Capacitor Bank Configuration

[sberbece]

Hello!

I would like to have an advice on how to configure a capacitor bank, for power factor correction application.

The networks voltage is 6.6 kV.
Doing the maths, to improve the PF from 0.8 to 0.95, it requires almost 1.2 MVAr, lets say I need a capacitor bank able to deliver Q = 1.2 MVAr.

The question is what configuration the bank shall have, star or delta?

Using a typical capacitor can of, let say Q1= 400 kVAr, how many cans do I need?
For a star connection configuration, how many cans do I need? 3 or 9? What about delta connection ?

Thank you in advance for your support.

 

[Marmite]

There's lots of information on capacitors on the web. Check out

http://www.nokiancapacitors.com/articles.htm.

Also there are Cahier Techniques available by registering on Schneider's website which explain the many issues. Personally I wouldn't get involved in designing the capacitor bank itself.
Decide on your spec, IEC60871-1, or IEEE 18-2002 depending on where you are.
Rated reactive power
Rated voltage
No of phases
Frequency
BIL
Operating Temp
Max inrush current
Whether you need discharge resistors
Whether you want fused or unfused caps
and then go out to tender and let the manufacturer design the unit.
Important things to note are harmonics- you may want to get a harmonic survey done. The unit may need to be detuned to make it suitable for the harmonics and the natural resonant frequency of your system. Also the rating of the controlling switchgear. It is typical to de-rate the circuit breaker by 30%, also there are transient overcurrents of high amplitude and frequency when you energise a capacitor bank which is very onerous for switchgear. The switchgear will need to be type tested for capacitor switching. It gets worse if you add a second bank, and not many circuit breakers have an assigned back to back capacitor switching rating.
The attached paper explains the pros and conns of the different configurations.
Regards
Marmite