Fault Locator - GE MiCOM P40 Agile Technical Manual

Application Notes
MiCOM P40 Agile P442, P444
2.6

Fault Locator

The relay has an integral fault locator that uses information from the current and voltage
inputs to provide a distance-to-fault measurement. The fault locator measures the distance
by applying the same distance calculation principle as that used for the fault-clearing,
distance-measurement algorithm.
The dedicated fault locator measurement is more accurate as it is based on a greater
number of samples, and it uses the fault currents Ifault as models, as shown below:
• For a single-phase fault
• For a two-phase fault
• For a three-phase fault
The sampled data from the analogue input circuits is written to a cyclic buffer until a fault
condition is detected. The data in the input buffer is then held to allow the fault calculation to
be made. When the fault calculation is complete the fault location information is available in
the relay fault record.
When applied to parallel circuits, mutual flux coupling can alter the impedance seen by the
fault locator. The coupling will contain positive, negative and zero sequence components. In
practice the positive and negative sequence coupling is insignificant. The effect on the fault
locator of the zero sequence mutual coupling can be eliminated by using the mutual
compensation feature provided. This requires that the residual current on the parallel line is
measured, as shown in Appendix B.
The calculation for single phase loop is based on the following equation:
R
0
V = R .D .I +
AN 1 fault A
dl
m
+ L .
m
dt
R
0
V = R .D .I +
BN 1 fault B
dl
m
+ L .
m
dt
R
0
V = R .D .I +
CN 1 fault C
dl
m
+ L .
m
dt
Where:
R : zero-sequence mutual resistance
m
L : zero-sequence mutual inductance
m
I : zero-sequence mutual current
m
I : fault current =
fault
−
R
1
.D .3I + L .D
fault 0 AA fault
3
−
R
1
.D .3I + L .D
fault 0 AB fault
3
−
R
1
.D .3I + L .D
fault 0 AC fault
3
∆
I – I0
∆
AN : Ifault
∆
BN : Ifault
∆
CN : Ifault
∆
AB : Ifault
∆
BC : Ifault
∆
CA : Ifault
∆
ABC : Ifault
dl dl
A B
. + L .D . + L
AB fault
dt dt
dl dl
A B
. + L .D . + L
BB fault
dt dt
dl dl
A B
. + L .D . + L
BC fault
dt dt
P44x/EN AP/Hb6
(AP) 5-29
(IA – I0)
(IB – I0)
(IC – I0)
(IA–IB)
(IB–IC)
(IC–IA)
(IA–IB)
dl
C
.D . + R .I
AC fault fault fault
dt
dl
C
.D . + R .I
BC fault fault fault
dt
dl
C
.D . + R .I
CC fault fault fault
dt
+ R .I
m m
+ R .I
m m
+ R .I
m m