One VFD and four motors
One VFD and four motors
(OP)
Hi
there is idea to connect one VFD and three (or four) same motors in parallel (motors for axial fans)
Some advises would be appreciated
(search done)
Thanks
there is idea to connect one VFD and three (or four) same motors in parallel (motors for axial fans)
Some advises would be appreciated
(search done)
Thanks





RE: One VFD and four motors
A few basics:
1) Use the current of all four motors as the minimum level of the 1 x VFD current rating. It is advisable to add some level of overload factor (typically 10%). So, each motor is (for eg) 5 amps then 5 x 4=20amps then, if you can afford it, *1.1=22amps. So your VFD should have a minimum current rating of 22amps.
2) be mindful of the motor cable length. You VFD manufacturer will advise a maximum cable length when operating motors. Using multiple motors connected to one VFD should take in the total cable length between VFD to Motor 1, then VFD to Motor 2 etc. This is important if you are working towards EMC levels as the EMC compliance of cable length will not be the same as "maximum cable length allowed".
3) It is advised to have individual motor protection (thermal overloads as an example) and these are either wired to the VFD or other means to stop the system if one motor is in overload. A multi-motor application will mean the VFD does not see individual overloads.
4) If stopping/starting motors individually then be aware that starting a motor on the output of a VFD will demand high start-up current so it is generally not advisable unless you have some sequence of switching over motors when VFD is stopped.
5) VFD functions like "flying start" (catching a spinning motor) do not tend to work on multimotors so should be disabled, but check with your VFD supplier.
I'm sure there are a few more to check but that's a few for starters.
RE: One VFD and four motors
2) be mindful of the motor cable length. You VFD manufacturer will advise a maximum cable length when operating motors.
Using multiple motors connected to one VFD should take in the total cable length between VFD to Motor 1, then VFD to Motor 2 etc
What about star topology?
3) It is advised to have individual motor protection (thermal overloads as an example)
and these are either wired to the VFD or other means to stop the system if one motor is in overload
Question is what if failed motor will be cut off line by contactor and the system continues to work
or all system should be off?Is it possible put in line between VFD and motors some devices switchers contactors and so on?
RE: One VFD and four motors
ozmosis has some good advice on how to do it. I would only add that his recommendation for individual motor overloads is a legal requirement in the US.
RE: One VFD and four motors
While I know of no electrical code rules regarding this, in addition to separate thermal overloads for each motor, once you get to three or more motors, I would advise time-delay fusing in each motor lead as well. This is because the drive ampacity is getting so much higher than the individual motor FLA's that a fire could conceivably be started in one motor and the drive not fault on output overcurrent or output short circuit.
Most drive manufacturers will not permit loads (motors) being pulled off an active drive output but not switched back in. You need a contactor that has an adequate interrupt flash rating. You must stop the drive first to reconnect any or all motors or the drive will fault on overcurrent due to the motor inrush.
RE: One VFD and four motors
RE: One VFD and four motors