44x/EN AP/Hb6
-30 MiCOM P40 Agile
The calculation for phase-to-phase loop is based on the following equation:
V
AB
= R
1
.D
fault
.(I
A
– I
B
) + (L
AA
– L
AB
).D
fault
.
+ (L
AB
– L
BB
).D
fault
.
+ (L
AC
– L
BC
).D
fault
.
+
.I
fault
V
BC
= R
1
.D
fault
.(I
B
– I
C
) + (L
AB
– L
AC
).D
fault
.
+ (L
BB
– L
BC
).D
fault
.
+ (L
BC
– L
CC
).D
fault
.
+
.I
fault
V
AC
= R
1
.D
fault
.(I
C
– I
A
) + (L
AC
– L
AA
).D
fault
.
+ (L
BC
– L
AB
).D
fault
.
+ (L
CC
– L
AC
).D
fault
.
+
.I
fault
Where:
I
fault
= ∆I (∆I = ∆I' - ∆I")
∆I
A
- ∆I
B
∆I
B
- ∆I
C
∆I
C
- ∆I
A
2.6.1 Selecting the fault location data
Selection of the analogue data that is used depends on:
• How the fault is processed by the algorithms.
• The line model.
2.6.2 Processing algorithms
Distance to fault calculation will use the high speed algorithms if:
• A fault is detected by the high-speed algorithms
• The tripping occurred within the T1 or T2 time delays
• The distance to the fault is less than 105% of the line.
In this case, the distance to fault saved in the fault report will be displayed as:
Distance to the fault = 24.48km (L) accuracy 3%
If all three of these conditions are not met, the distance to fault value will be the same value
used by the distance protection. The format of the display will then be as follows:
Distance to the fault = 31.02km accuracy 5%
Note: The more accurate fault location will be post scripted with an (L). This will
occur when conditions are favourable for using the more accurate algorithm
for distance to fault calculation.
2.6.2.1 Line Model Selection
The fault locator can distinguish between two types of line, as follows:
• Single lines.
• Parallel lines with mutual coupling.
Mutual coupling between transmission lines is common on power systems. Significant
effects on distance relay operation during faults involving earth may occur. Typically, the
positive and negative, mutual-sequence impedances are negligible, but zero-sequence
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