444 Mr. Alan A. Campbell Sivinton [April 19, 



variations in load and the short periods for which the full load is in 

 operation necessarily adversely affect economy both as regards fuel 

 and as regards labour. Steam has to be got up to provide for the 

 maximum load, and during the period of minimum load either the 

 fires have to be banked, or steam has to be let down and then got up 

 again, with consequent inefficiency. Similarly, under the conditions 

 of small load factors it is very difficult to secure economy as regards 

 labour. 



It is this question of load factor which is the explanation of 

 what most people fail to realize the reason for, namely, the differ- 

 ences in prices that the consumer has to pay for electricity for lighting 

 and electricity for heating and power purposes. When the machinery 

 has once been provided to deal Avith the maximum load which the 

 lighting requirements entail, supply undertakings can afford to pro- 

 vide electricity for use during the hours of daylight, when electricity 

 for lighting is not wanted, at a very cheap rate, for the plant and the 

 attendance is there, and it only means a small extra consumption in 

 fuel ; it is, indeed, expressly for the purpose of improving the load 

 during the day, and consequently the load factor, that these differences 

 in prices are quoted. 



There is another very important factor controlling the cost of 

 electricity to which full attention has only quite recently been paid, 

 that is, the scale on which the electricity is being generated. Only a 

 few years ago this question of scale was not much thought of ; indeed, 

 in evidence given on behalf of some of the earlier Power Bills before 

 Parliamentary Committees, eminent engineers gave it as their opinion 

 that there were comparatively low limits beyond which the scale of 

 the operations would make no difference. Their idea was that the 

 largest engines and dynamos then existing, giving some two or three 

 thousand horse-power apiece, were as large as was advisable, and that 

 no great advantage, either as regards first cost or as regards economy 

 in fuel or operating, would be obtained by increasing the size of these 

 units, and that it was simply a question of multiplying their number. 

 Xo doubt, with the reciprocating engine there was something in this 

 point of view, but, anyway, the advent of the steam turbine has 

 entirely altered matters, as with these machines there seems to be 

 practically no Ikuit to the extent whereby greater economy is obtained 

 by a larger size, and this not only as regards steam consumption and 

 working costs, but also as regards capital expenditure. 



And here notice may be drawn to the latest thing in the way of 

 steam turbine plants, and it is interesting to compare it with the 

 original Parsons turbine and dynamo of six horse-power, capable of 

 giving about 4^ kilowatts of electric energy. The new machine, 

 which is illustrated in Fig. 10, is capable of giving a maximum con- 

 tinuous output of 25,000 kilowatts at unity pow^er factor, 25 cycles, 

 4500 volts, this corresponding to over 3o,000 electrical horse-power. 

 This machine has recently been ordered from Messrs. Parsons by the 



