PRACTICAL OPERATION OF DYNAMOS. 223 



Curve C. Fixed charges per horse-power-year. This item is 

 reckoned at 14 per cent, on the total cost, and it includes interest 

 at 6 per cent, depreciation 4 per cent., repairs 2 per cent, insur- 

 ance I per cent., and taxes I per cent. 



Curve D. Cost of coal per horse-power-year at $4.00 per ton 

 of 2,000 pounds. 



Curve E. Wages per horse-power-year. 



Curve F. Cost of oil and supplies per horse-power-year. 



Curve G. Total cost per horse-power-year. 



These curves are based on the assumption that the smaller 

 sizes of engines are simple non-condensing engines of the Corliss 

 type, that the medium and large-sized engines are run condens- 

 ing, and that the largest sizes are compound engines. 



The item of wages in a 100 horse-power plant would include 

 an engineer at $2.50 per day and a fireman at $1.50 per day, 

 which would amount to about $1,200 per year. In a 1,000 

 horse-power plant the item of wages would include one engineer 

 at $3.00 per day, one assistant engineer at $2.00 per day, three 

 men in the boiler room during the day and one night watchman 

 at $1.50 per day, which would amount to about $3,500 per year. 



Where the cost of coal is more or less than $4.00 per ton, the 

 cost of coal per horse-power-year may be easily determined from 

 curve D, Fig. 139, the ordinates of which represent the cost of 

 coal per horse-power-year . at $4.00 per ton, and the total cost 

 per horse-power-year, as given by curve G, may be corrected 

 accordingly. 



It is important to remember that the cost of power as given 

 by curve G, Fig. 139, is based on the assumption that the en- 

 gines are working at full load for 10 hours per day, 308 days in 

 the year. When a plant operates at a fraction of its full-load 

 capacity the cost per horse-power-hour is increased as explained 

 in Art 97. 



The cost of electrical power at the switchboard. The load 

 factor * of an ordinary electric light station varies from o. 1 5 for 



* See Art. 97. 



