4th cut out on wye delta banks

[LAMartin.CVEC]

I was wondering if anyone had a technical drawing (i.e. print) that I could share with our engineers here at CVEC that shows the installation of the 4th door for the neutral float on the high side.

any help would be appreciated. I'd really like it if some one could provide such a drawing in reference to a corner grounded delta.

Thank you and

work safely,

L.A.Martin
Journeyman Div III
CVEC

[birdog37]

Never heard of such a thing on a wye delta bank all thou I guess it wouldn't be bad if ya could find room.I guess ya would leave it open and load side tapped to floated H2.The other end tied to ground.Like i said door open thou unless ya need to operate the bank as an open bank.I think i would rather just use a shotgun and a ground jumper to tye er down thou,as this is only temporary conditions or ya could burn up the bank.

[kooman]

i have seen several of these banks, you find them alot in the irragation areas, alot of times they send out a single man to energize/de-energize the banks before and after the irrigation season, its alot safer and easier when the bank is put in and out of service. usually the higher the voltage the greater the chance of having problems with the floating h2 while fusing, ground the float with the 4th cutout, open or close the other 3 and open the 4th back up and there ya go.

[Bighorn Ape]

we just tie the h2's together and keep it running to the top of the cut out that is usually installed on the transformer bracket or sometimes on the pole. the bottom of the cutout goes to the pole ground...never seen a drawing for it though...

anybody ever seen one of these bank blow up or other damage occur from not tying down the h2's?

[Lineman North Florida]

we just tie the h2's together and keep it running to the top of the cut out that is usually installed on the transformer bracket or sometimes on the pole. the bottom of the cutout goes to the pole ground...never seen a drawing for it though...

anybody ever seen one of these bank blow up or other damage occur from not tying down the h2's? We just have problems with them blowing the lightning arrestors, ground down the floating neutral on the high side temporarily with the 4th cutout close in the bank open cutout and no blown arrestors, first time I ever saw this was on a closed delta overhead bank that was being fed by URD primary. It was common practice not to ground down the floating neutral temporarily where the primary voltage was 7200 or 7620 as it didn't seem to be a problem until you had higher primary voltage such as 14.4 or the rare URD feeding the overhead bank, at least down here where I'm at.There are a few utilities down here that have the 4th cutout as part of their standards, we have always only installed them on the few banks that gave us trouble.

[birdog37]

We never install a cutout on the floated wye delta closed bank.Always just floated the H2.If we need to operate the bank as an open bank then you would tie the floating neutral down.The only time we would have a lightning arrester blow would be on a fused line that feeds a wye delta bank like this.The reason is because you have a back feed from the delta on the wye delta bank.This puts an opposite voltage at your blown fuse.When you close in the fuse you will here the arrester blow @ the bank because of the spike in phase to phase voltage at the blown fuse.The voltage is higher than what the arrester is rated for.We have gone to an 18kv arrester on all fused lines.A 10 kv rated arrester exceeds the phase to phase voltage you have.It maybe instantaneous until the delta collapses .This solves the problem.Other wise you would have to isolate the arrester @ the bank.Close the fuse, then tap the arrester on.On 3phase lines you dont have this problem,only on a fused line.Most of our feeder lines have 3 phase breakers.

[Pootnaigle]

UMMMMMMMM LA we always just ran a lead from the floating primary buss to a cutout and hooked the hi side of that cutout to either the pole ground or the system neutral ,whichever was most accomodating. Some use a bladed rather than a fused disconnect. I suspect its the resident engineers call. We only did that on voltages above 13.2 K to combat ferrosresonance, And the Lightening arrestors are the least of your problems ,I have seen entire transformers blow a lid off without the use of that 4th cutout.

[bobcat]

4th c/o {grounding sw} we mount on pole bkt. back side of bank. reminder never close switch if you have open c/o bobcat delmarva pwr.:cool:

[dogman]

We put up a 10 ft x-arm, and put a solid blade cut-out on it. With the 3 other cut-outs. Had a wye/ corner grounded delta going to a seed cleaning company. Mat. man re-fused blown fuse with out grounding high side, burned up 3 transformers and kicked 1 Ø off at the OCR's. Bob

[LAMartin.CVEC]

bump

I'm still looking for a "print" to share with my engineering department :)

[birdog37]

Have a question on the wye delta bank.Where do you install your arrester protection @.Is it in series with the fuse up above on the arm before the fuse or do you put it on the side of the xformer below the fuse and why?We had a bank like this the other day and one area is mounting the arrester below the fuse on the side of the xformer.The lineman I was with said they should not do that because of circulating voltage and this will blow the arrester.I think he meant current,will circulating current blow the arrester?I figured a spike on the voltage would do it not current..??

[T-Man]

Lightening arrestors are a path for high voltage to get to ground before it goes into equipment and destroys things.

Imagine a wave coming to shore and hitting a sea wall. The water will splash against the wall and rise up and if big enough it will go over the top. That build up of water at the wall is what happens to the voltage coming to the end of the line, it magnifies itself.

An arrestor is like drilling holes in the wall to let some of the water thru with some control and not allowing the surge to build so high. Arrestors safely let the spike in voltage disapate.

In the older arrestors there are a number of little brass barrels set up in a ladder and the voltage would jump across the barrels and travel to ground.

Now the arrestors have FOV discs,(like little hocky pucks) stacked and glued with a special current carrying glue and these pucks will act as insulators to a determined voltage, when that voltage is reached the pucks become conductors and allow current to ground.

I'm not sure an arrestor could affect circulating current. They will blow from circulating current but They wouldn't be the cause.

Where they get installed is dependant on the engineers for the company you work for. That can be different from one company to the next. Ahead of the fuse is a good place, but I have seen them after on the transformer tank also.

[birdog37]

Our spec says to put them before the fuse but some still put them on the tub.I do like the 4th cut-out idea.I understand the way an arrester functions but i believe its not circulating current that will blow the arrester,agreed?We had to open the bank up to upgrade the service.He tied down the h2 so the arresters would not blow.The load was dumped and i dont think it was nessasary to actually tie down the floated side.Thoughts?

[T-Man]

If you open the cutouts to the H1's (the phase cutouts) the floating neutral is out of the picture once that is done, it no longer completes the wye connection.

Tying the neutral together on each tub is what creates the comon point for the wye connection. I see what a fourth cutout would disconnect the neutral completely but not sure it is any value. I could be missing something though.

Where I work we didn't use a cutout with the neutral. We only had this floating connection on 4800/8320, on the 14.4/24.9 the tubs couldn't be connected with a floating wye due to the
H2's where also grouned.