LOAD AND DIVERSITY FACTOR 679 



cheaper, but as the load factor increases above this value water 

 power may show up to the better advantage. This is evident 

 from the fact that the cost of hydro-electric power is made top 

 chiefly by the fixed charges and is very little dependent on the 

 operating charges and the amount of power used. 



There is an enormous variety of uses to which electricity is 

 applied, the yearly load factors of which also vary widely, as 

 shown in Table LXI. 



The yearly load factor for any class of service is determined 

 largely by the seasons, the habits of the people, and other con- 

 ditions which ordinarily do not change very materially. Im- 

 provement in the load factor must, therefore, be obtained largely 

 by combining different classes of service, the maximum demands 

 of which occur at different times of the day or of the year. Also, 

 the larger the number of customers in any class the better will be 

 the load factor. 



A recognition of the importance of the diversity factor has 

 undoubtedly the most marked effect in increasing the load factor 

 and thereby the economy of production. This factor is the ratio 

 between the sum of the maximum demands of various classes of 

 service to the actual simultaneous maximum demand, and the 

 more non-coincident these peak services are, the greater will be 

 this factor. 



The chief means 01 improving the load factor has been the 

 addition of industrial load. In the early days of electric lighting 

 companies, the load factors were very low, due to the absence of 

 day load. To-day many central stations sell far more energy 

 for power than for light, and this is naturally distributed over a 

 longer part of the twenty-four hours. The power load, also, not 

 being simultaneous with the lighting load to any great extent, 

 still further improves the load factor. Residence load has gen- 

 erally been characterized by a poor load factor, but by the use of 

 day-load devices such as flat irons, cooking devices, fans, heating 

 apparatus, vacuum cleaners, etc., a much improved result is 

 obtained. 



The problem of combining electric railway loads and central 

 station loads on one system has received increasing attention in 

 recent years, and in some cities of this country great strides have 

 been made toward effecting such combinations successfully. 

 Fig. 399 thus shows a typical load curve for a large city. 



