226 BFXL SYSTEM TECHNICAL JOURNAL 



pipes, cables, and other structures along which current in the earth 

 will flow to a greater or less extent. These structures have varying 

 degrees of conductivity and some of them have, either by design or by 

 accident, high resistance joints. Consequently the paths of earth 

 currents are exceedingly complex. The conditions as to earth currents 

 and earth potentials necessary to be known in order to work out any 

 coordinated scheme of grounding would usually have to be determined 

 by tests. 



The different kinds of grounds to be considered include those on: 

 power transmission circuit neutrals, lightning arresters, power distribu- 

 tion primary neutrals, power distribution secondaries, railway systems, 

 building conduits, telephone protectors, batteries, ringers, telegraph 

 circuits, lightning rods, electrolysis protection systems, various types 

 of signal circuits such as fire and police alarm systems, and so on. 

 The grounding practises for all these different systems should be care- 

 fully studied and coordinated in order to prevent so far as possible 

 harmful reactions among them. Such a study of course goes consid- 

 erably beyond the scope of this subcommittee. 



Comparison of Different Protective Measures. — The ideal protective 

 measure would be one which furnished adequate protection and had 

 no unfavorable reaction from an economic or service standpoint on 

 the system to which it is applied. However, the work thus far has 

 not disclosed any measure which fully meets this ideal. 



The relative advantage of different measures resolves itself into a 

 question of the best technical results which can be obtained at the 

 least over-all cost. The solution of problems consists of finding meas- 

 ures which afford the highest degree of protection which is practicable 

 and reasonable under the circumstances. In the investigation of a 

 specific case it may be found that certain protective measures can be 

 combined with other work in such manner that the cost is not wholly 

 chargeable to coordination for the reason that other results of value 

 are secured. For example, shielding may be obtained at small cost 

 if improvement of performance of a transmission line justifies the in- 

 stallation of ground wires; or, the benefits of shorter duration of in- 

 duced voltage by the use of high speed circuit breakers and high speed 

 relays may be secured in connection with a program for improving the 

 stability of power systems. 



No other measure affords such complete protection against all effects 

 of induction as adequate separation. However, measures applied to 

 power systems such as fault current limitation which strike directly at 

 the source of low-frequency induction are of a basic character and per- 

 mit a closer association of the two classes of lines, a very important 



