GE C70 Instruction Manual page 485

CHAPTER 7: COMMANDS AND TARGETS
If the voltage differential function is disabled or blocked, then the auto-setting process is not functional and the 87V NOT
RUNNING message displays in the second line.
Application with automatic supervision of the automatically calculated factors
When the
VOLTAGE DIF 1 AUTO SETTING
balancing coefficients is fully automatic. Typical applications require setting this function to "Auto" with the bank de-
energized, then energizing the capacitor bank. When the bank is energized and the five-cycle timer of the 87V function
expires, the balancing coefficients are calculated and automatically applied. After the new balancing factors are applied,
the function switches automatically from "Auto" to "Disabled" and 87V becomes operational. In essence, when in the
"Auto" mode, the user confirmation is processed immediately after the balancing values become available. The C70 does
not display the applied coefficients in "Auto" mode; rather, they are be viewed in the
If the supervisory conditions are not satisfied in the "Auto" mode within the time specified by the
setting, the AUTO FAIL message displays and the 87V function starts running with the pre-existing settings for the
TIMEOUT
balancing factors.
The advantage of automatically calculating factors is that the bank is immediately protected after energization. However,
due to energization inrush and distortion of voltages, the factors may not be accurate enough for the most sensitive
stages. Therefore, it is good practice to block the most sensitive stages on energization, manually adjust the factors to
reduce the differential signal, and then enable the most sensitive stages.
7.1.1.3 Neutral voltage unbalance
COMMANDS  CAPACITOR BANK AUTO SETTING  NEUTRAL VOLTAGE UNBALANCE  NEUTRAL VOLTAGE
UNBALANCE 1(3)
 NEUTRAL VOLTAGE
 UNBALANCE 1
Use the auto-setting feature when the capacitor bank is online and the 59NU function is enabled. For security reasons,
consider applying less sensitive settings during the auto-setting process. Switching temporarily to a different setting group
with less sensitive pickup thresholds is a method to provide the extra security.
This feature can be used with a manual acceptance of the auto-calculated coefficients (the
command switched to "Manual"), or with an automatic acceptance of the calculated factors (the
command switched to "Auto").
SET
The feature is used as follows.
Manual supervision of automatically calculated factors
When the
NTRL VOL UNBAL 1 AUTO SET
factors) display values that best balance the function and prompt for permission to apply the calculated value as a new
setting. When confirmed, the auto-selected value is applied to all setting groups having same source as the active group
during auto-setting procedure. Both ratios (XA / XB and XA / XC) must be set correctly to clear the inherent bank unbalance.
After consent to apply the calculated coefficient is received via the keypad, the "k =?.???? APPLIED" confirmation message
idisplays for the duration of the flash message time. The time-out period is intended for field staff to make note of the
newly applied coefficient. However, it is possible to immediately navigate from this screen. The new setting values can be
viewed in the menu at any time.
SETTINGS
After the process finishes, it is recommended to disable the auto-setting feature. If not manually disabled, the feature
automatically disables itself when user-initiated front panel interface activity ceases and the C70 display is dimmed.
Certain security conditions are checked during the auto-setting process, such as the frequency deviation from the nominal
frequency and the magnitude of the positive-sequence current above 0.1 pu. If any of these conditions are violated, the
SUPV FAIL message displays in the second line.
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
command is switched to "Auto," the process of calculating and applying the
NTRL VOL UNBAL 1

AUTO SET: Disabled
XA/XB RATIO k=0.0000

APPLY? No
XA/XC RATIO k=0.0000

APPLY? No
command is switched to "Manual," the auto-setting screens (one for each of the two
menu.
SETTINGS
DEFAULT MESSAGE
Range: Disabled, Manual, Auto
Range: Yes, No
Range: Yes, No
NTRL VOL UNBAL 1 AUTO SET
NTRL VOL UNBAL 1 AUTO
COMMANDS MENU
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