CHAPTER 9: THEORY OF OPERATION
FAULT LOCATOR
L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
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9
If none of the fault types outlined in the table is determined, then three-phase fault conditions are checked to detect the
presence of positive-sequence current and the absence of both zero-sequence and negative-sequence current. If these
conditions are met, then the
PHASE SELECT 3P
FlexLogic operand is asserted; otherwise, the
PHASE SELECT VOID
operand is
asserted, indicating that the phase selector failed to identify the fault type.
Finally, the states of the following additional FlexLogic operands are determined.
Table 9-3: FlexLogic operands asserted
The phase selector operands are reset a half cycle after the
OPEN POLE OP
FlexLogic operand is asserted or after delay
defined by the
PHASE SELECTOR RESET
setting (in the Trip Output element) once the disturbance detector (50DD) initially
operated.
Figure 9-30: Phase selector logic
9.3 Fault locator
9.3.1 Fault type determination
Fault type determination is required for calculation of fault location. The algorithm uses the angle between the negative
and positive sequence components of the relay currents. To improve accuracy and speed of operation, the fault
components of the currents are used; that is, the pre-fault phasors are subtracted from the measured current phasors. In
addition to the angle relationships, certain extra checks are performed on magnitudes of the negative and zero-sequence
currents.
The single-ended fault location method assumes that the fault components of the currents supplied from the local (A) and
remote (B) systems are in phase. The figure shows an equivalent system for fault location.
Operand
Description
PHASE SELECT SLG
Asserted if any of
PHASE SELECT AG
,
PHASE SELECT BG
, or
PHASE SELECT CG
operands is active
PHASE SELECT MULTI-P
Asserted if neither the
PHASE SELECT SLG
nor
PHASE SELECT VOID
operands are being asserted
