10.6
SEL-751 Relay Instruction Manual Date Code 20170927
Analyzing Events
Event Reporting
The event type logic (PHASE_A, PHASE_B, PHASE_C) uses Relay Word
bits FSA, FSB, and FSC to help determine the fault type and to select the
appropriate fault location method. The SEL-751 asserts one of the Relay Word
bits FSA, FSB, or FSC based on the magnitude and angle difference of
negative- and zero-sequence current. The A-, B-, or C-phase naming of the
FSA, FSB, and FSC Relay Word bits does not directly translate to assertion of
PHASE_A, PHASE_B, PHASE_C. When the relay processes a new EVENT,
the status of the FSA, FSB, and FSC Relay Word bits help to determine which
phase (PHASE_A, PHASE_B, PHASE_C) to assert.
The event type logic (PHASE_A, PHASE_B, PHASE_C) also uses Relay
Word bits NSA, NSB, and NSC to help determine the fault type and to select
the appropriate fault location method. The SEL-751 asserts one of the Relay
Word bits NSA, NSB, or NSC based on the angle difference of neutral current
and positive sequence voltage or the angle difference of the zero-sequence
voltage and positive-sequence voltage. The A-, B-, or C-phase naming of the
NSA, NSB, and NSC Relay Word bits directly translate to assertion of
PHASE_A, PHASE_B, PHASE_C. When the relay processes a new EVENT,
the status of the NSA, NSB, and NSC Relay Word bits help to determine
which phase (PHASE_A, PHASE_B, PHASE_C) to assert.
If PHASE_A, PHASE_B, or PHASE_C assert, the type in Table 10.1: Event
Types is replaced by the type in Table 10.2: Phase Involvement Event Type.
Fault Location
The relay reports the fault location if the EFLOC setting := Y and the fault
locator operates successfully after an event report is generated. If the fault
locator does not operate successfully, $$$$$$ is listed in the field. Fault
location is based on the line impedance settings Z1MAG, Z1ANG, Z0MAG,
and Z0ANG; source impedance settings Z0SMAG and Z0SANG; and
corresponding line length setting LL. (See the Line Parameter Settings on
page 4.10.) Because the fault locating function requires three-phase voltages,
the Group setting EFLOC cannot be set to Y when Group setting VNOM :=
OFF. Similarly, the Group setting EFLOC is hidden and set to N internally
when the Group setting SINGLEV := Y.
Fault Detector Elements
The fault locator algorithm uses the overcurrent elements: 50P1P–50P4P,
50N1P–50N4P, 50G1P–50G4P, 50Q1P–50Q4P, 51AP, 51BP, 51CP, 67P1P–
67P4P, 67Q1P–67Q4P, 67G1P–67G4P, 67N1T–67N4T, 51P1P, 51P2P,
51N1P, 51N2P, 51G1P, 51G2P, and 51Q as fault detectors. If you set any of
these elements to low pickup values for use as load indicators, they can assert
during nonfault conditions. In this situation, even though these elements are
not being used for tripping the relay, they can still affect the operation of the
fault locator, because the start of the disturbance may be unclear.
CAG T PHASE_C * PHASE_A * GFLT * TRIP
AG T PHASE_A * TRIP
BG T PHASE_B * TRIP
CG T PHASE_C * TRIP
Table 10.2 Phase Involvement Event Type (Sheet 2 of 2)
Type Condition
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