5.118
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Functions
Switch-Onto-Fault Logic
Circuit Breaker Closed SOTF Logic
You can detect circuit breaker close bus assertion by monitoring the dc close bus.
Connect a control input on the SEL-421 to the dc close bus. The control input
energizes whenever a manual close or automatic reclosure occurs. Set SEL
OGIC
control equation CLSMON (Close Signal Monitor) to monitor the control input
(e.g., CLSMON := IN102) and consequently detect close bus assertion.
Set ESOTF to Y and set CLOEND to other than OFF to enable the circuit
breaker-closed SOTF logic. The CLOEND timer operates when one or three
poles open (SPO or 3PO asserts). If the 3PO or SPO condition continues longer
than the CLOEND time and the close bus asserts (SEL
OGIC control equation
CLSMON equals logical 1), Relay Word bit SOTFE asserts and remains asserted
for dropout time setting SOTFD or until the logic detects a healthy voltage condi-
tion (if EVRST := Y, see SOTF Options on page 5.118).
SOTF Options
Set EVRST = Y to enable the Voltage Reset logic. If the system voltage is bal-
anced (ratio of negative-sequence voltage to positive-sequence voltage is below
0.1), Relay Word bit SOTFE resets when the relay measures positive-sequence
voltage at greater than VRSTPU times nominal voltage.
If setting ESPSTF (Single-Pole SOTF Enable) is enabled (ESPSTF := Y), the
relay provides SOTF protection for an SPO condition.
Table 5.67 SOTF Settings
Setting Prompt Range
Default
(5 A)
ESOTF Switch-Onto-Fault Y, N Y
ESPSTF Single-Pole Switch-Onto-Fault Y, N N
EVRST Switch-Onto-Fault Voltage Reset Y, N N
VRSTPU Switch-Onto-Fault Reset Voltage (0.60–1.00 Pu) 0.60–1.00 pu 0.8
52AEND 52a Pole Open Time Delay (cycles) OFF, 0.000–16000 10.000
CLOEND CLSMON or Single Pole Open Delay (cycles) OFF, 0.000–16000 OFF
SOTFD Switch-Onto-Fault Enable Duration (cycles) 0.500–16000 10.000
CLSMON Close Signal Monitor SEL
OGIC Equation NA
Ta b l e 5 . 6 8 SOT F Relay Wo r d Bits
Name Description
SOTFE Switch-Onto-Fault Trip Logic Enabled
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