V. SIMULATION RESULTS
AND DISCUSSION
The problem with conventional detection
schemes is that it monitors only low-impedance
faults (LIFs that result in instantaneous and large
increments of current due to a low-impedance path
to ground (short circuit). A HIF seems invisible to
such detection methods because it presents only a
small increment in line current and appears to be a
normal load increment.
As depicted in figure 8, HIF is simulated
on sample distribution system and fault current is
measured at breaker. Waveforms obtained are
shown in fig 9. It can be seen that there is phase
shift occurred in HIF waveforms; this phase shift is
used to find a reliable protection scheme for HIF in
distribution system.
As discussed conventional protection
scheme id insufficient to detect such faults hence a
new method to protect distribution system for these
faults is essential. A numerical relay can be
designed in such a way that it will detect presence
of these patterns and isolate system. A novel
method of differential protection with numerical
relay can be used to protect system against all types
of faults.