Harmonics and VFDs 22

[Marke]

One of the areas that I operate in, has a high density of VFDs on pumps on relatively weak supplies. The result is that the high levels of harmonics on the VFD inputs has accumulate in the supply and is causing a high THD of the supply voltage. While we do have supply regulations covering harmonics, in this instance, the harmonics are higher than they should be.

There is an option of using zig zag transformers and six phase rectifiers as a means of reducing the harmonics drawn by drives however in this case, the drives are already installed.

There is a transformer for each drive and sizes range up to 200KW.

One thought that I had, was that for future installations, and there are new installations going in all the time, that the new supply transformers be designed with a zig or a zag winding to give a phase shift, and install equal loading on the leading and lagging phase shifts. This should act like a twelve pulse input on one drive, only it will be across two drives.

Any thoughts on this??

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[crazytexacan]

GREETINGS: HARMONICS... WELL ALLEN BRADLY has a new VFD drive out, it has 6, 12, or even more pulses on the input side to balance out the input SPIKES...We see these problems on oil well pumps ... down -hole submersiables A tough app. LAST VFDS are now sweet, I started out 34 years ago with only DC drives.... to work with.. A vfd must always be considered a narrow range controller say 35HZ to yepp 70HZ.. if the motor is sized correctly you can run it over base speed of 60 hz ,,, BUT USUALLY a range of 35?hz to 60HZ was considered a good range... I am courious though .... about the fall off of EFF. in large motors under 50 hz... HOPE this helps... When I lose a drive I can usually run in Bypass mode...

 

[Valvecrazy]

"Understanding that the power consumption is related to the work being done is not a difficult
concept."

I completely disagree with the above statement. If it were not a difficult concept to understand, a simple pump curve would be all that is needed to make the point. In this thread we have batted the math back and forth, studied pump curve after pump curve, and even demonstrated the idea with a working pump system. Apparently we are still arguing the point. Again, if you can read a pump curve, the test rig is simply proving the obvious. I don't agree that an amp meter to measure power on our test rig should cause a "big red flag". 167 watts or 1.2 amps difference is not much difference anyway you look at it. I guess if I am using a compass instead of a GPS, I cannot prove the sun rises in the east either, even though it is obvious.


I agree that each application should be evaluated to determine the best system to install. However, I believe that each application should be evaluated to see if it can be controlled efficiently by any other means, before a Drive is even considered. Adding a Drive to applications where the system could be easily controlled by other means, adds a multitude of other complications that must also be dealt with. Harmonics, as is the title to this thread, along with reflective waves, voltage spikes, resonance frequencies, bearing currents, and many other problems are never present, if you don't throw a Drive into an application that could easily be controlled by other means.

"Just because you built a system that can demonstrate that a valve is a good solution does not mean a valve is always a good solution."

Just because you can build a system that can demonstrate that a Drive is a good solution, does not mean that a Drive is always a good solution. However, most people have been brain washed to falsely believe that a Drive can always save energy. Therefore, they think that a Drive is the best solution, and that all the side effects that go with a Drive are worth it, because you are supposedly saving energy.

Hello Waross
"We sometimes have to modify existing equipment and do the best we can with equipment chosen by someone else."

This is what I deal with everyday. Someone who didn't know what they were doing, chose the wrong pump. Now the volume is too high, or the pump is cycling itself to death. As long as the pump has some drop in horse power, a valve can still be the best alternative. The existing and badly chosen pump may only drop from 30 HP to 22 HP when throttled with a valve. If the correct pump were chosen or a Drive were used, the 30 HP could drop to 15 HP at low flow rates. This small difference in power consumption still may not be worth changing out the pump, or the problems of added side effects when using a Drive.

"If throttling the pump output develops a fairly large pressure drop across the control valve is this an indication that the savings with a VFD may be more than shown with your test rig?"This is the concept that is hard to understand. It doesn't matter how much pressure differential you have across the valve, what matters is the Brake Horse Power characteristics of the pump. This is why I say that back pressure is a free byproduct of horse power. Even though the back pressure increases, the horse power decreases. This is also how you choose the best pump. Don't just look at horse power for maximum flow, also look at horse power required for smaller flow rates. The only reason back pressure is even considered, is to make sure the control valve and associated piping can handle the pressure, it has nothing to do with how much energy is supposedly "burned across a valve".

As I have explained many times, 1200 GPM at 100 HP is using much less energy per gallon, than when a Drive is used on the same pump to produce 100 GPM with 38 HP. So in this respect, you are also "burning energy with the Drive".

Now for picking a pump that works best with a Drive, you need a performance curve that is as steep as possible. Because head is reduced by the square of the speed, a steep performance curve gives you more possible reduction in speed while still producing the head required. You should temper this steep performance curve, with the Brake Horse Power curve as well. Because once you have reached the minimum speed that will produce the head required, further reduction in power come only from the pumps natural Brake Horse Power characteristics, the same as with valve control. You simply don't start using the pumps natural Brake Horse Power characteristics, until the Drive has slowed the pump down to the minimum possible speed, that will still produce the head required.

Greetings Crazytexacan, which I am also one of. Since you started using Drives 34 years ago, there have been new Drives introduced every few months. New Drives are supposed to solve the problems of the last Drives, which are only a few months old themselves. They do seem to be coming up with a few band aids for some problems but, unless you can change the laws of nature, most of the problems associated with Drives CANNOT be fixed. What I understand about the 18 pulse Drives, is that they do counteract much of the harmonics but, at the expense of decreased efficiency which causes increased power consumption. Kind of defeats the original purpose of the Drive. Also, the more pulses, the faster the rate of voltage rise, the more damage is done to the windings.

Down hole oil well submersibles, because of their very steep performance curve, can be reduced in speed more than other pumps, and still produce the head required. Also, oil well submersibles do not usually have to produce a constant outlet pressure as needed with such things as irrigation sprinklers. Maintaining a level in the well, instead of a constant outlet pressure, a Drive is able to further reduce the speed and horse power required. Of course efficiency is not as much of a concern as precise level control with these systems, as the fluid you are pumping is now worth more than $100 per barrel. I would think that the extra long wires to the motor could cause a problem. I am sure you must be using a really high voltage cable with extra shielding? You say a narrow range is 35 to 70 hertz, I say for most pump applications the range is even more narrow than that. 50 to 60 hertz is usually the range limit for a correctly sized pump in a constant pressure application.

"When I lose a drive I can usually run in Bypass mode..."

All the drives I installed ran in Bypass mode more than they ran in the Drive mode. Of course we used valves to control the flow when running on Bypass. This is how I discovered that the power consumption was the same with Valve control as with Drive control. This is also how I figured out that Valve control was much more reliable than Drive control. Then I should also mention that all the problems with harmonics, vibration, voltage spikes, electrical fluting of ball bearings, and other problems DO NOT even exist when running in Bypass with Valve control.

I know that many of you make your living by mitigating problems of Drive controls. I know you don't want to hear that Drives do not save energy, cause many side effects, and even cause health problems with animals and humans.

You can tell me that "Drives are hear to stay", and "I should just get used to it". I submit that I replace Drives with Valves everyday. You may not want to hear it but, the best way to solve the problems of Drive control, is to not cause the problems in the first place. Making me feel like I have stuck my head in a bee hive every time I bring it up, is not going to change this fact. People who use Drives on every application, and then try to mitigate the problems with the Drive, are just a few years behind the learning curve. There are good applications for Drives but, Drives are not good for many applications. Sorry for the long post but, it seems I am still having to prove the obvious.

 

[waross]

Thank you Valvecrazy.
Thank you also gepman.
Yours

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Valvecrazy,

Many of us have listened to you. And some of us (me, for instance) have considered what you are saying and made our own decisions how to evaluate the pros and cons of VFDs. I have come to the conclusion that we need to be more careful when selecting technology. Especially when taking things like EMI, short bearing life, cost for VFD specialists and also for replacing a VFD because there are no spare parts or anyone that can repair it any more. We have gained from such insights. And I think we owe you for making us think.

But, praise stops here.

You do not at all have the same attitude. You are not prepared to listen to us. You march blindly with your VALVES FOR PRESIDENT banner held high and you are so busy shouting your message that you miss a whole lot of facts that we try to tell you.

One particular point that you may need to understand is that current (amps) do not at all represent load of a motor. Only power meters (showing watts) do that. There are actually motors where amps go down when the shaft is loaded. It is a result of changing power factor. So, please, hold your horses and try to understand what we are saying. You may also benefit from it. If you continue like this, someone (I would say many) may get so tired with your one-eyed view on this matter that you are not welcome here any more. And I would not like that.

Please.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Marke]

Hello Valvecrazy

I, and I am sure that many others, totally understand that there are alternatives to all technologies and I totally agree that some VFD sales people get far to overzealous when it comes to making promises, however I do believe that there is a place for all equipment and all have their strengths and weaknesses. Valves also do have problems. Valves can be damaged by freezing, by solids such as lime in the water etc.

If we worked in the ideal world, then the correct engineering would be done and overall efficiency would be much improved. This argument applies to all forms of engineering, not just valves vers VFDs, but the practical reality is that this is not the case.
I recently visited an installation where the pump was in the ground and a VFD as installed and running and in this case, the VFD was achieving results. If the engineering was done properly at the beginning, the cost would have been much less, but it was not.
The pump was a 75KW and it runs at almost constant flow. When I looked at the installation, the pump was drawing 42KW, so the pump was well oversized. If then engineering was done correctly, a 45KW pump would have been used along with a soft starter. Instead, the irrigation specialist sold a 75KW pump and VFD. - The farmer paid far more than he should have, but it was cheaper to leave it there than to pull it out and replace it with a smaller pump and soft starter. So often, by the time I get involved, it is too late. The capital cost is higher but the energy used is reduced because a VFD is fitted. Granted, a flat curve pump of the appropriate size would do even better, but that is beyond our control. The selection of VFD or valve is also well beyond our control.

One issue that I do have through all this discussion is this :

This is why I say that back pressure is a free byproduct of horse power. Even though the back pressure increases, the horse power decreases.

If we consider the pump output, the hydraulic power is a function of flow and volume, just like electrical power is the product of voltage and current. The pressure is the hydraulic voltage and the flow is the hydraulic current.
As we reduce the flow from the pump at a constant head, the power reduces. If we add a resistive component in series with the flow in order to control the pressure across the load, there is a pressure drop across this resistive element and so there is a a power loss. It is not a free byproduct.
If we have variable flow requirements and we have a constant pressure requirement across the load, then we can either select a source (pump) that has a very low impedance and provides the correct pressure output across the flow range, (Flat curve pump), and it we do so correctly there is no need for a series element, or we can use a source with a higher output and reduce it by applying a series element, or we can regulate the source and use no series element.
The VFD is a means of regulating the source with out the losses associated with a series element and therefore reduces the losses associated with the series element.
There is no doubt that the different pumps can have different efficiencies at different parts of their curves, and there is also no doubt that there are losses in the addition of a valve or series element in the line.
All approaches have merit, but too often the correct engineering is not done. I could argue that the use of the valve is due to bad pump selection also. If the pump was selected to have a constant pressure output at the right pressure, then the valve would not be required.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[LionelHutz]

I was going to respond in more detail but Gunner and Marke gave very good responses. I wouldn't be so kind and you wouldn't listen anyways so what's the point?

Actually, I will say this. Anyone who comes to me and tries to prove that their AC device saves power by showing me that the amps have dropped pretty much gets discredited right on the spot. Sorry, but if you don't understand basic AC theory then don't bother trying to BS an electrical engineer pretending you do.

Also, the number of pulses in the front end rectifier has nothing to do with the dV/Dt on the motor.

 

[Valvecrazy]

“To measure the real power or reactive power, a wattmeter designed to properly work with non-sinusoidal currents must be used.”
Yeah, OK. I have always used amps as an easy indicator of power because with these type systems, the voltage and power factor change very little. Apparently the amps ARE a direct indicator of power on my demonstrator as was shown by the reading of the watt meter. This was the same thing I discovered 15 years ago, when I stopped worrying about having a watt meter. However, with the harmonic component of a Drive, I can see where measuring watts would be the only correct way, and could make power consumption of a Drive look even worse.

I forgot most of this stuff as my electronics classes were over 30 years ago. That far back, and before AC Drives, I honestly don’t even remember discussing harmonics as a problem. Maybe that is because there were no AC Drives back then to cause the problems?

This discussion is not about Valves. I have never once mentioned a particular kind of valve. I am simply comparing Drives to Valves because they BOTH burn about the same amount of energy. This discussion is about Drives being given credit for saving energy, when it is simply not true. Every application I have seen, or every article I have read, that gives credit for saving energy to a Drive, has been incorrect. If you read these articles carefully, you will see that a dump valve was discontinued, a smaller pump was installed, or larger pipe lines were installed to reduce the pressure required. A Drive may have made it easier for these steps to be implemented but, it was these steps that decreased the energy consumption, not the Drive itself. Slowing the pump with a Drive always increases the energy used per gallon pumped, especially in a constant pressure application. So Drives also “burn energy”!

As I have explained many times, a 100 HP pump moving 1200 GPM is using .083 HP per gallon. The same pump slowed down with a Drive to produce 100 GPM while using 38 HP is using .38 HP per gallon. This means the Drive is “burning” 4.5 times more power per gallon than a properly sized pump, or when compared to the same pump with pressure or level switches, feeding a pressure or elevated tank. This does not even take into consideration the parasitic losses, short life span, and other problems of Drive control.

I have learned a lot from many people on this forum. Now as Gunner would say, the praise stops here. I don’t believe it is MY attitude that is the problem. It is MY message that no one wants to hear. Almost everyone here is marching blindly with their DRIVES FOR PRESIDENT banner held high, and you are still missing the point. You should just admit to yourselves and to everyone else that as a Drive reduces the RPM of a pump, the power consumed per gallon increases.

Apparently everyone needs to see an actual demonstration as gepman did. I thought gepmans test would prove this once and for all. I hope the brainwashing by the VFD companies, along with the ever increasing “stray voltage” problem, has not already caused permanent and irreversible brain damage. The Romans thought lead pipes were the greatest technology. However, the lead poisoning that followed caused mental problems that kept them from seeing clearly, and ultimately lead to the destruction of their entire society.

BTW, gepman should have taken readings on the harmonics with and without the Drive. This would have proven that doing away with the Drive is the best way to eliminate the harmonics, as is the point of this thread.

I appreciate Marke bringing up that traditional valves can have problems themselves. I would love to discuss this and other REAL issues on a different thread, if you guys can ever get past the allusion that “Drives save energy”.

I am not the one who is full of BS, and I am not the one with the attitude problem. I am wide open to learning something here but, no one has yet proved me wrong on this point. You keep saying Valves burn energy, and Drives save energy. I keep saying only when “ifs and buts are candy and nuts”.

Anyone who mentions something negative about a VFD in this forum, even though it is the truth, can expect a tongue lashing or a keyboard whipping. I am beginning to wonder if you want real answers, or if this site is owned and controlled by a VFD company?

 

[Skogsgurra]

No use answering any more. This guy is beyond education. Power factor seems to be a mythical being to him - an elf, perhaps? How could he ever understand?

Ever read Don Quixote?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Valvecrazy]

http://www.powerqualityanddrives.com/energy_savings_pump_vfd_part_1/

http://www.powerqualityanddrives.com/payback_analysis_vfd/

 

[trevorm]

This thread has been most interesting and entertaining.

I must admit that initially the reduced current had me thinking maybe Valvecrazy is onto something, until I realized that all that happened is that the load had been reduced and less work was being done. Naturally the amps will drop.

The current on the drive cannot be compared to that of a throttled valve because the frequency and voltage are varied, so the current may actually be higher.

The true test will be to measure the output power of the pump and compare it to the power drawn from the supply.
efficiency = output/input.

How much different is throttling a valve to closing dampers on a fan. When dampers are closed the fan housing heats up. Surely that is energy lost. Maybe it is not as apparent where the fluid being pumped absorbs this energy and it is carried away.

Regards
Trevor Morrison

 

[waross]

Valvecrazy made some good points about valves versus drives and I thank him for the insights I have gained,
BUT, sadly, when he displays starts talking about power factor, he loses all credibility to talk about the efficiency of drives and motors.
This is becoming as nonproductive as an argument with someone who has a perpetual motion machine.
End

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Valvecrazy]

“This is becoming as nonproductive as an argument with someone who has a perpetual motion machine.”

That is exactly what this is. However, I am not the one claiming to have a VFD perpetual motion machine. Please, I give up. Nothing left but to start talking about my mother.

 

[ScumPunk]

Hi, all
A couple of points have confused me in this fascinating thread:
1. ValveCrazy said of the demonstrator results:
"Reducing the flow down to 8 nozzles, 4 nozzles, and 1 nozzle, you can see that there is only a couple hundred watts difference between valve control and VFD"

This "couple of hundred watts" needs to be expressed as a percentage, or the numbers are meaningless for any other scale of installation. The VFD is using between 94.2% of the power that the valve uses (8 nozzles) and 79.2% with 1 nozzle. Up to 20% saving on power consumption seems fairly significant to me.

2. Valvecrazy made this point:
"Every application I have seen, or every article I have read, that gives credit for saving energy to a Drive, has been incorrect. If you read these articles carefully, you will see that a dump valve was discontinued, a smaller pump was installed, or larger pipe lines were installed to reduce the pressure required. A Drive may have made it easier for these steps to be implemented but, it was these steps that decreased the energy consumption, not the Drive itself."

Surely this is precisely the point? My experience of pumping systems is very limited, but from the customers viewpoint, they don't care which part of the system is saving them money, they look at lower installation costs, running costs, maintenance costs, etc.
I'm also very confused about this "free by-product" of back pressure. My mother always told me you didn't get anything for free in this world....
Regards,
Mort (still trying to find the quote button - looks so much nicer )

 

[Valvecrazy]

Average with gepmans test was 14% better for the VFD, without considering any runs at maximum flow, or any load or line filters. Adding the needed filters and considering different possible flow rates, the Drive can do anything from costing you 5% to saving you maybe 10% on average. Not usually enough to justify the added expense or the trouble. See this link;

http://www.powerqualityanddrives.com/payback_analysis_vfd/

“”A Drive may have made it easier for these steps to be implemented but, it was these steps that decreased the energy consumption, not the Drive itself.”“

“Surely this is precisely the point?”

92 pages and this is the only point I am trying to make!!


Also I realize that there is no such thing as free energy. I just use the “free byproduct” thing to help explain that as the back pressure of a centrifugal pump goes up, the horse power required goes down. It is just a hard thing to explain. Even people who say they understand it, loose credibility when they do not realize that throttling can reduce energy consumption within a few percent of variable speed.

 

[Marke]

as the back pressure of a centrifugal pump goes up, the horse power required goes down

If you consider constant flow, then as the back pressure goes up for the same flow, hydraulic power also goes up. (flow x pressure) The fall in power is due to the reduction in flow, not the increase in pressure. If you reduced the flow, and kept the pressure constant, then the hydraulic power would reduce.
The restriction of the valve is reducing the flow and increasing the pressure at the pump. The reduction in power due to the reduction in flow is greater than the increase in power due to the increase in pressure.
Reduce the flow without an increase in pressure and you get a better reduction in power, hence the flat curve pumps yield a better efficiency when throttled than the steeper curve.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[LionelHutz]

Valvecrazy, I have seen VFD pumping installations running at a constant pressure with a low flow. These installation are a waste of money because, just like you have argued, the $/gallon pumped goes up. The pump may be running slower and using less kW but the required kWh to pump X amount of liquid is higher.

However, your valve installed in the same application would still be the same waste of money, maybe even slightly more so depending on the system. At any rate, the valve is not going to save any money compared to the VFD in the above mentioned applications.

I was recently in a pumping station with 500hp-1000hp pumps where they used valve control to adjust the flow. As the pump valve was closed to lower the flow the pump or valve would begin to make a fair bit of noise. In fact, it was quite loud in the station when running at minimum flow. So, there has to be some negative effect caused by this turbulence in the pipes.

I have seen other VFD installations on down hole screw pumps where, besides controlling the pump speed, the VFD also helps to keep from twisting off the rod. These applications are outside in harsh environments but the much higher priced VFD (compared to a full-voltage starter) is still purchased because the well owners have tried a few solutions and feel it is the best one.

So, as I and others have already said before, every application needs to be evaluated for the best solution. Remember, some people here don't just work in one field (irrigation?) but rather see every application you could think of.

One thing not discussed yet is Marke's application. It may be an application where different solutions have already be tried and the VFD has already been proven to be the best solution. Maybe a valve can not work or does not work nearly as well.

 

[Valvecrazy]

"At any rate, the valve is not going to save any money compared to the VFD in the above mentioned applications."

I never said a Valve would save money over a VFD. What I said was that in constant pressure applications, a Drive can rarely save energy over a Valve.


"I have seen VFD pumping installations running at a constant pressure with a low flow. These installation are a waste of money because, just like you have argued, the $/gallon pumped goes up. The pump may be running slower and using less kW but the required kWh to pump X amount of liquid is higher."

Thank you for this, as this is really the only point I am trying to make here.


"As the pump valve was closed to lower the flow the pump or valve would begin to make a fair bit of noise. In fact, it was quite loud in the station when running at minimum flow. So, there has to be some negative effect caused by this turbulence in the pipes."

The noise you were hearing was from the water squirting through a small opening as the valve was throttling the flow. This turbulence does not hurt the pipe but, causes the seat in the valve to wear, known as "wire draw". This wear causes the valve and seat to leak when closed. The valves I use are designed to never completely close so, wear on the seat that would make other style valves fail, has little effect on these type valves.


There are many good uses for Drives. I would only use valves to control pumps that produce fairly clean, fairly cool, water only, produced at a constant pressure or head. This is a very small niche in a very big market for pump systems. However, there is a very large number of pump systems in this particular niche. This niche includes irrigation but, also includes domestic housing, municipal systems, booster systems, feed lots, chicken farms, pork producers, dairies, car washes, concrete plants, heat pump systems, snow making machines, and thousands of other types of systems.

Every system does need to be evaluated. First evaluation is to see if the pump systems fits into the niche described above. If it does, then further evaluation needs to be done to see if a pump with good brake horse power characteristics can be used. If this is possible, then a valve will make a good control system without adding the side effects of Drive control.

If you are referring to Markes system where a 75 KW pump was used when a 45 KW would have done the job, a valve would have probably restricted the pump to about the same 45 KW as the Drive. If the pump had good brake horse power characteristics, a valve would be so close to drawing the same 45 KW as the Drive, that the cost of the Drive would never see a payoff.

I would never chime in on a thread unless the pump application fit the particular niche described above. Because Drives work so well on many applications not within this niche, many people make the wrong assumption that a Drive is also the best fit for pump systems within this niche. I personally would have to first rule out valves, level switches, pressure tanks, and any other possibility before I would even consider a Drive. Anytime you can successfully control a pump system with anything other than a Drive, you do not have the problems or side effects that are injected into a system when a Drive is added to the equation.

 

[ScumPunk]

Oh my god, I've re-read some of this thread and apparently VFD's cause brain damage through the "stray voltage" problem?
I've googled it and come up with phrases such as "Dirty Power", "Electric pollution", etc.
Check this out:
"But, similar to fluoride, tobacco, alcohol, drugs, dioxin and certain chlorinated hydrocarbons, when electricity is not properly controlled, or when biological systems (people and all other living creatures) are over-exposed, electricity destroys certain functions of the brain and the immune system and increases proliferation of cancer. This is an unseen and unheard killer."

I'm terrified!! Valvecrazy, thank you for warning me of this "Unseen Killer". I'm off to find a job that doesn't involve VFD's....maybe something with valves?
Cheers,
Mort.

 

[GTstartup]

Personally I thank Valvecrazy for his insight, which at the very minimum gives me pause for thought.

As for the previous post. The phrase "sarcasm is the lowest form of wit" comes to mind.

 

[macmil]

This has been a most informative thread. I have been viewing its development from the original post, and the numerous diversions from there. Declaration, I'm a mechanical engineer, and this is definitely an electrical engineering forum, and I admire those of you who understand electrons.
I would never presume to intrude on the electrical engineer's domain, but let us reflect that while we mechanical people bow to the wisdom of the electrical people regarding drives, and the behaviour, and yes losses inherent in the drives, we also have some knowledge regarding the loads to which these drives are connected, and hopefully something constructive to contribute to the greater good.
Let's not get upset, let's not get overexcited, and above all let's not get personal. There's a lot of value in the contributions here, and I would be disappointed if it gets lost in people taking 'positions'.
Every application has to evaluated on its own merits. As professionals, it's important to remember that. Typically, we rely on our own experience to evaluate initially the comments made, which may have been made on a different set of parameters, and that may influence our perception.
And another point is that the $$$ involved in the project should be considered on a lifetime basis, including capital and operating costs , including energy and maintenance and downtime and perhaps even frustration.
mac