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3-40
Protection Functions
Capacitor bank
unbalance protection
857-UM001A-EN-P – July 2009
Table 3.22 – Recorded values of the directional intermittent transient earth
fault stage (8 latest faults) I
Parameter
yyyy-mm-dd
hh:mm:ss.ms
Flt
EDly
Uo
SetGrp
The device enables versatile capacitor, filter and reactor bank
protection, with its five current measurement inputs. The fifth input
is typically useful for unbalance current measurement of a double-
wye connected unearthed bank. Furthermore, the unbalance
protection is highly sensitive to internal faults of a bank because of
the sophisticated natural unbalance compensation. However, the
location method gives the protection a new dimension and enables
easy maintenance monitoring for a bank.
This protection scheme is specially used in double wye connected
capacitor banks. The unbalance current is measured with a dedicated
current transformer (could be like 5A/5A) between two starpoints of
the bank. The unbalance current is not affected by system unbalance.
However, due to manufacturing tolerances, some amount of natural
unbalance current exists between the starpoints. This natural
unbalance current affects the settings, thus, the setting has to be
increased.
L1
L2
L3
Figure 2.23 – Typical capacitor bank protection application with Allen-Bradley devices
> (67NT)
0T
Value
Unit
Time stamp of the recording, date
Time stamp, time of day
pu
Maximum detected earth fault current
%
Elapsed time of the operating time setting.
100% = trip
%
Max. U
1
Active setting group during fault
2
VAMP 255
Description
voltage during the fault
0
X1:1
IL1
T1
X1:2
X1:3
IL2
X1:4
X1:5
IL3
X1:6
X1:7
I
X1:8
01
X1:9
I
02
X1:10
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