GE C70 Instruction Manual page 320

5.6 GROUPED ELEMENTS
• VOLTAGE DIF 1 BUS SOURCE: Indicate signal source that signifies the bus voltage of the bank. The function uses
this source as reference for pu settings of pickup thresholds, and scales the tap voltages to this signal level. The VT
ratio and secondary nominal voltage are set under separate menu. Voltages of this source must be connected in wye
for the function to operate.
• VOLTAGE DIF 1 TAP SOURCE: Indicate signal source that signifies the tap voltage of the bank. The function scales
this voltage to the bus level using the matching factor setting. The matching is performed on primary voltages, or per
unit of the bus voltage. The VT ratio and secondary nominal voltage are set under separate menu. Voltages of this
source must be connected in wye for the function to operate. If this function is used on ungrounded banks, the tap
source must have the neutral point voltage of the bank configured under the auxiliary voltage channel. That auxiliary
voltage must be labelled "Vn" under the VT setup menu.
• VOLTAGE DIF 1 BANK GROUND: Indicate if the protected bank is grounded or ungrounded. In the latter case, the
auxiliary voltage configured under the tap source will be subtracted from the phase voltages of both the bus and tap.
This results in the actual voltage drop along the capacitor string, and thus facilitates the voltage differential principle.
The relay automatically compensates for different VT ratios and secondary voltages of the neutral point voltage and
the bus and tap voltages.
• VOLTAGE DIF 1 MATCH FACTOR A to VOLTAGE DIF 1 MATCH FACTOR C: This setting specifies the division ratio
of the healthy bank, i.e. the ratio between the bus and tap voltages (value greater than 1). The matching factor is
applied as multiplier for the primary tap voltage before comparing with the primary bus voltage. Quality of balancing the
bank with a given value of this setting can be viewed under
available under the
• VOLTAGE DIF 1 STG 1A PICKUP to VOLTAGE DIF 1 STG 4C PICKUP: These settings specify pickup thresholds for
stages 1 through 4 for phases A to C in per-units (pu) of the nominal bus voltage. A value of 1 pu is a product of the
nominal secondary voltage and VT ratio of the voltage bank configured under the bus source of this function. Four
independent stages are provided for each phase of protection.
5
• VOLTAGE DIF 1 STG 1 PKP DELAY: This setting specifies the pickup time delay, individually per each stage of alarm-
ing/tripping. Note that each of the twelve comparators (four stages in three phases) uses an individual timer, but set-
tings for these timers are controlled individually per each stage, not per phase. The timers use a common drop out time
delay specified by the next setting.
• VOLTAGE DIF 1 DPO DELAY: This setting controls a drop out delay for the operate FlexLogic operands. Note that
individual stages apply individually configurable pickup delays, but use this common drop out delay.
• VOLT DIF 1 BLK STG 1 to VOLT DIF 1 BLK STG 4: These inputs are used to block the function on a per stage basis
when required. At minimum this function shall be blocked when the bank is off-line, or else it will operate unnecessarily.
Either breaker position or undercurrent indication via any available instantaneous function, or a combination, may be
used for blocking. The VT fuse fail condition from both the bus and tap VT should also be considered. Note that when
unblocked, the function becomes operational after five cycles of intentional delay.
5-196
menu to calculate the matching factors automatically.
COMMANDS
C70 Capacitor Bank Protection and Control System
menu. An automatic setting procedure is
ACTUAL VALUES
5 SETTINGS
GE Multilin