Ungrounded Wye

nhee2

Senior Member
Location
NH
In reviewing some field notes and pictures from a plant where we are doing some unrelated control system work I noted that the site's existing 1200A service (480V) appears to be ungrounded wye. The plant operator had noted to me in a visit that the electrical dist. was ungrounded delta, and I had not looked closely at the connections on the outdoor transformers when on-site. I have seen ungrounded delta systems with Ground detection systems but I don't think I've seen ungrounded wye - is this a common installation?

Site is an industrial utility plant, some large motor loads, probably 50 yrs old. Fed from (3) 1 ph. transformers connected delta primary. They do have indicating lights installed on each incoming phase for monitoring loss of phase but don't have any alarming or any of the markings identified in 250.21(C). At least not from what I can see in pictures.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
In reviewing some field notes and pictures from a plant where we are doing some unrelated control system work I noted that the site's existing 1200A service (480V) appears to be ungrounded wye. The plant operator had noted to me in a visit that the electrical dist. was ungrounded delta, and I had not looked closely at the connections on the outdoor transformers when on-site. I have seen ungrounded delta systems with Ground detection systems but I don't think I've seen ungrounded wye - is this a common installation?

Site is an industrial utility plant, some large motor loads, probably 50 yrs old. Fed from (3) 1 ph. transformers connected delta primary. They do have indicating lights installed on each incoming phase for monitoring loss of phase but don't have any alarming or any of the markings identified in 250.21(C). At least not from what I can see in pictures.
Ungrouded wye and delta are the same thing. The only thing different is the transformer secondary is wye and left floating rather than delta; everything else is exactly like an ungrounded delta. Very common. This allows for one transformer stock to cover both 277/480 grounded wye customers as well as 480 volt customers seeking an ungrounded system. The bond strap is simply removed from the XO bushing, rather than having to order a delta secondary unit which works the same as a wye with the strap removed.


Just to point out, where the secondary is left floating or is anything other than grounded wye, having a delta primary connection is a good idea. All else is the same.
 

nhee2

Senior Member
Location
NH
OK, thanks. Like I said, most installation I have seen are 4W grounded wye or and if ungrounded are 3W delta. Note this was (3) 1 ph. and not a 3ph transformer however I understand your explanation. I guess common to everyone else, new to me. Or maybe just not recognized by me previously.
 

kwired

Electron manager
Location
NE Nebraska
Is there a neutral conductor with the service conductors? May have originally been delta but got changed to a wye transformer for whatever reason. Hopefully the left the neutral floating at the transformer or you do have a grounded system with no grounded conductor to the service - not a good idea, as ground faults will leave you with up to 277 volts to ground on EGC's and anything bonded to them but will not operate any overcurrent devices unless you are lucky enough to have a very low impedance ground path back to the source somehow:eek:
 

GoldDigger

Moderator
Staff member
A delta-delta and delta-wye transformer will necessarily belong to different vector groups, if anything unusual about the wiring and loads makes that significant.
And if POCO brings a neutral (but ungrounded) conductor to the service, the NEC makes it more restrictive to go ungrounded.
 
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nhee2

Senior Member
Location
NH
There is no neutral supplied from the utility transformers. We are only upgrading some controls and not doing anything with the power distribution, so I did not look closely at the service configuration while on site. However I had taken a picture of the service transformers and in filing the photos, had taken a closer look.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
A delta-delta and delta-wye transformer will necessarily belong to different vector groups, if anything unusual about the wiring and loads makes that significant.
And if POCO brings a neutral (but ungrounded) conductor to the service, the NEC makes it more restrictive to go ungrounded.

You do have a 30 degree displacement on a standard delta wye but in a radial feed system with nothing paralleled it makes no difference.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
OK, thanks. Like I said, most installation I have seen are 4W grounded wye or and if ungrounded are 3W delta. Note this was (3) 1 ph. and not a 3ph transformer however I understand your explanation. I guess common to everyone else, new to me. Or maybe just not recognized by me previously.
The concept still applies to single phase banks since stocking just 277 volt cans is cheaper than 277 and 240/480 volt cans. You may not have looked at the connections before. When ever a person walks into a facility fed by only 3 wires and is ungrounded the actual transformer secondary connection may be delta, open delta, wye or Tee. But to keep it simple people just call it "ungrounded delta"
 
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mbrooke

Batteries Not Included
Location
United States
Occupation
*
There is no neutral supplied from the utility transformers. We are only upgrading some controls and not doing anything with the power distribution, so I did not look closely at the service configuration while on site. However I had taken a picture of the service transformers and in filing the photos, had taken a closer look.
If you can post the pics I can confirm whats going on. Others do bring up a good concern, if your wye is grounded (and it might be as simple as a 10 guage wire crimped to the neutral wire briding the pots together going over to a ground rod) you will need the neutral run to the building and connected to the grounding system. A ground fault will energize the grounding system creating both a shock and fire hazard.
 

kwired

Electron manager
Location
NE Nebraska
Here's a pic of the secondary side of the transformer installation. Don't see any ground connection to the neutral.
Is that POCO or customer's equipment in the photo's?

I don't see one either, wouldn't know if it is possibly bonded to the transformer cases or not, but still not seeing any GEC even to the case - maybe on the primary side - that one is a little harder to see just what is there.
 

kwired

Electron manager
Location
NE Nebraska
My understanding is that the POCO owns those transformers.
Is it the sole supply to the facility?

Where is metering equipment located?

Is there any grounding done elsewhere?

If it is POCO you would expect it to be grounded at the transformer(s) if it is intended to be a grounded system, but without knowing some history you could have an unusual situation there. Though it may be a good idea to address the unusual situation and make changes to make it more clear just what the system is - could save someone's life someday.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Looks like Delta ungrounded wye. Typical when poco wants to keep 1 stock of transformers or has no 240/480 volt units. BTW, the stress cones and the bare concentric termination on those cables isn't done right.
 
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nhee2

Senior Member
Location
NH
Is it the sole supply to the facility?

Where is metering equipment located?

Is there any grounding done elsewhere?

If it is POCO you would expect it to be grounded at the transformer(s) if it is intended to be a grounded system, but without knowing some history you could have an unusual situation there. Though it may be a good idea to address the unusual situation and make changes to make it more clear just what the system is - could save someone's life someday.
This is the only utility service - there is also a standby generator on site. The service feeds an MCC with 1000A mains, and metering is located at the MCC. I did not explore the grounding while on site, as I was there for some control system work and we are not doing anything to the existing electrical dist.
 

kwired

Electron manager
Location
NE Nebraska
This is the only utility service - there is also a standby generator on site. The service feeds an MCC with 1000A mains, and metering is located at the MCC. I did not explore the grounding while on site, as I was there for some control system work and we are not doing anything to the existing electrical dist.
I guess depending on if the controls are separately derived, it may not effect what you were doing too directly. It is still a little more assuring to know just what you are working with or around.
 

nhee2

Senior Member
Location
NH
I guess depending on if the controls are separately derived, it may not effect what you were doing too directly. It is still a little more assuring to know just what you are working with or around.
I agree. I want to take another look when I am back at the site, and if needed I would alert the customer to any potential safety issues. It just wasn't something I was focused on during my last visit. I took the photos of the transformers in passing, as normally I don't get to look at them that closely.

Thanks for the input/advice.
 
In reviewing some field notes and pictures from a plant where we are doing some unrelated control system work I noted that the site's existing 1200A service (480V) appears to be ungrounded wye. The plant operator had noted to me in a visit that the electrical dist. was ungrounded delta, and I had not looked closely at the connections on the outdoor transformers when on-site. I have seen ungrounded delta systems with Ground detection systems but I don't think I've seen ungrounded wye - is this a common installation?

Site is an industrial utility plant, some large motor loads, probably 50 yrs old. Fed from (3) 1 ph. transformers connected delta primary. They do have indicating lights installed on each incoming phase for monitoring loss of phase but don't have any alarming or any of the markings identified in 250.21(C). At least not from what I can see in pictures.
I have reviewed the images you posted of the transformer bank. The primary is wired as a grounded wye but secondary side is wye but ungrounded. It seems somebody has omitted the grounding of the paralleled secondary side, but you have to remember, it will function like this without a neutral, however to make accommodations for updated controls and other devices, such as ground fault breakers and specific new instrumentation, since they require a neutral and ground wire, which forces engineering to add a ground to the unused side of the coils, as well, supply neutral to the inner panels the customer needs replaced, etc. Without having the neutral won't change anything electrically, for the function of the existing components, but will be needed to operate anything that runs from a grounded wye system (using the neutral)

I saw another post regarding that the wye is the same as delta without the neutral. That is far from the truth, the delta returns from other phases through another phase. The WYE or STAR connects one end of all three coils together and feeds the phases with the other three. If the three bushings for neutral are not connected to a load, the current will return back through another phase giving much different results, it gives each phase the ability to return an imbalance through another phase instead of through a neutral wire. The ground just ensures casings are bonded and of they aren't the manufacturer provides ground straps either internally or externally on transformers.

Before anybody continues, the power should have been shut down from the power company or customer owned aerial cutouts, if they exist, then test for potential to ensure there is no generation backfeed or induction, then if ok, makesafe such as grounding of all primary and secondary phase bushings.. Then remove tops of transformers to see if grounding straps have been connected to any of the bushings that would normally ground the paralleled secondaries that normally would be connected to the neutral conductor. To continue and put in what you need to do the work... (adding neutral wire, ground wire and conduit between the transformer pad and the interior switch panel)

I haven't seen this scenario many times, but I did encounter a neutral free wye generator system built in the 20's by Westinghouse at one of the older dams in CT. It had the ability to add multiple tap resistor neutral taps or it would be run without any neutral as Tesla did with his experimental generation circuits that supposedly would all produce power from hydro generation, but would deliver 11 kV of energy through ungrounded, non neutral wye generators which then fed delta transformers for power companies. We are NOT supposed to connect wye systems ungrounded, nor does the NEC allow wye systems to be installed on any new installation without a neutral conductor. As long as they remain a federally funded operation that feeds federally funded electrical transmission systems, they could use whatever means necessary to fill our power lines with electricity that basically costs them nothing to operate other than maintenance of the generators and dams that hold the water to use gravity to generate power.

I can't get into the specifics, but I can say if we did this today in every installation, we would all have no job in the electrical industry, so thank JP Morgan for stopping Tesla otherwise our society would not make money from electricity and no distribution of anything, no wires, no nothing between homes and commercial or industrial systems, no meters, no power companies, etc..

My guess is that the transformers at this company fed a panel, then were possibly stepped down or ran delta machines such as lathes, mills, or other motorized equipment? To understand what is really happening, when the system is forced into upgrade, such as electrical metering, and a grounded wye system with neutral added, My bet is their electric bill will go up substantially, maybe even triple in cost.

This has happened to us in the past when one of our customers, who is actually one of the top prep schools in the country have upgraded from an ungrounded, neutral free wye system to a brand new delta/wye system with padmounted transformers that use grounded neutrals, and even after having electrical testing to verify the power companies new meters were accurate, the campus's electric bill went up from 13k per month to almost 40k per month.

The system installed is perfectly operational today but the change in utility transformers, electrical metering, and of course how they were wired is what cost them the difference since they were using less electricity but getting more for some reason for many years. This effect is rarely documented but I am a witness of this actually happening and many others in the industry right here in New England.

My statement to you is that I would have them replace what they could to remain operational and don't change much so they don't pay more, but, this does endanger our industry.
 
I agree. I want to take another look when I am back at the site, and if needed I would alert the customer to any potential safety issues. It just wasn't something I was focused on during my last visit. I took the photos of the transformers in passing, as normally I don't get to look at them that closely.

Thanks for the input/advice.
take a second look at the primary side, you said it is delta fed, that is not correct. Delta does not have any of the three bushings paralleled. The 3 primary bushings on each can are tied together, then are bonded to ground. The secondary side is the same, but are not ground, nor have neutral wires.

The primary side would have the first and last terminal tied as phase 1, the 1st and 2nd transformer's 2 closest bushings would be tied with a jumper and fed as phase 2., and the 2nd and 3rd transformer's closes terminals would be tied together and connected to phase 3 of the incoming system. There isn't a any neutral because it was meant to be this way, to use less power. When the old timers in the industry started to fade away, so did this method, and to this day, nobody teaches this anymore. In essence, only one phase is used from the POCO to feed the facility, the last 2 phases pick up their energy by a resonance that happens within an electric motor from some strange reactive energy brought in either by induction or capacitance of some sort. Not completely understood but it happens and we still have some of this out there that hasn't been upgraded yet.
 
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