GE C60 Instruction Manual page 528

SINGLE-POLE TRIPPING
Under unusual circumstances, such as weak-infeed conditions with the zero-sequence current dominating during any
ground fault, or during cross-country faults, the current-based phase selector may not recognize any of the known fault
pattern. If this is the case, voltages are used for phase selection. The voltage algorithm is the same as the current-based
algorithm. For example, phase angles between the zero-sequence, negative-sequence, and positive-sequence voltages
are used. The pre-fault values are subtracted prior to any calculations.
The pre-fault quantities are captured and the calculations start when the disturbance detector (50DD) operates. When an
open pole is declared, the phase selector resets all its outputs operands and ignores any subsequent operations of the
disturbance detector.
The phase selector runs continuously. When there is no disturbance in the power system, and the disturbance detector
(50DD) from the source assigned as the
all other phase selector operands are reset. All current and voltage sequence components are memorized and
continuously updated.
When the disturbance detector (50DD) operates, memory stops being updated and retains two cycles of old current and
voltage values. First, purely fault components of current and voltage are calculated by removing the pre-fault (memory)
quantities from presently calculated values. A series of conditions are checked with respect to magnitudes and phase
angles of current and voltage symmetrical components in order to detect the fault type. Secondly, currents are used to
identify the fault type (AG, BG, CG, AB, BC, CA, ABG, BCG, or CAG) according to the Phase Selection Principle figure. If the
currents fail to identify the fault type, and voltages are available, then voltages are used. If any of the above types is
determined, then the corresponding FlexLogic operand outlined in the following table is asserted.
Table 8-1: FlexLogic operands asserted
Operand
PHASE SELECT AG
PHASE SELECT BG
PHASE SELECT CG
PHASE SELECT AB
PHASE SELECT BC
PHASE SELECT CA
PHASE SELECT ABG
PHASE SELECT BCG
PHASE SELECT CAG
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
asserted, indicating that the phase selector failed to identify the fault type.
Finally, the states of the following additional FlexLogic operands are determined.
Table 8-2: FlexLogic operands asserted
8 Operand
PHASE SELECT SLG
PHASE SELECT MULTI-P
The phase selector operands are reset a half cycle after the
defined by the
PHASE SELECTOR RESET
operated.
8-8
DISTANCE SOURCE
Description
Asserted when a phase A to ground fault is detected
Asserted when a phase B to ground fault is detected
Asserted when a phase C to ground fault is detected
Asserted when a phase A to B fault is detected
Asserted when a phase B to C fault is detected
Asserted when a phase C to A fault is detected
Asserted when a phase A to B to ground fault is detected
Asserted when a phase B to C to ground fault is detected
Asserted when a phase C to A to ground fault is detected
FlexLogic operand is asserted; otherwise, the
PHASE SELECT 3P
Description
Asserted if any of
PHASE SELECT AG,
Asserted if neither the
PHASE SELECT SLG
setting (in the Trip Output element) once the disturbance detector (50DD) initially
is reset, then the
PHASE SELECT VOID
BG, or
PHASE SELECT PHASE SELECT CG
nor operands are being asserted
PHASE SELECT VOID
FlexLogic operand is asserted or after delay
OPEN POLE OP
C60 BREAKER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 8: THEORY OF OPERATION
FlexLogic operand is set and
operand is
PHASE SELECT VOID
operands is active