POWER EMPLOYED IN MANUFACTURES 225 



ator dynamos of 3,000 horsepower each, and 4 of 1,500 horse- 

 power each, these being of the 'Hhree phase" current type. 

 The current is generated in these dynamo machines at 2,400 

 volts pressure, and is then raised by transforming apparatus 

 to a pressure of 40,000 and 60,000 volts, even 80,000 vohs 

 having been reached, while the lowest pressure named is 

 normal. This current is delivered to two circuits of 3 wires 

 each, one being composed of copper and the other of alu- 

 minum. The wires are carried upon Oregon cedar poles 

 averaging from 25 to 60 feet high, upon wliich are screwed 

 porcelain and glass umbrella insulators 12 inches in diameter. 



The transmission current is carried across the well 

 known Straits of Karquines in an enormous span of 4,448 

 feet, supported 200 feet above the rapid waters emptying 

 into San Pablo ba}^ by means of steel latticed towers, the 

 circuits being composed of stranded plow steel to obtain the 

 requisite tensile strength. 



The efficiency of the transmission S3'stem is such that 

 1,000 horsepower at the Colgate wheels nets about 750 horse- 

 power at San Francisco, 6 per cent being lost in the generators, 

 2 per cent in the step up transformers, 2 per cent in the step 

 down transformers at the receiving substations, and 15 per 

 cent in regulation and in the line. 



The emplo\TQent of the current is not less varied than 

 at Niagara, ranging from the operation of street cars in Oak- 

 land to the running of a flourmill at Stockton, and from use 

 in mines in various parts of the state to use in miscellaneous 

 industries at Sacramento, Benicia, San Jose, and elsewhere. 

 The plants must be maintained in regular and systematic 

 operation, and as their initial base of dependence is the 

 water supph^, storage reserv'oirs have been pro\4ded in the 

 high Sierras in Alpine county, 6,000 to 8,000 feet above the 

 sea level, furnishing a supply equal to one hundred and fifty 

 days, which is the maximum dr\' period of the state as 

 recorded in its annals. 



The tliird type of power transmission plant which de- 

 serv^es mention is that at the Snoqualmie falls, Washington, 

 where the» dynamo room with 10,000 horsepower of electrical 

 apparatus is situated 250 feet below the surface in a large 



Vol. 7-15 



