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10 APPLICATION OF SETTINGS
Therefore, the alarm delay is specified as 10 seconds. The following setting values are programmed in the EnerVista UR
Setup software.
The pickup setting for the stage 2 current unbalance trip element is specified as the unbalance current during maximum
system conditions midway between the third and fourth capacitor element failure unbalance currents.
60P trip
=
Therefore, the trip delay is chosen 50 ms.
To protect the capacitor bank from overvoltage resulting from abnormal system conditions, the capability of the bank to
withstand transient overvoltages must be evaluated according to the IEEE 1036-1992 standard or to manufacturer specifi-
cations. For example, consider the following manufacturer overvoltage data:
•
2 pu overvoltage toleration for 0.25 second.
•
1.5 pu overvoltage toleration for 15 seconds.
•
1.25 pu overvoltage toleration for 5 minutes.
When the relay settings are calculated, the number of prospective overvoltage transients stressing the capacitor insulation
during the bank lifetime must be taken into account. As such, it is preferable to set the relay conservatively.
Based on the manufacturer overvoltage data above, three overvoltage trip stages are applied using a factor of 0.9 for the
stage pickup overvoltage levels and half of the allowable time indicated above.
GE Multilin
I
+
I
(
)
(
)
unbal f4_max
unbal f3_max
----------------------------------------------------------------------- -
=
2
59B pickup (stage 1)
0.9
=
59B pickup (stage 2)
=
59B pickup (stage 3)
=
C70 Capacitor Bank Protection and Control System
0.0904 pu
+
0.0660 pu
----------------------------------------------------------- -
=
0.078 pu
2
10.4.7 BANK PHASE OVERVOLTAGE SETTINGS
×
1.25
1.125 pu
=
×
0.9 1.5
1.35 pu
=
×
0.9
2
1.80 pu
=
10.4 SETTING EXAMPLE
(EQ 10.25)
(EQ 10.26)
10-19
10
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