Prophi
®
12R / 12 RS
20
- 19 -
Section 9 Control principle
The control response of the device can be selected in programming mode.
The controller has four different control modes:
1. Sequential connection
In sequential connection, the required capacitor stages are successively connected
and disconnected in stages (last in - first out). The ranking of each step always
corresponds to the power of the smallest stage.
Advantage
: Exact definition of the next capacitor to be connected in each case
Disadvantage
: Long settling time, high switching frequency of the small stages
In order to shorten the settling time, the controller switches several stages
simultaneously for a large power-factor requirement. This applies to all
control types. The maximum dimensions of the simultaneously switching
branches can be changed in expert mode. If the value of the smallest stage
is pre-selected, the conventional sequential connection is obtained.
2. Loop connection
In this variant, the controller operates in loop mode (first in - first out) which
minimizes the wear on the capacitor bank, i.e. where stages are of equivalent
dimensions, the stage which was disconnected for the longest period of time is
always connected next.
Advantage
: Balanced utilization of equivalent stages and thus an increased
operating life of the capacitor bank.
Disadvantage
: This mode can only be used in control series with groups of the same
stage power and long settling time, as every switching step corresponds to the value
of the smallest stage.
3. Intelligent loop connection (default setting )
The intelligent control principle combines the advantages of the network-sparing
loop connection (first in - first out) with a much faster settling time, even for large
load skips, and reaches this goal with the fewest possible switching operations of the
capacitor stages. The optimized time response is achieved by the simultaneous
switching of several or larger capacitor groups as a function of the missing power
factor in the power line. Both the number of real switching frequencies of the
capacitors as well as the turn-on times of the branches are considered.
Advantage
: Reaches the target cos phi in a fast-optimized settling time with a low
switching frequency of the capacitors.
4. Combined de-tuning (special case for combined de-tuned banks)
Within a combined de-tuned application, 2 adjoining equal steps are switched with
just one joint choke. This pairwise de-tuning requires an appropriate closed control
series (i.e. 1:1:1:1..., 1:1:2:2..., 1:1:2:2:4:4... or similar)
The condition for the switching behavior is defined in such a way that the number of
activated odd steps is always greater than or equal to the number of activated even
steps. The controller complies with the requirements of the control regime while
largely conforming to the intelligent switching behavior.
The particular capacitor steps are permanently monitored.
In case of a defect
capacitor or higher deviation from the nominal output the capacitor will be
displayed inverted.
