Fault Infeed From Remote End - ABB RELION 650 Series Applications Manual

Section 7
Impedance protection
IEC05000216 V2 EN-US
Figure 54: 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.
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 elements 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.
7.1.2.2

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 55, the equation for the bus voltage U
U = I
A
EQUATION1273-IEC-650 V2 EN-US
If we divide U
U
Z =
A
I
EQUATION1274-IEC-650 V1 EN-US
The infeed factor (I
impedances at local and remote end.
104
( )
⋅ ⋅ p Z + I + I ⋅ Rf
A L A B
by I we get Z present to the IED at A side.
A A
I + I
A
A B
= p ·Z +
L
I
A A
+I )/I can be very high, 10-20 depending on the differences in source
A B A
·R
f
1MRK 505 363-UEN A
GUID-E28CCC52-497F-4B79-9430-8A2155FED936 v4
at A side is:
A
(Equation 37)
(Equation 38)
Application manual