ABB RET670 - Page 331

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
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
51.
From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation 59.
ph ph
0 1 ph 0 N
ph 0
1
U U
Z Z I 3I K
I 3I
3 Z
Z = =
- + ×
+ ×
×
EQUATION2311 V1 EN (Equation 250)
ph ph
0 1 ph 0 N
ph 0
1
V V
Z Z I 3I K
I 3I
3 Z
Z = =
- + ×
+ ×
×
EQUATION1275 V2 EN (Equation 250)
Where:
V
ph
is phase to ground voltage at the relay point
I
ph
is phase current in the faulty phase
3I
0
is ground fault current
Z
1
is positive sequence impedance
Z
0
is zero sequence impedance
1MRK504116-UUS C Section 3
IED application
325
Application manual