CABLE TESTING 



807 



connection, the generator voltage was practically doubled BO 

 that the effective voltage at the cable was the same in l><>th 

 cases. 



It is seen that with the same generator, the same transformer, 

 the same frequency and the same cable an approximately sinu- 

 soidal P.D. wave becomes badly distorted by simply changing 

 the transformer ratio and the generator voltage. 



These effects may be explained in a general way as follows: 

 As the generator is a single-phase machine, the tendency of the 

 armature reaction is to introduce a third harmonic in the P.D. 

 wave. The transformer is worked at high saturation and through 



FIG 438 P.D. and exciting current waves when cable having a capacity 

 of 0.13 M.F. is attached to transformer; 25,000-volt connection used. 



variations in the permeability of the core introduces harmonics, 

 especially the third, into the magnetizing current. These har- 

 monics appear in the voltage wave and are intensified by the 

 capacity load on the secondary of the transformer. 



In addition, resonance effects are probably present. Attemp 

 at tuning the circuit by an iron-cored reactance in parall 

 the transformer were not successful, for: 



1. The minimum current does not necessarily correspo 

 the best wave form. . 



2. The best wave form may occur at an abnormally 1 



value of lagging current. 



3. The wave form cannot be made sinusoidal in every case. 



