4.85
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
EXAMPLE 4.12 HIFITUNE Operation
For this example, assume that the following conditions occur:
➤ The HIF algorithm is operating in normal tuning mode.
➤ The system configuration changes permanently or for the
long term. (The line that the SEL-751 is protecting may have
picked up/dropped off significant load.)
Since the line configuration being monitored by the SEL-751 has changed,
the load characteristics of the system may have also changed. You should
consider forcing the HIF algorithm into the 24-hour initial tuning mode by
asserting (manually or remotely) the SEL
OGIC control equation, HIFITUNE,
or by issuing the INI HIF command.
While the recloser is timing towards the reset state after a successful reclosure
Relay Word bit 79RI asserts the output for SV Timer 16. The timer stays
asserted for the duration of the dropout setting, which is 30 minutes in this
example. During this 30 minutes, the timer assertion maintains the assertion of
HIFMODE, assuring a window of time for increased sensitivity of the HIF
detection algorithm.
Group SEL
OGIC control equation setting HIFER allows for the automatic trig-
gering of HIF detection event reports. Assertion of HIFER sets the Relay
Word bit HIFREC and triggers an event report.
HIF Detection Logical Outputs
The SEL-751 indicates HIF detection through the Relay Word Bit outputs
detailed in Table 4.29. You can use Relay word bits in custom logic program-
ming to indicate high-impedance fault detection activity.
Because the small amount of fault current from an HIF may not be a danger to
power system operation, service continuity may be enhanced by using HIF
detection to only alarm for a downed conductor (i.e., not including the
HIF1_x, HIA1_x, HIF2_x, and HIA2_x Relay Word bits in the TRIP equation
directly). The utility may dispatch a crew to patrol the affected feeder without
interrupting service to customers and may issue a public advisory notice about
the danger. The ultimate decision depends on the operational policies of your
utility.
Ta b l e 4 . 29 HI F R e lay Wo rd B it s (Sheet 1 of 2)
HIF Activity Relay Word Bits
HIF ISM ALARM HIA1_A, HIA1_B, HIA1_C
HIF SDI ALARM HIA2_A, HIA2_B, HIA2_C
HIF ISM FAULT HIF1_A, HIF1_B, HIF1_C
HIF SDI FAULT HIF2_A, HIF2_B, HIF2_C
HIF Externally Triggered Event HIFER
HIF Detection Mode Sensitivity HIFMODE
HIF Event Report is being collected HIFREC
Freeze and retain the learned HIF quanti-
ties during a system disturbance
FRZCLRA, FRZCLRB, FRZCLRC
Current Disturbance DIA_DIS, DIB_DIS, DIC_DIS
Voltage Disturbance DVA_DIS, DVB_DIS, DVC_DIS
Disable HIF Decision Logic DL2CLRA, DL2CLRB, DL2CLRC
Initial HIF Tuning in Progress ITUNE_A, ITUNE_B, ITUNE_C
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