10.2.2 FunctionalityThe aim of the fuse failure supervision function SDDRFUF is to block voltage measuringfunctions at failures in the secondary circuits between the voltage transformer and the IEDin order to avoid inadvertent operations that otherwise might occur.The fuse failure supervision function basically has three different detection methods,negative sequence and zero sequence based detection and an additional delta voltage anddelta current detection.The negative sequence detection is recommended for IEDs used in isolated or high-impedance grounded networks. It is based on the negative-sequence measuring quantities,a high value of negative sequence voltage 3V2 without the presence of the negative-sequence current 3I2.The zero sequence detection is recommended for IEDs used in directly or low impedancegrounded networks. It is based on the zero sequence measuring quantities, a high value ofzero sequence voltage 3V0 without the presence of the zero sequence current 3I0.For better adaptation to system requirements, an operation mode setting has beenintroduced which makes it possible to select the operating conditions for negativesequence and zero sequence based function. The selection of different operation modesmakes it possible to choose different interaction possibilities between the negativesequence and zero sequence based detection.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, which in practiceis more associated with voltage transformer switching during station operations.10.2.3 Function blockANSI08000220-1-en.vsdSDDRFUFI3P*V3P*BLOCK52AMCBOP89BBLKZBLKV3PHDLD1PHDLD3PHANSI08000220 V1 ENFigure 157: SDDRFUF function block1MRK 506 335-UUS A Section 10Secondary system supervision333Technical manual
