What is a capacitor bank and why is it used?

Capacitor stores energy in electric field. The stored energy is not maintained indefinitely, as the dielectric present between the plates allows for a certain amount of current leakage which results in the gradual dissipation of the stored energy.

Capacitor bank is an interconnection of such capacitors either in series or parallel based on requirement. Capacitor banks are generally used to

1. Power Factor Correction

2. Reactive Power Compensation.

Under Electrical Transmission, the demand of active power is expressing Kilo watt (kw) or mega watt (mw). This power should be supplied from electrical generating station. All the arrangements in electrical power system are done to meet up this basic requirement.

Although in alternating power system, reactive power always comes in to picture. This reactive power is expressed in Kilo VAR or Mega VAR.. The demand of this reactive power is mainly originated from inductive load connected to the system.

Inductive loads are generally

Electromagnetic circuit of electric motors,Electrical transformers,Inductance of transmission and distribution networks,Induction furnaces, fluorescent lighting etc.                            This reactive power should be properly compensated otherwise, the ratio of actual power consumed by the load, to the total power i.e. vector sum of active and reactive power, of the system becomes quite less.

This ratio is alternatively known as electrical power factor, and fewer ratios indicates poor power factor of the system. If the power factor of the system is poor, the ampere burden of the transmission, distribution network, transformers, alternators and other equipment connected to the system, becomes high for required active power. And hence reactive power compensation becomes so important.

Let me explain in details, we know that

Active power  = VIcosθ  where,cosθ is the power factor of the system.

Hence, if this power factor has got less valve, the corresponding current (I) increases for same active power P.

As the current of the system increases, the ohmic loss of the system increases. Ohmic loss means, generated electrical power is lost as unwanted heat originated in the system. The cross-section of the conducting parts of the system may also have to be increased for carrying extra ampere burden, which is also not economical in the commercial point of view.Another major disadvantage, is poor voltage regulation of the system, which mainly caused due to poor power factor.

The equipment used to compensate reactive power. There are mainly two equipment used for this purpose.

(1) Synchronous Condensers

(2) Static Capacitors or Capacitor Banks.

Static Capacitors can again be classified into Series capacitors and Shunt Capacitors based on usage.

Origin:https://www.quora.com/What-is-a-capacitor-bank-and-why-is-it-used