Schweitzer Engineering SEL-351P - Switch-Onto-Fault Logic Output (SOTFE); Switch-Onto-Fault Trip Logic Trip Setting (TRSOTF)

5-8 Trip and Target Logic Date Code 990215
SEL-351P Manual Técnico
CLMON = IN107
When optoisolated input IN107 is energized, CLMON asserts to logical 1. At the instant that
optoisolated input IN107 is energized (close bus is energized), the circuit breaker is still open so
the output of the CLOEND timer continues to be asserted to logical 1. Thus, the ANDed
combination of these conditions latches in the SOTFD timer. The SOTFD timer outputs a
logical 1 for a time duration of “SOTFD” cycles any time it sees a rising edge
on its input
(logical 0 to logical 1 transition), if it is not already timing. The SOTF logic output, SOTFE,
asserts to logical 1 for SOTFD time.
Switch-Onto-Fault Logic Output (SOTFE)
Relay Word bit SOTFE is the output of the circuit breaker operated SOTF logic or the close bus
operated SOTF logic described previously. Time setting SOTFD in each of these logic paths
provides the effective time window for the overcurrent elements in SEL
OGIC Control Equation
trip setting TRSOTF to trip after the circuit breaker closes (see
Figure SECTION 5: .1 – middle
of figure). Time setting SOTFD is usually set around 30 cycles.
A SOTF trip illuminates the SOTF front-panel LED.
Switch-Onto-Fault Trip Logic Trip Setting (TRSOTF)
An instantaneous overcurrent element is usually set to trip in the SEL
OGIC Control Equation trip
setting TRSOTF (e.g., TRSOTF = 50P2).
If the voltage potential for the relay is from the line-side of the circuit breaker, the instantaneous
overcurrent element in the SEL
OGIC Control Equation trip setting TRSOTF should be
nondirectional. When the circuit breaker is open and the line is deengergized, the relay sees zero
voltage. If a close-in three-phase fault condition exists on the line (e.g., safety grounds
accidentally left attached to the line after a clearance) and then the circuit breaker is closed, the
relay continues to see zero voltage. The directional elements have no voltage for reference and
cannot operate. In this case, the instantaneous overcurrent element in the SOTF trip logic should
be nondirectional.