Sel SEL-300 Series, Application Manual

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8
SEL Application Guide 2020-04 Date Code 20200326
POTT L
OGIC
After you have enabled each relay for a POTT scheme, you must program the elements that qualify
a communications-assisted trip. To program the logic, consider the following:
➤
In the SEL-421-5 and SEL-311C-1, the setting for the communications-assisted trip
condition is TRCOMM, and in the SEL-321-1, the setting is MTCS. SEL recommends
setting TRCOMM and MTCS by using the same elements so that each terminal
responds similarly to fault conditions.
➤
Note the polarization choices for the directional element in the relays. The
SEL-321-0, -1, -2, -3, -4 only have negative-sequence voltage (Q) polarization; the
SEL-321-5 has both negative-sequence voltage (Q) and zero-sequence voltage (V)
polarization. The SEL-421-5, SEL-311L, and SEL-311C-1 allow you to choose a com-
bination of negative-sequence voltage (Q), zero-sequence voltage (V), or zero-sequence
current (I) polarization in any order. To prevent miscoordination, set the SEL-421-5 to
use the same directional elements used by the SEL-300 series relay on the other end of
the line.
➤
Each relay must be able to transmit a PT signal. In the SEL-421-5 and SEL-311C-1,
send the permissive signal via TMB1A. In the SEL-321-1, send it via TMB1. Set each
of these elements to
KEY .
➤
The relays must be programmed to map the key from the remote end into the POTT
logic. Map the PT to the received Mirrored Bit. In the SEL-421-5 and SEL-311C-1,
program PT1 to
RMB1A . In the SEL-321-1, program RMB1 to PT .
➤
A tripping output must be assigned to trip the respective circuit breaker of each relay. In
the SEL-421-5, set OUT201 to
TRIP ; in the SEL-311C-1, set OUT101 to TRIP ; and in
the SEL-321-1, set OUT1 to 3PT , as shown in Figure 9 and Figure 10 .
➤
You should wire a breaker contact status to each relay. In the SEL-421-5, wire 52A to
IN201; in the SEL-311C-1, wire 52A to IN101; and in the SEL-321-1, wire 52A to IN1.
It is not required to wire the 52A contact status for DCB and POTT schemes, but it is
beneficial to wire the 52A contact for other elements in the relay.
Table 8 SEL-421-5 POTT Logic
Setting Setting Description Setting Value Comment
TRCOMM Communications-Assisted Trip
Conditions
M2P OR Z2G
a
a
Negative-sequence and ground-directional overcurrent elements can be added to the TRCOMM equation, along with the mho
phase- and mho ground-distance elements.
Elements that allow high-speed communications-
assisted tripping.
TMB1A Transmit Channel A Mirrored
Bit 1 KEY Send a PT to the remote end.
PT1 Permissive Trip 1 Equation RMB1A Receive a PT from the remote end.
OUT201 Output Contact 201 Equation TRIP Trip the output to the circuit breaker.
52AA1 Circuit Breaker Status Equation IN201 Assign to the circuit breaker 52a status.
Table 9 SEL-311C-1 POTT Logic (Sheet 1 of 2)
Setting Setting Description Setting Value Comment
TRCOMM Communications-Assisted Trip
Conditions
M2P + Z2G
a
(default)
Elements that allow high-speed communications-
assisted tripping.
TMB1A Transmit Channel A Mirrored
Bit 1 KEY Send a PT to the remote end.