The article presents the results of research in the field of limiting the effects of overvoltages and improving the conditions for the self-extinguishing of transient faults in medium voltage networks with earth fault current compensation. The aim of the research was to estimate the level of overvoltages generated by an earth fault during re-ignition of the electric arc and to assess the possibility of reducing them by increasing the attenuation of the earth fault circuit. The results of the conducted tests show that to increase the attenuation, which ensures a significant effect of limiting such overvoltages, it is enough to change the way of operation of the devices forcing an additional active component of the earth fault current (AWSCz/ACFA). In Poland, such devices are commonly used to improve the effectiveness of earth fault protection. It was also found that the proposed solution enables accurate tuning of the Petersen coil in networks with natural asymmetry of earth capacitances. Therefore, changes in the operation of AWSCz/ACFA devices may have a beneficial effect on the limiting the effects of repeated ignitions during earth faults and, at the same time, enable the accurate tuning of the Petersen coil and increase its ability to extinguish arc-fed faults. Research and theoretical analysis of the issue were carried out on the basis of data characterizing the parameters of the earth fault circuits of the real 15 kV network.

In this paper, the benefits resulting from the application of YY0 and G0> earth fault protection with adaptive functions − limiting the risk of outsiders being shocked and reducing the likelihood of two-phase short-circuiting with the ground, are presented. The possibilities of improving the effectiveness of admittance protection by introducing special adaptive functions in control algorithms of station automation and decision algorithms of YY0 and G0> criteria are shown. The rules for using such functions have been described and it has been shown that they have a very significant impact on improvement the effectiveness of protection system. It can be stated that in typical medium voltage networks and solutions of active adaptive functions, good conditions are obtained for the operation of admittance protections even at several times higher resistances in the place of earth fault than when these functions are deactivated or not implemented.