Most common mistake.

[wtdoor67]

I have not set any records in longevity or most places worked. I only worked 36 years in the trade and mostly for about 4 power co's and a couple of govt. transmission entities.

The thing that I found most often done wrongly in distribution by troublemen is one little item. Consistently I found the simple thing of cutting a 3 pot bank to a 2 pot bank regularly missed by most troublemen. Every apprenticeship I've been party to always brings this up, that is changing a 3 pot to a 2 pot bank. Yet I can never recall a troubleman doing it. So simple. I doubt if most of them can decide the proper load and are afraid they'll overload the bank. I asked a guy once, after a lengthy outage , why he just didn't 2 pot it. He said. I thought it would change the rotation. Where I worked, the old closed Wye/Delta was and still is common as flies. They just don't think.

[Lineman North Florida]

Are transformers that scarce or hard to get in some places? I'm just wondering why you would'nt change out the pot, I understand how to make a open delta out of a closed delta as I am sure a lot of those troublemen that you are referring to do as well, I'm just curious why you consider it a mistake not to do it.

[wtdoor67]

I can recall offhand about 3 lengthy outages that could have been very short outages if this had been done.

I consider it a mistake to leave customers in the dark for 3 or 4 hours when you can usually make a 3 pot with a bad pot into an open Delta etc. in about 10 minutes. Not rocket science.

Went on a changeout crew at a small manufactoring plant. All the workers had arrived and the power had been off about 2 or 3 hrs. Some were gathering their things and getting in their cars as management had evidently told them to go home. We made an open wye/open delta quickly. They came back in and went to work. We spent about 20 minutes changing the bad pot. The original trouble man could have separated it.

Anytime a trouble man leaves customers in the dark for a lengthy time in these situations, I consider it a mistake.

[T-Man]

Let's see if I can explain in writting how easy it is:

In the Wye/Delta bank all the H1 bushings go to a seperate phase.

All the H2 bushings are tied together but not grounded.(floating)

Each X1 secondary is tied to an X3 on another tub so there is a series connection between the three tubs.

A tap from each one of these X1/X3 connections goes to the main or service.

To make it Open Wye/ Open Delta

Open the cutouts to de-energize

remove the H2 connection from the bad tub don't disconnect it from the other tubs and tie it to a ground.

Remove the X1 and X3 connections from from the bad tub, coil them seperate and maybe tape the ends keep them clear of each other.

Close the two good fused tubs and you should be able to get the 240 volt Open Delta power and the customer can operate at 57% of what they used to with three good tubs.

Like "Door" said, get the customer going then have a crew replace the bad tub later. This can be done relatively quickly, be sure to work safely.

[Lineman North Florida]

Your title was most common mistake, it was about outage times I understand where your coming from now thank's for clarfying, I have seen some great troublemen through the years but most of the one's that I have seen that would do what you are talking about ie leave people off for hours when there was a simple fix did so out of laziness not lack of knowledge.:D

[wtdoor67]

A little of both. I worked with a guy once who should have known better. To show you how experienced he was I recall he graduated from HS in 1945.

Been in linework since the early 50's. I lost track of the pots he bad ordered when they were good and vice versa. Just dumb and didn't want to climb a pole and pull the leads and then test. He always seemed to guess the wrong way. Incidentally was an IBEW hand from the get go.

The thing that irritated me most was management never said a word to him. He would not have wanted me to be his boss.

[watzamta]

Hey 67 I have one for ya. Kinda goes along with your origanal post. A week ago we got called out on a partial light call. Found two power tubs smoked in a closed wye delta bank. Lighting tub was a 50kva power tubs were 25kva's. The fuses on the 25's were blown. Bank was brand new about month and a half old. The bank was built by an outside contractor so I'am not sure of the standards where they come from. The bank was two bushing conventional tubs. We build this bank with a floating neutral unless we open it then we ground the high side. They bonded the high side bushings to the system neutral. The bank was not over loaded. The fusing was wrong they had 25k's in the power tubs and a 30n inthe lighting tub. It fed a small motel and a single house. Weekend,hot day you know. I'am assuming the combination the three H2's being bonded the fuses that were two large(causing the tubs to burn up rather then blow a proper size fuse) and the load of a hot day caused this bank to fail. Remember the bank did work for a month and a half. Any thoughts?

[Edge]

Hey 67 I have one for ya. Kinda goes along with your origanal post. A week ago we got called out on a partial light call. Found two power tubs smoked in a closed wye delta bank. Lighting tub was a 50kva power tubs were 25kva's. The fuses on the 25's were blown. Bank was brand new about month and a half old. The bank was built by an outside contractor so I'am not sure of the standards where they come from. The bank was two bushing conventional tubs. We build this bank with a floating neutral unless we open it then we ground the high side. They bonded the high side bushings to the system neutral. The bank was not over loaded. The fusing was wrong they had 25k's in the power tubs and a 30n inthe lighting tub. It fed a small motel and a single house. Weekend,hot day you know. I'am assuming the combination the three H2's being bonded the fuses that were two large(causing the tubs to burn up rather then blow a proper size fuse) and the load of a hot day caused this bank to fail. Remember the bank did work for a month and a half. Any thoughts?

simple really... once the high side bushing were bonded to the system neutral it became a grounding bank for the entire primary system... anytime there was a blink along the primary feeder the secondary coils will fluctuate trying to balance the system... if fused properly u usually have a fizzled fuse at the bank and the link looks more like overload then if it took a fault.... which is why you float the wye on a wye/delta...

you bond the high side neutral for switchin to avoid sympathetic tripin... when your switching.... if you don't shunt the high side neutrals to the system while switching 9 times out of ten you shut in a phase no problem you shut in B or C and then KABLAMO! they basicly buck phases... they wont to then when the neutrals are tyed...

so tye the float do your switching untye and return to float...

maybe someone else can explain it better...



for what it's worth...

Edge

[wtdoor67]

On a closed Wye/Delta it's a mistake. Ordinarily it'll just burn up one pot and then the other 2 remaining just sit there. As the voltage is normal no one complains. Eventually overload will kill another pot and then you have to go and change 2. I've seen it where the little primary wire to the H1 or
H2 (which ever they're using) would burn into and not blow the cutout. Everything looks normal until another pot bites the dirt. You go out, change the one with the blown fuse, float the high side and it's still screwed up. Worked at a Muni once and they had a bunch like that. I always checked all 3 pots if it had been hooked into the system neutral.

I saw a big platform bank once and thought I'd be smart as I noticed it was not floated, but hooked into the system neutral. I went up and cut the tie to the system neutral. It was a driveup bank. Lady came out and said. Our electricity is messed up. I went up and rehooked it and it went back to normal. I amp tonged the secondaries and you could tell which pot wasn't putting out although the cutout was good. We went and got another pot and changed the bad one and "floated" the sucker. I told the guys. I don't care if they're all like that in town I'm not messing with any more of em. Sometimes it don't pay to be a good guy.

They had a contractor cut over a bunch of 4160 to 13200 in a small town where I formerly worked. The Elliot Davis boys grounded all the closed Wye/Delta banks to the system neutral. By and by a take off or line fuse feeding several of these banks blew. This caused all the banks hooked incorrectly to began backfeeding into this phase with the blown fuse. It burned up about 7 or 8 pots in about an hour's time.

[MI-Lineman]

On a closed Wye/Delta it's a mistake. Ordinarily it'll just burn up one pot and then the other 2 remaining just sit there. As the voltage is normal no one complains. Eventually overload will kill another pot and then you have to go and change 2. I've seen it where the little primary wire to the H1 or
H2 (which ever they're using) would burn into and not blow the cutout. Everything looks normal until another pot bites the dirt. You go out, change the one with the blown fuse, float the high side and it's still screwed up. Worked at a Muni once and they had a bunch like that. I always checked all 3 pots if it had been hooked into the system neutral.

I saw a big platform bank once and thought I'd be smart as I noticed it was not floated, but hooked into the system neutral. I went up and cut the tie to the system neutral. It was a driveup bank. Lady came out and said. Our electricity is messed up. I went up and rehooked it and it went back to normal. I amp tonged the secondaries and you could tell which pot wasn't putting out although the cutout was good. We went and got another pot and changed the bad one and "floated" the sucker. I told the guys. I don't care if they're all like that in town I'm not messing with any more of em. Sometimes it don't pay to be a good guy.

They had a contractor cut over a bunch of 4160 to 13200 in a small town where I formerly worked. The Elliot Davis boys grounded all the closed Wye/Delta banks to the system neutral. By and by a take off or line fuse feeding several of these banks blew. This caused all the banks hooked incorrectly to began backfeeding into this phase with the blown fuse. It burned up about 7 or 8 pots in about an hour's time.

We had a contractor do that same thing here!:D Used single bushing pots for about a half dozen banks on a reconductor they were doing! I'm not sure what their voltage out there was but they swapped all these over in a day and later that night the businesses were callin in complaints of screwy voltages! Our guys must have made a killin that night!

Funny thing is IT WAS ON THEIR PRINT!!!!:eek: WHO'S THAT REMIND YA OF??:D AND YES THEY WERE UNION CONTRACTORS!!!!::rolleyes:

[heelwinch]

We had a contractor do that same thing here!:D Used single bushing pots for about a half dozen banks on a reconductor they were doing! I'm not sure what their voltage out there was but they swapped all these over in a day and later that night the businesses were callin in complaints of screwy voltages! Our guys must have made a killin that night!

Funny thing is IT WAS ON THEIR PRINT!!!!:eek: WHO'S THAT REMIND YA OF??:D AND YES THEY WERE UNION CONTRACTORS!!!!::rolleyes:

WHo issued them the single bushed pots? We normally got our materials from the co. we were working for.

Can't remember only a handfull of government jobs where the contractor ordered materials from the vendor.

[MI-Lineman]

WHo issued them the single bushed pots? We normally got our materials from the co. we were working for.

Can't remember only a handfull of government jobs where the contractor ordered materials from the vendor.

YEP! That's a good question! The same engineers who drew up the job! The store room people then set the material out for them and they wouldn't know! But OUR engineers should've! AND THE GUYS HANGING THEM SEEING HOW THEY ALSO HAD THE OLD BANKS TO REFERENCE!

The job still showed the banks as wye/deltas NOT wye/wyes!!!;)

[Trbl639]

67..............

I have cut a lot of banks 2 pot when I was a T-man..................but usually if there was a long delay before a crew would be getting there, or another T-man to help me change the bad pot.........................on most occasions, it was less than an hour or maybe 2 tops before we had the customer back on.........our SOP was to change it then if we had a replacement pot...there were times, on holidays, were hands were real scarce and we cut it 2 pot.or if we didn't have a replacement on hand......

I can remember 1 outage, early 80's, when I was on the crew and we had either a 250 or 333KVA bad feeding the courthouse/sheriff's ofc/jail and no replacement was available for 4 days (holiday)...............the foreman and sr lineman and supt were scratching their heads (all had more years than me) and I suggested going 2 pots and they were like ............damn why didn't I think about that!!

[wtdoor67]

one I was ever aware of was a small makeshift type sub. Source was 13.2 and the secondary was 2400 delta. The hookup was Delta/Delta. The load was probably about 60 or so residential customers and I don't even know if it had any 3 phase customers.

They were off at least 16 hrs. to my recollection. It wouldn't have been so bad if about 7 hands weren't involved. Admittedly 5 of them were sub hands but the 2 original hands were supposedly old salt linemen. Probably would have taken 30 to 45 minutes to get the folks back on. I just thought they were very stupid. The 3 pots were 250's. Pitiful. One bad pot.

One thing about it I never made a mistake. I thought I did once but I later found out I hadn't.