When I was working for a factory, 15 years ago, the factory electricity bill was not reasonable! It was extremely high.
The reason was, a poor power factor of the factory loads! The electricity company charged the factory the reactive power too. To force us to improve the power factor.
To overcome this issue, we connected a capacitor bank in parallel with the factory income power source, to improve the power factor of the overall loads. It worked!
What is Power Factor?
Power factor is the ratio of active power, measured in kilowatts, to apparent power, measured in kilo-volt amperes (or in kVA), power factor is the measure of effective use of electrical energy.
Below, is the power factor triangle, it shows the relation between power factor, active and reactive power.
Apparent power, is the measure of the total amount of power which is used to run electrical equipment, active and reactive.
Power factor is how effectively you are using electrical energy. Its expressed as a number less than or equal to 1.
The lower the power factor, the less efficient electrical power usage. For well designed electrical motors the PF = 0.95 while for single phase bad motors pf = 0.75
Power factor formula
As shown on the PF triangle above, Power factor = P/ S
While:
S: is apparent power (kVA) = (V*I)
P: is active power (KW)
From the power triangle the power factor is the cosine of the phase angle of voltage and current. PF=cos Φ
Replacing the Value of PF
PF = (P / V*I) = cos Φ
Read Also my other article Power factor correction, 8 important answers.
- PF is the ratio of active power used by a load to the apparent power delivered to that load.
- The higher the PF is, the more efficiency power usage is.
What is Power Factor Correction?
Power factor correction is a technical solution to make the efficiency of power usage higher, by adding capacitors in parallel with the inductive loads, to decrease the reactive power and increase the power factor value.
All types of loads which we use in our daily life, at home and work, such as motors used in mixer, lifts, fans, escalator, elevators etc have different efficiency ratings.
This efficiency is directly affected by power factor. The process of improving power factor is called, power factor correction.
Using the Power factor correction capacitors in parallel with the circuit, is the easiest way to improve the power factor.
This process will improve the efficiency of electrical supply, in this way less electrical energy production is required to feed the same loads.
The simple example of this process is, a 1MVA transformer. It has loads of power factor value 0.75, P = S * pf
With this value, it can only supply 750KW of loads, active power, the rest of its power is reactive power.
By using the power factor correction , the load power factor value can be increased up to the value of 0.95, the transformer can supply an extra 200KW of load.
Should I improve Power Factor at My Home?
You don’t have to improve your home power factor. Improving PF for home loads is useless because, most home appliances have unity PF, And the total PF of the home generally is greater than 0.9, so no benefit in correction capacitor.
If you buy a Power Factor Correction device for your home, it will just save a negligible money of your electricity bill. So its not practical to add PFC device in your home.
Importance of Power Factor Correction
Industrial loads, Power factor correction is extremely important, in some countries it is a must to correct power factor of large industrial applications. to improve power efficiency.
The importance of power factor correction are as following:
- Reducing the charges on the power system
- Increase in load carrying capabilities of the circuits.
- It also reduces the power losses.
- Increases the energy usage efficiency.
- Decreases the electricity cost.
- Reducing the installation cost. This is because improved PF reduces current and as a result reduces the cables needed for this load.
Let’s discuss other pros of power factor correction in more detailed.
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Avoid Power Factor Penalties
A large number of induction motors are used in industrial processing facilities.
All these induction motors inherently decrease the power factor for facility. Due to this reason many electricity companies assess low power factor penalty. Like the factory I told you about at the top of this article.
Factories have one solution, improve its power factor to avoid the penalty by adding capacitor bank.
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Reduced Demand Charges
As we know, many electricity companies take extra charges for maximum metered demand.
The maximum metered demand is based on highest demand in kilowatts or sometimes in percentage of highest registered demand in kilo volt ampere.
In case of low power factor the percentage of the measured KVA increases in large amount than the KW demand.
In such cases, improving the loads power factor by using the power factor correction method will lower the charge.
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Increased Load Carrying Capabilities
All equipment or machines running on active power also need reactive power.
The current each circuit carry can be reduced by installing the power factor correction capacitors near the inductive loads. As a result of pf correction the reduction in current allow the circuits to carry new loads.
This process saves the cost of upgrading network. It also saves the thousands of dollars of any company by reducing the unnecessary upgrade costs when network distribution is required.
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Improved Voltage
The lower the power factor the higher current flows of a given load.
When the line current increases, it also increases the voltage drop in the conductors. As a result of the voltage drop, the equipment running on that current also receive less voltage.
This problem can be easily solved by using the power factor correction.
What causes low power factor?
Inductive loads, like induction motors, are the main cause of low power factor.
Large industrial applications have large inductive loads, these loads consume active power in KW, and also need for proper operation a consumption of reactive power from the power grid (KVAR) to sustain a magnetic field.
The higher the reactive power the lower the power factor.
Low power factor disadvantages
- Lower power usage efficiency, A low power factor means you are wasting a lot of power. A power factor of 0.7 means only 70% of total supplied power is used by your business of industry and 30% is wasted in the circuits and networks. The wasted power is the reactive power.
- Higher cost, Most industrial loads are inductive, which means that the power factor is less than unity. The lower the power factor the greater amount of power is drawn. Which indicates that the greater current is drawn for the loads.
PF = cos Φ = (P / VI)
I = P / (V cos Φ)
The increased current requires a larger generator size, larger transformer and larger cables sizing.
Increased amount of current also increases the amount of heat produce due to power losses, i.e the life time of the equipment is also reduced.
All these things increase the large amount of cost of installation and also limit the expansion of plant or industry.
How to improve power factor?
The simplest way to improve pf is by adding capacitors to the electrical system parallel with the load.
Correction capacitors act as reactive current generators to add reactive power for the inductive load like motors.
Capacitors improve pf because, the effects of capacitance are exactly opposite those of motor inductance.
The groups of capacitors used to improve pf are known as capacitor bank, and are connected in parallel with the load.
Power factor correction capacitors
Power factor correction capacitor is a capacitor used to provide inductive loads with reactive power, to improve the power factor and increase the power usage efficiency.
Power factor correction capacitors are either fixed or automatic types.
The fixed capacitors are connected usually to individual loads to provide the needed amount of reactive power to the load to increase its power factor.
While the automatic capacitors, also known as switched capacitors, are switched on and off as required by the utility power factor value i.e the amount of the reactive power varies, they are connected in parallel with the incoming power source.
They are controlled by a microprocessor controller.
Which one is better, fixed or automatic capacitors?
If you have an individual load or some individual loads that require power factor correction, then a fixed capacitor may be a good choice for you.
While, in case of a large industrial building with many loads which varies all the time this means the power factor will be variable value all the time depending o the loads in service, in this case an automatic capacitor bank will be better than fixed capacitors.
Power factor improvement formula.
How to calculate capacitor bank to improve power factor? is an important question, Use our online pf correction capacitor calculator below.
But, as a quick Tip the PF correction capacitor formula is C = 1/(2πf ( V2/Q))
Where,
V is voltage
Q is reactive power
Q = √(S2 – P2),
P is active power and S is apparent power
Power factor improvement example
Assume we have three phase induction motor. Its power = 10 kw, PF = 0.78, working on 400V 50 HZ, source we need to add capacitor in parallel with the motor to improve it power factor.
PF = P / S
S = P/PF = 10000 / 0.78 = 12.8 KVA
While P is active power of the load in Watt.
S is the apparent power in VA.
Reactive power Q formula is:
Q = √(S2 – P2) = 7.98 KVAR
Q =V2 / X ⇒ X = V2/Q
X = V2/Q = 1/2πfC
C = 1/(2πf ( V2/Q)) = 15.8 µf
This means, this motor need a 15.8 µf power factor correction capacitor to be connected in parallel.
Use the below power factor improvement calculator.
What is unity power factor?
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