Many
different power frequencies were used in the 19th century. Very early isolated
AC generating schemes used arbitrary frequencies based on convenience for steam
engine, water turbine and electrical generator design. Frequencies between 16⅔ Hz and 133⅓ Hz were used on
different systems. For example, the city of Coventry, England, in 1895 had a
unique 87 Hz single-phase distribution system that was in use until 1906. The
proliferation of frequencies grew out of the rapid development of electrical
machines in the period 1880 through 1900. In the early incandescent lighting
period, single-phase AC was common and typical generators were 8-pole machines
operated at 2000 RPM, giving a frequency of 133 cycles per second.
Though
many theories exist, and quite a few entertaining urban legends, there is
little certitude in the details of the history of 60 Hz vs 50 Hz.
The
German company AEG (descended from a company founded by Edison in Germany)
built the first German generating facility to run at 50 Hz, allegedly because
60 was not a preferred number. AEG's choice of 50 Hz is thought by some to
relate to a more "metric-friendly" number than 60. At the time, AEG
had a virtual monopoly and their standard spread to the rest of Europe. After
observing flicker of lamps operated by the 40 Hz power transmitted by the
Lauffen-Frankfurt link in 1891, AEG raised their standard frequency to 50 Hz in
1891.
Westinghouse
Electric decided to standardize on a lower frequency to permit operation of
both electric lighting and induction motors on the same generating system.
Although 50 Hz was suitable for both, in 1890 Westinghouse considered that
existing arc-lighting equipment operated slightly better on 60 Hz, and so that
frequency was chosen.[5] Frequencies much below 50 Hz gave noticeable flicker
of arc or incandescent lighting. The operation of Tesla's induction motor
required a lower frequency than the 133 Hz common for lighting systems in 1890.
In 1893 General Electric Corporation, which was affiliated with AEG in Germany,
built a generating project at Mill Creek, California using 50 Hz, but changed
to 60 Hz a year later to maintain market share with the Westinghouse standard.
25
Hz origins
The
first generators at the Niagara Falls project, built by Westinghouse in 1895,
were 25 Hz because the turbine speed had already been set before alternating
current power transmission had been definitively selected. Westinghouse would
have selected a low frequency of 30 Hz to drive motor loads, but the turbines
for the project had already been specified at 250 RPM. The machines could have
been made to deliver 16⅔
Hz power suitable for heavy commutator-type motors but the Westinghouse company
objected that this would be undesirable for lighting, and suggested 33⅓ Hz. Eventually a
compromise of 25 Hz, with 12 pole 250 RPM generators, was chosen. Because the
Niagara project was so influential on electric power systems design, 25 Hz
prevailed as the North American standard for low-frequency AC.
40
Hz origins
A
General Electric study concluded that 40 Hz would have been a good compromise
between lighting, motor, and transmission needs, given the materials and
equipment available in the first quarter of the 20th Century. Several 40 Hz
systems were built. The Lauffen-Frankfurt demonstration used 40 Hz to transmit
power 175 km in 1891. A large interconnected 40 Hz network existed in
north-east England (the Newcastle-upon-Tyne Electric Supply Company, NESCO)
until the advent of the National Grid (UK) in the late 1920s, and projects in
Italy used 42 Hz. The oldest continuously-operating commercial hydroelectric
power plant in the United States, at Mechanicville, New York, still produces
electric power at 40 Hz and supplies power to the local 60 Hz transmission
system through frequency changers. Industrial plants and mines in North America
and Australia sometimes were built with 40 Hz electrical systems which were
maintained until too uneconomic to continue. Although frequencies near 40 Hz
found much commercial use, these were bypassed by standardized frequencies of
25, 50 and 60 Hz preferred by higher volume equipment manufacturers.
Standardization
In
the early days of electrification, so many frequencies were used that no one
value prevailed (London in 1918 had 10 different frequencies). As the 20th
century continued, more power was produced at 60 Hz (North America) or 50 Hz
(Europe and most of Asia). Standardization allowed international trade in
electrical equipment. Much later, the use of standard frequencies allowed
interconection of power grids. It wasn't until after World War II with the
advent of affordable electrical consumer goods that more uniform standards were
enacted.
In
Britain, implementation of the National Grid starting in 1926 compelled the
standardization of frequencies among the many interconnected electrical service
providers. The 50 Hz standard was completely established only after World War
II.
Because
of the cost of conversion, some parts of the distribution system may continue
to operate on original frequencies even after a new frequency is chosen. 25 Hz
power was used in Ontario, Quebec, the northern USA, and for railway
electrification. In the 1950s, many 25 Hz systems, from the generators right
through to household appliances, were converted and standardized. Some 25 Hz
generators still exist at the Beck 1 and Rankine generating stations near
Niagara Falls to provide power for large industrial customers who did not want
to replace existing equipment; and some 25 Hz motors and a 25 Hz electrical
generator power station exist in New Orleans for floodwater pumps. Some of the
metre gauge railway lines in Switzerland operate at 16⅔ Hz, which can
obtained from the local 50 Hz 3 phase power grid through frequency converters.
In
some cases, where most load was to be railway or motor loads, it was considered
economic to generate power at 25 Hz and install rotary converters for 60 Hz
distribution.Converters for production of DC from alternating current were
larger and more efficient at 25 Hz compared with 60 Hz. Remnant fragments of
older systems may be tied to the standard frequency system via a rotary
converter or static inverter frequency changer. These allow energy to be
interchanged between two power networks at different frequencies, but the systems
are large, costly, and consume some energy in operation.
Rotating-machine
frequency changers used to convert between 25 Hz and 60 Hz systems were awkward
to design; a 60 Hz machine with 24 poles would turn at the same speed as a 25
Hz machine with 10 poles, making the machines large, slow-speed and expensive.
A ratio of 60/30 would have simplified these designs, but the installed base at
25 Hz was too large to be economically opposed.
In
the United States, the Southern California Edison company had standardized on
50 Hz. Much of Southern California operated on 50 Hz and did not completely
change frequency of their generators and customer equipment to 60 Hz until
around 1948. Some projects by the Au Sable Electric Company used 30 Hz at
transmission voltages up to 110,000 volts in 1914.
In
Mexico, areas operating on 50 Hz grid were converted during the 1970s, uniting
the country under 60 Hz.
In
Japan, the western part of the country (Kyoto and west) uses 60 Hz and the
eastern part (Tokyo and east) uses 50 Hz. This originates in the first
purchases of generators from AEG in 1895, installed for Tokyo, and General
Electric in 1896, installed in Osaka.
Utility
Frequencies in Use in 1897 in North America
Cycles
Description
140
Wood arc-lighting dynamo
133
Stanley-Kelly Company
125
General Electric single-phase
66.7
Stanley-Kelly company
62.5
General Electric "monocyclic"
60
Many manufacturers, becoming "increasing common" in 1897
58.3
General Electric Lachine Rapids
40
General Electric
33
General Electric at Portland Oregon for rotary converters
27
Crocker-Wheeler for calcium carbide furnaces
25
Westinghouse Niagara Falls 2-phase - for operating motors
Even
by the middle of the 20th century, utility frequencies were still not entirely
standardized at the now-common 50 Hz or 60 Hz. In 1946, a reference manual for
designers of radio equipment listed the following now obsolete frequencies as
in use. Many of these regions also had 50 cycle, 60 cycle or direct current
supplies.
Frequencies
in Use in 1946 (As well as 50 Hz and 60 Hz)
Cycles
Region
25
Canada (Southern Ontario), Panama Canal Zone(*), France, Germany, Sweden, UK,
China, Hawaii,India, Manchuria,
40
Jamaica, Belgium, Switzerland, UK, Federated Malay States, Egypt, West
Australia(*)
42
Czechoslovakia, Hungary, Italy, Monaco(*), Portugal, Romania, Yugoslavia, Libya
(Tripoli)
43
Argentina
45
Italy, Libya (Tripoli)
76
Gibraltar(*)
100
Malta(*), British East Africa
Where
regions are marked (*), this is the only utility frequency shown for that
region.
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