4.127
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
An explanation of ways to mitigate Aurora threats to power systems can be
found in the SEL technical paper, Mitigating the Aurora Vulnerability With
Existing Technology, available on the SEL website. More detailed application
considerations can be found in the SEL Application Guide, AG2010-03, Aurora
Mitigation Using the SEL-751 Relay, also available on the SEL website.
Figure 4.78 shows the logic diagram of the 81RF element. Enable the element
by setting E81RF to Y (Yes). Settings 81RFDFP and 81RFRP configure the
81RF characteristics. These settings are typically coordinated with the fre-
quency (81) and rate-of-change-of-frequency (81R) element settings. The
slope of the characteristic, 81RFSLP, shown in the logic diagram is equal to
–1 • (81RFRP/81RFDFP).
Use 81RFVBLK or 81RFIBLK to block the operation of the 81RF element for
undervoltage or overcurrent fault conditions. You can use the 81RFBL
SEL
OGIC control equation to include additional blocking elements. 81RFI
asserts if the operating point is in Trip Region 1 or Trip Region 2. Program the
81RFT Relay Word bit in one of the relay outputs for the intended operation.
Table 4.51 Fast Rate-of-Change-of-Frequency Settings
Setting Prompt Range Setting Name := Factory Default
ENABLE 81RF Y, N E81RF := N
FREQDIF SETPOINT 0.1–10.0 Hz 81RFDFP := 1.0
DFDT SETPOINT 0.2–15.0 Hz/sec 81RFRP := 2.5
81RF PU DELAY 0.10–1.00 sec 81RFPU := 0.10
81RF DO DELAY 0.00–1.00 sec 81RFDO := 0.10
81RF VOLTAGE BLK OFF, 2–300 V
a
a
Setting range shown is for DELTA_Y := DELTA.
81RFVBLK := OFF
OFF, 2–520 V
b
b
Setting range shown is for DELTA_Y := WYE.
81RFVBLK := OFF
81RF CURRENT BLK OFF, 0.1–20 A • I
NOM
81RFIBLK := 10 • I
NOM
81RF BLOCK SELOGIC 81RFBL := 0
81RF BLOCK DO 0.02–5.00 sec 81RFBLDO := 1.00
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