Schweitzer Engineering Laboratories SEL-421-4 - Table 5.69 ECOMM Setting; Figure 5.91 Required Zone Directional Settings; Communications-Assisted Tripping Logic

5.120
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Functions
Communications-Assisted Tripping Logic
Communications-Assisted Tripping Logic
Communications-assisted tripping schemes provide unit protection for transmis-
sion lines without any need for external coordination devices. The relay includes
the following five schemes.
➤ POTT—Permissive-Overreaching Transfer Trip
➤ POTT2—Two-Channel Permissive Overreaching Transfer Trip
➤ POTT3—Phase-Segregated Permissive Overreaching Transfer Trip
➤ DCUB—Directional Comparison Unblocking
➤ DCB—Directional Comparison Blocking
All of these schemes work in both two-terminal and three-terminal line applica-
tions. For the DCUB scheme, you have separate settings choices for these appli-
cations (ECOMM equals DCUB1 or DCUB2) because of unique DCUB logic
considerations.
You must set Zone 3 reverse-looking (DIR3 equals R) for all three schemes.
Table 5.69 ECOMM Setting
Setting Prompt Range
Default
(5 A)
ECOMM Communications-Assisted Tripping N, DCB, POTT,
POTT2, POTT3,
DCUB1, DCUB2
POTT
Figure 5.91 Required Zone Directional Settings
SEL-421 Relay
BK1
Transmission Line
Bus S
BK2
SEL-421 Relay
Comm.
Equip.
Comm.
Equip.
TX
RX
TX
RX
Bus R
Zone 3 (R)
Zone 1 (R)
Zone 2 (R)
Zone 3 (S)
Zone 1 (S)
Zone 2 (S)