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8.5.2.3
Fault infeed from remote end
SEMOD154680-84 v2
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
, we can draw the equation for the bus voltage Va at
left side as:
(
)
A
A
L
A
B
f
V
I p Z
I
I
R
= × ×
+
+
×
EQUATION1273 V1 EN-US
(Equation 190)
If we divide Va by IA 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 191)
The infeed factor (IA+IB)/IA can be very high, 10-20 depending on the differences
in source impedances at local and remote end.
Z <
ZL
Z <
Es
A
V
A
VA
A
B
Es
B
I
A
I
B
R
f
p*ZL
(1-p)*ZL
Z
SA
Z
SB
en05000217.vsd
IEC05000217 V1 EN-US
Figure 135:
Influence of fault infeed from remote end.
The effect of fault current infeed from remote end is one of the most driving factors
for justify complementary protection to distance protection.
8.5.2.4
Load encroachment
SEMOD154680-97 v3
In some cases the load impedance might enter the zone characteristic without any
fault on the protected line. The phenomenon is called load encroachment and it
might occur when an external fault is cleared and high emergency load is
transferred on the protected line. The effect of load encroachment is illustrated to
the left in figure
. The entrance of the load impedance inside the characteristic
is of cause not allowed and the way to handle this with conventional distance
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC
265
Application manual
Содержание REL670 2.2 IEC
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