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.
8.9.2.2
Fault infeed from remote end
GUID-4380CD3A-BCB0-45F1-A821-BC3E6D070C04 v1
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
, the equation for the bus voltage U
A
at A side is:
(
)
A
A
L
A
B
f
V
I p Z
I
I
R
= × ×
+
+
×
EQUATION1273 V1 EN-US
(Equation 234)
If we divide U
A
by I
A
we get Z present to the IED at A side.
a
A
B
A
L
f
A
A
V
I
I
Z
p Z
R
I
I
+
=
= ×
+
×
EQUATION1274 V2 EN-US
(Equation 235)
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 148:
Influence of fault current infeed from remote line end
The effect of fault current infeed from remote line end is one of the most driving
factors for justify complementary protection to 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
Section 8
1MRK 506 369-UEN B
Impedance protection
294
Line distance protection REL670 2.2 IEC
Application manual
Содержание REL670 2.2 IEC
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