April 26, 1894J 



NA TURE 



609 



process. The use of electrical energy for power, i.e. for trans- 

 formation into mechanical energy, is, the President pointed out, 

 a matter which lies obviously in the closest possible communi- 

 cation with mechanical engineering. He divided this branch of 

 the subject into three sections, namely : (i) Transmission from 

 a distance for whatever purpose ; (2) transmission to a number of 

 isolated points pretty near together, as the tools in a factory ; 

 (3) transmission for the purpose of traction on railways or tram- 

 ways. Transmission comes in in every case, because we have 

 as yet no electric prime mover analogous to a steam engine. 

 With regard to transmission of power from a distance, the 

 President said that Prof Unwinhadso fully and ably dealt with 

 the matter recently, that it was unnecessary for him to go over 

 the same ground again. The question of driving tools in a fac- 

 tory by electric motors instead of through counter shafting, is 

 one which has recently come to the front. The carrying out of 

 such work is obviously purely a matter of mechanical engineer- 

 ing. Prof Kennedy had been at pains to collect information in 

 regard to practical work bearing on this subject. In any given 

 factory running on the ordinary system there is a large con- 

 tinuous waste of power due to the running of the whole shafting, 

 no matter how many or how few machines are at work. The 

 President gave the following figures as the approximate 

 distribution of total work : — 



Average useful work 



Waste in belts and shafting 



Waste in engine friction, the engine being sup- 

 posed large enough to give 150 horse-power at 

 tools as a maximum (at about 10 per cent, of 

 maximum horse-power) .. 



H.F. 



1 00 



2> 



145 



On the other hand, if all machines in a similar case were driven 

 by separate motors, each having an electrical efficiency of 88 

 per cent., and these motors worked from a dynamo having an 

 efficiency of 92 per cent, (both of which are high figures for 

 ordinary work at two-thirds of the output), the figures would 

 stand as follows : — 



Average useful work 

 Waste in motors and dynamo 

 Waste in leads (say 2 per cent.) 

 Waste in engine friction ... 



H.P. 



100 



24 



146 



The two sets of figures it will be seen are practically the 

 same, and the President pointed out that the electrical efficiencies 

 which he had assumed were not likely to be exceeded. It is 

 not, however, the really absolute saving so much as the pro- 

 portionate saving which should be considered. It is little use 

 to show an engineer that he can make even 20 per cent, saving 

 in one item of expenditure, if that item only represents 3 or 4 

 per cent, of his costs, and if at the same time he has to expend 

 a considerable amount of capital in making the change. One 

 does not make important and expensive changes, especially 

 •changes whose results are by no means very certainly predicted 

 to bring about an estimated saving of one-half of i per cent, to 

 I per cent, in one's total expenditure. There are, however, 

 other points to be considered, such as the practical convenience 

 •of getting rid of the huge mass of shafting gear and belling 

 which fills up the upper half of many engineers' shops, and also 

 that a properly arranged motor may give a much larger range 

 ■of speed to each tool, than can be readily obtained in the 

 ordinary way. On the other hand, the President pointed out 

 that the cost of dynamo, leads, and motors is very greatly in 

 •excess of the cost of shafting in almost every case. It is hardly 

 certain as yet, he said, how the costs of attendance, lubrication, 

 renewals and repairs to the electrical plant, compare with the 

 similar costs in the case of shafts and belling ; probably, he 

 said, on the whole they would be less. 



The difficulty which besets the electrical engineer, of unequal 

 demand for energy, was dwelt upon in the address. As is suffi- 

 -ciently well known, the demand for lighting energy varies 

 enormously throughout the twenty-four hours, so that a plant 

 which is giving 2500 horse-power for a couple of hours every 

 day, will only be giving an average of 350 hor3epov\er for the 

 whole week, and not even half this for many hours every day 

 and night. If it could be arranged that during the time of light 



NO. 1278, VOL. 49] 



load for lighting purposes, the plant could be used for powe 

 purposes, then electrical energy might be sold at a low price 

 This, however, is not possible, the electrical station must be 

 prepared for any demand, and in case of fog, for instance, lights 

 might be required when the factories were at work ; the plant 

 would therefore have to be designed to supply both demands. 

 Electric transmission of power has, however, this advantage over 

 belts and shafting, that when the machinery is not at work there 

 are no losses in the motors ; whereas, whilst shafts are being run 

 and belts are at work there is loss through friction. 



Prof. Kennedy, in referring to the driving of trains or tram- 

 cars by electric power, said that conditions were by no means so 

 favourable as were sometimes supposed. The ordinary engine 

 exerted about 80 per cent, of the gross indicated horse-power in 

 pulling its load along the line. In an electric railway there was 

 a somewhat lighter locomotive to be moved, but against this 

 advantage, and the fact that a stationary engine can have a 

 greater economy than a locomotive, was to be placed the fact 

 that only about 35 per cent, of the indicated horse-power is 

 available for useful work for pulling a train, the loss of course 

 being the number of transformations through which the energy 

 has to pass. In reference to this part of the question the following 

 figures were given : — 



Per cent. 

 Mechanical efficiency of engine ... ... ... 85 



Efficiency of belt driving, if employed ... ... 94 



Efficiency of dynamos ... ... ... ... 90 



Efficiency of line .. ... .. ... ... 85 



Efficiency of motors... ... ... ... ... 85 



Efficiency of gearing of motors ... ... ... 75 



Total efficiency ... ... ... 39 



From this would be deducted the power required for driving 

 the locomotive, leaving 35 per cent, for pulhng the train. In 

 spite of this great drawback of loss of power, some conditions 

 rendered electrical traction absolutely necessary. In the public 

 streets there is the great mechanical difficulty of getting the 

 current to the motors on the cars. In America overhead wires 

 are used, and in country 1 laces, the President said, this is pos- 

 sibly the best solution of the problem ; but in cities he con- 

 sidered it to be impossible, and that the introduction of electricity 

 for car driving in this country will still wait for a practical under- 

 ground system to be devised. In the meanwhile, electricity is 

 being hard pressed by its livals, cable and compressed gas, Prof. 

 Kennedy thinking the latter far the more formidable. It has 

 the advantage of being even more direct than a steam engine, 

 and it can be applied to each individual car even more easily 

 than an electric motor, and it enables the car to run freely on 

 ordinary lines without their reconstruction and without any 

 mains either above or below ground. It has had but a short 

 trial, but what the President had seen of it made him sanguine 

 as to its ultimate possibilities. Prof Kennedy also referred to 

 the Serpollet boiler and engine, which he wondered had not 

 been introduced for tram work. The Serpollet machinery takes 

 so little space that it might very possibly be put on the car 

 itself, but he supposed some difficulty had been found in the 

 application ; at any late, the proposal had not been made, so 

 far as he knew. We may mention that a number of road car- 

 riages, propelled by the Serpollet boiler and engine, have been 

 in use for some time past in Paris. 



The address next dwelt at some length on the question of 

 security in running, in efficiency of regulation, and economy of 

 work. In regard to the former the President pointed out the 

 necessity of duplication of plant in order to provide against 

 breakdown of engines or dynamos, and the difficulty of starting 

 boilers with rapidity supposing a sudden call to be made for 

 additional steam. In regard to security in connection with 

 mains, he referred to Mr. Bailey's looped main system. In 

 speaking upon the question of economy. Prof Kennedy said 

 that in an electric light station the cost of coal averages not 

 far from four-tenths of the total of woiking expenses. He did 

 not know of any one type of boiler which was better than all 

 others under the conditions of an electric light station ; in fact, 

 he said there were five or six types equally good. One thing ' 

 which tells very much against the economy of electric light 

 stations is that fires must be kept alight and pressures maintained 

 in boilers capable of giving eight or ten times the actual out- 

 put ; added to this is the extent to which in all stations fuel 

 must be expended in getting boilers ready for the heavy load 



