VFD fault detect

[fere69]

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.

 

[ozmosis]

The altivar 61 has a fault code FCF2 that indicates to the drive that the output contactor has opened when it shouldn't have done. I'm not sure how it works, whether or not it is monitoring the load on the output or if there is some control logic internal in the drive that links into contactor on the output.
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.

 

[DickDV]

As a general rule, opening a drive output contactor with the motor running is not a good idea. Some drive manuals state that the drive can be damaged when this is done and some few others state that the drive is ok but, if the contactor is reclosed with the drive still in the run mode, an output short circuit, output overcurrent, or motor overcurrent fault will surely result.

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.

 

[jraef]

I was always taught (back in the days of Darlingtons) that the arcing of the contacts opening under load creates high voltages until the air gap quells the arc, and these high voltages represent a high dv/dt at the transistors, risking damage to them.

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.

JRaef.com
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