Fig. 47.—Interior of Power-house at Garvin’s Falls on the Merrimac River.
Fig. 48.—500-Kilowatt Generator in Station at Great Falls on the Presumpscot River.
As to frequency, existing practice extends all the way from 133 cycles per second on the lines at Marysville, Cal., down to only 15 cycles on the transmission for the Washington & Baltimore Electric Railway.
More common practice ranges between 25 and 60 cycles. Niagara Falls saw the first great plant installed for 25 cycles, but others of that frequency are now engaged in the supply of light and power for general distribution. For transmission to electric railway lines a frequency of 25 cycles has been and is being widely used, prominent examples of which may be seen in the New Hampshire traction, the Berkshire, and the Albany & Hudson systems.
Fig. 49.—Columbus, Ga., Water-power Station.
The strong feature of a system at 25 cycles is that it is well suited to the supply of continuous currents through rotary converters with reasonable numbers of poles, armature slots, and commutator bars.
