Sel SEL-300 Series, Инструкция по применению, Страница: 5 / 24

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Date Code 20200326 SEL Application Guide 2020-04
entering the TAR 20 command. These bits, when asserted, indicate that the M
IRRORED
B
ITS
com-
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.
R
ELAY
E
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.
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,
=>> TAR ROKA <Enter>
ROKA RBADA CBADA LBOKA ANOKA DOKA * *
1 0 0 0 0 0 0 0
Figure 2 Status of the ROKA Bit in the SEL-421-5
=>> TAR ROKA <Enter>
LBOKB CBADB RBADB ROKB LBOKA CBADA RBADA ROKA
0 0 0 0 0 0 0 1
Figure 3 Status of the ROKA Bit in the SEL-311C-1
=>> TAR 20 <Enter>
RBAD CBAD LBOK ROK * * * TOP
1 0 0 0 0 0 0 0
Figure 4 Status of the ROK Bit in the SEL-321-1
Table 4 Common Pilot Scheme Relay Elements
Relay Element Protective Zone
M2P Zone 2 mho-phase forward-distance element
Z2G Zone 2 mho ground-distance element
67G2 Level 2 residual-ground forward-overcurrent element
67Q2 Level 2 negative-sequence forward-overcurrent element
M3P Zone 3 mho-phase reverse-distance element
Z3G Zone 3 reverse mho ground-distance element
67G3 Level 3 residual-ground reverse-overcurrent element
67Q3 Level 3 negative-sequence reverse-overcurrent element