R
X
AngDir
AngNegRes
en05000722_ansi.vsd
ANSI05000722 V1 EN
Figure 162: 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 100ms 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.
1MRK505222-UUS C Section 6
Impedance protection
315
Technical reference manual
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