Understanding an Open-Delta Bank

[fio1022]

Hi all,
I don't know where else to ask this question and I have been trying to find the answer for a while now(no one seems to know for sure).
I am an apprentice lineman for my local utility company and I'm trying to understand how an open delta bank provides TRUE three phase power.
A regular wye or closed delta bank has three transformers with three phases feeding the primary side, 3 phases in 3 phases out(3 different phase angles).An open delta only has two transformers with two primary feeds.2 phases in 3 out?I don't get it.
Is an open delta bank secondary supplying true three phase power(120 degree phase shift)or is it two phases compensating for the lack of a third.
Just wondering if I am far off track on my thinking...
Any information is appreciated.

[dbrown20]

Very good question. It is a little bit out of the expertise of the average lineman. Probably more in the realm of a good Electrical engineer. Usually with something of this sort I try to find a good reference book that I can hopefully understand. Usually the math required in things of this nature are a little bit beyond my ken.

The following are some excerps from a publication from GE that I picked up one place where I worked. It is a manual that is more geared toward Power Transformers or as some refer to them Sub Station Transformers. However the principles still hold true I'm sure. With this and what little I know maybe you can get a little better understanding. Probably someone else will chime in with some more info also.

Here's the GE stuff. " Although this connection delivers three-phase currents which are approximately symmetrical to a three-phase symetrical load, the currents flowing in the high voltage circuit are not equal nor are they 120 degrees apart.
The maximum safe output of the bank operating in this manner is 58% of a 3 pot Wye/Delta bank. The system is grossly unbalanced, both electrostatically and electromagnetically."

Here's what little I know about them. They will parallel with a 3 pot Wye/Delta bank. Done that many times. You can add an additional wing or power pot with out interuption. Done that a few times. Most companies limit their load to about 20 HP total 3 phase.

Here's something else I noticed in this book and I just thought I'd throw it in also as it's interesting. "Units of widely different impedances may be used to form a Y-delta bank without appreciably affecting the current division. Furthermore, there is no danger of excessive circulating currents in the delta, though the ratios are not the same, for these currents cannot be reproduced in the Y and therefore they are magnetizing currents and necessarily very small."

If you wish perhaps you might contact GE about such a book as this. It's not to be confused with the little GE Distribution handbook that is so common everywhere. This small book was compiled by the Power Transformer Department, Pittsfield,Massachusetts. dbrown20

[topgroove]

Here is a pretty good picture of an open delta. clink on the link below. After the picture loads if you click on it again it will enlarge it.

http://www.dropshots.com/day.php?userid=134479&cdate=20060707&ctime=184203

[Trampbag]

Open Delta is a 3 phase transformer bank using 2 transformers. In essence one side of the secondary Delta is physically missing, however an electrical measurement is still possible across the missing side and so it is 3 phase. It will phase in with a closed delta bank. It is not as efficient as a 3 transformer bank, but saves one transformer. It also can save one conductor on the primary, whether using Wye or Delta primary, which can be a great savings as well. A lighting connection can be used in an open Delta bank. An open Delta connection can be used in an emergency when one transformer of three in a Delta bank is inoperable or burnt out.

No such hook up in a Y secondary is possible, always use three transformers.

[NJlineman55]

One large use of open deltas is feeding one small customer that needs three phase while using the lighting pot to feed the remaining customers on a block. This use is the most common I have seen, especially in city areas where pole space is sparse. The lighting pot is usually a larger kva than the power pot since it is feeding many customers and the power pot is only feeding one customer.

[dbrown20]

Open Delta is a 3 phase transformer bank using 2 transformers. In essence one side of the secondary Delta is physically missing, however an electrical measurement is still possible across the missing side and so it is 3 phase. It will phase in with a closed delta bank. It is not as efficient as a 3 transformer bank, but saves one transformer. It also can save one conductor on the primary, whether using Wye or Delta primary, which can be a great savings as well. A lighting connection can be used in an open Delta bank. An open Delta connection can be used in an emergency when one transformer of three in a Delta bank is inoperable or burnt out.

No such hook up in a Y secondary is possible, always use three transformers.

Yes a hookup with a Wye secondary is possible. It is possible to use 2 transformers for example in a 3 phase 208 or to use 3 transformers for a 3 phase 208. Either hookup can be made in a Wye with only 2 primary phases and the system neutral. Very uncommon but actually have the 3 pot example in the area where I now work. The 2 pot hookup must have one pot with external secondary bushings. We talked about this once before several years ago. dbrown20

[hifihaxor]

wow dbrown, i never thought about it but you may be right. with a 100kva or larger, with the 4 sec bushings, connect it like parallel except leave one leg unconnected... the common leg is your neutral and ties to the other pots neutral, and theres your 3 wye phases. ive never tried or seen it but it looks like it would work.

anyone have 3 phase txes in one overhead can? we dont use t hem here, but ive seen them in cali.. 3 pri bushings, 4 sec... really weird wheen i first saw one.

swamp is absolutly correct. ive seen banks with a 75 lighting pot and a 10 or 15 wing pot to feed a gas station and a half block of houses... since we have many areas that are mixed use with houses and businesses open deltas are useful. some old neighborhoods (the gables) have open delta residential services... many houses had three phase well pumps, airconditioners and.. elevators!! in practice, the lighting pot is usually larger in a closed delta bank as well, figuring if you have max load on the wind pots, then youll still need some additional capacity to run single phase loads.

cwye/cdelta banks arent used much in miami because of ferroresonance issues, especially on the 23kv areas.. many older industrial areas have them though. for those in the area, my favorite bank is at merrill stevens drydock on nw7ave and north river drive, its a feeder dead end platform bank. closed delta, very old equpiment, alllllll original and still in excellent condition.

i asked my boss once why on cwye/cdeltas the primary neutral is left floating, he said its in an attempt to balance the currents on the primary side.

[44kv]

in nc here on the duke system. we call them stack banks, 3 prim,4 sec. ive seen them in 30 kva, 75,150. im sure there are more but when they go bad we trade them out for 3 pot banks.

[topgroove]

i asked my boss once why on cwye/cdeltas the primary neutral is left floating, he said its in an attempt to balance the currents on the primary side.
If the primary neutral is grounded on a bank of wye delta distribution transformers, the transformers may be overloaded to the point of burnout by circulating currents caused by unbalanced primary voltages.
In the event of a phase loss the transformer bank will try to replace the missing phase. Its success in replacing the missing phase will depend on the relative size of the transformer bank compared to the load connected to the circuit past the point of phase loss.
Been there, Done that.
Note. It is not the connection to ground but the connection to the system neutral which is the cause of the issues. This is a fine point as the system neutral is well grounded.
When a primary phase is lost, transformer bank primary fuses frequently blow . Transformers burn out often. When two primary phases are lost, there is a backfeed of current from both unpowered transformers. These voltages will be determined by the connected load past the point of phase loss, but the maximum sum of the two voltages will be the normal voltage. That's when the freezers and refrigerators start burning up.

[dbrown20]

All the info. about open banks being for small 3 phase loads etc. is mentioned in the little GE distb. booklet so common at all work places. There are a few more little tidbits of info. about them in this book also. Really there is not much technical info. in those little books. Guess they don't figure linemen need to know that stuff. Of course the angular displacement of a 2 pot wye/delta bank can only be 30 degrees or 210 degrees which matches with the closed bank. Therefore paralleling is possible. One of the requirements of paralleling.

I have some data from a place I once worked that goes into ferro resonance. It is only considered to be a nuisance at about 20 KV and up. I have seen it on 34.5 and it was a classic book example. I have noticed some REC's place a grounding cut out hooked to the floater in order to avoid this problem when opening and closing such a bank. This on their 24.9 systems. I notice that the local power co. where I live, builds no 3 pot wye/delta banks on their 34.5 distb. Only open wye/open deltas and wye/wye.

Floating the neutral high side is primarily to prevent the bank from having all ground faults in the vicinity via the ground and the system neutral, from traveling through the pots and damaging one. When grounded to the system neutral the bank will continue to operate without anyone the wiser, although one pot may be dead and the customer never notices. When one of the remaining 2 goes bad then you have 2 pots to change out. Seen this happen a few times. Worked at a municipal once where some dummies floated the high side on a wye/wye 208 bank. This caused so much damage to the customer's equipment that the supt. ordered all banks regardless of hookup, to be grounded to the system neutral. Eventually this caused more problems.

3 phase overhead pots? Yeah, have seen quite a few on military bases. Once again they're illustrated in the little GE book.

An uncommon pot I saw once, at least for me, was a 3 phase 480 Wye/Delta padmount. Had a wild leg of course and I guess the high side was floated insided the thing. I guess if you want a particular thing, someone will build it. dbrown20

[dog38]

Was that pad installed on our property. It seems like we have one of everything here.

[dbrown20]

I have never worked where it was legit to ground the primary neutral on a 3 pot Wye/Delta bank. I have seen it done but it is considered to be the wrong way. dbrown20

[dbrown20]

I have never worked where it was legit to ground the primary neutral on a 3 pot Wye/Delta bank. I have seen it done but it is considered to be the wrong way.

Grounding the high side of a 3 pot bank, hooked Wye/Delta can cause this bank to act as a grounding bank as all imbalance in the vicinity will travel through the bank and all faults and lightening strikes in the area will go through it also subjecting it to a greater likilhood of damage. Ever transf. book I have read mentions this always. dbrown20

[Ryan]

Hey Dbrown remember when you and topgroove got all high and mighty on me, well this thread is what I was wondering about.

[dbrown20]

Noone got high and mighty with you. You just insisted on asking inane questions after it was repeatedly explained to you in great detail how to connect a bank. This current subject is not about how to hook one up, but actually some of the operating characteristics of such a bank. I still find it hard to believe that you work in this industry. If you will display your background in the bio. section maybe we won't be hard on you. dbrown20

[topgroove]

Hey Dbrown remember when you and topgroove got all high and mighty on me, well this thread is what I was wondering about.

Hey... I'm not the one who got all high and mighty. I was the first one to post a reply to your original post. I truly tried to help.

[Trampbag]

Yes a hookup with a Wye secondary is possible. It is possible to use 2 transformers for example in a 3 phase 208 or to use 3 transformers for a 3 phase 208. Either hookup can be made in a Wye with only 2 primary phases and the system neutral. Very uncommon but actually have the 3 pot example in the area where I now work. The 2 pot hookup must have one pot with external secondary bushings. We talked about this once before several years ago. dbrown20

:confused: :confused:
.
[B]I have to stand corrected, I guess. I thought I was answering an inquiry to an apprentice lineman about open as opposed to closed delta banks. I was trying hard not to confuse more someone already confused.

To fio1024, it is not common, nor practical from your point of view to try and get a 4 wire 3 phase connection on the secondary side with 2 transformers. Use 3 transformers in your Wye secondary connections.

[dbrown20]

Ah, these things always get off on a tangent. dbrown20

[Trampbag]

You hurt my little feelings.

[topgroove]

You hurt my little feelings.I'm afraid your gonna have to download this file fill it out and and post the the completed paperwork back on this forum.

[Viperexaf]

lol top you must hand those out quit a bit to have em in a pdf file. How many of em actually get turned back in to ya?

[topgroove]

Never seen one filled out yet. The key is to keep a straight face when you hand them the report. Tell them Employee Relations needs the paperwork filled out for there records

[fio1022]

The maximum safe output of the bank operating in this manner is 58% of a 3 pot Wye/Delta bank. The system is grossly unbalanced, both electrostatically and electromagnetically."

dbrown20
To get back to the subject.
Is there 2 or 3 seperate phases coming out of an open delta?If there is only 2,how do these 3 phase motors start rotating and could't that do damage over time to customers equipment?
I know this is above and beyond what I need to know to be a good lineman,but I always like to know how things work.
It's just my nature :)

[Ryan]

Hey sorry topgroove, I mistook you for someone else.
Apologies.
I wish everyone used there real names.

[topgroove]

take a look at this diagram again, You'll see how you can get three phases of secondary voltage using only two transformers. Its why its called open wye open delta. Its perfect for a customer who only has a small three phase load.

http://www.dropshots.com/day.php?userid=134479&cdate=20060707&ctime=184203

After you click on the link above ckick the image again and it will make it more clear.

[fio1022]

I understand how it is wired,I don't understand how you can get 3 phases out when only 2 are going in.

[Trampbag]

Fio1022
There are 3 phases, exactly like a closed delta. It is difficult to wrap your head around the concept until you have actually hooked up a dozen or so, but it is 3 wire and phases in with a closed Delta bank. If you draw a Delta, a triangle, on paper in pencil then erase one side of the Delta you get an open Delta. You can measure across all three points, a to b – b to c – c to a, but the one side is missing. In a Delta all sides are of equal length and so what you can measure physically you can also measure electrically with a volt meter. Example 240v – 240v – 240v.

On the primary side you simply need to energise the H coils, with a completed circuit, either with a Wye or Delta connection. The open Delta is on the secondary side.

All thanks to Nicolas Tesla.

[topgroove]

All thanks to Nicolas Tesla. now theres one guy in history who never got any respect.I bet Edison never had any thing nice to say about him.

[Trampbag]

By the way, I love the feelings thing.

[playtime]

To get back to the subject.
Is there 2 or 3 seperate phases coming out of an open delta?If there is only 2,how do these 3 phase motors start rotating and could't that do damage over time to customers equipment?
I know this is above and beyond what I need to know to be a good lineman,but I always like to know how things work.
It's just my nature :)

2 tubs, 2 phases.
X3 of transformer 1 We'll call this A(240 volt leg) X1 of trans 1 and X3 of trans 2 tied together we'll call this B(240 volt leg) X1 of trans 2 we'll call this C(240 volt leg). Now if you get your trusty Voltmeter out A to B= 480 volt. B to C= 480 volt. C to A= 480 volt. For this example say each tub is a 50 kva (2X50kva=100kva rating of bank.) this connection is only rated at 86% of the 100kva or 86kva. The 58% number comes from the total of a 3 tub bank ( ex. 50 kva X 3= 150 kva) 86 kva is 58% of 150kva.

Make sure you remove the bonding strap from the tank to the X2 bushing on transformer 2.

This is used by alot of REC's or RUS's for safety reasons. It cuts down on backfeeds.

[BigClive]

All thanks to Nicolas Tesla. now theres one guy in history who never got any respect.I bet Edison never had any thing nice to say about him.

Yeah, but he probably didn't care since he was just full-on into the technology. I'm sure he had plenty of down moments, but he must have had incredibly exciting moments that we could only dream of.

There's a good chance that he also had mild autism which often results in total dedication to a particular area of work.

[Trampbag]

It was a major corporate war between Edison and Tesla. Edison welshed on a payment promised to Tesla and that sparked off the fight. Tesla developed AC power and Edison put all his resources into DC. Westinghouse was heavily involved. The electric chair was a big factor in the propaganda played by Edison. It’s a great story, but not for this thread.

[Viperexaf]

Never seen one filled out yet. The key is to keep a straight face when you hand them the report. Tell them Employee Relations needs the paperwork filled out for there records
yeah and how often have you kept a straight face?

[edski104]

just by the by, we still build closed wye/delta banks with a floating neutral just for the reason mr. brown stated. if you don't do it,you'll never know when one of the cans go bad. and up north we used lots of 3 phase single can overhead transformers.polybanks,we call them in boston and thereabouts. really nice when you need a 208 and don't want to build one in the rain. just hang it and go.

[edski104]

no switch, but the engineers are trying to figure out how to close all the open delta pots on the system we have that are wired to UG feed with C phase as the lighting pot and A phase as the power pot. BUT ALL 3 phase banks use B phase as the lighting pot so the engineers want us to open them in the order B-A-C and go hot with C or A then the other then B, which goes against everything i was taught. which was to close the lighting pot first so you had the neutral. yes -no???? thoughts please??oh ,this is because the LA's were blowing out when they went hot,i guess. i was told this. never seen it myself.

[Trampbag]

:eek: Scariest words in the line trade, “Hi, I’m an engineer. I’m here to help.” :eek:

[dbrown20]

2 tubs, 2 phases.
X3 of transformer 1 We'll call this A(240 volt leg) X1 of trans 1 and X3 of trans 2 tied together we'll call this B(240 volt leg) X1 of trans 2 we'll call this C(240 volt leg). Now if you get your trusty Voltmeter out A to B= 480 volt. B to C= 480 volt. C to A= 480 volt. For this example say each tub is a 50 kva (2X50kva=100kva rating of bank.) this connection is only rated at 86% of the 100kva or 86kva. The 58% number comes from the total of a 3 tub bank ( ex. 50 kva X 3= 150 kva) 86 kva is 58% of 150kva.

Make sure you remove the bonding strap from the tank to the X2 bushing on transformer 2.

This is used by alot of REC's or RUS's for safety reasons. It cuts down on backfeeds.

How can that cut down on backfeed? An open Wye/Delta bank backfeeds very well. dbrown20

[dbrown20]

You hurt my little feelings.

Sorrwee. dbrown20

[edski104]

right, i knew i wasn't off my rocker. sometimes these guys can almost make it sound real. but i know it's not. if you close a power pot first you'll get flucuating voltage due due a lack of a neutral the the lighting pot is supposed to provide by closing it first. but you know engineers," i studied online at night for 6 or 7 weeks so I'm a freaking genius,listen to ME."can't stand 'em. thanks swampy, for helping keep my head where it needs to be.

[dbrown20]

Maybe the engineers are trying to get the banks hooked up with the lighting pot on the leading phase. There is supposed to be some advantage to this on open banks.

As for which pot to close first. It is my understanding that closing the lighting pot first and opening it last on an open bank is best. On a 3 pot bank, it doesn' make any difference as the neutral is not stabilized until the last pot is closed. dbrown20

[edski104]

even tho the secondary,which is wired delta, is only stable thru the lighting pot,which you should close first? on the primary side it has a floating or ,phantom,on the H2 tied together. i was taught,and always assumed,that if you did close one of the power pots the phases on the secondary with no relation to the neutral could fluxuate past the point of safe voltage and burn equipment up. am i wrong, or is this a case of carrying something too far, because i belive most of us feel, and were taught, the same thing. i never wanted to try out closing it wrong,because it does make sense from a electrical point of view. :confused: next!!

[dbrown20]

Sort of an interesting conjecture I guess. I too was always taught to open the lighting pot last and close it first when messing with a 3 pot bank. I've seen it done both ways however and never knew of anything getting messed up. I really think this may be a myth as I've been on trouble calls when only the lighting pot fuse was blown and nothing was hurt to my knowledge. In transformer books "floating" the high side is presented as the proper way to build these banks because when any one of the fuses is open the customer's voltage is awry and he then calls the pwr. co. with a trouble call. This is explained as the reason for not grounding the "floater" and also for the reason discussed before because when one pot burns up when erronously grounding the "floater" then the bank won't continue to operate as an open delta bank and burn up an additional pot.

The power co. is not liable for any burnup in these situations as far as I have experienced. I believe in most parts that the responsibility for the protection of motors is the responsibility of the customer. I talked to an electrician once and he said that most equipment can be protected against any thing except high voltage. Plenty of businesses don't have this protection as they just take their chances. About the only thing I have witnessed the power co. take responsibility for is high voltage and an open neutral, which of course causes high voltage. Of course I don't think they hesitate in blaming lightening for a lot of things. It's a handy excuse. dbrown20

[edski104]

ok,thats basicly what i was wondering. because if you do close the other two cans their they still have a relationship to the neutral thru the phases tyed into the lighting pot. the freaking engineers here try to come up with all kinds of new ways of expaining why they can't figure out ways for us to do our job,and then when we get out there in the field it turuns out to be a walk in the park. but i thank you for you time and input, :rolleyes:

[jptrammell]

:confused:I want to see if I can answer the question about why you get three phase out of an open delta transformer bank .I have been out of line work for 9 years now but I think I can still answer it .I think the confusion is you think you have to have 3 primary phases to get three phase on the secondary side . If you think about it ,when you hook up a single phase transformer you get 2 phases secondary therefore, when you add the second transformer you get your third phase .The question is when you have an open delta and you close the bank by adding the third transformer and third phase why do you only get three phase secondary and not four . Maybe someone else can answer that one I did know the answer but i forgot it,s been awhile . Johnny Trammell

[wtdoor67]

J.T., are you back in the trade or what?

An open delta bank is usually closed to accomodate added load. An additional pot will use the same high side hookup. Yes you could have an additional phase but it would match the phase of one of the other pots. What would be the point then?

If you add another pot it's X1 and X3 will match the secondaries of the other 2 pots. To gain more load potential it's secondary bushings must be connected to the secondary bushings of the other 2 pots.

Acquire a transformer book and refresh yourself. There's actually some diagrams etc. that can be accessed on line.

[Boomer gone soft]

JT,

you do not get two "phases" from a single phase transformer. You get one phase split in two. (The coil on the sec. side is attached to the X1 on one side and the X3 on the other. The X2 is physically tapped to the center of the coil.) That splits the turns ratio in half which in turn splits the phase in half. It does not "create" a second phase.

3 phase connections can easily understood by learning how to vector phase angles.

drawings and simple explanations can be found here:
http://www.allaboutcircuits.com/vol_2/chpt_10/6.html

This link has more useful information for our applications:
http://www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm

If you notice the drawings of a delta bank, they form a triangle with the sides representing the transformer coils and the points are where the phases (lines) are attached. When one transformer is missing (an open delta) a "v" shape is formed. The geometric and "electrical" distance from the two phases at the points of the missing transformer remain the same as if the transformer were still there. That is why the voltage and phase angle (the third phase) remains the same on an open or closed delta.

By the way, I noticed some previous posts stating an open wye secondary is possible. The fact is that it is DEFINITELY NOT.

I hope this information helps.;)

[Roger Sandwith]

My understanding is your open delta will be 85.5% of the KVA of the two pots. If that is confusing it is 57.7% if you had three. But a far as three phase power, yes it is all there. If you know how to vector check it out, or ask your Journeyman.(I would love to draw you one out, but I don't know how to on the reply thing) Your Journeyman will be happy to do this, and if not contact me and I'll send a damn letter. Try your instructor at JATC too.
Be safe,
Roger

[electric squirrel]

JT,

you do not get two "phases" from a single phase transformer. You get one phase split in two. (The coil on the sec. side is attached to the X1 on one side and the X3 on the other. The X2 is physically tapped to the center of the coil.) That splits the turns ratio in half which in turn splits the phase in half. It does not "create" a second phase.

3 phase connections can easily understood by learning how to vector phase angles.

drawings and simple explanations can be found here:
http://www.allaboutcircuits.com/vol_2/chpt_10/6.html

This link has more useful information for our applications:
http://www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm

If you notice the drawings of a delta bank, they form a triangle with the sides representing the transformer coils and the points are where the phases (lines) are attached. When one transformer is missing (an open delta) a "v" shape is formed. The geometric and "electrical" distance from the two phases at the points of the missing transformer remain the same as if the transformer were still there. That is why the voltage and phase angle (the third phase) remains the same on an open or closed delta.

By the way, I noticed some previous posts stating an open wye secondary is possible. The fact is that it is DEFINITELY NOT.

I hope this information helps.;)

You have two separate phases coming in don't you,,,,,,,if this is so,then a single phase delta can would seem to me, not very efficient !
I understand that the whole delta system is kind of a bastard system,but where I topped out from that's what they use.

Now if you convert the system to a Wye and pull in a neutral ,you could lesson the load ,???. I'm positive there is still a lot I do not know, like I said a delta system is all I know. Am I on the right track??? E.S.:cool:

[brian931]

Haven't read all the replys but simply put a delta trans is meant to have the phase to neut voltage across the high side, this is acomplished with three trans and floating the neutral. When a phase is lost you are left with two trans in series with the phase to phase voltage across them - this is the trouble call, by grounding the floating neutral the proper phase to phase voltage is now put across the high side of the two good cans and 3phase secondary is restored. Simply put the down phase is replaced with a neutral connection.

[lewy]

Haven't read all the replys but simply put a delta trans is meant to have the phase to neut voltage across the high side, this is acomplished with three trans and floating the neutral. When a phase is lost you are left with two trans in series with the phase to phase voltage across them - this is the trouble call, by grounding the floating neutral the proper phase to phase voltage is now put across the high side of the two good cans and 3phase secondary is restored. Simply put the down phase is replaced with a neutral connection.

With 3 transformers you do not have to float the neutral , but if you loose 1 transformer or phase you would likely not know it & could possibly burn out of the other transformers.

[brian931]

Of course your right, but typically at least were I am the neutral is floated. You can get caught up and confused by all the theory but keep in mind that a Delta high side is to have a hot phase across each priamary winding (phase to phase voltage) and a wye high side is to have phase to ground voltage across each primary winding by way of a direct or floating neutral. Either way 3phase sec can be produced with only 2phases and a neutral in a wye system or 3 phases in a delta using only two cans.

[Highplains Drifter]

If it is agreed that an anchor has a finite amount of weight that it can hold before it begins to pull, what is the wisdom in using some of its weight retention abilities to simply bend a pole back before conductor weight is even considered? Also by bending a pole I (that is deforming it from its natural state) I believe its ability to carry weight is also also somewhat reduced.
By the way I am an 18yr lineman in Canada. I have watched guys crank way back on poles with no conductor in place and have always questioned the thinking to that.



Can you guys believe this an 18 year old ape a first stepper!!!!! In stead of learning material and how to frame wants to step up to the plate and dicuss theory with seasoned folks!!! When I was an ape I keep my mouth shut and my lineman took care of me!!! But maybe that is the way they let it get done in the Great North....:confused:.Drifter

[brian931]

Gosh, this is one hostile DISCUSSION board!
On the pole raking issue I believe a few agreed that bending poles was a bad idea, and the on the transformer issue wich part did you not agree with? I offered information that was pertinent to the topic "understanding and Open-Delta Bank".
You are right though, up north I gues we do things different, like respecting others even if we disagree, your a poor representation of a lineman let alone an ape!

[Highplains Drifter]

Gosh, this is one hostile DISCUSSION board!
On the pole raking issue I believe a few agreed that bending poles was a bad idea, and the on the transformer issue wich part did you not agree with? I offered information that was pertinent to the topic "understanding and Open-Delta Bank".
You are right though, up north I gues we do things different, like respecting others even if we disagree, your a poor representation of a lineman let alone an ape!



What a fowl mouth piece of sh*t!!!! Brian931, you need to learn how to walk the walk before you talk the talk!!!!!You are an 18 year old puke that has so much knowledge of linework, there is no way you should be even be thinking about working transformers, yet be talking about them. Tell us about you're experiences in linework, so we all can have a good laugh!!! The 18 year old prodigy of the Great and Free North!! Our Apes do know their place and do get a little respect, but with the attitude you got Brian, I would not share any of my knowledge with you!!!!!!! Drifter

[Meat]

I like a good fight but I believe he said he's been journeyed out for 18 years. Something to keep in mind when building an open delta bank is possibly closing it in the future while its energized. Using A and C phase may seem ok at the time but someone might cuss you later. Meat.

[wtdoor67]

Meat man, them damn pots don't care what phase they're hooked to.

[Boomer gone soft]

Door, you're right. Of course those pots don't care what phases feed them as long as the voltage is right. But, I have to agree with Meat about thinking about the next guy.;)

[wtdoor67]

I like to mess with him.

[Meat]

And like mama always said "beware of backfeed adding that third pot Meat".

[1st Class Husker]

Open Delta is a 3 phase transformer bank using 2 transformers. In essence one side of the secondary Delta is physically missing, however an electrical measurement is still possible across the missing side and so it is 3 phase. It will phase in with a closed delta bank. It is not as efficient as a 3 transformer bank, but saves one transformer. It also can save one conductor on the primary, whether using Wye or Delta primary, which can be a great savings as well. A lighting connection can be used in an open Delta bank. An open Delta connection can be used in an emergency when one transformer of three in a Delta bank is inoperable or burnt out.

No such hook up in a Y secondary is possible, always use three transformers.


You are correct, but dont forget that if you go from 3 transformers to 2 the wild leg will change positions!!!!! The same reason that you should float the H2's so the load will shut down!!!!

[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.:eek:

[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:D

[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:D

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!!!!:eek: Had to remember where you were if one went south and the rabbit in ya came out:D

[Special ED]

Had to remember where you were if one went south and the rabbit in ya came out:D

Surely a little fire at the end of a extendo or switch stick wouldnt scare ya off the roof would it? lol

[wtdoor67]

Using a CSP in a Delta secondary bank isn't good. If a CSP is the lighting pot, and the secondary breaker trips, it will act like an open neutral. Seen it happen once.

Worked on a property once where they seemed to use CSP's routinely in small open/delta banks. I thought it dumb. However they did have sense enough to mount an arm below the primary arm and put horizonally mounted pins to tie the stinger jumpers onto. That way if you forgot to trip off the breaker, or it didn't work, you could lift off the hotclamp and release the dangling jumper without it getting into anything if it were backfeeding. Other than that I thought it was a dumb setup.

Worked on another property once where a lot of open wire secondary was paralled via Johnny balls and secondary fuses. They referred to it as a grid system I think. A lot of single phase and 208 banks paralleled this way. Supposed to reduce flicker and better reliability. I think they finally quit it. Had to keep cut in when messing with their banks. Swimp would probably gotten toasted working there. It was mostly 12470/7200, so he could have gloved it from the pole.

[Trbl639]

Surely a little fire at the end of a extendo or switch stick wouldnt scare ya off the roof would it? lol

Not so much a little fire at the switch......when on the roof, you were level with the platform.........saw the top come off of one and it went up in the primary and it was a nice little fire!!!:)

[Trbl639]

Door.............

In the late 80's or early 90's, the company was sending old pots out to a contractor to re-build em....started having lots of problems...some in a bank.....the Re-builder was taking the CSP Handle off, welding a plate over the hole,...but leaving the secondary breaker in:eek: It would make ya scratch your head !!!

what you were talking about...the Grid system....was what we called Network......it worked good, but you had to be careful working the secondary hot, cause if you built a fire, it was a big one.........sometimes a 30 minute job to hook up a new service took a lot longer, opening up the limiters to isolate the one bank or secondary pole you were working.....but we got paid by the hour:)

[lowend15@gmail.com]

http://www.eng-tips.com/viewthread.cfm?qid=296620&page=1

Please see the post here under my "Lowend15" handle. I uploaded the PDF that explains graphically how the Open Wye Open Delta works. I haven't read through all the replies, but I'm sure it was explained textually. As they say, a picture is worth a thousand words.

A utility I used to work for used this connection exclusively in their substations for station service, and I felt I needed to understand it for myself. As I have read, unless you draw this you'll never understand it, at least not to a point you can teach somebody else how it works! I drew this up a while back, and feel, in light of how much I have learned through volunteers on the internet, it was time to give back a little :). Hopefully this helps somebody that may do a search for this.

I am an engineer, and want to thank you guys for what you do. We all have our places, but I've always been of the mindset to always value everybody and listen to the guys in the field. I think some of the biggest hurdles to great work is condescending attitude from a desk engineer. I've always taken time to listen to the field guys on whether it is a better way to run conduit, how to form up foundations, why what I drew was stupid :) , etc. So there are a few good engineers out there haha.

[wtdoor67]

Appreciate having an Engineer to peruse these pages. Look at the thread on Capacitors by RCDALLAS and give us your input there if you don't mind. Thanks.