The above was meant more as a sarcastic comment on truth-in-advertising than as a request for a pointer. (Maybe I should have added a smile. :) Once you've been told what to look for it's fairly easy to find a reference authority and relegate the question to triviality in retrospect. Of course, I still think that the circuit analysis required to understand this particular puzzle _is_ in fact trivial, and no reference should be necessary. What's bothersome is the number of people over the years who could neither find a reference _nor_ follow the simple analysis but instead resorted to (incorrect) hand-waving arguments to support their premise that the meter could not be subject to this error. Mr. Alexanderson is the first USENET poster I've encountered who showed an understanding of the effect, and he had the references to boot. [I jot down his name for future reference. :)]
----------- I have problems with the above statements. There appears to be almost a mantra in place "pf correction is good for all evils" It isn't and whether it is justified or not depends on the situation-both technical and economic analysis is needed to determine whether it is needed and, if so, how much (correction to unity pf is generally not economic or necessary).
. Adding power factor correction capacitors on industrial motors does < not
increase efficiency slightly as typically efficiency is best at
100-105% of rated voltage. Of course, if the voltage is a bit higher than normal - pf of the motor drops which has a counter effect. It also does provide a better pf to other apparatus (to say so is meaningless ). Motors and other apparatus have their own pf depending on their loads -they suck or blow vars as well as watts- provide 400V 3 phase to a motor and it really doesn't know or care that there is a capacitor bank hung across its terminals. It "sees" 400V 3 phase and it sees a load- the power factor of the motor follows from that (overall pf is increased by the pf but the motor behaviour is not modified). If the pf correction makes it "see" some other voltage then there is modification of motor behaviour which may be good, bad or indifferent. All power factor correction does is provide "upstream" benefits by providing some or all of the reactive needs from a local source rather than the utility. A side benefit is better voltages at heavy load (and possible overvoltages at light load). In some cases power factor capacitors attached to and switched with the motors can lead to serious problems- particularly where a transfer is made from the utility to a backup system.
| > | | > | Having read through 'Dan Lanciani's discussion, I can say that what he's | > | describing is *not* a metering problem. He discusses if the voltage | > drop | > | from the meter to the load is significant, | >
| > No, I clearly stated that the long run is from the meter to the | > transformer. | > The voltage drop that is significant is from the transformer to the meter, | > not from the meter to the load. You can't change the example circuit and | > then complain that the math is no longer correct. :) | | Okay, I somehow misread that before. You are correct if the voltage | imbalance is at the meter (caused by resistance/reactance upstream of the | meter), then it won't correctly register such an unbalanced load. | | I don't know of any 'trick' in electromechanical kwh meters that can detect | this problem. An electronic meter *could* be configured if it senses the | current imbalance and has a manual input for the neutral resistance. But I | haven't heard of any digital meter algorithm that has this feature.
It wouldn't work anyway if there were more than one meter served by the transformer. Around here they run those tiny aluminum neutrals for blocks as part of the post-transformer distirbution system to multiple houses. If you ask them why it is ok to use such thin wire they say that everything probably balances out in the end. The fail to add that even if it doesn't balance out, the customers eat 150% of the loss. I have to believe that this point is not lost on the transmission engineers. :)
---------- I disagree with you. The bill reduction is due to the reduction in demand charges. Any effect on energy charges is generally only due to some reduction in losses -if the pf correction is distributed at the various load points- very often it is not but made at or near the service entrance and this will not reduce losses and kWh charges.Pf correction will have only a small to negligable effect on motor efficiency.
Industry practice does use pf correction but not because of improved efficiency which may or may not be there. If pf correction is being sold on the basis of improved efficiency then someone is being taken for a ride. If it is being sold on the basis of reduced kVA demand - that is correct. If customers are being told that one should correct to unity pf - again they are being taken for a ride.
but you were advocating pf correction for residential cases.
-----------
------------ You have put the cart before the horse. The pf of a motor is determined by the voltage at its terminals and the load on the motor. The torque, current, power, efficiency are also determined by the same factors. If the voltage drops- then you will have higher slip and lowered efficiency etc. Yes the owner will have higher losses at off normal voltages but the watthour meter will read the energy taken independently of the pf.
Note that pf compensation will have no effect on the motor unless it modifies the voltage-nor will it affect the energy measured. Typical Pf correction at a central location in the plant will not reduce the losses due to poor voltage at the motors. Also-if the incoming voltage from the utility is too low or too high- then the utility has to bring it within bounds.
-----------------------
------- I would suggest that you get a good motors text and find out what affects the behaviour of induction motors -input and output and what affects them. . A circuits (not electronics) text would also help. It appears that you are drawing conclusions from the reference above which aren't justified.
Nah I don't sell anything ...I'm semi retired and working about 20 hours a week consulting, mostly industrial mechanical and electrical. Background Petrochem, nuclear weapons (the lab side) and containment, semi conductor fabs, and large scale refrigeration such as in breweries and blast freezing operations.
The rest of the time i am flat tracking or tweeking on the bikes ( motorcycles on 1/4 mile dirt ovals, I run a 600cc 4 valve ohc single..Rotax in an american frame..Im one of the worlds oldest flat trackers ... age 63.. and I look my age. So you are correct. Its not entirely dead center on this end at all times). I totally terminally agravated the nice folks at the USDept of Energy. They hate me do you know that Charlie? then we had the court disaster and that led to the congressional mess where yers truly endured a few hose jobs attempts but in the end the bastards at Westinghouse Hanford went down. (Fluor runs the Hanford site now)..
Its been an eventful life... and educational. I do seminars some now. Usually to young engineer types thier employer wishes to disabuse of various bogus notions picked up in school and from an entirely corrupt corporate america... I begin by assuring them that on a scale of absolutes (thats all that could or will ever be known) that I am an almost complete idiot in my specialty areas.
One thing I ran into in many areas...mechanical engineering, medical research.. electrical etc. Odd and impossible as it seems, I found geographical aberations and variable use of terms. Each sure that his region was the standard... and you would think that would be the case since so many text books and technical articles are standard.
but Ive found many apparently dont read them or for whatever reason have divergent regional notions on the same issues... and thats true for this term 'harmonics' as well.
correct... I had not been arguing differently, although the OP was raising these issues mixed with some other things such as his unbalanced load down stream of the meter.
appearances can be decieving...along with assumptions. Beyond the voltage reads at the motor terminals are wave distortions in the AC current flow... harmonic distortions...and these can and do produce significant disturbance in the stator field of the motor and that creates slip and as you know, things so south in that case fast.
you have been addressing pf issues out of context with harmonic distortion issues... (whaps respondent in head with dead trout)... but thats excusable... not knowing everything about everything in utterly complete and accurate detail is a
From what I have seen in that area and in many corporations in other areas I would say you are accurate in your assessment. Ive seen hard core attempts to hide demand charges from industrial customers and elaborate ruses and non compliance with questioning when the issue was brought up.
There are two movies out you would appreciate 'The Yes Men'...and 'The corporation'...both hot onto this range of topics and funny as hell. both documentaries.
The yes men tests the level of corruption and gullability in corporate america by infiltrating their organizations and seeing how ludicrious they can get with scum bag plans before the industry leaders begin to see what a farce they have running... one part of the yes men was an industry presentation, with the science, and the suits and charts etc and power point...great introduction... showing that a person only actually metabolized 20% of what they ate and that by capturing this waste (from the sewer) it could be recycled back into hamburger patties and fed to third world citizens increasing profits and reducing hunger in the world... dead serious... the presentation to a university class finally got the students questioning the approach and the end lobbing debris onto the stage....the same presentation to a group of world trade officials got conservative if somewhat tennative applause...even as the machines were shown plopping brown crud onto McDonalds frying conveyors... a few strange looks..but in the end, conservative applause.
You still don't get it. I will waste my time and give you a little primer. If the customer has electromechanical metering (kWh and a KVA demand for example), harmonics will not appreciably affect his bill in any way. These meters are "tuned" to respond to 60hz. There is a slight response to harmonics, but it is negligable. So harmonics will not effect the bill. Likewise, no affect to the billing power factor.
Now, when you go to an electronic meter, things get more interesting. If the utility bills on a displacement power factor (something that electronic meters can measure, and no, it does NOT include harmonics by definition) then harmonics again do not effect the billing. If the utility uses a kVA demand charge as their means of power factor penalty, then harmonics MAY make a difference. But they may not. All modern electronic meters have the option of measureing demand with or without the effects of harmonics. It is up to the utility to decide which to use. Many use "without" since that gives them the same answer as if they were using an electromechancal meter. This makes regulators happy since the simple act of changing a meter should not impact the bill.
As you can see, merely discussing "power factor" is misleading. Displacement power factor is the phase angle between the fundamental frequency compenent of voltage and current. It is the power factor that can be corrected with capacitors. True power factor is the ratio of active power and apparent power (volt amperes) and does include harmonics. Without knowing which one the utility uses for billing, a customer may unecessarily invest in correction equipment with the hopes of lowering their bill.
The motor is NOT creating the harmonics.....YOU are correct. The motor IS creating *harmonic distortions*. Those harmonic distortions in the line feed back out of phase into the plant or local area power grid. Those harmonic distortions are variously describes, as that, harmonic distortions, or back EMF. ..and yes indeedie, back EMF could be described in other ways or simply as back EMF. It is however, due to lack of total control of the language also accurately described, depending on yer point of view as harmonic distortion....because it does in fact distort the phase relationships and all of that is indeed one general fiasco.... which of course can be corrected or eliminated and regardless of how you split the hairs improve yer customers cost benefit ratio.
What in hell is wrong with you? This thread is a thread on metering. Did you fail to read the original post? And I did not morph anything. Look at my posts. I said over and over that harmonics have nothing to do with displacement power factor. That is still true.
As for your misuse of the term "back EMF", you really should read a few more technical journals before you post again.
Also, I really enjoyed your "The motor is NOT creating the harmonics.....YOU are correct. The motor IS creating *harmonic distortions*." answer. Hahahaha. Now that was funny.
Who mentioned the meter creating distortion? To do any real energy savings consulting, which you have at least hinted that you do, you need to know what, and how, the meter measures.
I wish you would stop using that term and find the correct one. That way maybe somone on this forum could have an intelligent discussion on the subject. Back EMF occurs within a motor but it does NOT propogate onto the power system.
The original post was meter related, you are the one who keeps going off topic.
Wrong. Back EMF is a phenomenon inside the motor. It does not affect the utility. Unless of course you are using the term "back emf" to talk about something else, which I fully believe is the case.
You should spend a little time in a lab. I know of a good one. It is fully equipped and capable of testing motors (sadly only up to 400hp), variable speed drives, UPS, static var, series compensation, distributed generation equipment, relays, meters, power quality monitoring equipment, process control equipment, etc. The best part is it is located mere feet from my desk.
Your remark here of course is entirely incorrect... back EMF is a prime factor in disrupted power grids well beyond many industrial facilities.. back though the line transformers and down the line to neighboring users... its a major issue...not some secret.
Sorry, thats just how it is bud. You are clueless in this range of issues and have now fully demonstrated it by your remark...
....but thats fine... cluelessness is part of the human condition...spinning and trashing though thats regrettable... such tactics ruin thier host.
You can do better in that area.
to
are
keeps going off
at
with
not affect the
to talk about
Just about everyone posting this thread knows better than that Charles...its not rocket science, Its not a secret... the phenomena is quite well known and its a big issue with industrial facilities world wide and is addressed directly and frequently by utilitiy companies with their industrial users...it is a major concern.
Your remark demonstrates not just a lack of that knowledge but of the physics applicable to these and other situations in the electrical engineering business ... sorry...but you are diging your own hole here then trying to deny there is a hole...
one. It is fully
400hp), variable
distributed generation
equipment, process
feet from my
You have not learned much in the lab then if you hold the consideration that back emf stops in the motor and does not propagate back though the utility grid.
Sorry... its your foot thats in your face... not much I can do about that. These are commonly known and understood phenomena. And yes Charles these greatly influence the efficiency of everything on the grid... lower efficiency of course is costly as with motors the loss is goes into motor heating no torque... but you pay for that power...(correctly metered power).
And................... you snipped my flat trackin' story... not impressive.
Your attempt is to justify your error and put down any challenge to it... that always and invariably goes south, unless one buffalo's his idiot associates...then he gets to live with them... not the pinacle of what one can aspire to in life.
Well, I just polled three phd's who do power system modelling for clients all over the world and they all think you are batty.
I spent 12 years in a utility handling power quality problems and oddly this is the first time I ever heard of a utility having problems with back emf from motors. Of course I worked for a rather small utility, 30+ MW and 3 million customers.
In article , snipped-for-privacy@peeshaw.ca (Don Kelly) writes: | The main illogic (other than some numerical problems)
Could you detail the numerical problems so I can fix them?
| is that it is assumed | that the meter is somehow measuring power loss "upstream" of the meter.
That's not the assumption; it's the result. :)
| It | doesn't- It measures the power on the consumer side of the meter. This will | include losses on the consumer's side - for which the consumer is | responsible - not those on the utility side.
I think pretty much everyone else now agrees that the typical 4-terminal (i.e., "1.5 element") split-phase meter does indeed measure power losses in the neutral on the utility's side of the meter. If you do not agree could you explain exactly how the meter avoids this error?
| I suggest that you check Charles Perry's reference
Mr. Perry has posted a reference and provides one way of looking at the error as proportional to "1/2 of" the voltage difference. (I quote "1/2 of" since it doesn't actually add any information to a proportional relation, but I think we know what it means in this context.) I prefer to think of it in terms of the customer paying for 150% of the loss in the utility's neutral wiring, but that's just for the simple one-meter case.
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