Star Delta to Inverter?

[Ronnie Sullivan]

Here's a question I thought I'd never ask with all my 50 years of experience but I don't know - so I'm asking.

I have to change a star delta (wye) set of contactors (11KW motor) for an inverter.
Is the phase rotation or motor rotation the same if I keep the phases exactly as they were?
That is, the 3-phase power in, in the same order and the motor out terminals doubled up in the same order as they were in the line and delta contactors.

I really don't want this machine to start in reverse.

Of course, I'll take precautions - like initially starting very slow but this machine might cause damage in reverse.

 

[cardosocea]

To be honest, I don't know the answer to this one. Do you have a phase sequence check instrument to match phases? Check before and after the VFD is installed, but before the motor is hooked up? Which now that I typed it may not be possible depending on how advanced the VFD is.

 

[the_msp]

Should be, but couldn't guarantee 100%.

I'm doing the same, only changing to soft start not inverter.

My precaution is decoupling the motors for first run to ensure.

 

[parky]

Reversing the phases on the input to the VFD make no difference, however, the output does assume the original was correct i.e. the phases are correct & you follow the same throughout then should be no problem, I have seen where although the colours for the phases were as expected i.e RYB (panel internl & motors) but for some reason the phases were swapped over at the sub. when these were converted to VFD's caused all motors we fitted to VFD's to run wrong way as we assumed the incoming was correct as we had followed what was then RYB through the contactors to outgoing motors, it was a simple change though we put the feeder the correct way. so the colours were correct & re-terminated all the motors in each motor terminal box.
I can only assume in the original installation who ever commissioned it had more motors running backwards so to reduce the time in changing the phases on the majority of motor terminal boxes decided to change the feeder over at the sub (these were all black by the way) & only change a limited of motor terminations.

 

[BryanG]

The question is impossible to answer because it depends on what the drive manufacturer decided was the 'normal' forward phase rotation and what the site calls 'normal' phase rotation. On the bright side, you have a 50/50 chance, like what Clint said "tell me punk, are you feeling lucky"

This is from the ABB Manual, obviously there is some backside covering going on, but it is still correct.

Check that the starting of the motor does not cause any danger. De-couple the
driven machine if:
• there is a risk of damage in case of incorrect direction of rotation, or
• an ID run needs to be performed during the drive start-up. ID run is essential only
in applications that require the ultimate in motor control accuracy.

 

[JesperMP]

On the bright side, you have a 50/50 chance,

I tend to go by Murphy's law. If you assume something, the reality is the opposite, always.

If there can be damage if the motor runs in reverse, then you absolutely must verify the rotation before starting for real.
As has been pointed out by others, the installation of the original motor may have swapped the phases anywhere between the supply and the motor terminals.

You must also study the VFDs control carefully. Some VFDs change direction if the speed setpoint changes the sign. Some VFDs have a dedicated 'reverse' input or control bit.

If the damage may be severe it could be a sensible thing to install a reverse rotation block on the motor shaft (dont remember the english name).

 

[parky]

As I experienced, if the phases are correct going in then there should not be a problem, however, fitting an inverter if the feed to the motor was L3,L2,L1 i.e. reversed then the output to the motor must be the same, the problem if the phases are not correct is an inverter will always put out the correct phases i.e. L1,L2,L3 (or what ever they are called), so if on a standard contactor starter the input was L3,L2,L1 (i.e. reversed) then the ouput to the motor will be just that, however, if an inverter is fitted and the input stays the same then the output will be L1, L2, L3 so in effect reversed. It is unlikely this is the case so as the motors are already wired, the only thing to check is the feed to the existing system is correcttly phased & the conversion to VFD to the motor is correct (Star/Delta wiring or how ever it is connected) then it should be ok, I personally if possible as others have said disconect the drives from the motor if possible, but at the very least try one first & be ready with the e-stop.
If it is correct then there would be no reason why the others would not, But I would attempt rotation of all of them one at a time.

 

[Ronnie Sullivan]

Ah, that's why I didn't know - it seems not many do either.
De-coupling is not really an option as the motor is buried deep in the machine - and I aren't doing it lol.
I'll set it for a long ramp up and slow speed with my finger on the stop button

 

[parky]

@Ronnie, +1, that is what I did, it was only conveyors in my case but a long reverse would buckle the metal slats & cause a jam.

 

[VictorBit]

If you keep the phases exactly as they were in the star delta connection and connect the motor to the inverter output terminals in the same order as they were connected in the line and delta contactors, the motor rotation should remain the same as it was before. This assumes that the inverter has been programmed correctly to match the motor parameters and the desired direction of rotation.

However, it's always a good practice to verify the rotation of the motor after making any electrical changes to the system...
You can do this by using a phase rotation meter or by manually turning the motor shaft and observing the direction of rotation.

 

[BryanG]

I tend to go by Murphy's law

Murphy is a close personal friend of mine, I hadn't realised that he had travelled as far as Denmark But some research appears to show his is known around most of the world.

Some more thoughts on Murphy and his friends, some not necessarily for the less broad minded, or more prudish:
https://www.cs.cmu.edu/~fgandon/miscellaneous/murphy/
https://www.angelo.edu/faculty/kboudrea/cheap/cheap3_murphy.htm
I liked the thought that Murphy was an optimist.

 

[trialbyfire]

I would test the inverter output with a small motor to determine direction of rotation with XYZ hooked up to 123. Then hook up the drive motor with the knowledge that it still could be wrong.

You could also lower the v/hz settings in the drive and overcurrent settings to intentionally fault. What you are looking for is a "bump" in the correct direction before the drive shuts down. When you feel confident...

Best of luck.

 

[MarkNightingale]

On the bright side, you have a 50/50 chance

An old boss used to tell me you have a 33% chance.

33% it will run forward.
33% it will run backward.
33% it won't run at all.

Cheers

Mark

 

[jraef]

Inverter drives do not care what the incoming phase rotation is, all it does is rectify to DC. Sequence is 100% irrelevant and has no relation to the output sequence, which is wholly fabricated digitally.

On the output side, just make sure the 6 leads going to the motor are correct with relation to each other. Rotation can be inverted in the VFD output.

The only time it makes any difference is if you have a bypass starter in case the VFD goes down. If that’s the case, you set the proper rotation with the bypass, then match the VFD output rotation to that.

 

[cardosocea]

I would test the inverter output with a small motor to determine direction of rotation with XYZ hooked up to 123. Then hook up the drive motor with the knowledge that it still could be wrong.

Hooking up another motor tells him that the motor hooked runs a certain way. Not that the other motor he has will. Unless he knows for a fact the windings have been done in the exact same way.

33% it will run forward.
33% it will run backward.
33% it won't run at all.

Never thought about it this way, but... he's very much right. LOL