ABB Relion 670 series, Technical Reference Manual

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13.8.9.1 Introduction
Zero sequence components are present in all abnormal conditions involving ground.
They have a considerably high value during ground faults.
13.8.9.2 Principle of operation
Zero sequence overcurrent protection (LCZSPTOC, 51N) is a definite time stage
comparator function. The zero sequence input current from the SMAI block is
connected as input to the function through a group connection I3P in PCM600. This
current is compared against the preset value and a pickup signal will be set high if the
input zero sequence current is greater than the preset value
3I0 PU . Trip signal will be
set high after a time delay setting of t3I0 . BLOCK input will block the complete
function. BLKTR will block the trip output. The zero sequence current is available as
service value output 3I0.
13.8.9.3 Function block
ANSI09000770-1-en.vsd
LCZSPTOC (51N)
I3P*
BLOCK
BLKTR TRIP
RI
ANSI09000770 V1 EN
Figure 424: LCZSPTOC (51N) Function block
13.8.9.4 Input and output signals
Table 479: LCZSPTOC (51N) Input signals
Name Type Default Description
I3P GROUP
SIGNAL
- Three phase group signal for current inputs
BLOCK BOOLEAN 0 Block overall function
BLKTR BOOLEAN 0 Block trip output
Table 480: LCZSPTOC (51N) Output signals
Name Type Description
TRIP BOOLEAN Trip signal for zero sequence over current protection
RI BOOLEAN Start signal for zero sequence over current protection
1MRK505222-UUS C
Section 13
Scheme communication
851
Technical reference manual