What are the effects of a leading power factor?

Please provide additional details such as:

What leads (pun unintended :-] ) you to believe you do in fact have a leading power factor.

What instrumentation was used for quantification, and who was operating/interpreting the resulting data?

What you describe is a rather unusual situation, and with the equipment listed, unless there is equipment we are unaware of, the power factor should be approximately what you list except lagging.

Louis

Power company charges your more or less depending upon your average PF, Contact them, they like extra capacitive loading and will reduce your rates.

Actually, depending on the tariff, you can pay MORE if you are leading. If your penalby is based on a kVA charge, leading or lagging will get you the same penalty. From the utilities viewpoint lagging is bad, leading is bad, unity is good.

Charles Perry P.E.

| Actually, depending on the tariff, you can pay MORE if you are leading. If | your penalby is based on a kVA charge, leading or lagging will get you the | same penalty. From the utilities viewpoint lagging is bad, leading is bad, | unity is good.

I'll certainly agree with Mr. Perry on this. Both lagging and leading are forms of power sloshing (you take in power, and hand it back a 1/4 cycle, or maybe 3/4 cycle, later). While no real power is used for the reactive angle, it is wasted in transmission and distribution line loss in both directions. It is to be avoided and the power company rightly wants to encourage you to avoid it. But if what you have is really leading, that would give you some capacity to put on some lagging load (and slosh power back and forth between your loads).

yes, it does hurt to go leading. i've had customers complaining about blowing fuses, losing SCRs, heating transformers, etc. we pulled the billing for electric and found, even without metering, the problem. we disconnected some caps to get back to lagging and the problem disappeared. this happened at two different plants of unassociated companies. sammmm

We have this problem at work but after the main UPS for our server. This is caused by none liner psu`s and as a result we have had to de-rate our UPS by

25%

Extra capacitive loading helps hold voltage up but any demand metering doesn't give a damn as to whether you are leading or lagging. You might not get any more than thanks if you are helping.

Hello, and I've never heard of a kVA cost. Certainly in residential service one pays only for the energy (kW-hrs) consumed. Your electric bill is based upon energy usage (as indicated by the utility meter reading) regardless of whether current and voltage are in phase or not. The idea that a customer can somehow change the power factor and pay a lower monthly bill is pure urban myth. Sincerely,

John Wood (Code 5550) e-mail: snipped-for-privacy@itd.nrl.navy.mil Naval Research Laboratory

4555 Overlook Avenue, SW Washington, DC 20375-5337

KVA (demand) charges are almost standard practice for industrial customers, and are quite common for commercial tariffs also. Average pf, kvarh, etc power factor penalties are common for commercial customers. For the most part, only residential customers get a free ride with regard to power factor. Tariffs for many utilities are available online. Look them up. Of course, knowledge of metering practices and terminology will be necessary to interpret them.

Charles Perry P.E

Rumour has it that "true" KVA-demand metering [aside from residential] is fairly well entrenched.above the 49th.

?s falke

|> Actually, depending on the tariff, you can pay MORE if you are leading. If |> your penalby is based on a kVA charge, leading or lagging will get you the |> same penalty. From the utilities viewpoint lagging is bad, leading is bad, |> unity is good. |> |> Charles Perry P.E. | | Hello, and I've never heard of a kVA cost. Certainly in residential | service one pays only for the energy (kW-hrs) consumed. Your electric | bill is based upon energy usage (as indicated by the utility meter | reading) regardless of whether current and voltage are in phase or not. | The idea that a customer can somehow change the power factor and pay a | lower monthly bill is pure urban myth. Sincerely,

A given kVA at a power factor less than zero is less kW used. So not only is it a myth, it is a non-usage. If your current phase angle is other than

0 degrees from the voltage phase angle, you're giving power back during at least part of the cycle. So that's power you are not using. At 90 degrees you're giving back all you take, so none can be used. At 180 degrees you're running a generator.

The notion that you can cheat the power company with a bunch of capacitors or inductors to swing the phase of your current angle fails simply because you still end up with a real component equal to your real usage, regardless of how much additional power gets sloshed around in your reactance. The meter is still going to show the difference between what is coming and what is going (if it's one that runs backwards on what is going).

"I've never heard of it and don't understand it so it can't be."

What you are saying is true for residential customers, but not so for industrial. I once changed the taps on a couple of transformers feeding SCR rectifiers (5MW DC supplies) that were running phased back and eliminated a $4000 / month kvar charge.

That may be true- it was routinely done in the area that I used to live in. Note that KVA demand metering was based on monthly peak where the meter had a thermal(?) lag so that it rode through starting transients and short peaks and represented what was important to the utility - temperature rises in equipment.

A US utility with which I worked closely (this was in the1960s) metered all

4 parameters on large commercial and industrial services; kW-hr, kW demand, kVAR-hr and kVAR demand. The demand was the highest demand over a 15 minute interval, but the meter was reset monthly. The demand was calculated as 4 times the kW-hrs used over a 15 minute interval, so if you used 1 kW-hr in 15 minutes the metered demand was 4 kW. Same concept applied for kVAR demand. The load profile during any 15 minute window was therefore irrelevant, starting transients and such were effectively registered as usage rather than demand, which totally deflated the hopes of all the soft-starter salesmen.

The customer was allowed without charge a kVAR-hr usage equal to 35% of the kW-hr usage, which calculated out to mean that there was no PF penalty if the all-month PF was above about 95%. Past the 35% allowance the customer was billed for kVAR-hrs used. I don't recall the details of the kVAR demand billing, which probably means that it wasn't an issue for most customers.

The (purely mechanical) metering did distinguish leading and lagging PF. A leading PF registered as 0 kVAR demand, but the kVAR-hr meter did run backwards, so you could receive a credit for supplying kVARS. A few large users with synchronous machines did this, but it was under the control and direction of the utility.

There were a few rural and co-op utilities that tried to deal with PF directly, but that was always a silly mess. You would have plants that shut down and would register 100 kW at 50% overnight, but 1000 kW at 92% during the day. Obviously in this case the night-time PF is totally irrelevant, but I'd hate to tell you how much money was spent to correct the night-time PF.

I have not seen (in US practice) any examples of metering/billing based on kVA, but I suppose they exist.

Well, Mr. "I do understand it and it can be", you are being redundant by using the term "SCR rectifiers." Sincerely, and with jab intended,

John Wood (Code 5550) e-mail: snipped-for-privacy@itd.nrl.navy.mil Naval Research Laboratory

4555 Overlook Avenue, SW Washington, DC 20375-5337

| KVA demand charges do take into account power factor (by the way I believe | that tyou meant less than 1 not less than 0) The energy seen by a KWH meter

Yes, I meant less than one. Sorry about that.

| is unchanged as you indicate - except that, at any power factor except | unity the current, at a given voltage will be higher than the minimum | required to produce power. 1)the losses will be higher - customer pays more | in energy charges.

If your power factor is 1.0, you're not wasting any more power than in the proportion to what you use, relative to the efficiency of the whole system.

| 2)( and this is more important) the heating of the utilities transformers, | lines, generators, etc will be higher and such equipment must be sized on | the basis of KVA, not KW.

And of course this extra waste has two components. The facility cost to scale it up to be able to slosh the power around for the customer's sloppy load, and the energy lost while sloshing it around.

| Poor power factor costs the utility (a 2.5 KW load at 0.5 pf is a 5KVA load | as seen by the transformer and it must be sized accordingly), and this cost | is passed on to the customer with such a poor power factor (or poor load | factor) in the form of demand charges based on KVA. This is not done for | residential customers as it is simply cheaper and easier to take into | account typical residential pf in the rate structure.

As long as the demand charges relate ONLY to physical facility capacity costs, then that is the right thing to do. The loss of energy due to the inefficiency (small percentage) in transmission and distribution should also be paid for by the customer that insists on doing that, but it should be based on actual usage; a demand figure doesn't measure this part.

| 3) Poor pf -lagging- can cause excessive voltage drops. excessive leading | vars can also cause problems. | | No myths, either urban or otherwise are involved- just economics.

I think the myth is that all one has to do is get their current and voltage to be out of phase by 90 degrees relative to each other and the classic home power meter won't measure it. To whoever believes that then I suggest going all the way to 180 degrees and run the meter backwards so the power company pays you to use their electricicty :-)

Of course, none of that is real.

| It is then often advantageous for commercial and industrial customers to | provide some pf compensation - and this is done. Correction to exactly unity | pf is not done nor is it economic- There is an optimum point but few bother | with the calculation of such an optimum in design..

The problems I run into in designing and build computer data centers is more a harmonic issue. But even then there are phasing issues as many computer power supplies have narrow current spikes and are thus not evenly distributed over the AC cycle. One of the things I want to study is ways to balance such large non-linear loads (100's to 1000's of computers) so that current peaks do not get excessive (which can happen if all the power supplies work at the same part of the cycle, which tends to be true). I've started putting some thought into splitting things up into 6 or 12 phases. But then, that can also create lower power factor, too. Maybe balancing just how many of the various loads are sucking current at specific phase angles could approach making it look linear and unity.

| That may be true- it was routinely done in the area that I used to live in. | Note that KVA demand metering was based on monthly peak where the meter had | a thermal(?) lag so that it rode through starting transients and short peaks | and represented what was important to the utility - temperature rises in | equipment.

Sounds like exactly the right way to measure for the component of costs that relates to purchasing, installing, and maintaining transmission and distribution facilities.

So, given 2 customers that periodically have a 1000 kVAR demand, but run regularly around 100 kW, where one of them has pf 0.97 and the other has pf 0.66, how are they going to measure the added charges for the second? A kVAR usage meter?

You said, "Hello, and I've never heard of a kVA cost...." and, "The idea that a customer can somehow change the power factor and pay a lower monthly bill is pure urban myth."

No it isn't an urban myth, as some have pointed out.

And in the industry where I work, we refer to a large, as in several megawatt, DC power supply as a "rectifier." It happens that the "rectifiers" that I adjusted the transformer taps on, used SCRs as the devices. We have others that use diodes. So I guess you really got me in the department of redundancy department. Pun intended.

Jab taken and sincerely back at ya! :-)