How do I select the right capacitors for my specific needs?

Power factor correction

Once you have decided that your installation can benefit from power factor correction, you need to choose the optimal type, size, and number of capacitors for your installation.

How do I select the right capacitors for my specific needs? (photo credit: mediarede.com)

There are two basic types of capacitor installations: individual capacitors on linear or sinusoidal loads, and fixed or automatically switched capacitor banks at the feeder or at the substation.

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capacitors

Individual installations versus banking facilities

7 advantages of individual capacitors to the load:

  1. Full control // Capacitors cannot cause problems on the line under low load conditions
  2. No need for separate switching // Motor always works with a capacitor
  3. Improved motor performance through more efficient use of energy and reduced voltage drop
  4. Motors and capacitors can be easily moved together
  5. Easier to choose the right capacitor for the load
  6. Reduced line losses
  7. System capacity increase

3 advantages of banking facilities at the start or at the substation:

  1. Reduced cost per kVAR
  2. Improved total plant power factor – reduces or eliminates all forms of kVAR loads
  3. Automatic switching ensures exact power factor correction, eliminates overcapacity and resulting surges

Table 1 // Summary of the advantages / disadvantages of individual, fixed, automatic, combined banks

MethodBenefitsDisadvantages
Individual capacitorsThe most technically efficient, the most flexibleHigher installation and maintenance cost
Fixed bankMore economical, fewer installationsLess flexible, requires switches and / or circuit breakers
Automatic bankIdeal for variable loads, prevents power surges, low installation costHigher equipment cost
CombinationMore practical for a larger number of enginesThe least flexible

Consider the 5 special needs of your plant

When deciding which type of capacitor installation best meets your needs, you will need to weigh the pros and cons of each and take into account several installation variables including type of load, load, load constancy, load capacity, engine starting methods and billing.

1. Type of load

If your plant has a lot of large motors, 50 hp and above , it is usually economical to install one capacitor per motor and switch the capacitor and motor together. If your installation is made up of many small motors, from 1/2 to 25 hp, you can group them together and install a capacitor at a central point in the distribution system.

Often the best solution for installations with small and large motors is to use both types of capacitor installations.

2. Load size

Installations with large loads benefit from a combination of individual load, group load and fixed and automatically switched capacitor unit banks. In contrast, a small installation may only require one capacitor at the control panel.

Sometimes only an isolated problem point requires a power factor correction. This can be the case if your plant has soldering machines , induction heaters , or DC drives . If a specific power line operating with a low power factor load is corrected, the overall power factor of the installation may be high enough that additional capacitors are not required.

3. Constant load

If your installation operates 24 hours a day and the load demand is constant, Fixed capacitors offer the greatest savings . If the load is determined by eight-hour shifts five days a week, you will want more units switched to decrease capacity during periods of reduced load.

4. Load capacity

If your feeders or transformers are overloaded, or if you want to add an additional load to the lines already loaded, a correction must be applied to the load. If your installation has excess amperage, you can install capacitor banks at the main feeders.

If the load varies a lot, automatic switching is probably the answer.

5. Billing of utilities

The severity of the local utility tariff because the power factor will affect your return on investment and your return on investment (return on investment). In many areas, an optimally designed power factor correction system will pay off in less than two years.

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