The minimum operate current,IMinOp, must be set as a minimum to twice the residual current inthe supervised CT circuits under normal service conditions and rated primary current.The parameterPickup_Block is normally set at150% to block the function during transientconditions.The FAIL output is connected to the blocking input of the protection function to be blocked atfaulty CT secondary circuits.12.2 Fuse failure supervision FUFSPVC IP14556-1 v312.2.1 IdentificationM14869-1 v4Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberFuse failure supervision FUFSPVC - -12.2.2 Application SEMOD113803-4 v10Different protection functions within the protection IED, operates on the basis of the measuredvoltage in the relay point. Examples are:• impedance protection functions• undervoltage function• energizing check function and voltage check for the weak infeed logicThese functions can operate unintentionally if a fault occurs in the secondary circuits between thevoltage instrument transformers and the IED.It is possible to use different measures to prevent such unwanted operations. Miniature circuitbreakers in the voltage measuring circuits should be located as close as possible to the voltageinstrument transformers, and shall be equipped with auxiliary contacts that are wired to the IEDs.Separate fuse-failure monitoring IEDs or elements within the protection and monitoring devicesare another possibilities. These solutions are combined to get the best possible effect in the fusefailure supervision function (FUFSPVC).FUFSPVC function built into the IED products can operate on the basis of external binary signalsfrom the miniature circuit breaker or from the line disconnector. The first case influences theoperation of all voltage-dependent functions while the second one does not affect the impedancemeasuring functions.The negative sequence detection algorithm, based on the negative-sequence measuringquantities is recommended for use in isolated or high-impedance grounded networks: a high valueof voltage 3V2 without the presence of the negative-sequence current 3I2 is a condition that isrelated to a fuse failure event.The zero sequence detection algorithm, based on the zero sequence measuring quantities isrecommended for use in directly or low impedance grounded networks: a high value of voltage 3V0without the presence of the residual current 3I0 is a condition that is related to a fuse failure event.Section 12 1MRK 511 358-UUS ASecondary system supervision246Application manual
