Spontaneous reversal of 3-phase motor

Gentlemen,

Last Friday, an impeller fell off the shaft of a 10Hp. 3-phase 600 volt 3500 RPM motor, causing the motor to jam and the VFD to fault. I don't knoiw what fault was displayed. VFD is an Omron G5+.

The volute was removed and the impeller was re-installed.

Today, I noticed that the flow from the pump was greatly diminished lately, which let me to investigate a bit. If I compare the circular charts from yesterday with those from last Friday, there's about a 25% drop in flow rate. Amp draw on motor was OK, but we found rotation to be reverse. Additional review of the charts indicated the flow was reduced after the impeller was re-installed. The electrician swears that he didn't remove any wires from the pump to service it.

The FWD/REV button on the VFD is not active.

My questions are:

Can a motor spontaneously change rotation if it jams up?

Are there any conditions when direction of rotation can change without human intervention?

Can a motor spontaneously change rotation if it jams up?

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Not likely, but it would be very easy for the VFD to get switched to run the opposite direction. Who restarted the VFD and what did they have to do and what assumptions did they make? Did that person assume that "Forward" in the VFD was the way this pump normally turned? If the button is not active, then the direction is being set elsewhere, maybe in the programmable parameters.

The motor has always been turning in reverse. That's why the impeller fell off the shaft in the first place!

DickDV said:

The motor has always been turning in reverse. That's why the impeller fell off the shaft in the first place!

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Nope. It's a Waukesha C-Series and the impeller is held in place with a pin on a square shaft. There's no way the impeller can "spin" off.

It couldn't have been operating in reverse last week, or it wouldn't have produced 120+ GPM flow. It was only about 85GPM this morning.

I'm guessing someone messed with the VFD.

rguimond said:

I'm guessing someone messed with the VFD.

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Me too especially if it's a PF70 or 700. You have to take extra steps in many cases to prevent the keypad from reversing the direction with a single bump of the direction button.

We've had machines in which this has happened, and although they swear they didn't touch anything, it only takes the slightest bump to do it.

I went back in on some of them and disabled reverse completely, and on others where reversing is required, I masked out the keypad direction control.

Do you know what the motor amps and rpm were at 120 gpm? And what is it now?
Is there a chance that there is damage to the impeller or bowl?
Since it is a centrifugal pump is there an obstruction in the discharge line?
I'm not a pump guy but a good look at mechanical stuff is in order.

The motor has always been turning in reverse.

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Dick could be right about the VFD. It may have been necessary to set the VFD to run in reverse in order to make the motor turn forward (if motor is wired wrong). Then after the impeller loss, someone reset the VFD back to forward, thus reversing the pump. The VFD might even be set up to default to forward, so if reverse was needed, then after a locked motor, a reset might have been necessary so the drive got reset to forward.

Another possibility: When the motor jammed in locked rotor mode, it burned out one phase, and now the motor is "single-phasing", or running at partial speed. No forget that, because I went back and RG said the amps are okay, so motor thinks it is okay.