. Electric traction and transmission engineering . 5 NUMBER OF NEGATIVE FEEDERSFig. 69. equal, the negative bus bar being insulated from the groundat the station. If, in addition, use be made of negative boosters in thefeeders, the potentials at the feeding points can be rnain-tained uniform with that of the negative bus-bar even withwidely fluctuating loads. The amount to which the original leakage current isreduced by various numbers of such negative feeders andboosters as a percentage of what would exist in the caseof no feeders, is shown in Fig. 69. THE DISTRIBUTING SYSTEM. l6l If the cont
. Electric traction and transmission engineering . 5 NUMBER OF NEGATIVE FEEDERSFig. 69. equal, the negative bus bar being insulated from the groundat the station. If, in addition, use be made of negative boosters in thefeeders, the potentials at the feeding points can be rnain-tained uniform with that of the negative bus-bar even withwidely fluctuating loads. The amount to which the original leakage current isreduced by various numbers of such negative feeders andboosters as a percentage of what would exist in the caseof no feeders, is shown in Fig. 69. THE DISTRIBUTING SYSTEM. l6l If the contact-conductor sections be supplied by individ-ual feeders and the current of each be passed through thefield exciting coil of the booster which is connected to thetrack feeder for the corresponding section, as indicated inFig. 70, the potential of the track feeding points can bekept practically equal to that of the negative bus at thestation. It should be noted that the track rails are insu-lated from the negative bus. This arrangement of connec-. NEGATIVE TRACK FEEDERSFig. 70. tions is the most effective one for minimizing electrolyticcorrosion in those systems which return current throughthe grounded track rails. 56. Electrolytic Surveys. — The determination as towhether and to what extent track feeders shall be installeddepends upon the conditions which result from the opera-tion of a road. These conditions are usually found by mak-ing an electrolytic survey and stud3dng the results therebyattained. The difference of potential between the tracksand the various pipe systems is measured at many pointsthroughout the roadway. Care must be taken that goodterminal contacts be secured, for these differences seldomamount to more than a few volts. Upon a map, whichclearly shows all the tracks, the potential differences areplotted as ordinates with respect to the track as abscissae,and a curve is drawn through their ends. Wherever the l62 TRACTION AND TRANSMISSION. track is positive
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