GE Multilin C70 Capacitor Bank Protection and Control System 7-37 COMMANDS AND TARGETS 7.1 COMMANDS7c) NEUTRAL VOLTAGE UNBALANCEPATH: COMMANDS CAPACITOR BANK AUTO... NEUTRAL VOLTAGE UNBALANCE NEUTRAL VOLTAGE UNBALANCE 1(3)The auto-setting feature shall be used when the capacitor bank is on-line and the 59NU function is enabled. For securityreasons, it may be necessary to consider applying less sensitive settings during the auto-setting process. Switching tempo-rarily to a different setting group with less sensitive pickup thresholds is a method to provide for this extra security.This feature can be used with a manual acceptance of the auto-calculated coefficients (the NTRL VOL UNBAL 1 AUTO SETcommand switched to “Manual”), or with an automatic acceptance of the calculated factors (the NTRL VOL UNBAL 1 AUTOSET command switched to “Auto”).The feature is used as follows.MANUAL SUPERVISION OF AUTOMATICALLY CALCULATED FACTORS:When the NTRL VOL UNBAL 1 AUTO SET command is switched to “Manual”, the auto-setting screens (one for each of the twofactors) display values that best balance the function and prompt for permission to apply the calculated value as a new set-ting. When confirmed, the auto-selected value is applied to all setting groups having same source as the active group dur-ing 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 isdisplayed for the duration of the flash message time. The time-out period is intended for field staff to make a note of thenewly applied coefficient. However, it is possible to immediately navigate from this screen. The new setting values can beviewed in the SETTING menu at any time.After the process if finished, it is recommended to disable the auto-setting feature. If not manually disabled, the featureautomatically 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 nominalfrequency and the magnitude of the positive-sequence current above 0.1 pu. If any of these conditions are violated, theSUPV FAIL message is displayed in the second line.If the neutral voltage unbalance function is disabled or blocked, the auto-setting process is not functional and the 59NU NOTRUNNING message is displayed in the second line.AUTOMATIC SUPERVISION OF AUTOMATICALLY CALCULATED FACTORS:When the NTRL VOL UNBAL 1 AUTO SET command is switched to “Auto”, the process of calculating and applying the balanc-ing coefficients is fully automatic. Typical applications require setting this function to “Auto” with the bank de-energized,then energizing the capacitor bank. After the function is set to “Auto”, it expects to read valid input signals as a result ofbank energization within the display flash message time duration to calculate and apply factors; otherwise, the function isreturned to “Disabled”. When the bank is energized and the five-cycle timer of the 59NU function expires, the balancingcoefficients are calculated and automatically applied. When the new balancing factors are applied, the function switchesautomatically from “Auto” to “Disabled” and the 59NU function becomes operational. In essence, the when in the “Auto”mode, the confirmation command is automatically executed immediately after the balancing values are available. The C70does not display the applied coefficients in the “Auto” mode; rather, they are be viewed in the SETTINGS menu.When the supervisory conditions are not satisfied in “Auto” mode, the AUTO FAIL message is displayed and the 59NU func-tion starts running with the pre-existing settings for the balancing factors. NEUTRAL VOLTAGE UNBALANCE 1NTRL VOL UNBAL 1AUTO SET: DisabledRange: Disabled, Manual, AutoMESSAGE XA/XB RATIO k=0.0000APPLY? NoRange: Yes, NoMESSAGE XA/XC RATIO k=0.0000APPLY? NoRange: Yes, No
