ordinary fault. However, a good protection system should be able to operate correctly
before and after gap flashing occurs.
IEC06000625 V1 EN-US
Figure 108: Cross-polarized
quadrilateral
characteristic
jX
R
X
11
X
12
X
C
Z
S
X
FW
X
RV
R
FW
R
RV
IEC06000584-SMALL V1 EN-US
Figure 109: Quadrilateral
characteristic with
separate impedance
and directional
measurement
If the distance protection is equipped with a ground-fault measuring unit, the negative
impedance occurs when
1_11 0 _11
3 2× > × +
C
X X X
EQUATION1919 V1 EN-US (Equation 78)
Cross-polarized distance protection (either with mho or quadrilateral characteristic)
will normally handle ground-faults satisfactory if the negative impedance occurs inside
the characteristic. The operating area for negative impedance depends upon the
magnitude of the source impedance and calculations must be made on a case by case
basis, as shown in figure 108. Distance IEDs with separate impedance and directional
measurement of
fer additional setting and operational flexibility when it comes to
measurement of negative apparent impedance (as shown in figure 109).
Negative IED impedance, negative fault current (current inversion)
SEMOD168320-408 v2
If equation 79
EQUATION2036 V2 EN-US (Equation 79)
in figure 94 and a fault occurs behind the capacitor, the resultant reactance becomes
negative and the fault current will have an opposite direction compared with fault
Section 8 1MRK 504 163-UUS A
Impedance protection
232 Transformer protection RET670 2.2 ANSI
Application manual
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