Fault Locator; Overview; Multi-Ended Fault Locator - GE L90 Instruction Manual

CHAPTER 10: THEORY OF OPERATION

10.6 Fault locator

10.6.1 Overview

The L90 uses the following two methods to determine fault type and fault location:
• A multi-ended fault location algorithm using synchronized currents and voltage measurements from all line terminals
• A single-ended method based on the measurement from local terminal relay only during channel failures

10.6.2 Multi-ended fault locator

10.6.2.1 Description
When the L90 ordered has in-zone functionality, it does not support the multi-ended fault locator. This is because the use
of the in-zone transformer replaces part of the existing data with in-zone data, which restricts multi-ended fault location.
The multi-ended fault location method is based on synchronized voltage and current measurements at all ends of the
transmission line. This method makes it possible to compute the fault location without any assumptions or
approximations. A single composite voltage and single composite current signal represent voltage and current
measurements at any line terminal. These composite voltage and current signals are non-zero regardless of the fault type.
The composite voltage at the fault can be computed from each end of the line by subtracting the line drop to the fault from
the voltage at that end.
The multi-ended algorithm executes separately on each terminal. All terminals compute the same fault location, since they
use the same equations applied to the same set of data. The algorithm is executed for both two-terminal and three-
terminal applications. The three-terminal algorithm executes at each terminal that has information from all three
terminals. If there is a communications failure on one channel, it affects only one of the three terminals, since there are
fault phasors from all three terminals to compute the fault location. The three-terminal algorithm has two parts: one part
that determines which line segment is faulted, and another part that locates the fault on the faulted segment. Each
terminal can report a slightly different fault resistance. The algorithm achieves greater accuracy by removing the line
charging current.
The fault location algorithm does not need to explicitly determine the composite voltage at the fault. Instead, it eliminates
the fault voltage from the equations for fault location by using other information instead.
For the purpose of fault location, the ABC quantities are represented by a single composite signal using the following base
equation.
where b is a complex number defined as:
and b* is the conjugate of b, or mathematically:
where α = 45°
The expanded Clarke transformation (also known as the alpha-beta transformation) shown is selected to yield non-zero
operating signals under balanced and unbalanced conditions. This allows reducing the amount of exchanged information
between devices and avoiding phase selection. The equation applies to the wye connection of signals under ABC phase
rotation. For delta connections and ACB rotation, there is a small modification in this equation.
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
FAULT LOCATOR
Eq. 10-44
Eq. 10-45
Eq. 10-46
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10-51