ABB Relion 670 series, Technical Manual

Page: 572 / 1432

Where
I
NS
is the measured negative sequence current
I
Pickup
is the desired pickup level in pu of rated generator current
ResetMultip is multiplier of the generator capability constant K equal to setting K1 and thus defines reset
time of inverse time characteristic
8.14.7.1 Pickup sensitivity
GUID-1D038486-7086-466F-A92F-30E1A47D0298 v3
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.
8.14.7.2 Alarm function
GUID-1B932D89-3233-4841-977A-5B61346B057B v2
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.
8.14.7.3 Logic diagram
GUID-71553DAF-374C-4980-82D8-D3AF79861C5B v3
ANSI08000466-4-en.vsd
Operation=Enabled
BLK1
Inverse
PU_ST1
TRST1
AND
OR
BLOCK
a
b
a>b
Negative sequence current
I2-1>
0
0-t1 CurveType1=Definite
CurveType1=Inverse
0
0-txMin
AND
ANSI08000466 V4 EN-US
Figure 300: 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.
Section 8 1MRK 502 066-UUS B
Current protection
566
Technical manual