Novar 1xxx KMB systems
47
a valid value prior to this. If this parameter value has not been specified (-
--
-.--
----
--
shown), connected
chokes will not be detected.
After controller initialization, parameter 27 value is not specified, so compensation by choke is
disabled by default.
4.4.1 Basic Choke Compensation
Usually, one or few chokes only are installed in combined compensation systems. To reach sufficient
precision of power factor control, a suitable set of capacitors are added to the choke(s) and controller
freely combines both the chokes and the capacitors as needed to reach preset target power factor.
We will call this ,,asymmetric“ mode as basic mode.
For the basic mode activation the choke power factor limit value (parameter 27) must be set within a
range from 0.8 lag to 0.8 lead. If this parameter is not defined (-.-- shown), compensation by
choke does not take place (if chokes are available at some of the outputs, these outputs are
permanently disconnected).
If the compensation by choke power factor limit value is specified as a valid setting, a choke is
connected in the following situation:
• controller has disconnected all capacitive sections
• power factor is still more capacitive (leading) than that required and also more capacitive than
the compensation by choke power factor limit value specified ( exception: while offset control
activation, this limit is not checked; see description of parameter 27 )
• this condition has lasted for five times longer than the overcompensation control time
(parameters 3, 9)
• a choke is available at least at one output and it has such a value that after its connection it will
be possible to control the power factor to desired value using a combination of capacitive
sections, that is large undercompensation will not occur after its connection
If a number of chokes are available to the controller, the most suitable one, depending on their values,
is connected, and another one is connected if the above described situation has lasted for another five
times longer than overcompensation control time specified.
If a combination of chokes are connected and undercompensation occurs, such a number of chokes
are disconnected after a normal undercompensation control time has elapsed (parameters 2, 8), which
prevent overcompensation.
4.4.2 Symmetric Choke Compensation
There exist some applications (such as renewable resources power plants) where continuous power
factor control in some range, usually symmetric to both sides from neutral value of 1, is required. In
such cases the same or similar sets of both capacitors and chokes are installed.
The basic choke compensation mode is often unsuitable for such installations. Therefore, so called
symmetric mode is implemented, that differs from the basic one in following :
• control period corresponds (similarly as for capacitors) to the overcompensation control time
(parameters 3, 9)
• during one control step, the controller switches combination of chokes to reach optimal power
factor
• the controller never combines capacitors with chokes (firstly, it switches all of capacitors off,
then switches chokes on and vice versa)
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