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Thread: Wye-Delta Banks

  1. #1

    Default Wye-Delta Banks

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    Am I correct in saying with a 3 pot wye-delta bank you connect the primary neutrals together but float them or isolate them from system neutral?
    With a wye-open delta 2 or 3 pot bank the primary neutrals are also isolated?

  2. #2
    Join Date
    Jan 2008
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    usa/ Oklahoma
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    Default Wye/Delta banks.

    Stormtrooper. We have beat Wye/Delta banks to death on here. If you want to check the archives you can find all of your answers.

    My advice to you is to get a Kurtz lineman's book and a GE Distribution handbook and have a look. Those will answer all your questions. No apprentice should be without the Kurtz Lineman and Cablemans handbook.

  3. #3

    Talking Look at

    Jumper or not to jumper forum
    Last edited by PA BEN; 03-06-2008 at 06:37 PM.

  4. #4
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    Feb 2007
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    Ontario Canada
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    Default

    With a 3 pot delta bank you can float them (they are connected to each other but not to neutral) or connect them to the neutral
    If you do not float them & you loose 1 tx you would not know & the other 2 would try and carry all the load. when you do float them & you loose 1 your secondary voltage will be lower e.g 520 compared to 600.
    If you are just using 2 txs you would have to ground both neutrals & you would have an open delta which would give you 57% of the the original bank or 86% of the total capacity of the 2 txs

  5. #5

    Default Well said....

    Quote Originally Posted by lewy View Post
    With a 3 pot delta bank you can float them (they are connected to each other but not to neutral) or connect them to the neutral
    If you do not float them & you loose 1 tx you would not know & the other 2 would try and carry all the load. when you do float them & you loose 1 your secondary voltage will be lower e.g 520 compared to 600.
    If you are just using 2 txs you would have to ground both neutrals & you would have an open delta which would give you 57% of the the original bank or 86% of the total capacity of the 2 txs
    You can tie the floated neutral when energizing and removed when energized. Small banks usually you should'nt have to, but the higher the voltage the worse the problem. The larger the bank loaded or unloaded the worser the problem. If you bank anything 50 or over I recommend tieing it to the system neut. A 4th cut out? Ok if the outfit can afford it, sometimes it clutters the pole up depending on the costruction. A gang switch? I dont know who puts that kinda money in to a system. A cheap easy way is to put a hot tap on a piece of 4 or six copper what ever size your pole ground is that is bonded to the system neut, than tie down your floated neut, energize the bank, then remove your hot tap with a shotgun so your highside neut is again floated.

    It is common that you float the high side, other benifits include that you can run a regular 120/240 house service and also 3 phase 120/240/208 power that can run someones well or shop. If you blow a fuse on one pot as long as it isn't the 120/240 pot that you tied X2 down. You will loose your 3 phase but the house will stay in service until crews arrive to make repairs.
    Last edited by johnbellamy; 03-06-2008 at 09:51 PM.

  6. #6
    Join Date
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    Southern Indiana is home. But I work all over.
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    Default Ferroresonance

    Bellamy:

    We would install a solid blade switch on large 3 pot delta banks. You would have to close it before you opened any of the switches and after you closed all the switches you had to bust the ground switch with a load buster. Otherwise it made a pretty nice ball of fire.

  7. Default wye-delta banks!

    Quote Originally Posted by Stormtrooper View Post
    Am I correct in saying with a 3 pot wye-delta bank you connect the primary neutrals together but float them or isolate them from system neutral?
    With a wye-open delta 2 or 3 pot bank the primary neutrals are also isolated?
    on a open delta - reference the neutrals back to system neutral!
    on a closed delta- float neutral if you want the motor to shut down when a phase is lost, otherwise the wild leg will switch pots !

  8. #8
    Join Date
    Mar 2008
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    LEE'S SUMMIT, MISSOURI
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    Default I Was Taught...

    TO USE A GROUND JUMPER AND GROUND THE FLOATER DOWN BEFORE RE-ENERGIZING. WE ALSO USE PHASE TO PHASE RATED ARRESTORS. SO OUR SYSTEM IS 7200V/12,470V GRD WYE AND ON OUR WYE-DELTA BANKS WE USE 12KV LIGHTNING ARRESTORS. I CLOSE THE 1 TRANSFORMER WITH THE GROUNDED NEUTRAL FIRST,THEN THE OTHER TWO. THEN AT THE END OF MY 8' SHOTGUN (A.K.A. GRAB-ALL) REMOVE THE GROUND JUMPER FROM THE FLOATER ON THE HIGH SIDE THEN REMOVE IT FROM THE NEUTRAL. THESE GUYS ARE ALL CORRECT. FLOATED NOT GROUNDED SO IF YOU LOSE ONE IT (THE REMAINING TX'S) WON'T SEEK TO OPERATE IN AN OPEN DELTA POSITION AND THE WILDLEG COULD BECOME A DIFFERENT LEG STILL WORKING. BAD FOR THE CUSTOMER....

    STAY SAFE OUT THERE

  9. #9

    Default Single bushing

    I've been at this utility for 3 years now, and my first morning here for my interview I stepped out of my Motel and looked at the Wye-Delta bank across the street and saw a cutout open on one of the power pots. This was a apartment building so I thought they were single phasing. But no utility people were around? I took a closer look and the three transformers were single bushing transformers. Will I've seen it all now. I guess years ago engineering approved the set-up. We use two bushing transformers on all new Wye-Delta banks. Every time we have a primary feeder go down that feeds down town, we lose a s#!t load of cutouts and have a s#!t load of 3 pot, open-delta banks that we have to refuse.

  10. #10
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    Default

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    Quote Originally Posted by PA BEN View Post
    I've been at this utility for 3 years now, and my first morning here for my interview I stepped out of my Motel and looked at the Wye-Delta bank across the street and saw a cutout open on one of the power pots. This was a apartment building so I thought they were single phasing. But no utility people were around? I took a closer look and the three transformers were single bushing transformers. Will I've seen it all now. I guess years ago engineering approved the set-up. We use two bushing transformers on all new Wye-Delta banks. Every time we have a primary feeder go down that feeds down town, we lose a s#!t load of cutouts and have a s#!t load of 3 pot, open-delta banks that we have to refuse.
    A couple of questions if the transformers were single bushing are you sure it was a delta secondary & if it was how do you have a floating neutral as it could be alive at line voltage
    I am asking this because of the switch you said was open which I understand you have to use on a delta secondary on the higher voltages ( this is something I am not familiar with because we do not have any delta secondary on our 27.6 kv distribution)
    I also thought that open delta banks were 2 pot banks, again maybe just something different
    All of our delta transformers are also 2 bushing

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