Relay Elements - Sel -300 Series Application Manual

entering the TAR 20 command. These bits, when asserted, indicate that the M
munications channel is operational and ready to transmit and receive data. Figure 2, Figure 3, and
Figure 4 display the expected responses to the commands for each relay.
=>>TAR ROKA <Enter>
ROKA
1
Figure 2 Status of the ROKA Bit in the SEL-421-5
=>>TAR ROKA <Enter>
LBOKB
0
Figure 3 Status of the ROKA Bit in the SEL-311C-1
=>>TAR 20 <Enter>
RBAD
1
Figure 4 Status of the ROK Bit in the SEL-321-1
R E
ELAY LEMENTS
Pilot schemes use forward-looking overreaching elements and reverse-looking elements. To imple-
ment the pilot scheme, you can use distance elements, directional overcurrent elements, or both.
Table 4 lists the most commonly used relay elements for pilot schemes.
Table 4 Common Pilot Scheme Relay Elements
Relay Element
M2P
Z2G
67G2
67Q2
M3P
Z3G
67G3
67Q3
POTT O
VERVIEW
A POTT scheme is a communications scheme in which an asserted overreaching element at the
local terminal must receive permission to trip from the remote terminal. When a forward-looking
overreaching zone (Zone 2) asserts, it can only trip the breaker at a high speed if permission has
been received from the remote end. A reverse-looking zone (Zone 3) blocks permission to the
remote terminal.
For example, referencing Figure 5, if a fault occurs at Point F1, the overreaching Zone 2 element at
Relay 1 asserts while the reverse-looking Zone 3 element remains deasserted. This makes the out-
put of AND 1 (shown in Figure 6) assert, sending a permissive trip (PT) signal (key) to Relay 2,
Date Code 20200326
RBADA CBADA
0 0
CBADB RBADB
0 0
CBAD LBOK ROK
0 0
Protective Zone
Zone 2 mho-phase forward-distance element
Zone 2 mho ground-distance element
Level 2 residual-ground forward-overcurrent element
Level 2 negative-sequence forward-overcurrent element
Zone 3 mho-phase reverse-distance element
Zone 3 reverse mho ground-distance element
Level 3 residual-ground reverse-overcurrent element
Level 3 negative-sequence reverse-overcurrent element
LBOKA ANOKA
0 0
ROKB LBOKA
0 0
*
0 0
B
IRRORED
DOKA * *
0 0 0
CBADA RBADA
0 0
* *
0 0
SEL Application Guide 2020-04
5
com-
ITS
ROKA
1
TOP
0