ELECTRICAL ENERGY. 211 



ELECTRICAL DISTRIBUTION. 



The distribution of electrical energy to consumers as distinguished 

 from its transmission to long distances has been largely accomplished 

 by the agency of continuous currents, although alternating currents 

 have played an important part in incandescent lighting. As I have 

 stated, a considerable proportion of current for lighting is distributed 

 at constant potential on the three-wire system or at constant current 

 on arc-light circuits, while power for traction circuits is distributed at 

 approximately constant potential at an average of, say, 550 volts. 



I shall first consider the condition of affairs in a traction system in 

 a large city, where a number of suburban lines are operated. If direct 

 distribution is attempted from a single station, it will be found that 

 when the distance exceeds 5 or 6 miles a large amount of copper must 

 be employed to prevent both excessive loss and excessive variation of 

 potential on the lines. On suburban lines it is the latter consideration 

 that usually determines the amount of copper used, and this is espe- 

 cially true on lines where there is a considerable excursion traffic. 

 Even in the city itself, the supplying of sections at distances 3 or 4 

 miles from the station may require so much copper that it would be 

 less expensive to operate separate stations. Several methods other 

 than the direct method may be employed to remedy these difficulties. 

 For outlying lines where the traffic is mainly of the excursion order, 

 being variable both during the day aud for different seasons, boosters 

 may be advantageously used. It is perhaps best from reasons of econ- 

 omy to run the boosting dynamos from motors. These dynamos are 

 series- wound, and are connected to feeders of such resistance that the 

 fall of potential in the wire for a given current is compensated for by 

 the rise in voltage of the booster. There is a decreased cost of copper 

 incidental to this system due to the fact that the drop is not limited by 

 considerations of regulation — the voltage at the end of the feeder being 

 constant — while the transmission is at an increased potential. If the 

 average station potential is 600 volts, and it is boosted 300 volts, then 

 the copper for a given loss would be decreased in the ratio of 36 

 to 81. The booster system has the advantage of the direct system 

 when the cost of the additional apparatus, together with the increased 

 loss on the line, capitalized, is less than the increased cost of the 

 copper necessary to produce the same result by the direct system. 

 Whether the balance is in favor of one or the other depends on the 

 distance and the variation of the load, audit is indifferent whether the 

 variation in the latter occurs often or not. 



If any transforming device is employed to feed a distant section of the 

 line it must be remembered that the capacity of the device must be 

 great enough to look out for the maximum demand on this section. 

 Suppose, now, that we wish to feed some suburban line where the load 

 has considerable momentary fluctuations, but where the traffic is mod- 

 erately constant during the year; in this case the booster could be 



