# Power regeneration thru a VFD



## SWDweller (Dec 9, 2020)

All of the pumps I have dealt with do not reverse rotation by design. 
I would challenge the whole concept as a snipe hunt. You spending money to push the water backwards and the amount of energy that you will get back is going to be less than what your paying to pump. Let alone the wear and tear on the equipment.
I have worked on the two reservoir concept where the water flows down during the day making electricity and gets pumped back up at night using off peak rates for use the next day.

Safety reminder, if the power shuts down for any reason this back feed could be a problem. We all know once the flow starts it will continue as a siphon.


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## just the cowboy (Sep 4, 2013)

SWDweller said:


> All of the pumps I have dealt with do not reverse rotation by design.
> I would challenge the whole concept as a snipe hunt. You spending money to push the water backwards and the amount of energy that you will get back is going to be less than what your paying to pump. Let alone the wear and tear on the equipment.
> I have worked on the two reservoir concept where the water flows down during the day making electricity and gets pumped back up at night using off peak rates for use the next day.
> 
> Safety reminder, if the power shuts down for any reason this back feed could be a problem. We all know once the flow starts it will continue as a siphon.


What they are doing on this project is storing water for later use. We pump down hole in winter when water allotments are high and bring the water back up in summer when needed. Yes the money end is not a good ROI but the underground storage is priceless. This is the first well to do power regeneration to try and get some money back since we are shooting water down hole already. 

Cowboy


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## micromind (Aug 11, 2007)

What type of pump?

If it's a hollowshaft, there's a good chance that it'll spin the bowls off the shaft.

If it's a solid shaft, the shaft coupling might unspin with backward torque.

If it's submersible, it'll likely be ok but usually there's a check valve at the top of the pump as well as another one every 100' of vertical pipe.

I'm just throwing this out there, I don't know if it'd work or not but I wonder if it'd be better to have the water spin the pump backward then close in a contractor with reverse phase rotation across the lines. No VFD, the motor simply generates back into the grid.

As noted, power disconnection could be an issue. Will the pump and motor tolerate a serious overspeed?

You might need to get PUCO approval to be a generating facility. Around here, you need their blessing if your generating system will turn their meter backward. And of course, the generating rate is about 1/3 of the normal usage rate........


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## SteveBayshore (Apr 7, 2013)

just the cowboy said:


> What they are doing on this project is storing water for later use. We pump down hole in winter when water allotments are high and bring the water back up in summer when needed. Yes the money end is not a good ROI but the underground storage is priceless. This is the first well to do power regeneration to try and get some money back since we are shooting water down hole already.
> 
> Cowboy


We call those ASR wells, Aquifer-Storage & Recovery. We actually pump treated water down the well shaft in the off peak season and recover it during the high demand season. Millions of gallons of storage without tanks or reservoirs. New Jersey limits the amount of water drawn from the municipal wells and aquifers.


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## just the cowboy (Sep 4, 2013)

micromind said:


> What type of pump?
> 
> If it's a hollowshaft, there's a good chance that it'll spin the bowls off the shaft.
> 
> ...


It is our well driller/supplier that is doing this whole project. The check valve is a bidirectional valve controlled by hydraulics that lets water back down hole. It is a 600 hp submersible 1500 feet down hole, amazing they can make a motor about 15" round x 30' long.


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## just the cowboy (Sep 4, 2013)

SteveBayshore said:


> We call those ASR wells, Aquifer-Storage & Recovery. We actually pump treated water down the well shaft in the off peak season and recover it during the high demand season. Millions of gallons of storage without tanks or reservoirs. New Jersey limits the amount of water drawn from the municipal wells and aquifers.


Yep that is what it is ASR we have them at other sites also but this one is trying to recoup some money when we drop the water.


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## 460 Delta (May 9, 2018)

Is this a synchronous motor? If not I'm wondering how it will be voltage regulated as an induction generator.


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## paulengr (Oct 8, 2017)

First off to the guy that keeps going off on reversing a pump: you are WAY up a creek without a paddle here. All kinds of hydroelectric storage facilities exist. There is Raccoon Mountain on the Alabama/Tennessee border for instance, one of the largest. The biggest issue is the impeller shape and the cut water but both are easily solved. You can always just valve around it if you can’t/don’t spin backwards. Fixing an impeller to a shaft is the least of your issues.

Second, you said regeneration but your application doesn’t. It sounds like you expect to use the pump as a valve to restrict flow in one direction but not the other. In the case of pumped storage for power they typically hollow out a mountain or use a reservoir then pump water up into the reservoir at low rates and return it back (generation) at high rates. You are just basically making a water tower but storing it below grade. So I guess you can regen as you flow down into the reservoir but you’d have to valve the pump to achieve this.

Now as to the regeneration issue first off you said medium voltage. With low voltage regeneration is quite common. You can buy basically 3 VFDs: diode front end non-regen pump/fan drives (cheap), active front end regenerative conveyor/machinery drives, and multi pulse “clean power” drives.with tapped transformers and diode front ends. Aside from this realistically there isn’t a lot of differentiation among brands.

In medium voltage it is quite different. To begin with you can get MV diodes and SCRs (up to a point) but IGBTs only go to around 3 kV. Designs tend to use low voltage IGBTs, MV IGBTs, or GCTs in several different configurations but the overriding theme is that the vast majority are tapoed transformer multipulse “clean power” non-regenerative designs. AB is only different in that they are selling a 30 year old design, a load commutated GCT system. It has almost no advantages and the fact that every other MV drive manufacturer dumped that design decades ago tells you something.

To do regeneration you’d need essentially an entire second power stack including another multi pulse transformer. They do exist but they are RARE. So Siemens is partly right. But this just has all kinds of stupid written all over it. Check and recheck the numbers.

Siemens sells two drives. If it’s a Robicon that’s one thing. If it’s the Siemens one, RUN AWAY. And Siemens is full of crap that it’s “their” drive. They bought Robicon and the power stack design and modules are all made by Semikron. Siemens is just marketing. Make sure you are talking to Robicon. Or talk to Toshiba. I’ve put in one AB MV drive (3000 HP). Never again. What a piece of garbage. Toshiba is popular for a reason.

Now as to all that Siemens whatever, uhh yeah. Can they guarantee no more Stuxnet type attacks? How did they secure it? When any second rate government or hacker can blow up your million dollar drive with a USB stick, that’s a problem, ask the City of Cincinnati wastewater how it worked out for them. Have they fixed their crappy hardware? How about their nonexistent support? If you support your own system 100% pretending that Siemens and their garbage web site is just an “Amazon” with no shipping guarantees, go for it. They are horrible to deal with. If you feel you are being strong-armed that’s because you are.

The thing is any drive, not just Siemens, is sort of a moving target. Every ten years there is a major breakthrough in hardware and has been for close to a century. From your point of view you need to communicate via discrete signals...dry contacts and 4-20 mA and that’s it. No fiber or Ethernet or especially Profitnet mumbo jumbo because ten years from now that stuff will all change flavors and now changing software or hardware is a major pain because you are trying to support something which doesn’t exist probably on a version of say Windows that doesn’t exist. No thanks....stay clear away from that crap. Also Profitnet is so evil and screwed up that it uses Ethernet chips and hardware but uses a screwy nonstandard way of sending packets so that it purposely breaks everything. You have to use Profitnet switches for instance, not standard Ethernet switches. And their card connectors are constantly failing or intermittently turning on it off on their own on their drives. And support? Ha! Never heard of that. Even if you pay for it like AB. As another example AB promotes Ethernet/IP right now. It has a “VFD profile” which means ANY VFD should talk directly to their PLCs and should be interchangeable. It’s like buying any mouse at Walmart and plugging it in...Microsoft defined “mouse”, “keyboard”, “serial port”, etc. But guess which major ODVA vendor uses super secret proprietary nonstandard formats for EVERYTHiNG and refuses to follow ODVA specs even though they basically invented it? Yep, AB. So you can’t just swap drives out or PLCs out without a major undertaking. I do these a lot so I know what it takes. HARDWARE handshaking is the only way to do it so the PLC and such don’t matter. Tell the Germans to screw off.

For this application I’d seriously talk to Toshiba first and then maybe a couple others. Robicon isn’t bad but I’d avoid their insanely bad PLC designs. I’ve worked with Robicons too. They’re not bad. But I wouldn’t go any further than that.

I wouldn’t bother with AB. Their hardware is crap and they’ve never done a regenerative MV VFD to date that I know of. Not even sure how you could do that on a load commutated design. Really a 3 or 5 level design is becoming an industry standard for a reason.


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## just the cowboy (Sep 4, 2013)

460 Delta said:


> Is this a synchronous motor? If not I'm wondering how it will be voltage regulated as an induction generator.


Good question. 
I don’t know the theory of how the system works. I’m sure Jeff or Paul will chime in. 
that’s why I started the post to learn.
I had the same thought but was told it is a standard well motor


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## 460 Delta (May 9, 2018)

just the cowboy said:


> Good question.
> I don’t know the theory of how the system works. I’m sure Jeff or Paul will chime in.
> that’s why I started the post to learn.
> I had the same thought but was told it is a standard well motor


If you call a 600hp well pump standard!


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## JRaef (Mar 23, 2009)

I did a project like this last year, it worked so well that they have added 2 more pumps. We used 600HP Rockwell PowerFlex 7000 MV drives because they are Active Front End (AFE) CSI drives and therefore inherently line regenerative. In this case MOST of the time the water is coming down hill from the reservoir, but twice per day they have to pump it up hill to backwash the filter system, so they needed a pump and the VFD to control the back pressure so as to not blow it out. So they are MOSTLY using the pumps in regen mode, getting "free" energy from them, until they are backwashing. Worked so good they just bought 2 more.

Here's a potential pitfall though. You have to be able to USE the energy in YOUR system, i.e. for other loads connected to your service transformer. In the case of my client, it is a WW treatment plant so they are ALWAYS using way more energy than these pumps can produce, so it's not a problem. But in order to put energy back onto the grid and get paid for it, you must have what's called a "Net Metering Contract" with your utility, and to get that, the "distributed energy resource" system must be "utility line interactive", meaning it must be certified to NOT put energy back into the utility grid if the grid is down (to avoid killing linemen). That status is attained by getting the equipment listed under *UL standard 1741, "Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources "*. There are no VFDs on the market that have this listing, it is prohibitively expensive to attain it and also involves different types of liability insurance than VFD mfrs want to carry. So if your client has other pumps and systems that can utilize the energy WHEN they are capturing it, then that's great and they indirectly get paid by not consuming that energy from the utility. But if not, then they cannot get a check from the utility for it, because they will not be able to get a Net Metering Contract.


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## just the cowboy (Sep 4, 2013)

JRaef said:


> I did a project like this last year, it worked so well that they have added 2 more pumps. We used 600HP Rockwell PowerFlex 7000 MV drives because they are Active Front End (AFE) CSI drives and therefore inherently line regenerative. In this case MOST of the time the water is coming down hill from the reservoir, but twice per day they have to pump it up hill to backwash the filter system, so they needed a pump and the VFD to control the back pressure so as to not blow it out. So they are MOSTLY using the pumps in regen mode, getting "free" energy from them, until they are backwashing. Worked so good they just bought 2 more.
> 
> Here's a potential pitfall though. You have to be able to USE the energy in YOUR system, i.e. for other loads connected to your service transformer. In the case of my client, it is a WW treatment plant so they are ALWAYS using way more energy than these pumps can produce, so it's not a problem. But in order to put energy back onto the grid and get paid for it, you must have what's called a "Net Metering Contract" with your utility, and to get that, the "distributed energy resource" system must be "utility line interactive", meaning it must be certified to NOT put energy back into the utility grid if the grid is down (to avoid killing linemen). That status is attained by getting the equipment listed under *UL standard 1741, "Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources "*. There are no VFDs on the market that have this listing, it is prohibitively expensive to attain it and also involves different types of liability insurance than VFD mfrs want to carry. So if your client has other pumps and systems that can utilize the energy WHEN they are capturing it, then that's great and they indirectly get paid by not consuming that energy from the utility. But if not, then they cannot get a check from the utility for it, because they will not be able to get a Net Metering Contract.


For this part of the project these are at a filter plant and we always have a load on the plant. But it is great information because they are claiming we can implement them on other wells and that is where we won't have a load to utilize the power regenerated. I did win the fight and after the pilot program testing this it will be replaced with AB PLC and Drive. 
Your the best thanks.
Harvey


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