Date Code 20001006 Trip and Target Logic 5-7
SEL-351 Instruction Manual
Program an Output Contact for Tripping
In the factory settings, the resultant of the trip logic in Figure 5.1 is routed to output contact OUT1
with the following SELOGIC Control Equation setting:
OUT1 = TRIP
If more than one TRIP output contact is needed, program other output contacts with the TRIP
Relay Word bit. Examples of uses for additional TRIP output contacts:
• Tripping more than one breaker
• Keying an external breaker failure relay
• Keying communication equipment in a Direct Transfer Trip scheme
See Output Contacts in Section 7: Inputs, Outputs, Timers, and Other Control Logic for more
information on programming output contacts.
SWITCH-ONTO-FAULT (SOTF) TRIP LOGIC
Switch-Onto-Fault (SOTF) trip logic provides a programmable time window for selected elements
to trip right after the circuit breaker closes. “Switch-onto-fault” implies that a circuit breaker is
closed into an existing fault condition. For example, suppose safety grounds are accidentally left
attached to a line after a clearance. If the circuit breaker is closed into such a condition, the
resulting fault needs to be cleared right away and reclosing blocked. An instantaneous overcurrent
element is usually set to trip in the three-pole open (3PO) logic and the SOTF trip logic.
Refer to the switch-onto-fault trip logic in Figure 5.1 (middle of figure). The SOTF trip logic
permits tripping if both the following occur:
• An element asserts in SELOGIC Control Equation trip setting TRSOTF
• Relay Word bit SOTFE is asserted to logical 1
Relay Word bit SOTFE (the output of the SOTF logic) provides the effective time window for an
element in trip setting TRSOTF (e.g., TRSOTF = 50P2) to trip after the circuit breaker closes.
Figure 5.3 and the following discussion describe the three-pole open (3PO) logic and the SOTF
logic.
Courtesy of NationalSwitchgear.com
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