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5.6 CONTROL ELEMENTS
will clear an overcurrent fault. It is recommended that this setting is above the maximum 3Io (residual) current due to
unbalanced loading.
•
HI-Z PHASE RATE OF CHANGE: Establishes a threshold for determining when a high rate-of-change event occurs on
a phase RMS current. An extremely high rate of change is not characteristic of most high impedance faults; it is more
indicative of a low impedance fault or of the inrush of breaker closing. The inrush current produces substantial varia-
tions in the harmonics used by the high impedance algorithms. Therefore these algorithms ignore all data for several
seconds following a high rate-of-change event that exceeds this setting.
The RMS currents in the Hi-Z algorithms are calculated over a two-cycle time window. The rate-of-change is calculated
as the difference between two consecutive two-cycle RMS readings. The recommended setting is 150 A per two-cycle
interval. The setting is given in primary amperes.
•
HI-Z NEUTRAL RATE OF CHANGE: Establishes a threshold for determining when a high rate-of-change event occurs
on a neutral RMS current. An extremely high rate of change is not characteristic of most high impedance faults; it is
more indicative of a breaker closing, causing associated inrush. The inrush current produces substantial variations in
the harmonics used by the high impedance algorithms. Therefore, these algorithms ignore all data for several seconds
following a high rate-of-change event exceeding this setting.
The RMS currents in the Hi-Z algorithms are calculated over a two-cycle time window. The rate-of-change is calculated
as the difference between two consecutive two-cycle RMS readings. The recommended setting is 150 A per two-cycle
interval. The setting is given in primary amperes.
•
HI-Z LOSS OF LOAD THRESHOLD: Establishes the loss of load level used as an indication of a downed conductor. A
Loss of Load flag is set if the Hi-Z algorithms detect a percentage drop in phase current between two successive two-
cycle RMS values that equals or exceeds the Loss of Load Threshold. The amount the phase current must decrease
between successive two-cycle RMS values is based on this setting times the recent average phase current level. The
range is 5 to 100%; 5% being the most sensitive.
5
•
HI-Z 3-PHASE EVENT THRESHOLD: Establishes the level at which the Hi-Z element characterizes a sudden three-
phase current increase as a three-phase event. The Hi-Z detection algorithms ignore the data generated by a large
three-phase event. The recommended setting is 25 A (primary).
•
HI-Z VOLTAGE SUPV THRESHOLD: In the event that a fault simultaneously occurs on two adjacent feeders (line volt-
age from the same bus), the drop in line voltage will cause a subsequent drop in load current. This function will block
the Loss of Load flag from being set while the voltage is depressed. Thus, if the voltage level drops by a percentage
greater than this threshold in successive two-cycle RMS samples, the Loss of Load flag will be blocked. If the setting is
"0", the voltage supervision function will be disabled.
•
HI-Z VOLTAGE SUPV DELAY: This setting adds time delay to the voltage supervision function. Specifically, the Loss
of Load flag will continue to be blocked for the number of cycles specified by this setting.
•
HI-Z EVEN HARMONIC RESTRAINT: This setting determines the level of the even harmonic at which the setting of
the overcurrent flags is inhibited. The even harmonic content is evaluated on each phase current as a percentage of
that phase's RMS current. The intent is to inhibit the setting of the overcurrent flags if the overcurrent is simply a surge
caused by cold-load pickup or other inrush event.
IMPORTANT NOTE REGARDING INSTALLATION: The F60 Hi-Z algorithm is adaptive in nature. The algo-
rithm's internal thresholds gradually adapt to background "noise" on circuits with a moderate to high level
of transient activity. For the first three to five days after installation (or after being out-of-service for a sig-
NOTE
nificant period), the F60 may identify some of this noise as arcing. This should be taken into account when
responding to alarms during these type of operating periods.
5-178
F60 Feeder Protection System
5 SETTINGS
GE Multilin
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