PETERSEN SYSTEM OF GROUNDING 47 



a low resistance. There will appear, however, electrically^ induced 

 voltages of fundamental frequency substantially identical with those 

 that would occur with neutral isolated. Where the communication 

 circuits are in underground cable, these voltages are of inappreciable 

 magnitude, and with aerial cables (with metallic sheaths) their effects 

 can in general be controlled without great difficulty. With open 

 wire communication circuits, electrically induced voltages are of 

 much more consequence. They may in some cases equal or exceed 

 the voltages which would be induced electromagnetically with dead- 

 grounded neutral. However, except perhaps in cases of long ex- 

 posure to high voltage power circuits at close separations, their 

 effects are generally much less severe than the electromagnetic effects, 

 because of the smaller amount of energy transferred to the disturbed 

 circuit. This is in general accordance with experience with open 

 wire circuits exposed to power circuits of moderate voltage. As is 

 explained in the next paragraph, the use of a Petersen reactor to ground 

 the neutral may be expected to lessen the severity of inductive effects 

 which would be experienced from an isolated system, by preventing 

 additional parts of the power system from becoming involved. 



As compared to the isolated system, the use of the Petersen coil in 

 the connection from neutral to ground may be expected to have the 

 advantage, according to the theory of the first subdivision of this 

 section, of preventing the formation of an "arcing ground." As ex- 

 perience has shown, an arcing ground in an isolated system is fre- 

 quently the cause of serious disturbances which may involve portions 

 of a network remote from the location of the original trouble. The 

 advantage of the reactor in this respect is, of course, a fundamental 

 one from the standpoint of power operation. It is in general of pro- 

 portionate importance from the inductive interference point of view, 

 at least where a power network is involved in parallels with com- 

 munication circuits at several places, as is not infrequenctly the case 

 near large cities. A breakdown to ground in the power network on a 

 different phase from that originally involved, and in a different locality, 

 may lead to large phase-to-phase currents in the earth, from the 

 second fault to the first, or to a ground intentionally placed on the 

 phase first involved, in order to short circuit the arc. The inductive 

 effects thus become electromagnetic in character, and the inter- 

 ference produced in this manner may be severe. 



The possibility that the reactor might tend to produce a greater 



'"Electrically" is used here and elsewhere in this paper in the sense in which 

 "electrostatically" is perhaps more commonly used. The phenomena involved 

 are not static and the latter word is inappropriate on this account. 



