Chapter 1) 7SR242 Duobias Description Of Operation
©2015 Siemens Protection Devices Limited
Chapter 1 Page 22 of 60
2.11 Self Monitoring
The relay incorporates a number of self-monitoring features. Each of these features can initiate a controlled reset
recovery sequence.
Supervision includes a power supply watchdog, code execution watchdog, memory checks by checksum and
processor/ADC health checks. When all checks indicate the relay is operating correctly the ‘Protection Healthy’
LED is illuminated.
If an internal failure is detected, a message will be displayed. The relay will reset in an attempt to rectify the
failure. This will result in de-energisation of any binary output mapped to ‘protection healthy’ and flashing of the
protection healthy LED. If a successful reset is achieved by the relay the LED and output contact will revert back
to normal operational mode, and the relay will restart, therefore ensuring the circuit is protected for the maximum
time.
A Start-up Counter Meter is provided to display the number of start-ups the relay has performed. Once the
number of start-ups has exceeded a set number, an Alarm output can be given.
Figure 2.11-1 Start-up Counter Meter
Reset of the counter can be done from the meter or via a binary input or a command.
Various types of start-up are monitored by the relay:
1.
power-on starts
(auxiliary supply initiation)
2.
expected starts
(user initiated via comms, language changes, custom protection curve etc.)
3.
unexpected starts
(caused by the relay watchdog)
Any combination of these can be selected for the start-up count. This is done in the MAINTENANCE
MENU>START COUNT menu using the
Start Up Types
setting. All the start-up types selected will be added to
the overall start-up count.
The number of restarts before the alarm output is raised is set in the MAINTENANCE MENU>START COUNT
menu using the
Start Up Count Target
setting.
When the number of relay start-ups reaches the target value an output is raised, OUTPUT MATRIX>
Start Up
Count Alarm
, which can be programmed to any combination of binary outputs, LED’s or virtual outputs.
2.11.1 Protection Healthy/Defective
A normally open contact can be used to signal protection healthy. When the relay has DC supply and it has
successfully passed its self-checking procedure then the Protection Healthy contacts are made.
A normally closed contact is used to signal protection defective. When the DC supply is not applied to the relay or
a problem is detected within the relay then this output is de-energised and the normally closed contacts make to
provide an external alarm.
An alarm can be provided if the relay is withdrawn from the case. A contact is provided in the case at positions
25-26 of the PSU module, this contact closes when the relay is withdrawn.
Summary of Contents for 7SR242 Duobias
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