CHAPTER 10: THEORY OF OPERATION SINGLE-POLE TRIPPING
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 10-41
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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 10-13: 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 10-16: Phase selector logic
PHASE SELECT CG Asserted when a phase C to ground fault is detected
PHASE SELECT AB Asserted when a phase A to B fault is detected
PHASE SELECT BC Asserted when a phase B to C fault is detected
PHASE SELECT CA Asserted when a phase C to A fault is detected
PHASE SELECT ABG Asserted when a phase A to B to ground fault is detected
PHASE SELECT BCG Asserted when a phase B to C to ground fault is detected
PHASE SELECT CAG Asserted when a phase C to A to ground fault is detected
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
Operand Description
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