2 equal sized motors on 1 VFD
2 equal sized motors on 1 VFD
(OP)
Is it possible or will one motor feedback onto the other and cause problems??
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2 equal sized motors on 1 VFD
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2 equal sized motors on 1 VFD2 equal sized motors on 1 VFD(OP)
Is it possible or will one motor feedback onto the other and cause problems??
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RE: 2 equal sized motors on 1 VFD
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
just remember to size the VFD hp x 1.33 (total hp of all motors) or you will undersize the vfd.
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
Other advice is to size the drive(VFD) on the current rating of each motor x 1.1 to provide a safety margin for overloads.
RE: 2 equal sized motors on 1 VFD
I know this sounds obvious, but you'd be surprised how many people don't think this through...
RE: 2 equal sized motors on 1 VFD
I've got to ask, why a safey factor for multiple motors?
RE: 2 equal sized motors on 1 VFD
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 2 equal sized motors on 1 VFD
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If we learn from our mistakes I'm getting a great education!
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
I guess fans that are the same do not need this multiplier.
RE: 2 equal sized motors on 1 VFD
Another comment as controlsdude surmised is that centrifugal fans and pumps are variable torque loads where conveyors, positive displacement blowers and pumps, etc. are constant torque loads which will make a difference in loading at less than nominal speeds.
RE: 2 equal sized motors on 1 VFD
Good way of killing drives unless they are specifically designed for this. I know some are supposedly able to withstand opening of an output contactor or load-break switch but not all drives will put up with this. Of course shutting down the drive for a few seconds would work too, and on a fin-fan cooler this would probably have little consequence.
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If we learn from our mistakes I'm getting a great education!
RE: 2 equal sized motors on 1 VFD
I believe you would get an overvoltage fault on the drive if you switched one of the disconnects off. You should as a general pratice to have an aux contact on the disconnect that pulls the enable on the vfd to prevent this type of situation either through the plc or hardwired.
I had a job where their was a backup motor and used contactors to swapped between motors with a keyswitch. Their was some interlocking between the disconnect aux and the contactors, and the enable on drive to prevent opening the output between the motor and vfd.
If your going lock out one, then you need a written procedure posted at vfd that you need to shut both off before switching over to just one.
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
But here's the upshot: when you have multiple motors running downstream of a VFD and one trips off line, the dv/dt issues with regards to damaging the output transistors are somewhat mitigated by the fact that there is still an inductive load running in parallel, absorbing a lot of the voltage spike issues created by the contacts opening. I have used Motor Starter protectors (IEC manual motor starters) as downstream protective devices for years, never had a problem. They take care of the individual OL protection as well as the short circuit protection, provide the means of disconnect that LionelHutz mentioned, and open all three phases, which prevent single phasing one of the motors.
By the way, to LionelHutz's defense (not that he needs it), I don't believe he meant using the downstream disconnect to open one motor circuit while running. His comment came after ScottyUK's concern about running one fan after the other had failed. So if one motor fails, a lockable disconnect allows the user to RESTART the remaining fan while the failed one is being serviced.
RE: 2 equal sized motors on 1 VFD
another point to ponder.
You mention that the VFD is going on a ship.
VFD's on ships will generally require some sort of certification from Lloyds Register or ABS otherwise the ship owner might get a little upset you putting it on there. They generally have to be carefully selected with regards leakage current and control isolation. Make sure any sort of RFI filter is disconnected or specially designed for ship applicatiuons otherwise the leakage current will be a problem.
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
RE: 2 equal sized motors on 1 VFD
The same entities require individual motor overload protection (they don't all agree on the settings, but ABS is 100-125% FLA), but you can have the OL relay isolate the drive input.