6.10
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
230 kV Overhead Distribution Line Example
SOTF Duration
Setting SOTFD determines the longest period the SOTF logic can assert after the
circuit breaker closes.
SOTFD := 10.000. Switch-Onto-Fault Enable Duration (0.500–16000 cycles)
Close Signal Monitor
Assign the Relay Word bit CLSMON to a control input, so the relay can detect
execution of the close command. Connect IN102 in parallel with the circuit
breaker close coil.
CLSMON := IN102. Close Signal Monitor (SELOGIC Equation)
Phase Instantaneous/Definite-Time Overcurrent Elements
Use 50P1, Level 1 phase instantaneous overcurrent element, as a nondirectional
high-set phase overcurrent element for SOTF protection. If the local circuit
breaker closes into a close-in three-phase bolted fault with line-side potential
transformers, the polarizing voltage for the phase-distance elements is zero.
Therefore, the distance protection does not operate. In this case, the 50P1 ele-
ment quickly trips the circuit breaker because this overcurrent element does not
rely on the polarizing voltage.
To rapidly clear faults, set 50P1P equal to 50 percent of the fault current mea-
sured at the local terminal for a close-in three-phase fault; use weak source condi-
tions so that the relay operates for low-level fault current.
50P1P := 13.29. Level 1 Pickup (OFF, 0.25–100 A secondary)
This application uses 50P1 as an instantaneous overcurrent element; you do not
need time delay.
67P1D := 0.000. Level 1 Time Delay (0.000–16000 cycles)
This application uses 50P1 as a nondirectional overcurrent element; you do not
need torque control.
67P1TC := 1. Level 1 Torque Control (SELOGIC Equation)
Selectable Operating Quantity Time Overcurrent Element 1
Use inverse-time overcurrent protection to provide backup protection for high-
resistance ground faults. The 51S1 element provides backup protection for unbal-
anced faults if the step distance protection fails to operate.
Select zero-sequence line current as the operating quantity.
NOTE: Use your company practices
and philosophy when determining
these settings.
51S1O := 3I0L. 51S1 Operate Quantity (IAn, IBn, ICn, IMAXn, I1L, 3I2L, 3I0n)
The n in the 51S1O setting is L for line, 1 for BK1, and 2 for BK2.
The relay measures 8.61 A secondary of 3I
0
for a bolted single phase-to-ground
fault at the remote terminal. Set the pickup to 20 percent of 3I
0
.
51S1P := 1.72. 51S1 Overcurrent Pickup (0.25–16 A secondary)
NOTE: If the relay is using a remote
data acquisition system, such as TiDL,
the operating times will be delayed by
1.5 ms. Use caution when setting the
relay coordination times to account
for this added delay.
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