## What is a Capacitor Bank : Working and Its Calculation

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When a number of capacitors are connected together it forms a capacitor bank. They can be connected in series or parallel. A capacitor bank has numerous advantages and applications. Most of the time, these are used for reactive power compensation and power factor improvement. The arrangement of these can be done at substation or power plants. The unit for capacitance in Farads. A capacitor bank of lower scale is frequently used in industrial buildings, college campus, large residential communities to improve power factor. The necessity of improving the power factor is very critical, as a low power factor at one point would disturb the power balance among the vicinity and would also attract penalties from local electrical distribution companies.

Capacitor Bank Definition
When a number of capacitors are connected together in series or parallel, forms a capacitor bank. These are used for reactive power compensation. Connecting the capacitor bank to the grid improves reactive power and hence the power factor.

Capacitor Bank
Capacitor Bank

As shown in the figure, capacitors are connected in series to improve the power factor rating. Different materials like paper, mica, etc. are used for the manufacturing of the capacitors as insulating materials.

Capacitor Bank Symbol
This symbol is often used in a single line diagram of the substation. The symbol is shown in the following figure.

Capacitor Bank Symbol
Capacitor Bank Symbol

As shown in the figure, a capacitor bank is represented either in star or delta connection.

Capacitor Bank Types
The capacitor bank is classified as:

Externally Fused – For this type of connection, each fuse unit is connected externally to the capacitor bank. This helps to save the capacitor bank from faults like surge voltage, temperature, etc. without any interruption in the operation.
Internally Fused – In this type, the fuse is kept inside the casing of the capacitor bank. Since the protection cannot be provided without any interruption, such banks are used for low rating capacitor banks. The disadvantage of such an arrangement is, under any fault case, the whole unit has to be replaced.
Fuse Less – This unit has no fuse placed along with the bank. These units are used for low ratings and specifications where the unit can be easily replaced.
Capacitor Bank Calculation
The calculation is an important feature that needs to be considered while designing a substation or residential community. The steps involved in the calculation are as follows.

To calculate the rating of the bank, we must have the following data available directly on indirectly. First is the power factor. The present power factor must be calculated to know the desired power factor. This can be done by using a power factor meter. The power factor meter is an instrument that measures power factor cos ø based on load and active power consumption.

Based on the active and reactive power consumptions, the power factor can be calculated as

Epi and Eqi are the values of active and reactive power respectively. These values are measured initially or at the beginning of one cycle. The cycle refers to a period, it may be a day or a few hours. Similarly, Epf and Eqf are the values of active and reactive power at the end of the cycle. Once we get these four values, we can calculate the initial value of the power factor.

Once the present value of the power factor is known, next is to know the desired power factor. That is the power factor that we want to obtain. Let the initial value be cos φ1 and the desired value is cos φ2. From the initial and final values of power factor, active power P can be evaluated as shown in the below figure

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