GE Multilin F60 Feeder Protection System 5-1855 SETTINGS 5.6 CONTROL ELEMENTS5Some faults in overhead distribution feeders are characterized by low fault current due to high ground resistance. If the faultcurrent is in the order of expected unbalance load or less, it cannot be reliably detected by overcurrent protection. Thesefaults are classified as high-impedance (Hi-Z) faults. Since a Hi-Z fault is not accompanied by excessive current, it is gener-ally not dangerous to the electrical installation except for some damage to the overhead conductor at the fault location.However, an undetected Hi-Z fault is a risk to people and property as well as having a potential to evolve into a full-blownfault.The following event types are associated with Hi-Z faults. It is assumed that for all cases that ground is involved.• High impedance fault: a fault with fault impedance sufficiently high such that it is not detected by overcurrent protection• High impedance, downed conductor fault: a high impedance fault for which the primary conductor is no longer intact onpole top insulators, but instead is in contact with earth or a grounded object• Arcing fault: any high impedance fault which exhibits arcingCombinations of these events are possible: for example, an arcing high impedance, downed conductor fault. The Hi-Z ele-ment is intended to detect high impedance faults that arc and to differentiate those that are downed conductors from thosethat are not. It should be noted that no known technology can detect all Hi-Z faults.The Hi-Z element was primarily designed for solidly grounded systems. The similar Hi-Z element in the DFM200 relay hasbeen tested with some success on impedance grounded systems as well. However, there are no guarantees of certainoperation of the high impedance fault detection element on non-solidly grounded systems.The Hi-Z data collection consists of RMS Data Capture and Hi-Z Data capture:• RMS Data Capture: The RMS data captures are triggered by two-cycle Hi-Z overcurrent conditions, loss of load con-ditions, and high arc confidence conditions. Captures triggered by loss of load and high arc confidence conditions aresaved to a temporary capture table, and deleted if the event does not result in an Arcing or Downed Conductor condi-tion. The relay maintains a history of four captures and utilizes a combination of age, priority and access for determin-ing which capture to save.The RMS data capture contains the two-cycle RMS values for the voltage and current for each of the phases and cur-rent for the neutral channel. The capture frequency is half the system frequency. Each capture contains 1800 points.• High-Z Data Capture: Hi-Z Data Captures are triggered and maintained in an identical manner as RMS Data Cap-tures. The relay maintains four captures of 300 records each. The capture frequency is 1 Hz and the data collected isdefined in the following two tables.MESSAGE HI-Z NEUTRAL OC MINPICKUP: 1.00 puRange: 0.01 to 10.00 pu in steps of 0.01MESSAGE HI-Z PHASE RATE OFCHANGE: 150 A/2cycleRange: 1 to 999 A/2cycle in steps of 1MESSAGE HI-Z NEUTRAL RATE OFCHANGE: 150 A/2cycleRange: 1 to 999 A/2cycle in steps of 1MESSAGE HI-Z LOSS OF LOADTHRESHOLD: 15%Range: 5 to 100% in steps of 1MESSAGE HI-Z 3-PHASE EVENTTHRESHOLD: 25 ARange: 1 to 1000 A in steps of 1MESSAGE HI-Z VOLTAGE SUPVTHRESHOLD: 5%Range: 0 (off) to 100% in steps of 1MESSAGE HI-Z VOLTAGE SUPVDELAY: 60 cyclesRange: 0 to 300 cycles in steps of 2MESSAGE HI-Z EVEN HARMONICRESTRAINT: 20%Range: 0 to 100% in steps of 1MESSAGE HI-Z TARGET:Self-resetRange: Self-reset, Latched, DisabledMESSAGE HI-Z EVENTS:DisabledRange: Disabled, Enabled
