6 lead motor & VFD

[Jraef]

OK, being that it is an ACH550, that is a drive that ABB sells specifically for the HVAC market, so I'm going to Ass-U-Me that this was purchased as a packaged unit from ABB with a bypass system, most likely what is called a "3 contactor bypass" package. In that system, there is a contactor ahead of the VFD, then there are 2 mechanically interlocked contactors down stream of the VFD, one with an overload relay for use as an Across-the-Line bypass starter. When you are in Bypass, the VFD is totally isolated off of both the line and load connections. This allows the motor to run while the VFD is removed for servicing without anyone re-wiring anything, a very commonly specified feature in HVAC systems because most HVAC techs are not sufficiently trained as electricians.

So was the motor wired wrong? Doesn't sound like it to me, I think your ABB tech is unfamiliar with PW motors and just spewed that out to deflect blame. Sounds to me as though the contactor failed, maybe welded shut, the motor could not be shut down and eventually overloaded until someone noticed and killed the disconnect switch, damaging the motor.

Possible problems that may have contributed:

1. ABB contactors have a row of convenient "buttons" right in the middle of the armature (the moving part of the contactor) and a lot of people erroneously looked at that as if it was a "Go" button. So they would get lazy about trying to figure out a control scheme when they wanted to just see the motor run, and stick a finger on that row of buttons and push. Problem is, no way can they push hard enough to overcome the magnetic forces of the contacts trying to separate, so they vibrate and fry REALLY FAST, as in seconds. Then by the time the pusher realizes they have done something wrong and let go, it's too late, the contacts have welded. Happens a LOT with ABB contactors, that's why I rarely use them on smaller systems.
   
   
   
   
   
   
2. It could be that your building engineer cycled it on and off several times in rapid succession. Same issue, it can cause the contacts to weld especially if they were a little undersized, as may have happened for a PW motor being started ATL.

Either way, it's doubtful you are going to be able to conclusively prove it and I seriously doubt anyone is going to admit being dumb like that.

 

[joebell]

Jraef,


Thanks for all your help!

That is exactly the contactor installed in the enclosure. I doubt that it was manually manipulated because it is located behind the disconnect for the unit, very strange arrangement. I am certain that the motor was wired correctly we have not gotten the diagnosis back from the motor shop yet hopefully that will yield some clue as to what happened. I too doubt we will come to a conclusion. Thanks again for sharing your knowledge.

 

[jim dungar]

... I think your ABB tech is unfamiliar with PW motors and just spewed that out to deflect blame...

I agree with this premise.
Many drive startup 'technicians' aren't technical. They are people, often from the local distributor, that know how to follow the start-up flow chart in the manual. While they are good at deciphering error codes, they are usually not up on what items, external to the VFD, would cause the problem.

 

[iaov]

Great info guys. I will be trying to get a 100hp, China made, y start, delta run motor to run with an AB SMC soft start today. The winding leads no longer have the id numbers on them and I think I would rather go fishing!

 

[Jraef]

Great info guys. I will be trying to get a 100hp, China made, y start, delta run motor to run with an AB SMC soft start today. The winding leads no longer have the id numbers on them and I think I would rather go fishing!

I think if you search in here and elsewhere on the web, there are numerous posts on how to identify unmarked leads using a multimeter. Worth the time to find out how in advance, it's a PITA to do in the field with no help. Just remember that when using the soft starter you can forget the Y start issue, just connect it in Delta.

Rotsa ruck.

 

[Strife]

I could be wrong, but based on the leads number it seems to me you have a WYE/DELTA motor. Haven't seen it here in US, but I remember back in Europe these were common for 25-100 KW motors. Basically there were two contactors with 6 leads going to the motor and a time delay relay, so at start 7, 8, and 9 would be connected together(to make a WYE), and on run they'd be in parallel(1,7 - 2,8 - 3,9, to make a DELTA). Or something like that, I need some paper to remember the diagram

We are attempting to connect a 6 lead 460 volt 100 HP part winding motor to a VFD. We connected leads 1 & 7 to T1, 2 & 8 to T2 and 3 & 9 to T3. We are getting fault codes on the drive and was told that the breaker in the panel tripped when the drive was put in bypass. I'm wondering if this motor and drive are compatible or if we have the motor wired correctly?