6.82
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
Trip Timers
The SEL-421 provides dedicated timers for minimum trip duration.
Minimum Trip Duration
The minimum trip duration timer setting, TDUR3D, determines the minimum
time that Relay Word bit 3PT asserts. For this application example, Relay Word
bit 3PT is assigned to OUT101. The corresponding control output closes for
TDUR3D time or the duration of the trip condition, whichever is longer.
A typical setting for this timer is 9 cycles.
TDUR3D := 9.000. Three-Pole Trip Minimum Trip Duration Time Delay
(2.000–8000 cycles)
Three-Pole Tripping Enable
The relay contains both three-pole and single-pole tripping logic. Set E3PT
(Three-Pole Trip Enable) to logical 1 to enable three-pole tripping only.
E3PT := 1. Three-Pole Trip Enable (SELOGIC Equation)
Also set the appropriate three-pole tripping SEL
OGIC control equation for Circuit
Breaker BK1.
E3PT1 := 1. Breaker 1 3PT (SELOGIC Equation)
Control Outputs
Main Board
OUT101 trips Circuit Breaker 1.
OUT101 := 3PT.
OUT102 keys the local transmitter to send the blocking signal to the remote ter-
minal during out-of-section faults behind Station S.
OUT102 := NSTRT AND NOT STOP OR DSTRT.
OUT103 stops the local transmitter from sending the blocking signal to the
remote terminal.
OUT103 := STOP OR 3PT.
Example Completed
This completes the application example that describes setting of the SEL-421 for
communications-assisted protection of a 345 kV tapped overhead transmission
line. Analyze your particular power system to determine the appropriate settings.
Relay Settings
Table 6.21 lists all protective relay settings for this example.
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