VFD fault detect
VFD fault detect
(OP)
Hello,
Im using one VFD for two pumps, only one pump at a time, so there are contactors between the VFD and the pumps. Question: if the contactor is opened with the VFD running on one of the pumps, can the VFD be messed up?, or it will detect a fault and stop? Its a telemecanique ATV61HD45N4 for 60HP motors.
Im using one VFD for two pumps, only one pump at a time, so there are contactors between the VFD and the pumps. Question: if the contactor is opened with the VFD running on one of the pumps, can the VFD be messed up?, or it will detect a fault and stop? Its a telemecanique ATV61HD45N4 for 60HP motors.





RE: VFD fault detect
Generally it wouldn't cause a problem opening the contactor but if you do not have any protective logic that will prevent the contactor from closing again if the VFD is still running, then this will incur some potential problems due to the fact that your VFD is, in effect, going DOL (Direct-on-Line) between the VFD and motor. The drive should either go into current limit, trip on over-current but if you are doing this regular, you could eventually weaken the power transistors in the VFD and at some stage they could go pop.
RE: VFD fault detect
Best practice, in my opinion, is to use an output contactor with a pre-action switch on the handle with the switch wired into a Run Enable loop on the drive control terminals. That way, when the contactor handle is moved to open the main contacts, before they open, the drive output is de-energized. Inversely, when the contactor is reclosed, the drive cannot restart until after the main contactors are closed again.
RE: VFD fault detect
I have since had a couple of drive manufacturing engineers tell me this is no longer a problem. I don't know if they mean it is no longer a problem in the industry because of some change in transistor specs when IGBTs displaced Darlingtons, or if they meant their particular design had inductive filtering to prevent the damage. One of them was an engineer working on the ATV71 drive, so that bodes well for you. I'm not sure if it is a universal thruth however. DickDVs solution is the most prudent approach IMHO.
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