G.— ENGINEERING. 159 



decreasing each year. From speeds of 500 to 600 r.p.m. there was a stride 

 to 1,500, 2,400, or 3,000 r.p.m., according to the frequency of system 

 and size of generator. There was ahnost immediately a significant improve- 

 ment in the machinery constructed for electric-supply purposes. 



In 1898 an important inquiry was conducted by a Committee, under 

 the chairmanship of Lord Cross, from whose Report sprang the power 

 companies which now operate in most of our industrial districts, and whose 

 areas of supply extend over whole counties and in some cases over several 

 county areas. 



There had thus been growing up not only a constant increase in the 

 size and output of the generating stations, but constant increases in the 

 pressures adopted for transmission brought about an ever-widening radius 

 of supply and enlargement of the area served. 



To-day we find a rapidly increasing growth of output, a decreasing 

 cost and consequent widening circles of application ; and as in due season 

 the industry simplifies its position still further by adopting one standard 

 frequency and by reducing the number of supply pressures to the minimum 

 practicable, the demands for electricity in this densely populated country 

 are bound to expand to a degree which is not yet visualised. An attempt 

 is made hereafter to envisage this growth of demand. 



An important result follows from widening an area of distribution — 

 it enables supplies to be given from a common source to many industries, 

 to railways and tramways, and all kinds of domestic and trade require- 

 ments. It is found by investigation that the maximum requirements of 

 the various classes of consumer do not coincide in point of time, and, speak- 

 ing generally, if all their maximum demands occurred simultaneously, 

 no less than from 2| to 3 times the generating plant would be necessary 

 to meet the load than is the case when their several supplies are drawn 

 from one common source of generation. It is, in fact, only by supplying 

 all the needs of a community within a large area from one common system 

 that the maximum use can be made of the capital employed. 



When one remembers that the annual capital charges on a generating 

 station represent some two-fifths of the total cost of generation, it will be 

 seen how important it is to obtain the greatest user of the plant installed. 

 In fact, the combination of all requirements of a community, whether for 

 domestic purposes, traction or industrial power, is a fundamental condition 

 of economy in the public supply of electricity. 



The ' load factor,' an expression for which the industry was indebted 

 to Colonel Crompton at an early date in its history, is therefore a very 

 important matter. It may shortly be defined as the ratio of the electrical 

 energy actually produced by any generating plant in any period of time 

 to the amount which would have been produced had that plant been 

 ■working at full load continuously during that time. A kilowatt of plant 

 working continually throughout a year (which is not a leap year !) 

 will produce 8,760 units or kilowatt hours. 



Now the average v'early load factor (on units sold by undertakings) 

 throughout Great Britain to-day is under 25 per cent. — that is to say, the 

 aggregate kilowatts required to meet the individual demands for hundreds 

 of systems only produce one-quarter of the units possible were the plant 

 working continuouslv. 



