POWER FACTOR CORRECTION
If the power factor of the plant is low, it uses more power than it needs to do the work. Poor power factor should be corrected as it substantially increases costs. Capacitors generally are the most economical means to improve power factors. Power factor correction is the term given to a technology that has been used since the turn of the 20th century to restore the power factor to as close to unity as is economically stable. This is normally achieved by the addition of capacitors to the electrical network which compensate for the reactive power demand of the inductive load and thus reduce the burden on the supply. There should be no effect on the operation of the equipment.
A sample analogy for power factor is to relate it to a garden hose. Circumstances, if you need 10 liters of water per minute to come out at the end of the hose, the tap should be turned on to deliver that amount of water. But if your hose leaks, is squashed between rocks, or is kinked because it is cheap, you will experience a drop in pressure. To achieve your target of 10 liters per minute, therefore, you need to turn up the tap and force more water through the hose. That is Power Factor Correction.
BENEFITS OF POWER FACTOR CORRECTION
The advantages that can be achieved by applying the correct power factor correction are:
- Environmental benefit-reduction of power consumption due to improved energy efficiency. Reduced power consumption means less greenhouse gas emissions and fossil fuel depletion by power stations.
- Reduction of electricity bills.
- Extra kVA available from the existing supply.
- Reduction of I2R losses in transformers and distribution equipment.
- Reduction of voltage drop in long cables.
- Extended equipment life- reduced electrical burden on cables and electrical components.
METHODS OF CAPACITOR INSTALLATIONS
We need to choose the optimum type, size and number of capacitors for the plant. There are four methods of capacitor installations:
Method 1: Capacitor at load
Installed a single capacitor at each sizeable motor and energize it whenever the motor is in operation. This method usually offer the greatest advantage of all, and the capacitors could be connected either in location (A) as (B) in
Method 2: Fixed capacitor bank
Installed a fixed quality of kVar electrically connected at one or more locations in the plant’s electrical distribution systems, and energized at all times. This method is often used when the facility has few motors of any sizeable horsepower to which capacitors can economically be added. When the system is lightly loaded, and the amount of kVar energized is too large, the voltage can be so great that motors, lamps, and controls can burn out. It is a important fact to remember that kVar equal to 20% of the transformer kVA is the maximum size of a fixed kVar bank. Valued greater than this can result in a large resonant current, which is potentially harmful to the system.
Method 3: Automatic capacitor bank
Since no two electrical distribution systems are identical, each must be carefully analyzed to arrive at the most cost- effective solution, using are or more of the method.
Method Advantages Disadvantages
Individual Capacitors
Most technically efficient, most flexible
Higher installation and maintenance cost
Fixed Bank
Most economical, fewer installations Less flexible, requires switches and/or circuit breakers
Automatic Bank
Best for variable loads, prevents over voltages, low installation cost
Higher equipment cost Combination
Most practical for larger numbers of motors
Least flexible
PARTICULAR NEEDS OF THE PLANT
When deciding which type of capacitor installation best meets weight the advantages and disadvantages of each and consider several plant variables, including load type, load constancy, load capacity, motor starting method.
When deciding which type of capacitor installation best meets weight the advantages and disadvantages of each and consider several plant variables, including load type, load constancy, load capacity, motor starting method.
Facilities with large loads benefit from a combination of individual load, group load and banks of fixed and automatically-switched capacitor units. A small facility may need only one capacitor as the control board. Sometimes, only an isolated trouble spot requires power factor correction. This may be the case if the plant has welding machines, induction heaters or dc drives. If a particular feeder serving s low power factor load is connected, it may raise overall plant power factor enough that additional capacitors are unnecessary.
If the plant operates around the clock and has a constant load demand, fixed capacitors offer the greatest economy. If lead is determined by eight-hour shift five day a week, switched units are wanted more to decrease capacitance during times of reduced load.
If the feeder or transformers are overloaded, or if additional load is added to already load lines, correction needs at the load if the facility has surplus amperage, the capacitor banks are installed at main feeders. If load varied a great deal, automatic switching is probably the solution.
METHODOLOGY FOR POWER FACTOR BILLING ADJUSTMENT
Assume a 400 kW load with a power factor of 70 percent. To improve power factor to 90 percent, the total kVar added to your plant (rating of capacity bank) is 200kVar.
Total annual kWh = 2, 400, 000
Average kWh charge = 50 kyats
Annual charge = 120, 000, 000 kyats
Power factor adjustment is 0.06 percent or each percentage point below or above 85 percent.
Power factor adjustment for 70 percent (penalty value)
= 85 – 70
= 15 x 0.06 %
= 0.9 % x 120, 000, 000
= 1, 080, 000 kyats
Power factor adjustment for 90 percent (credit value)
= 90 – 85
= 5 x 0.06%
= 0.3 % x 120, 000, 000
= 360, 000 kyats
Net gain (Annual saving)
= 1, 080, 000 + 360, 00
= 1, 440, 000 kyats
Therefore, annual saving is 1.2 percent of annual charge. This is to illustrate a hypothetical annual estimate. Single line diagram and control circuit diagram of 200 kVAR automatic capacitor bank are designed in appendix.
The linear payback period of this installation is described below.
Total cost of installation (survey cost, advice, capacitance and labour) is 3, 2000, 000 kyats. Annual saving is 1, 440, 000 kyats. Therefore, the payback period is 2 years and 3 months.
DISCUSSIONS AND CONCLUSION
The most frequent case at industrial plants is to compensate the reactive power at low voltage. To do this, there are on the market a large no. of manufacturers that offer standardized products with power ratings up to and even exceeding 1000 kVar. This is a very well known and widespread product and, as a result, on many occasions it is installed without enough study.
Therefore, the effects of disturbances are suffered mostly by the owner of the capacitor bank. Please ensure that installation meet your requirements, manufacturers, installations and all applicable codes, standards and regulations.
Assume a 400 kW load with a power factor of 70 percent. To improve power factor to 90 percent, the total kVar added to your plant (rating of capacity bank) is 200kVar.
Total annual kWh = 2, 400, 000
Average kWh charge = 50 kyats
Annual charge = 120, 000, 000 kyats
Power factor adjustment is 0.06 percent or each percentage point below or above 85 percent.
Power factor adjustment for 70 percent (penalty value)
= 85 – 70
= 15 x 0.06 %
= 0.9 % x 120, 000, 000
= 1, 080, 000 kyats
Power factor adjustment for 90 percent (credit value)
= 90 – 85
= 5 x 0.06%
= 0.3 % x 120, 000, 000
= 360, 000 kyats
Net gain (Annual saving)
= 1, 080, 000 + 360, 00
= 1, 440, 000 kyats
Therefore, annual saving is 1.2 percent of annual charge. This is to illustrate a hypothetical annual estimate. Single line diagram and control circuit diagram of 200 kVAR automatic capacitor bank are designed in appendix.
The linear payback period of this installation is described below.
Total cost of installation (survey cost, advice, capacitance and labour) is 3, 2000, 000 kyats. Annual saving is 1, 440, 000 kyats. Therefore, the payback period is 2 years and 3 months.
DISCUSSIONS AND CONCLUSION
The most frequent case at industrial plants is to compensate the reactive power at low voltage. To do this, there are on the market a large no. of manufacturers that offer standardized products with power ratings up to and even exceeding 1000 kVar. This is a very well known and widespread product and, as a result, on many occasions it is installed without enough study.
Therefore, the effects of disturbances are suffered mostly by the owner of the capacitor bank. Please ensure that installation meet your requirements, manufacturers, installations and all applicable codes, standards and regulations.
RECOMMENDATIONS
Size electric motors to match mechanical loads to increase the overall p.f.
Use capacitor banks at motor control center or service entrances to facilitate switching for varying load.
Install conditions as harmonic filters to avoid harmonic resonance problems and excessive voltage distortion levels.
the main reason why a customer installs a capacitor bank is to avoid penalization in the electricity bill. This inappropriate installation without enough study gives rise to a great variety of technical problems. Therefore, the fact that capacitor banks are designed for long-term use should be considered.