The Relation of the Petersen System of Grounding 



Power Networks to Inductive Effects in 



Neighboring Communication Circuits 



By H. M. TRUEBLOOD 



THE purpose of this paper is to present a simple theoretical treat- 

 ment of those features of the Petersen methcd of grounding a 

 power network which are of principal interest from the standpoint 

 of inductive effects in neighboring communication circuits. In this 

 method, the neutral of the system is grounded through an inductance 

 which is in resonance, at the fundamental frequency, with the total 

 direct capacity of the system to ground. The theory of the behavior 

 of a power system thus grounded at times of accidental faults to 

 earth has been developed by Petersen in a paper published in 1919,' 

 in which the results of field tests and of operating experience with an 

 installation in Germany are also described. The methcd has also 

 found application in other places in Europe, chiefly in Italy and 

 Switzerland. It does not appear in any of these cases that inductive 

 interference was a factor requiring, or at any rate receiving, consider- 

 ation. In fact, it does not seem that either Petersen himself, or other 

 engineers in Europe who have made use of his scheme, have considered 

 it except as a method of protecting power systems from the effects of 

 accidental grounds. 



The features of the method that are of interest from the viewpoint 

 of inductive interference relate both to normal operating conditions 

 of the power system and to the phenomena which occur when a phase 

 of the system is grounded. With regard to the former, it is principally, 

 though not entirely, the effect of the neutral reactor on the harmonics 

 of frequencies within the voice range that require examination; with 

 respect to the latter, the things of chief, though not exclusive, import- 

 ance, are the ground currents and unbalanced voltages to ground of 

 fundamental frequency, which are possible sources of disturbance 

 in exposed communication circuits. 



These features, particularly those concerned with effects at funda- 

 mental frequency, are more or less closely related to questions of 

 primary importance from the standpoint of power system operation. 

 It is impossible that this should not be the case. Accidental dis- 

 turbances of a character which may interrupt service or endanger 

 apparatus or equipment in a power system may produce inductive 



»W. Petersen, Elektrotechnische Zeitschrit, 40, pp. 5-7 and 17-19, 1919; Sci. 

 Abs. B, Nov. 29, 1919. 



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