2-10 Specifications Date Code 20011026
SEL-321/321-1 Instruction Manual
Echo Duration EDURD Limits echo duration, to prevent channel lockup.
Logic Outputs
Zone 3 Reverse Block Z3RB Current reversal guard asserted.
Echo Conversion to Trip ECTT PT received, converted to a tripping condition for
weak-infeed.
Key Permissive Trip KEY Signals communications equipment to transmit per-
missive trip.
Echo Key Permissive Trip EKEY Permissive trip signal keyed by Echo logic.
Assisted Trip Block ATB Blocks MTCS variable. Driven by ECHO and
DCUB logic.
Supporting Drawing: Figure 2.31.
Directional Comparison Unblocking (DCUB) Logic
The DCUB logic is an extension of the POTT logic. The extension monitors the loss-of-guard
output from the communications receiver, through an input programmed to the LOG function.
The typical application is a POTT scheme using FSK carrier as the communications medium.
External Inputs
Received Permissive
Trip Signal PT Assign PT to a programmable input. Drive with
receiver output.
Loss-of-Guard LOG Assign LOG to a programmable input. Drive with
contact from communications equipment.
Timer Settings
Guard-Present Delay GARD1D Sets minimum time requirement for reinstating
permissive tripping following a loss-of-channel
condition.
DCUB Disable Delay UBDURD Prevents tripping by POTT logic after a settable
time following a loss-of-channel condition.
DCUB Duration Delay UBEND Sets minimum time required to declare a loss-of-
guard condition.
Logic Outputs
Same as POTT outputs
Unblocking Block UBB Disables tripping by the DCUB logic.
Permissive Trip Receive PTRX Permissive trip signal receive input to POTT logic.
Supporting Drawings: Figure 2.31 and Figure 2.32.
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