Yaskawa A1000

rpoet

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I have a 15Hp (CT) Yaskawa A1000 drive, rated for 200-240V input. I have scoured Yaskawa's website and the drive manual, but I can't definitely find out if the drive will accept 240V corner-grounded delta power.

Yaskawa's phone support hasn't gotten back to be yet, and the powers-that-be would really like to know if the shiny new compressor they bought at auction can be hooked up.

Thoughts from regular users of Yaskawa's drives? I believe it will work, but I wonder if something in the drive's front end would have trouble with non-symmetrical voltages to ground.


Thanks,

-rpoet
 
provide an isolation transformer with grounded wye secondary


Is that stated in the drive manual, or is that just a suggestion of good practice? The current service is corner-grounded, and we'd like to avoid the expense and space of a transformer, if possible.




-rpoet
 
just a suggestion:
I have not completed reading the manual I was looking at other info on VFD related problems on Corner grounded systems
 
just a suggestion:
I have not completed reading the manual I was looking at other info on VFD related problems on Corner grounded systems

The damn corner-grounded service in this building is nothing but annoying. Transformers everywhere... ugh.

I agree that using an isolation transformer would probably be best, but the powers-that-be would like to avoid spending the $$$ if possible.

If Yaskawa ever gets back to me, I'll post an update on what they recommend.


-rpoet
 
From another web site:
winnie winnie is offline
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Most common VFDs are _not_ separately derived systems.

Presuming a grounded source supplying the VFD, a ground fault on the VFD output (or motor) will result in current flowing back to the source ground point. The thing that makes VFDs interesting in terms of faults is the rectification stage.

The rectification stage connects each input phase to one of the 'DC' rails in turn. So when phase A is the most positive, it is connected to the DC rail; then when phase B is the most positive, it takes its turn, then phase C. Similarly when phase A is the most negative, it gets connected to the DC rail, and so on for B and C. (Depending upon the filtering, the capacitor bank, and the load, there will likely be periods when none of the phases are actually connected to the rails.)

This means that a fault on the output of the VFD will be connected to each input phase in turn, depending upon where things are in the input AC cycle and the output switching cycle.

Bringing this back to 'VFD on a corner grounded delta', when a given rail is connected to a given phase, the 'rail to groun' voltage is the same as the 'phase to ground' voltage. With a neutral grounded wye source, this means that the rail to ground voltage will vary, but will remain pretty close to 1/2 VDC. But with a corner grounded delta, for 1/3 of the AC cycle each rail gets connected to a _grounded_ supply conductor. This means that while the DC voltage (voltage between + and - rails) remains the same with either a grounded wye or corner grounded delta supply to the VFD, the AC 'rail to ground' voltage is quite different.

Since you are _not_ supposed to have a current carrying path between the rails and _ground_, then as long as the insulation system is sufficient, then this AC 'rail to ground' voltage should not matter. However I would not install a VFD on a corner grounded delta system without involving the VFD manufacturer.

-Jon
 
PAGE 742 A1000 User Manual
Grounding
The drive is designed to be used in T-N (grounded neutral point) networks. If installing the drive in other types of grounded
systems, contact your Yaskawa representative for instructions.
 
I noticed the manual says also not to cycle power to the drive more than once every 30 minutes or could damage drive, this seems excessively long I believe AB says wait 1 minute. I put timers in my systems to wait prevent quick cycling power to VFD's. Years ago I went rounds with ABB on an OEM new machine, they had a contactor removing power to a VFD that was being switched off and on on a setup and they cooked 2 before it was was figured out why. With some of the new safety rules for ZES (Zero Energy State) I can't imagine waiting 30 minutes between power cycles.
 
PAGE 742 A1000 User Manual
Grounding
The drive is designed to be used in T-N (grounded neutral point) networks. If installing the drive in other types of grounded
systems, contact your Yaskawa representative for instructions.


Yaskawa got back to me and let me know that corner-grounded delta is fine. They have concerns when operating from open delta sources, as leg-to-leg voltages can vary based on loading.




-rpoet
 
Thanks for the info: I was trying to see if Corner Grounded Delta is a TN System, Which I believe it is, In which case the manual says its OK
 
Thanks for the info: I was trying to see if Corner Grounded Delta is a TN System, Which I believe it is, In which case the manual says its OK
No, there is no IEC terminology for a delta system at all, ALL power systems are Y of some sort everywhere except North America. That's why most Asian drive mfrs ignore this issue in their technical data; we represent a tiny fraction of their world wide sales. T-N means a Wye power system, so they are telling you that it is ONLY designed to be connected in a Wye system, but "contact us" if that's not what you have. But then nowhere in their available tech support documents does it actually say what to do, even their phone tech support people are untrained in this issue. I used to be a Yaskawa official integrator via Magnetek when they were the main "brand label" for Yaskawa. But after Yaskawa bought out the Magnetek contract and fired all of the rest of their US partners, they lost a lot of the "tribal knowledge" of the established sales and support teams these companies had put together. This issue frustrated the heck out of me and I complained about it a LOT, but it fell on deaf ears. They just didn't get it. Back in those days I WAS eventually able to find a single US based Engineer on their staff in L.A. who understood this issue and his solution was: install a Delta-Wye drive isolation Transformer ahead of each drive (or group of drives). While this is a solution that I usually recommend because of what you expose the VFD to by removing the ground reference, it is sad that once that one guy at Yaskawa left, nobody there picked up the ball.


Bottom line, ALL VFDs that have been designed for Y systems, (meaning all VFDs really) will have an issue with a delta system, corner grounded or not. I suspect that your Yaskawa representative was unaware of this issue and gave you an answer that would make you go away. One of their tech support people once claimed that the MOVs on the diode bridge (the main issue with a Delta system) are connected Line-to-Line, so it's not a problem. But that CANNOT be true, because all CE labeled equipment, which includes everything Yaskawa makes, is REQUIRED to be referenced to ground, that that is inclusive of the MOVs on the front end of the drive. In fact on the VFDs that are available where you are given the option of removing that ground reference (A-B and ABB for example) to use them on a Delta system, they will warn you that doing so violates the CE and UL listing of the units. So the fact that a Yaskawa representative made that statement proves my theory that there is nobody left there that truly understands this issue.
 
+1 jraef

We have a lot of corner ground in this area. ?Better? than back before they grounded a phase and had an open delta... Maybe. At least you know where the voltage to ground is.

Anyway, Yaskawa used to connect their MOV's in Delta across the line on the G5 and earlier, but I believe today they are Y connected to ground. This means 2 of them will have full voltage across them, and are likely rated for too low of a voltage.

I know some European drives have R/C networks and MOV's to ground for CE noise suppression, and clearly state in the manual to disconnect them for Delta power systems (which means virtually all of the 230v applications). In fact, the OEM's I deal with disconnect them on every drive, since they don't know what's out there at the customer. If the customer cares, they can re-connect the filters.

I have had to rotate the incoming phases on some corner ground systems with some drives that have SCR soft-charge front ends, FWIW.
 
jraef and Gene,
Does the issue with corner delta lie in teh fact that two of the phases will be a full 480V line to ground instead of the 277 found on a wye system?
 
jraef and Gene,
Does the issue with corner delta lie in teh fact that two of the phases will be a full 480V line to ground instead of the 277 found on a wye system?

That's one of the issues. The higher voltage to ground is always a concern for safety and insulation. The potential ground fault as described in roxusa's post interesting, but I've never considered it.

The filter elements for CE are not rated for 480v to ground (on 480v drives) or 230v to ground (on 230v drives). I've seen many a blown MOV in 230v drives.

The SCR front end for soft charge is an issue with the return current path for the gate pulses, thus the reason I've had to rotate phases a few times.

BTW, I've also seen problems on ungrounded Wye systems!
 
No, there is no IEC terminology for a delta system at all, ALL power systems are Y of some sort everywhere except North America. That's why most Asian drive mfrs ignore this issue in their technical data; we represent a tiny fraction of their world wide sales. T-N means a Wye power system, so they are telling you that it is ONLY designed to be connected in a Wye system, but "contact us" if that's not what you have. But then nowhere in their available tech support documents does it actually say what to do, even their phone tech support people are untrained in this issue. I used to be a Yaskawa official integrator via Magnetek when they were the main "brand label" for Yaskawa. But after Yaskawa bought out the Magnetek contract and fired all of the rest of their US partners, they lost a lot of the "tribal knowledge" of the established sales and support teams these companies had put together. This issue frustrated the heck out of me and I complained about it a LOT, but it fell on deaf ears. They just didn't get it. Back in those days I WAS eventually able to find a single US based Engineer on their staff in L.A. who understood this issue and his solution was: install a Delta-Wye drive isolation Transformer ahead of each drive (or group of drives). While this is a solution that I usually recommend because of what you expose the VFD to by removing the ground reference, it is sad that once that one guy at Yaskawa left, nobody there picked up the ball.


Bottom line, ALL VFDs that have been designed for Y systems, (meaning all VFDs really) will have an issue with a delta system, corner grounded or not. I suspect that your Yaskawa representative was unaware of this issue and gave you an answer that would make you go away. One of their tech support people once claimed that the MOVs on the diode bridge (the main issue with a Delta system) are connected Line-to-Line, so it's not a problem. But that CANNOT be true, because all CE labeled equipment, which includes everything Yaskawa makes, is REQUIRED to be referenced to ground, that that is inclusive of the MOVs on the front end of the drive. In fact on the VFDs that are available where you are given the option of removing that ground reference (A-B and ABB for example) to use them on a Delta system, they will warn you that doing so violates the CE and UL listing of the units. So the fact that a Yaskawa representative made that statement proves my theory that there is nobody left there that truly understands this issue.




So.... where does that leave me? Can I safely connect the A1000 drive to corner-grounded 240V power without letting the smoke out or not? Do I have to remove the MOV filter network in the front end / is that possible?




-rpoet
 

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