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.
7.12.2.2
Fault infeed from remote end
GUID-E28CCC52-497F-4B79-9430-8A2155FED936 v3
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.
, the equation for the bus voltage U
A
at A side is:
U
I
p Z
I
I
Rf
A
A
L
A
B
=
⋅
⋅
+
+
(
)
⋅
EQUATION1273-IEC-650 V2 EN-US
(Equation 315)
If we divide U
A
by I
A
we get Z present to the IED at A side.
I
A
+ I
B
U
A
I
A
I
A
Z
A
= = p ·Z
L
+ ·R
f
EQUATION1274-IEC-650 V1 EN-US
(Equation 316)
The infeed factor (I
A
+I
B
)/I
A
can be very high, 10-20 depending on the differences in source
impedances at local and remote end.
Z <
ZL
Z <
E
SA
U
A
U
B
A
B
E
SB
I
A
I
B
R
f
p*ZL
(1-p)*ZL
Z
SA
Z
SB
IEC09000247-1-en.vsd
IEC09000247 V1 EN-US
Figure 187: Influence of fault current infeed from remote line end
The effect of fault current infeed from the remote line end is one of the most driving factors to
justify complementary protection for distance protection.
When the line is heavily loaded, the distance protection at the exporting end will have a
tendency to overreach. To handle this phenomenon, the IED has an adaptive built-in algorithm,
which compensates the overreach tendency of zone 1 at the exporting end. No settings are
required for this feature.
1MRK 505 343-UEN B
Section 7
Impedance protection
305
Application manual
Summary of Contents for Relion 670 series
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