GE L90 Instruction Manual page 731

CHAPTER 10: THEORY OF OPERATION
The faulted segment can be found by recognizing that the sum of the voltage drops around a loop through the unfaulted
segments is zero. The residual voltage phasors are computed for each loop. The loop with the lowest residual voltage
contains the two unfaulted segments. Therefore, the differences between each pair of estimates is calculated as follows:
The faulted segment is selected as follows:
where
A similar set of equations is applied to determine whether the fault is between the tap and the local terminal or between
the tap and remote terminal 1.
Next, having all the data prepared, the following universal equation is used to calculate the fault location:
For this equation, two-terminal applications, the following equalities hold:
For two-terminal applications, the distance is reported from the local relay. In three-terminal applications, the distance is
reported from the terminal of a given line segment.
Phase rotation must be the same at all line terminals for correct operation of the multi-ended fault locator.
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
FAULT LOCATOR
Eq. 10-53
Eq. 10-54
Eq. 10-55
Eq. 10-56
Eq. 10-57
10
10-53