PETERSEN SYSTEM OF GROUNDING 



49 



resistance which, as a method of grounding the neutral, would gener- 

 ally suffice to prevent interference from ground currents at times of 

 faults to ground, but which apparently presents difficulties from the 

 relay standpoint similar to those involved in the use of the Petersen 

 coil. 



II. Effects with Power System in Normal Condition 



1. Fundamental Frequency 



Referring to Fig. 5 (we now take account of inequalities in the ad- 

 mittances to ground), 



Fig. 5 — Three-phase System with Neutral Grounded Through Reactor. Admit- 

 tances to Ground Not Balanced. 



£oi — Tt^ ~ -^02 — 'Tr~ -^03 — TF ~~ ^n^n, 



/l + /2 + /a = In, 



so that 



In 



FiEoi + 72^02 + Y,E, 



1 + Z„7 



where F = Fi + F2 + F3 = total direct admittance to ground. 

 If the impressed voltages are balanced 



-Eoi 



/n = 



(Fi + Y2eJ'''°-^ YseJ'*n- 



1 +Z„Y 



The parenthesis is the " residual admittance " ^ to ground and, if 

 the three leakances to ground are equal, it can vanish only if 



' Inductive Interference between Power and Communication Circuits, California 

 Railroad Commission, p. 269. 



