# VFD Power Source Configurations



## JRaef (Mar 23, 2009)

First off, _*ALL *_VFDs are designed for solidly grounded Wye systems. A FEW of them can be modified to be used on Delta or resistance grounded Wye systems. Some of those then make it easy (like A-B and ABB), some not so much (Siemens makes you disassemble the front-end of the drive to make the change), still others (mostly Asian drives) either ignore the issue and allow you to find out it was a problem when you try to make a warranty claim, or just flat out tell you that you can't use them, often using terminologies that mean nothing to people in North America, something to the effect of _"Drive must be connected to a TN or TT system, not suitable for connection to an IT system."_ (I copied that from an Asian drive manual). Does anyone here in North America understand what that means? Not likely many... (the "T" in TN or TT means "Terra", or "earth", what we call Ground, IT means "Isolated Terra"; there is NO connection to ground.) North America is the only place where Delta power systems are still used but for big international comglomerates that sell their VFDs all over the world, we don't represent a very large part of their marketplace, so they don't pay enough attention to this issue. Then customers here interpret the LACK of mentioning it as to mean their drives are NOT susceptible to the problems, which is incorrect.

In the drives that provide a way of disabling the MOVs and CM noise caps or filters to keep them from blowing up and damaging other parts, you have to understand that you are ALSO removing their functionality in protecting the VFD components. Yes, you can do it, but now you are more susceptible to line side transients and the drive will create more Common Mode noise, which may cause interference. In that A-B document, notice the footnote:
(1) When MOVs are disconnected, the power system must have its own transient protection to Achieve known and controlled voltages​.
What that means is that a line side transient can now damage the diode bridge more easily, so YOU must protect the drive from that by installing your own high quality SPD ahead of the drive. Most people don't read that footnote and the VFD gets damaged anyway. Even so, you will also have the CM noise issue.

So bottom line, _*even if the drive says you CAN do it, doesn't mean you should.*_ This ability is put in there by US based VFD mfrs because there are some cases where people have to use VFDs and cannot change their source, so it's their only choice. Refineries are one common place like that, because most refineries can never shut down, so they are on ungrounded Delta systems or resistance grounded Wye systems. But when you have a choice, DON'T use a Delta system.


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## Wiresmith (Feb 9, 2013)

JRaef said:


> First off, _*ALL *_VFDs are designed for solidly grounded Wye systems. A FEW of them can be modified to be used on Delta or resistance grounded Wye systems.


thank you very much.


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## Cow (Jan 16, 2008)

JRaef said:


> First off, _*ALL *_VFDs are designed for solidly grounded Wye systems. A FEW of them can be modified to be used on Delta or resistance grounded Wye systems. Some of those then make it easy (like A-B and ABB), some not so much (Siemens makes you disassemble the front-end of the drive to make the change), still others (mostly Asian drives) either ignore the issue and allow you to find out it was a problem when you try to make a warranty claim, or just flat out tell you that you can't use them, often using terminologies that mean nothing to people in North America, something to the effect of _"Drive must be connected to a TN or TT system, not suitable for connection to an IT system."_ (I copied that from an Asian drive manual). Does anyone here in North America understand what that means? Not likely many... (the "T" in TN or TT means "Terra", or "earth", what we call Ground, IT means "Isolated Terra"; there is NO connection to ground.) North America is the only place where Delta power systems are still used but for big international comglomerates that sell their VFDs all over the world, we don't represent a very large part of their marketplace, so they don't pay enough attention to this issue. Then customers here interpret the LACK of mentioning it as to mean their drives are NOT susceptible to the problems, which is incorrect.
> 
> In the drives that provide a way of disabling the MOVs and CM noise caps or filters to keep them from blowing up and damaging other parts, you have to understand that you are ALSO removing their functionality in protecting the VFD components. Yes, you can do it, but now you are more susceptible to line side transients and the drive will create more Common Mode noise, which may cause interference. In that A-B document, notice the footnote:(1) When MOVs are disconnected, the power system must have its own transient protection to Achieve known and controlled voltages​.
> What that means is that a line side transient can now damage the diode bridge more easily, so YOU must protect the drive from that by installing your own high quality SPD ahead of the drive. Most people don't read that footnote and the VFD gets damaged anyway. Even so, you will also have the CM noise issue.
> ...


Jraef,

I just bought a 10HP 240v ABB ACS310 that mentions a similar thing as you've posted. 

From their ACS310 manual:

_Checking the compatibility with IT (ungrounded) and corner-grounded TN systems
WARNING! Disconnect the internal EMC filter when installing the drive on an
IT system (an ungrounded power system or a high-resistance-grounded [over 30 ohms] power system), otherwise the system is connected to ground potential through the EMC filter capacitors. This may cause danger or damage the drive. Disconnect the internal EMC filter when installing the drive on a corner-grounded TN system, otherwise the drive will be damaged.
Note: When the internal EMC filter is disconnected, the drive is not EMC compatible.
1. If you have an IT (ungrounded) or corner-grounded TN system, disconnect the internal EMC filter by removing the EMC screw. For 3-phase U-type drives (with type designation ACS310-03U-), *the EMC screw is already removed at the factory and replaced by a plastic one*._

_https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiFsZnpuuTeAhWQmeAKHd0fDiIQFjAAegQIAxAC&url=https%3A%2F%2Flibrary.e.abb.com%2Fpublic%2F0eda39cbd8494c4596d426b81e7884b3%2FEN_ACS310_UM_D_A4.pdf&usg=AOvVaw3bG7YRDHA5XOdr4k6RbZJV
_
So after reading your post and this excerpt from the manual, is this drive able to have the EMC filter reconnected when used on a 240v Delta system?


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## SpaceMonkey (Sep 19, 2018)

Jraef that was an awesome explanation. For clarification though, just so I know for sure in the future, you’re referring to all delta configured systems right? Whether center tapped, corner grounded, or ungrounded?


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## micromind (Aug 11, 2007)

SpaceMonkey said:


> Jraef that was an awesome explanation. For clarification though, just so I know for sure in the future, you’re referring to all delta configured systems right? Whether center tapped, corner grounded, or ungrounded?
> 
> 
> Sent from my iPhone using Tapatalk


The reference is to any system that's not a solidly grounded Y. 

Even if the system is a high-impedance grounded Y, you'll need to disable the MOVs, surge caps, etc. same as a ∆.


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## micromind (Aug 11, 2007)

Cow said:


> Jraef,
> 
> I just bought a 10HP 240v ABB ACS310 that mentions a similar thing as you've posted.
> 
> ...


If it's any type of a ∆ system, you need to have the EMC filter disconnected. 

The only time it can be connected is if the supply is a solidly grounded Y.


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## SpaceMonkey (Sep 19, 2018)

It’s confusing to me if any system with a delta configuration needs the MOV’s removed why don’t they just say it? Is a center tapped delta considered “resistive grounded?”


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## frenchelectrican (Mar 15, 2007)

SpaceMonkey said:


> It’s confusing to me if any system with a delta configuration needs the MOV’s removed why don’t they just say it? Is a center tapped delta considered “resistive grounded?”
> 
> 
> Sent from my iPhone using Tapatalk


SpaceMonkey .,

The centre grounded delta aka 4 wire 240/120 volts system in NA area is genrally not much a issue at all due it *is* typically solid grounded.

The reason why it mention about delta especially on 480 volts delta system due the line to ground voltage can varies a bit depending on the set up and with 480 volt to ground that can blow the MOV unless the drive came with 600 volt verison it may handle ok or modified by factory or follow the installment instruction make sure you read the fine print note carefully as Jreaf and Mircominded and myself and few others will mention this clear.


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## micromind (Aug 11, 2007)

SpaceMonkey said:


> Is a center tapped delta considered “resistive grounded?”
> 
> 
> Sent from my iPhone using Tapatalk


A ∆ system is usually solidly grounded but not always. A resistance grounded system is usually a Y connection but the center of the Y is connected to ground with a resistor. 

Think of it as instead of a solid neutral-ground jumper, the 'jumper' is a resistor. 

Normally, there is very little voltage present across the resistor but if one phase is faulted to ground, voltage will appear across it.

The main advantage to this is so that a fault from any one phase to ground will not trip the breaker, it will cause some sort of an alarm and the system will stay energized. 

The disadvantage is that another fault on another phase is a phase-to-phase fault instead of phase-to-ground. The net result is far more spectacular.......


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## mpetro (Jan 6, 2016)

Ran into this on an ungrounded delta system recently, definitely easily overlooked if you don't know about it.


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## gpop (May 14, 2018)

In a lot of the older plants you will come across a 3 wire Y. Its still a solidly grounded Y they just never bothered bringing the N into the mcc.


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## frenchelectrican (Mar 15, 2007)

mpetro said:


> Ran into this on an ungrounded delta system recently, definitely easily overlooked if you don't know about it.


That is very true if you are not prepared for it and that why I always be alert for it. I have ran into pretty often over here in my islands ( Philippines ) so I am used to it. but slowly switch over to either 400 Wye or 480 wye system. 

That why anytime I deal with VSD I have to check the type of grounding system it have on the location to prepared the correct set up I burn one up before after that I get wise with it.


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## mpetro (Jan 6, 2016)

frenchelectrican said:


> That is very true if you are not prepared for it and that why I always be alert for it. I have ran into pretty often over here in my islands ( Philippines ) so I am used to it. but slowly switch over to either 400 Wye or 480 wye system.
> 
> That why anytime I deal with VSD I have to check the type of grounding system it have on the location to prepared the correct set up I burn one up before after that I get wise with it.



When I was talking to the local AB distributor, he was quite surprised that we had an ungrounded delta, so I get the impression it's fairly uncommon in my area. We did account for it in the design, so it didn't catch me off guard, but I could see it causing issues if someone with less experience thought they could just swap out an old drive for a new one.


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