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5.65
Date Code 20171021
Instruction Manual
SEL-421 Relay
Protection Functions
Out-of-Step Logic (Zero Settings)
shows DOSB, the OR combination of the output from
(DOSBY1) and the output from
(DOSBY). Only Relay Word bit
DOSB is available; DOSBY1 and DOSBY are for internal use in the relay.
Three-Phase Fault Detector
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
Summary of Contents for SEL-421-4
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