In addition to the above conditions, at least one of the following conditions shall be
fulfilled in order to activate the internal FuseFailDetDUDI signal:
• The magnitude of the phase currents in three phases are higher than the setting
IPh>
• The circuit breaker is closed (CBCLOSED = True)
The first criterion means that detection of failure in three phases together with high
current for the three phases will set the output. The measured phase current is used to
reduce the risk of false fuse failure detection. If the current on the protected line is low,
a voltage drop in the system (not caused by fuse failure) may be followed by current
change lower than the setting DI<, and therefore a false fuse failure might occur.
The second criterion requires that the delta condition shall be fulfilled at the same time
as circuit breaker is closed. If CBCLOSED input is connected to FALSE , then only
the first criterion can enable the delta function.If the DUDI detections of three phases
set the internal signal FuseFailDetDUDI at the level high, then the signal
FuseFailDetDUDI will remain high as long as the voltages of three phases are lower
then the setting Uph>.
In addition to fuse failure detection, two internal signals DeltaU and DeltaI are also
generated by the delta current and delta voltage DUDI detection algorithm. The
internal signals DelatU and DeltaI are activated when a sudden change of voltage, or
respectively current, is detected. The detection of the sudden change is based on a
sample analysis algorithm. In particular DelatU is activated if at least three
consecutive voltage samples are higher then the setting DU>. In a similar way DelatI
is activated if at least three consecutive current samples are higher then the setting
DI<. When DeltaU or DeltaI are active, the output signals STDUL1, STDUL2,
STDUL3 and respectively STDIL1, STDIL2, STDIL3, based on a sudden change of
voltage or current detection, are activated with a 20 ms time off delay. The common
start output signals STDU or STDI are activated with a 60 ms time off delay, if any
sudden change of voltage or current is detected.
The delta function (except the sudden change of voltage and current
detection) is deactivated by setting the parameter OpDUDI to Off.
1MRK502052-UEN B Section 13
Secondary system supervision
613
Technical manual
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