R
X
RLdFwd
RLdRev
LdAngle
LdAngle
LdAngle
LdAngle
R
X
RLdFwd
RLdRev
LdAngle
90%
10%
10%
LdAngle
Possible
load
LdAngle
LdAngle
ANSI12000176-1-en.vsd
ANSI12000176 V1 EN-US
Figure 92: Load impedance limitation with load encroachment
During the initial current change for phase-to-phase and for phase-to-ground faults,
operation may be allowed also when the apparent impedance of the load encroachment
element is located in the load area. This improves the dependability for fault at the
remote end of the line during high load. Although it is not associated to any standard
event, there is one potentially hazardous situation that should be considered. Should
one phase of a parallel circuit open a single pole, even though there is no fault, and the
load current of that phase increase, there is actually no way of distinguish this from a
real fault with similar characteristics. Should this accidental event be given precaution,
the phase-to-ground reach (RFPG) of all instantaneous zones has to be set below the
emergency load for the pole-open situation. Again, this is only for the application
where there is a risk that one breaker pole would open without a preceding fault. If this
never happens, for example when there is no parallel circuit, there is no need to change
any phase-to-ground reach according to the pole-open scenario.
8.2.3.9 Other settings
GUID-9D65B411-6FE2-433B-AE6C-C6DD716D1181 v7
IMinOpPGZx and IMinOpPPZx
The ability for a specific loop and zone to issue a start or a trip is inhibited if the
magnitude of the input current for this loop falls below the threshold value defined by
these settings. The output of a phase-to-ground loop n is blocked if In <
IminOpPG(Zx). In is the RMS value of the fundamental current in phase n.
The output of a phase-to-phase loop mn is blocked if Imn < IMinOpPP(Zx). Imn is the
RMS value of the vector difference between phase currents m and Ln.
Section 8 1MRK 502 071-UUS A
Impedance protection
224 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
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