C.2
SEL-751A Relay Instruction Manual Date Code 20100129
SEL Communications Processors
SEL Communications Protocols
Table C.2 lists the Compressed ASCII commands and contents of the
command responses.
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 through use of 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 mechanism uses a single communications channel for
ASCII communication (transmission 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 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 SEL-751A
communicates with an SEL communications processor. These SEL
communications processors perform autoconfiguration by using a single data
stream and SEL Compressed ASCII and binary messages. In subsequent
operations, the SEL communications processor uses the binary data stream for
Fast Meter and Fast Operate messages to populate a local database and to
perform SCADA operations. At the same time, you can use the binary data
stream to connect transparently to the SEL-751A and use the ASCII data
stream for commands and responses.
SEL Fast Meter, Fast
Operate, and Fast SER
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 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.
Table C.2 Compressed ASCII Commands
Command Response Access Level
BNAME ASCII names of Fast Meter status bits 0
CASCII Configuration data of all Compressed ASCII com-
mands available at access levels > 0
0
CEVENT Event report 1
CHISTORY List of events 1
CLDP Load Profile Data 1
CMETER Metering data, including fundamental, thermal
demand, peak demand, energy, max/min, rms, ana-
log inputs, and math variables
1
CSE Sequence Of Events Data 1
CSTATUS Relay status 1
CSUMMARY Summary of an event report 1
DNAME ASCII names of digital I/O reported in Fast Meter 0
ID Relay identification 0
SNS ASCII names for SER data reported in Fast Meter 0
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