GE Multilin L90 Line Current Differential System 5-2655 SETTINGS 5.7 CONTROL ELEMENTS5THREE VT BREAKER FLASHOVER APPLICATIONWhen only one set of VTs is available across the breaker, the BRK 1 FLSHOVR SIDE 2 SRC setting should be “None”. To detectan open breaker condition in this application, the scheme checks if the per-phase voltages were recovered (picked up), thestatus of the breaker is open (contact input indicating the breaker status is off), and no flashover current is flowing. A con-tact showing the breaker status must be provided to the relay. The voltage difference will not be considered as a conditionfor open breaker in this part of the logic.Voltages must be present prior to flashover conditions. If the three VTs are placed after the breaker on the line (orfeeder), and the downstream breaker is open, the measured voltage would be zero and the flashover element willnot be initiated.The flashover detection will reset if the current drops back to zero, the breaker closes, or the selected FlexLogic operandfor supervision changes to high. Using supervision through the BRK 1 FLSHOVR SPV A, BRK 1 FLSHOVR SPV B, and BRK 1FLSHOVR SPV C settings is recommended by selecting a trip operand that will not allow the flashover element to pickup priorto the trip.The flashover detection can be used for external alarm, re-tripping the breaker, or energizing the lockout relay.Consider the following configuration:The source 1 (SRC1) phase currents are feeder CTs and phase voltages are bus VTs, and Contact Input 1 is set as Breaker52a contact. The conditions prior to flashover detection are:1. 52a status = 0.2. VAg, VBg, or VCg is greater than the pickup setting.3. IA, IB, IC = 0; no current flows through the breaker.4. VA is greater than pickup (not applicable in this scheme).The conditions at flashover detection are:1. 52a status = 0.2. IA, IB, or IC is greater than the pickup current flowing through the breaker.3. VA is greater than pickup (not applicable in this scheme).SIX VT BREAKER FLASHOVER APPLICATIONThe per-phase voltage difference approaches zero when the breaker is closed. The is well below any typical minimumpickup voltage. Select the level of the BRK 1 FLSHOVR DIFF V PKP setting to be less than the voltage difference measuredacross the breaker when the close or open breaker resistors are left in service. Prior to flashover, the voltage difference islarger than BRK 1 FLSHOVR DIFF V PKP. This applies to either the difference between two live voltages per phase or when thevoltage from one side of the breaker has dropped to zero (line de-energized), at least one per-phase voltage is larger thanthe BRK 1 FLSHOVR V PKP setting, and no current flows through the breaker poles. During breaker flashover, the per-phasevoltages from both sides of the breaker drops below the pickup value defined by the BRK 1 FLSHOVR V PKP setting, the volt-age difference drops below the pickup setting, and flashover current is detected. These flashover conditions initiate Flex-Logic pickup operands and start the BRK 1 FLSHOVR PKP DELAY timer.This application do not require detection of breaker status via a 52a contact, as it uses a voltage difference larger than theBRK 1 FLSHOVR DIFF V PKP setting. However, monitoring the breaker contact will ensure scheme stability.NOTE842746A1.CDRBus VTsLine/FeederBreakerCTsBus
