CABLE TESTING ti'.n 



definite procedure should be adopted and used throughout tin- 

 iest, in order that the effects of absorption may be eliminated. 



The ballistic deflection of the galvanometer which occurs when 

 the key, K 2 , is thrown to the right, is read and compared with the 

 ballistic deflection obtained when the standard condenser is 

 substituted for the cable, the battery being kept constant. It 

 may be necessary to change the effective sensitivity of the gal- 

 vanometer, consequently an Aryton shunt may be used, as sug- 

 gested by the Fig. 432. The lead from the key to the cable core 

 should be as short as possible. If necessary, its capacity may 

 be determined and a suitable correction made. 



The capacity may also be measured by the simple bridge 

 method (see page 392). The connections for a single-conductor 

 cable or its equivalent are shown in Fig. 433. 



Generator 



Ground OT Unlaulted Conductor 



FIG. 433. Simple bridge method for measuring electrostatic capacity of a 

 short length of cable. 



In this case it is convenient to use an alternating current or a 

 rapidly interrupted direct current and to employ a telephone as 

 the detector. When the ratio ~ has been adjusted so that 



M C, 



there is the minimum sound in the telephone, Jj - Q t 



c - C M - 



x N 



The capacity of the other section, C n may bo similarly de- 

 termined by tests from the far end of the line. 



Then: / C \ 



Distance to the fault = total length of cable (^c) ( 15) 

 The condensers used for C. should be of good quality and the 

 procedure adopted should be the same as that employed wher 

 their capacities were measured. 



