The parameterIp>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 themeasured voltage 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 betweenthe voltage 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 thevoltage instrument transformers, and shall be equipped with auxiliary contacts that are wiredto the IEDs. Separate fuse-failure monitoring IEDs or elements within the protection andmonitoring devices are another possibilities. These solutions are combined to get the bestpossible effect in the fuse failure supervision function (FUFSPVC).FUFSPVC function built into the IED products can operate on the basis of external binarysignals from the miniature circuit breaker or from the line disconnector. The first caseinfluences the operation of all voltage-dependent functions while the second one does notaffect the impedance measuring functions.The negative sequence detection algorithm, based on the negative-sequence measuringquantities is recommended for use in isolated or high-impedance earthed networks: a highvalue of voltage 3U2 without the presence of the negative-sequence current 3I2 is a conditionthat is related 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 earthed networks: a high value of voltage3U0 without the presence of the residual current 3I0 is a condition that is related to a fusefailure event. In cases where the line can have a weak-infeed of zero sequence current thisfunction shall be avoided.A criterion based on delta current and delta voltage measurements can be added to the fusefailure supervision function in order to detect a three phase fuse failure. This is beneficial forexample during three phase transformer switching.Section 12 1MRK 511 358-UEN ASecondary system supervision218Application manual
