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).