Most of the electrical network faults are earth faults. Conventional protection systemsbased on overcurrent, impedance or other principles are suitable for detectingrelatively low-impedance faults which have a relatively large fault current.However, a small percentage of the earth faults have a very large impedance. They arecomparable to load impedance and consequently have very little fault current. Thesehigh-impedance faults do not pose imminent danger to power system equipment.However, they are a considerable threat to people and property. The IEEE PowerSystem Relay Committee working group on High Impedance Fault DetectionTechnology defines High Impedance Faults as those that 'do not produce enough faultcurrent to be detectable by conventional overcurrent relays or fuses.PHIZ always needs sensitive Io measurement.High-impedance fault (PHIZ) detection requires a different approach than that forconventional low-impedance faults. Reliable detection of PHIZ provides safety tohumans and animals. ABB has developed innovative technology for high-impedancefault detection with over ten years of research resulting in many successful field tests.5.4.7 SignalsTable 1023:PHIZ Input signalsName Type Default DescriptionI3P SIGNAL - Three-phase currentsIRES SIGNAL - Residual currentBLOCK BOOLEAN 0=False Block signal for activating the blocking modeCB_CLOSED BOOLEAN 0=False Circuit Breaker Closed inputCB_OPEN BOOLEAN 0=False Circuit Breaker Open inputTable 1024:PHIZ Output signalsName Type DescriptionOPERATE BOOLEAN Operate5.4.8 SettingsTable 1025:PHIZ Group settings (Basic)Parameter Values (Range) Unit Step Default DescriptionSecurity Level 1...10 1 5 Security LevelSection 5 1MRS759142 CProtection related functions1086 REX640Technical Manual
