Commercial office buildings are usually somewhere between 0. If we compare two induction motors, both have an output of 10kW and are connected to a three phase V 50Hz supply. One has a power factor of 0. The first motor will need to draw The second motor will need to draw just If we had a purely restive load such as an electrical restive heater then the voltage and current wave forms would be in sync or very close.
They would both pass their maximum and minimum point and pass through the zero axis at the same time. The power factor in this case is 1 which is perfect. If we drew a phasor diagram then the voltage and current would be parallel, so all the energy drawn from the electricity supply goes into doing work, in this case creating heat. If we took an Inductive load such as an induction motor, the coils magnetic field holds back the current and results in a phase shift where the voltage and current wave forms fall out of sync with the current and so it passes through the zero point after the voltage, this is referred to as lagging power factor.
The reactive power is wasted in the sense that we get no work from it but still have to pay for it, although we do need it to be able to do the work in the first place. We covered how induction motors work previously, click here to see that tutorial. If we drew a phasor diagram for a purely inductive load then the current will be at an angle below the voltage line, meaning not all the electricity consumed is doing work.
If we took a purely capacitive load then the opposite happens to the inductive load. The voltage and current are out of phase except this time the voltage is held back.
This causes leading power factor. Again this will mean not all the electricity is being used to do work, but we have to pay for it regardless. If we drew a phasor diagram for a purely capacitive load then the current line would be at an angle above the voltage line as it is leading. What can we do to correct poor power factor and reactive power charges? In most cases we come across lagging power factor caused by inductive loads, but we can come across leading power factor.
To correct poor power factor, we can add capacitors or inductors to the circuit which will realign the current back into phase and bring the power factor closer to 1.
If we have a lagging power factor caused by high inductive loads in the circuit then we add capacitors, this is most common. If we have a leading power factor caused by high capacitive loads then we add an inductive load to the circuit. If the power factor become too low then the electricity supplier might charge you a penalty fee or reactive power charge. Poor power factor can cause losses in equipment like transformers and leads to high heat gains. It can lead to voltage drops and can even reduce the life expectancy of equipment in extreme scenarios.
Lets look at a simplified example of calculating the size of a capacitor to improve the power factor of a load. The building has a 3 phase power supply and has a total load of 50kW of work and has a power factor of 0.
Currently the building has a total apparent power kVA value of It also has a reactive power of So take the square root of The capacitor therefore needs to make up the difference between these two so This is a simplified example, check with a supplier. I needed a simple explanation for Board members because of an upcoming change to electrical billing from our utility company.
This is great. I would like to comment your post. You did a great work here. I am happy to share this post to my friends. In the table of Engineering formulas Trigonometry there is a typo. Power Factor expresses the ratio of real power actually used in a circuit to the apparent power delivered to the circuit. The total power demand on the network is usually greater than the real power.
Save my name, email, and website in this browser for the next time I comment. The Engineering Mindset. Electrical Building services power factor. What is power factor. Power Factor beer analogy. Power factor formula. Power Triangle — Power factor correction. Power Factor Formulas. Reactive Power Charges. Induction motor power factor comparison. Induction motor power factor calculations. Purely resistive load. Purely inductive load. Purely capacitive load.
Power factor correction wave diagram. Why fix poor power factor. Power factor correction capacitor calculation. Motor Speed Controller Tutorial. Its value is unity for DC circuit and may vary in between zero to one for AC circuit.
We know that power consumed in a DC circuit is given by the multiplication of voltage V and current I. This mean,. But for AC circuit, the above formula is not correct. A third parameter, called the power factor is also included. Thus for AC circuit,. In this post we will discuss,.
Power factor is defined as the cosine of angle between the voltage phasor and current phasor in an AC circuit. It is denoted as pf. Let us consider a simple AC circuit to better understand the concept. Since the above circuit is an inductive circuit, the current through the circuit will lag the voltage by some angle. Now we draw the phasor diagram.
The power factor formulas are listed below:.
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