Padmount Questions

[Electriceel]

Wondering how many trust the phasing to be correct from the mfg. of padmount transformers, is H1A the same phase as H1B and so on?

Has anyone ever tried using a spray on silicone product for new de-energized elbows, seems the provided silicone does not work that well or else we are not getting installed properly?
:mad::mad:I know this issue has been brought up before.

[topgroove]

Any time you find a elbow on a stand-off in a padmount always check phase before plugging it in. Never use the spray on silicone along with the Gell type, the two together seam to form a glue over time. you'll end up pulling the pad off its base before you lift the elbow. Large tubes of silicone are available from elastamold. Its a storeroom item for us.

[Special ED]

Yeah.. Im with Topgroove on this one.. Always check your phasing before you plug in an elbow.. For example you went to the NO on a URD loop feed and had to close it. Some of our loop feeds say on the print and in the dispatch control center that they its fed off of A phase on both sides for example but upon further investigation you will find it is actually fed from A phase on one end and B phase on the other.

So basically prove to yourself with out a shadow of a doubt the phasing is correct.. Cover your own ass..

[44kv]

we have had one a couple of years ago from abb that was not right, right from the factory h1a was hooked to h3b inside the xformer and when we turned the handle from just the feed from the a side to the a and b side it went phase to phase in the back of the padmount and blowed the cutout doors opened and because our sub breakers are set to trip at 480 amps it blinked one of are subs

[Electriceel]

We keep the silicone around in the tubes also, just need to get the rest of the know-it-alls to use it.

I knew someone on here had a case where the unit was wired incorrectly from the factory, same as above, seems anyone under the age of 30 has hearing problems or maybe plugged up ears, then the supervisors seem to have deaf ears when they are told that just because the factory built it does not mean it is correct.

Thanks for the input guys!;)

[topgroove]

with single phase padmount transformers with only one single phase feed there is really no possibility for a phase angle shift. I have heard of problems with 3 phase transformers wired incorectly from the factory. Thats why we always build the new installation and then energize it and test voltage before any load is installed. With that said... I have seen cases where the three phase transformers inpedence and the primary conducter capacitence just happened to be perfectly matched. That becomes a huge problem when you close the switches in one at a time.

[T-Man]

We have had the oppurtunity to tour the Coopper transformer plant and see how Transformers are made. I was amazed at what bells and whistles can be added to a Padmount transformer. Oil temp Gauge, Load break switches, Phase potential lights, you name it, it can be installed for a price of course. You open the door and there are gauges all over inside them things. . .who comes out to read that stuff and why? They will paint them any color and wire them anyway you want them to be wired. So when you think they screwed up at the factory maybe all thay did is ship you some other outfits transformer. I have had three phase units with the H1a and H1b on the left side then the H2a and H2b on the bottom and the H3a and H3b on the right side. All of our normal three phase Pads are H1a, H2a, H3a on the left and
H1b, H2b, H3b on the right in a V shape. So in the wrong Pad If you don't catch the way iot's laid out you will have big problems. So when Groove says Phase before you close on three phase he means it. . .

[JUS]

with single phase padmount transformers with only one single phase feed there is really no possibility for a phase angle shift. I have heard of problems with 3 phase transformers wired incorectly from the factory. Thats why we always build the new installation and then energize it and test voltage before any load is installed. With that said... I have seen cases where the three phase transformers inpedence and the primary conducter capacitence just happened to be perfectly matched. That becomes a huge problem when you close the switches in one at a time.


Ferro resonance.

We had problems with Powell's, which were made in Mexico. We dropped them and later had the same issues with Howard's...which were being made in America by illegal Mexican immigrants...go figure.

[topgroove]

we could start a new thread on Ferro resonance. I only touched on it briefly here. whenever you do single phase switching on a three phase system with little or no load there is the posibilty for tremendous circulating current to develop. when I say single phase switching i'm talking about a set of three phase switches which you close one at a time. this problem gets much worse when you have transformer impedence which comes close or matches conductor capasitence. we've had banks of 333kva ratio banks explode like something out of a hollywood movie set. We also had a crew build a three phase ratio bank which fed underground primary to a switch gear. they finished the job and energized it to test voltage (no load). by the time they closed the third switch the underground primary was completely destroyed. they figured they must have got some bad conducter from the the manufacturer. they pulled in fresh conductor, this time from perelli and the exact same thing happened. had a lot of people scratching their heads. they finally tried placing a dummy load downstream of the switch gear and it solved the problem. Another way to solve this problem is to install a gang opperated switch that closes all three phases at once.

[THE KID]

is what we had when we had a new sub division tied to an old one. Energized the new line and 5 txs from a switch cabinet. We were going to check phasing on riser pole, when we plug in the 3rd phase it blew the arrester on the riser pole. we had no load on the txs. and thats why we had ferro resonance. Engineer said if we had just a little load on the line that we would not have the problem. We also have a ABB tx. that the tag is completly mark wrong.

[T-Man]

Ferro Resonance is usually associated with a Delta system feeding a Delta wound transformer. The capasitance comes from a length of cable.( The cable being a conductor and an insulator can work just like a capisitor.) The transformer being coils of wire wrapped around a steel core is the inductance.

When you energize this combination which has to almost be a "perfect storm" so to speak, the first and second energized cable have an added length, the current travels thru the delta windings of the Tr and backfeeds a return on the third cable adding to the length of the total capasitance. before you can close the third source you will most likely have ferro resonance develop which can increase the avaliable voltage by as much on paper as 11 times the source, but it's said probably only 6 times actually occurs. ( which is plenty)

The way to avoid this is to:

1. have load on the Tr, just a clip cord with a 100 watt bulb or your wifes hair dryer (don't tell her I said you could take it) is said to be enough.

2. gang switch the source. (same reason you gang operate a cap bank)

3. Or you could switch at the tr closing one treminator at a time but this is more risky because the prefect formula needs the right length of wire and the right induction. By switching at the tr you only add one cable at a time and don't have the thrid cable part of the equation till you close and then no problem. Not recommended just trying to give example of what can happen.

This is why ferro resonance is sneaky cause in some installations it won't show up , but on another with the same configuration but change in length or load it shows it's ugly head.

You yonger guys learn your trade and work safe.

T

[climbsomemore]

if capacitance and induction are "opposites" in AC therory.

If you get equal and opposite values of capacatance and induction in a circuit... resistance drops and voltage rises in that circuit.

In a wye fed-closed delta secondary bank the math with change if you place a temporary ground from the floating wye tie (all the H2 busings are tied together) to a known ground or grounded neutral the capacitance provided by the transformer itself is limited.

NEVER try to ground the floating H2's with one phase open All three phases have to be OPEN or CLOSED to install or remove the jumper without drawing an arc.

AEP and a couple of other companys have installed a solid blade switch and a warning sign on their 19.9/34.5 banks for that reason.

[climbsomemore]

I worked for a REA a while..

One day the radio goes off...."were are you? Me... out here around "walk and dont walk" in Radiator Springs... what do you need?

"Gotta extendo on the truck?"

YEP

"clear up and meet us at"

So I do... and drive about 40 miles to find those guys.

A new 3 phase closed delta bank in at a irrigation pump...

Those guys have 2 extendos in A & B... they want me and mine for C phase...

"1,2,3 close"... thats how REA's do it up north... LOL They didnt have a clue about the temprorary jumper or leaving some lights on for load or anything like that.

I cant make this stuff up... true story... and not that long ago.

[Bull Dog]

Always test, never trust the phasing and you will live long time. I have seen 3 phase pad mounts wired wrong internally right out of the factory. When switching or any time elbows are being plugged in test. Check for load with clip on. Use phase sticks. Test Test and never trust anyone. Especially some hillbilly in a factory in Tim Buck Too. Cover your ass at all times. If anyone tells you not to hand them the job. Its how you make it to retirement. I have seen a man not test an elbow. Then stick a tool in to remove a pecker. "He thought it was dead." He got a real big problem since he had leather gloves on and was kneeling on the bare ground. Never take anything for granted. Test and ground before you touch anything! Don't forget feed back can kill also. Three phase pad mounts can feed back into a single phase xfmr and even tough you have pulled the elbow it can have feed back. Never open a cover without rubber gloves. I have seen things inside of pad mounts that would make your eyes hurt. You don't know what you have till you open that cover. There could be a trap waiting to ketch you. Good luck be safe.

[44kv]

you know we still have alot of live front underground transformers on our system to and live front underground switch gear, they worry the hell out of me, I hate working on them even just changing a fuse is a job lol! were trying to get rid of them for dead fronts but you know how that goes (moneys tight right now maybe next year) yeah bullshit, so we change em only when they go bad right now

[thrasher]

As Bull Dog said you don't know what you will find when you open UG equipment. Worse case I knew of was we had a 175 Amp dip pole fuse go one cold morning. The crew drove thru the subdivision and did not see any potential dig-ins so they tried the fuse one time to make sure it wasn't aged. The fuse closed and held. However when we made call backs only 2/3 of the houses came back on. Started opening transformers and vaults to see what was going on. Opened a padmount (with gloves) and found the incoming elbow blown completely in two pieces with the burnt compression stud hanging out energized and about three inches from the door of the transformer. This was on a 7200 volt line with old 175mil XLP insulation, that was about 15 years old then.
Have also lost count of the number of times I have been inspecting new wire put in the ground by contractors (Union or Non-Union) and found the phase tagging wrong.
Don't assume anything. Test (and see the test yourself) then ground it or treat it as energized and carrying load.

[loodvig]

you know we still have alot of live front underground transformers on our system to and live front underground switch gear, they worry the hell out of me, I hate working on them even just changing a fuse is a job lol! were trying to get rid of them for dead fronts but you know how that goes (moneys tight right now maybe next year) yeah bullshit, so we change em only when they go bad right now

A few years ago a new building was built and they supplied their own padmount trans. It was an old live front. New paint! One of the crew noticed that the live bushings stuck out farther than the door! So when ya close the door it's a direct short!

[44kv]

lol yeah those live fronts worry the hell out of me every time i have to go in one!! I suit up for war when i get a call and know that there are live fronts out there, I would rather open or work on dead fronts anyday of the week lol!!!