3 VFD's sync together

Davebones

Senior Member
We have three 150 hp pump's on a test stand that are started by across the line starting . Management is talking about possibility adding VFD's to each stand in the future . Sometimes they might run one , two , or all three pumps at the same time . Can these be synchronized to run off one pot if we added VFD's ?
 
Yes, you can feed the same speed reference (pot) to each VFD, but what exactly are you trying to do? Sending the same speed reference won't ensure that they are running the exact same speed or that the pumps are maintaining the same flow rate, for example. It is possible to do these things, but you may need additional feedback and possibly a PLC, unless your drive of choice has PID capability.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Yes, you can feed the same speed reference (pot) to each VFD, but what exactly are you trying to do? Sending the same speed reference won't ensure that they are running the exact same speed or that the pumps are maintaining the same flow rate, for example. It is possible to do these things, but you may need additional feedback and possibly a PLC, unless your drive of choice has PID capability.
Correct.
Once again, just because you can, doesn't mean you should.

The first step is to identify your goal(s) with putting VFDs on the pumps. Are you trying to maintain a specific flow rate? Pressure? Tank level? Combination of any number of those things? Do you have any sort of feedback of what you are trying to control?
 

paulengr

Senior Member
Multiple pumps in series or parallel, VFD or not, are common on long pipelines. In parallel you just use check valves so the flow doesn’t back feed through pumps that are offline. On series just make sure you start them in the right order.

I know that the Altivar 630s have built in multiple pump logic so no PLC needed.

Don’t try to feed a pot to all 3. If you truly want to sync (not needed with pumps) the best way is with a follower arrangement. You program drive 1 as the master and control the one. Program an analog output with the current. Drives 2 and 3 are programmed as followers and simply match the current of the master drive so that they effectively load share.
 

JeffKiper

Electrical geek
Occupation
Controls guy
I use the method Paulengr recommends a lot for multiple pump packages. Make sure you set the speed limits on the drive so you don't drop below the pump safe lower working limit.
 

Macbeth

Member
Location
Livonia NY
Since you said "Test Stand" I Will assume this runs temporarily and may be a bit Rubergish and not continuously operating. Also without any concern of energy efficiency. I will also assume you understand MLF and BEP, so i will skip min and max flow aspects and directly answer this.

Yes, a single pot can control multiple VFD. Wire first VFD with pot as show by VFD manufacture, second wire the Com side of the pot to all remaining VFDs, then wire the wiper of the pot to the same terminal as the first drive to the other VFD. The first VFD will supply the reference voltage to the other VFDs, so the first VFD will allays need to be on.
 

kwired

Electron manager
Location
NE Nebraska
Multiple pumps in series or parallel, VFD or not, are common on long pipelines. In parallel you just use check valves so the flow doesn’t back feed through pumps that are offline. On series just make sure you start them in the right order.

I know that the Altivar 630s have built in multiple pump logic so no PLC needed.

Don’t try to feed a pot to all 3. If you truly want to sync (not needed with pumps) the best way is with a follower arrangement. You program drive 1 as the master and control the one. Program an analog output with the current. Drives 2 and 3 are programmed as followers and simply match the current of the master drive so that they effectively load share.
centrifugal pumps I can see not needed but positive displacement pump maybe is needed?
 

paulengr

Senior Member
centrifugal pumps I can see not needed but positive displacement pump maybe is needed?
PD pumps are as the name suggests. Series’s u just doesn’t work or could but is not done. I’ve seen a 55 mile pipeline running clay slurry on double piston double acting pumps in parallel. They are inherently blocking so just turn in/off or speed up/down.

When you need to “sync” is centrifugal a in series. Don’t starve it (lose prime) by shutting off a more “upstream” one. Start the one closest to the source first then progress in order. Depending on the arrangement though as long as you don’t fall off the curve you can sometimes violate this.
 
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