ABB RELION REX640, Техническое руководство, Страница: 1214 / 1960

Taps or spurs in the feeder
If the protected feeder consists of taps or spurs, the measured fault impedance
corresponds to several physical fault locations (For example, A or B in
Figure
693
). The actual fault location must be identified using additional information, for
example, short circuit current indicators placed on tapping points.
Figure 693: Fault on a distribution line with spurs
5.7.5.4 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.
Figure 694
illustrates typical behavior of fault
distance estimate of SCEFRFLO as a function of time.
Protection related functions 1MRS759142 F
1214 REX640
Technical Manual