SOME ASPECTS OF NOISE INDUCTION 489 



transformer eflfects are usually less important than the generator 

 effects (unless the "triples" in the generator are unimportant or are 

 suppressed). 



To demonstrate the effect of triple harmonic currents, the arrange- 

 ments shown in Fig. 13 have been set up. This set-up is similar to that 

 used in showing the effect of differences in wave shapes of balanced 

 voltages except that, to show the added effect of triple harmonic 

 residuals, the delta winding is opened. This removes the path for 

 triples to circulate within the transformer bank and permits them to 

 be impressed on the line. Figures 14-^1 and B are oscillograms showing 

 the effect on the wave shape of the voltage to neutral of opening the 

 delta. The noise from the loud speaker increases when the delta is 

 opened showing that the triple harmonics cause an increase in the 

 influence of the power line. 





14-A 



Fig. 14 — Oscillograms showing voltage wave shape including triple harmonics. 



14-.i4 — Impressed voltage, 



14-5 — Distorted voltage to neutral, including triple harmonics. 



An interesting demonstration showing the relation as regards resid- 

 uals of triple and non-triple harmonics on an otherwise well balanced 

 three-phase system can be performed as follows: 



1. The untransposed power line is first energized with balanced dis- 



torted voltages as described previously. The amount and 

 character of the noise are observed closely. 



2. Triple harmonic voltages are added by opening the delta winding 



on the transformer bank. Under these conditions, the induc- 

 tion from both the triple and non-triple harmonics can be 

 recognized by the differences in the character of the sounds. 



3. The power line is now transposed and the noise due to the non- 



triples practically disappears leaving the noise from the triples 

 unaffected. 



This illustrates the residual character of the triples since, as shown 

 previously, the power system transpositions do not affect the induction 

 from residuals. 



