Fault Infeed From Remote End - ABB RELION 670 Series Applications Manual

Section 7
Impedance protection
=
3I
0
EQUATION1271 V3 EN-US
Where:
3I
0
I
R
I
L
I
C
The neutral point reactor is normally designed so that it can be tuned to a position where the
reactive current balances the capacitive current from the network that is:
w
=
L
× ×
3
EQUATION1272 V1 EN-US
IEC05000216 V2 EN-US
Figure 138: High impedance earthing network.
The operation of high impedance earthed networks is different compared to solid earthed
networks where all major faults have to be cleared very fast. In high impedance earthed
networks, some system operators do not clear single phase-to- earth faults immediately; they
clear the line later when it is more convenient. In case of cross-country faults, many network
operators want to selectively clear one of the two earth-faults. To handle this type phenomena,
a separate function called Phase preference logic (PPLPHIZ) is needed, which is not common
to be used in transmission applications.
In this type of network, it is mostly not possible to use distance protection for detection and
clearance of earth-faults. The low magnitude of the earth-fault current might not give start of
the zero sequence measurement element or the sensitivity will be too low for acceptance. For
this reason a separate high sensitive earth-fault protection is necessary to carry out the fault
clearance for single phase-to-earth fault.
7.9.2.2

Fault infeed from remote end

All transmission and most all sub-transmission networks are operated meshed. Typical for this
type of network is that fault infeed from remote end will happen when fault occurs on the
protected line. The fault current infeed will enlarge the fault impedance seen by the distance
protection. This effect is very important to keep in mind when both planning the protection
system and making the settings.
With reference to figure 139, the equation for the bus voltage U
250
( )
2
+ -
I I I
2
R
L C
is the earth-fault current (A)
is the current through the neutral point resistor (A)
is the current through the neutral point reactor (A)
is the total capacitive earth-fault current (A)
1
w
C
1MRK 504 152-UEN B
(Equation 211)
(Equation 212)
GUID-4380CD3A-BCB0-45F1-A821-BC3E6D070C04 v1
at A side is:
A
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