open delta bank

[Redbeard3261]

single bushing pots - lighting pot hooked up normal, power pot X3 bushing hooked to X3 on lighting pot and X1 voltage will be what? regular wild leg voltage (208v-215v)? fault? a freind of mine and I disagree on the output on this build just throwing it out there to other linemen.

[Lineman North Florida]

Are both transformers the same polarity? If not I am guessing 120 volts.

[Redbeard3261]

yes both are additive (regular distribution), let's 50KVA lighting pot and 10KVA power pot

[reppy007]

single bushing pots - lighting pot hooked up normal, power pot X3 bushing hooked to X3 on lighting pot and X1 voltage will be what? regular wild leg voltage (208v-215v)? fault? a freind of mine and I disagree on the output on this build just throwing it out there to other linemen.

You kind of lost me with the term single bushing,on the high side,19.9?Why would you even try that if you knew the correct way.Or are you saying both pots have different polarities,and if so maybe try rolling the high sides.Personally ive only had one instance where pots were different polaritys.and that was ,if i remember right a 167kva 2 bushing pot and a 3 bushing pot,i may be wrong ?But wait,,i think i got you now,,,,,,,,,,i think you would blow a fuse wiring it that way,x3 tied to another x-3 you would cause it to buck.

[lewy]

single bushing pots - lighting pot hooked up normal, power pot X3 bushing hooked to X3 on lighting pot and X1 voltage will be what? regular wild leg voltage (208v-215v)? fault? a freind of mine and I disagree on the output on this build just throwing it out there to other linemen.

If they are both additive or subtractive you can not connect both X3s together you will blow a fuse.

[Lineman North Florida]

If they are both additive or subtractive you can not connect both X3s together you will blow a fuse.
That's what I meant, I was thinking that maybe 1 was additive and the other subtractive.

[Lineman North Florida]

Along those same lines, once after a major hurricane we got in a bunch of transformers from a bunch of different company's, it was about 2:00 AM and I had a desroyed 2 pot bank so I built a new one, closed it in and some of my co-horts started laughing and said I had messed that one up as we had some outrageously high voltage on the kitty leg, we had the meter pulled as was our policy, I told them that the bank was built right as at that time I had probably built over a hundred of em, well sure enough the voltage was off the chart, I asked if anybody checked the polarity of the pot that came from somewhere else and no one had. I went back up and there it was on the back side of the pot ( a dual voltage switch ) at that time I knew it was a subtractive pot and I had wired the bank for two additive pots therefore I had the X1 on the additive tied to the X1 on the subtractive pot, I fixed it on the secondary side and wired it X1 to X3 as I figured it would be easier for someone to spot than swapping 1 of the topsides and might keep someone from making the same mistake I made.

[topgroove]

Do you guys use single primary bushing pots on an open delta 2 pot bank?

I always thought you had to use double bushing transformers?

[Lineman North Florida]

The high side of all of our pots are 2 bushing.

[topgroove]

Thats what I thought... in the first post I noticed redbeard was talking about a single bushing open delta bank?

[hotwiretamer]

Thats what I thought... in the first post I noticed redbeard was talking about a single bushing open delta bank?

I've built many open wye/open delta banks with single bushing pots.

[topgroove]

I've built many open wye/open delta banks with single bushing pots.

I'm sure you have, But didn't he say single bushing open delta? he never mentioned open wye

[reppy007]

Do you guys use single primary bushing pots on an open delta 2 pot bank?

I always thought you had to use double bushing transformers?

Usually on our 12 kv pots there are 2 primary bushings,while our 34.5 system transformers are single bushing pots on the high-side,the case ground is considered the other bushing ,understand ?OR ground.

[hotwiretamer]

I'm sure you have, But didn't he say single bushing open delta? he never mentioned open wye

Oops! Comprende, I get it now!

[rcdallas]

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[rcdallas]

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[hotwiretamer]

Here's a good looking Delta Bank!
Single bushings, and what else is wrong with this picture?

4035

[rcdallas]

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[hotwiretamer]

Completly
Self
Protected

Correct, sir. Too **** easy for a Texas hand, Huh?

[lewy]

I've seen it two different times - X3 to X3 on an open delta 120/240. It never blew a fuse; voltage however was around 340 volts on the power leg.

Well I have never seen it & I would have thought it would be a short as you never connect your X3s or X1s together in a delta if all the trans are additive or subtractive.

[rcdallas]

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[rcdallas]

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[LAMartin.CVEC]

The bushing on a 34.5 has to be about what 3 foot tall?

34.5 to N is 19.9 bushing are usually 16 to 18 inches high, lol remember the "laps" add to the track over.
But you know this.

The thought I had was this: here at CVEC it bothered be that an open delta bank was called a 2 phase service, to me there is no such thing. Then I realized that they refer to it here by the primary not the secondary.
It was an odd transition for me to make.

Perhaps this is what is going on with the OP not sure maybe I need to re-read the posts.

Work safely,

L.A. Martin
Journeyman Div III
CVEC

[rcdallas]

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[LAMartin.CVEC]

thats some funny stuff RC and I'll tell you when I went to work at CVEC all that a3 vc6 c8 vc6 stuff made me INSANE! But I just learned it the same way I learned all the AEDS (american electrical design standards {AEP}) and the dominion va power standards and every other property standards I've worked on.

I'll stick to learning and remembering the theory behind banks so that when I see the phasor diagram on the print or get my work order from the boss or am asked buy the foreman to check the bank before we rebuild/re-insulate for a cut over-- it's gonna be RIGHT!

I know hook ups like the next guy, but we have some ancient stuff from the early 1900's that "hooks up" won't work on because they aren't your stranded six hook ups you learn for modern applications.

But yeah If you're every up this way to see the site or I'm down your way to see the sand... I'd love to toss back some brew and build some line lol...

L.A. Martin

[rcdallas]

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[wtdoor67]

Saw one built once with the H1 on one pot and the H2 on the other connected to the primaries. It was 4 KV and 120/240 secondary. New service, no connected load. It was connected X1 to X1 (because the top was flopped of course). It was closed in and the foreman checked the voltage at the meter base. He said. That one leg pegged the voltmeter. It was opened of course and the high side was changed.

For clarity I always just said. 2 pot bank. That made it simple I thought.

PSO , them pogues. They had a code of numbers that told you what each transformer was. Instead of calling in and saying. Send me a 25 KVA, 7620, 120/240 double bushing pole mount pot you just said. Got a bad 25, 711. The 3 numbers at the end gave you all the info. you needed. Any more I don't even remember the code numbers. I guess it was a good system though. Hate to give them credit for anything tho.

[rcdallas]

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[Redbeard3261]

I just asked because a lineman I work with said he ended up with 840v on the wild leg and noticed that it had been wired wrong X3 to X3. I would not see that voltage possible without a neutral problem or a bad pot. I would think it would just blow the door if wired like that.
We always use single bushing pot for wye/open delta banks. We would only make use of a two bushing pot where the H2 would need to float and a fourth door to avoid ferroressenance. We never seem to run into the subtractive pot as rule they are 200KVA or greater and all >200KVAs are additive. (never anticipated that discussion) Pretty clever for someone to mention the two bushing pot with one rolled ******* (power on H2), that would work because the orientation on low side bushings then would change.

[LAMartin.CVEC]

The only way I could see this voltage would be with 480 pots. Even 2 240 pots tied together can only give you 600v. I to would think improper return but that doesn't always open the door.

L. A. Martin

[Orgnizdlbr]

Saw one built once with the H1 on one pot and the H2 on the other connected to the primaries. It was 4 KV and 120/240 secondary. New service, no connected load. It was connected X1 to X1 (because the top was flopped of course). It was closed in and the foreman checked the voltage at the meter base. He said. That one leg pegged the voltmeter. It was opened of course and the high side was changed.




Seen the same thing after contractors did a job for us, problem was they threw it in and drove away......needless to say, the owner of the bakery it fed wasnt real happy cuz he had some equipment burned up and coudlnt make his cakes and pies.......

[rcdallas]

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[hotwiretamer]

Well you posted the picture of the two pot bank with CSP's and has luck should have it I come back from a trouble call with just that.

Simple problem; power leg is broke at the secondary bushing. Easy simple fix right. Nope. Feeds a convenient store and the owner conveniently doesn't speak english too well to get him to kill his load. Well after tackling that battle now it comes down to lifting the hot tap off line line on some armless construction. By golly the hot tap on the power pot is seized up.

Anyway finally called for someone to come watch me in the primary and ended up getting it done. Got the hot tap off; killed the lighting, etc. CSP's suck. They suck even more when their built like crap on armless construction in a two pot bank.

Yeah, you got to love lifting those stingers off csp's, relying on that switch to be in working order! I normally check voltage at the secondary bushings to confer that it is working. Especially when it is a bank!
That stinger you lift and then release to grab the next can be suspect to backfeed.

[Tester]

single bushing pots - lighting pot hooked up normal, power pot X3 bushing hooked to X3 on lighting pot and X1 voltage will be what? regular wild leg voltage (208v-215v)? fault? a freind of mine and I disagree on the output on this build just throwing it out there to other linemen.

If you have 240 volt transformers, and connect the x3 bushing together, you will have bad voltage, but nothing will blow up. Both the transformers will have 240 x1-x3. The x1-x1 will be 415 volts. The wild leg, (power leg) to neutral voltage will be 317 volts.

[reppy007]

If you have 240 volt transformers, and connect the x3 bushing together, you will have bad voltage, but nothing will blow up. Both the transformers will have 240 x1-x3. The x1-x1 will be 415 volts. The wild leg, (power leg) to neutral voltage will be 317 volts.

Just wondering if ........did you actually wire one out this way and check voltage?

[bobbo]

We have all different terminologies from different areas and different systems. One bushing cans I think of those Y system cans. Can ground is bonded to the coils and neutral? and one primary bushing thats it? Just trying to get apicture in my head.

[Tester]

Just wondering if ........did you actually wire one out this way and check voltage?

Yes I have, in a transformer class that is a controlled setting.
Using 7200/120/240 volt transformers.
Here is how we hooked it up.

[Tester]

If they are both additive or subtractive you can not connect both X3s together you will blow a fuse.

They will not blow a fuse. You will just have bad voltage.

[lewy]

They will not blow a fuse. You will just have bad voltage.

Ya your right 240/416 the same as 120/208 an old voltage they had here long before I started.

[lewy]

We have all different terminologies from different areas and different systems. One bushing cans I think of those Y system cans. Can ground is bonded to the coils and neutral? and one primary bushing thats it? Just trying to get apicture in my head.

Ya most of our new transformers are single bushing, with the bushing on the top. 1 side of the primary winding is connected to the bushing & the other end is connected to the inside of the tank, at the same spot on the outside is a tab to connect your lead to the system neutral. On the secondary side there is a tank strap that is connected to X2 along with a separate case ground. Our 347/600s are the same except they only have 2 bushings.

[davis.lineman]

would not work. it would not blow the fuse instantly like everyone thinks unless the coils were in bad shape. but your transformers already being banked together out of phase from each other on the high side. so on your secondary coil side your going phase to phase until it burns those coils up. seen this done contractors didn't know how to build an open bank and messed up quite a few times. so if your fuse holds long enough your voltage will be anything until something blows. but like the others have already stated if the transformers were different polarities from each other would work just fine as an open. as for it being an open bank with single bushings that's fine. because you have an internal ground on what would be your h2 bushing to your tank. because in order for it to work you have to have your hi side grounded out. unlike a 3 pot wye/delta where you would float your hi-side to prevent your bank turning itself into an open on its on and cause a burnout trying to back feed. also if you grounded your hi-side on a 3 pot wye delta if you have an imbalanced feeder when one phase on the secondary coil side your other transformer would try to compensate and back feed the other transformer to maintain voltage trying to regulate your system, this will also cause excess current to be thrown back on the system and you can see odd phenomenons like sympathetic tripping. making single bushings on 3 pot wye/deltas a no no. but investor owned utilites seem to use single bushings more than most it seems.

[rcdallas_]

would not work. it would not blow the fuse instantly like everyone thinks unless the coils were in bad shape. but your transformers already being banked together out of phase from each other on the high side. so on your secondary coil side your going phase to phase until it burns those coils up. seen this done contractors didn't know how to build an open bank and messed up quite a few times. so if your fuse holds long enough your voltage will be anything until something blows. but like the others have already stated if the transformers were different polarities from each other would work just fine as an open. as for it being an open bank with single bushings that's fine. because you have an internal ground on what would be your h2 bushing to your tank. because in order for it to work you have to have your hi side grounded out. unlike a 3 pot wye/delta where you would float your hi-side to prevent your bank turning itself into an open on its on and cause a burnout trying to back feed. also if you grounded your hi-side on a 3 pot wye delta if you have an imbalanced feeder when one phase on the secondary coil side your other transformer would try to compensate and back feed the other transformer to maintain voltage trying to regulate your system, this will also cause excess current to be thrown back on the system and you can see odd phenomenons like sympathetic tripping. making single bushings on 3 pot wye/deltas a no no. but investor owned utilites seem to use single bushings more than most it seems.Woah...that is very hard to read.Have seen the secondary side that had x1 to x1 and had screwy voltage, remember it being over 300 some volts.Some old school junk out there where CSP's were used.