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17.6.4
Backup unit activation events
See the events table in the chapter "Event masks" to know the events that contribute to activate the backup units, highlighted
by their code in bold.
If one of the units in operation stops due to one of the alarms described above and causes activation of a back-up unit, calculation
of the time for rotation is stopped until all the units return to normal operation and are no longer in alarm mode.
In the event that no other backup units are available, all units will maintain their operating status unless unit blocking alarms are
generated or OFF commands are issued.
Below is an example of calculation of the time for rotation:
Assuming there are two units where U1 is the Priority and U2 is the Secondary, counting of the time for rotation is as follows:
A.
STARTING SITUATION
•
U1: stand-by
•
U2: ON
Counting of the time of unit 2 for rotation is in progress.
B.
EVENT 1
•
U1: ON
•
U2: OFF for alarm
Counting of the time for rotation is blocked at the last value reached.
C. RETURN TO NORMAL CONDITIONS
•
U1: stand-by
•
U2: ON
Counting of the time of unit 2 for rotation resumes at the last value reached before the alarm.
In general, the logic will activate the backup unit with the lowest available address, i.e. the ones put in standby by the Priority
unit.
17.6.5
Exceeding the limits
The backup units activate and deactivate automatically depending of the four activation steps shown below. It is sufficient for
one of the four steps to be active to request units activation.
WARNING:
The setpoints in the diagrams below are different from those normally used for adjustment, and are those
specifically set for the backup unit.
The differentials, on the other hand, are the same as those set for normal adjustment.
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