ABB RELION REX640 Technical Manual page 1122

Section 5
Protection related functions
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Figure 606: Fault on a distribution line with spurs
Trigger detection
The fault distance estimate is obtained when SCEFRFLO is triggered. The triggering
method is defined with setting Calculation Trg mode. The options for selection are
"External" or "Internal", where the default value is "External". The TRIGG_OUT
event indicates the fault distance value recording moment. The fault distance estimate,
Flt distance, together with the time stamp of actual triggering are saved in the recorded
data of SCEFRFLO.
• In case of external triggering, an external trigger signal should be connected to the
TRIGG_REC input. The triggering signal is typically a trip signal from a
protective function. At triggering moment the fault distance is stored into
recorded data. It is important that triggering be timed suitably to provide
sufficient time for the distance estimation calculation before tripping of the feeder
circuit breaker.
• In case of internal triggering, the TRIGG_REC input is not used for triggering.
Instead, the trigger signal is created internally so that the estimation is started
when Phase selection logic detects a fault and the estimate is triggered when its
value has stabilized sufficiently. This is judged by maximum variation in fault
distance estimate and defined with setting Distance estimate Va (in the same unit
as the fault distance estimate). When successive estimates during one
fundamental cycle are within "final value ± Distance estimate Va", the fault
distance estimate (mean of successive estimates) is recorded. If the stabilization
criterion has not been fulfilled, the fault distance estimate is given right before the
fault ends. Phase selection logic is a non-directional function so internal
triggering should not be used when directionality is required.
Generally, SCEFRFLO requires a minimum of two fundamental cycles of measuring
time after the fault occurrence.
distance estimate of SCEFRFLO as a function of time.
Figure 607 illustrates the typical behavior of fault
1MRS759142 C
REX640
Technical Manual