Definition of Power Factor

The Power Factor is an element of utmost importance for a good grid. It is very common for professional electricity that has plenty of experience in correcting power factor but does not know what this term really means. So I decided to mount this article trying to explain what is the power factor in a well illustrated and didactic.

The grid in Brazil is fed with alternating current (AC) of 127 volts RMS per phase and 60 Hz Some sites are not 127 volts, but they are still 60 Hz What does that mean?

Voltage Network

The tension in our network ranges from -179.6 to 179.6 V V every 0.008 seconds, which gives us a cycle (out of zero, go to 179.6 V, back to zero volts, go to -179, 6 V and again go to zero volts) and to run a cycle that it takes 0.016 seconds. Occur in 1 second of 60 cycles, so 60 Hz But our network is 127 V? Why 179.6 V? The 127 V, RMS. It would be the equivalent of saying that an AC current in the form of sine wave, which varies between 179.6 and -179.6 V V has the same effect, for example in a lapada than a voltage (like a battery) at 127 V. Another, more general, than to say that a cycle is 0.016 seconds (only 60 Hz) to say that he has 360 of which this statement is valid for any frequency. So let the power factor.

The Power Factor is a parameter measuring the gap between the voltage and current circulating through a network. He is the cosine of the angle of lag. If the gap is one-eighth cycle, 45, the power factor is the cosine of 45 is 0.71. The largest gap that can take as much current as head of the tension as being behind it is 90 degrees, so the power factor is always between zero and 1.

There are basically 3 types of loads that can be connected in a grid: a resistive load (eg irons, light bulbs, showers), inductive loads (eg motors, transformers) and capacitive loads (eg bank capacitors, fluorescent lights, computers).

When you connect to a network a resistive load, the current that flows through the load is also alternating and follows exactly the applied voltage. When is the peak voltage is the peak current and valley when the tension is worth in current. When this occurs it is said that the voltage and current are in phase, ie, synchronized. Once the gap is zero degrees and cosine of zero is 1. Power Factor is 1. All purely resistive load has Power Factor 1.

Puramete Resistive

Have an inductive load, it causes a delay of the chain. It ensures that, when turned on, the current starts to flow only when the complete cycle of ¼, 90, of tension. This is due to magnetic fields created by coils of wire (coil) in the existing inductive loads. In this case the cosine of 90 degrees is zero. Power factor is zero. All purely inductive load power factor has zero.

Purely Inductive

In contrast, a capacitive load causes a delay in tension. It ensures that, when turned on, the voltage only starts to appear only when ¼ full cycle, 90, of the current. This is due to electric fields created by the existing capacitors in the loads. In this case the cosine of 90 degrees is zero. Power factor is zero. Every purely capacitive load has zero power factor.

Purely Capacitive

But this only happens when the load is purely resistive or purely inductive or purely capacitive. But the most common is a mixture of these charges. A charge may have resistive and inductive characteristics at the same time, as well as resistive and capacitive, but never inductive and capacitive, this is impossible. In this case, depending on the degree of these mixtures, the angle of the gap varies and can reach any value between zero degrees and 90 degrees.

Inductive

In the case above, we have such a mix: half inductive and resistive half, causing a delay in the current 1 / 8 cycle, 45. Soon the Power Factor is the cosine of 45 is 0.71.

But why a low power factor is bad? The power of an electric circuit is given by P = ix U, where P is the power, i is the current flowing and U is the applied voltage. Just multiply the current by the voltage that has the power. In a resistive load that is true, because the voltage goes along with the current. In an inductive load is no longer so. When the voltage is at zero volts, the current is at its maximum and when the voltage is at its maximum, the current is zero amps. The same goes for the capacitive load. Thus the power of a purely capacitive load or purely inductive is always zero. With that has current running through the network and no power being supplied. It is for this reason that the power utilities require a power factor of at least 0.92, otherwise they would have to have a grid of great capacity, that would support large currents, but would provide little power. Increasing the Power Factor, you can even use thinner cable, as the current decrease, and thus saving much money in cables and transformers. This power is called active power. It is this power that performs work in industries. Then, to calculate the real power was introduced more than one term in the formula of power: the power factor.

P = ix U x fp -> Active power unit (Watts)

To correct this low power factor, simply install the two types of cargo simultaneously. If you have a lot of inductive load, installs capacitive load, the load is capacitive, inductive load installs. As a delay and other advances, the sum of the two is a neutral charge, that neither advances nor delay, ie, a purely resistive load. It's like a tug of war: one person on each side pulling the cord.

Tug of war

If two people have the same strength, the rope is in the middle (resistive load). If the inductive is stronger than the capacitor, the power factor decreases, then install capacitor banks in order to match the two. In this analogy, it's like to be called one more person to help pull the rope from the weaker side to balance with the stronger side.

With this hope I have helped to understand this concept so important to the electrical system in general.

Author: Jamil Baltazar - Electrical Engineer by UFV-MG.