Date Code 20080213 Instruction Manual SEL-351A Relay
Section 5
Trip and Target Logic
Trip Logic
The trip logic in Figure 5.1 provides flexible tripping with SELOGIC
®
control
equation settings.
DTT (Direct Transfer Trip Conditions). Note that in Figure 5.1 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 on page 5.11).
A typical setting for DTT is:
DTT = IN106
where input IN106 is connected to the output of direct transfer trip
communications equipment.
TRSOTF (Switch-Onto-Fault Trip Conditions). Setting TRSOTF is
supervised by the switch-onto-fault logic enable SOTFE. See the
Switch-Onto-Fault (SOTF) Trip Logic on page 5.7.
TR (Other Trip Conditions). Setting TR is the SELOGIC control equation
trip setting most often used if tripping does not involve
communications-assisted (setting DTT) or switch-onto-fault (setting
TRSOTF) trip logic.
Note that in Figure 5.1 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 a
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 three trip settings: DTT, TRSOTF, and TR)
can be set. For example, in a Direct Transfer Trip (DTT) scheme, DTT is set
with the DTT initiating input, TRSOTF is set with nondirectional overcurrent
elements, and TR is set with directional time overcurrent elements.
Courtesy of NationalSwitchgear.com
To Next Page
Loading...