ABB RELION RET670, Applications Manual

Page: 198 / 1016

way as for solid grounded 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.
8.1.2.3 Fault infeed from remote end
SEMOD168232-84 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 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 69 , 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 33)
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 34)
The infeed factor (IA+IB)/IA can be very high, 10-20 depending on the differences in
source impedances at local and remote end.
21
ZL
21
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_ansi.vsd
ANSI05000217 V1 EN-US
Figure 69: Influence of fault infeed from remote end
The effect of fault current infeed from remote end is one of the most driving factors to
justify complementary protection to distance protection.
Section 8
1MRK 504 163-UUS A
Impedance protection
192 Transformer protection RET670 2.2 ANSI
Application manual