Abstract
This paper presents novel zero sequence current filter and earth fault protection relay, which utilize cable screens earthing current in protection algorithm. Different problems connected with state of the art of zero sequence current filters and protection relays are presented and compared with the proposed solution. The presented concept is verified in PowerFactory simulation software, experiment concerning modeling the earth fault current flow in medium voltage (MV) cable supplied from the low voltage (LV) network and measurements in the MV network in the Polish distribution system. The proposed solution is characterized by higher sensitivity and reduced number of erroneous trips. The presented solution is suitable for any MV cable lines. Biggest advantages are observed in power output lines from renewable energy sources, which are often operated under no-load conditions.
Highlights
Experience in the operation of distribution system networks indicates that among all electrical disturbances, approximately 70% are earth faults [1]
Earth faults are connected with different phenomena, which have an unfavorable impact on power quality and reliability of supply, as well as on the risk of overvoltages and electrical shocks
The risk is high in the vicinity of phase to earth fault site, in some cases, the dangerous voltage can be transferred to the low voltage network through a common earthing system [8]
Summary
Experience in the operation of distribution system networks indicates that among all electrical disturbances, approximately 70% are earth faults [1]. Results of scientific research indicate, that the wide utilization of medium voltage (MV) cables with screens, which are common in distribution system network, create the possibility of using screens current measurements during the earth faults to increase the efficiency of protection relays operation. It is believed that presented zero sequence current filter could be used for detection of phase to phase short circuits and, has the potential to be an independent protection relay, which utilizes only one current input that could greatly simplify the protection relay hardware since the number of current inputs could be reduced Another innovation presented in the paper is the possibility to distinguish if earth fault occurred in the cable or overhead line of mixed—cable overhead feeder.
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