480v high leg motor issue

[jim dungar]

We have many 480 high leg open delta here, mostly feeding limited loads.

And what percentage of total US installations do you think these represent?

 

[ptonsparky]

And what percentage of total US installations do you think these represent?

It can't be much. For all the same Kwire & I share statewide, I don't ever remember seeing a 480 hi leg delta and only a couple corner grounded. Two ungrounded.

One system that a grounded conductor was added at some point in time, making it a wye, but I have no idea what it was prior.

 

[Jraef]

Back to the original point...
The fact that the SOURCE transformer is supposedly "high leg" has no bearing on what happens at this transformer. This delta-delta transformer is just taking the 240V L-L voltages up to 480V. That's it. The high leg is not high with respect to the L-L voltages, so it has no bearing here.

If you are getting UV trips on a voltage monitor relay MIGHT be related to the specs and configuration of that relay, but we don't know because you haven't provided any details. But IF, for example, that voltage monitor relay is set up for 480/277 3 phase 4 wire, and you are feeding it with 480V ungrounded delta, then the L-G ground reference is based solely on capacitance to ground, so it is going to fluctuate, so that might be giving it fits. But that is again just speculation. Post some details on the relay and how it is wired.

 

[kwired]

And what percentage of total US installations do you think these represent?

Likely less than 1%.

There has to be some out there in other rather remote places simply because of an open delta bank being used. Though they also could go with corner ground on those.

 

[kwired]

I don't ever remember seeing a 480 hi leg delta and only a couple corner grounded.

You certainly have the occasional open delta bank for limited load like a center pivot only or maybe a smaller capacity well here or there?

I know of one that is open delta and is supplying a 100 HP motor. It been there a long time and is fed by two primary phases (and neutral of course) from two different directions. If it were a situation of applying for new service at that same location today they wouldn't ever done it that way on that large of a well, customer would have had to pay to have three phase primary brought to the location.

Funny thing is the substation is on the far side of that particular section from where this bank is, there just never been any three phase lines run down the road where this is supplied from.

 

[jim dungar]

Likely less than 1%.

Then I stand by my statement they are extremely rare.

 

[ptonsparky]

The 480 corner ground was open delta. At the time I couldn't figure out how they got three phase out of single.

 

[kwired]

Then I stand by my statement they are extremely rare.

Just not in my little corner of the country. Might still be only a small percentage of the services supplied, but enough of them are around that if you do work on farms you will run into them. The commercial/industrial only guys may never see them, especially those from outside the area. Some of them don't even know what 240 high leg delta is.

Way back in 90's local school put an elevator in a older building. mostly out of area contractors did this, including their electrician. I was probably still an apprentice or not much more than first year or so journeyman. We got called to the school, which we typically did a lot of work there just not that particular project, not long before new school year started. Lots of burned out lighting ballasts, and other items here and there. The EC doing elevator moved feeders around to accommodate their feed to the elevator and in the process moved high leg on some of them to a different conductor. I didn't talk to them but my boss did, sounds like they had no clue what a high leg system was.

Why did it have a high leg service? It doesn't anymore but at that time it was two older buildings that only had single phase and was mostly still original wiring in those. When the newest building was built there was limited amount of three phase load in it. Primarily some kitchen loads and some HVAC loads. That building was built in late 60's and they put in new high leg delta service and fed existing older buildings with single phase and left them mostly as is otherwise.

 

[jim dungar]

Just not in my little corner of the country. Mi

This is a national forum, not one focused just on Nebraska.
I stand by my statement that high leg 480V systems are extremely rare.
The average electrician will never see one.

 

[Jraef]

240/120 3ph 4W delta systems, very common.

480/240 3ph 4W delta, I’ve only seen mentioned in textbooks and a couple of times in Internet forums. I see no purpose for it. Someone needs 480 3 phase and a LITTLE BIT of 240 single phase without needing 120 single phase too? What for? Must be farm thing, but even the farms here in California don’t get that from any of the utilities that I have ever come across.

 

[kwired]

What for? Must be farm thing,

Electric driven center pivot irrigation machines are always 480 volt three phase.

There is many with an internal combustion engine driving a well but they may have either generator driven by that ICE or is usually preferred to have utility power for the center pivot machine. They generally are not that high of a power machine. Never seen one with more than a 30 amp supply circuit. Most the control panels have a standard 30 amp fused disconnect but depending on how many sections the build is the majority I ever seen will run fine with 15 amp fuses in them, so they usually are less than 10-12 kVA. Services supplying only a center pivot machine often are supplied by open delta transformer configuration. Corner grounded delta was common, may still be in some areas. But remember often the farmer that doesn't really know enough about what he is doing has gotten themselves into trouble over dealing with corner ground delta and probably some even been electrocuted or someone else has because of their ignorance. That is likely why the one POCO I am most familiar did away with all the corner grounded delta systems they used to have about 30-35 years ago. That leaves them no choice but ungrounded or high leg system. These farmers generally aren't even aware it is a high leg, but at least they don't do anything stupid with a grounded phase anymore and don't really know any difference between wye system and high leg delta, just that each "phase conductor" is a "hot conductor".

 

[tortuga]

Just not in my little corner of the country.

@kwired I think it rains more out east where these guys are from, probably not as much irrigation, Here in Oregon there is probably an area the size of Wisconsin in eastern Oregon with 480 volt hi-leg open delta irrigation services all over the place.
Its expensive to run rural 3-phase for miles to just one meter so I'd say its not uncommon to see it here, reason as you stated is POCO can run two primary's and a neutral down the road and omit the 3rd phase for miles. (I have never ever seen a corner grounded one that I would call extremely rare) The 240V tap can power a MH light on the pole (some utilities will offer you a flat rate for the pole light). Go up to eastern Washington and probably the same thing. But there might be only a handful of electricians in that area that have ever worked on one or will see one.

 

[herding_cats]

I have never seen Delta transformer at 480 vac. ??

 

[kwired]

@kwired I think it rains more out east where these guys are from, probably not as much irrigation,

The other thing is we have the water. Wisconsin I suppose may have quite a bit of surface water but not sure what the have for underground aquifers. That along with crop genetics they can get higher yields but those won't do so well on "dry land" fields if they don't get a lot of water through key parts of the growing season which makes this area a great place to grow those particular varieties. You don't spend the money for irrigation if you don't intend to use it correctly to get maximum yield.

Some these POCO still using open delta even if all three primary phases are present for such limited load applications like center pivot only and no electric well. Why no electric well in some those cases? more people have been converting over the years to electric. But irrigation load is a major load in the summer months around here. These POCO's will give you better rate contracts if you are willing to let them install load control on your equipment to manage load on their system during peak demand periods. Some guys may have a well that supplies water to two center pivot systems, but is not sized to supply both at same time, they don't want to be on load management during a time when they need to keep the water going because they are running 24/7 and alternating which system they pump to.

 

[kwired]

240/120 3ph 4W delta systems, very common.

480/240 3ph 4W delta, I’ve only seen mentioned in textbooks and a couple of times in Internet forums. I see no purpose for it. Someone needs 480 3 phase and a LITTLE BIT of 240 single phase without needing 120 single phase too? What for? Must be farm thing, but even the farms here in California don’t get that from any of the utilities that I have ever come across.

Places with oil wells may very possibly see delta systems as well. IDK what size pumps or what voltage is common but is a rather limited load just like these irrigation services are with possibly no 120/240 needed.

Also if you have 480/240 supplying a rotary phase converter- the three phase output by nature of the converter is almost the same thing as a high leg delta, even if the converter windings are a wye connection. The high leg is not as fixed of a voltage on such phase converter as on a utility supplied high leg system and will vary with loading conditions, but in either case pretty much nobody connects any load between that high leg and neutral so doesn't matter much. They also avoid even having a control transformer on the high leg in either situation though voltage should remain reasonably stable on the utility supplied service.