THE LOCALISATION OF BREAKS AND FAULTS. 



485 



The connections for the test with the slides are as shown in 

 Fig. 269. Before taking observations, the cable and condenser 

 should be thoroughly discharged by running the slides index to 

 zero (the earthed end) and closing the galvanometer key. 

 When there is no deflection on the galvanometer the conditions 

 are right for the test. This should be done every time the 

 observations are repeated, so that every set of readings is 

 started with the cable and condenser completely discharged. 



The battery is then applied to the condenser and cable by 

 closing and clamping down the charge key. After a few 

 seconds' charge the galvanometer key is tapped, and the slides 

 adjusted until a position is found in which the galvanometer is 

 not affected. The charge key is then released, thus earthing 



Cable (Capacity K) 



Condenser 

 (Capacity F) 



'M'h 



Fig. 270. — Distribution of Potentials in Gott's Capacity Test. 



the condenser, and the point V discharged through galvano- 

 meter to earth as described. 



The operation of charge and balance Is then repeated, this 

 time putting the final touch on the slides to balance after a 

 period of charge suflBcient to fully charge the cable, which may 

 be taken at 5 seconds on cables up to 500 miles, 10 seconds up 

 to 1,000, 15 up to 1,500, 20 up to 1,800 and 30 up to 2,000 and 

 over. 



As recommended by Sir William Thomson in the Paper 

 above referred to, the observations should be repeated with the 

 current reversed to eliminate earth current efiect. The balance 

 with both currents should be to zero of the galvanometer, and 

 the mean of the two slide readings taken as the result. 



