4–290 889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUALMONITORING CHAPTER 4: SETPOINTSBreaker ArcingCurrentThe 889 relay provides one Breaker Arcing Current element.This element calculates anestimate of the per-phase wear on the breaker contacts by measuring and integrating thecurrent squared passing through the breaker contacts as an arc. These per-phase valuesare added to accumulated totals for each phase and compared to a programmedthreshold value. When the threshold is exceeded in any phase, the relay can set an outputoperand and set an alarm. The accumulated value for each phase can be displayed as anactual value.The same output operands that are selected to operate the Trip output relay that is usedto trip the breaker indicating a tripping sequence has begun, are used to initiate thisfeature. A time delay is introduced between initiation and starting of integration to preventintegration of current flow through the breaker before the contacts have parted. Thisinterval includes the operating time of the output relay, any other auxiliary relays and thebreaker mechanism. For maximum measurement accuracy, the interval between thechange-of-state of the operand (from 0 to 1) and contact separation should be measuredfor the specific installation. Integration of the measured current continues for 100 ms,which is expected to include the total arcing period.Figure 4-119: Breaker Arcing Current MeasurementPath: Setpoints > Monitoring > Breaker > BKR 1 Monitor > BKR 1 Arcing CurrentFUNCTIONRange: Disabled, Alarm, Latched Alarm, ConfigurableDefault: DisabledSIGNAL INPUTRange: dependant upon the order codeDefault: CT Bank1-J1INITIATIONRange: Off, Any FlexLogic operandDefault: OffThe setpoint selects the FlexLogic operand, digital input, virtual input or remote inputthat initiates the Breaker Arcing Current scheme, typically the Trip signals from internalprotection functions.DELAYRange: 0.000 to 6000.00 s in steps of 0.001 sDefault: 0.030 sThe setpoint provides a delay interval between the time the tripping sequence isinitiated and the time the breaker contacts are expected to part, starting the integrationof the measured current.
