3 Phase Wye/Delta - primary voltage on H2

[The Instructor]

Same exact thing will happen with three conventional transformers if a fuse blows on one cutout. With the H2 (neutral bushing) not tied down the remaining two trainsformers are in series accross the phase to phase voltage. If primary is 7620/13200 the two transformer connected in series are now operating on 13,200. If the load is balanced on the secondary each transformer iis operating on 1/2 of the 13,200 or 6600 volts. If you measure from h2 to neutral you will read 6600 volts. If the transformers are unbalanced that voltage will shift in accordance to the load of each transformer; it could possibly (with no load on one transformer go as high as 13,200 from the h2 to neutral.

These banks are tricky best bet is to ground the neutral float when energizing or de-enrgizing but, you should not do this if one of the cutouts is blown on the high side.

Just another note - arresters should not be left mounted on the tank for H1 bushings - they should always be placed on the high (line) side of the cutout.

[lewy]

Same exact thing will happen with three conventional transformers if a fuse blows on one cutout. With the H2 (neutral bushing) not tied down the remaining two trainsformers are in series accross the phase to phase voltage. If primary is 7620/13200 the two transformer connected in series are now operating on 13,200. If the load is balanced on the secondary each transformer iis operating on 1/2 of the 13,200 or 6600 volts. If you measure from h2 to neutral you will read 6600 volts. If the transformers are unbalanced that voltage will shift in accordance to the load of each transformer; it could possibly (with no load on one transformer go as high as 13,200 from the h2 to neutral.

These banks are tricky best bet is to ground the neutral float when energizing or de-enrgizing but, you should not do this if one of the cutouts is blown on the high side.

Just another note - arresters should not be left mounted on the tank for H1 bushings - they should always be placed on the high (line) side of the cutout.

A question about the arrestors. Do you not mount them on the tank because of the delta secondary? We mount all of our arrestors either on the tank(preferred) or on the load side of the cutout if the fusing is below 20k above that and we mount them on the line side. We only just started doing it this way in the last few years and we do not have any new delta connections and we try and convert our delta customers over to wye.

[Koga]

Whats the deal with movin the arrestor to the high side of the cut out ? Our engineers tellin us to do the opposite.

[lewy]

Whats the deal with movin the arrestor to the high side of the cut out ? Our engineers tellin us to do the opposite.

We are told only if the fusing is above 20k which for us mostly applys to everything but our 28/16 kv. We are told when the fusing is below 20k it will cause too many nuisance interruptions. Me I would prefer to put them all on the load side.

[Koga]

they tell us one way then a new head degreed man comes in and goes the other way.Have heard all the pros and cons of both ways so just wonderin. Biggest reason I like the low side is I can be away from it when it gets closed in.

Koga

[Pootnaigle]

Ummmmmmm all them engineer types tell ya to do stuff like they THINK it works best. Truth is none of em really know what is best.If I had a dollar for every one of those guys that came onboard and mandated some stoopid "change for the better" not realizing someone a few years ahead of them had the same idea 20 years ago and it didnt work then either, Id be filthy rich.Personally I like mountin em behind the cutouts rather than ahead of em. I aint really sure the damn things help anyways. Case in point....... a few days after a severe lightning storm bad transformers start showing up all over the system. some had em ahead of the cutouts n some had em behind the cutouts.
Point is Lightning got in em either way.

[Koga]

Seen alot of come through. Still I like em on the bottom side of the cut out.
When I was a helper I witnessed a porcelin 20kv arrestor go off. I had to clean my drawers out, and thought my lineman was a gonner for what seemed like forever. Id much rather be on the ground when they do blow.

Koga

[Pootnaigle]

Prolly the best reason for puttin em behind the fuse rather than ahead of it is a faulted arrestor will blow the transformer fuse rather than taking out an entire tap.Its way easier to find and a troubleman can clear the bad arrestor behind an open fuse with no assistance.

[Trbl639]

Prolly the best reason for puttin em behind the fuse rather than ahead of it is a faulted arrestor will blow the transformer fuse rather than taking out an entire tap.Its way easier to find and a troubleman can clear the bad arrestor behind an open fuse with no assistance.

That was their reasoning Poot...especially when they started the Big Reliability push....that and cutting in fuse switches on CSP's..........