Date Code 20150130 Instruction Manual SEL-787 Relay
Appendix C
SEL Communications Processors
Instruction Manual
SEL Communications Protocols
The SEL-787 Transformer Protection Relay supports the SEL protocols and
command sets shown in Table C.1.
SEL ASCII Commands
We originally designed SEL ASCII commands for communication between
the relay and a human operator via a keyboard and monitor or a printing
terminal. A computer with a serial port can also use the SEL ASCII protocol
to communicate with the relay, collect data, and issue commands.
SEL Compressed
ASCII Commands
The relay supports a subset of SEL ASCII commands identified as
Compressed ASCII commands. Each of these commands results in a comma-
delimited message that includes a checksum field. Most spreadsheet and
database programs can directly import comma-delimited files. Devices with
embedded processors connected to the relay can execute software to parse and
interpret comma-delimited messages without expending the customization
and maintenance labor needed to interpret nondelimited messages. The relay
calculates a checksum for each line by numerically summing all of the bytes
that precede the checksum field in the message. The program that uses the
data can detect transmission errors in the message by summing the characters
of the received message and comparing this sum to the received checksum.
Most commands are available in either SEL ASCII or Compressed ASCII.
Selected commands have versions in both standard SEL ASCII and
Compressed ASCII formats. Compressed ASCII reports generally have fewer
characters than conventional SEL ASCII reports because the compressed
reports reduce blanks, tabs, and other white space between data fields to a
single comma.
Table C.1 Supported Serial Command Sets
Command Set Description
SEL ASCII Use this protocol to send ASCII commands and receive
ASCII responses that are human readable with an appropriate
terminal emulation program.
SEL Compressed ASCII Use this protocol to send ASCII commands and receive
Compressed ASCII responses that are comma-delimited for
use with spreadsheet and database programs or for use by
intelligent electronic devices.
SEL Fast Meter Use this protocol to send binary commands and receive
binary meter and target responses.
SEL Fast Operate Use this protocol to receive binary control commands.
SEL Fast SER Use this protocol to receive binary Sequential Events
Recorder unsolicited responses.
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