The voltage threshold VPPU is used to identify low voltage condition in the system. Set
VPPU below the minimum operating voltage that might occur during emergency
conditions. We propose a setting of approximately 70% of VBase.
The drop off time of 200 ms for dead phase detection makes it recommended to always set
SealIn to Enabled since this will secure a fuse failure indication at persistent fuse fail when
closing the local breaker when the line is already energized from the other end. When the
remote breaker closes the voltage will return except in the phase that 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.
14.2.3.3 Negative sequence based
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
527.
EQUATION1757-ANSI V4 EN (Equation 527)
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
Section 14 1MRK 506 369-UUS -
Secondary system supervision
626 Line distance protection REL670 2.2 ANSI
Application manual
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