5-10 Trip and Target Logic Date Code 20001006
SEL-351 Instruction Manual
or automatic reclosure occurs, optoisolated input IN7 is energized. SELOGIC Control Equation
setting CLMON (close bus monitor) monitors the optoisolated input IN7:
CLMON = IN7
When optoisolated input IN7 is energized, CLMON asserts to logical 1. At the instant that
optoisolated input IN7 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 SELOGIC Control Equation trip
setting TRSOTF to trip after the circuit breaker closes (see Figure 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 SELOGIC 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 SELOGIC 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.
Courtesy of NationalSwitchgear.com
To Next Page
Loading...
