RFL Electronics RFL 9300 - Figure 3-19. Transformer In-Rush

Figure 3-19. Transformer in-rush
In general, this makes the RFL 9300 suitable for all tapped lines, except for those applications where the trans-
former allows significant zero-sequence current to flow from the high-side to feed low-side faults. An example of
this is the wye-wye transformer configuration shown in Figure 3-20, where both sides are solidly grounded. The
RFL 9300 would not work well in this application because its 3I
0
bias level would have to be raised to prevent
the RFL 9300 from false-tripping on low-side SLG (single line-to-ground) faults. This prevents the RFL 9300
from detecting low-current SLG faults on the protected line, such as the ones caused by high resistance ground
faults. Fortunately, the condition shown in Figure 3-20 appears to be quite rare. Most tapped transformer appli-
cations appear to be delta high-side and grounded-wye low-side.
RFL 9300 RFL Electronics Inc.
August 25, 2000 3 - 21 (973) 334-3100