Schweitzer Engineering Laboratories SEL-700G Series, Инструкция по эксплуатации

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I.4
SEL-700G Relay Instruction Manual Date Code 20170814
M
IRRORED
B
ITS
Communications
Operation
In summary, when a relay detects an error, it transmits an attention message
until it receives an attention message with its own TX_ID included. If three or
four relays are connected in a ring topology, the attention message goes all the
way around the loop until the originating relay receives it. The message then
dies and data transmission resumes. This method of synchronization allows
the relays to reliably determine which byte is the first byte of the message. It
also forces unsynchronized UARTs to become resynchronized. On the down
side, this method takes down the entire loop for a receive error at any relay in
the loop. This decreases availability. It also makes one-way communications
impossible.
Loopback Testing
Use the LOOP command to enable loopback testing. In the loopback mode,
you loop the transmit port to the receive port of the same relay to verify
transmission messages. While in loopback mode, ROKc is deasserted, and
another user accessible Relay Word bit, LBOKc (Loopback OK) asserts and
deasserts based on the received data checks (see the Section 7:
Communications for the ACSII commands).
Channel Monitoring
Based on the results of data checks (described previously), the relay collects
information regarding the 255 most recent communications errors. Each
record contains at least the following fields:
➤
DATE—Date when the dropout occurred
➤
TIME—Time when the dropout occurred
➤
RECOVERY_DATE—Date when the channel returned to
service (if the channel is currently failed, it is displayed and
included in the calculations, as if its recovery were to occur at
the time the report was requested)
➤
RECOVERY_TIME—Time when the channel returned to
service (if the channel is currently failed, it is displayed and
included in the calculations, as if its recovery were to occur at
the time the report was requested)
➤
DURATION—Time elapsed during dropout
➤
CAUSE—Reason for dropout (see Message Decoding and
Integrity Checks on page I.2)
There is a single record for each outage, but an outage can evolve. For
example, the initial cause could be a data disagreement, but framing errors can
extend the outage. If the channel is currently failed, it is displayed and
included in the calculations, as if its recovery were to occur at the time the
report was requested.
NOTE:
Combine error conditions
including RBADA, RBADB, CBADA, and
CBADB with other alarm conditions
using SEL
OGIC
control equations. You
can use these alarm conditions to
program the relay to take appropriate
action when it detects a
communications channel failure.
When the duration of an outage on Channel A or B exceeds a user-definable
threshold, the relay asserts a user-accessible Relay Word bit, RBADA or
RBADB. When channel unavailability exceeds a user-definable threshold for
Channel A or B, the relay asserts a user-accessible Relay Word bit, CBADA or
CBADB. Use the COMM command to generate a long or summary report of
the communications errors.
Use the RBADPU setting to determine how long a channel error must last
before the meter element RBADA is asserted. RBADA is deasserted when the
channel error is corrected. RBADPU is accurate to ±1 second.