Software Monitoring - Siemens SIPROTEC 7SD600 System Manual

Numerical line differential protection SIPROTEC 7SD600 V3.0
D Command relay circuits
The command relays for operation of the trip and
and close coils of the circuit-breaker are switched
with two command channels and an additional re
lease channel. As long as there is no start pen
ding, the processor cyclically checks that each
channel is functioning correctly by switching each
one individually and checking its response. In the
event that the check reveals a fault in a channel or
a fault in the command relay coil, the command
output is immediately blocked and an alarm is
sued.
D Memory chips
During device startup (i.e. after the auxiliary sup
ply voltage has been applied) a data pattern is writ
ten into the working memory (RAM) read out
again and compared.
The remaining memory chips are checked periodi
cally for faults by
- generating a check sum for the program me
mory (EPROM) and comparing with the stored
check sum,
- generating a check sum for the parameter me
mory (EEPROM) and comparing with the newly
determined check sum generated with each
parameterization process.
Siemens AG January 1999
Method of operation
System manual Order no. E50417-G1176-C069-A1
4.5.5.2

Software monitoring

For continuous monitoring of the sequence of pro
gram execution, a time monitor (watchdog) is provi
ded. If the processor fails, or the program sequence
is disrupted, the watchdog timer expires and resets
the processor. Further internal plausibility checks du
ring the program execution ensure that any faults are
detected, thus initiating a reset and restart of the pro
cessor.
In the event that a fault is not eliminated by the re
start, another restart is attempted. After three unsuc
cessful restarts, the protection shuts down autono
mously and the red "Fault" LED lights up. The device
ready relay (if marshalled) drops off and signals "De
vice failed" with its normally closed contact.
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