6.114
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
EHV Parallel 230 kV Underground Cables 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 the SEL-421 for three-pole trip-
ping 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
Use SELOGIC control equations to assign the control output for tripping.
Use the main board control outputs for tripping and keying the transmitter of the
external teleprotection equipment.
OUT101 := 3PT. (SELOGIC Equation)
OUT102 := KEY. (SELOGIC Equation)
Example Completed
This completes the application example that describes setting of the SEL-421 for
communications-assisted protection of 230 kV underground cables. You can use
this example as a guide when setting the relay for similar applications. Analyze
your particular power system to determine the proper settings for your application.
Relay Settings
Table 6.31 lists the protective relay settings available for this example.
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