ABB REL670 2.2 IEC, Руководство по применению

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case basis, as shown in figure 213 . 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
214 ).
Negative IED impedance, negative fault current (current inversion)
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If equation 377 is valid in Figure 201 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 fault current
will cause a high voltage on the network. The situation will be the same even if a
MOV is used. However, depending upon the setting of the MOV, the fault current
will have a resistive component.
X X X
C S
> +
11
EQUATION2036 V2 EN-US
(Equation 377)
The problems described here are accentuated with a three phase or phase-to-phase
fault, but the negative fault current can also exist for a single-phase fault. The
condition for a negative current in case of an earth fault can be written as follows:
1_ 1 0 _ 1 0 _ 1_
3 2 2
× > × + + × +
C L L S S
X X X X X
EQUATION1920 V1 EN-US
(Equation 378)
All designations relates to figure 201 . A good protection system must be able to
cope with both positive and negative direction of the fault current, if such
conditions can occur. A distance protection cannot operate for negative fault
current. The directional element gives the wrong direction. Therefore, if a problem
with negative fault current exists, distance protection is not a suitable solution. In
practice, negative fault current seldom occurs. In normal network configurations
the gaps will flash in this case.
Double circuit, parallel operating series compensated lines
GUID-7A384A24-143F-4695-8214-33E181AD0AB7 v2
Two parallel power lines running in electrically close vicinity to each other and
ending at the same busbar at both ends (as shown in figure
215 ) causes some
challenges for distance protection because of the mutual impedance in the zero
sequence system. The current reversal phenomenon also raises problems from the
protection point of view, particularly when the power lines are short and when
permissive overreach schemes are used.
en06000627.vsd
-jX
C
-jX
C
Z
AC
Z
CB
Z
AC
Z
CB
A B
Z
m0AC
Z
m0CB
IEC06000627 V1 EN-US
Figure 215: Double circuit, parallel operating line
Section 8
1MRK 506 369-UEN B
Impedance protection
390 Line distance protection REL670 2.2 IEC
Application manual