. Electric traction and transmission engineering . its average value may be determined byreference to Fig. 58, which is based upon experience. End Feeding. Consider a section of length L feet, fedat one end as in Fig. 57, and let it be uniformly the current density /o = I/L, and the distance of thecenter of gravity of tlie aggregate load /o = L/2, the totaldrop over the section is whence V 2Ae feet. (4) 138 TRACTION AND TRANSMISSION. The total drop is therefore proportional to the square ofthe length of the section, and the maximum permissiblelength of section is to be obtained by
. Electric traction and transmission engineering . its average value may be determined byreference to Fig. 58, which is based upon experience. End Feeding. Consider a section of length L feet, fedat one end as in Fig. 57, and let it be uniformly the current density /o = I/L, and the distance of thecenter of gravity of tlie aggregate load /o = L/2, the totaldrop over the section is whence V 2Ae feet. (4) 138 TRACTION AND TRANSMISSION. The total drop is therefore proportional to the square ofthe length of the section, and the maximum permissiblelength of section is to be obtained by use of equation (4). Center Feeding. If the section be fed at its middle pointinstead of at the end, the permissible length of contactconductor section is twice that indicated by equation (4).Such a system is schematically represented in Fig. 59, andis considered ideal from an operating viewpoint, for eachsection may be controlled by a circuit breaker at the stationin the feeder supplying that section. This gives complete . .BREAKERS ^^^^^^3-BUS. Fig- 59- control of each and every section in case of overload, shortcircuit, accident, or repairment. It is the system mostfrequently used for urban roads. It may be desirable toconnect the adjacent ends of the sections of the contactconductor through a section breaker which may be locatedon a near-by pole. When these circuit breakers are closedthere results an equalization of the current distribution andthe conductivity of the whole positive system becomesavailable. The remoteness of these breakers from thestation, however, is objectionable as lacking Lost in Conductor. While the cross section of thecontact conductor is usually prescribed by the maximumpermissible drop or by mechanical considerations, casesmay arise where a larger cross section will prove more THE DISTRIBUTING SYSTEM. 139 economical. In such cases the power lost in the contactconductor may be found as follows:Let le = effective current per foot i
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