Schweitzer Engineering Laboratories SEL-751 - Figure 4.76 81 R Frequency Rate-Of-Change Scheme Logic; Table 4.50 Time Window Versus 81 Rntp Setting

4.125
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
Use E81R setting to enable the number of elements you want; Figure 4.76
shows the element logic. The SEL-751 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 percent of 81RnTP setting
and dropout is 95 percent. Table 4.50 shows the time windows for different
trip level settings. Additionally, the Relay Word bit ORED81RT := 81R1T OR
81R2T OR 81R3T OR 81R4T.
Figure 4.76 81R Frequency Rate-of-Change Scheme Logic
81R4 TRIP LEVEL OFF, 0.10–15.00 Hz/sec 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
81R4 TRQCTRL SEL
OGIC 81R4TC := 1
a
I
NOM
is nominal rating of the phase CTs (1 A or 5 A).
Table 4.49 Rate-of-Change-of-Frequency Settings (Sheet 2 of 2)
Setting Prompt Setting Range
Setting Name :=
Fac to ry Defa ult
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
81RnTC
PU = 81RnTD
DO = 81RnDO
3 SEC
0
(mf2–mf1)/dt
PU
DO
81RnT
Relay
Word
Bit
95%
95%
95%
ABS
*(-1)
Table 4.50 Time Window Versus 81RnTP Setting (Sheet 1 of 2)
81RnTP Setting (Hz/sec) Time Window (Cycles)
15.00–2.33 3
2.32–1.17 6
1.16–0.78 9
0.77–0.58 12
0.57–0.47 15
0.46–0.38 18
0.37–0.33 21