The subject of this thesis is to examine how the size of a distribution network,
which primarily consists of underground cables, influences single phase earth fault
currents and poliphase fault currents in various locations of the network and also how
this influences protective relay detection and operation.
For better understanding of this subject the basic operating principles of
directional earth fault relays and non-directional overcurrent relays are explained.
In this thesis calculations of various faults in different locations were made on a
theoretical model of a distribution network which consists of four long radial cable
feeders, which is shown in appendix A. For each fault type and location we also
calculate and simulate protective relay measurements.
A great emphasis is given on how the fault location influences single phase earth
fault currents and directional earth fault relay measurements.
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