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8.9.7.1
Pickup sensitivity
The trip pickup levels Current
I2-1>
and
I2-2>
of NS2PTOC (46I2) are freely settable
over a range of 3 to 500 % of rated generator current
IBase
. The wide range of pickup
setting is required in order to be able to protect generators of different types and sizes.
After pickup, a certain hysteresis is used before resetting pickup levels. For both steps the
reset ratio is 0.97.
8.9.7.2
Alarm function
The alarm function is operated by PICKUP 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.
8.9.7.3
Logic diagram
ANSI08000466-3-en.vsd
Operation=Enabled
BLK1
Inverse time
selected
Inverse
DT time
selected
PU_ST1
TRST1
AND
OR
BLOCK
a
b
a>b
Negative sequence current
I2-1>
0
0-t1
ANSI08000466 V3 EN
Figure 123:
Simplified logic diagram for step 1 of Negative sequence time overcurrent
protection for machines (NS2PTOC, 46I2)
Step 2 for Negative sequence time overcurrent protection for machines (NS2PTOC, 46I2)
is similar to step 1 above except that it lacks the inverse characteristic.
1MRK 502 048-UUS A
Section 8
Current protection
271
Technical manual
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