# Corner Ground delta and Danfoss drive



## tates1882 (Sep 3, 2010)

Page 3.3 http://files.danfoss.com/download/Drives/MG20N602.pdf


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## MotoGP1199 (Aug 11, 2014)

OK customer just called me and said they believe it's a open Delta system. I have not been to the site to verify. Will that cause any complications with the drive?


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## John Valdes (May 17, 2007)

I would call Dan Foss (the rep) and get an answer.
I know drives do not like either mentioned here. But JaRaef had the answer for this. Removing a jumper or something like that. But that drive was AB.


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## just the cowboy (Sep 4, 2013)

Ask Danfoss about non Wye hookup. It has to due with MOV's in the drive. Some just remove a jumper, others had to cut out MOV.


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## JRaef (Mar 23, 2009)

I have never ever heard of 208V being a delta system, open, closed, corner grounded or otherwise. I think someone might be misinformed. Just because they are only using 3 wires doesn't mean it is a delta system, what matters is the secondary of their service transformer. If the center of the wye point is grounded, that's a Wye system, regardless of whether they ever or never actually use a neutral connection.

Danfoss drives are made to IEC standards, and they NEVER have a Delta system in IEC world, so they are NOT made for that. The closets they get is what they call an "IT System" which is (to their mind) still a 4 wire system, but there is no connection to the 4th wire. In the Danfoss drives, if you have an IT system, you must add what's called an "Insulation Resistance Monitor" (IRM) accessory to the drive. From my experience when you call the Danfoss rep and ask for that, they will have no clue what it is and if they eventually find out, they will have to order it from Europe and you will wait 5-10 weeks for it.

So you either need to hope that they are wrong about it being a 208V delta system, or suggest they buy a VFD that is designed to be used in the US where we occasionally have Delta power systems.

Open, closed or corner grounded would not matter by the way, the VFD only cares about the L-L voltage.


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## SpaceMonkey (Sep 19, 2018)

JRaef said:


> I have never ever heard of 208V being a delta system, open, closed, corner grounded or otherwise. I think someone might be misinformed. Just because they are only using 3 wires doesn't mean it is a delta system, what matters is the secondary of their service transformer. If the center of the wye point is grounded, that's a Wye system, regardless of whether they ever or never actually use a neutral connection.
> 
> Danfoss drives are made to IEC standards, and they NEVER have a Delta system in IEC world, so they are NOT made for that. The closets they get is what they call an "IT System" which is (to their mind) still a 4 wire system, but there is no connection to the 4th wire. In the Danfoss drives, if you have an IT system, you must add what's called an "Insulation Resistance Monitor" (IRM) accessory to the drive. From my experience when you call the Danfoss rep and ask for that, they will have no clue what it is and if they eventually find out, they will have to order it from Europe and you will wait 5-10 weeks for it.
> 
> ...




With your last paragraph in mind, why would it matter whether is a delta connected supply or wye? 


Sent from my iPhone using Tapatalk


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## gpop (May 14, 2018)

SpaceMonkey said:


> With your last paragraph in mind, why would it matter whether is a delta connected supply or wye?
> 
> 
> Sent from my iPhone using Tapatalk


They add spike protection and filtering to the front side of the drive before the diodes (vfd really starts at the diodes). These items are tied between the phases and ground so they expect to see a certain voltage. On a corner grounded the other 2 phases will be double what is expected and magic smoke will be released.


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## varmit (Apr 19, 2009)

SpaceMonkey said:


> With your last paragraph in mind, why would it matter whether is a delta connected supply or wye?
> 
> 
> Sent from my iPhone using Tapatalk


Most VFDs want to have a power system where each phase to ground is the same value. An ungrounded system has no intentional reference to ground. On a corner grounded system, one phase is zero volts to ground. The other two phases, on a corner ground, are the same voltage to ground as they are phase to phase.


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## MotoGP1199 (Aug 11, 2014)

So I spoke with Danfoss and they basically just referenced what I had found in the manual about disabling the RFI filter. So it seems it will work, I guess I was hoping for some additional info as real world experience often is slightly different and I found with drives that when you find an answer in the manual there are other things that come up they don't list in that part of the instructions.



> 4. When supplied from an isolated mains source (IT
> mains or floating delta) or TT/TN-S mains with a
> grounded leg (grounded delta), ensure that
> parameter 14-50 RFI Filter is set to [0] Off to avoid
> ...


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## Grounded-B (Jan 5, 2011)

varmit said:


> Most VFDs want to have a power system where each phase to ground is the same value. An ungrounded system has no intentional reference to ground. On a corner grounded system, one phase is zero volts to ground. The other two phases, on a corner ground, are the same voltage to ground as they are phase to phase.


I have never had a problem connecting a A-B PowerFlex drives to a corner grounded delta system. As you can tell from my screen name, we work in a lot of factories that still run 240V 3 phase, corner ground.

How would a drive know what the phase to ground voltage is anyways? They don't care, as long as all phase to phase voltages are close.

Phase loss is detected when 2 of the 3, line to line voltages drop. Example,: you lose A phase, then A-B = 0 volts, A-C = 0 volts, and only B-C = line voltage.

Steve
Milwaukee, WI


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## splatz (May 23, 2015)

Grounded-B said:


> How would a drive know what the phase to ground voltage is anyways? They don't care, as long as all phase to phase voltages are close.





gpop said:


> They add spike protection and filtering to the front side of the drive before the diodes (vfd really starts at the diodes). These items are tied between the phases and ground so they expect to see a certain voltage. On a corner grounded the other 2 phases will be double what is expected and magic smoke will be released.



My understanding is with some drives the surge protection are MOVs installed between the lines and ground. The MOVs (metal oxide varistors) decrease resistance as voltage increases. They are designed to so their resistance is very large at normal operating voltages then drops quickly at surge voltages. The voltage where they start really conducting is their "clamping voltage." 



If this is the case, and they are designed for 480V/277V wye, with 277V line to ground across the MOVs, but connected to a corner grounded delta, there's 0V to ground on one phase and 480V to ground on the other two. Those two may clamp - start conducting - as if that 480V is a transient, but it's not transient, it keeps coming, and burn up / blow up the MOVs. 



If there are jumpers to remove they are simply in series with the MOVs, by removing the jumpers you disconnect the MOVs so there's no protection but no white smoke with a grounded delta system. 



Someone hopefully will correct me if that's not the case, just what I have gathered.


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## JRaef (Mar 23, 2009)

You (splatz) and gpop are right as to the why. The only minor correction is that when you remove the jumper on A-B drives, you are removing the reference to GROUND, not the entire MOVs (or CM noise caps). It removes SOME of the protection, not all of it.

If you don't remove the ground reference of the line side MOVs or the CM noise capacitors, they represent a low impedance path to ground for your ENTIRE system. Think of it like this; you have a Delta system and devices connected in Wye and referenced to ground, almost like a Wye transformer would be. So in effect, those devices are becoming the neutral bonding point for the ENTIRE GRID they are connected to. As soon as there is a fault ANYWHERE else on the system, the current will TRY to flow through those devices, but only for as long as it takes for them to vaporize, usually taking out everything around them with a flash over because of the conductive materials (metal oxides) that they spew.

If you (Grounded-B) have "had no problems" for years, it's either because someone knew to order the A-B drives with the jumpers already removed (you can do that), or you have been lucky in that there hasn't been a fault on your system yet, or the MOVs have ALREADY vaporized and didn't cause a flash over.


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## micromind (Aug 11, 2007)

The local sewer plant here was renovated to a simple pump station about 15 years ago. The specs called for 2 Danfoss VFDs to operate the new 40HP pumps. The system is 240 3Ø 4 wire ∆.

I was told by yet plant operator that when they first powered one of them up, it blew up. They didn't power the second one. 

I didn't hear what the cause was but I suspect that the MOVs were still connected and they saw the high leg as a fault and were not able to reduce the voltage to ground so they exploded. 

Another case of the design limitations being exceeded resulting in catastrophic dis-integration of the device.


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## MotoGP1199 (Aug 11, 2014)

So between what Danfoss's literature says and if I'm understanding what you guys explained correctly. The drive should work fine. However I would be removing some of the protection the drive has under normal conditions. However if I have a fault somewhere else in the system the voltage is going to try to make its way to ground using the MOV and potentially burn up the drive.


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## MotoGP1199 (Aug 11, 2014)

Went to the site and it is Open Delta but its 240 Volts, 3 phase. I will be installing a transformer before the drive. Any recommendations on a transformer for the drive. Don't have specs on the drive it self yet but the motor is 230v, 3 phase, 30 HP, 75 amps. I've installed lots of transformers but none from 240 open delta to 230 Wye or Delta for a drive. They want to stick with danfoss as they have a bunch of them already. Any specific brands or specs I should look for?

I was looking at the ACME 40kva, 230 v to 230Y. Dive isolation transformer. M/N: DTFA0404S


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## gpop (May 14, 2018)

MotoGP1199 said:


> So between what Danfoss's literature says and if I'm understanding what you guys explained correctly. The drive should work fine. However I would be removing some of the protection the drive has under normal conditions. However if I have a fault somewhere else in the system the voltage is going to try to make its way to ground using the MOV and potentially burn up the drive.


Think of your filters and MOV's from each phase going to a isolated terminal block. That block is connect to ground via a jumper or screw.

Now with the jumper removed you still have 2 MOV's between the phases (think y connection) so any spike on one phase will be dumped to another phase. (When we say spike we are talking in milliseconds). So you have some protection.

In the event of a close lightning strike if you haven't dealt with it before it gets to the vfd MOV's they are not going to save you no matter how they are connected.


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## JRaef (Mar 23, 2009)

MotoGP1199 said:


> Went to the site and it is Open Delta but its 240 Volts, 3 phase. I will be installing a transformer before the drive. Any recommendations on a transformer for the drive. Don't have specs on the drive it self yet but the motor is 230v, 3 phase, 30 HP, 75 amps. I've installed lots of transformers but none from 240 open delta to 230 Wye or Delta for a drive. They want to stick with danfoss as they have a bunch of them already. Any specific brands or specs I should look for?
> 
> I was looking at the ACME 40kva, 230 v to 230Y. Dive isolation transformer. M/N: DTFA0404S


That's a good solution. And ground the Wye point of the secondary of that transformer of course.


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## mccla5214 (Mar 7, 2021)

JRaef said:


> I have never ever heard of 208V being a delta system, open, closed, corner grounded or otherwise. I think someone might be misinformed. Just because they are only using 3 wires doesn't mean it is a delta system, what matters is the secondary of their service transformer. If the center of the wye point is grounded, that's a Wye system, regardless of whether they ever or never actually use a neutral connection.
> 
> Danfoss drives are made to IEC standards, and they NEVER have a Delta system in IEC world, so they are NOT made for that. The closets they get is what they call an "IT System" which is (to their mind) still a 4 wire system, but there is no connection to the 4th wire. In the Danfoss drives, if you have an IT system, you must add what's called an "Insulation Resistance Monitor" (IRM) accessory to the drive. From my experience when you call the Danfoss rep and ask for that, they will have no clue what it is and if they eventually find out, they will have to order it from Europe and you will wait 5-10 weeks for it.
> 
> ...


Are you going to be in for a surprise the first time you hook up a drive to a grounded delta system and it has MOV units that are referenced to ground. These usually start conducting around 500 VAC. With a grounded delta system each phase has full line to line voltage referenced to ground. This will fire the MOV and let the angry little pixies out in a hurry.


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## mccla5214 (Mar 7, 2021)

Grounded-B said:


> I have never had a problem connecting a A-B PowerFlex drives to a corner grounded delta system. As you can tell from my screen name, we work in a lot of factories that still run 240V 3 phase, corner ground.
> 
> How would a drive know what the phase to ground voltage is anyways? They don't care, as long as all phase to phase voltages are close.
> 
> ...


Input power protection that is referenced to ground is very common and not designed for 500 VAC across it.


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## mccla5214 (Mar 7, 2021)

micromind said:


> The local sewer plant here was renovated to a simple pump station about 15 years ago. The specs called for 2 Danfoss VFDs to operate the new 40HP pumps. The system is 240 3Ø 4 wire ∆.
> 
> I was told by yet plant operator that when they first powered one of them up, it blew up. They didn't power the second one.
> 
> ...


EXACTLY.


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