VFD retofitting for pumps
VFD retofitting for pumps
(OP)
I would like to know how difficult is it to replace the induction motor for an existing pump with VFD motor. what are the things which we have to change. Regards,
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VFD retofitting for pumps
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VFD retofitting for pumpsVFD retofitting for pumps(OP)
I would like to know how difficult is it to replace the induction motor for an existing pump with VFD motor. what are the things which we have to change. Regards,
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RE: VFD retofitting for pumps
If it's a standard horizontal mount motor, long coupled, all you need to worry about is matching the frame size of the motor, and putting the coupling hub on the motor.
If it's close coupled, where the impeller is on the motor shaft, it's more involved.
More details will make for a more useful answer to your question.
RE: VFD retofitting for pumps
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RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
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RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
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RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
Thanks. I should have said something about both alternatives.
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RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
I don't buy that throttling will save you the same amount of money over time as a VSD in this application.
I would go with Artisi's suggestions. Hopefully you have room to increase impeller diameter and can slow the pump down. But it needs to be a good fit on the variable speed curves.
RE: VFD retofitting for pumps
Fixed Speed at 938' TDH
400 GPM @ 938' TDH
10.75" Impeller
3550 RPM
Efficiency 66%
144 HP
Same Pump, Variable Speed @ 469' TDH
400 GPM @ 469' TDH
10.75" Impeller
2650 RPM (25% turndown, do-able)
Efficiency 68%
70 HP <--- BIG savings
No way a valve can do this. Simple first law thermo.
RE: VFD retofitting for pumps
Keep in mind that this is a bit of an unusual case. How many times does flow remain the same with head reducing by 50%?
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RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
In most of the typical cases, he's not going to be too far off from his claim. You just have to realize that VSDs arn't usually a viable solution when heads don't change in proportion to the afinity laws. Where they do, VSDs usually can be made to work, where they don't, valves usually work. VSDs work best when heads and flows both change proportionally to the affinity laws, flowrates vary widely and time for each flowrate is short AND tanks are expensive, can't be accomodated or the process MUST have variable flows. If flows and heads experience some variation, but are mostly constant, valves can work well.
In lots [not all] of the everyday typical practical applications that VSDs are being pushed to fill these days, slight benefits of VSDs can be totally eliminated by extraneous considerations and may really be disadvantageous when consideration of such things as shaft currents, adverse power supply harmonics and maintenance costs are included.
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RE: VFD retofitting for pumps
I hesitate to apply the Affinity Laws to every pump. In my hypothetical above, the head is reduced by half and the flow is constant. Yet the same pump can accomplish this (with the same impeller diameter) by reducing speed. The pump is just running further to the right on its curve.
Only a representative of big oil could look past the energy savings a VSD could offer in this application :) Although I agree with you completely that VSD's are NOT a fix all.
RE: VFD retofitting for pumps
And .. valvecrazy is, I gather from past posts, not involved in big oil, but in the lower pressure water distribution applications, where his generalizations are usually more representative of typical situations and economics are much tighter, not to mention the effects of the other VSD associated operational problems that can wreck havoc for a whole lot of people in a very short time. I don't think its irresponsible to talk in the general sense, since there can be many variables, other than cost or variables that are not convenient to reduce to cost, that can influence the ultimate selection of any one solution over another. In that respect, he does draw attention to several factors which could have a bearing on the ultimate decision for this OP or many others.
As for any individual situation is concerned including this OP, for any one application you can produce showing energy savings with VSDs, I could give you two scenarios where valves would perform better in the overall project, but might even possibly use more energy in the process (maybe not), so there can be many facets to consider other than energy cost. (I've been forced to choose electric motors as drivers when diesel would have been better just to defer the emission "cost" to the central power supplier.) So, energy use or cost may not represent the objective for all projects and the rest is 6 of 1 and half-dozen of another, so I see the only solution is to look at your overall project requirements and make selections accordingly. What else can one do?
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RE: VFD retofitting for pumps
Clicketyclack is right however. If this is an application where the flow remains the same but the head is twice what it needs to be, then a drive will reduce the power required considerably. The drive will reduce the power required by the pump to 70 HP. Add back in the parasitic and other losses contributed to the drive and you will be pulling 75 HP or more. But again the drive is not saving any energy. Because if this is the only design point, then a correctly sized pump will probably only pull slightly above 60 HP.
So the drive is actually wasting power over what really needs to be done, which is change out the pump. Like Biginch said, "slight benefits of VSDs can be totally eliminated by extraneous considerations and may really be disadvantageous when consideration of such things as shaft currents, adverse power supply harmonics and maintenance costs are included".
I am glad you said that a VSD is not a fix all, because that is what is driving me crazy. Each application is different. What is irresponsible is to assume that VSD will always save energy. There is nearly always a better or at least as good a way of saving energy as a VSD. Correctly sizing the pump is the best way, and many times a simple control valve can be just as good or better.
RE: VFD retofitting for pumps
On a pump at speed = a, flowrate = x and head = y. At speed = 2a, then flowrate = 2x and head = 4y. Nice fit.
RE: VFD retofitting for pumps
In fact, even VSD have alternates. Other non electrical options. Diesel engines are the original pipeline VSDs, although the VSD benefits were not specifically intended, just a natural result of their modus operandi. They don't require major electrical demands, don't require 3rd party electric power furnished to often remote locations, no power supply harmonics, no shaft currents, have reasonable reliability, but true they arn't as efficient as electric drivers. The number of those installations still in use or still being designed just goes to prove that maximum energy efficiency at the pump-driver isn't always the ultimate consideration.
...but I digress.
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RE: VFD retofitting for pumps
I would also consider the other benefits that a well programmed drive can offer. There are some out there that offer dry run, dead head, min flow, run out and cavitation protection.
I run hundreds of pumps in my location and about 20 (which only one has caused me any issues) have drives on them. So I fully understand and agree with you both on your valve position.
It sounds like Sam has already purchased a pump since he says trimming the impeller is not an option. Otherwise he would just have another pump selected. My point is simply that in this situation, when you need to reduce pressure from 28 bar to 14 bar, if it looks good on the variable speed pump curve, you should seriously consider a drive.
RE: VFD retofitting for pumps
There are also automatic transmissions out there that can handle 1000 HP drives with 95% efficency.
RE: VFD retofitting for pumps
Ya, I agree its probably not going to be a waste of time to consider a VSD for this case.
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RE: VFD retofitting for pumps
Regards for all contributions.
RE: VFD retofitting for pumps
Is your motor standard?
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RE: VFD retofitting for pumps
thread237-190754: VFD operation of a wound rotor induction motor
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RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
If the motor is older and still has 600 volt insulation, it will fail very quickly on a drive. If you have to replace the motor to use a drive. It would be less expensive to just purchase a new pump and motor of the correct size. Then you would not need the drive and you would not have to deal with all the negative side effects of VSD, which 2,000 volt spikes it just one of.
RE: VFD retofitting for pumps
New 75 HP motor $8000
Baseplate modifications $2000
OR
New pump assy about $15,000
Piping changes $2000
ValveCrazy makes a very good point.
RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
Of course this is an estimate anyways based on my Goulds example. With an older pump he may need a 100 HP drive / motor combination, depending on the pump characteristics.
If the pump is very old and you have to buy a new motor and drive anyways, I would go for a NEW fixed speed pump that better fits the application, even if I had to make piping changes. Why spend 75% of the cost of a new pump assy to bandaid an old pump? Sounds like something an accountant at corporate purchasing would do.
RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
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RE: VFD retofitting for pumps
In many cases the savings in power costs can soon pay for new equipment - but then we have to fight with the "bean-counters" who consider this as capital expenditure for which we don't have the funds - but burn as much power as you like as this is operating expenditure and is your problem.
RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD retofitting for pumps
I have almost no problems with the auto transformer soft starters. No electronics, just a couple relays, transformers, and a timer. I can't say that about the VSD's and electronic soft starters I have used.
RE: VFD retofitting for pumps
Soft Starters cost less than Auto Transformers and provide a bunch of other features too!(like safety monitoring)
Most are completely out of the circuit once the start is complete as they have bypass contactors in them. They can also soft-stop the loads too, (just ask them). They take up about 1/6 the space.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD retofitting for pumps
I have probably sold or installed an average of 1,000 pumps a year for the last 30 years. When you are responsible for this many pump systems, simplicity and dependability are the key. Nobody cares if it is electronic or mechanical when water stops coming out of their faucets. They just know who to call and scream at, their pump man.
If the bypass relay of the electronic soft starter is not large enough to handle and across the line start, when the electronics fail, somebody is out of water. When somebody is out of water, they are chewing on my butt.
I studied electronics. The guys I went to school with, think it is funny that I use what I learned about electronics to help build completely mechanical systems. I can add an electronic monitor of several different kinds when needed. I can also bypass these electronic devices and get the pump running and water pressure restored when needed. Many times the electronics in a monitor, drive, or PLC cause me more out of water conditions than the failures they are designed to prevent.
Because the pumps I work with are correctly sized for the application, very little reduction in speed is possible. Most of these pumps will not lift water out of a well and build enough pressure to buck the static head unless they are spinning about 90% of full speed. This means when a soft starter is programed to get the pump to full speed in 30 seconds, for the first 25 seconds the pump is not spinning fast enough to start moving any water. Head falls off by the square of the speed, which is so quick that a soft stop doesn't do much good either.
If the drive or soft starter can start or stop the pump at 90% of speed and gradually go up from there, it might help with the water hammer. However, when a pump comes on it is usually because a demand already exist. The longer it takes to get the pump to match the demand, the more amplified the transients are.
That is just my two cents but, I have a very narrow market. ½ HP to 300 HP pumps that supply cool, clean water on demand. I know there are lots of other applications where electronics are worth there weight in gold but, I believe most of my applications are better off without it.
RE: VFD retofitting for pumps
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RE: VFD retofitting for pumps
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD retofitting for pumps
I use Cycle Stop Valves to "modulate the flow rate to match the demand and avoid the start stop cycling and pressure variations." I can also prevent over draw on a problematic well with the same simple valve. These valves react almost instantaneously which eliminates amplifying transients or "twist and slap" When a demand is there, they meet it instantly. When the demand changes, they change the flow rate instantly. A slow response from a drive or speed controlled valve in these cases, is what amplifies the transients.
I have even used these valves to control the pump system when a drive is converting single phase to three phase and acting like a soft starter.
If you choose the right pump, throttling with a valve will give you the same reduction in power as a drive. Simple control is what makes a dependable pump system.
I love electronics. I have all the latest gadgets. I would just never use one of them to control my pump system. I am a little annoyed when my computer, cell phone, TV, or even my electronic thermostat go south on me. However, when water is no longer coming out of the faucet, it is more than just an annoyance. The simpler a pump control system, the more likely water will come out of the faucet when you open it.
RE: VFD retofitting for pumps
1-You will have a temperature increase about 10 deg C. So, if you are running away below from its rated capacity you should not have any problem. This is because the sine wave from VFD is not perfect sine wave.
2-Verify mechanical vibration, i.e. not running through a critical speed.
3-By installing VFD you should remember that that its efficiency is around 98%. If it is installed in a substation you need additional power to remove that heat, so you should calculate these losses and additional maintenance cost and compare these expenses Vs other alternatives.
Best Regards to all
RE: VFD retofitting for pumps
I would add that you need to be careful if the distance between the VFD and the motor gets beyond about 100 feet.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: VFD retofitting for pumps
RE: VFD retofitting for pumps
Best regards
Morten
RE: VFD retofitting for pumps
Lots of interesting discussion though, learnt alot - thanks !!
Ash Fenn
www.cdrpumps.co.uk