Date Code 20080103 Instruction Manual SEL-351S Relay
Section 5
Trip and Target Logic
Trip Logic
The trip logic in Figure 5.1 provides flexible tripping with SELOGIC
®
control
equation settings:
TRCOMM—Communications-Assisted Trip Conditions. Setting TRCOMM is
supervised by communications-assisted trip logic. See
Communications-Assisted Trip Logic—General Overview on
page 5.11 for more information on communications-assisted tripping.
DTT—Direct Transfer Trip Conditions. Note in Figure 5.1 that setting DTT
is unsupervised. Any element that asserts in setting DTT will cause
Relay Word bit TRIP to assert to logical 1.
Although setting TR is also unsupervised, setting DTT is provided
separate from setting TR for target LED purposes. (COMM target LED
on the front panel illuminates when DTT asserts to logical 1; see COMM
target LED discussion in Front-Panel Target LEDs on page 5.32).
A typical setting for DTT is:
DTT = IN106
where input IN106 is connected to the output of direct transfer trip
communications equipment.
Setting DTT is also used for Direct Underreaching Transfer Trip
(DUTT) schemes.
TRSOTF—Switch-Onto-Fault Trip Conditions. Setting TRSOTF is supervised
by the switch-onto-fault condition SOTFE. See Switch-Onto-Fault
(SOTF) Trip Logic on page 5.8 for more information on switch-onto-
fault logic.
TR—Other Trip Conditions. Setting TR is the SELOGIC control equation trip
setting most often used if tripping does not involve communications-
assisted (settings TRCOMM and DTT) or switch-onto-fault (setting
TRSOTF) trip logic.
Note in Figure 5.1 that setting TR is unsupervised. Any element that
asserts in setting TR will cause Relay Word bit TRIP to assert to
logical 1.
ULTR—Unlatch Trip Conditions.
TDURD—Minimum Trip Duration Time.
This timer establishes the minimum
time duration for which the TRIP Relay Word bit asserts. This is rising
edge initiated timer. The settable range for this timer is 4–16,000
cycles. See Figure 5.2.
More than one trip setting (or all four trip settings TRCOMM, DTT, TRSOTF,
and TR) can be set. For example, in a communications-assisted trip scheme,
TRCOMM is set with direction forward overreaching Level 2 overcurrent
elements, TR is set with direction forward underreaching Level 1 overcurrent
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