GE C70 Instruction Manual page 336

GROUPED ELEMENTS
BANK OV 1 BANK GROUND
voltage measured, and ungrounded without the neutral point voltage. The relay automatically compensates for potentially
different VT ratios and secondary voltages of the bus and neutral point voltages. The following table explains the operating
signals of the function based on the input signals available to the relay.
Table 5-34: Operating signals based on input signals
VT connection
Wye
Delta
— This setting specifies a FlexCurve used by the fourth inverse time stage of this function. FlexCurves are
BANK OV 1 CURVE
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 common 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
5
partially energized function.
BANK OV 1 STG 1A PICKUP
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
independent stages of definite-time operation are provided for each phase of the bank.
BANK OV 1 STG 4A PICKUP
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 secondary voltage and VT ratio divided
by 3 . The inverse time stage uses a user-programmable FlexCurve selected by the
BANK OV 1 STG 1 PKP DELAY
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
stages apply individually configurable pickup delays, but use this common dropout delay.
— This input is used to block the function when required; in particular, when the bank is offline.
BANK OV 1 BLK
5-212
— This setting indicates if the protected bank is grounded, ungrounded with the neutral point
Bank configuration
Grounded Ungrounded
Vop_A = VA Vop_A = VA – VX
Vop_B = VB Vop_B = VB – VX
Vop_C = VC Vop_C = VC – VX
Vop_A = (VCA – VAB) / 3
Vop_B = (VAB – VBC) / 3
Vop_C = (VBC – VCA) / 3
to
BANK OV 1 STG 3C PICKUP
to
BANK OV 1 STG 4C PICKUP
to
BANK OV 1 STG 3 PKP DELAY
BANK OV 1 DPO DELAY
— This setting controls a dropout delay for the operate FlexLogic operands. Note that individual
Ungrounded w/o VN
Vop_A = (VCA – VAB) / 3
Vop_B = (VAB – VBC) / 3
Vop_C = (VBC – VCA) / 3
— Specify pickup thresholds for stages 1 through 3 in phases A
— Secify pickup thresholds for the inverse time stage 4 in phase A
— Specify the pickup time delays for each definite time stage of
setting.
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
. Three
3
setting.
BANK OV 1 CURVE