ABB RELION 670 SERIES Applications Manual page 205

1MRK 506 369-UUS -
Line distance protection REL670 2.2 ANSI
Application manual
jX
X
12
X
11
Z
S
X
C
en06000625.vsd
IEC06000625 V1 EN
Figure 97: Cross-polarized
quadrilateral
characteristic
If the distance protection is equipped with a ground-fault measuring unit, the negative
impedance occurs when
× > × +
3 X 2 X X
C 1 _ 11 0 _ 11
EQUATION1919 V1 EN
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 97. Distance IEDs with separate impedance and directional measurement offer
additional setting and operational flexibility when it comes to measurement of negative
apparent impedance (as shown in figure 98).
Negative IED impedance, negative fault current (current inversion)
If equation 74
X X X
> +
11
C S
EQUATION2036 V2 EN
in figure 83 and a fault occurs behind the capacitor, the resultant reactance becomes
negative and the fault current will have an opposite direction compared with fault current
in a power line without a capacitor (current inversion). The negative direction of the fault
current will persist until the spark gap has flashed. Sometimes there will be no flashover
at all, because the fault current is less than the setting value of the spark gap. The negative
jX
R
RV
R
Z
S
IEC06000584-SMALL V1 EN
Figure 98:
Section 8
Impedance protection
X
12
X
11
R
R
FW
X
C
en06000584_small.vsd
Quadrilateral
characteristic with
separate impedance and
directional measurement
(Equation 73)
(Equation 74)
199