Tunable Capacitor Banks?

[jgoebel]

Hi everyone,
A recent discussion with an engineer here got me to thinking - are there such things as tunable capacitor banks? IE you have a bank of caps and depending on the inductive properties of the load (which should be able to be measured by probing the voltage and current waveforms and measureing the phase angle) you turn on/off a bunch of switches/relays that place caps in series/parellel, which give you an equivalent capacitance to match the inductance, etc, giving you a purely real load as seen by your source.

Does such a thing exist? If not, why

 

[wareagle]

There are banks of capacitors that are switched in and out of the power system to correct power factor.

 

[apowerengr]

A truly "tunable" capacitor bank would be a synchronous condensor. Another interpretation of your question would be the use of a specially designed capacitor bank "tuned" to absorb specific harmonic content for harmonic filtering. Multiple switched capacitor banks of various discrete sizes with a master controller could be constructed to closely size the capacitve output of this "system" to the load characteristics. You have to watch out for sympathetic tripping when operating multiple switched capacitor banks in close proximity to one another. From a cost standpoint the power system does not normally require such fine tuning as your "tuned" capacitor bank. +/- 2-5% from unity powerfactor is usually good enough at the power system level.

 

[waross]

A commercial power factor controller measures the power factor (or phase angle if you prefer) and controls contactors to bring in as many steps of capacitors as are needed. The capacitors are added in parallel. The control is close enough that there is no need for fine tuning with series parallel connections.
As apowerengr mentions, you can get stepless control with a synchronous condensor or with an underloaded synchronous motor.
respectfully

 

[nightfox1925]

A tuned capacitor bank consist of a reactor in series with the capacitor. The capacitor will be designed to correct the power factor. The reactor is "tuned" to mitigate the offending system harmonic (at resonant frequency). Hence, it protects the system and the capacitor against harmonics.

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[jengi]

Here is one reference for a dynamic synchronous condenser:

http://www.amsc.com/products/motorsGenerators/quickVAR.cfm

 

[bacon4life]

Try looking into Thyristor Switched Capacitors (TSC). They turn sections of cap banks on and off every cycle.

How close you want to be to "purely resistive" would depend on how many thyristors you could afford to install.

Switching inductors mid cycle is easier on equipment than switching capacitors, so a Static Var Compensator might use a few banks of switched capacitors for rough control and then a thyristor controlled reactor for the fine tuning.