ABB Relion 670 Series Technical Reference Manual page 158

Section 6
Current protection
152
=
U U I
refL 1 L 1 dirL 1
EQUATION1452 V1 EN
=
U U I
refL 2 L 2 dirL 2
EQUATION1453 V1 EN
=
U U I
refL 3 L 3 dirL 3
EQUATION1454 V1 EN
The polarizing voltage is available as long as the positive-sequence voltage
exceeds 4% of the set base voltage UBase. So the directional element can use it for
all unsymmetrical faults including close-in faults.
For close-in three-phase faults, the U1
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 terminal 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.
The directional setting is given as a characteristic angle AngleRCA for the function
and an angle window AngleROA.
=
I
L 1
=
I
L 2
=
I
L 3
memory voltage, based on the same
L1M
1MRK 505 208-UEN B
(Equation 7)
(Equation 8)
(Equation 9)
Technical reference manual