Who still has this? Delta delta ungrounded transformers

[Isaiah]

Is there any out there still using a delta-delta ungrounded system e.g. XFMRS with 4160V-480V?
I worked a refinery with one many years ago but haven’t seen it since then.


Sent from my iPhone using Tapatalk

 

[don_resqcapt19]

There are still some around here, but most have been converted to corner grounded systems.

 

[Isaiah]

There are still some around here, but most have been converted to corner grounded systems.

That’s what I thought.


Sent from my iPhone using Tapatalk

 

[hillbilly1]

I know of a water treatment plant that still is. The county water manager called me one day trying to figure out why the had a weird voltage problem. The plant had a ground detector his guy’s didn’t know about, they couldn’t figure out what that light was for. Ended up being a pump motor shorted to ground.

 

[Isaiah]

I know of a water treatment plant that still is. The county water manager called me one day trying to figure out why the had a weird voltage problem. The plant had a ground detector his guy’s didn’t know about, they couldn’t figure out what that light was for. Ended up being a pump motor shorted to ground.

To have detectors is a code requirement right if the system is ungrounded? If one corner of the delta is grounded what advantage is there other than a ground reference point?


Sent from my iPhone using Tapatalk

 

[don_resqcapt19]

To have detectors is a code requirement right if the system is ungrounded? If one corner of the delta is grounded what advantage is there other than a ground reference point?


Sent from my iPhone using Tapatalk

While a lot of old ungrounded systems had ground detectors, I don't think it was required 20 or 30 years ago.

One of the issues with an ungrounded system, is the very high voltages that can occur with a restriking ground fault. That can happen with equipment that vibrates and there is a phase to ground fault. There have been cases where this voltage exceed 900 volts and 480 volt motors were damaged.

 

[Joethemechanic]

is the very high voltages that can occur with a restriking ground fault

Never thought about that, but I can see it happening. Probably plays all kinds of games with the transformer's magnetic field

 

[busman]

You will find plenty of this aboard ships.

Mark

 

[Isaiah]

You will find plenty of this aboard ships.

Mark

Mark, ships have a lot of delta delta ungrounded transformers?


Sent from my iPhone using Tapatalk

 

[busman]

Mark, ships have a lot of delta delta ungrounded transformers?


Sent from my iPhone using Tapatalk

Yes they do. Havin a phase-ground fault on a ship mean Dark Ship; not a good situation. No lights, no steering, no propulsion, no navigation, etc. Most newer vessels have GFD.

Mark

 

[David Castor]

Plenty of old paper mills and saw mills with ungrounded 480 V delta systems.

 

[masterinbama]

MSFC and Redstone Arsenal still have a few lurking around

 

[augie47]

Back when this area was far more industrialized, delta systems were fairly common especially in paper product plants and facilities associated with Dupont. Now it is almost impossible to get such from our POCOs.

 

[busman]

Back when this area was far more industrialized, delta systems were fairly common especially in paper product plants and facilities associated with Dupont. Now it is almost impossible to get such from our POCOs.

It's not so much the PoCo's. We get Wye service from them and use transformers to convert to Ungrounded Delta for shoreside installations (when we want to match shipboard).

Mark

 

[Isaiah]

It's not so much the PoCo's. We get Wye service from them and use transformers to convert to Ungrounded Delta for shoreside installations (when we want to match shipboard).

Mark

Mark, what kind of grounding issues have you encountered with the Delta-Delta system?


Sent from my iPhone using Tapatalk

 

[Jraef]

Plenty of old paper mills and saw mills with ungrounded 480 V delta systems.

And steel mills. You don’t want a melt furnace shutting down because of a meaningless ground fault somewhere else in the plant causing a main breaker to trip. I started out in this biz at a steel mill, we were ungrounded delta with phase lights in our electric shop. When we got an indication of a ground fault we wouldn’t know where it was, so we would jump into our golf carts and run around looking for a puff of smoke or a production supervisor pulling his hair out. (That’s an exaggeration of course, we had phones even back then!)

I went by there a couple of years before COVID, they were still ungrounded, even though the melt furnace is long gone.

 

[busman]

Mark, what kind of grounding issues have you encountered with the Delta-Delta system?


Sent from my iPhone using Tapatalk

I'm not sure I really understand the question. The biggest issue with ungrounded systems is trading voltage to ground stability for system reliability. Ungrounded systems are largely being replaced by HRG systems as they provide the best of both in a compromise.

I did have an interesting troubleshooting experience when I first started working with these systems. An engineer (not an electrician) had designed an ungrounded system 480V delta with TVSS designed for 277V systems and NO ground fault monitoring. They had been "blowing" the TVSS for years and could not figure out why. I asked them if it was all three phases that blew? They said, no, only A and C phases. I told them to check B phase for a ground fault. Of course the 277V TVSS had a cutover voltage of about 450V so a GF on one phase took the other two up to 480V to ground.

Mark