Permissive Overreaching Transfer Trip (Pott) Logic; Use Existing Sel-321 Relay Pott Application Guide For The Sel-311L Relay; External Inputs - Schweitzer Engineering Laboratories SEL-311L Instruction Manual

P O
ERMISSIVE VERREACHING
Enable the POTT logic by setting ECOMM = POTT. The POTT logic in Figure 5.8 is also
enabled for directional comparison unblocking schemes (ECOMM = DCUB1 or
ECOMM = DCUB2). The POTT logic performs the following tasks:
Keys communication equipment to send permissive trip when any element included in
vÁ
the SEL
and the current reversal logic is not asserted.
Prevents keying and tripping by the POTT logic following a current reversal.
vÁ
Echoes the received permissive signal to the remote terminal.
vÁ
Prevents channel lockup during echo and test.
vÁ
Provides a secure means of tripping for weak- and/or zero-infeed line terminals.
vÁ

Use Existing SEL-321 Relay POTT Application Guide for the SEL-311L Relay

Use the existing SEL-321 Relay POTT application guide (AG95-29) to help set up the SEL-311L
Relay in a POTT scheme (see preceding subsection Communications-Assisted Trip Logic—
General Overview for more setting comparison information on the SEL-321/SEL-311L Relays).

External Inputs

See Optoisolated Inputs in Section 7: Inputs, Outputs, Timers, and Other Control Logic for
more information on optoisolated inputs.
PT1—Received Permissive Trip Signal(s)
In two-terminal line POTT applications, a permissive trip signal is received from one remote
terminal. One optoisolated input on the SEL-311L Relay (e.g., input IN104) is driven by a
communications equipment receiver output (see Figure 5.10). Make SEL
setting PT1:
PT1 = IN104
In three-terminal line POTT applications, permissive trip signals are received from two remote
terminals. Two optoisolated inputs on the SEL-311L Relay (e.g., input IN104 and IN106) are
driven by communications equipment receiver outputs (see Figure 5.11). Make SEL
equation setting PT1 as follows:
PT1 = IN104 * IN106
SEL control equation setting PT1 in Figure 5.7 is routed to control Relay Word bit PT if
OGIC
enable setting ECOMM = POTT. Relay Word bit PT is then an input into the POTT logic in
Figure 5.8 (for echo keying).
Date Code 20010625
T
RANSFER
control equation communications-assisted trip equation TRCOMM asserts
OGIC
(two-terminal line application)
(three-terminal line application)
Trip and Target Logic
SEL-311L Instruction Manual
T (POTT) L
RIP OGIC
control equation
OGIC
control
OGIC
5-17