5-6
Trip and Target Logic
Date Code 20011205
SEL-311B Instruction Manual
If more than two TRIP output contacts are needed, program other output contacts with the TRIP
Relay Word bit. Examples of uses for additional TRIP output contacts:
·
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.
S
WITCH
-O
NTO
-F
AULT
(SOTF) T
RIP
L
OGIC
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. If the circuit breaker is closed into such a condition, the
resulting fault needs to be cleared right away and reclosing blocked. An instantaneous 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 SEL
OGIC
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.
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