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

1MRK 504 152-UEN B
Another definition for effectively earthed network is when the following relationships between
the symmetrical components of the network impedances are valid, as shown in equation
and equation 39.
≤ ⋅ 3
X
0
EQUATION1269 V4 EN-US
£
R X
0
EQUATION1270 V4 EN-US
The magnitude of the earth fault current in effectively earthed networks is high enough for
impedance measuring element to detect earth-fault. However, in the same way as for solid
earthed networks, distance protection has limited possibilities to detect high resistance faults
and must, therefore, always be complemented with other protection function(s) that can carry
out the fault clearance in this case.
7.1.2.3

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 may 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 56, 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.
Es
A
IEC05000217 V1 EN-US
Figure 56: Influence of fault infeed from remote end
Application manual
X
1
1
× × + + ×
( I I ) R
L A B f
+
I I
= × + ×
a p Z A B R
L
I
A A
V
A
A
I
Z A
SA
Z <
f
p*ZL
(1-p)*ZL
ZL
R
f
Impedance protection
VA
Es
B
B
I
Z
B
SB
Z <
en05000217.vsd
Section 7
38
(Equation 38)
(Equation 39)
SEMOD168232-84 v2
(Equation 40)
(Equation 41)
147