Transfrm and Mains Freq

[trem]

Another stellar explanation.
Thank you so much.
The Education/Experience level on this forum is both impressive and humbling.
Thanks Again

[Enzo]

I live in rural farm land. We have one hot high tension wire and a ground wire, strung pole to pole. Each house has a transformer on the pole to convert that to center tapped 240 for the house service panel. In town we see the three hot wires strung along.

[R.G.]

Yeah, so do I. Well, rural ranch and cactus land. Rural electrification runs differently from urban transmission. The price of wire is the biggie there, and the per-user power is small enough to make three phase uneconomical. This moves the three phase back to really big, remote transformers if they're used at all, and the distribution is 10kV and higher (usually, this varies a lot) single phase, single wire. This keeps the wire cost low by keeping the current down, and uses the planet itself as the return wire.

Rural stuff is high voltage single phase, but what goes into the house is still 240CT single phase in all the setups I know of. There are probably differences there too.

[J M Fahey]

@ Enzo: do you have any idea what that high voltage single wire is?
I'd think 1200/1600V would be a practical value, but of course would like actual data. Thanks.

@ Loudthud: to make life interesting, Brazil originally (LONG ago) used USA type flat blade plugs for 110V and round european pins for 220 , but since people moves around all the timeand most electrical stuff is bivolt, with corresponding switch, "for comaptibility"most common wall socket is dual flat/round type, accepting both, so you can NOT trust it at all.

[trem]

Interesting about the difference in distribution methods...Rural Vs. Urban.
I will have to see if any of that is mentioned in the few text books I have.....

[Enzo]

Juan, I have no idea. It is too cold to climb my pole with a meter. Maybe RG could do that, he is in a warmer climate.


I have 13kv in my head, but I think that is because I have been reading about railroads a lot lately, and 13kv is a common catenary voltage on electrified rail lines.

[R.G.]

I almost typed "13kV", but held myself back when I realized from my discussions with the line crew when they were bringing in my line and setting my pole/transformer that they talked about adusting taps. What I really think is that it's nominally 13kV, but tinkered with to get the nominal user voltage right with long lines and variable numbers of neighbors.

Next time I catch a crew nearby, I'll ask.

[g1]

They put a new transformer at our farm last year. It says:
25
Siemens
7.2kv x 14.4 kv
Before they put it up, they came by to let us know they would have to change it (and the pole to a much larger one). We moved here 40yrs ago so it was at least that old. I asked about the upgrade and it seems he said they were going from 7kvA to 21kvA though I could be mistaken. I wanted to find out about power rating so I asked when they came to do the job. 21kvA didn't sound like much to me, our furnace is 20kw alone, and we have what they call 400A farm service, with 200A into the house. The guy I asked didn't know much about it, but said it wasn't really a peak rating, I think he mentioned heat but not much else as far as an explanation.
If anyone knows about the power ratings for these big can transformers or what 21kva might mean, I'm all ears!

[Enzo]

Call your utility and ask them. The installation crew doesn't need to know anything about it other than "Install this unit at this address." They may well know a lot, but just like this business, if you bring me a Twin Reverb with a bad power transformer, all I need to know about it is the part number. I may know some voltage and current ratings, but to do my job, those are extra. Someone in the engineering department could probably tell you more than you want to know.


I have a customer here who happens to work at a local power plant, and we get into discussions of fluidized bed and all manner of esoteric power plant stuff.

[R.G.]

VA = "volt-ampere", that being the reactive version of a watt.

Because of the phase shift in loads, a load pulling 10A at 120V might NOT be pulling 1.2kW. It might only be using 800W. But the current flowing would still be 10A, and that's what heats the wire. For sizing transmission lines and transformer coils, they use the VA or kVA (kilo-volt-amp). I learned as the VAR - Volt-Amp-Reactive.

21kVA = 21 thousand volt-amps.

We have a 50kVA transformer out here; I found it only cost me $35 to get the 35kVA one they were going to put in upgraded, and I plan to put in a shop someday.

[Enzo]

I was about to walk into my house one night long ago, and noticed a raccoon climbing around on my utility pole. And just as I looked, he stepped between here and there and evaporated himself in a purple flash. Of course at that instant all the lights in my house went dark.

The repair crew came out after a while, and determined I needed a new transformer. They were out of the size I needed on their rtruck, so rather than driving 20 miles round trip to get the exact one, they just installed a larger size. I have no idea what size it is, nor what size I needed, but by golly I got a larger one than my neighbors. I can see it is physically larger than the old one was.

I have a 150A service panel in the house, and it sends power to my "garage" for a 60A sub-service out there.

Looks like I may have saved $35.

[R.G.]

Yep, $35 to the good. And you thought raccoons were electrically and economically useless.

[trobbins]

In Australia there are large rural areas serviced by such SWER distribution networks, where a SWER network is connected either directly (via a connection to one of the phases) or via an isolating transformer (primary connected phase-phase) to a 3-phase distribution network. Typical SWER network voltages here are 12.7kV and 19.1kV (the phase to earth equivalents of 22kV and 33kV 3ph networks) although some 11/6.4kV systems also exist. SWER networks can run for hundreds of kilometres and supply just tens of customers, each using a dedicated MV/LV transformer. I'm guessing the voltage tolerance and outage statistics would be not too good, especially if you were at the end of the SWER line !

[trem]

I was about to walk into my house one night long ago, and noticed a raccoon climbing around on my utility pole. And just as I looked, he stepped between here and there and evaporated himself in a purple flash. Of course at that instant all the lights in my house went dark.

The repair crew came out after a while, and determined I needed a new transformer. They were out of the size I needed on their rtruck, so rather than driving 20 miles round trip to get the exact one, they just installed a larger size. I have no idea what size it is, nor what size I needed, but by golly I got a larger one than my neighbors. I can see it is physically larger than the old one was.

I have a 150A service panel in the house, and it sends power to my "garage" for a 60A sub-service out there.

Looks like I may have saved $35.

Oh Christ...!!
I can see it now...rural Michiganders, standing out in the middle of the lane, corn-cob pipes huffing and puffing, and sneering and leering at Enzos new and BIGGER transformer...
..."Yep, a government conspiracy, that's what it is. Why does HE get a new one, and we have these dinky old jobs dating back from The New Deal. God Damn Democrats".
"What kind of a name is Enzo anyway...?? Sounds I-Tal-Yun to me. He's probably planning on brinigin' over the whole family from the old country. Aunts, Uncles, Cousins...the whole shootin' match. THAT'S why he got the bigger transformer to begin with, no doubt."

[Enzo]

Hey, what can I tell you? Mine is bigger than yours...