GE L60, Инструкция по эксплуатации

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9-40 L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
SINGLE-POLE TRIPPING CHAPTER 9: THEORY OF OPERATION
9
Figure 9-29: Phase selection principle (ABC phase rotation)
Due to dual comparisons, the algorithm is very secure. For increased accuracy and to facilitate operation in weak systems,
the pre-fault components are removed from the analyzed currents. The algorithm is very fast and ensures proper phase
selection before any of the correctly set protection elements operates.
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
DISTANCE SOURCE
is reset, then the
PHASE SELECT VOID
FlexLogic operand is set and
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 9-2: FlexLogic operands asserted
Operand Description
PHASE SELECT AG Asserted when a phase A to ground fault is detected
PHASE SELECT BG Asserted when a phase B to ground fault is detected
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