5-20 Trip and Target Logic Date Code 20001006
SEL-351 Instruction Manual
The DCUB logic in Figure 5.10 takes in the loss-of-guard and permissive trip outputs from the
communication receivers (see Figure 5.12 and Figure 5.13) and makes permissive
(PTRX1/PTRX2) and unblocking block (UBB1/UBB2) logic output decisions.
DCUB schemes are typically implemented with FSK (frequency shift carrier) or analog microwave
as the communications medium.
Use Existing SEL-321 Relay DCUB Application Guide for the SEL-351 Relay
Use the existing SEL-321 Relay DCUB application guide (AG96-19) to help set up the SEL-351
Relay in a DCUB scheme (see preceding subsection Communications-Assisted Trip Logic -
General Overview for more setting comparison information on the SEL-321/SEL-351 Relays).
External Inputs
See Optoisolated Inputs in Section 7: Inputs, Outputs, Timers, and Other Control Logic for
more information on optoisolated inputs.
PT1, PT2 – Received Permissive Trip Signal(s)
In two-terminal line DCUB applications (setting ECOMM = DCUB1), a permissive trip signal is
received from one remote terminal. One optoisolated input on the SEL-351 Relay (e.g., input IN4)
is driven by a communications equipment receiver output (see Figure 5.12). Make SELOGIC
Control Equation setting PT1:
PT1 = IN4 (two-terminal line application)
In three-terminal line DCUB applications (setting ECOMM = DCUB2), permissive trip signals are
received from two remote terminals. Two optoisolated inputs on the SEL-351 Relay (e.g., inputs
IN4 and IN6) are driven by communications equipment receiver outputs (see Figure 5.13). Make
SELOGIC Control Equation settings PT1 and PT2 as follows:
PT1 = IN4 (three-terminal line application)
PT2 = IN6
SELOGIC Control Equation settings PT1 and PT2 are routed into the DCUB logic in Figure 5.10
for “unblocking block” and “permissive trip receive” logic decisions.
As explained in the preceding POTT subsection, the SELOGIC Control Equation settings PT1 and
PT2 in Figure 5.5 are routed in various combinations to control Relay Word bit PT, depending on
enable setting ECOMM = DCUB1 or DCUB2. Relay Word bit PT is then an input into the POTT
logic in Figure 5.6 (for echo keying).
LOG1, LOG2 – Loss-of-Guard Signal(s)
In two-terminal line DCUB applications (setting ECOMM = DCUB1), a loss-of-guard signal is
received from one remote terminal. One optoisolated input on the SEL-351 Relay (e.g., input IN5)
is driven by a communications equipment receiver output (see Figure 5.12). Make SELOGIC
Control Equation setting LOG1:
LOG1 = IN5 (two-terminal line application)
Courtesy of NationalSwitchgear.com
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