Date Code 20001006
Trip and Target Logic
5-21
SEL-351 Instruction Manual
In three-terminal line DCUB applications (setting ECOMM = DCUB2), loss-of-guard signals are
received from two remote terminals. Two optoisolated inputs on the SEL-351 Relay (e.g., input
IN5 and IN7) are driven by communications equipment receiver outputs (see Figure 5.13). Make
SEL
OGIC
Control Equation settings LOG1 and LOG2 as follows:
LOG1 = IN5
(three-terminal line application)
LOG2 = IN7
SEL
OGIC
Control Equation settings LOG1 and LOG2 are routed into the DCUB logic in
Figure 5.10 for “unblocking block” and “permissive trip receive” logic decisions.
Timer Settings
See
Section 9: Setting the Relay
for setting ranges.
GARD1D – Guard-Present Delay
Sets minimum time requirement for reinstating permissive tripping following a loss-of-channel
condition – typically set at 10 cycles. Channel 1 and 2 logic use separate timers but have this same
delay setting.
UBDURD – DCUB Disable Delay
Prevents tripping by POTT logic after a settable time following a loss-of-channel condition –
typically set at 9 cycles (150 ms). Channel 1 and 2 logic use separate timers but have this same
delay setting.
UBEND – DCUB Duration Delay
Sets minimum time required to declare a loss-of-channel condition – typically set at 0.5 cycles.
Channel 1 and 2 logic use separate timers but have this same delay setting.
Logic Outputs
The following logic outputs can be tested by assigning them to output contacts. See
Output
Contacts
in
Section 7: Inputs, Outputs, Timers, and Other Control Logic
for more information
on output contacts.
UBB1, UBB2 – Unblocking Block Output(s)
In two-terminal line DCUB applications (setting ECOMM = DCUB1), UBB1 disables tripping if
the loss-of-channel condition continues for longer than time UBDURD.
In three-terminal line DCUB applications (setting ECOMM = DCUB2), UBB1 or UBB2 disable
tripping if the loss-of-channel condition (for the respective Channel 1 or 2) continues for longer
than time UBDURD.
The UBB1 and UBB2 are routed in various combinations in Figure 5.11 to control Relay Word bit
UBB, depending on enable setting ECOMM = DCUB1 or DCUB2. Relay Word bit UBB is the
Summary of Contents for SEL-351
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