Arcing Grounds and Effect of Neutral Grounding Impedance

This paper was written to review and extend the theory of overvoltages due to arcing grounds because of the increasing tendency to use impedances between the neutral point and the ground, thereby losing the advantage of the solidly grounded neutral. The ``third class conductor´´ theory of Steinmetz is touched upon very briefly and is considered as not applying to transmission line conditions. The theory when the phenomenon is controlled by normal frequency arc extinction, as presented by Peters and Slepian, is reviewed and the maximum voltage for this analysis is found to be 3 ¿ E, where E is the normal line to neutral voltage. The theory when the phenomenon is controlled by oscillatory frequency arc extinction as originated by Dr. Petersen is given in detail but in a modified and extended form. The maximum voltage for a single-phase circuit when no damping is considered is found to be 6 E. The analysis for the three-phase circuit is newly developed for the case in which there is an impedance between the neutral and ground and the maximum voltage is found to be 7 ¿ E when the effect of the damping factors and capacitance between lines is neglected. The method of determining the various reductions or damping factors is outlined. The effect of a neutral grounding resistor is discussed and it is pointed out that a suprisingly high value of resistance can be used without incurring the possibility of dangerous overvoltages.