15.33
Date Code 20171006 Instruction Manual SEL-400 Series Relays
Communications Interfaces
SEL M
IRRORED BITS Communication
NOTE: The MBG protocol option is
only available in some SEL-400 series
relays.
To enable the MBG protocol, set the Port setting PROTO := MBGA to enable
Channel A M
IRRORED BITS, or PROTO := MBGB for Channel B MIRRORED
B
ITS. Next, the protocol will need to be enabled in the Group settings.
Under Group settings, enable the MBG protocol for Channel A by setting
EMBA := Y. When this setting is enabled, the transmit equation settings
TX_IDA, RX_IDA, and TMBnA will be available in the Group settings and will
be hidden from the Port settings.
The MBG protocol can also be enabled for Channel B by setting EMBB := Y.
When this setting is enabled, the transmit equation settings TX_IDB, RX_IDB,
and TMBnB will be available in the Group settings and will be hidden from the
Port settings.
MB8
While the relay does not have a setting for the MB8 protocol implemented in
some SEL products, you can configure the relay to communicate with devices set
to MB8A or MB8B (such as the SEL-351S or SEL-2505). Set the protocol set-
ting PROTO to MBA or MBB. Set the STOPBIT setting to 2. Set all other set-
tings to match those in the other device.
Message Transmission
The relay transmits a MIRRORED BITS communications message as fast as it can
for the configured data rate. At 9600 bps, this is approximately one message
every
1/4-cycle. At 19200 bps, it is approximately every 1/8-cycle. At 38400 bps, it is
approximately two every 1/8-cycle. However, if pacing is enabled, it slows to one
message every 3 ms at 19200 and 38400 bps (see Table 15.26). Each message
contains the most recent values of the transmit bits. If you enabled any of the
extended features through the settings, note that the relay transmits a portion of
the extended data in each message.
If you have specified virtual terminal data channels for this port, the designated
data channels are normally idle. If you use the PORT command to open a virtual
terminal session for this port and type characters, the relay transmits these char-
acters through the virtual terminal logical data channels.
Message Reception Overview
When the devices are synchronized and the MIRRORED BITS communications
channel is in a normal state, the relay decodes and checks each received message.
If the message is valid, the relay performs the following operations:
➤ Sends each received logic bit (RMBn) to the corresponding pickup
and dropout security counters, that in turn set or clear the RMBnc
relay element bits.
NOTE:
c
represents the MIRRORED
B
ITS channel (A or B),
n
represents the
M
IRRORED BITS data channel data
number (1–8).
➤ Accumulates the analog data, and every 18th message, updates the
received analog quantities.
➤ Accumulates the virtual terminal information, and every 18th
message, makes the received character or characters available to the
virtual terminal.
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