Understanding an Open-Delta Bank

[wtdoor67]

I don't think that's right Husker. I have paralled 2 pot banks with 3 pot banks several times.

[Boomer gone soft]

I don't think that's right Husker. I have paralled 2 pot banks with 3 pot banks several times.

Door's right....the only time the wild leg moves is if you are not paying attention to where it's at in the first place.

[Special ED]

Yesterday got a trouble call.. transformer is out on a 3 phase service is what the call was.. Get there and its a bank of stepdown transformers.. 7200/12470Y steped down to 2400/4160 Delta.. Closest transformer to replace the bad one was about 10 hours away in Ohio so they wanted to come up with something..

Anyone ever wire up a step down bank like that wye- open delta? It should be same as regular 3 phase bank for a 120/240 service that I've done countless times before to put a "band aid" on over the weekend till a crew was able to come out but I've never done it on primary step down transformers and was curious if anyone has..

Ended up calling a buddy at the power company and got a new 4kv secondary bushing and replaced it and the lead from the coil and it was good as new instead cause thats all the was messed up.. Connection broke and burnt open and melted the hand screw part of the bushing..

[Trbl639]

Special ED..............

Never done it on Primary step downs, but cut many a closed delta to open-delta in make it a few days...........

Ever had a Wye/Wye bank in a Network system, where 1 pot goes bad and the old ones are 2 bushing primary (120/240, cut 2 wire) and the only replacement is a single bushing? Got to remember to flip the secondary on that pot or it'll gum the works up........makes the next guy scratch his head, if he gets a trbl call there

[Special ED]

Special ED..............

Never done it on Primary step downs, but cut many a closed delta to open-delta in make it a few days...........

Ever had a Wye/Wye bank in a Network system, where 1 pot goes bad and the old ones are 2 bushing primary (120/240, cut 2 wire) and the only replacement is a single bushing? Got to remember to flip the secondary on that pot or it'll gum the works up........makes the next guy scratch his head, if he gets a trbl call there

Made many closed deltas open on secondary volatages..

wye/wye in a network system.. Is that single bushing only have 2 or 3 X bushings on the secondary side.. We dont have network issues here... But Im rackin my brain and I thought you could use the single bushing pot you ground the tank and it is the neutral.. Maybe ive misunderstood you...

[Pootnaigle]

Anyone ever wire up a step down bank like that wye- open delta? It should be same as regular 3 phase bank for a 120/240 service that I've done countless times before to put a "band aid" on over the weekend till a crew was able to come out but I've never done it on primary step down transformers and was curious if anyone has..



Ummmm ya hafta remember that a 120 240 transformer has basically 2 coils on the secondary side and a stepdown primary transformer dont. I dont bleve that would work.

[wtdoor67]

It would work. Only thing you'd have to worry about would be the amperage. Make a drawing. You'll see.

Using a single bushing primary pot in a former "floated" bank would have to be a temporary fix. You could use it for load purposes but it would be the same as grounding down the high side which is improperly done sometimes. Usually causes a problem when one pot burns up then the other 2 are overloaded. Have to figure the amps.

[Trbl639]

Made many closed deltas open on secondary volatages..

wye/wye in a network system.. Is that single bushing only have 2 or 3 X bushings on the secondary side.. We dont have network issues here... But Im rackin my brain and I thought you could use the single bushing pot you ground the tank and it is the neutral.. Maybe ive misunderstood you...

What we called Network, was all banks in the Downtown area were Y/Y...all platform banks (everything on H structures)......all sized to carry additional load...all secondary was 4/0 cu ........... all phased together, separated by Current Limiters...was a big fire if you screwed up...........you could lose a bank or 1 pot in a bank, and if your limiters were good, no one would be out of service or have part lights...............in the area/town I worked, I had maybe 15 banks in the Network, about 7-8 years ago, one section was rebuilt to single pole structures and individual banks, and by the time I retired, we had removed all the limiters.....the holders/sleeves for them are still in place, but no limiters there................in the incident I was talking about, the way some, well most of these were built, in the 40's or earlier, the H2 was the hot bushing, and H1 grounded..................was funny, after the 1 section was rebuilt, I kept 6 of the old pots, had to raise hell to do it, cause the uppers didn't know the situation or care...........then about 6 weeks after the first bad pot, the next bank down the line lost a pot and we had to flip the secondary and go back with a single bushing there...........then about 6 months later the middle pot in the first bank went bad, but I had one of them saved 2 bushings for it!! 25 years in that town, 21 1/2 as a T-man there and I had 3 bad pots in that network, and all of them were in the same 2 span, same 2 banks...1 bad pot in 1, and 2 in the other....funny how it worked out like that.......

[Special ED]

Our network system here is 3 phase underground and only the "network boys" are allowed to mess with it.. It was designed so no matter what transformer failure, bad cable, ect. The power would stay on for everyone.. Its kinda messed up and Im assuming thats why they only let the network boys mess with it.. Anymore they been keepin it in the family so to speak.. The oldtimers are teachin their sons how to operate the system so they kinda gotta ace in the hole come time for layoffs. lol And the bad thing is its ex power company guys that retired or were bought out and they work for pike now.

[Trbl639]

Our network system here is 3 phase underground and only the "network boys" are allowed to mess with it.. It was designed so no matter what transformer failure, bad cable, ect. The power would stay on for everyone.. Its kinda messed up and Im assuming thats why they only let the network boys mess with it.. Anymore they been keepin it in the family so to speak.. The oldtimers are teachin their sons how to operate the system so they kinda gotta ace in the hole come time for layoffs. lol And the bad thing is its ex power company guys that retired or were bought out and they work for pike now.

We had the same thing in other downtown areas..........all of mine was ovhd Network, secondary side only........most of these banks were on Laterals off the feeder, at one time all had underslungs on the take off poles, but when 'reliability' became a Hot topic, the underslungs were changed to fused switches.........just wish all of those banks had been rebuilt....of course I don't have to work on em anymore..........some of them still have the old wire-top switches (on the banks), and to refuse a couple of the banks now, you use the bucket to get on top of the building, climb out on the roof, thank god they are flat roofs, and then use the slimjim to re-fuse em!!!! Had to remember where you were if one went south and the rabbit in ya came out