ABB RELION RET670 Applications Manual page 290

Section 8
Impedance protection
284
X
ANSI05000722 V1 EN-US
Figure 133: 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
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.
AngNegRes
AngDir
R
en05000722_ansi.vsd
memory voltage, based on the same positive
AM
1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual