212 ELECTRICAL ENERGY. 



used with a storage battery at the end of its feeder, the battery sup- 

 plying the line. The advantages of this combination are greater than 

 with the simple booster, and in many cases they will compensate for the 

 interest and depreciation on the battery and the loss in it. If the 

 arrangement is properly made the load on the booster and line wire 

 will be practically constant, thus decreasing the capacity of the booster 

 to that required for the average load, while less copper will be required 

 for a given loss. As to the latter point, suppose a given amount of 

 power is to be distributed in 24 hours, say 200 amperes at 600 volts, if 

 the load is uniform, the loss will be proportional to 200 2 x24 hours. If 

 it is all distributed in 12 hours, the loss will be proportional to 400 2 x 12 

 hours, or twice as much. So, in the case of the steady load, the same 

 power could be transmitted with the same loss with half the copper. 

 It makes no difference whether the variation extends over 12 hours in 

 24 or occurs every other minute, the result will be the same. It is 

 apparent, then, that it is of the utmost importance to keep the line 

 steadily loaded, as well as the station, and this points to the location of 

 the battery near the points of consumption and not in the station. By 

 this system — a booster with storage batteries — it is possible, assuming 

 the same loss, to transmit power to a distance of 10 miles with approx- 

 imately the same amount of copper that would be required for a 

 5-mile transmission on the direct system. It would increase the econom- 

 ical radius of distribution twice and the area of distribution four times. 

 A single station could economically supply lines within distances up 

 to 10 or 12 miles. If it is desired to still further increase the radius 

 of distribution, it is possible to do this by employing some of the alter- 

 nating current methods that have come into use. 1 will discuss these 

 methods later, but at this point I may remark that the use of stationary 

 and rotary transformers permits the energy to be transmitted in the 

 form of alternating currents, and to be changed again into continuous 

 currents of any required voltage. These rotary transformers supplied 

 by an alternating current, which is transmitted from the station at a 

 high voltage, may be used to feed the line directly or they may be used 

 to supply storage batteries which are connected to the line. In the 

 latter case we have the advantage of decreased size of apparatus, of 

 steady load on the station, and of a minimum cost of copper on the line; 

 which system it would be best to employ would depend upon the 

 distances and the character of the line and load. 



Of the systems that I have proposed for city and suburban distribu- 

 tion from a single station, three have been successfully employed, 

 namely, the booster system, the booster system with batteries, and 

 rotary transformers operating directly on the line. When we consider 

 the advantages of a single station and a steady load, it seems evident 

 to me that many of the large traction systems would do well to con- 

 centrate their stations into one and to use the booster system with bat- 

 teries for their outlying lines, and if necessary use rotary transformers 

 for lines beyond the limit of ordinary suburban work. As to the pos- 



