Date Code 20081022
Instruction Manual
SEL-787 Relay
Appendix I
M
IRRORED
B
ITS
Communications
Instructi on Manual
Overview
M
IRRORED
B
ITS®
is a direct relay-to-relay communications protocol that
allows IEDs to exchange information quickly, securely, and with minimal
expense. Use M
IRRORED
B
ITS
for functions such as remote control and remote
sensing. The SEL-787 Transformer Protection Relay supports two M
IRRORED
B
ITS
communications channels, designated A and B. Use the port setting
PROTO to assign one of the M
IRRORED
B
ITS
communications channels to a
serial port; PROTO:= MBA for M
IRRORED
B
ITS
communications Channel A
or PROTO := MBB for M
IRRORED
B
ITS
communications Channel B.
M
IRRORED
B
ITS
are either Transmit M
IRRORED
B
ITS
(TMB) or Received
M
IRRORED
B
ITS
(RMB). Transmit M
IRRORED
B
ITS
include TMB1A–TMB8A
(channel A) and TMB1B–TMB8B (channel B). The last letter (A or B)
designates with which channel the bits are associated. Received bits include
RMB1A–RMB8A and RMB1B–RMB8B. Control the transmit M
IRRORED
B
ITS
in SEL
OGIC®
control equations. Use the received M
IRRORED
B
ITS
as
arguments in SEL
OGIC
control equations. The channel status bits are ROKA,
RBADA, CBADA, LBOKA, ROKB, RBADB, CBADB, and LBOKB. You
can also use these channel status bits as arguments in SEL
OGIC
control
equations. Use the
COM
) for
additional channel status information.
Because of different applications, the SEL product range supports several
variations of the M
IRRORED
B
ITS
communications protocol. Through port
settings, you can set the SEL-787 for compatible operation with SEL-300
series devices, SEL-2505 Remote I/O Modules, and SEL-2100 Logic
Processors. When communicating with an SEL-400 series relay, be sure to set
the transmission mode setting in the SEL-400 series relay to paced
transmission (TXMODE: = P).
Operation
Message
Transmission
In the SEL-787, the M
IRRORED
B
ITS
transmission rate is a function of both the
baud rate and the power system cycle. At baud rates below 9600, the SEL-787
transmits M
IRRORED
B
ITS
as fast as possible for the given baud. At rates at
and above 9600 baud the SEL-787 self-paces, using a technique similar to the
SEL-400 series pacing mode. There are no settings to enable or disable the
self-pacing mode; the SEL-787 automatically enters the self-pacing mode at
baud rates of 9600, 19200, and 38400.
shows the transmission rates
of the M
IRRORED
B
ITS
messages at different baud.
IMPORTANT:
Be sure to configure
the port before connecting to a
M
IRRORED
B
ITS
device. If you connect
an unconfigured port to a M
IRRORED
B
ITS
device, the device will appear to
be locked up.
NOTE:
Complete all of the port
settings for a port that you use for
M
IRRORED
B
ITS
communications before
you connect an external M
IRRORED
B
ITS
communications device. If you
connect a M
IRRORED
B
ITS
communications device to a port that
is not set for M
IRRORED
B
ITS
communications operation, the port
will be continuously busy.
Summary of Contents for SEL-787
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