hga-5-active-harmonic-filter/


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## JRaef (Mar 23, 2009)

PFC Caps and VFDs... bad juju. PFC caps can (will) resonate with the DC bus caps in the VFDs and cause all manor of havoc. On top of that, standard VFDs will claim .95 PF at best, but you cannot correct to .97 with PFC caps on them without causing something to blow up. Maintaining a PF of .97 is unrealistic using standard VFDs.

Were it me, I would propose using the new Active Front End VFDs that can be run in a LEADING power factor. That way the VFDs by themselves will meet harmonic requirements and the the .97 PF requirement, plus when the VFD is running and one of the other pumps on a soft starter starts and is running, the VFD can correct the PF of that pump (assuming the VARs work out). You would have to know in advance all of the motor / load combination details though. For example if the VFD is not running, it can't do squat to compensate for the others. But really, this is going to be a very tricky situation no matter what. Whatever you do is going to have to be carefully designed and executed in concert with the VFD mfr.

This AFE drive option though is especially viable on the 2300V station, but your choices on AFE drives that can run in a leading PF are limited and the VFDs are going to be more expensive.


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## paulengr (Oct 8, 2017)

If you aren’t penalized in power factor the financial return is so low social security might be a better investment. Check your utility rate
schedule. If nothing else it will show up on your bills.. For example in Dominion territory and Duke West they penalize below 0.85 power factor so much it pays for itself in months. In Duke East (former Progress Energy territory) its a total waste of money even if they apply the penalty. That covers the Carolinas and Virginia.

Otherwise there is some money to be saved based on losses in the biggest transformer. But expect things like saving $100/month on a 100 MVA load which is obviously a total waste of money.

In terms of VFDs and PFC never, ever, ever do this. If you have those then you need to look at a harmonic filter. Typically if it is tuned to the 4.3rd harmonic they work well together without the inductors making the price too outrageous.

The cheapest approach if you haven’t bought everything yet is a synchronous condenser...aka synchronous motor adjusted to leading power factor. Tried and true technology. Plus it can easily vary the vars. A generator can do this too. No VFD issues.

I’ve tried the leading power factor VFD front ends 10 years ago (large custom VFDs). There are serious trade offs and it often doesn’t deliver on the promise because it only works well with heavy loads and it also robs you of some power.




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## Flyingsod (Jul 11, 2013)

JRaef said:


> PFC Caps and VFDs... bad juju. PFC caps can (will) resonate with the DC bus caps in the VFDs and cause all manor of havoc. On top of that, standard VFDs will claim .95 PF at best, but you cannot correct to .97 with PFC caps on them without causing something to blow up. Maintaining a PF of .97 is unrealistic using standard VFDs.
> .


Is thus a faraday/lenz law thing?
Also am I wrong to assume a dc drive is going to have the same issue? One last thing, are we talking about PFC only directly ahead of the drive or will a whole system PFC bank also create these issues?




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## JRaef (Mar 23, 2009)

Flyingsod said:


> Is thus a faraday/lenz law thing?


No, not really. Capacitor resonance is extremely complicated to describe, but the best shortened version is that the DC bus capacitors are behind diode bridge rectifiers, which cause ripples in the DC that are absorbed by the capacitors. But when you have AC capacitors on the line feeding the VFD, they too are creating ripple-like distortions on the incoming AC line. At some point those ripples going THROUGH the diode bridge will combine with those on the other side and sync up with each other to "pump up" the voltage until one or the other fails. If you are lucky the VFD will trip on Over Voltage, but that only protects the motor, not the drive itself.



> Also am I wrong to assume a dc drive is going to have the same issue?


Depends on the DC drive. It's the caps on the bus that is the problem. An SCR based DC drive may not have capacitors on the DC bus, a PWM type will. 



> One last thing, are we talking about PFC only directly ahead of the drive or will a whole system PFC bank also create these issues?


It depends on the distance between the VFD(s) and the APFC (Automatic Power Factor Correction) system, and whether or not the APFC has de-tuning reactors or is on the other side of an isolation transformer, or if the VFDs have line reactors and DC bus chokes, because impedance is often the cure. But for sure, I have seen it happen. I did some VFDs at a fish processing facility in Alaska once and I put reactors ahead of every drive, because that's how I roll. But people before me did not, and when they added an APFC system, they blew up about 40 Toshiba and Yaskawa drives within an hour of turning it on. All of my drives (ABB) survived, but I attribute it to the line reactors and that this new building was about 500yards from the original building where they put in the APFC.


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## 3DDesign (Oct 25, 2014)

Look at the Power Company's bill. Is there a charge for Power Factor?
One local utility invoices for it, One does not.
The one that doesn't, why would you go through the expense of installing them?
The one that does charge, it's definitely worth it.
In one company with a 75hp and 125 hp air compressor, I installed capacitors and saved them $600/month.


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