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5 SETTINGS
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Some faults in overhead distribution feeders are characterized by low fault current due to high ground resistance. If the fault
current is in the order of expected unbalance load or less, it cannot be reliably detected by overcurrent protection. These
faults 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-blown
fault.
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 on
pole top insulators, but instead is in contact with earth or a grounded object
•
Arcing fault: any high impedance fault which exhibits arcing
Combinations 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 those
that 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 has
been tested with some success on impedance grounded systems as well. However, there are no guarantees of certain
operation 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 are
saved 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 is
defined in the following two tables.
GE Multilin
HI-Z NEUTRAL OC MIN
PICKUP:
1.00 pu
HI-Z PHASE RATE OF
CHANGE: 150 A/2cycle
HI-Z NEUTRAL RATE OF
CHANGE: 150 A/2cycle
HI-Z LOSS OF LOAD
THRESHOLD:
15%
HI-Z 3-PHASE EVENT
THRESHOLD:
25 A
HI-Z VOLTAGE SUPV
THRESHOLD:
5%
HI-Z VOLTAGE SUPV
DELAY:
60 cycles
HI-Z EVEN HARMONIC
RESTRAINT:
20%
HI-Z TARGET:
Self-reset
HI-Z EVENTS:
Disabled
F60 Feeder Protection System
5.6 CONTROL ELEMENTS
Range: 0.01 to 10.00 pu in steps of 0.01
Range: 1 to 999 A/2cycle in steps of 1
Range: 1 to 999 A/2cycle in steps of 1
Range: 5 to 100% in steps of 1
Range: 1 to 1000 A in steps of 1
Range: 0 (off) to 100% in steps of 1
Range: 0 to 300 cycles in steps of 2
Range: 0 to 100% in steps of 1
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
5
5-185
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