Resonant grounded grids - quo vadis!?

Abstract

In earth fault compensated networks the basically capacitive earth fault current is counterbalanced by the injection of an inductive current through the arc suppression coils in such a way, that for most overhead line faults these arcs extinguish without the necessity of disconnecting the faulty grid section. Therefore these grids can be classified as self healing grids which have good power quality. Due to the fact of sometime prolonged earth fault current flow special safety precautions must be met. When present-day grids are extended by the installation of additional cables, their operation is subjected to limitations concerning the effects of the earth fault current. The current can exceed the admissible limits and an innovative neutral point treatment is necessary. This effect leads to costly modifications of either the grounding systems or modifications in the protection schemes or both. As far as standardization is concerned, the present standards in central Europe may undergo changes which will lead to modifying the design and operation mode of these networks. This network operation implicates problems in localization of earth faults, especially concerning the in-depth localization. Under these aspects the operation mode of principally continuing the regime of resonance grounded networks with a change to transient middle ohmic earth fault compensated networks in case of a persisting earth fault appears to be in many cases an attractive solution. (4 pages)