has a persistent fuse fail. Since the local breaker is open there is no current and the
dead phase indication will persist in the phase with the blown fuse. When the local
breaker closes the current will start to flow and the function detects the fuse failure
situation. But due to the 200 ms drop off timer the output BLKZ will not be activated
until after 200 ms. This means that distance functions are not blocked and due to the
“no voltage but current” situation might issue a trip.
The operation mode selector
OpModeSel
has been introduced for better adaptation to
system requirements. The mode selector enables selecting interactions between the
negative sequence and zero sequence algorithm. In normal applications, the
OpModeSel
is set to either
V2I2
for selecting negative sequence algorithm or
V0I0
for
zero sequence based algorithm. If system studies or field experiences shows that there
is a risk that the fuse failure function will not be activated due to the system conditions,
the dependability of the fuse failure function can be increased if the
OpModeSel
is set
to
V0I0 OR V2I2
or
OptimZsNs
. In mode
V0I0 OR V2I2
both negative and zero
sequence based algorithms are activated and working in an OR-condition. Also in
mode
OptimZsNs
both negative and zero sequence algorithms are activated and the one
that has the highest magnitude of measured negative or zero sequence current will
operate. If there is a requirement to increase the security of the fuse failure function
OpModeSel
can be selected to
V0I0 AND V2I2
which gives that both negative and zero
sequence algorithms are activated and working in an AND-condition, that is, both
algorithms must give condition for block in order to activate the output signals BLKV
or BLKZ.
11.1.3.3
Negative sequence based
M13683-17 v9
The relay setting value
3V2PU
is given in percentage of the base voltage
VBase
and
should not be set lower than the value that is calculated according to equation
100
3
2
2
3
VBase
V
PU
V
EQUATION1757-ANSI V4 EN-US
(Equation 82)
where:
V2PU
is the maximal negative sequence voltage during normal operation conditions, plus a margin of
10...20%
VBase is the base voltage for the function according to the setting GlobalBaseSel
The setting of the current limit
3I2PU
is in percentage of parameter
IBase
. The setting
of
3I2PU
must be higher than the normal unbalance current that might exist in the
system and can be calculated according to equation
1MRK 505 370-UUS A
Section 11
Secondary system supervision
Busbar protection REB670 2.2 ANSI
287
Application manual
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