Reactive Power

Reactive Powercan best be defined as the amount of "unused" power developed by reactive components in an AC circuit or system.

The multiplication of "volt x amperage" in a DC circuit gives the power consumed in watts by the circuit.However, although this formula also applies to fully resistant AC circuits, the situation is somewhat more complicated in an AC circuit with reactive components, since this volt-amp product can change with frequency.

In an AC circuit, the multiplication of voltage and current is expressed as volt-amperage (VA) or kilo volt-amper (kVA), and visible poweris known as the S symbol.In a completely resistant circuit that is not inductive, such as heaters, irons and filament bulbs, etc., their reassurance is practically zero, so the impedance of the circuit consists almost entirely of resistance.

For an AC-resistant circuit, the current and voltage are in the same phase, and the power at any given moment can be found by multiplying the voltage by the current at the moment, and due to this "in-phase" relationship, the rms values can be as follows: used to find equivalent DC power or heating effect.

However, if the circuit contains reactive components, the voltage and current waveforms will be somewhat "out of phase" determined by the phase angle of the circuit.If the phase angle between voltage and current is a maximum of 90o, the volt-amp product will have equal positive and negative values.

In other words, the reactive circuit returns to the source as much as it consumes, which causes the average power consumed by the circuit to be zero, since the same amount of energy alternately continues to flow from the source to the load and from load to source.

Since we have a voltage and a current, but the power is not expended, the expression P = IV (rms) is no longer valid, and therefore it turns out that the volt-amp product in an AC circuit does not necessarily give the consumed power.Next, to determine the "real power" consumed by an AC circuit, also called the P symbol, we need to take into account not only the volt-amp product, but also the phase angle difference between the given voltage and current waveforms. Equation: VI.cosΦ

Then we can write about the relationship between visible power and active or real power as follows:

Reactive Power

Keep in mind that the power factor (PF) is defined as the ratio between active power in watts and power that appears in volt-amps, indicating how effectively electric power is used.In a non-inductive resistant AC circuit, the active power will be equal to the visible power, as the fraction of the P/S is equal to one.The power factor of a circuit can be expressed as a decimal value or percentage.

But in addition to the active and visible forces in AC circuits, there is another power component that is present when there is a phase angle.This component is called Reactive Power (sometimes called imaginary power) and is expressed by a unit called "volt-amperage reagent" (VAr), it is the Q symbol and is given with the following equation: VI.sinΦ .

Reactive power, or VAr, is not really power, but represents the multiplication of volts and amps that are out of phase with each other.Reactive power is the part of electricity that helps create and maintain the electrical and magnetic fields required by alternating current equipment.The amount of reactive power contained in an AC circuit will depend on the phase shift or phase angle between voltage and current, and just like active power, the reactive power is positive when "fed" and negative when "consumed".

Reactive power is used by most types of electrical equipment that use magnetic field, such as engines, generators and transformers.In addition, reactive losses in power transmission lines should be ensured.

The relationship of three elements : power in an AC circuit, active power, (watt) visible power, (VA) and reactive power (VAr) can be represented by the three sides of the right-angle triangle.This representation is called a Power Triangle, as shown:

Power in AC Circuit

Reactive Power

From the power triangle above we can see that AC circuits provide or consume two types of power: active power and reactive power.Also, active power is never negative, reactive power can be positive or negative in value, so it is always advantageous to reduce reactive power to improve system efficiency.

The main advantage of using AC electric power distribution is that the level of supply voltage can be changed using transformers, but transformers and induction motors of household appliances, air conditioners and industrial equipment all consume reactive power that takes up space on transmission lines due to larger conductors. But different transformers are required to process larger currents, resulting in extra charges.

Reactive Power
Showing Reactive Power with Coke

In many ways, reactive power can be thought of as the foam part in a coke cup.You pay for a glass of Coke in a café, but only the real liquid coke itself, which in most cases is always less than a full glass.

This is because the foam of the cola takes up extra space in the glass, leaving less room for the real liquid coke you consume, and the same idea applies in many ways to reactive power.

But for many industrial power applications, reactive power is often useful for having an electrical circuit.While real or active power is the energy provided to start an engine, heat a house or illuminate an electric light bulb, reactive power provides an important function, such as regulating voltage, thereby helping to move power effectively through the mains and transmission lines.

While reducing reactive power to help improve the power factor and system efficiency is a good thing, one of the disadvantages of reactive power is that it is necessary in sufficient quantities to control voltage and overcome losses in a transmission network.This is due to the inability to provide active power if the mains voltage is not high enough.However, too much reactive power circulating in the grid can cause overheating (I 2 *R losses) and unwanted voltage drops and power loss along transmission lines.

Power Factor Correction of Reactive Power

One way to avoid reactive power loads is to install power factor correction capacitors. Normally, those who use residential lines are charged only for active power consumed in kilo-watt hours (kWhr), since almost all residential and single-phase power factor values are essentially the same due to the power factor correction capacitors built into most household appliances by the manufacturer.

Industrial customers using 3-phase resources have very different power factors and therefore, electricity companies may have to take into account the power factors of these industrial customers and may have the consumer pay a penalty if they fall below the power factors.

In general, more reactive power is required for a load with a power factor of less than 0.95.A load with a power factor value higher than 0.95 is considered good because the power is consumed more efficiently, and a load with a power factor of 1.0 is considered excellent and does not use any reactive power.

Then we found that "visible power" was a combination of both "reactive power" and "active power".Active or real power is the result of a circuit that contains only resistant components, while reactive power is caused by a circuit containing capacitive and inductive components.Almost all AC circuits will include a combination of these R, L and C components.

Since reactive power is away from active power, it should be taken into account in an electrical system to ensure that the visible power provided is sufficient to feed the load.This is a critical aspect of understanding AC power supplies, since the power supply must be able to provide the volt-amp (VA) power required for any given load.