4.49
Date Code 20100129
Instruction Manual
SEL-751A Relay
Protection and Logic Functions
Rate-of-Change of Frequency Protection
Use E81R setting to enable number of the elements desired,
shows the element logic. The SEL-751A measures frequency (mf1) and
second frequency (mf2) after a time window (dt) determined by Trip Level
setting (81RnTP). Hysteresis is such that pickup is 100% of 81RnTP setting
and dropout is 95%.
shows the time windows for different trip level
settings.
Figure 4.28
81R Frequency Rate-of-Change Scheme Logic
81R2 DO DELAY
0.00–60.00 sec
81R2DO := 0.00
81R3 TRIP LEVEL
OFF, 0.10–15.00
81R3TP := OFF
81R3 TREND
INC, DEC, ABS
81R3TRND := ABS
81R3 TRIP DELAY
0.10–60.00 sec
81R3TD := 1.00
81R3 DO DELAY
0.00–60.00 sec
81R3DO := 0.00
81R4 TRIP LEVEL
OFF, 0.10–15.00
81R4TP := OFF
81R4 TREND
INC, DEC, ABS
81R4TRND := ABS
81R4 TRIP DELAY
0.10–60.00 sec
81R4TD := 1.00
81R4 DO DELAY
0.00–60.00 sec
81R4DO := 0.00
a
See
for explanation of Vnm.
b
I
NOM
is nominal rating of the phase CTs (1A or 5A).
Table 4.23
Rate-of-Change-of-Frequency Settings
(Sheet 2 of 2)
Setting Prompt
Setting Range
Setting Name :=
Factory Default
Setting 81RnTp
where n = 1–4
Frequency
81RnTRND = INC
81RnTRND = ABS
81RnTRND = DEC
mf2 > FNOM
mf2 < FNOM
FREQTRK
81RVSUP = OFF
81RISUP = OFF
V1
I1
81RVSUP
81RISUP
PU = 81RnTD
DO = 81RnDO
3 SEC
0
(mf2–mf1)/dt
PU
DO
81RnT
Relay
Word
Bit
95%
95%
95%
ABS
*(-1)
Summary of Contents for 751A
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