Why 110 (now 120) volts?

[Jeff Wisnia]

From time to time I've wondered why the standard US lighting voltage was (when I was a kid) 110 volts and not a "rounder" number like 100 or maybe 150.

I think I may have located a believable answer, purportedly in Edison's own words, on page 66 of this document, under the heading "Why 110 Volts":

Now, can someone tell me when and why it was "increased" to 115 and then

120 volts? Will I live to see it become 125 volts in a few years?

Jeff

(Next, why did the early phonograph records revolve at 78 RPM? and have you ever wondered why 33 and 45 add up to 78?)

[dpb]

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Heck, I see anywhere from 123 to 130 now! (Although it usually seems closer to 127) :)

[Doug Miller]

"Earliest rotation speeds varied widely, but between 1900-1925 most records were recorded between 74-82 rpm. In 1925, 78.26 rpm was chosen as the standard because of the introduction of the electrically powered synchronous turntable motor. This motor ran at 3600 rpm with a 46:1 gear ratio which produced 78.26 rpm. In parts of the world that used 50 Hz current, the standard was 77.92 RPM ..."

[hallerb]

higher voltage reduces current a little too.....

euope uses higher voltage to keep conductors smaller, and remember the power to your home gets converted many times by transformers before arriving at your socket. low voltage can cause big grief so the keep raising it over ime

[Stubby]

True, but they use 50 Hz rather that 60 Hz in the US. That makes for bigger transformers. If we were serious about saving, we'd increase the frequency to about 10,000 Hz.

[Doug Miller]

Who's going to pay for replacing every alternating-current motor on the continent?

[Jeff Wisnia]

Plus I'd bet that the significantly higher capacitive currents between conductors would waste a huge amount of power in resistive losses.

IIRC 400Hz power was used in aircraft circa WWII, I lost track of whether it's still a standard there.

Jeff

[Mark Lloyd]

The frequency used also depends on the limits of rotating machinery (generators and motors). This decision was made before inexpensive power electronics made high frequency reasonable.

[gfretwell]

400hz is still used in aircraft. The computer industry used 400hz for their big machines up until fairly recently when switching power supplies and CMOS made it unnecessary. We used to have big MG sets in computer rooms or a switching UPS that provided the 400hz.

[Malcolm Hoar]

And how much energy would be consumed in the process of making the conversion?

[David Nebenzahl]

Jeff Wisnia spake thus:

I think 400 Hz or thereabouts is used in some electric rail transit systems (like BART).

[krw]

From what I can tell, most US systems are 60Hz since they can buy standard equipment. Some older systems are strange for historical reasons (generation equipment). I believe the NYC subway system is

25Hz, or some such. I'd be very surprised if any used 400Hz since saving weight isn't as important as reducing losses.

[Don Klipstein]

In , krw wrote in part:

If a transformer designed for 60 Hz is operated at 400 Hz, losses would be less than at 60 Hz, although output voltage with a heavy load may droop if not much work went into reducing leakage inductance. 400 Hz transformers at 400 Hz also normally have less losses than 60 Hz ones of same volt/amp ratings being operated at 60 Hz. And a 400 Hz transformer would cost less to make than a 60 Hz one of the same ratings, since it would be smaller and use fewer turns of wire.

The way I heard it, a lower frequency was preferred for motors and that's why 60 Hz was chosen. Also, 400 Hz could be high enough for wire inductance to be a problem with longer distance transmission lines, but I don't know how badly or if transmission line inductance affected 60 Hz being chosen for our main AC power frequency.

- Don Klipstein ( [e-mail])

[krw]

It's not an issue of transformer losses, rather distribution losses.

FOr the AUS distribution system? AFAIK, 60Hz was chosen because it was a good tradeoff of several variables (transformer cost, losses, generation ease, and likely a dozen other considerations). As far as locomotion, I believe 60Hz is rather recent and used because the equipment is off-the-shelf. Most older subway and commuter systems are in the 25Hz range. I highly doubt modern DE engines are 60Hz. ;-)

Capacitance?

I do believe it was one of the factors in the selection. Flicker could be the reason that it went no lower too. Dunno.

[David Nebenzahl]

krw spake thus:

Actually, it turns out that BART is 1,000 volts DC:

[David Nebenzahl]

David Nebenzahl spake thus:

Turns out the Apollo Lunar Module used 400 Hz power (that is, if Wikipedia is to be believed):

And the Monterey Bay Aquarium Research Institute's underwater ROV (Remotely Operated Vehicle) runs on 400 Hz: Lots of others if you google for "propulsion system" "400 hz" (with the quotes).

[Mikey S.]

Large aircraft ( like jetliners) are generally 400 Hz, 115/200 volts 3 phase ac , some smaller ones have 28 volt dc systems. The 400 Hz power is supplied on the ground either by engine driven alternators or by converters, they used to be large motor/generator sets but these have mostly been replaced by solid state converters, which are smaller, lighter and more efficient especially at low loads, though not so reliable as the old MG sets.

[JGolan]

[Rich256]

Primary reason for going to 400 Hz is that the instrumentation devices such as synchros and resolvers could be much smaller. There are some up to 1600 Hz.

[hallerb]

this permitted easy speed control dc motors are variable speed by nature, the high voltage keeps the conductor sizes down......