THE LOCALISATION OF BREAKS AND FAULTS 



547 



tages of the testing battery. The observations a and b in each 

 pair are marked off on the base line from their respective ends 

 and lines drawn connecting these points with vertical voltage 

 line. The perpendicular at the intersection of these lines will 

 represent the difference of potential at the fault and will cut 

 the base line at the fault's position. 



In order to keep the resistance lines within the limits of the 

 board in pairs 3, 4 and 5 the voltage scale was taken at half 

 and the resistance scale at one-tenth its former value. The 



Fig. 312. — Graphic Localisation by Betts' Method. 



result of all intersections gives the position of fault as approxi- 

 mately 2,500 ohms from A : the actual distance was 2,475 ohms. 

 The difference is due to the resistance of galvanometers and 

 batteries at A and B not having been allowed for. 



It will be seen by formula (4) that the resistance of the fault 

 varied from 180 ohms in the first pair to 5,200 ohms in the last 

 pair of observations, the battery power being unaltered. 



By this method, as only part of the cable is under test, there 

 is a corresponding gain in quickness of charge, lower resistance 

 and reduction of earth current effect, so that a large number 

 of distinct tests can be quickly made. No comparison or 



N n2 



