Fuse failure detection criterion Conditions and function response
Current and voltage delta function criterion If the current and voltage delta criterion detects a
fuse failure condition, but all the voltages are not
below the
Seal in voltage
setting, 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
Enable seal in
turned to
"True", the function activates 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 signal 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 failure detection is one
of the means to block voltage-based functions before they operate.
1MRS758755 A Section 6
Supervision functions
REC615 and RER615 523
Technical Manual
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