The distance protection within the IED can compensate for the influence of a zero
sequence mutual coupling on the measurement at single phase-to-ground faults in the
following ways, by using:
•
The possibility of different setting values that influence the ground-return
compensation for different distance zones within the same group of setting
parameters.
• Different groups of setting parameters for different operating conditions of a
protected multi circuit line.
Most multi circuit lines have two parallel operating circuits.
Parallel line applications
GUID-905ACED8-CD00-4651-90F1-96D1885BA856 v1
This type of networks is defined as those networks where the parallel transmission
lines terminate at common nodes at both ends.
The three most common operation modes are:
1. Parallel line in service.
2. Parallel line out of service and grounded.
3. Parallel line out of service and not grounded.
Parallel line in service
GUID-22E1A46C-92BD-4EE4-9A2D-9EFE2DB7B4D8 v3
This type of application is very common and applies to all normal sub-transmission
and transmission networks.
Let us analyze what happens when a fault occurs on the parallel line see figure
177.
From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation 266.
ph ph
0 1 ph N
ph 0
1
0
V V
Z Z I 3 K
I 3I
3 Z
I
Z = =
- + ×
+ ×
×
EQUATION1275 V3 EN-US (Equation 266)
Where:
Vph is phase to ground voltage at the relay point
Iph is phase current in the faulty phase
3I0 is ground fault current
Z1 is positive sequence impedance
Z0 is zero sequence impedance
Section 8 1MRK 504 163-UUS A
Impedance protection
376 Transformer protection RET670 2.2 ANSI
Application manual
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