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

Section 7
Impedance protection
IEC05000216 V2 EN-US
Figure 125: High impedance earthing network
The operation of high impedance earthed networks is different compare 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.
7.5.2.3

Fault infeed from remote end

All transmission and most all sub transmission networks are operated meshed. Typical for this
type of network is that we will have fault infeed from remote end when fault occurs on the
protected line. The fault 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 126, we can draw the equation for the bus voltage Va at left side as:
=
V I p Z
A A
EQUATION1273 V1 EN-US
If we divide Va by IA we get Z present to the IED at A side
V
=
Z
A
I
EQUATION1274 V2 EN-US
The infeed factor (IA+IB)/IA can be very high, 10-20 depending on the differences in source
impedances at local and remote end.
226
× × + + ×
( I I ) R
L A B f
+
I I
= × + ×
a
p Z A B R
L
I
A A
f
1MRK 504 152-UEN B
SEMOD154680-84 v2
(Equation 169)
(Equation 170)
Application manual