GE F60 Instruction Manual page 565

CHAPTER 9: THEORY OF OPERATION
The following equations hold true for this equivalent system.
where
m = sought pu distance to fault
Z = positive sequence impedance of the line
I = fault current flowing through the fault point
F
The fault network during a fault can be decomposed into a pre-fault and a pure-fault network. Therefore, the fault current
I is calculated as follows by using the current division rule in the pure-fault network.
F
where
d is the current distribution factor, which is a complex value
Substituting the second equation into the first equation and multiplying both sides by the complex conjugate of IAF,
where
* denotes complex conjugate
Assuming the system is homogeneous, d is then a real number. The fault resistance does not have any imaginary part. The
preceding equation solved for the unknown m yields the following fault location algorithm:
where
Im( ) stands for the imaginary part of a complex number
Depending on the fault type, appropriate voltage and current signals are selected from the phase quantities before
applying the preceding equation (the superscripts denote phases, the subscripts denote stations).
For AG faults:
F60 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 9-1: Equivalent system for fault location
FAULT LOCATOR
Eq. 9-1
Eq. 9-2
Eq. 9-3
Eq. 9-4
9
Eq. 9-5
9-5