Comparison of Zero Sequence Based Directional Protection Methods for Single Line to Ground Fault in Radial Distribution Systems

With the increase in urbanization, underground cable
usage in distribution systems has increased. This has
led to the inability of traditional non-directional
protection practice in distribution systems and in some
cases the practice of directional protection has become
imperative. Directional protection is more expensive
than conventional methods as additional instrument
transformers are required. For this reason, it is
necessary to know the cases in which directional
protection is required The amplitude of the fault current
seen by the protective relays during the fault is affected
by the neutral grounding resistance and the phase-toearth capacity depending on cable length . The
protective relays may misoperate depending on these
two parameters. In this study, under the single line to
ground fault condition the selective ranges of the simple
non-directional method are determined in terms of
cable length and grounding resistance. In this way,
useful information has been provided in order to
prevent the system operator from false tripping and to
increase the supply security. Zero sequence-based
directional protection methods, which are well known in
the literature, are tested in regions where the selectivity
is not provided. These methods are compared in terms
of their selectivity percentages.