ABB RELION RET670, Applications Manual

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preference logic (PPLPHIZ) is needed, which is not common to be used in
transmission applications.
In this type of network, it is mostly not possible to use distance protection for detection
and clearance of ground-faults. The low magnitude of the ground-fault 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 ground-fault protection is
necessary to carry out the fault clearance for single phase-to-ground fault.
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 139 , 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 162)
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 163)
The infeed factor (IA+IB)/IA can be very high, 10-20 depending on the differences in
source impedances at local and remote end.
Section 8
1MRK 504 163-UUS A
Impedance protection
294 Transformer protection RET670 2.2 ANSI
Application manual