Chapt. 33Alternating Current or AC249033 qmult 00140 1 1 4 easy memory: unit of frequency5. The MKS unprefixed unit of frequency is the:a) kilovolt (kV).b) volt (V)c) revolution per minute (RPM).d) hertz (Hz).e) kilohertz (kHz).033 qmult 00150 1 1 3 easy memory: standard north american frequency6. The optimum choice of AC frequency for a particular application probably depends on manythings. But for a power grid, one must have a standard frequency which is reasonably good formay applications. In the early days of power grids many frequencies were used by the pioneeringpower plants. Frequencies between 16.666...Hz and 133.333...Hz have used. The Niagara Fallshydropower plants generated 25 Hz for a long time which is a bit too low for lighting: there isa detectable flicker to the eye. Coventry, England once using the oddball value 87 Hz. But inthe course of the 20th century, an overall optimum frequency of about 50 Hz was arrived at. InEurope, 50 Hz exactly became the standard probably because it seemed sort of metric. In NorthAmerica,exactly was settled probably since it seemed most Sumerian. Most of
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