P.3.225
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
Permissive Overreaching Transfer Tripping Scheme
POTT Scheme
Selection
The relay offers three POTT schemes: POTT, POTT2, and POTT3. The type
of communications channel(s) in your application best determines which
scheme to implement.
POTT
Use the conventional POTT scheme for an application with a single
communications channel.
For details about implementing a conventional POTT scheme, see POTT
Scheme Logic.
POTT2
Use the POTT2 scheme for applications with two communications channels,
one for single-phase fault identification and one for multi-phase fault
identification. This scheme is useful in applications where there is a high
likelihood of cross-country faults.
For details about implementing a POTT2 scheme, see Cross-Country Faults.
POTT3
Use the POTT3 scheme for phase-segregated applications with three
communications channels. In this scheme, each channel indicates permissive
trip for single-phase. Multi-phase fault detection results in all three channels
transmitting a permissive trip.
For details about implementing a POTT3 scheme, see Cross-Country Faults.
POTT Scheme Logic
The POTT scheme logic performs the following tasks:
➤ Keys the communications equipment to send permissive trip
(PT) when any element you include in the
TRCOMM/TRCOMMD SEL
OGIC control equation asserts and
the current reversal logic is not asserted.
➤ Prevents keying and tripping by the POTT logic following a
current reversal.
➤ Echoes the received permissive signal to the remote terminal.
➤ Prevents channel lockup during echo and test.
➤ Provides a secure means of tripping for weak- and/or zero-
infeed terminals.
➤ Ensures proper tripping at both terminals during cross-country
faults (via special logic implemented with SEL
OGIC control
equations).
The POTT scheme logic consists of the following:
➤ Current reversal guard logic
➤ Echo
➤ Weak infeed logic
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