Some of the old-timers remind me that once, we used 25 Hz, but 60 Hz was more efficient.

DC voltage was quite common before this. The streetcars ran on 600VDC, which was about the max the insulation of the motors could handle. Factories had DC generators as well. Pratt Institute in Brooklyn was an old shoe factory and had steam DC generators that were regularly used even into the 1970s.

You'll need to do web searches for Tesla, Niagara, Columbian Exposition, and Westinghouse to follow the development of power.
I'm not aware of any significant 25 cycle power in the states.

Update with source links:

http://www.iaw.com/~falls/power.html
"Today, eleven generators produce 10,000 horsepower (7,500 kilowatts). The generators have vertical shafts, wound for three-phase current, producing 11,000 volts of 25 cycle power at 250 revolutions per minute...
The current water rights agreement that supplies this power station expires in 2009. Negotiations are underway with Ontario Power Generation and the Niagara Parks Commission in order to renew this lease and to allow a switch from its current 25 hertz power to 60 hertz power."
http://www.execulink.com/~ocbogs/oxhquiz/oxha046.html
Aside from a fairly comprehensive answer about the changeover there is this blurb-
"Also, there was a power plant at St. Catharines, called DeCew Falls, that took its water from the Welland Canal. It was constructed about 1898 and has continued to supply power to Hamilton. It still had its original German turbines and had a most unusual frequency of 66 2/3 cycles"

This leads to the best explanation at: http://www.antiquewireless.org/otb/60cycles.htm

"When Westinghouse and others were determining the frequency for alternating current back in 1889 and 1890, several frequencies were developed. One of the first to be used was 133. (twice the 66 2/3 noted above) The choice of this odd frequency was based on their generating unit which ran at 2000 rpm, had 8 poles and gave 16,000 alternations per minute or 133 1/3 cycles (16, 000 divided by complete alternation or 60 plus 60 = 133 1/3).

Other frequencies were tried depending on the power source: steam engines and water power. The cylinder type steam engine ran at a relatively low speed. At one time some thought was given to 16 2/3 cycles since an 8-pole generator at a lesser driving speed gave 2000 alternations or 16 2/3 cycles.

The lower frequencies worked great for large low rpm electric motors but were impractical for lighting purposes because of the pronounced lamp flicker.

A strong contender and one used for many years, particularly in heavy industry, was 25 cycles. This frequency originated at the Niagara Falls hydro power plant in the 1890's. After several compromises they settled on a 12 pole, 250 rpm machine which gave 3000 alternations or 25 cycles. It is only in recent years that 25 cycle has been phased out in most industry.

High speed turbo generators did the trick for soon six-pole, 1800 rpm generators became standard giving 60 cycles which was a compromise for drive speed and machine design. "

When Tesla was designing his electric motor, Westinghouse engineers wanted him to design it for 133 cycle power. Tesla had his way at 60 cycles, which was a compromise that allowed power to supply both reasonably powerful motors (especially if gear-reduced to provide torque) and flicker-free lighting effectively. Generating systems installed after Niagara found 60 cycle power cost less to generate and distribute because the single triad of wires (plus ground) could supply all needs rather than requiring seperate distribution wires for power and lighting. My sense is that industry eventually found these smaller 60 cycle motors much more efficient and less costly than huge motors for most applications. Remember that early industry used water power with a large shaft driving leather belts which then powered individual tools. Initial conversions were probably made by replacing the water turbine with a single large motor. As smaller motors became more practical, many industries would have changed over. At some point early on, the general demand for 60 cycle power would have outstripped the demand for 25 hz power, but Niagara was invested in its own system and couldn't afford to change over cheaply. The final straw was the tremendously efficient flourescent lighting, which would flicker badly at low frequencies, thus requiring higher frequency power or individual vibrating contact converters on the lamps (this was before solid state electronics). Interestingly, many of today's compact flourescents incorporate their own frequency converter to up the frequency even more and provide flickerless light.

More detailed info on Niagara is available at: http://www.rootsweb.com/~onniagar/history/hydro.htm
"There was also the question of what frequency to use and here the outcome was not so fortunate. In the fall of 1892 the Westinghouse Company had adopted the two standard frequencies; 60 cycles per second for lighting; 30 cycles where power in large units and rotary converters were to be used. At Niagara, what was required was electric power with incidental lighting rather than electric light with incidental power. It was hoped that the flicker in the lights due to the low frequency would not be objectionable , or that some way would be found eventually of eliminating it. Vain hope. As mentioned above, the speed of the turbines had been set at 250 rpm. Finally it was agreed that the generators should have 12 poles and this gave 25 cycles per second. This same frequency was adopted at all the earlier plants at Niagara whereas 60 cycles was adopted gradually elsewhere. The result was that in time Niagara became a 25-cycle island in a 60-cycle continent. Finally, the introduction of fluorescent lighting tipped the scale. The change to 60 cycles for all domestic lines was made first on the United States side of the river and this was followed later by the Hydro-Electric Power Commission of Ontario (Ontario Hydro). However, many of the large electro-chemical plants still use 25 cycles and are supplied either from the remaining 25-cycle generators or by converters. "

Still more on Niagara and the area in general: http://www.nywea.org/303020.html
"The tunnels allowed the construction of combined sewers throughout the area, which discharged into the tunnels at drop shafts.
Waste loadings grew as the city grew, eventually causing legitimate concerns about human health, wildlife effects, and tourism aesthetics. Incidents, such as showering Great Gorge Route passengers with garbage and sewage one July afternoon when a plugged pipe suddenly cleared, earned more visibility for the problem. "

Power in the U.S. is generally 120 volts RMS (160-170 peak) for household use. For a good overview;
http://www.howstuffworks.com/power.htm

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Cheers, Thomas
..in70mm - The 70mm Newsletter

Of course there is a certin amount of variation allowed. In the UK at the moment I believe it is -5% +10% and in mainland Europe -10% + 5%.

But shortly it will be +/- 10% all over Europe giving us a range of 207 to 253volts . And this truly screws up the sensitive amps from Sonics

The Chicago "El" system (subway/elevated lines) still uses a third-rail DC power system, so high-power DC is not yet extinct.

I remember reading a book about Tesla & Edison, and one of the "disadvantages" of municipal DC power is that every time someone accidently creates a short circuit on an unfused DC line, it melts the transmission wires from the short all the way back to the generator!

The article was about whether New York city should standardize the type of electricy sent to homes and business's. At the time, you bought your power from whichever power company was closest, which could be direct current (DC) or alternating current (AC). To reduce costs, it was recognized that it would be more efficent to share available power across the city, for distribution to homes and business's. Since taxpayers would be helping to pay for this distribution system, every decent proposal had to be considered.

Thomas Edison, (considered a "god" of technology at the time) wanted to use DC. He said that DC provides more raw power (which is true.)

George Westinghouse (founder of General Electric) proposed using AC. AC's voltage can be stepped up or down using simple transformers. The benefit is that if electricy is going to be sent over long distances, stepping up the voltage allows thinner (and cheaper) wire to be used for the long distance. It can then be stepped down to a usable level. However, because it cycles, it does not have as much raw power as DC.

Thomas Edison did not get along with George Westinghouse, and was quite upset when goverment and industry people preferred the practical cost-savings of AC.

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To quote a friend:
"Most interurban cars had at least two different motor configurations
that were used, depending on the speed the car needed to move at.
From rest up to the first normal running speed the motors were
connected in series with each other, and a set of resistances was
quickly cut out in turn until the series connected motors were on
full line voltage, with each motor getting 50% of that voltage. The
motors were then reconnected in parallel and the resistances again cut
out in turn until the motors were running on in parallel on full line
voltage, with each motor getting 100% of the line voltage. (These steps are the surges of acceleration felt in a streetcar.)

All the connection changes were done in the controller as the motorman
moved the handle around. A controller could have up to a dozen of so
"notches" but only two of those were "running notches" that could be
held for prolonged periods. All the other were "resistances notches"
that had to be passed through quickly as the car accelerated.

The result was that the car had two "balancing speed" at "full series"
and "full parallel" notches, either of which could be maintained
indefinitely (track and power permitting), but any other speed could
only be attained while accelerating, braking, coasting, or under power
for only very short time, such as shunting at the car barn. If the
resistances had power applied to them for too long they would burn
out.

So, even when the line voltage was as low as 50% of normal, the car
could be "notched up" to full parallel and would still move, but only
at the speed you'd get from normal full series operation.

The "balancing speeds" for a particular car were set by a combination
of the wind resistance of the car, the horsepower of the motors, the
gear ratio, the size of the wheels, the grade and the trolley wire
voltage."

Early trolley power distribution systems often had line drops of as much as 50% of the voltage from line losses. A line that I have been researching had two copper 4 ought power wires and power was at 50% about 8 miles away from the generator. Without such motor configurations, the trolleys would never have been able to get up the hill there. As it was, the freight motors pulling a car would barely creep along.

Modern trolleys may use "chopper" technology to control voltage. DC traction motors are a different beast than AC motors and at slow speeds are capable of creating tremendous torque (and waste heat) where an AC motor will stall out, which is why Edison was able to make the claim about "raw power." In point of fact, a watt is the same amount of power whether it measures AC or DC.

Many years ago, my home was plagued with low voltage "brownout" problems, especially in the summer. By documenting the pattern of voltage variations to the power company, they installed a new pole transformer close to my house with fewer households on-line, solving the problem.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

An example of what I mean can be found at http://www.rcmtravelsite.com/ta_ndx/elec_rgt/elec_rgt.htm

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How did they reduce the voltage to the operating range required for a carbon arc lamp? A typical 11mm x 20-inch High Intensity rotating carbon trim would run at 120 amperes and only about 65 volts. Using a resistive ballast would certainly waste lots of power and generate lots of heat. Striking the arc with 440 volts open circuit would generate quite a few sparks and probably vaporize the carbons!!!

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion