10.31
Date Code 20170927 Instruction Manual SEL-751 Relay
Analyzing Events
High-Impedance Fault (HIF) Event Reporting
➤ System frequency
➤ Pre-trigger and post-trigger phase currents, sum of difference
currents, and total odd harmonic content of currents (from the
initial trigger point and the first point of the event report)
Table 10.6 lists event types in fault reporting priority. For example, alarm
event types have reporting priority over triggered events. You can trigger
events in one of two ways. The TRI HIF command triggers an event (see
Triggering on page 10.2 for complete information on the TRI command)
locally. Report setting HIFER allows you to trigger an event automatically at
the assertion of the corresponding Relay Word bit (see Table 4.28). You can
also program this setting in a manner to aid in simultaneous event triggering in
multiple relays.
Table 10.7 lists HIF phase involvement conditions. Multiple phases can be
listed if the relay detects more than one phase involvement. If an HIF fault
occurs (HIFn_x), alarmed phases are not listed. When an event report is
triggered for any of these conditions, Relay Word bit HIFREC is asserted until
the HIF event report is finished being collected. The relay does not generate
additional event reports for triggering conditions that follow the initial
triggering condition and are within the same report.
When a high-impedance fault is caused by a downed conductor, there can be a
load current reduction. Depending on the position of the down conductor and
the amount of load dropped, this load reduction event may or may not be
detectable back in a substation. The load reduction element is used to detect
any load reduction at the time that the relay detects a high-impedance fault.
The element is used to report a possible downed conductor event. Table 10.8
lists HIF downed conductor conditions.
If the HIF1_x or HIF2_x Relay Word bits have been programmed to alarm,
then these alarms can be further secured by ANDing them with the load
reduction (LR) bits. A drawback of this approach, however, is that if an event
does not lead to enough of a drop in load current, the load reduction logic may
not operate (and hence not alarm).
Table 10.6 HIF Event Types
Event Event Trigger
HIF ALARM Assertion of any one of the following Relay Word bits and if no HIF fault
has occurred: HIA1_A, HIA1_B, HIA1_C, HIA2_A, HIA2_B, HIA2_C
HIF FAULT Assertion of any one of the following Relay Word bits: HIF1_A,
HIF1_B, HIF1_C, HIF2_A, HIF2_B, HIF2_C
HIF Ext. TRI Assertion of HIFER SEL
OGIC variable.
HIF TRI Execution of the TRI HIF command.
Table 10.7 HIF Event Phases
Phase Conditions
A Assertion of any one of the following Relay Word bits: HIA1_A, HIA2_A,
HIF1_A, HIF2_A
B Assertion of any one of the following Relay Word bits: HIA1_B, HIA2_B,
HIF1_B, HIF2_B
C Assertion of any one of the following Relay Word bits: HIA1_C, HIA2_C,
HIF1_C, HIF2_C
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