General considerations in grounding the neutral of power systems

In the early days of power transmission, there was no consistent practise in respect to operating with neutral isolated or with neutral grounded. The rapid growth of transmission systems with their extensive networks soon began to show disastrous results from arcing grounds on isolated neutral systems and now most power transmissson networks have their neutrals grounded in some manner. The discussion of general considerations of neutral grounding is divided into two parts, that of overhead line systems and underground cable systems. He brings out the fact that while most overhead systems are grounded there is some difference in practise as to the extent to which they are grounded, that is as to whether they are grounded solidly or through resistance. Prevailing practise tends toward little or no resistance. Attention is called to different possible methods of grounding a system and shows by diagrams the flow of short-circuit current with the different methods. Underground cable systems are consistently operated with neutral grounded but general practise tends toward the use of resistance in neutral. General considerations as to protection from the voltage strains due to arcing grounds on cable systems are similar to overhead line systems and the author analyzes briefly the character of cable breakdowns and general effect of such breakdowns with a view to determining the importance of the extent to which a cable system should be grounded. The conclusion in regard to cable systems indicates about the same limitations as those found for overhead systems and no very good reasons are found for a distinctive difference in practise. The paper considers the use of grounding resistors of different types and gives some cast figures to show the effect of time and current in the design of metallic resistors. The general conclusion arrived at is that, on either overhead or underground transmission systems, high-voltage strains are more to be feared than high-current strains and that resistance to limit ground current, if used at all, should be of very low value.