encroachment. Separate resistive blinder setting is available in forward and reverse
direction.
The use of the load encroachment feature is essential for long heavily loaded lines,
where there might be a conflict between the necessary emergency load transfer and
necessary sensitivity of the distance protection. The function can also preferably be
used on heavy loaded, medium long lines. For short lines, the major concern is to get
sufficient fault resistance coverage. Load encroachment is not a major problem. See
section
""
.
R
X
Z1
Load impedance
area in forward
direction
RLdRv
R
Z1
ArgLd
RLdFw
IEC09000248-2-en.vsd
X
IEC09000248 V2 EN
Figure 85:
Load encroachment phenomena and shaped load encroachment
characteristic
7.3.7.9
Simplified logic schemes
PHSL1, PHSL2,...PHSL3L1 are internal binary logical signals from the Phase-
selection element. They correspond directly to the six loops of the distance zones and
determine which loops should be released to operate.
FWL1, FWL2,...FWL3L1 and RVL1, RVL2,...RVL3L1 are the internal binary
signals from the Directional element. An FW signal is activated if the criteria for a
forward fault or load is fulfilled for its particular loop. The equivalent applies to the
reverse (RV) signals.
The internal input 'IN present' is activated if the residual current (3I0) exceeds 10% of
the maximum phase current magnitude and at the same time is above 5% of IBase.
However, if current transformer saturation is detected, this criterion is changed to
residual voltage (3U0) exceeding 5% of UBase/sqrt(3) instead.
Section 7
1MRK502052-UEN B
Impedance protection
220
Technical manual
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