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Old 06-27-2009, 10:05 AM   #16
 
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A transformer in my backyard was replaced last night. The guys had a nifty little machine like the one in the pictures above.

The power had been out for several hours. It has been extremely hot down here (La Porte, TX) 100 plus everyday. I was glad to let them in my yard. lol

What are some common causes for a transformer to go bad? Is ( are ) the new one(s) better? Are they more efficient to me the consumer?

Just curious


Thanks
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Old 06-27-2009, 12:37 PM   #17
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Originally Posted by coolfords View Post

What are some common causes for a transformer to go bad? Is ( are ) the new one(s) better? Are they more efficient to me the consumer?

Just curious


Thanks
Recent standards have been passed that require all transformer manufacturers to meet extremely stringent efficiency guidelines. Of course, this also makes them much more expensive. They are generally rated in terms of full load losses (the energy dissipated as heat within the transformer itself at full load) and no load losses (the energy consumed with no load on the transformer).

Old ones in some ways were better than new ones in that they were larger (more oil = more cooling, more steel in the cores, etc.) which usually let them handle overloads better. When you design something with a slide rule
instead of a computer, you tend to build in a little more oomph.

Transformers will last decades if adequately protected from surges (lightning) and not overloaded for extended periods of time. The insulation is cellulose (paper) in oil (which also serves as an insulation and a heat transfer medium), which will degrade in time when exposed to heat, oxygen, or moisture. Eventually it can deteriorate to the point that it shorts internally.
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Old 06-27-2009, 07:58 PM   #18
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Originally Posted by AndrewF View Post
I live in a somewhat rural area. The primary out here is 7200.
Given a sparser population, namely longer distances between homes, I would have expected the primary voltage to be higher.

Now a 12.5 KV (hot to hot aka phase to phase) 3 phase primary circuit has phase to ground voltage of approximately 7200 volts.

Also, if a system had pole transformers with 4160 volt primaries, designed for the older 2400/4160 volt feed, then it is conceivable that it could be upgraded to 4160 volt phase to ground and the equivalent phase to phase voltage is 7200. Raising the primary voltage allows the same wires to carry more watts with less percentage loss, and serve more or heavier users. There is still a limit to how high the voltage can go before other things like pole insulators need to be upgraded.

Most distribution circuits are three phase as they leave the substation although some streets will have just one or perhaps two of the phase conductors strung on the poles and supplying the houses. The nominal voltage is the phase to phase voltage, for example 12.5 KV phase to phase, 7200 volt phase to ground is called a 12.5 KV circuit. In order for a customer to have three phase power, all three phases of the distribution lines have to come down his street and usually three standard (single phase) pole transformers are installed side by side.
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Last edited by AllanJ; 06-30-2009 at 08:16 AM.
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Old 06-29-2009, 01:04 PM   #19
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issue of longevity of transformer life


The transofrmer windings (primary vs. secondary) are designed on a ratio basis. (usually 10/1)! The higher voltage range is reserved for long distance transmission. The medium range is usually for intra-city (sub-station) distribution. and the pole-transformers are actually called Distribution transformers. It's not practical (even if theoretically possible) to reduce voltage from 250,000 to 240v.!!!Don't Drink and Drive!!!
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Old 06-30-2009, 12:34 AM   #20
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Generally speaking, the voltage of distribution lines (the ones that transformers that feed houses and such are connected to) are 2400/4160; 7200/12,470; 7616/13,200; 13,800 (usually a 3 wire delta, common in power plants), 13,200/22,860; 14,400/24,940; and 34,500 (again, usually a 3 wire delta, more transmission than distribution). This is not an exhaustive list, there are others but they're rare.

Transmission lines (the kind that go from power plants to substations or subs to subs) are usually 3 wire. The feed transformers are usually wye connected, and the neutral is used for ground fault detection only. The common voltages here are 34,500; 60,000; 69,000, 120,000; 230,000; 345,000, and 500,000. The highest voltage transmission line I've ever heard of is 765,000 volts. After you've worked on enough of these, you can pretty much tell what the voltage is just by looking at the line and insulators, though 60 and 69 look alot alike, and 345 and 500 look similar as well.

Sort of interesting to note, 34,500 connected delta is (obviously) 34,500. 34,500 connected wye is 60,000. 69,000 connected wye is 120,000.

Transformers are made that will reduce 500,000 volts to 120, but they're potential transformers. Very low current, usually milliamps. Used for instrumentation, not driving loads. These transformers are capacitor coupled, not core-and-coils. The ones I've seen are about 2' diameter and about 20' long, not counting the insulator on top.

All the different components that go into a transmission and distribution system are really interesting.
Well, to at least one of us anyway.

Rob
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Old 06-30-2009, 06:23 PM   #21
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All the different components that go into a transmission and distribution system are really interesting.
Well, to at least one of us anyway.

Rob
Me thinks there lies a closet POCO employee behind that "World Class Bilge Rat" moniker.
Nice post!

Quote:
originally Posted by InPhase277 How strange... there appears to only be two guys watching the guy on the pole. Usually, there's at least four guys doing nothing.

Waaaaay harsh, dude! Must have been a Union job!
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Old 06-30-2009, 08:36 PM   #22
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That must of been impressive to watch. Those things look quite heavy too. I'ive picked up small transformers (10v 1:1 isolation, and stuff of that kind) and those are quite heavy on their own.

Would be fun to play with a functional pole transformer. Build a nice tesla coil or something.
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Old 06-30-2009, 09:16 PM   #23
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Actually, I've never worked directly for a POCO, but the one around here hires electrical contractors for linework fairly regularly.

Most of it is underground, new development and such, once in a while we get to play with overhead though. Sometimes we'll get to do a whole substation or a switchyard. Meterhouses are always enjoyable.

Mostly I do commercial/industrial inside wire. Linemen have a nickname for inside wiremen, 'narrowbacks'. (Mainly because they view us as wimps.) Since I do both inside and outside, does that make me a 'switchback'?!??

Inside wiremen who are familiar with linework have a nickname for linemen, 'knuckle-dragging stump jumpers'.

Both of these are usually used affectionately, but sometimes....

Rob
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