Section 6 1MAC309294-MB FCondition monitoring functions380 RER620Technical ManualSince incorrectly measured voltage can result in a mis-operation of some of the protectionfunctions, fast failure detection is one of the means to block voltage-based functions beforethey operate.Figure 206: Fault in a circuit from the voltage transformer to the relayA fuse failure occurs due to blown fuses, broken wires or intended substation operations.The negative sequence component-based function can be used to detect different types ofsingle-phase or two-phase fuse failures. However, at least one of the three circuits from thevoltage transformers must not be broken. The supporting delta-based function can alsodetect a fuse failure due to three-phase interruptions.In the negative sequence component-based part of the function, a fuse failure is detectedby comparing the calculated value of the negative sequence component voltage to thenegative sequence component current. The sequence entities are calculated from themeasured current and voltage data for all three phases. The purpose of this function is toblock voltage-dependent functions when a fuse failure is detected. Since the voltagedependence differs between these functions, 60 has two outputs for this purpose.
