What Is Reactive Power, Why Is It Important?

The unused power caused by the inductive and capacitive effects of transmission lines or electrical loads using alternating current is called reactive power. Reactive power, also known as virtual power or phantom power, is measured by VAR (Volt-ampere reactive).

What Is Reactive Power, Why Is It Important?
16.07.2023
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The unused power caused by the inductive and capacitive effects of transmission lines or electrical loads using alternating current is called reactive power. Reactive power, also known as virtual power or phantom power, is measured by VAR (Volt-ampere reactive).

Although capacitors and coils in circuits do not consume power, they cause a change in current and voltage values with the formation of an electric or magnetic field. The angle difference between the current and voltage phases gives information about the reactive power versus the apparent power.

In AC circuits, power is of three types: active power (P-Watt), reactive power (Q-VAR) and apparent power (S=P+jQ VA) which is the vectorial sum of these powers. Apparent power is taken into account when calculating conductors, transformers and generators.

Practical electrical loads can have only resistive or resistive, capacitive and inductive characteristics. Resistive circuits have only active power and the power factor value is 1. Circuits with capacitive, inductive and resistive characteristics have both active and reactive power.

In order to fully transfer active power to electrical loads, voltage drops must be prevented. Reactive power is required for this transfer to be healthy and to prevent voltage drops. In order for the electrical loads to operate properly, ±5% of the nominal supply voltage value should not be exceeded.

The angle between active and reactive power is the phase difference between the current (I) and voltage (V) signals. The power angle is expressed as ⱷ (ⱷV-ⱷI). Power factor is the ratio of active power to apparent power, cos ⱷ.

Capacitors are passive circuit elements that store energy using an electric field. The capacitor is charged by increasing the polarity voltage (reverse polarity) up to a certain level by allowing current to flow up to its capacity. In AC supply, the input voltage is constantly changing. In response to this, the capacitor leaves the voltage phase behind the current phase.

Coils are passive circuit elements that store energy using the magnetic field. When voltage is applied, the current flow increases gradually. For this reason, the current phase lags behind the voltage phase.

If the circuit is inductive, the current phase is 90 degrees behind the voltage. If it is capacitive, the current is 90 degrees ahead of the voltage. Inductive and capacitive reactive powers (QL and QC) act in opposite directions. Capacitive electrical loads generate reactive power and inductive electrical loads have the opposite effect, causing capacitive reactive power to be consumed.

Reactive power is required in some cases, such as voltage regulation and reduction of losses in transmission lines. When there is too much reactive power in transmission lines, voltage drops and power losses increase. In addition, in different areas of use of electrical energy where the power factor is intended to be corrected, it is tried to be damped by compensation methods.

Capacitor groups are used to regulate the reverse power factor value of induction motors. Asynchronous generators, which are frequently used in wind power plants, consume reactive power for excitation and magnetization in the stator. In other words, it reduces the voltage level by drawing reactive power from the grid to which it is connected to transfer the generated electricity. In order to prevent this, balancing is done by bringing the power factor closer to 1 value with capacitor groups. In this way, the voltage level will be prevented from dropping by drawing less reactive power from the grid to which it is connected in parallel. Voltage levels should always be monitored to prevent possible grid collapses.

Since reactive power cannot be transported very far in transmission lines, it is generated and used where relevant. The inductive characteristic of electrical loads should be taken into account when making power factor adjustments. Incorrect power factor adjustments may cause an increase in harmonics.

The author completed his undergraduate and graduate studies at Kırıkkale University, Department of Electrical and Electronics Engineering. After gaining private sector experience for a while in the fields of power electronics and LED lighting, he started to work as an academician at Bingöl University. Kocadağ continues his doctoral studies at Kocaeli University, Department of Electrical Engineering.
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