GUID-312EE60E-1CB9-4334-83BD-39DF3FC5815E V3 EN
Figure 420: Fault on a distribution line with spurs
5.7.4.3 Trigger detection
The fault distance estimate is obtained when 21FL 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 fault
distance value recording moment. The fault distance estimate, Flt distance, together with
the timestamp of actual triggering are saved in the recorded data of 21FL.
• In case of external triggering, an external trigger signal should be connected to the
TRIGG 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 is timed suitably to provide sufficient distance estimation
calculation time before tripping of the feeder circuit breaker.
• In case of internal triggering, the TRIGG 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. In case stabilization criterion has not been fulfilled,
the fault distance estimate is given just before the phase currents are interrupted. The
phase selection logic is a non-directional function, and thus internal triggering should
not be used when directionality is required.
Section 5 1MAC059074-MB A
Protection related functions
822 615 series ANSI
Technical Manual
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