ABB Relion 670 series, Technical Manual

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R
X
AngDir
AngNegRes
en05000722_ansi.vsd
ANSI05000722 V1 EN-US
Figure 76: Setting angles for discrimination of forward and reverse fault in Directional
impedance quadrilateral function ZDRDIR (21D)
The reverse directional characteristic is equal to the forward characteristic rotated by 180
degrees.
The polarizing voltage is available as long as the positive sequence voltage exceeds 5% of the set
base voltage
VBase. So the directional element can use it for all unsymmetrical faults including
close-in faults.
For close-in three-phase faults, the V1
AM
memory voltage, based on the same positive sequence
voltage, ensures correct directional discrimination.
The memory voltage is used for 100 ms or until the positive sequence voltage is restored.
After 100 ms the following occurs:
• If the current is still above the set value of the minimum operating current (between 10 and
30% of the set IED rated current
IBase), the condition seals in.
• If the fault has caused tripping, the trip endures.
• If the fault was detected in the reverse direction, the measuring element in the reverse
direction remains in operation.
• If the current decreases below the minimum operating value, the memory resets until the
positive sequence voltage exceeds 10% of its rated value.
7.1.7.6 Simplified logic diagrams
M13841-35 v2
Section 7 1MRK 502 066-UUS B
Impedance protection
192
Technical manual