Introduction
Power factor is a term used in electrical engineering to describe the ratio of Real Power (W) to Apparent Power (kVA) in an electrical circuit.
It is a measure of how effectively electrical power is being converted into useful work output.
The Power Triangle
We have previously discussed three phase power and the power triangle in our blog post understanding the power triangle please do check it out if you haven’t done so already.
As discussed in that article there are three type of power that make up the Power triangle these being real power, apparent power and reactive power and the power factor is the ratio of real power to apparent power.
With reference to the above right-angled triangle and making use of our trigonometry knowledge, we can quickly deduce that the power factor can be represented by the equation;
The power factor is expressed as a number between 0 and 1, or as a percentage between 0% and 100%.
A power factor of 1 (or 100%) indicates that all the electrical power is being used for useful work.
A lower power factor means that some of the power is being lost as reactive power, which does not perform useful work.
The beer analogy
The beer glass capacity represents apparent power (kVA).
The beer itself represents active power (kW), while the foam represents reactive power (kVAR).
Power factor is the ratio between active power (kW) and apparent power (kVA).
Using the beer analogy, we obtain the power factor by dividing the beer by the glass capacity.
It’s clear that you’re getting less beer than you’re paying for with all that foam taking up space.
Hence, the need to correct power factor or reduce the beer foam. We will go through the steps later in this article
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Causes of low Power Factor
There are several factors that contribute to a low power factor in an electrical system, and the main ones are as follows:
Inductive Loads: Equipment such as electric motors, transformers, and fluorescent lighting can introduce inductive loads. These devices draw reactive power from the electrical system, which can lower the power factor.
Incorrect Sizing of Equipment: Using equipment that is oversized for the required application can result in a lower power factor. For example, using an oversized motor for a particular task.
Unbalanced Transformers: Transformers that are not balanced properly can lead to a lower power factor.
Non-Linear Loads: Devices like variable frequency drives, uninterruptible power supplies (UPS), and certain types of lighting can introduce harmonics into the system, which can contribute to a lower power factor.
Problems caused by a low Power Factor
A low power factor is far from ideal. As engineers, we typically take steps to avoid or reduce it as much as possible, aiming for it to approach 1.
Some of the problems caused by a low power factor include:
- Increased Energy Costs: Utilities often impose higher rates or penalties on customers with low power factors, resulting in higher electricity bills for businesses and industries.
- Overloaded Equipment: Transformers, generators, and other electrical equipment may become overloaded due to the excess reactive power in the system.
- Reduced System Efficiency: A lower power factor means that more current is required to deliver a given amount of power, which can lead to increased losses in the distribution system.
- Voltage Drops: A low power factor can lead to voltage drops, affecting the performance of sensitive equipment and potentially causing malfunctions.
- Heating of Equipment: Transformers, motors, and other equipment may experience increased heating due to the higher currents required with a low power factor.
Tripping of Circuit Breakers: In extreme cases, a low power factor can lead to nuisance trips of circuit breakers, resulting in disruptions to the power supply.
How can we correct low Power Factor
Power factor correction is obtained via the connection of capacitors which produce reactive energy in opposition to the energy absorbed by loads such as motors, locally close to the load or otherwise.
This improves the power factor from the point where the reactive power source is connected, preventing the unnecessary circulation of current in the network.
The location of low-voltage capacitors in an installation can either be central (one location for the entire installation), by sector (section-by-section), at load level, or a combination of the latter two as shown in the figures below.
In principle, the ideal compensation is applied at a point of consumption and at the level required at any moment in time.
In practice, technical and economic factors govern the choice.
Power factor Capacitor Sizing
Now that we understand the different options and locations available to us for installing the power factor correction capacitor, let’s look at how this capacitor can be sized.
The power factor correction capacitor is sized using the following formulas;
Where; Pf1 is the existing power factor, Pf2 is the target power factor, P is the load power, Qc is the required reactive power and C is the required capacitor size.
You don’t need to remember all these formulas because we have already designed a power factor correction capacitor sizing calculator with you in mind. Please check it out if you haven’t already
Rounding Up
That’s all we have for you today on this topic. If you’ve learnt something new from this post, you might also be interested in other articles we offer on related subjects available on our blog’s homepage.
While you’re here, take a moment to explore our collection of electrical engineering calculators. Cheers!