Why do we need reactive power compensation?

Why do we need reactive power compensation? And its principles and forms! Power factor is measured for different loads. In the previous era of direct current, there was no such thing as power factor. At that time, the power factor was 1. Later, Tesla brought us into the era of alternating current, and since then, power factor has always been with us (generally, the power factor is less than 1). Below, I will explain the principles and forms of reactive power compensation for your reference. (1) Why do we need reactive power compensation? Reactive power is by no means useless power. In an AC power supply system, inductance and capacitance are both essential loads, such as ferromagnetic loads such as motors and transformers. Without the excitation of inductive reactive power, the equipment cannot work properly. For example, the line for transmitting power over a certain distance is a capacitive load. As long as power is being transmitted, it is equivalent to a capacitor working. In other words, in an AC power supply system, the existence of reactive power is of great significance to the transmission and exchange of energy. It is indispensable, or in other words, the exchange system cannot work properly without reactive power. So, where does a large amount of reactive power come from? The system contains numerous reactive loads, especially inductive ones. Normally, the reactive power absorbed by these loads is supplied by the power plant. This means that when operating, the generator releases active energy into the system while simultaneously providing a corresponding amount of reactive energy to the inductive loads. Generators must maintain adequate reactive output during operation; a lack of reactive output can have devastating effects on the power generation system, making it crucial to maintain the system’s reactive power balance.

When reactive power demand in the system increases, without the installation of reactive power compensation devices, the power plant must increase reactive power output through phase shifting. However, due to the limited capacity of the generator, this inevitably reduces active power output, effectively reducing the generator’s output capacity. To meet power demand, the capacity of the generator, power lines, and transformers must be increased. This not only increases power supply investment and reduces equipment utilization, but also increases line losses.

To reduce the reactive power supply pressure on the power plant, capacitors are installed at points in the power system where inductive loads consume significant amounts of reactive power. This significantly reduces the reactive power supply pressure on the power plant. Users should design and install reactive power compensation devices based on improving the natural power factor of their electricity consumption, and ensure that they are promptly activated or deactivated according to load and voltage fluctuations to prevent reactive power backflow. At the same time, users’ power factor should meet appropriate standards to avoid power factor surcharges from power supply departments. Therefore, automatic reactive power compensation to improve power factor and prevent reactive power backflow is of great significance to both power supply departments and users, saving energy and improving operational quality. (2) Basic principles of reactive power compensation
The reactive loads generally referred to in the system are mostly inductive reactive loads. When a device with a capacitive power load is connected in parallel with an inductive power load in the same circuit, when the inductive reactive load absorbs energy, the capacitive load releases energy, and when the inductive load releases energy, the capacitive load absorbs energy. Energy is exchanged between the capacitive load and the inductive load. In this way, the reactive power absorbed by the capacitive load can be compensated by the reactive power output by the capacitive load device. The reactive power is balanced locally to reduce line losses, improve load capacity, reduce voltage losses and alleviate the power supply pressure of the power plant. This is the basic principle of reactive power compensation.
The basic principle of phase analysis reactive power compensation:
The current IL in the inductive load lags the voltage by 90°, while the current Ic in the pure capacitor leads the voltage by 90°. The current in the capacitor and the current in the inductor are 180° out of phase and can cancel each other out. Most of the loads in the power system are inductive loads, so the total current I will lag the voltage by an angle of Φ1. If a parallel capacitor is connected in parallel with the load, then I′＝I+IC, and the current of the capacitor will offset part of the inductive current, thereby reducing the total current from I to I′, and the phase angle is reduced from Φ1 to Φ2, which can improve the power factor and balance the reactive power locally.
(3) Compensation forms of reactive power compensation
1) Individual compensation
Individual compensation is a method of locally compensating the reactive power required by a single electrical equipment. The capacitor is directly connected to the same electrical circuit of the single electrical equipment, controlled by the same switch, and put into operation or disconnected at the same time. This compensation method has the best effect. The capacitor is close to the electrical equipment and balances the reactive current locally, which can avoid overcompensation when there is no load, and ensure the power supply quality. This compensation method is often used for electrical equipment such as high and low voltage motors. However, when the user equipment is non-continuously operating, the utilization rate of the capacitor is low and its compensation effect cannot be fully utilized.
2) Distributed compensation Distributed compensation is to install capacitors in groups on the outgoing lines of the workshop distribution room or each branch of the substation. It can be connected or disconnected according to the changes in the system load, and the compensation effect is relatively good. However, the cost is relatively high. 3) Centralized compensation Centralized compensation is to install all capacitors on the primary or secondary busbar of the substation. This compensation method is simple to install and reliable in operation, but the compensation effect is worse than the previous two compensation methods, and the cost is relatively high. (4) Benefits of reactive compensation 1) Compensate for reactive power and improve power factor (as shown in the figure below) 2) Reduce the loss of transmission lines and transformers Reasonable compensation can effectively reduce the system current. Taking the system natural power of 0.7 as an example, if the system power factor is increased to a level close to 1 through the compensation device, the system current will drop by about 30%, that is, the loss of the line and transformer can be reduced to P=I2R＝(1-30%)2R=0.49R, that is, the loss of the line and transformer can be reduced by 51%. The natural power factor of electricity users is generally around 0.7. The reduction in line losses and transformer copper losses when the power factor is increased from 0.7 to above 0.95 is shown in the following table:

Reducing line and transformer losses and saving active energy are important energy-saving measures. For example, in the oil industry, where lines are long and complex, adding reactive power compensation equipment can reduce operating current, thereby reducing line losses and saving active energy, resulting in significant energy savings.
3) Increasing the transmission capacity of the power grid and improving equipment utilization
Because compensation devices can effectively reduce system current and apparent power, they can effectively reduce the capacity of all related equipment in power grid construction, thereby reducing investment in grid construction. For systems with a power factor of around 0.7, effective compensation can reduce system current by 30%, increasing the load capacity of power plants and substations by 30%.
If transformers and lines are undersized and insufficient, installing reactive power compensation devices can address this issue. Installing a reactive power compensation device balances reactive power locally, reducing the current flowing through the line and transformer, slowing the aging of conductor and transformer insulation and extending its service life. It also frees up transformer and line capacity, increasing their load capacity.
For example, consider a 100kVA transformer currently operating at 85% load, with a COSΦ of 0.7. Installing reactive power compensation equipment can free up 30% of the transformer’s load capacity, allowing users to increase loads and expand production without increasing the transformer’s capacity.
4) Improving Voltage Quality
The presence of a large number of inductive loads in the system will cause voltage drop in the power supply line, especially at the end of the line. Proper compensation can effectively mitigate this voltage drop and improve power quality.
The formula for calculating voltage loss in the line is as follows:
Because the system’s inductive reactance is much greater than its impedance, changes in reactive power can cause significant voltage changes. When reactive power Q decreases in the line, voltage loss also decreases.
For low voltages at the end of the power supply line, adding a reactive power compensation device can increase the voltage, ensuring safe and reliable operation of the equipment. On the other hand, with the development of industry, the increasing use of automated control equipment and nonlinear loads has led to the flow of significant harmonics within the power supply and distribution network, polluting the grid. One of the primary means of improving power quality is to suppress or significantly reduce the impact of harmonics on the power supply system and consumer equipment through the appropriate configuration of compensation and filtering equipment.
5) Saving Electricity Bills
Through appropriate compensation, ensuring that the power factor at the metering point meets national standards can eliminate factor-based electricity charges, significantly reducing electricity bills for power users.
Note: The active energy savings achieved by dynamic reactive power compensation devices only reduce power supply and distribution losses between the compensation point and the generator. Therefore, reactive power compensation on the high-voltage grid side cannot reduce losses on the low-voltage valve side, nor can it increase the utilization rate of the low-voltage power transformer. According to optimal compensation theory, local dynamic reactive power compensation offers the most significant energy savings.