Fan Speed Control - Siemens LMS14 User Manual

6.35.11 Fan speed control

Fan speed control is active during startup, shutdown, home run, and the operating
phase. The purpose of fan speed control is to influence the fan motor in a way that the
resulting fan speed (after settling) will lie within a permissible band of the current
operating phase. Fan speed control allows the compensation of external influences,
such as over- or undervoltage, shortest flue gas paths or longest flue gas paths, in
Speed Kp Speed Tn
defined ranges. Fan speed control can be adjusted via (9630),
Speed Tv
(9631) und (9632) (refer to chapter Fan control). The pulses from fan speed
Hall sensor pulses/rev
feedback can be parameterized using (9617).
During adjustment of the fan speed by fan speed control, a transient response might
occur. It is recommended to parameterize prepurging and ignition to the same level,
thereby making use of prepurging for the settling process. If, for example, prepurging is
parameterized > ignition, a second settling process will take place. This would extend
the time required for startup.
Fan speed control and speed parameters
The fan control values are to be parameterized such that the values required and
desired from the combustion point of view will be reached (flue way and rated voltage).
Then, the associated fan speeds are to be defined based on the fan characteristics. In
a first approach, the limit values for the permitted bands must be set to a high level
( Speed tolerance prepurging Speed tolerance ignition
(9506) and (9514) etc.). The
values for fan speed control and fan speed can now be optimized. When the speed
controller and the speeds in the individual phases are set, the speed bands are reduced
to such a degree that in the event of unfavorable conditions, startup, operation and
shutdown take place without triggering any fault status messages.
Speed limits
If readjustment of speed is desired, it should be made first. When optimization is
completed, or the settings have been made, the speed limits are to be defined and set
next.
The limit values for the permissible bands should be set to a level where the fan speed
lies inside the band, even if conditions are most unfavorable. If, by mistake, the fan
speed is higher or lower, the worst-case consideration and the speed band are violated,
leading to appropriate responses in the process (refer to Sequence diagrams).
However, for a defined tolerance time, the sequence of phases tolerates certain
deviations from the preset speed bands in the individual phases. This way, it is made
certain that in the case of potential settling processes the speed controller will not
immediately respond to violations of the speed bands, and that a response is triggered
only if there is a lasting speed deviation in one if the phases.
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6 The settings in detail 28.01.2015