Fuse failure detection criterion Conditions and function response
voltage is above
Neg Seq voltage Lev
for
more than 5 seconds, all the phase currents
are below the
Current dead Lin Val
setting
and the circuit breaker is closed, that is,
CB_CLOSED is TRUE.
Current and voltage delta function criterion If the current and voltage delta criterion de-
tects a fuse failure condition, but all the vol-
tages are not below the
Seal in voltage
set-
ting, only the FUSEF_U output is activated.
If the fuse failure detection is active for more
than five seconds and at the same time all
the phase voltage values are below the set
value of the
Seal in voltage
setting with
Ena-
ble seal in
turned to "True", the function acti-
vates the FUSE_3PH output signal.
External fuse failure detection
The MINCB_OPEN input signal is supposed
to be connected through a protection relay
binary input to the N.C. auxiliary contact of
the miniature circuit breaker protecting the
VT secondary circuit. The MINCB_OPEN sig-
nal sets the FUSEF_U output signal to block
all the voltage-related functions when MCB is
in the open state.
The DISCON_OPEN input signal is supposed
to be connected through a protection relay
binary input to the N.C. auxiliary contact of
the line disconnector. The DISCON_OPEN
signal sets the FUSEF_U output signal to
block the voltage-related functions when the
line disconnector is in the open state.
It is recommended to always set
Enable seal in
to "True". This secures
that the blocked protection functions remain blocked until normal
voltage conditions are restored if the fuse failure has been active for
5 seconds, that is, the fuse failure outputs are deactivated when the
normal voltage conditions are restored.
The activation of the BLOCK input deactivates both FUSEF_U and FUSEF_3PH
outputs.
6.2.5 Application
Some protection functions operate on the basis of the measured voltage value
in the protection relay point. These functions can fail if there is a fault in the
measuring circuits between the voltage transformer (or combi sensor or voltage
sensor) and protection relay.
A fault in the voltage-measuring circuit is called a fuse failure. This term is
misleading since a blown fuse is just one of the many possible reasons for a broken
circuit. Since incorrectly measured voltage can result in a faulty operation of some
of the protection functions, it is important to detect the fuse failures. A fast fuse
Supervision functions
1MRS758755 C
538 REC615 & RER615
Technical Manual
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