After start, a certain hysteresis is used before resetting start levels. For both steps the
reset ratio is 0.97.
8.12.7.2
Alarm function
The alarm function is operated by START signal and used to warn the operator for an
abnormal situation, for example, when generator continuous negative sequence
current capability is exceeded, thereby allowing corrective action to be taken before
removing the generator from service. A settable time delay
tAlarm
is provided for the
alarm function to avoid false alarms during short-time unbalanced conditions.
8.12.7.3
Logic diagram
IEC080004661-4-en.vsdx
Operation=ON
Inverse
TR1
OR
BLKST1
a
b
a>b
Negative sequence current
I2-1>
CurveType1=Definite
CurveType1=Inverse
t1Min
AND
ST1
AND
BLOCK
AND
AND
t1Max
t1
IEC08000466-1-EN V4 EN
Figure 203:
Simplified logic diagram for step 1 of Negative sequence time
overcurrent protection for machines (NS2PTOC)
Step 2 for Negative sequence time overcurrent protection for machines (NS2PTOC)
is similar to step 1.
ST1
IEC09000690-2-en.vsd
START
OR
OR
ST2
TR2
TR1
ALARM
TRIP
tAlarm
IEC09000690 V2 EN
Figure 204:
Simplified logic diagram for the START, ALARM and TRIP signals for
NS2PTOC
1MRK502052-UEN B
Section 8
Current protection
441
Technical manual
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