ENGINEERING BEFORE AND AFTER WAR 51 



cost and greater economy in fuel. The size of the turbines 

 may vary from a few thousand horse-power up to about 

 50,000 horse-power. At the end of last year the central 

 electric stations in the United Kingdom contained plant 

 aggregating 2^4 million kilowatts, 79 per cent, of which 

 was driven by steam turbines. 



Much discussion has taken place as to the most eco- 

 nomical size of generating stations, their number, the size 

 of the generating units, and the size of the area to be sup- 

 plied. On the one hand, a comparatively small number 

 of very large or super-stations, instead of a large number 

 of moderate-sized stations dotted over the area, results 

 in a small decrease in the cost of production of the elec- 

 tricity, because in the super-stations larger and slightly 

 more economical engines are employed, while the larger 

 stations p ? ermit of higher organization and more elaborate 

 labor-saving appliances. Further, if in the future the 

 recovery of the by-products of coal should become a prac- 

 tical realization as part of the process in the manufacture 

 of the electric current, the larger super-stations present 

 greater facilities than the smaller stations. On the other 

 hand, super-stations involve the transmission of the elec- 

 tricity over greater distances, and consequently greater 

 capital expenditure and cost of maintenance of mains and 

 transmission apparatus, and greater electrical transmission 

 losses, while the larger generating unit takes longer to 

 overhaul or repair, and consequently a larger percentage 

 of spare plant is necessary. 



The greatest element in reducing the cost of electricity 

 is the provision of a good load factor; in other words, the 

 utilization of the generating plant and mains to the great- 

 est extent during the twenty-four hours of each day 

 throughout the year. This is a far more important con- 

 sideration than the size of the station, and it is secured 

 to the best advantage in most cases by a widespread net- 

 work of mains, supplying a diversity of consumers and 

 uses, each requiring current at different times of the day. 



