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_V
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_V
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_V
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_V
and
FUSEF_3PH
outputs.
6.5.5
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 trip.
Section 6
1MAC059074-MB A
Supervision functions
870
615 series ANSI
Technical Manual
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