208 ELECTRICAL ENERGY. 



It is my purpose to take up the different methods of transmission 

 and distribution and to consider the limits that are actually fixed by 

 the present status of electrical development. The question is a com- 

 mercial one, each problem presenting different conditions which must 

 be considered, but certain general principles govern each case, and our 

 knowledge and experience makes it possible to judge the practicability 

 of each particular transmission. , 



GENERATING PLANTS. 



At the present time practically all of the electrical energy distrib- 

 uted is generated in plants operated either by steam or water power, 

 and it is important to consider the conditions of maximum economy in 

 large generating plants, as this bears directly on the subject of trans- 

 mission and distribution. 



A large proportion of the electrical plants in this country are steam 

 plants. In the last ten years we have advanced from small stations 

 using high-speed dynamos for light and power distribution to large 

 stations, using, as a rule, low-speed direct-connected machines. The 

 simple engines that were used some years ago have in many cases been 

 changed to compound and even triple expansion engines, and where 

 it is possible condensers have been employed. Some of the latest 

 plants have machinery of the highest possible efficiency, and yet if we 

 consider the price per horsepower of the power generated we will find 

 that it is greater than we expect. This is partly due to the fact that 

 for both lighting and power purposes the load on the station is, as a 

 rule, not uniform and the apparatus is not working under the best con- 

 ditions for economy. In this country electrical energy is principally 

 generated for electric lighting, for electric traction, and for supplying 

 stationary motors, these stationary motors, as a rule, being supplied 

 with current from lighting stations. If we take the load diagram of 

 such stations in large towns, we will find that the average output is 

 not greater than 30 to 40 per cent of the maximum output. We have, 

 therefore, to supply a large amount of machinery corresponding to the 

 maximum demand on the station, while for distribution a large amount 

 of copper is required, that is only being used at its maximum capacity 

 for a comparatively short period of the time. In stations supplying 

 power for traction purposes we find a variation of load, but the varia- 

 tion is a different kind from that found in a lighting station. In the 

 latter the load varies at different hours in the day, but for any partic- 

 ular instant it is practically constant. In the former the average load 

 for different hours during which the station is operated will be practi- 

 cally constant, but there will be momentary variations, depending upon 

 the size of the station and the type of traffic. Taking, for instance, a 

 2,000-horsepower station in Baltimore, I find that the average load is 

 48 per cent of the momentary maximum load. This difference in the 

 kind of variation for the two types of stations necessitates employment 



