User Manual

Control concept
Superposed plant controls
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Profile 2
Profile 2 shows that the order in which boiler stages are to be enabled has been changed, and that
sequences which will cause a drop in the power output have been defined in the power profile. In the
example illustrated, Boiler 3, which is currently delivering 200 kW, is switched OFF via sequence entry 2.
Boiler 1, which could achieve a power output of 150 kW with its enabled stages, is defined as the next
object in the sequence. This results in a drop in the power output, causing the function block to enable all
sequence steps automatically until an actual increase in power is achieved.
In sequence entry 4, Boiler 2 is enabled up to stage 2, giving a further 150 kW output. Boilers 1 and 2 are
thus enabled simultaneously up to stage 2, to prevent a drop in power. The effective delay time for the
simultaneous switching process is determined the maximum delay time of the boilers concerned. Since it is
Boiler 1 which has the longest delay (15 minutes), the simultaneous switching operation will be delayed for
this period of time.
Sequence entry 5 would again result in a drop in performance, because stage 2 of Boiler 2 is no longer
enabled. The block therefore switches straight to sequence entry 6, enabling Boiler 3 to compensate for the
power deficit. In this case the effective switch-on time is based on the switch-on delay for Boiler 3 (10
minutes).