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SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
Autoreclose and Synchronism-Check Example
In this application example, the relay does not perform a synchronism check on
single-pole reclosing.
Synchronism-Check Solution
Apply the synchronism-check function as follows for Circuit Breaker 2:
➤ Use the A-Phase voltages from the line and Bus 2 for the
synchronism check across Circuit Breaker 2.
➤ Select the high voltage magnitude and low voltage magnitude
thresholds for the synchronism check.
➤ Select the maximum voltage angle difference allowed for both
reclosing and manual closing.
➤ Select conditions that block the synchronism check.
Synchronism-Check Relay Settings
Select the relay settings for this application example.
Relay Configuration
Enable synchronism check for Circuit Breaker 2 only.
E25BK1 := N. Synchronism Check for Breaker 1 (Y, N, Y1, Y2)
E25BK2 := Y. Synchronism Check for Breaker 2 (Y, N, Y1, Y2)
Synchronism-Check Element Reference
Select A-Phase voltage from the line source for the synchronism check reference.
VAY is the reference for the synchronism check because this analog input is con-
nected to the line potential.
SYNCP := VAY. S y n c h R e f e r e n c e ( VAY, V B Y, V C Y, VA Z , V B Z , V C Z )
Set the low-voltage threshold that supervises synchronism check equal to 60 V
secondary.
25VL := 60.0. Voltage Window Low Threshold (20.0–200 V secondary)
Set the high-voltage threshold that supervises synchronism check equal to 70 V
secondary.
25VH := 70.0. Voltage Window High Threshold (20.0–200 V secondary)
Circuit Breaker 2 Synchronism Check
Select A-Phase voltage from Bus 2 for the synchronism check source. VBZ is the
source for the synchronism check because this is the bus potential.
SYNCS2 := VBZ. Synch Source 2 (VAY, VBY, VCY, VAZ, VBZ, VCZ)
Both the line reference and bus source voltages are measured line-to-neutral. Set
the ratio factor equal to unity.
KS2M : = 1.00. Synch Source 2 Ratio Factor (0.000–30)
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