GE C70 Instruction Manual page 324

5.6 GROUPED ELEMENTS
• BANK OV 1 CURVE: This setting specifies a FlexCurve used by the fourth inverse time stage of this function. Flex-
Curves are user-programmable on a point-by-point basis. This function applies a common curve shape in all three
phases. However, the curve is specified as time versus multiple of pickup. With three individually programmable pickup
values per phase one accommodates possible differences between individual phases of the bank even though a com-
mon curve shape is used.
Implementation of the inverse-time stage is based on the concept of a virtual disk emulating electromechanical relays.
When above the pickup level, the function integrates towards the trip level at the rate dictated by the curve at a given
multiple of pickup. When activated but with the operating signal below the pickup, the function integrates down toward
a complete reset. This mode of operation assures dependability in situations when the voltage oscillates and causes
stress to the protected capacitor in repetitive cycles each lasting too short to expire a straight timer. As a result of this
implementation, the shape of the curve below multiple of pickup of 1 is important as it controls the speed of reset of a
partially energized function.
• BANK OV 1 STG 1A PICKUP to BANK OV 1 STG 3C PICKUP: These settings specify pickup thresholds for stages 1
through 3 in phases A through C in per-units (pu) of the nominal phase-to-ground 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. With a delta VT configuration, a value of 1 pu is a product of the nominal secondary voltage and VT ratio
divided by 3 . Three independent stages of definite-time operation are provided for each phase of the bank.
• BANK OV 1 STG 4A PICKUP to BANK OV 1 STG 4C PICKUP: These settings specify pickup thresholds for the
inverse time stage 4 in phase A through C in per-units (pu) of the nominal phase-to-ground bus voltage. With a wye VT
configuration, 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. With a delta VT configuration, a value of 1 pu is a product of the nominal second-
ary voltage and VT ratio divided by
BANK OV 1 CURVE
• BANK OV 1 STG 1 PKP DELAY to BANK OV 1 STG 3 PKP DELAY: These settings specify the pickup time delays for
5
each definite time stage of alarming/tripping. Note that each of the nine comparators (three definite-time stages in
three phases) uses an individual timer, but settings for these timers are controlled individually per each stage, not per
phase. The timers use a common dropout time delay specified by the
• BANK OV 1 DPO DELAY: This setting controls a dropout delay for the operate FlexLogic operands. Note that individ-
ual stages apply individually configurable pickup delays, but use this common dropout delay.
• BANK OV 1 BLK: This input is used to block the function when required; in particular, when the bank is offline.
5-200
3 . The inverse time stage uses a user-programmable FlexCurve selected by the
setting.
C70 Capacitor Bank Protection and Control System
setting.
BANK OV 1 DPO DELAY
5 SETTINGS
GE Multilin