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Reply To: Electrical Riddle No.49 – Power system frequency


    In the United States, the use of alternating current (AC) was championed by George Westinghouse and Nikola Tesla. In 1885, a commercially practical transformer was developed, which allowed the development of an AC system. A 4000 volt AC transmission line was installed between Oregon City and Portland, 13 miles away. A 112 mile, 12,000 volt, three-phase line went into operation in 1891 in Germany. The first three-phase line in the United States (2300 volts and 7.5 miles) was installed in 1893 in California.3In 1897, a 44,000-volt transmission line was built in Utah. In 1903, a 60,000-volt transmission line was energized in Mexico. In this early AC period, frequency had not been standardized. In 1891, the desirability of a standard frequency was recognized and 60 Hertz (Hz) was proposed. For many years 25, 50, and 60 Hz were standard frequencies in the United States. Much of the 25 Hz was used for railway electrification and has been retired over the years. The City of Los Angeles Department of Water and Power and the Southern California Edison Company both operated at 50 Hz, but converted to 60 Hz at the time that Hoover Dam power became available, with conversion completed in 1949. The Salt River Project was originally a 25 Hz system; most of it was converted to 60 Hz by the end of 1954 and the balance by the end of 1973. For generators, lower frequencies tend to be preferable because this requires fewer magnetic poles inside the rotor, though this constraint became less significant as high-speed steam turbines supplemented and replaced slow-moving hydroturbines and reciprocating steam engines. For transmission, lower frequencies are especially desirable because a line