Power Quality devices vs VFD's and Power Factor Correction devices.

Why do I get the impression that you are a simple mechanical device like a tube of toothpaste. You need much more information and knowledge pushed into you before you can ask a question that even makes sense and or get you to a level that any answer is meaningful.

There is no vs in power quality, VFD and power factors. Those are all descriptions of existing conditions that have consequences. Power Quality and PF correction has its own values and benefits if needed. Not an either or selection processes. They will exist in your power system even when or if the VSD is installed. The VSD use and energy savings will be determined by other system operation factors. Even the above comments are conditional on the assumption you are simply asking a question about energy conservation with a VSD. The answer is yes if all the conditions are right.

I am glad that this site exists. When I don't know anything and I mean nothing about what I need to know for my supposed job why waste my time in formal education or in researching the problem to find out the answer. I will simply ask my idiot question on this blog and viola! I will be an expert and use a cute blog name to hide my identity and abject ignorance all at the same time.

I am even mad at myself for commenting on this lunacy and I would suggest the first thing you do is get rid of the "smart"handle. It apparently has stopped you from knowing anything since you are already "smart".

Thats a Bit harsh..... don´t you think !!

Thank you for being the voice of reason. I think he kills his house flys with a sledge hammer.

You are right--of course it was that's why I was mad at myself.

OK, Jack...ease up there tough guy. I'm going to take the high road. I am smart enough to ask questions. I'm Smart enough to have an open mind to others opinions and learn from practical experience. This is not meant as a short cut to the correct answer. Researching is also asking others of their experiences. The 100% sure answer comes only from experience in applying the devices. Period. I am searching for others who have had to make similar choices. I am really directing my question towards energy conservation, rather than the other benefits of the devices. In todays market, the ROI is #1 priority to most facilities.

There are new green tech energy conservation devices coming into the market place daily, each with it's own effect on an existing electrical situation. I know for a fact that most plant supervisors choose between the different options available between PFC and VFD's for pump applications. Even the plant engineers and supervisors are uncertain which is truly the best energy conservation solution on a given facility. I deal with engineers and facility managers daily and most are unaware of the new technologies available. In some cases the PFC devises do not work well with VFD's, thus the VFD vs. PFC scenario arises. Another reason it IS a selection process between the two or more options is due to the fact most facilities only have the financial capability to choose one energy conservation solution. Additionally, new technologies may have a learning curve as to their cause and affect. I realize there is more information needed to give a precise answer, it was a general question directed specifically on pumps that run most of the day. I didn't feel the need to attach the facilities one line diagram, facility equipment site survey and 1 years worth of electric bills.

There is no need for your condescending personal attacks. I will deal with you with a direct message Jack. Sure would love to meet you.

No problem.

It sounds like the decisions that are being made around you suffer from the same problem you have. Not enough information, knowledge and experience. It all sorts out into no problem at all if you simply know the differences. We--you are now dealing in the day to day mundane problems where hard knowledge and specific experience is needed. Not idiot summaries and stuck together words to make decisions out of BS derived from management looking into something without a clue. I would suggest you go out on the floor and look at the problem you are trying to solve or better yet find and define the specific problem you are trying to solve. Resolve them one at a time based on some operational need based on priority and eventually you may have an efficient operating system. Let the smoke out first. If you did this you may be able to come up with an intelligent question or two.

Also think about this. This site is a good site and there are plenty of people on it who will try to fill in all the blanks to make sense out of your question and give you information based on the filled in blanks. Which may or may not be applicable. In any event you wouldn't know the difference.

I take another tack. More effective I believe. It sorts people out just as you have sorted out. I attack the source of the real problem at this point. You. It is also of course based on what the purpose of this CR-4 site is. I have one concept of what it should be. I may or may not be alone in this---but it is what it is. You may notice that as of yet you have no one answering your "question" other than yourself in defensive posturing. Keep up the good work with the smoke screens---using the words green tech. is always a good start.

How dare us commoners get involved in your forum...There is definitely a communication gap between us. I do appreciate your input, aside the wise crack, better then thou comments. The main objective of the facilities is to cut KWH consumption. If there were a specific issue such as harmonics, phase balancing etc...we can evaluate the issues through our power quality expert's testing equipment and metering devices, and address a specific problem. I agree with you 100%, but that was not the question. He does know the electrical intricacies as he is an engineer and master electrician.

We get calls to cut KWH consumption, and they are usually requesting VFD's and/or Power Quality units to achieve the savings. Facilities are putting in VFD's to save energy as a primary goal. Same with Power Quality devices.

The real issue is that even the manufacturers and engineers are not certain on how their new devices perform in every given condition, with multiple motors & existing power quality issues in some older facilities. No guarranty on savings. The technologies are simply too new to know exactly how each device reacts to a given situation. An added obstacle is every utility company bills differently, thus a cost saving measure in one facility does not save the same in another facility with a different power provider.

I have specific information, site surveys and one line diagrams....and each ambassador to a given product has an expert, engineer, electrician, etc., on their side stating their solution is best. Only time will tell through installations and long term proved savings results. That's where the "specific experience" you mentioned comes about. The new technologies do not have the specific experience due to being new. I guess that is really what I'm fishing for on this forum. We are pioneers in energy conservation measures...(I didn't mention green).

I am not defensive at all. I'll stand up to a geek like you any day (NJ Conditioning). We have proved narrow minded experts wrong in the past. The technologies are new. The sky's the limit. I have never claimed to be an expert. Just asking an opinion as to the devices on energy conservation value alone. You may know electric, but I'm out in the factories listening to each engineer claiming they have the best solution.

I don't hide behind Green Tech smoke screens so get out of the stone age...that's the terminology. ..what are you contributing , besides wise cracks and bully tactics, to help this country lessen fossil fuel dependency? Why don't you channel your efforts in a positive manner, help instead of criticize, share your unlimited plethora of knowledge with the commoners ......and then go kick your dog, go to Condesenders Anonymous, or whatever else it is that you do.

Are we meeting lunch or what?

No, and just so you are not under any illusions I am a contractor with over 35 years of direct field experience and we have been installing VFDs and the related system's DDC controls and custom software applications in design build applications for over 25 years. Nothing "new" here, you think you are inventing a wheel that already exists and has existed for many, many years. You would do well just to catch up instead of thinking you are breaking "new ground". At least catch up so that you can ask intelligent questions.

If you would like to talk about the newer PFC technologies that are on the market I would gladly have a conservation with you. I would guess you are an expert in the Field, but the new technologies my be a better answer than what you've been doing for the past 25 years. I will definitely catch up on my knowledge so as not to disappoint in my future inquiries. I love the business. My field of expertise as a GC for 25 years is not specifically on VFD's and electric, but I am an expert in energy efficient windows, general building practices, insurance restorations and an exceptional carpenter. I have spent the last 4 years finding the best of breed in a given energy conservation product line. Some I'm an expert in , some not, but I have the expert with me in each area. The biggest area of controversy seems to be with the new PFC devices...I guess time will tell. I have engineers for electric in my company. Seems most have conflicting opinions as to PFC and VFD solutions, speaking as to energy efficiency only, not in diagnosing a problem. That's why it's difficult to weed through to the best solutions. I guy like yourself with 25 years exp. in this Field would be a perfect candidate to weigh the energy conservation solution issues at hand. The wheel has been improved on though the years Jack and there are alternative solutions to improve KWH reduction in electrical motors that may leave you behind if your not privy. I know your the expert, but even a master can learn something from an apprentice. Many engineers have not heard or seen 40% of the products we use. Exciting times.

Outside the persoanal attacks I have enjoyed this debate. Thanx Jack.

The smartest contractor in the world by far. You know everything about everything from genetically modified foods, green housing, etc. Hopefully MENSA finds you soon before you spread your wealth of knowledge too thin.

I will not visit a site that allows people to berate others. That is called cyber bullying and it is committed by cyber children. Go get some friends Jack.

Power Factor Correction Devices are the answer.

They are the ones which actually reduce the power bills (and also efficiency by reducing the constant slip factor, thereby increasing the ratio of the slip factor proportional to load).

All other devices (e.g. VFD etc.) consume more power in converting.

If you want any further clarifications (free ofcourse, but please be short on phone), you may call me.

Ashok Shukla

Delhi

9810145598

II would like to agree, as I am familiar with PFC devices. Still learning on the VFD's, which seems to be the competition as to the facilities choice for energy conservation. Thus the inquiry.

I can show you share new PFC "stand alone" technologies with you if you like that actually bank energy to cut down on peak demand charges. This is not the typical KVAR technology. Thank you for your input.

Gentlemen,

Please come down.

Mr Gary,

There are many threads regarding VFD and power factor correction on this site, do a search (top right section of this page) and you will find a wealth of info.

It is true that you question is very vague. It is impossible to answer specifically. Please read other posts and come back with more specific questions.

Here is my two cents...

There is power saving is achieved by using VFD (almost) only when it allows you to exchange a dampener or a choking valve by a lower motor speed.

Another valid reason to use a VFD is when the process is improved by the variable flow of products but it may increase the power consumption from the VFD losses. Increased maintenance challenges is to be considered.

VFD do produce harmonics and power losses though. Unless you saved a lot of power from the speed reduction, you might make things worst for your employer.

Power factor correction is not a magic trick and can cost more that it saves. Don't listen to snake oil vendors. If you are presently paying penalties for low PF, you should look at it seriously. Otherwise be cautious especially when VFD are installed in the plant.

Good luck

Marco

Thank you for your well thought out reply, worth more than 2 cents...lol. I need to do more home work on the VFD's. I agree the question was vague, but it does not warrant that type of response ...I will take your advice and go through the site.

Just as in the market place, the gentleman answering this question before you recommends PFC devices over VFD's. A standard debate it seems. I would venture to say the VFD's are proved to date, where as the newer PFC devices are not. I see KVAR got a black eye from DOE reports on the DOE site, referring to snake oil as you did. VFD's add harmonics and in some applications we can not get PFC to play nice in the sand box with VFD's to clean up the harmonics.

My goal is to find the best of breed solution to a given power consumption reduction request. Even the engineer's disagree on the solutions. Good for debate...

Thanx again Marco. I appreciate your input.

Smartpowergary,

1. Take the proposals from the various vendors, block out any pricing they include, and have the competing vendors justify their approaches as being better than the competitors' approaches.
2. I suspect that no one approach will work properly for all the different specific loads in your facility. A good approach will look carefully at the equipment, the loads, the duty cycles, and the installation before determining the best methods/answers for each one. In many cases, you will see side-effects from any one method/answer; these may need to be evaluated to determine the ones that are least troublesome for your future.
3. Common engineering design includes a safety margin between the capability of the equipment and its actual load. It may be as little as 10% but may be as much as 30-50%. With motors, this shows up on the utility bills as a low power factor--depending on the motor design, an unloaded motor might draw as much as 50% of its nameplate amps, but at a very low power factor. Unless you can predict the future, I don't suggest eliminating this margin between capability and actual load--loads may change and equipment may deteriorate. However, you can and should consider ways to compensate for the effects this margin has on your plant loads. Read on.
4. VFD's are excellent for matching a motor's energy consumption to the actual load. However, they commonly impose harmonic noise on the incoming power line. The newest generation of VFD's can include circuitry to actively cancel these harmonics or to filter them out--look at the specifications and demand VFD's that have low THD (total harmonic distortion) on the power line. You'll pay more, but the rest of the plant will be better off. Some VFD's now come with protection against reverse wiring (line connected to load), the ability to be bypassed when the motor is running at full speed or if the VFD has faulted, and even the ability to automatically keep the motor running at a reduced speed and load if one of the incoming phases has failed.
5. VFD's recreate the sine wave to the motor by very rapid chopping of the DC bus voltage and assembling this in a way that the modestly filtered output looks like a sine wave of given frequency and voltage. Yet, buried in this modestly filtered output is still that high-frequency (6-20kHz) "carrier frequency" that was used to recreate the sine wave. When this reaches the motor, there almost always is an impedance imbalance between the supply conductors and the windings. The carrier frequency reacts to this impedance imbalance by reflecting itself back towards the VFD. Thus, the voltage imposed on the first few turns of the motor's windings can be double the nominal output voltage of the drive. This is no problem if you are operating a dual-voltage motor on its low voltage or if you are using an inverter-duty rated motor (which has better resistance to high voltage spikes). This problem gets worse when the distance from the VFD to the motor increases. Solutions--good load side reactors, drives with active filters, impedance balancing components at the motor terminals, etc.
6. Eliminating your reactive power can reduce your total current consumption, will reduce your charges for KVAR's, and can improve the voltage available throughout the plant. Because of their design, VFD's do not need power factor correction on their line side. The method used most often is capacitors. (Power factor correction on their load side is generally a big No-No.) The lowest cost power factor correction is to apply it at the individual loads, for all major loads. However, you can also purchase equipment to do power factor correction at the mains with automatic adjustment of the amount of KVAR's to keep the power factor close to unity (but usually slightly on the inductive side). Some plants, particularly older ones, had one large motor be a synchronous motor, which can generate KVAR's to correct the power factor for the plant. Many synchronous motor starters then can automatically adjust the field current to provide the required plant-wide KVAR's without the need for any capacitors at all.
7. Some voices will raise alarms (loudly) about the harm and disasters that can occur with circulating currents if the power factor is corrected past unity into the leading area. They are correct in the theory, but fail to see that the theory is true only when the circuit of capacitor, motor, and power conductors has an LC (or more accurately an LRC) resonance at the mains frequency. I have worked frequently in a plant with parallel incoming 13.8kV mains and a leading power factor of 0.7 to 0.8 on one of them because of some very large synchronous motors (on air compressors) and a lagging power factor of about the same amount on the other incoming main. In the 30+ years this plant has been in operation, no harm has been found to any of the connected equipment (the switchgear allows the compressors to be connected to either incoming main).
8. About 25-30 years ago, a device called a "power factor controller" was introduced to the market, based on NASA designs. Initially it was for single phase motors, but was then re-designed for 3-phase motors. It was hyped for a while as a means of saving energy by cutting the motor voltage (through SCR's) until the power factor approached unity. The theory is good, but the devices create their own problems and better approaches (such as VFD's) exist now.
9. You don't mention methods of peak shaving, to avoid the (typically 12-month duration) expense of an infrequent one-time peak demand. Or, of a cyclically recurring peak demand. Good energy management will look for the presence of these and suggest how you can modify processes or equipment to make your load more uniform. Demand management approaches include shedding non-essential loads, duty cycling chillers or other equipment, personnel scheduling changes to move certain processes or activities to times with reduced load, contracts with the utility to allow them to reward you for reducing your demand when their system-wide demand is highest, shifting portions of your plant load to alternate power sources (such as stand-by generators), etc.
10. Motors that run more than 12 hours per day every day are good candidates for replacement with premium-efficiency motors. Beware, however, because these motors have higher inrush currents when being started, so occasionally the supply wiring, fusing, and even starter may need to be re-sized.
11. Back to the first item. Read everything you can from each "vendor", and become as educated as you can on the benefits and pitfalls from each. The more you know, the better you can serve your employer and the future.

I hope this modest list helps you in your work. The future will bring us most of these following things: 1) increased electronic noise and problems from it, 2) mandatory peak shaving for large energy consumers, 3) better ways to do co-generation as well as increased understanding of when it can be very beneficial, 4) higher utility bills along with an increasing diversity of rates and rebates within the rates, 5) natural gas charges that rise less quickly than those for coal and other fossil fuels, and 6) a shift away from fluorescent lighting (because of the environmental problems with mercury).

--John M.

I will review in the AM...thank you for the information John.