232 ELEMENTS OF ELECTRICAL ENGINEERING. 



current generator direct connected to a 300 horse-power engine, 

 and a Brush arc generator driven by a 90 horse-power electric 

 motor. The entire plant represents an investment of $89,880 of 

 which $60,165 is in the building and equipment of the station and 

 $29,7 1 5 is in the distributing system. The total number of lamps 

 installed is 6,300 16 candle-power incandescent lamps and 109 

 arc lamps. A separate account is not kept in this station of the 

 cost of trimming and cleaning the arc lamps. The cost of re- 

 pairs is the average for three years. The same remarks con- 

 cerning interest, depreciation, and taxes apply to this station as 

 to station A. This plant supplies current to consumers on a 

 meter basis, the monthly bill being made out at the following net 

 prices : 



For lighting and for fan motors : 



First 100 kilowatt-hours at 9.0 cents per kilowatt-hour. 



Next 200 " " " 7.2 " " 



Over 300 " " " 5.4 " " " " 



For motive power (not including fan motors) : 



First 200 kilowatt-hours at 4. 5 cents per kilowatt-hour. 



Next 400 " " " 3.6 " 



Over 600 " " " 2.7 " " " " 



The plant is operated continuously except from one hour after 

 sunrise to one hour before sunset on Sundays. 



It is seen from the table that the average cost of generation of 

 electrical energy is between 5 and 6 cents per kilowatt-hour and 

 it may seem that station B supplies energy for motive power be- 

 low cost. This is, however, not the case ; the station is run day 

 and night irrespective of the demand for current for motive 

 power, and the added cost of operating the station due to the 

 supply of current to motors is probably less than one cent per 

 kilowatt-hour. This matter is discussed in the next article. 



100. Systems of charging for electrical energy. ( i ) The flat 

 rate system. Many small electric light stations supply current 



