GE C70 Instruction Manual page 290

5.6 GROUPED ELEMENTS
The relay allows manual setting of the inherent unbalance factor or automatic setting via a dedicated command. For addi-
tional information, refer to the Theory of operation and Application of settings chapters.
5
The following settings are available. The settings shown below are for the neutral current unbalance 1 element. The same
descriptions apply to the neutral current unbalance 2 and 3 elements.
• NTRL CUR UNBALCE 1 BANK SOURCE: This setting indicates the signal source that signifies the split-phase neutral
current in its ground current channel. At minimum the ground channel of this source must be set. If the factor compen-
sating for inherent bank unbalance is set above zero signalling the intent of using the compensation, the phase cur-
rents of this source must be configured as well. Without the phase currents configured under this source, the function
would run only if the magnitude of the inherent unbalance factor is set to zero.
To improve accuracy, a relatively low-ratio window CT can be used for instrumentation of the split-phase neutral cur-
rent, and be wired to a 1 A or even sensitive ground relay input for extra sensitivity. CT primary and secondary ratings
are entered under a separate menu. Directionality of wiring of the split-phase current is not important for proper func-
tioning of the feature as long as the angle of the factor compensating for the inherent unbalance is set appropriately.
• NTRL CUR UNBALCE 1 K MAG: This setting defines magnitude of the factor compensating for the inherent unbal-
ance of the bank. Under balanced conditions, the amount of the spill current measured in the neutral connection
between the banks is proportional to the positive-sequence component of the total current of the two banks. This set-
ting defines the magnitude of the proportionality factor. Quality of balancing the bank with a given value of this setting
can be viewed under
calculate the compensating factor automatically. Setting the compensating factor to zero effectively disables the com-
pensation. If further the slope is set to zero as well, this feature becomes a plain overcurrent element responding to the
neutral split-phase current.
• NTRL CUR UNBALCE 1 K ANG: This setting defines angle of the factor compensating for the inherent unbalance of
the bank. Under balanced conditions, the amount of the spill current measured in the neutral connection between the
5-166
Regular, preferably
low-ratio CT for
ungrounded banks
Window / core-
balance CTs for
grounded banks
Figure 5–69: NEUTRAL CURRENT UNBALANCE CONNECTIONS
menu. An automatic setting procedure is available via the
ACTUAL VALUES
C70 Capacitor Bank Protection and Control System
5 SETTINGS
C70 CAPACITOR BANK RELAY
Neutral
CT bank
BANK
60N
SOURCE
Ground
CT
834735A1.CDR
COMMANDS
menu to
GE Multilin