VFD

Hey B&D or any other electricions.

What size VFD would I need to run a 75HP 3 PH 600V Motor with? What would something like that cost????

I"m starting to think of a Soft Start / Stop due to the water hammer I"ve been experiencing on the irrigation pump. It just sheared a 8" sch 80 PVC pipe at the Victolic coupler.
This was partly due to poor alignment, but something else is going on here. I have air bleeders at three points in the system so that shouldn"t be an issue.

Any ideas what is going on?????

Thanks, Grant

every one i have ever messed with are sized by amps/hp 110a/75hp list price in my Baldor catalog is 7k, but there are a lot less expensive out there other than Baldor.

Thanks, Jtex

Well I got it all back together, its pumping as I type - I just don't want to turn it off yet.

I talked to two different pump techs. Both said I have air in my lines. They suggested I close the isolation valve by half or more to run the pressure in the mains down around 35 - 40 psi and let it work the air out of the systen through the nozzels slowly.

I guess I'll see what happens in an hour when I shut it down.

Grant

Only listings I coud find were for 480v VFD's when i did a quick check. Hold on to your hat, they list around $4000 for a 75hp model. Hopefully you can find a cheaper solution.

village i work for just installed a new Dan Foss ? brand VFD on 75 HP well pumping 800 GPM. including a new check valve. start stop water hammer is less than 3 PSI as programmed for 2 minute ramp up ramp down. approx. $17,000 for VFD. also changed motor to more compatible type for vfd use. total package with trade in of motor with about 13,000 hours on it was about $24,000. this brand is supposed to be the most suitable for pump use were other VFD units are more for use on mechanical equipment such as feed mills, rock crushers ect. which need ramp up for surge load control

CBBC, are you pumping from a well or a creek? cause it sure sounds like you're drawing air or your pivot is draining back do you have a check valve to keep water in the system we had the same problem with our diesel pump but had to bring it up slowly to evacuate the air or it would blow the victaulic and make an 8' hole in the ground in a heartbeat. VFD's usually are about the cost of the motor soft starts usually work on timers so you would have figure out the time delay it would take to evacuate the the air I don't understand the bleeder idea because that is what your nozzles and guns do unless they are too restrictive you have to remember the water becomes a giant piston an 8" X however long the pivot is X velocity another words a giant hydraulic cylinder so you have to dump massive amounts of air quickly.

8" schedule 80 is rated for 148 PSI working, 890 PSI burst.
But Victaulic does not list a rating for Schedule 80 pipe, only Schedule 40, which is 120 PSI. So that may be the problem, certainly explains why it fails at the coupling.

I guess I better gulp at that $24000.

Anyway, this pump is irrigating a cranberry field. It is all solid set pvc irrigation with sprinklers set on a 40' X 50' grid. Currently the system is pumping on 16 acres at once. The pump is capable of 25 acres - in theory.
There is about 1000' of 10" main TEEing off in two directions and being reduced to 8" then 6" and then 4" mains over about 800' in each direction. Off these 8",6", and 4" mains are 1-1/2" laterals which have the sprinklers.
Air in laterals is no problem - it gets forced out the sprinkler nozzels. Air in the main can get traped at the end of the run. This can be a problem as it can be compressed. When the pump is turned off the compressed air expands back into the main pushing the water toward the pump.
Unfortunatly there is a anti-flow back check valve which slams shut as soon as the pump turns off. All this air / water comes back and "hammers" at the the check valve / pump / sprinklers etc until the presure is released through the weekest point - either the sprinkller, or a glue joint, flange / victolic fitting or the side of the pipe.

My problem is that I had the pump out. The mains were drained. When it all went back together the pump was not idealy lined up to the victolic coupling. I put the pump on. No leaks, pressure built up good (55psi). I turned it off, but I did not run it long enough to get all the air out. BANG. Pipe shear due to poor alignment and not getting all the air out.

This is the second time in 6 years this has happened to me. My own fault. I thought a VFD or Soft Start/Stop would be the answer, but at thouse cost I just need to tack better care of getting the air out.

Sorry about the long post, but the system is all back together and appears to be running fine for now.
Thanks for the replies guys, Grant.

I am currently running a Yaskawa VFD on a 35hp turbine pump. I paid $3,500 about 3 years ago and it was the cheapest I could find that had all of the features I needed. The soft start definitely can reduce/eliminate the water hammer, but for me the ability to hook a pressure transducer was the selling point. The center pivot this pump is connected to is a research machine in which we are continually turning sections on and off. With the pressure transducer control I just set the operating pressure desired and the VFD will change the pump speed to maintain that regardless of flow rate. I have had very good luck with the tech support at Yaskawa and have purchased a smaller 10hp version for my trickle pump.

-Harvesterguy

Thanks for the info. This is turbine also - most people don't seem to know what that is.

I like the idea of dialing in pressure, a lot smoother than closing isolation vale and dummping water to lower pressure.
Grant

CBBC you wouldn"t happen to be from the Bala area of Ontario and have a 50 series JD for hauling people movers at the marsh?
I noticed the diesel pump had been replaced with a three phase electrical service.
$24,000 is way sky high for a VFD.
In North Bay there is a fellow by the name of Richard, can"t recall his last name. He strips electrical equipment from decomissioned mines. VFD"s, cable, pumps, motors you name it for a bit mor ethan scrap but much cheaper than new.
The Franklin web site has an entire section on VFD"s with pressure transducers for water pressure control.
As previously stated the trapped air is a significant player.
A simple relief valve chould be tied into the system near the pump discharge. Or even a valve to open just prior to pump shut down.

B&D,
No, I'm on Vancouver Island. We know of the farm in Bala though.

Here is a link to my place, Grant
Yellow Point Cranberries

You are doing a fine job there, nicely done. Lots of work and planning but it"s a good feeling to see it coming together and working.
Johnstons had to leap through a pile of legal hoops and paperwork but the winery portion of the business has done well too.

Thanks B&D

I appreciate the compliment. It is a lot of hard work, but very gratifying.
Grant

Turbine pumps have been around for many years and I thing you have the right idea to do get rid of the air issue mechanically I'm very aware of the pressure regulating VFD issue which is used all the time in industry the one problem with that is if you have a break in the feed line and you happened to either be in bed for the night or gone away for a couple hours and have a break in the line the VFD kicks up to match the 4-20ma signal you have a massive crater where the break is and at 800 to 1000gpm that can be massive. The best thing we did was to add a low pressure switch to shutdown our diesel when the pressure dropped off suddenly with a startup overide it was the best thing we ever did saved our kesters many times. We had a water drive center pivot so when a hose blew it just sit and put 6" of water in one area of standing corn best yield I've ever seen over 200bpa.

Automation Direct has a 75 HP, 480 VAC VFD for $2500. I have used their drives and no problems. If your motor is not specifically rated for use, the life of it may be shortened. Adding a load reactor helps.
John