electric supply in the USA 3

[luca508]

Hi everybody,
could anybody tell me what kind of electric power Voltage I can expect to encounter in the US (single phase and 3 phase).
Also I would like to know what kind of tolerances I have to expect since the situation seems to me a little wilder than in the EU ;-)
If what I have heard is right in some places the Voltage is much higher and in some other wuch lower than what it is supposed to be.
Thanks
Luca

 

[jraef]

It is different from utility to utility, sorry.

In general, the 3 phase distribution is 208Y120, 230V delta or 480Y277. There are also plenty of variations to that, such as 230/120V Red Leg Delta, 230V Open Delta, 460V Delta etc. etc. All of these are "nominal" voltages, meaning that 208V may be 200V, 230V may be 220 or 240V, and 480V may be 460V.

Single phase is always 120/240V, but it may be 115/230 or 110/220 depending on the area.

Then you have some areas where they have 575V, and 1 or 2 others that still have 25Hz systems!

Tolerances are generally +-10%, but for instance if they supply 200V 3 phase, they generally will not allow that to go down to 180V because the 200V was already essentially 208V with some of the margin already used.

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[itsmoked]

Hey jraef where's that 25Hz lurking?

 

[jraef]

Around Niagra. Westinghouse and Tesla's first AC systems were 25Hz, and it was widespread at first. There are still some legacy systems in operation. Link

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[itsmoked]

Wow what a great site jraef!! Poor Buffalo, victum of the bleeding edge!

Thanks for that.

 

[jraef]

We had to make electronic controllers for somone in Buffalo who had 25Hz motors, that's how I found out. For the most part anything new with a motor is going in with 60Hz systems, it is just the older machinery (that STILL WORKS after 100 years by the way) that is problematic where frequency is concerned. I didn't get to actually see the machinery, but I heard it was cool.

I did get to work around some 2200V 25Hz wound rotor induction motor controls that were being replaced in Spokane Washington after 90 years of operation. Everything was yanked out and the new equipment was connected up to the 60Hz grid. The hydro generators, pumps and controls were built by Westinghouse in 1906, we replaced them in 1996. Controllers were the old open knife switches on giant slabs of slate, with uninsulated bus bars running around everywhere. One room where the resistor banks were located was so filled with open bus bars that it was called the "suicide room"! I have pix somewhere, but from the pre-digital camera days. If I ever get around to finding and scanning them, I'll post them.

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[itsmoked]

One room you don't want those keys hangn on your belt!

Can't most of the 25Hz motors be run through VFDs at 25Hz then when the motor finally croaks drop in a 60Hz? Spoze the 25Hz motors aren't rated for inverter duty!

 

[rcw retired EE]

I was shocked in that "suicide room" in 1970 while working on the granite slab control panels. Must have affected my brain because I am still working as an electrical engineer.

 

[itsmoked]

I can just see someone pin-balling around in there being thrown from shock to shock.

 

[BigWallyB]

Luca
"Also I would like to know what kind of tolerances I have to expect since the situation seems to me a little wilder than in the EU
If what I have heard is right in some places the Voltage is much higher and in some other wuch lower than what it is supposed to be."

This is just a WAG but somewhat in defense of North America and I'm sure I'll be told if its kooky. The EU was/is much smaller and more densly populated than NA. Line losses play a bigger role in tolerances here. Ie. originally, single phase was to be 110/220 Vac. When you got to the end of the line it was more like 100/200. So they boosted it to 115/230 and then to 120/240. Now in some areas one can measure 130/260.
So if one is lucky enough to live nearer the front end, kitty gets his food quicker cause the can opener runs a tad faster, but its life is a few monthts shorter (the can opener). U get the drift?

Cheers

Life is what happens while we're making other plans.

Wally

 

[jraef]

I had a can opener from the UK that needed 220V 50Hz, but I plugged into the 110V 60Hz kitchen outlet and it fried. My kitty died of starvation several weeks later

You are essentially correct BWB, but of course, you imply some intelligent design in all of that, and I doubt it wasn't that organized. As electrification demand grew prior to WWI, utilities sprang up in urban centers all over, each with their own solution to distribution problems. As they began to overlap, standards arose that blended some of those solutions with compromises all around. With the REA in the 30's, some semblance of order began to emerge but still there are different problems to overcome in every area, with varying solutions. We continue to struggle with that diversity to this day.

rcwilson,
Are you referring to that specific room at the hydro works in Spokane?


"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more."
Nikola Tesla

 

[Skogsgurra]

W&W! Awfully interesting, that Rankine station. Thanks jraef.

Gunnar Englund

http://www.gke.org

 

[luca508]

Thank you everybody now things are much clearer to me.
Bye
Luca

 

[rcw retired EE]

Jraef - I was zapped in the Monroe Street Station, but I think you were talking about the Upriver Dam, both on teh Spokane river.

 

[jraef]

Yes, I worked at the Upriver dam site. Still, it's a small world. My company upgraded the Monroe Street station a few years later, but I wasn't involved.