15.28
SEL-400 Series Relays
Instruction Manual
Date Code 20171006
Communications Interfaces
SEL Protocol
Interleaved ASCII and Binary Messages
SEL relays have two separate data streams that share the same physical serial
port. Human data communications with the relay consist of ASCII character
commands and reports that you view using a terminal or terminal emulation
package. The binary data streams can interrupt the ASCII data stream to obtain
information; the ASCII data stream continues after the interruption. This mecha-
nism uses a single communications channel for ASCII communication (transmis-
sion of an event report, for example) interleaved with short bursts of binary data
to support fast acquisition of metering data. The device connected to the other
end of the link requires software that uses the separate data streams to exploit this
feature. However, you do not need a device to interleave data streams in order to
use the binary or ASCII commands. Note that XON, XOFF, and CAN operations
operate on only the ASCII data stream.
An example of using these interleaved data streams is when the relay communi-
cates with an SEL communications processor. The communications processor
performs autoconfiguration by using a single data stream and SEL Compressed
ASCII and binary messages. In subsequent operations, the communications pro-
cessor uses the binary data stream for Fast Meter, Fast Operate, and Fast SER
messages to populate a local database and to perform SCADA operations. At the
same time, you can use the ASCII data stream for commands and responses.
SEL Fast Meter, Fast Operate, Fast SER Messages, and Fast Message
Data Access
SEL Fast Meter is a binary message that you solicit with binary commands. Fast
Operate is a binary message for control. The relay can also send unsolicited Fast
SER messages and unsolicited synchrophasor messages automatically. If the
relay is connected to an SEL communications processor, these messages provide
the mechanism that the communications processor uses for SCADA or DCS
functions that occur simultaneously with ASCII interaction.
This section summarizes the binary commands and messages and includes our
recommendation for using Fast Commands and Compressed ASCII configura-
tion information to communicate with the relay. You need this information to
develop or specify the software an external device uses to communicate using
Fast Messages with the relay. To support this type of development, you will also
need to contact SEL for Fast Message protocol details.
lists the two-byte Fast Commands and the actions the relay takes in
response to each command.
Table 15.19
Fast Commands and Response Descriptions (Sheet 1 of 2)
Command
(Hex)
Name
Response Description
A5B9h
Status acknowledge message
Clears Fast Meter status byte and sends cur-
rent status.
A5C0h
Relay Fast Meter definition block
Defines available Fast Meter messages and
general relay configuration information.
A5C1h
Fast Meter configuration block
Defines contents of Fast Meter data message.
A5C2h
Demand Fast Meter configuration
block
Defines contents of demand Fast Meter data
message.
A5C3h
Peak demand Fast Meter config-
uration block
Defines contents of peak demand Fast Meter
data message.
NOTE:
Not all SEL-400 series relays
support demand metering and the
corresponding fast commands.
Summary of Contents for SEL-421-4
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