History Of Power Frequency

Manydifferent power frequencies were used in the 19th century. Very early isolatedAC generating schemes used arbitrary frequencies based on convenience for steamengine, water turbine and electrical generator design. Frequencies between 16⅔ Hz and 133⅓ Hz were used ondifferent systems. For example, the city of Coventry, England, in 1895 had aunique 87 Hz single-phase distribution system that was in use until 1906. Theproliferation of frequencies grew out of the rapid development of electricalmachines in the period 1880 through 1900. In the early incandescent lightingperiod, single-phase AC was common and typical generators were 8-pole machinesoperated at 2000 RPM, giving a frequency of 133 cycles per second.

Thoughmany theories exist, and quite a few entertaining urban legends, there islittle certitude in the details of the history of 60 Hz vs 50 Hz.

TheGerman company AEG (descended from a company founded by Edison in Germany)built the first German generating facility to run at 50 Hz, allegedly because60 was not a preferred number. AEG's choice of 50 Hz is thought by some torelate to a more "metric-friendly" number than 60. At the time, AEGhad a virtual monopoly and their standard spread to the rest of Europe. Afterobserving flicker of lamps operated by the 40 Hz power transmitted by theLauffen-Frankfurt link in 1891, AEG raised their standard frequency to 50 Hz in1891.

WestinghouseElectric decided to standardize on a lower frequency to permit operation ofboth electric lighting and induction motors on the same generating system.Although 50 Hz was suitable for both, in 1890 Westinghouse considered thatexisting arc-lighting equipment operated slightly better on 60 Hz, and so thatfrequency was chosen.[5] Frequencies much below 50 Hz gave noticeable flickerof arc or incandescent lighting. The operation of Tesla's induction motorrequired 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 changedto 60 Hz a year later to maintain market share with the Westinghouse standard.

 

25Hz origins

 Thefirst generators at the Niagara Falls project, built by Westinghouse in 1895,were 25 Hz because the turbine speed had already been set before alternatingcurrent power transmission had been definitively selected. Westinghouse wouldhave selected a low frequency of 30 Hz to drive motor loads, but the turbinesfor the project had already been specified at 250 RPM. The machines could havebeen made to deliver 16⅔Hz power suitable for heavy commutator-type motors but the Westinghouse companyobjected that this would be undesirable for lighting, and suggested 33⅓ Hz. Eventually acompromise of 25 Hz, with 12 pole 250 RPM generators, was chosen. Because theNiagara project was so influential on electric power systems design, 25 Hzprevailed as the North American standard for low-frequency AC.

40Hz origins

 AGeneral Electric study concluded that 40 Hz would have been a good compromisebetween lighting, motor, and transmission needs, given the materials andequipment available in the first quarter of the 20th Century. Several 40 Hzsystems were built. The Lauffen-Frankfurt demonstration used 40 Hz to transmitpower 175 km in 1891. A large interconnected 40 Hz network existed innorth-east England (the Newcastle-upon-Tyne Electric Supply Company, NESCO)until the advent of the National Grid (UK) in the late 1920s, and projects inItaly used 42 Hz. The oldest continuously-operating commercial hydroelectricpower plant in the United States, at Mechanicville, New York, still produceselectric power at 40 Hz and supplies power to the local 60 Hz transmissionsystem through frequency changers. Industrial plants and mines in North Americaand Australia sometimes were built with 40 Hz electrical systems which weremaintained until too uneconomic to continue. Although frequencies near 40 Hzfound much commercial use, these were bypassed by standardized frequencies of25, 50 and 60 Hz preferred by higher volume equipment manufacturers.

Standardization

 Inthe early days of electrification, so many frequencies were used that no onevalue prevailed (London in 1918 had 10 different frequencies). As the 20thcentury continued, more power was produced at 60 Hz (North America) or 50 Hz(Europe and most of Asia). Standardization allowed international trade inelectrical equipment. Much later, the use of standard frequencies allowedinterconection of power grids. It wasn't until after World War II with theadvent of affordable electrical consumer goods that more uniform standards wereenacted.

InBritain, implementation of the National Grid starting in 1926 compelled thestandardization of frequencies among the many interconnected electrical serviceproviders. The 50 Hz standard was completely established only after World WarII.

Becauseof the cost of conversion, some parts of the distribution system may continueto operate on original frequencies even after a new frequency is chosen. 25 Hzpower was used in Ontario, Quebec, the northern USA, and for railwayelectrification. In the 1950s, many 25 Hz systems, from the generators rightthrough to household appliances, were converted and standardized. Some 25 Hzgenerators still exist at the Beck 1 and Rankine generating stations nearNiagara Falls to provide power for large industrial customers who did not wantto replace existing equipment; and some 25 Hz motors and a 25 Hz electricalgenerator power station exist in New Orleans for floodwater pumps. Some of themetre gauge railway lines in Switzerland operate at 16⅔ Hz, which canobtained from the local 50 Hz 3 phase power grid through frequency converters.

Insome cases, where most load was to be railway or motor loads, it was consideredeconomic to generate power at 25 Hz and install rotary converters for 60 Hzdistribution.Converters for production of DC from alternating current werelarger and more efficient at 25 Hz compared with 60 Hz. Remnant fragments ofolder systems may be tied to the standard frequency system via a rotaryconverter or static inverter frequency changer. These allow energy to beinterchanged between two power networks at different frequencies, but the systemsare large, costly, and consume some energy in operation.

Rotating-machinefrequency changers used to convert between 25 Hz and 60 Hz systems were awkwardto design; a 60 Hz machine with 24 poles would turn at the same speed as a 25Hz 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 at25 Hz was too large to be economically opposed.

Inthe United States, the Southern California Edison company had standardized on50 Hz. Much of Southern California operated on 50 Hz and did not completelychange frequency of their generators and customer equipment to 60 Hz untilaround 1948. Some projects by the Au Sable Electric Company used 30 Hz attransmission voltages up to 110,000 volts in 1914.

InMexico, areas operating on 50 Hz grid were converted during the 1970s, unitingthe country under 60 Hz.

InJapan, the western part of the country (Kyoto and west) uses 60 Hz and theeastern part (Tokyo and east) uses 50 Hz. This originates in the firstpurchases of generators from AEG in 1895, installed for Tokyo, and GeneralElectric in 1896, installed in Osaka.

UtilityFrequencies in Use in 1897 in North America

CyclesDescription

140Wood arc-lighting dynamo

133Stanley-Kelly Company

125General Electric single-phase

66.7Stanley-Kelly company

62.5General Electric "monocyclic"

60Many manufacturers, becoming "increasing common" in 1897

58.3General Electric Lachine Rapids

40General Electric

33General Electric at Portland Oregon for rotary converters

27Crocker-Wheeler for calcium carbide furnaces

25Westinghouse Niagara Falls 2-phase - for operating motors

Evenby the middle of the 20th century, utility frequencies were still not entirelystandardized at the now-common 50 Hz or 60 Hz. In 1946, a reference manual fordesigners of radio equipment listed the following now obsolete frequencies asin use. Many of these regions also had 50 cycle, 60 cycle or direct currentsupplies.

Frequenciesin Use in 1946 (As well as 50 Hz and 60 Hz)

CyclesRegion

25Canada (Southern Ontario), Panama Canal Zone(*), France, Germany, Sweden, UK,China, Hawaii,India, Manchuria,

40Jamaica, Belgium, Switzerland, UK, Federated Malay States, Egypt, WestAustralia(*)

42Czechoslovakia, Hungary, Italy, Monaco(*), Portugal, Romania, Yugoslavia, Libya(Tripoli)

43Argentina

45Italy, Libya (Tripoli)

76Gibraltar(*)

100Malta(*), British East Africa

Whereregions are marked (*), this is the only utility frequency shown for thatregion.