Power Factor Correction Add-On Products Viability

ka4koe

Member
As an engineer for the government, we frequently are required to review products from vendors. The latest product to cross my desk is an add on panel-enclosed capacitor bank to be installed at the main distribution panel of a commercial building with a substantial HVAC load. The bank is always hooked up and is never switched out of line.

The distribution system at our installation is owned by the local power utility. The utility already performs PF correction at the substations here using capacitor banks (switched as needed).

Our initial appraisal was that any benefit would be minimal. Can anyone refer me to proper studies on this topic? Is it all hype at the usage level? If there is any payback, are we talking a few years or decades?

Thanks.
 
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charlie b

Moderator
Staff member
If the tenant (in this case, the government) is not charged for having a power factor lower than 1.0, then the tenant has nothing to gain by adding PF correction at their building.
 

GoldDigger

Moderator
Staff member
And if unswitched PFC sometimes causes a leading (capacitve) net impedance, it can lead to voltage instability and other problems.
 

RD35

Member
I, too, work at a gov't installation. Our installation owns the MV distribution which consists of two very large subs. We have switched Cap banks at each sub. An entity recently approached us wanting to do PF correction "at the load". Their angle was that by correcting at the load, the caps would switch on and off with the load itself. Not a bad idea....however, in our case we are charged a penalty based on PF lower than .9 at the sub and the automatically switched cap banks take care of that. So, there is really no economic benefit. I am totally sold on the concept that PF correction "at the load" is by far the best approach scientifically, but economically it just doesn't work for us here.
 

Jraef

Moderator
Staff member
99.9999999% of these systems are snake-oil scams for unsuspecting people with little to no electrical background. Trust your instincts here, you were right to question it.
 

myspark

Senior Member
As an engineer for the government, we frequently are required to review products from vendors. The latest product to cross my desk is an add on panel-enclosed capacitor bank to be installed at the main distribution panel of a commercial building with a substantial HVAC load. The bank is always hooked up and is never switched out of line.

The distribution system at our installation is owned by the local power utility. The utility already performs PF correction at the substations here using capacitor banks (switched as needed).

Our initial appraisal was that any benefit would be minimal. Can anyone refer me to proper studies on this topic? Is it all hype at the usage level? If there is any payback, are we talking a few years or decades?

Thanks.

Philip Neidlinger

Power factor in electrical engineering is the ratio between real power and apparent power. The sales gimmick claiming that improving power factor could save consumer money is urban legend. I would not go overboard (however) to claim that it is a total hogwash.

You do not state where you are located and what utility that provides power in your area. Some utilities require power factor not less than 80%. Anywhere less than required and you are subjected to surcharge. I know it's a fact when I was a staff engineer for a global paper mfg years ago.

The company has a 200 HP Synchronous motor that runs 24/7. It was kept running without any driven load.This is used to improve PFC in lieu of capacitor banks. It serves like an in-house generator.

Lagging power factor is inherent in industrial locations where huge AC motors are common. In some commercial and residential locations where resistive loads are predominant. . .there is no discernible economic benefit that can be derived from it.

Efficient operation of consumer equipment can lead to better and trouble-free operation with higher power factor or at par since low power factor can cause motors to run at higher temperature that often lead to premature failure. This is the only benefit that can be derived from it.
As for dollar amount, it it s only as good as peanuts.

Improving power factor mostly benefits the utility company. . .not the poor consumer.

Maybe that is where the snake oil offer its lubricating attribute.
......
 

myspark

Senior Member
Improved power factor is indispensible in the proposed extensive HVAC application.

You have mainly inductive load (s) ie motors that will certainly bring in a carnival of power-lagging contributors to this phenomenon.

Abnormal power lag is easily and cheaply remedied by capacitors. OP probably still remember the mnemonic: ELI the ICEMAN in the senior years.

Voltage lead in an inductive circuit while current lead in capacitive circuit.

To correct the lagging voltage in inductive load, you use a capacitor in order for the current to take the lead in close proximity to match the voltage.

Although this anomaly can be mitigated by kVAR (reactive power) generated by the AC motors and by the kindness of Faraday's Law regarding conservation of energy initiated by Newton, such amount of reactive energy would not be enough.

Hence, the bank of capacitors become an absolute necessity. There is no smoke and mirrors involved. . .just plain and trusty old Physics.
 

GoldDigger

Moderator
Staff member
...
Efficient operation of consumer equipment can lead to better and trouble-free operation with higher power factor or at par since low power factor can cause motors to run at higher temperature that often lead to premature failure. This is the only benefit that can be derived from it.
As for dollar amount, it it s only as good as peanuts.
...

Maybe that is where the snake oil offer its lubricating attribute.
......
Power factor correction, either at the load or at the panel, will only improve motor operation if the voltage drop is excessive, particularly for starting current, or if the energy supply is current limited such as a local generator or a PV inverter. Improving the inherent power factor of the motor can only be done by design or by controlling its loading. And high inherent power factor does not correlate with high efficiency.
 

topgone

Senior Member
Power factor correction, either at the load or at the panel, will only improve motor operation if the voltage drop is excessive, particularly for starting current, or if the energy supply is current limited such as a local generator or a PV inverter. Improving the inherent power factor of the motor can only be done by design or by controlling its loading. And high inherent power factor does not correlate with high efficiency.
Agree. And the utility will be very happy if all its customers install PFC equipment at their distribution panels. It was the "in" thing way back decades ago. The positive thing for customers there will be that of doing away with possible penalties to be slapped on them by the utilities for having a very poor PF.
 

myspark

Senior Member
Power factor correction, either at the load or at the panel, will only improve motor operation if the voltage drop is excessive, particularly for starting current, or if the energy supply is current limited such as a local generator or a PV inverter. Improving the inherent power factor of the motor can only be done by design or by controlling its loading. And high inherent power factor does not correlate with high efficiency.
Efficiency encompasses everything especially in a situation where OP is in.
We are talking about efficiency at the utilization end. . .not at the power generation end. (generator or PV)
Efficiency is the state or quality of being efficient or being able to perform or accomplish something with the least amount of wasted time and effort and also minimum expense.
Improved power factor as I mentioned identifies with minimum of waste.

A motor for instance that is running at low efficiency (for the most part) generate heat. Heat is wasted energy (Joule's Law) that would otherwise would have been used productively.
 

ka4koe

Member
Thank you for the replies. I hardly ever deal with PF in my day to day duties. The problem is somehow these vendors get access to those near the top of the command chain and then we have to deal with it. Another issue as I see it is the devices in question are not switched out after the motor loads stop. Then the power factor goes the other way----now we are capacitive.
 

retirede

Senior Member
A motor for instance that is running at low efficiency (for the most part) generate heat. Heat is wasted energy (Joule's Law) that would otherwise would have been used productively.
But PF correction will have zero practical impact on an existing motor’s efficiency.

A minuscule impact may be seen if correction appreciably reduced voltage drop as pointed out previously.
 

Jraef

Moderator
Staff member
Sorry if I implied that PF correction itself was a scam, it is not. My comment was referring to the proliferation of people selling little boxes that connect to your distribution panel that will “save energy”, then attempt to back that up with data showing a reduction in current because of adding capacitors, assuming that most people will equate current as energy. The fact that this magic box has no means of switching capacitor banks in or out of the circuit based on actual VAR measurement almost guarantees that this is a scam artist because either they have ZERO regard for the potential harm that can heap on the user, or the AMOUNT of capacitance they are connecting is so low that it is virtually insignificant. Scam either way, one way is just less risky than the other.
 

Besoeker3

Senior Member
A motor for instance that is running at low efficiency (for the most part) generate heat. Heat is wasted energy (Joule's Law) that would otherwise would have been used productively.
PFC will not reduce motor losses. It can, and does, reduce losses in the supply conductors to the motor. It may, depending on the supplier regulations, also avoid charges for poor power factor.
Just another point to think about is non-linear loads resulting in harmonic distortion. De-tuning reactors may be required to prevent overcurrent in the capacitors.
 

Open Neutral

Senior Member
Lagging power factor is inherent in industrial locations where huge AC motors are common. In some commercial and residential locations where resistive loads are predominant. . .there is no discernible economic benefit that can be derived from it.
......

I wonder. What [remaining] loads in a residence are resistive? Well, electric dryer. Ooops, just heard of a heatpump based dryer. Lamps, err. Ovens? I assume they may be PWM controlled. Tesla charging?

Have there been any recent studies of residential power factor and non-linearity?
 

myspark

Senior Member
Thank you for the replies. I hardly ever deal with PF in my day to day duties. The problem is somehow these vendors get access to those near the top of the command chain and then we have to deal with it. Another issue as I see it is the devices in question are not switched out after the motor loads stop. Then the power factor goes the other way----now we are capacitive.
Since (as you stated) that this is vendor-supplied equipment, I would assume they would deal with “TURN KEY “ contracts.

This is the usual procedure in dealing with government projects. The government would invite contractors to bid on projects from scratch. . . meaning the contractors would only be given the criteria as to how and what purpose the project is going to be.

In essence, turn-key contracts are: you build us something and you give us the key to turn the thing on when its done.. . . that is all the contractor needs to do.
This is why we "paeans" (engineers) are not privy to powers-that-be decisions.
Here are the plans . . . you do it.

And people would wonder why it cost so much. . . to build a toilet to operate in gravity-free environment. Water doesn't flush up there in space you know. :)]

Is that off topic?

Lockheed for example is invited to create a supersonic fighter jet. This is all what the engineers have to go by. This also applies to projects like building structures.

Now, back to power factor correction using PFC capacitor.

Your idea of shutting down the caps when the motor loads stop is good. Anything you don't need when things are supposed to remain idle is a plus. Anything that emits heat when not in use is just wasted energy. Resistors known as vampire loads do consume energy those--that are used for controls and sensors.

But there is an issue when you connect/disconnect a capacitive load. Capacitors store energy that needs to be drained (discharged) before the next command to turn on. Undesirable results would happen if not heeded.

There is this inherent current surge every time you engage a capacitor in the circuit.

Your application (HVAC) loads are meant to cycle on and off. For huge capacitors in industrial application, this “draining “ process takes time. Normally (theoretically) it takes 60 seconds.

If your project can live with one minute waiting period after you shut down, then, by all means more power to you.

NEC requires this draining time. OK NEC hounds, I'm ready for the lynching.

Having said this, the equipment supplier must have included this feature in their design.
 
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ka4koe

Member
I just examined the bill for reactive power here. It's about .01% of the total. I'm going to try and slam-dunk this and put it away for good.
 

kwired

Electron manager
Efficiency encompasses everything especially in a situation where OP is in.
We are talking about efficiency at the utilization end. . .not at the power generation end. (generator or PV)
Efficiency is the state or quality of being efficient or being able to perform or accomplish something with the least amount of wasted time and effort and also minimum expense.
Improved power factor as I mentioned identifies with minimum of waste.

A motor for instance that is running at low efficiency (for the most part) generate heat. Heat is wasted energy (Joule's Law) that would otherwise would have been used productively.
Efficiency of a motor isn't necessarily directly related to the power factor.

Efficiency of a motror is simply the ratio of power in to power out. Low power factor indirectly leads to possible increased losses in the supply lines but doesn't change overall efficiency of the motor itself.
 
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