high voltage stumper?

[BULLogna]

had a voltage problem call in a very rural area. upon arrival checked transformer 157v/292v so i tested the single phase primary voltage to be around 8kv on a 7.2kv/12kv system? transformer had high voltage coming in on primary. first thought was a regulator malfunction. nope as drove line out back to three phase checked for three phase primary voltage at a three phase bank pole y delta. primary showed voltage on all three but secondary at bank had upset v. patrolled further back past some levy pumps on back to find two primary doors open and blown presumably from lighting and the other still hot. pump house had a 12kv/2.4kv delta delta transformer bank that only had one 7.2kv phase out of three feeding in. bank was back feeding out about 8kv. on the two blown phases and all customers were still on but had high voltage at houses. we refused the two blown cut outs and threw them in and all was well. just for your amusement

[Trbl639]

We get that...similar... in the oil fields....... a pumper will shut a well down, and it won't re-start...but all the other wells are still runing..most are open/delta 14.4 hi side/240/480v low side pots......7.6/13.2 primary........and ya find 1 , maybe 2 blown fuses at the take-off......backfeed on the delta banks ..........it'll get ya to scratching yer noggin!!!

[Boomer gone soft]

Our specs and Xcel specs require floating neut on high side wye-delta banks to prevent backfeeding the line.

[mx-5]

a third year apprentice should be able to figure that out...yes..:rolleyes:

[ssgerken]

I'm only an apprentice, but I don't believe floating the nuetral on the high side will not prevent backfeed. The reason for floating the neutral on a closed wye/delta bank is to prevent if from acting as an open bank if you lose a phase and cause the two remaining x-fmrs to become overloaded. Please correct me if i'm wrong, but that is what I was taught

[Boomer gone soft]

SSGerkin,

You are correct, but only partially;). When a wye-delta bank is operated with the neutral grounded, overloads can result due to the delta side trying to balance loads which creates circulating currents. Transformers can be destroyed due to a number of conditions that will exist when this bank is grounded. Grounding the wye side also produces a path in the delta side for third harmonics. Additionally, the grounded wye allows the remaining 2 primary phases to backfeed an open phase through the delta at voltages as high as 2.5 times the normal phase to ground voltage. Metal-oxide arrestors will often blow (sometimes violently) when this happens.

I appreciate an ape who is eager to learn.:D

FYI: The neutral must be tied in before energizing or de-energizing this bank. Some utilities (like Entergy) use a fourth cutout that is normally open. Some (like Xcel) have a "whisker" with a hot tap from the pole ground. Others you must bring a ground up with you.

More in depth information on this topic can be found at: http://www.hubbellpowersystems.com/powertest/literature_library/pdfs4lib/OB/EU1159-HR.pdf

[wtdoor67]

FYI: The neutral must be tied in before energizing or de-energizing this bank. Some utilities (like Entergy) use a fourth cutout that is normally open. Some (like Xcel) have a "whisker" with a hot tap from the pole ground. Others you must bring a ground up with you.



I've never seen this rule mandated except for voltages above about 20 KV and higher.

I would guess that you work for an REC. They have mostly 14.4/24.9 and of course you can get into ferroresonance by closing an unloaded Wye/Delta bank. With most companies the hands don't worry about this on 12470, 13.2, and 4 KV.

Used to work with an old boy who would sometimes sing a little ditty. The only line I can remember was. "Were you there the day we burned down the REA?"

[Boomer gone soft]

No, I don't work for an REA at this time.:rolleyes: I work for Alliant Energy (an investor owned utility). Before that, I worked for Xcel Energy (another investor owned utility). Before that I worked all over the country with the contractors.

Everywhere I have been, we have ALWAYS tied the floater in before opening or closing the cutouts on a wye-delta bank REGARDLESS of the feeder voltage.:rolleyes: This is to protect the cust. from 3rd harmonics and to protect the utility's metal-oxide arrestors as well as their transformers due to ferro resonance from the neutral shift. The switching problems are from a shift in the neutral when it is floating-- it has nothing to do with the voltages. THAT is why a reference to ground is required.

Additional information available at: http://books.google.com/books?id=2HoH512Z6xEC&pg=PA220&lpg=PA220&dq=wye+delta+float+neutral&source=web&ots=3TjIcfbj-C&sig=g20-3KGw3M8mg-mmH2wP7ZHQZsc&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA222,M1

BTW where I work and my previous experience is available on my profile and by viewing my previous posts.;)

[wtdoor67]

A person can usually just go by his past experience. I've never seen the high side grounded down on a Wye/Delta below 12 KV. Ferroresonance has been know about a long time. I've worked on about 5 properties with distb. from 34.5 Wye down to 2400 Delta and even the last few years where they had a lot of 34.5 they were just beginning to recognize that a grounding cutout was needed.

Harmonics protection for the customer was never mentioned where I have worked. I think in some states the problems of harmonics and problems that may ocurr for the customer are excluded in the various co's corporate legal agreements set forth in the public service agreements.

The only protection I've seen in this regard as far as metal oxide arresters are concerned was when they began to be mounted on the pots. Our specs. called on a Wye/Delta hookup for the arresters to be removed from the pots and continue to be arm mounted in the old conventional way. When the arresters are pot mounted in this hookup it is easy to see that with an open cutout that the arrester can be easily overstressed.

The reason I thought you might work for an REC was I have noticed a lot of their newer const. in 24.9/14.4 has a grounding cutout.

[LINEHAND]

What a "Breath of fresh air" your ass is.....:cool:


iTS CALLED being properly trianed in the trade!!!!! You dumb shit rat!!! Duh im not to dag gum there technical boys der really . . . . . . . . what!?!?! YOU DUMB RAT ****!!!!!~

[Boomer gone soft]

What a "Breath of fresh air" your ass is.....:cool:

whatever......I've been reading your posts for years and yet I remain unimpressed.

I never got involved due to you and others like you who insist on belittling others who may actually know more.....don't be intimidated--just use this forum for its purpose and learn something:rolleyes:

[Special ED]

I've never seen this rule mandated except for voltages above about 20 KV and higher.

I would guess that you work for an REC. They have mostly 14.4/24.9 and of course you can get into ferroresonance by closing an unloaded Wye/Delta bank. With most companies the hands don't worry about this on 12470, 13.2, and 4 KV.

Used to work with an old boy who would sometimes sing a little ditty. The only line I can remember was. "Were you there the day we burned down the REA?"


I'm with you WTDOOR.. REA work is the only time I've messed with ground switches like this for ferroresonance.

[billygoat]

you guys are my effin heros
im just starting my training on how not to die, so maybe later i can be around to learn trouble shooting
i had been repairing electric motors and gear boxs for a almost a year and my favorite days at work were the ones where i was scratchin my head

so if you don't mind telling me how does one get into trouble shooting position if there is such a position

[Boomer gone soft]

you guys are my effin heros
im just starting my training on how not to die, so maybe later i can be around to learn trouble shooting
i had been repairing electric motors and gear boxs for a almost a year and my favorite days at work were the ones where i was scratchin my head

so if you don't mind telling me how does one get into trouble shooting position if there is such a position


Yes, there is "such a position". They are called "troublemen" or "service reps".

We are journeyman linemen.

Step 1: pay attention
Step 2: top out
Step 3: don't get the cart before the horse;)

[johnbellamy]

you guys are my effin heros
im just starting my training on how not to die, so maybe later i can be around to learn trouble shooting
i had been repairing electric motors and gear boxs for a almost a year and my favorite days at work were the ones where i was scratchin my head

so if you don't mind telling me how does one get into trouble shooting position if there is such a position

Get burned out on all the new rules.

Piss the guy's off you work with.

Don't give a Fu$k no more.

And move to a small town like Touchet Wa.


Worked for me.

[johnbellamy]

I'm sorry, my bad.

[wtdoor67]

Typically a troubleman's job goes (in a Union shop) to the most senior person who bids or applies for it in a time frame given in the announcement bulletin for the job. Typical requirements are Journeyman status and perhaps a minimum time of service with the Co. Some agreements may have a stipulation that covers you if, for example, a job comes open while you are on vacation or sick etc. and don't know about it. Rare but sometimes happens. Occasionally a junior person will get a job such as this because no one else bids it. It happens sometimes. Some Co's have strange seniority requirements.

For a non-Union co. Usually the one with the most smooch.

[billygoat]

thanks for the info. its funny though this is the first trade i've been in that the older guy who know thier sh1t will take the time to help the younger guys who don't know anything.

[shaun]

120/208 wye bank. B phase is clear. (cut clear, no voltage,animal contact) The transformers are csp's and the sec switch turned to open on all trans. The county electricians wanted to clean out the meter pan because of mice living inside. When they tested the lugs they had 300V to ground on one? I had to pull the leads out of the transformers to make sure they were safe. Could a transformer (wye) leak voltage through the switch (if the pot was bad) or because b phase was shot? I turned the job in as replace the whole bank but they only replaced B phase transformer. The crew was getting 520V at A phase pot to grd when they came to fix it. The neutral was good. Their main was open.

[tramp67]

1) Don't count on the secondary breakers on CSP's as disconnecting means, there's no visual open
2) Open the high side - remove stingers, open cutouts if they are being used (some places use cutouts even with CSPs)
3) If you have a bad neutral connection, this could be another cause of the strange voltage readings at the meter or CT cabinet. Driving a temporary ground as a reference is a good way to test for this problem.

[wtdoor67]

It's not Kosher to use CSP's in a bank. Shouldn't be done. Not prudent.

[CPOPE]

It's not Kosher to use CSP's in a bank. Shouldn't be done. Not prudent.
Simple generalized answer to a complex question. Why can't you bank em?
http://rlv.zcache.com/reasonably_prudent_person_tshirt-p235460683912953865qzgo_400.jpg
Basically I think it's OK to use CSP's in a 240V application but when you pop the cover to parallel the coils in a 120/208 application current through the breaker doubles....... Correct?

The completely self-protected (CSP) transformer
typically includes:

Externallygapped silicon carbideprimaryarrester
Internal weak linkfuse
Internal secondary breaker
This protection scheme has technical merit and should provide a more reliable installation than a typical conventional transformerinstallation. However, utilities have continued to be concerned with the CSPtransformer
for many reasons, including:

No visible indication of failure
Continuity of service was more important than verloadprotection
Breaker operating problem-shafts, handles,
linkages,emergencyoverload,signal lights, etc.
Breaker calibration Concerns
Nuisance fuse blowings of internal weak link fuses

The nuisance fuse blowings of internal weak link fusesprobably hashadthe greatestimpacton aCSP user's decision to switch to conventional designs. This problem was identified as a serious concern by the REA administration, as early as 1950. The REA conducted a survey of their members in the early 1950's, concerning their experience with CSP transformers. The survey
results concluded that 13% of the failures of CSP transformers were causedby the internal weak link fuse blowing for no reason other than lightning. This resulted in an extended outage, since the transformer had to be replaced because the internal weak link fusewas not field
replaceable.

There was considerable speculation in that day that secondary surges were a major cause of these nuisance fuse blowings. Core saturation due to secondary surges was speculated to be one major cause of nuisance fuse
blowing especially where expulsion arresters were used onthe primary side of the transformer. This concern in addition to the above noted concerns prompted the utilities to move away from the CSP transformer.

Utilities have continued to move awayfrom CSPtype transformers to conventional transformers with remote fused cutouts and tank mounted arresters. Mainly because of increased sectionalizing capability where a smaller 3 or 6K fuse link on the high side allows for more coordinattion or better coordination with line sectionalizing fused disconnects

[wtdoor67]

I have an old engineering book that mentions this. However the only example it gives is of a Delta/Delta connection. The book says if the lighting pot is a CSP and the secondary breaker trips it will cause a "floating" neutral on the secondary which of course in case of any imbalance will possibly cause damage of any 120 volt load.

If it would do so on a Wye/Delta would be a good project for a sharp engineer to research.

I did find such a thing once on trouble but I do recall it was a Delta/Delta hookup such as the book mentions.

I would bet it would do so on a Wye/Delta also.

[Lineman North Florida]

FYI: The neutral must be tied in before energizing or de-energizing this bank. Some utilities (like Entergy) use a fourth cutout that is normally open. Some (like Xcel) have a "whisker" with a hot tap from the pole ground. Others you must bring a ground up with you.



I've never seen this rule mandated except for voltages above about 20 KV and higher.

I would guess that you work for an REC. They have mostly 14.4/24.9 and of course you can get into ferroresonance by closing an unloaded Wye/Delta bank. With most companies the hands don't worry about this on 12470, 13.2, and 4 KV.

Used to work with an old boy who would sometimes sing a little ditty. The only line I can remember was. "Were you there the day we burned down the REA?"
I have to agree with you WTDOOR our system is 12470 and never had a problem with ferroresonance on WYE\DELTA transformer banks except were there was 3 phase underground rising up a pole to feed an overhead bank, it would blow at least one arrestor when you tried to close it in, hung the fourth cutout and grounded down the floating neutral on the high side of the bank and it solved the problem, heard about it for years but this is the only scenario where I have seen it, probably because of the lower distribution voltage.

[wtdoor67]

You're right Florida hand. That UG can screw up a lot of stuff.


Quote~~~~~~~~
Basically I think it's OK to use CSP's in a 240V application but when you pop the cover to parallel the coils in a 120/208 application current through the breaker doubles....... Correct?

Why shore. That ought to tell you not to use them in a 208 bank. It's pretty simple to lift the lid and bypass the breaker though. Then you'd have to put up cutouts or call Swamp gas and ask him what to do.

[tramp67]

You're right Florida hand. That UG can screw up a lot of stuff.


Quote~~~~~~~~
Basically I think it's OK to use CSP's in a 240V application but when you pop the cover to parallel the coils in a 120/208 application current through the breaker doubles....... Correct?

Why shore. That ought to tell you not to use them in a 208 bank. It's pretty simple to lift the lid and bypass the breaker though. Then you'd have to put up cutouts or call Swamp gas and ask him what to do.

But you still are protected for the kva rating of the pot - cut voltage in half, current doubles. No problem there!:p

[wtdoor67]

I think what CPUPE er CPOPE was getting at was the doubling of the current might cause them secondary breakers to work improperly. I've no idea what they're set for normally. No offense now Chris.

[tramp67]

I have an old engineering book that mentions this. However the only example it gives is of a Delta/Delta connection. The book says if the lighting pot is a CSP and the secondary breaker trips it will cause a "floating" neutral on the secondary which of course in case of any imbalance will possibly cause damage of any 120 volt load.

If it would do so on a Wye/Delta would be a good project for a sharp engineer to research.

I did find such a thing once on trouble but I do recall it was a Delta/Delta hookup such as the book mentions.

I would bet it would do so on a Wye/Delta also.

If you had a bank consisting of CSP pots with a delta secondary, and the lighting pot tripped the secondary breaker, you would lose your ground reference for your bank, and you would have very strange voltage readings phase to neutral or phase to ground. Draw yourself a picture of a three phase delta secondary configuration, with your neutral connection. When you erase the lighter pot windings, as if the secondary breaker tripped, you would see something that looks a lot like an open delta connection. But the difference is that you have the 120 volt loads connected to the outside ends of the remaining windings. Those loads are of differing resistances, and they are connected together at the neutral bus, which no longer has any reference to your transformer bank. Therefore, whichever of your 120 volt legs has the lesser load, ie. higher resistance, will have a higher than 120 volt reading, and the other leg will have a corresponding lower voltage reading. If your 120 volt loads are balanced very closely, not much would be noticed. But if there was a large imbalance, you'd definitely run a risk of burning stuff up - boy, those lights sure got bright for a few seconds!!