PETERSEN SysrE^f OF CROL'NDINC S3 



in which the symbols for coil impedance and line admittance are 

 accented to denote that they refer to the harmonic freciuency in 

 question; 



_ Eoim* (x' - 1) . 

 y n — 



and 



1 + W2 {x' - 1)' 



1 ^n I = — ^^ . approximately. 



For isolated neutral, 



V„ = £oi 



The neutral is thus subjected to a third harmonic voltage some 12 

 per cent, greater than if it were isolated, but for the higher harmonics 

 belonging to this series (of the third and its odd multiples), the differ- 

 ence is inappreciable. 



The residual voltage for a harmonic of this series is 



F, = 3 (Eoi - V„) (7) 



1 



and 



~ ^^'' 1 -]- mHx' - 1)' 



^r I = — — ^» approximately. (8) 



w* — 1 



The corresponding neutral current is 



In = 



1 +z'„r' 



and 



I /« I = —TZTi' approximately. (9) 



From the standpoint of noise interference in telephone circuits, 

 residuals of the series consisting of the third harmonic and its odd 

 multiples are frequently troublesome where the neutral of a three- 

 phase system is grounded directly or through a low resistance. These 

 residuals, of course, are not affected by power circuit transpositions, 

 either as to their magnitudes or as to their inductive effects upon 

 exposed telephone circuits. It is therefore of interest to examine xhe 

 expressions just obtained for the case in which the neutral is grounded 

 through the coil. While the neutral current will not be the same as 



