Having a moment with motor rotation

Dsg319

Dsg319

Senior Member
Location
West Virginia
Occupation
Wv Master “lectrician”
I know to change rotation on a 3phase motor you obviously flop any two leads.

Well instead of doing it in the pecker head today I done it in the VFD cabinet. It is all factory wired on line side and load side of VFD with special termination kits so I had to swap it on the load reactor after the VFD.

I swapped two of the leads on the load side (motor side) of the load reactor.

Than a co-worker suggested I also swap the same two phases on the line side of the load reactor.

It was early and I agreed with him as he saw the different colors of phases beside each other and thought it would short circuit.

But now that I’ve had time to ponder I believe the motor will still run backwards from swapping the line side of the load reactor after swapping the motor load side leads.

It should have been just swap two phases on either side of the reactor and not both right?
 
Correct. One swap to change direction.

But why not simply tell the VFD to drive in the opposite direction?

Does the motor have any sort of encoder or speed sensor going to the VFD? If yes then swapping the motor leads will make motor rotation inconsistent with sensor rotation.
 
winnie said:
Correct. One swap to change direction.

But why not simply tell the VFD to drive in the opposite direction?

Does the motor have any sort of encoder or speed sensor going to the VFD? If yes then swapping the motor leads will make motor rotation inconsistent with sensor rotation.
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Thank you for the confirmation.

As for the VFD I’m not an automation guru and not sure what sensors they have for speed and exactly is what controlling its speed.
 
A reactor doesn’t change anything. You can kind of think of it as three long pieces of wire that are wrapped around that steel frame for convenience. So there was no need to change on both sides.
 
I swapped a couple of 20hp vfds by abb recently and conclusion was to approach it like a girl in a bar. With a smile and good vibe, spend some time, take it easy, press some button combination, restart the conversation couple of times. Otherwise it would not have worked out. Just to start it in manual.
 
Thanks everyone! Makes perfect since now, the reactor coils are just wired in series with each phase individually. I guess the way the terminations was beside each other tricked my brain (which doesn’t take much at times)
 
winnie said:
But why not simply tell the VFD to drive in the opposite direction?
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They don't listen very well. Works better to go into parameters and change the right settings.

Almost always is easy to just swap output leads with smaller drives. The display will show forward when running forward. If it is a motor that never gets reversed then I guess it still shows forward which sort of makes more sense than having it show reverse when running a motor that doesn't get reversed.
 
Dsg319 said:
I know to change rotation on a 3phase motor you obviously flop any two leads.

Well instead of doing it in the pecker head today I done it in the VFD cabinet. It is all factory wired on line side and load side of VFD with special termination kits so I had to swap it on the load reactor after the VFD.

I swapped two of the leads on the load side (motor side) of the load reactor.

Than a co-worker suggested I also swap the same two phases on the line side of the load reactor.

It was early and I agreed with him as he saw the different colors of phases beside each other and thought it would short circuit.

But now that I’ve had time to ponder I believe the motor will still run backwards from swapping the line side of the load reactor after swapping the motor load side leads.

It should have been just swap two phases on either side of the reactor and not both right?
Click to expand...
Never attempt to change direction on any three phase VFD'S by reversing two input wires.Reason being the line goes to a rectifier to produce the necessary DC for IGBT'S to operate. Easiest way on VFD'S without bypass option is just use the touch screen ( Danfoss calls it something like LCP = Local Control Panel ) to change rotation. Danfoss had a small halve round arrow showing arrow towards the either the right or left. If the VFD has a bypass best to interchange two output leads. Place I retired from had over 500 VFD'S with over a hundred with byoass. Unfortunately installer used the drive touchscreen to change rotation on several drives but never checked if bypass had motor running incorrect rotation.
 
garbo said:
Never attempt to change direction on any three phase VFD'S by reversing two input wires.Reason being the line goes to a rectifier to produce the necessary DC for IGBT'S to operate. Easiest way on VFD'S without bypass option is just use the touch screen ( Danfoss calls it something like LCP = Local Control Panel ) to change rotation. Danfoss had a small halve round arrow showing arrow towards the either the right or left. If the VFD has a bypass best to interchange two output leads. Place I retired from had over 500 VFD'S with over a hundred with byoass. Unfortunately installer used the drive touchscreen to change rotation on several drives but never checked if bypass had motor running incorrect rotation.
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Can't say I ever encountered a VFD with bypass, but seems you would need to verify rotation of input as well as output so that it won't want to reverse when the bypass is activated. seems would need to also be either more complex transition or at least an open transition between the drive output and the bypass mode to assure there is no phasing differential being applied simultaneously, which the drive itself probably will not like at all.
 
While I agree that changing direction on the keypad is a simple fix, there are risks involved in that most VFDs have directional indication (Fwd or Rev) both on the display and in software, which might be confusing to users unaware of the change or SCADA systems looking for that data. It’s something to be aware of. I prefer to swap leads on the output of the drive, just like you would on a motor starter. I mean come on guys, it’s not THAT difficult…
 
Jraef said:
While I agree that changing direction on the keypad is a simple fix, there are risks involved in that most VFDs have directional indication (Fwd or Rev) both on the display and in software, which might be confusing to users unaware of the change or SCADA systems looking for that data. It’s something to be aware of. I prefer to swap leads on the output of the drive, just like you would on a motor starter. I mean come on guys, it’s not THAT difficult…
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I don't know how many air handlers, with bypass contactors, I have had to troubleshoot. It seems, during commissioning, nobody noticed the bypass contactor reversed the motor. This problem was usually first noted after midnight during a storm some years after startup.
 
jim dungar said:
I don't know how many air handlers, with bypass contactors, I have had to troubleshoot. It seems, during commissioning, nobody noticed the bypass contactor reversed the motor. This problem was usually first noted after midnight during a storm some years after startup.
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That’s my experience too. I train people to check rotation using the bypass first, then make the wiring on the VFD output match that. Seems simple, but it doesn’t always come to mind for people not familiar with that quirk of VFDs.
 
My first thought is, is the main service running counter clockwise, where does the first counter clockwise rotation begin and was the VFD manufactured with counter clockwise rotation as the input? If not why is it an issue to correct it at the feeder to the input side of the VFD? changing the output seems silly. But I don't install VFD's so what do I know :cool:
 
acrwc10 said:
My first thought is, is the main service running counter clockwise, where does the first counter clockwise rotation begin and was the VFD manufactured with counter clockwise rotation as the input? If not why is it an issue to correct it at the feeder to the input side of the VFD? changing the output seems silly. But I don't install VFD's so what do I know :cool:
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IMO phase sequence at service means nothing to the operator that knows forward is when the conveyor moves product one way and reverse moves it the other way, regardless what direction the motor shaft happens to need to go to get that result. If operator happens to be able to view the drive display and it says forward, then he expects his machine to be going in whatever the process it drives to be "forward biased" to the process. No different than with simple magnetic reversing starter and labeling the control buttons forward and reverse. They don't care what some technical guy thinks is forward to the motor itself, they know what forward is to their process/operation.

If it is a motor that never changes direction in operations, then there is only "forward" and to see "reverse" on a controller display just will add confusion at some time.
 
acrwc10 said:
If not why is it an issue to correct it at the feeder to the input side of the VFD?
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It is amazing how many people get upset if the coloring coding of input conductors is not what they were taught, such as BYO instead of BOY.
 
For those that are not clear on this concept…

A VFD does not know nor care what the input phase rotation sequence is, it doesn’t even need to check, because the ONLY thing it does with input power is to rectify it into DC, which has NO rotation sequence. In fact, the input can even LOSE one phase and have no effect on the phase rotation, because again all it will do is convert into DC. So changing the INPUT phase rotation sequence makes zero difference to the VFD and does NOT change the output.

The AC OUPUT if a VFD is wholly re-manufactured from that DC middle stage and is always A-B-C, but that is only relevant to the motor direction. Plus, you can command the VFD to change the output sequence to A-C-B with the flick of a key in programming, it’s all the same to it.

The only BIG issue is when you have an Across-The-Line bypass starter for running the motor full speed if the VFD should go down, which is common in HVAC systems for redundancy. That’s because the bypass WILL follow the input phase sequencing, not the drive output phase sequencing. So the simple trick on install is to check the motor rotation in BYPASS first, then swap leads on the output of the VFD to make it match.
 
Funny thing about this. Permanent power supply at this place is a natural gas capstone generator.

The generator was clockwise.
Customer (engineers at the company) like their power to be brought into the facility counter clock wise.

Result. All 9 three phase motors on site had to have phases swapped.

What is the purpose of bringing in power CCW vs standard CW supply?
 
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