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What is a Capacitor Bank?

Paul Scott
Paul Scott

A capacitor bank is a grouping of several identical capacitors interconnected in parallel or in series with one another. These groups of capacitors are typically used to correct or counteract undesirable characteristics, such as power factor lag or phase shifts inherent in alternating current (AC) electrical power supplies. Capacitor banks may also be used in direct current (DC) power supplies to increase stored energy and improve the ripple current capacity of the power supply.

Single capacitors are electrical or electronic components which store electrical energy. Capacitors consist of two conductors that are separated by an insulating material or dielectric. When an electrical current is passed through the conductor pair, a static electric field develops in the dielectric which represents the stored energy. Unlike batteries, this stored energy is not maintained indefinitely, as the dielectric allows for a certain amount of current leakage which results in the gradual dissipation of the stored energy.


The energy storing characteristic of capacitors is known as capacitance and is expressed or measured by the unit farads. This is usually a known, fixed value for each individual capacitor which allows for considerable flexibility in a wide range of uses such as restricting DC current while allowing AC current to pass, output smoothing in DC power supplies, and in the construction of resonant circuits used in radio tuning. These characteristics also allow capacitors to be used in a group or capacitor bank to absorb and correct AC power supply faults.


The use of a capacitor bank to correct AC power supply anomalies is typically found in heavy industrial environments that feature working loads made up of electric motors and transformers. This type of working load is problematic from a power supply perspective as electric motors and transformers represent inductive loads, which cause a phenomenon known as phase shift or power factor lag in the power supply. The presence of this undesirable phenomenon can cause serious losses in terms of overall system efficiency with an associated increase in the cost of supplying the power.

An inductor generates a magnetic field when current is applied to it.
An inductor generates a magnetic field when current is applied to it.

The use of a capacitor bank in the power supply system effectively cancels out or counteracts these phase shift issues, making the power supply far more efficient and cost effective. The installation of a capacitor bank is also one of the cheapest methods of correcting power lag problems and maintaining a power factor capacitor bank is simple and cost effective. One thing that should always be kept in mind when working with any capacitor or capacitor bank is the fact that the stored energy, if incorrectly discharged, can cause serious burns or electric shocks. The incorrect handling or disposal of capacitors may also lead to explosions, so care should always be exercised when dealing with capacitors of any sort.

Discussion Comments


Is this capacitor bank is operated by any switch or does it get stored and discharged accordingly to the load?


Why is the capacitor bank required to correct power factor? How much does it cost for 400 kva?


I already know about the capacitor bank functioning... but I want to know whether the energy saving devices used by capacitor banks function efficiently or not for high wattage equipment (I mean heating and electric equipment).


Please give more information on PF and capacitor banks. Also please suggest how we decide (calculate) the capacitor bank size for a 100HP motor.


OK. Anon how does the meter read your kW consumption?

If you answered current, you are right and the capacitor banks do in fact reduce current of the inductive loads. So therefore must reduce the kW usage according to the meter not a theoretical mathematical equation.


If you are charged in KVA hours and you have significant inductive loads (motors, compressors, fridges etc). Then a capacitor bank will save you money on your power bill. If however, you only have resistive loads (mostly lights, heaters etc.) or if you are charged in KW hours (most residential places are) then a capacitor bank will save you nothing. Though if everyone had a perfect power factor it would make life easier for your utility.


@Charred —Frankly, I wouldn’t even go that route. Your electric company charges you for the current coming into your house. The capacitor bank simply corrects anomalies once that current has been delivered. I don’t think you would reduce your electric bill. It’s not like installing thermal windows or anything like that. A high voltage capacitor bank is best suited for a power plant, which is always trying to improve the efficiency of its electrical systems.


I’m looking to save some money on my electric bill. A friend suggested that I should consider a home capacitor bank. Does anyone have any recommendations or know more about how to install these systems?

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      By: zigzagmtart
      An inductor generates a magnetic field when current is applied to it.