Power Factor Correction
Executive Summary
Power Factor is the measure of efficiency of your electrical system.
Low Power Factor Results in;
Poor electrical efficiency
Lower system capacity
Higher utility bills
Most utilities have power factor penalties to encourage power factor correction. Otherwise the utility may have to;
o Build more power plants
o Purchase new transformers
o Use Larger cables
Power Factor Correction;
Reduces Power Cost
Releases system capacity
Reduces power losses
Improves voltage
With the current rise in the cost of energy, increased facility efficiency is very desirable. By implementing Power Factor correction into the power distribution circuit, the Power Factor is improved thus minimising wasted energy, improving the efficiency of your plant/building, liberating more kW from the available supply and saving you money!
The purchase cost of the installation is usually recouped between one and two years of electricity savings.
Please note that Harmonics are not discussed in this document in the interest of simplicity. Power Factor
What is Power Factor
2.1 The definitions
In order to understand Power Factor we have to know the following definitions;
KW
Working Power (also called Actual Power or Active Power or Real Power).
It is the power that actually powers the equipment and performs useful work
KVAR
Reactive Power
It is the power that magnetic equipment (transformer, motor and relay) needs to produce the magnetizing flux. It doesn't do useful "work". It simply sustains the electromagnetic field.
KVA
Apparent Power
It is the vector addition of Working Power and Reactive Power
Power factor is the ratio between the kW and the kVA drawn by an electrical load where the kW is the actual load power and the kVA is the apparent load power. It is a measure of how efficiently the load current is being converted into useful work output and more particularly is a good indicator of the effect of the load current on the efficiency of the supply system.
Simply put, it is a measure of efficiency!
2.2 The BeerAnalogy
Mug Capacity = Apparent Power (kVA)
Foam = Reactive Power (kVAR)
Beer = Real Power (kW)
So, now that we understand some basic terms, we are ready to learn about power factor:
Power Factor (P.F.) is the ratio of Working Power to Apparent Power.
Looking at our beer mug analogy above, power factor would be the ratio of beer (KW) to beer plus foam (KVA).
Thus, for a given KVA the more foam you have (the higher the percentage of KVAR), the lower your ratio of KW (beer) to KVA (beer plus foam). This means that you will have more reactive power and a lower power factor.
The less foam you have (the lower the percentage of KVAR), the higher your ratio of KW (beer) to KVA (beer plus foam). In fact, as your foam (or KVAR) approaches zero, your power factor approaches 1.0 which is the theoretical perfect power factor.
Our beer mug analogy is a bit simplistic. In reality, when we calculate KVA, we must determine the "vectorial summation" of KVAR and KW.
Therefore, we must go one step further and look at the angle between these vectors.
2.3 The barge Analogy
How power is wasted can be shown graphically since in 3 phase power supplies "power" can be represented and measured as a triangle. Active Power is the base line and is the "real" usable power measured and paid for in kW. Reactive power is the vertical or that part of the supply which causes the inductive load. The reactive power in is measured in kVAR (kilo voltamperes reactive). Apparent Power is the hypotenuse. This is the component the electricity generator must supply and it is the resultant of the other two components, measured in kVA.
Mathematically the power can be calculated by pythagoras or trigonometry whereby Power Factor is expressed as COS phi Ø (The angle between Apparent Power and Active power)
Since the horse cannot walk on water its pulling effort is reduced by the "angle" of the tow rope.
If the horse could walk on water then the angle Phi Ø would be zero and COSINE Ø=1. Meaning all the horse's power is being used to pull the load.
However the relative position of the horse influences the power. As the horse gets closer to the barge, angle Ø1 increases and power is wasted, but, as the horse is positioned further away, then angle Ø2 gets closer to zero and less power is wasted
So, by improving Power Factor (reducing the angle), the reactive power component is reduced
The "Power Triangle" illustrates this relationship between KW, KVA, KVAR, and Power Factor:
2.4 Conclusion
In an ideal world, looking at the beer mug analogy;
KVAR would be very small (foam would be approaching zero)
KW and KVA would be almost equal (more beer; less foam)
Similarly…in an ideal world, looking at the barge analogy;
KVAR would be very small (approaching zero)
KW and KVA would be almost equal (The horse wouldn't have to waste any power along his body height)
The angle Ø (formed between KW and KVA) would approach zero
Cosine Ø would then approach one
Power Factor would approach one
In order to have an "efficient" system (whether it is the beer mug or barge dragging a heavy load), we want power factor to be as close to 1.0 as possible. Sometimes, however, our electrical distribution has a power factor much less than 1.0.
3 What causes low Power Factor
Since power factor is defined as the ratio of KW to KVA, we see that low power factor results when KW is small in relation to KVA. Remembering our beer mug analogy, this would occur when KVAR is large.
Inductive loads causes large KVAR in the system. Inductive loads which are sources of Reactive Power include;
Transformers
Induction motors
Induction generators
High intensity discharge (HID) lighting
Similarly, consumers of Reactive Power increase power factor:
Capacitors
Synchronous generators (utility and emergency)
Synchronous motors
These inductive loads constitute a major portion of the power consumed in industrial complexes. Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA) in your distribution system. This increase in reactive and apparent power results in a larger angle Ø (measured between KW and KVA). Recall that, as Ø increases, cosine Ø (or power factor) decreases.
So, inductive loads (with large KVAR) result in low power factor.
4 Why is Power Factor Important
Low Power Factor Results in;
Poor electrical efficiency
Lower system capacity
Higher utility bills
Most utilities have power factor penalties to encourage power actor correction.
Otherwise the utility may have to;
o Build more power plants
o Purchase new transformers
o Use Larger cables
Power Factor Correction;
Reduces Power Cost
Releases system capacity
Reduces power losses
Improves voltage
Inductive loads, which require reactive power, cause a lower power factor. This increase in required reactive power (KVAR) causes an increase in required apparent power (KVA), which is what the utility is supplying.
So, a facility's low power factor causes the utility to have to increase its generation and transmission capacity in order to handle the extra demand. By raising your power factor, you use less KVAR. This results in less KW, which equates to a financial saving from the utility by eliminating the power factor penalty.
By increasing the power factor to 0.9, more KW can be supplied for the same amount of KVA.
Inefficient power factor causes power system losses in your distribution system. By improving your power factor, these losses can be reduced. With the current rise in the cost of energy, increased facility efficiency is very desirable. And with lower system losses, you are also able to add additional load to your system.
Power Factor correction will also improve your voltage levels in your electrical system. Incorrect power factor causes power system losses in your distribution system. As power losses increase, you may experience voltage drops. Excessive voltage drops can cause overheating and premature failure of motors and other inductive equipment. So, by raising your power factor, you will minimize these voltage drops along feeder cables and avoid related problems. Your motors will run cooler and be more efficient, with a slight increase in capacity and starting torque.
5 How do I Correct / Improve My Power Factor
Inductive loads cause large KVAR in the system. Inductive loads which are sources of Reactive Power include;
Transformers
Induction motors
Induction generators
High intensity discharge (HID) lighting
Similarly, consumers of Reactive Power increase power factor:
Capacitors
Synchronous generators (utility and emergency)
Synchronous motors
One way to increase power factor is to add capacitors to the system. This and other ways of increasing power factor include;
Installing Capacitors (KVAR Generators)
Minimizing operation of idling or lightly loaded motors.
Avoiding operation of equipment above its rated voltage.
Replacing standard motors as they burn out with energyefficient motors.
The easiest solution to improve power factor is to add power factor correction capacitors to your electrical distribution system. Current that is drawn from the voltage source is then only used to do real work (kW) and not to create a magnetic field (kVAR).
The source current is then minimized;
The customer only pays for the capacitor
Since the utility doesn't supply the kVAR, the customer doesn't pay for it
In short, capacitors save money
6 InvestmentReturn on Investment
eturn on InvestmentReturn on Investment Return on Investment Return on Investment Return on Investment
A proper site inspection has to be completed before we can establish your return on investment.
We find that most Power Factor correction implementations has a one to two year payback period.
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Click HERE to download the specifications PDF
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us on info@mmtech.co.za
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