### Power Factor Correction Capacitors Sizing Calculations – Part Five

Today, we will continue explaining other Types of Power Factor Correction Capacitors as in the previous article “Power Factor Correction Capacitors Sizing Calculations – Part Four”, we showed that the Types of Power Factor Correction Capacitors according to Location can be categorized to:

1. Individual compensation,
2. Group compensation,
3. Central compensation,
4. Hybrid compensation.

We explained the first type; Individual compensation in this previous article. So, today we will explain the following topics:

• Other Types of Power Factor Correction Capacitors according to Location.
•  Power Factor Correction Capacitors Sizing Calculations Steps

 2.2.B Group Compensation

 2.2.C Central Compensation

 2.2.D Hybrid Compensation

 This type of compensation has many other names like Mixed, hybrid or combined compensation. This configuration derives from a compromise between the three solutions of individual, group and centralized power factor correction and it exploits the advantages they offer (see Fig.3). In such way, the individual compensation is used for high power electrical equipment and the group and/or centralized modality for the remaining part. Economic considerations often show that it is advantageous to combine the three methods described above. Fig.3 Application: Hybrid power factor correction is prevailingly used in Installations not operating continuously and which may be supplied at high voltage but with low voltage loads. So, we should employ individual PFC for large / high voltage equipment and employ group and/or central low voltage capacitors for power factor improvement on Low voltage switch gear. This is much cheaper than adding the power factor improvement needed for low voltage loads with that of high voltage equipment because low voltage capacitors is available with much lower ratings which enable relatively small capacitor steps (100 KVAR and below) to be employed for automatically controlled capacitors. This ensures flexibility of operation without excessive switchgear costs. The advantages and disadvantages  The advantages and disadvantages of the hybrid compensation are same as discussed for the other three PFC types.

 3- General Notes on Different Types of Power Factor Correction

• The siting of the capacitors, does to some extent, depends on whether each piece of equipment (e.g. a motor or a transformer) is being individually corrected or the installation as a whole or part is being corrected as a central and/or group. In the first case the capacitor and the load (motor, transformer etc.) are as close together as possible. In the second case the capacitor is located at some convenient point in the system, such as a substation.
• In providing the power factor correction it should be remembered that distribution boards and circuits can carry a greater useful load if the capacitors are installed as near as possible to the source of low power factor. For this reason either group or individual correction, rather than central correction at the intake point, can almost invariably be justified.
• In an installation where the low voltage load is supplied from several distribution substations, local automatic control at each substation is generally much cheaper as well as operationally superior to an elaborate method of overall control operated from the point of incoming supply.
• After careful consideration of the advantages and disadvantages of the various installation options, care must be taken in sizing and placing power factor correction capacitors. Leading power factor, greater than 100%, must be avoided. The capacitors should only be on line when the load requires KVAR and disconnected when the load is reduced.
• As a summary for comparing different types of power factor correction the following table can be used:

 Capacitor Location Central On The Intake Central On The Main Bus(MLTP) Group On Various Feeders Individual On The Loads Technical Approach Best Flexibility Least Less Less Best Savings Least Less Less Max. Cost Per KVAR Least Lower Lower Highest

 4- Power Factor Correction Capacitors Sizing Calculations Steps

 Now, we are going to explain the Power Factor Correction Capacitors Sizing Calculations Steps for Different Cases of Installations: For Existing Installations, For New Designs.

 4.1 Power Factor Correction Capacitors Sizing Calculations  For Existing Installations

 the Power Factor Correction Capacitors Sizing Calculations Steps For Existing Installations include two phases as follows: Preliminary Evaluation Phase, Design Phase. Fig.4 shows the phases of Power Factor Correction Capacitors Sizing Calculations For Existing Installations. Fig.4

 First: Preliminary Evaluation Phase

 The preliminary evaluation is performed to determine if the application of power factor correction capacitors is likely to be economical or not. Fig.5 shows a typical flow chart for the preliminary evaluation process. Fig.5 The preliminary evaluation phase has many steps as follows: Step#1: Collect monthly billing data; this step is used to estimate how many capacitors are needed. Step#2: Make some preliminary measurements for current and voltage; this step is used to get a rough idea of how heavily loaded the plant cables and transformers are so that the loss savings can be better estimated. Step#3: Fill the Economic Screening Worksheet; this step is used to determine the approximate savings possible through power factor penalty reduction and loss reduction. The economic screening worksheet is actually made up of (4) smaller worksheets as follows: Step#3.A: Fill the Capacitor Costs Worksheet: to Estimate Total Capacitor Cost, Step#3.B: Fill the Loss Savings Worksheet: Estimate loss savings, Step#3.C: Fill the Power Factor Penalty Savings Worksheet: Estimate power factor penalty savings, Step#3.D: Fill the Economic Evaluation Worksheet: Evaluate economics and calculate the payback, present worth and benefit/cost. Step#4: Make preliminary measurements for harmonics; this step is used to help identify and report potential harmonic problems, Step#5: Repeat the Economic Screening Worksheet; this step is used to include the cost of studies and harmonic mitigation in the cost of the capacitors' installation, Step#6: Compare the savings with the probable cost of capacitors' installation; this step is to determine if the capacitors' installation process still economical or not? If economical proceed with the design phase, if not stop or proceed uneconomically.

 Second: Design Phase

 In this phase, we will design and select the best economical, efficient and applicable power factor capacitor scheme for an installation. Fig.6 shows a typical flow chart for the Design process. Fig.6 The Design phase has many steps as follows: Step#1: Performing a Detailed Plant Survey; this step is used to collect sufficient data about the plant to determine the optimal size of capacitor to place in each location. It is also for determining if there will be any detailed studies required to avoid some of the pitfalls associated with capacitor application. Step#1.A: Review One-Line Diagram; this step is used to make judgments about the most appropriate form of power factor correction. Step#1.B: Take into consideration the loads that produce harmonics or have sophisticated electronic controls that can interfere with power factor correction efforts. Step#1.C: collect sufficient data Inventory by using measuring instruments to understand how the system behaves so that optimal capacitor configurations may be determined. Step#2: Select Economical Capacitor Scheme; this step is used to find the lowest cost capacitor scheme that will adequately correct for the power factor while minimizing the losses. Step#3: Checking the "No Load" Voltage Rise: this step is used to check that if the Voltage Constraints Met or not. Step#4: Select Capacitor Switching Options. Step#5: Check the Harmonic Distortion and make Harmonic Mitigation Options; this step is used to check if the harmonic Constraints Met or not. Step#6: Use the Economic Screening Worksheet again; this step is used to evaluate the economics of the selected capacitor scheme, if economical then proceed with installation phase, if not, try to improve the economics by developing lower cost Capacitor Scheme or abort the design process.

 4.2 Power Factor Correction Capacitors Sizing Calculations For New Designs

 Power Factor Correction Capacitors Sizing Calculations Steps For New Designs will include the following steps: Step#1: Use the detailed loads schedules; this step is used to calculate the total KW, total KVAR and total existing PF at each feeder panel so that optimal capacitor configurations may be determined. Step#2: Review One-Line Diagram; this step is used to make judgments about the most appropriate form of power factor correction. Step#3: check for Potentially Troublesome Loads; in this step, we will take into consideration the Several different kinds of loads that produce harmonics or have sophisticated electronic controls can interfere with power factor correction efforts.  These loads like Adjustable speed drives, Variable frequency drives, DC Drives, Arc furnaces, large amounts of fluorescent or sodium-vapor lighting and Large UPS systems. Step#4: Select Economical Capacitor Scheme; this step is used to find the lowest cost capacitor scheme that will adequately correct for the power factor while minimizing the losses. Step#5: Develop a Fixed Capacitor Scheme: this step is used since the lowest cost installations are generally fixed capacitors with few additional accessories such as automatic switches and harmonic filters. Step#6: Checking the "No Load" Voltage Rise: this step is used to check that if the Voltage Constraints Met or not. Step#7: Select Capacitor Switching Options. Step#8: Check the Harmonic Distortion and make Harmonic Mitigation Options; this step is used to check if the harmonic Constraints Met or not. Step#9: Use the Economic Screening Worksheet; this step is used to evaluate the economics of the selected capacitor scheme, if economical then proceed with installation phase, if not, try to improve the economics by developing lower cost Capacitor Scheme or abort the design process.

In the next article, we will continue explaining the above Power Factor Correction Capacitors Sizing Calculations Steps in detail. Please, keep following.

The previous and related articles are listed in below table:

 Subject Of Previous Article Article Glossary of Power Factor Correction Capacitors Types of Loads, The Power Triangle, What is a power factor? Types of power factor Why utilities charge a power factor penalty? Billing Structure. What causes low power factor? Bad impacts of low power factor, Benefits of Power Factor correction. How to make Power Factor Correction? Types of Power Factor Correction Capacitors

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