Schweitzer Engineering Laboratories SEL-421-4 - Figure 5.45 Dependable Power-Swing Block Detector Logic (EOOS; Figure 5.46 Relay Word Bit DOSB Is the or Combination of DOSBY1 and DOSBY

5.65
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Out-of-Step Logic (Zero Settings)
Figure 5.46 shows DOSB, the OR combination of the output from Figure 5.44
(DOSBY1) and the output from Figure 5.45 (DOSBY). Only Relay Word bit
DOSB is available; DOSBY1 and DOSBY are for internal use in the relay.
Three-Phase Fault Detector
Figure 5.47 shows the logic diagram of the three-phase fault detector. If a three-
phase fault occurs on a transmission line during a power swing, a step change
occurs in the SCV1 waveform. This step change can be identified when the sec-
ond derivative of SCV1 has a higher than usual value. Furthermore, the SCV1 has
a low value and its rate of change is very small. These properties are taken into
account in the three-phase fault detector so as to implement a very fast detector,
independent from the swing speed. Three-phase faults will be detected with a
minimum and maximum time delay of two and five cycles, respectively.
Figure 5.45 Dependable Power-Swing Block Detector Logic (EOOS = Y)
DIR5 = F
DIR4 = F
Z5P
Z4P
Z3P
Z2P
OSB
TRIP
SERCAB
SERCBC
MAB1I
XAB1I
MBC1I
XBC1I
SERCCA
MCA1I
XCA1I
X7ABC
Z1MAG
| Z1F
k
— Z1F
k — 1
| • 8 • NFREQ
DIR3 = F
0
0.25
CYC
0
0.25
CYC
0
0.25
CYC
0
1.5
CYC
0
0.125
CYC
0
1.5
CYC
DOSBY
0
1.5
CYC
0
60
CYC
Figure 5.46 Relay Word Bit DOSB Is the OR Combination of DOSBY1 and DOSBY
DOSBY1
DOSBY
DOSB