1MAC309294-MB F Section 6Condition monitoring functionsRER620 379Technical ManualTable 331: Fuse failure output controlThe activation of the BLOCK input deactivates both FUSEF_U and FUSEF_3PH outputs.6.2.5 ApplicationSome protection functions operate on the basis of the measured voltage value in the relaypoint. These functions can fail if there is a fault in the measuring circuits between thevoltage transformers and the relay.A fault in the voltage measuring circuit is referred to as a fuse failure. This term ismisleading since a blown fuse is just one of the many possible reasons for a broken circuit.Fuse-failure detection criterion Conditions and function responseNegative phase sequence criterion If a fuse failure is detected based on the negativephase-sequence criterion, the FUSEF_U output isactivated.If the fuse-failure detection is active for more thanfive seconds and at the same time all the phasevoltage values are below the set value of theSeal involtage setting withEnable seal in turned to“Yes”,the function activates the FUSE_3PH output signal.The FUSEF_U output signal is also activated if all thephase voltages are above theSeal in voltage settingfor more than 60 seconds and at the same time thenegative sequence voltage is aboveNeg Seqvoltage Lev for more than 5 seconds, all the phasecurrents are below theCurrent dead Lin Val settingand the circuit breaker is closed, that is,CB_CLOSEDis TRUE.Current and voltage delta function criterion If the current and voltage delta criterion detects afuse failure condition, but all the voltages are notbelow theSeal in voltage setting, only the FUSEF_Uoutput is activated.If the fuse-failure detection is active for more thanfive seconds and at the same time all the phasevoltage values are below the set value of theSeal involtage setting withEnable seal in turned to“Yes”,the function activates the FUSE_3PH output signal.External fuse-failure detection The MINCB_OPEN input signal is supposed to beconnected through a relay binary input to the N.C.auxiliary contact of the miniature circuit breakerprotecting the VT secondary circuit.The MINCB_OPEN signal sets the FUSEF_U outputsignal to block all the voltage-related functions whenMCB is in the open state.The DISCON_OPEN input signal is supposed to beconnected through a relay binary input to the N.C.auxiliary contact of the line disconnector. TheDISCON_OPEN signal sets the FUSEF_U outputsignal to block the voltage-related functions whenthe line disconnector is in the open state.It is recommended to always set Enable seal in to “Yes”. This secures thatthe blocked protection functions remain blocked until normal voltageconditions are restored if the fuse-failure has been active for 5 seconds, thatis, the fuse failure outputs are deactivated when the normal voltageconditions are restored.
