Power Factor Correction Explained For Beginners

Power Factor Correction Explained For Beginners

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.

In order to understand about the importance of  power factor correction we should first understand the term power factor. So I started with the power factor definition to make it clear.

Below is the power factor triangle that shows the relation between power factor, active and inactive power.

Power factor triangle
Power factor triangle

Apparent power, is the measure of the total amount of the power which is used to run electrical equipment.

Power factor is how effectively you are using electrical energy. It is a popular expression of efficiency of energy using. And is 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)

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

(P / VI) = 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?

Its 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.

We get electrical energy with various types of power resources. All types of machines which we use in our daily life 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 is used to accomplish the same tasks.

The simple example of this process is a 1MVA transformer. It has loads of power factor of value 0.75,With this value, it can only supply 750KW of loads.

By using the power factor correction method, the load power factor value can be increased up to the value of 0.95, After this 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 and no benefit in correction capacitor.

If you buy a PFC device 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 and 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.

  • 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 power factor penalty due to lower power factor.

In order to overcome the decrease of power factor the process of power factor correction is very important and useful. The power factor penalty can be eliminated from the bill by adding capacitor bank.

  • Reduced Demand Charges

As we know that 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 power factor by using the power factor correction method will lower the charge. This will reduce the electricity bill.

  • Increased Load Carrying Capabilities

All the equipment or machines running on reactive power also need reactive power. The current carried out by each circuit 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 dollar of any company by reducing the unnecessary upgrade costs when network distribution is required. Furthermore when the reduce current passes thorough the circuit it also decreases the chances of current losses due to resistance.

  • 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 dropping of voltage the equipment running on that current also receive less voltage.

This problem can be easily solved by using the power factor correction. After using the power factor correction the voltage fall in the circuit is reduced and the voltage is improved for the equipment.

Low power factor causes and disadvantages

What causes low power factor?

Inductive loads 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.

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.

  • Higher cost

PF = cos Φ = (P / VI)

I = P / (V cos Φ)

Power factor affects the current. This means that the lower power factor the higher current of the same amount of load value.

The increased current requires a larger transformer with larger cables sizing. Increased amount of current also increase the amount of heat produce due to power losses and 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.

What is unity power factor?

A unity power factor means a power factor of value 1. This happens in ideal circuits when the voltage and current are in phase and the angle between them is zero.
 
Unity power factor is the case in DC circuits, while in AC circuits it can only happen in case of resonance i.e XL= XC (inductive reactance =capacitive reactance).

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 motor.

In other words 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.

The use of capacitor banks is economic with linear loads. Nowadays, loads are no longer linear, any other types of loads are in use in wider ranges, this means other ways are needed to improve power factor rather than capacitor banks. Here comes the below advanced method.

  • Some modern advanced power factor correction devices don’t use a capacitor bank, due to their compact and modular configuration they offer a large number of advantages.

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 mean the power factor will be variable, 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 and Q is reactive power Q = √(S2 – P2)

Power factor improvement example and calculator

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.

  • And 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 that this motor need a 15.8 µf power factor correction capacitor to be connected in parallel.

Use the below power factor improvement calculator.

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