ABB RET670 - Page 582

UZsIZs 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 UZsIZs OR UNsINs or OptimZsNs. In modeUZsIZs OR UNsINs
both the negative and zero sequence based algorithm is activated and working in an OR-
condition. Also in mode OptimZsNs both the negative and zero sequence algorithm 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 UZsIZs AND UNsINs which gives
that both negative and zero sequence algorithm is activated working in an AND-
condition, that is, both algorithm must give condition for block in order to activate the
output signals BLKU or BLKZ.
Negative sequence based
The relay setting value 3V2PU is given in percentage of the base voltage VBase and
should not be set lower than according to equation
414.
3 2
3 2 100= ×
V
V PU
VBase
EQUATION1757-ANSI V3 EN (Equation 414)
where:
3V2PU is the maximal negative sequence voltage during normal operation conditions, plus a margin of
10...20%
VBase is the setting of base voltage for the function
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
415.
3 2
3 2 100= ×
I
I PU
IBase
EQUATION1758-ANSI V3 EN (Equation 415)
where:
3I2 is the maximal negative sequence current during normal operating conditions, plus a margin of
10...20%
IBase is the setting of base current for the function
Section 3 1MRK504116-UUS C
IED application
576
Application manual