GE UR Series C70, Instruction Manual

Page: 368 / 614

7-2 C70 Capacitor Bank Protection and Control System GE Multilin
7.1 COMMANDS 7 COMMANDS AND TARGETS
7
b) VOLTAGE DIFFERENTIAL
PATH: COMMANDS
Ö
CAPACITOR BANK AUTO SETTING
Ö
VOLTAGE DIFFERENTIAL
Ö
VOLTAGE DIFFERENTIAL 1(3)
The automatic setting feature shall be used when the capacitor bank is on-line and the 87V function is enabled. For security
reasons one may consider applying less sensitive settings during the auto-setting process. Switching temporarily to a differ-
ent setting group with less sensitive pickup thresholds is a way to provide for the extra security.
The feature can be used with a manual acceptance of the auto-calculated coefficients (the
VOLTAGE DIF 1 AUTO SETTING
command switched to “Manual”), or with an automatic acceptance of the calculated factors (the
VOLTAGE DIF 1 AUTO SET-
TING
command switched to “Auto”).
The feature is used as follows.
Application with Manual Supervision of the Automatically Calculated Factors:
When the
VOLTAGE DIF 1 AUTO SETTING
command is switched to “Manual”, the auto-setting screens, one for each phase,
display the values that balance best the function in a given phase and prompt for permission to apply the calculated value
as a new setting. When confirmed, the auto-selected value gets applied to all setting groups configured with the same
source as the active group during the auto-setting procedure.
After consent to apply the calculated coefficient is received, the
k =?.???? APPLIED
confirmation message is displayed for
the duration of the flash message time in the second line of the screen. The time-out period is provided for the field staff to
make a note of the newly applied coefficient. However, it is possible to navigate from this screen immediately. The new set-
ting values can be viewed under the setting menu at any time.
After the process if finished, it is recommended to disable the auto-setting feature. If not disabled by the user, the feature
disables itself when user-initiated front panel interface activity ceases and the C70 display dims itself.
Certain security conditions are checked during the auto-setting process. This includes deviation from the nominal fre-
quency and verifying that the magnitudes of all three bus voltages are between 0.85 and 1.15 pu. If these conditions are
violated. the
SUPV FAIL
message is displayed in the second line.
If the voltage differential function is disabled or blocked, then the auto-setting process is not functional and the
87V NOT
RUNNING
message is displayed in the second line.
Application with Automatic Supervision of the Automatically Calculated Factors:
When the
VOLTAGE DIF 1 AUTO SETTING
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. 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 under in the
SETTINGS
menu.
If the supervisory conditions are not satisfied in the “Auto” mode within the time specified by the
DEFAULT MESSAGE TIMEOUT
setting, the
AUTO FAIL
message is displayed and the 87V function starts running with the pre-existing settings for the bal-
ancing 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 a 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.
„
VOLTAGE
„
DIFFERENTIAL 1
VOLTAGE DIF 1 AUTO
SETTING: Disabled
Range: Disabled, Manual, Auto
MESSAGE
V DIF 1A k=####.####
APPLY IN PHS A? No
Range: Yes, No
MESSAGE
V DIF 1A k=####.####
APPLY IN PHS B? No
Range: Yes, No
MESSAGE
V DIF 1A k=####.####
APPLY IN PHS C? No
Range: Yes, No