How Capacitor Banks Should Be Wired In Order To Improve Power Factor?

Question

I know that when trying to improve power factor capacitor banks should be inserted, but not knowing what the best solution is wired in Series OR Parallell?? Also what the formula for Power Factor is and what power factor loosage is acceptable in the United Kingdom,beacause in places i have heard that 0.8ohms is the maximum is this true. Please bare with me as i am new to PF and also Yahoo Answers Thanks for your help and support in advance!!!

Answer 1

Wiring capacitors in parallel will only increase the capacitance, in may not improve the power factor.

Answer 2

opposite of resistors:  two resistors in series are additive. two capacitors in parallel are additive.  The power factor will be maximum when the inductive reactance and the capacitive reactance are equal. Remember ELI the ICE man:

voltage leads current in an inductive circuit (L)

current leads voltage in a capacitive circuit (C).

Max power occurs when voltage and current are in phase.

To decide on the wiring of the cap bank, you must know the inductive reactance, RsubL.

Answer 3

Capacitors are wired in parallel to add capacitance.

The formulas for combining capacitors are the opposite of resistors.

The link below will assist you in computing the kVAr needed to improve your power factor.

I'm not sure what you mean by 0.8 ohms.  Some utilities expect customers to have a power factor of 0.80 or better.  Others expect a minimum of 0.85.  If the utility bills in kVA, then customers quickly learn that near unity PF will save them money.

Answer 4

The capacitor needs to be wired in parallel. There are two main ways of configuring them and you need to see which works best for your installation.

One is to install fixed capacitors to the main inductive loads (usually the large motors). The motor protection relays will need to be set lower.

The other is to have capacitor banks with a controller and different stages that are switched in or out as necessary (as the power factor changes with load)

You need to be careful not to ever have more capacitors connected than necessary (do not create a leading power factor) as this can lead to dangerous circulating currents.

An equipment supplier will help you determine the best approach and select the correct sizes if they want your business not that the maths is that difficult but if you specify the capacitor sizes, then you take the responsibility. If you have the supplier specify and supply then you can put some responsibility on them.

You don't say why you are trying to improve the pf. Most small users don't get penalties from the electricity supplier and the increased losses are usually small but worth comparing with cost of equipment and installing it with the rising power costs. You can use pf correction to increase capacity of an existing system if necessary.