Abstract: For power supply companies across the country, especially for some of the upgraded rural power grids nationwide, effective low-voltage compensation can not only alleviate the pressure on the upstream power grid and improve the power factor of users, but also effectively reduce energy losses and lower electricity costs for users. 1. Introduction Power factor refers to the percentage of apparent power in a power grid that is used to supply active power. In the operation of a power grid, a higher power factor is desirable. If this is achieved, most of the apparent power in the circuit will be used to supply active power, reducing reactive power consumption. The level of the user's power factor has a significant impact on the full utilization of power generation, supply, and consumption equipment in the power system. Appropriately improving the user's power factor can not only fully utilize the production capacity of power generation and supply equipment, reduce line losses, and improve voltage quality, but also improve the working efficiency of user equipment and save energy for the user. Therefore, for the vast number of power supply companies across the country, especially for some of the rural power grids that have undergone upgrades nationwide, effectively managing low-voltage compensation can not only alleviate the pressure on the upper-level power grid and improve the power factor for users, but also effectively reduce energy losses and lower electricity costs for users. The social and economic benefits will be very significant. 2. Main Factors Affecting Power Factor First, let's understand the main reasons for the generation of the power factor. The power factor is mainly generated because AC electrical equipment, in its operation, requires reactive power in addition to active power. When the active power P is constant, reducing the reactive power Q will improve the power factor. In extreme cases, when Q=0, the power factor = 1. Therefore, the essence of improving the power factor is to reduce the reactive power requirement of electrical equipment. 2-1. Asynchronous motors and power transformers are the main equipment consuming reactive power. The air gap between the stator and rotor of an asynchronous motor is the main factor determining the large amount of reactive power required by the asynchronous motor. The reactive power consumed by an asynchronous motor consists of two parts: its reactive power under no-load conditions and the increase in reactive power under a certain load. Therefore, to improve the power factor of an asynchronous motor, it is necessary to prevent the motor from operating under no-load conditions and to maximize the load factor. The main component of reactive power consumed by a transformer is its no-load reactive power, which is independent of the load factor. Therefore, to improve the power factor of the power system and enterprises, transformers should not operate under no-load conditions or be in a low-load operating state for extended periods. 2-2. Supply voltage exceeding the specified range will also have a significant impact on the power factor. When the supply voltage is 10% higher than the rated value, reactive power will increase rapidly due to the effect of magnetic circuit saturation. According to relevant statistics, when the supply voltage is 110% of the rated value, the reactive power in a typical factory will increase by about 35%. When the supply voltage is lower than the rated value, the reactive power will decrease accordingly, thus improving their power factor. However, a decrease in supply voltage will affect the normal operation of electrical equipment. Therefore, measures should be taken to keep the supply voltage of the power system as stable as possible. 2-3. Fluctuations in grid frequency can also affect the magnetizing reactive power of asynchronous motors and transformers. In summary, we know some of the main factors affecting the power factor of a power system. Therefore, we need to seek some effective and practical methods to improve the power factor of low-voltage power grids, enabling local reactive power balance and achieving energy saving. 3. General Methods of Reactive Power Compensation in Low-Voltage Grids There are three main methods commonly used for low-voltage reactive power compensation: random compensation, device-specific compensation, and tracking compensation. The following is a brief introduction to the applicable scope and advantages and disadvantages of these three compensation methods. 3-1 Random Compensation Random compensation involves connecting low-voltage capacitor banks in parallel with the motor, and switching them on and off simultaneously via control and protection devices. Random compensation is suitable for compensating the reactive power consumption of motors, mainly by compensating for excitation reactive power. This method can effectively limit peak reactive loads in rural power grids. The advantages of random compensation are: reactive power compensation is activated when the equipment is running, and deactivated when the equipment stops, without the need for frequent adjustments to the compensation capacity. It features low investment, small footprint, easy installation, convenient and flexible configuration, simple maintenance, and low failure rate. 3-2. On-line compensation On-line compensation refers to connecting low-voltage capacitors to the secondary side of the distribution transformer through low-voltage fuses to compensate for the no-load reactive power of the distribution transformer. The reactive load of the distribution transformer under light load or no load is mainly the no-load excitation reactive power of the transformer. The no-load reactive power of the distribution transformer is the main part of the reactive load of the rural power grid. For distribution transformers with light load, this part of the loss accounts for a large proportion of the power supply, resulting in an increase in the unit price of electricity, which is not conducive to the same price for electricity in the same grid. The advantages of on-line compensation are: simple wiring, convenient maintenance and management, effective compensation for the no-load reactive power of the distribution transformer, limiting the reactive base load of the rural power grid, and balancing this part of the reactive power locally, thereby improving the utilization rate of the distribution transformer, reducing reactive power network losses, and having high economic efficiency. It is one of the most effective means of reactive power compensation at present. 3-3. Tracking Compensation: Tracking compensation refers to a compensation method that uses a reactive power compensation switching device as a control and protection device to compensate low-voltage capacitor banks on the 0.4kV busbar of large users. It is suitable for dedicated distribution transformer users above 100kVA and can replace random and device-based compensation methods, with good compensation effect. The advantages of tracking compensation are flexible operation, less operation and maintenance workload, and a relatively longer lifespan and more reliable operation compared to the previous two compensation methods. However, the disadvantages are complex control and protection devices and relatively large initial investment. But when the economics of these three compensation methods are similar, tracking compensation should be given priority. 3-4. Taking Appropriate Measures to Improve the System's Natural Power Factor: Improving the natural power factor is a method of improving the power factor of industrial and mining enterprises by reducing the reactive power required by each electrical device and reducing the reactive power taken by the load without adding any compensation equipment. It does not require additional investment and is the most economical method to improve the power factor. A brief introduction to measures to improve the natural power factor will be given below. 3-5. Rational Use of Motors: Rationally select the model, specifications, and capacity of motors to ensure they operate close to full load. When selecting an electric motor, both its mechanical performance and electrical specifications must be considered. If a motor operates under low load for an extended period, it increases power loss and significantly deteriorates both the power factor and efficiency. Therefore, from the perspective of saving energy and improving the power factor, it is essential to correctly and rationally select the motor's capacity. 3-6 Improving the Maintenance Quality of Asynchronous Motors: Experiments show that variations in the number of turns in the stator winding and the air gap between the stator and rotor of an asynchronous motor have a significant impact on its reactive power. 3-7 Improving the Power Factor by Using Synchronous Motors or Synchronous Operation of Asynchronous Motors: As the principle of motors tells us, the active power consumed by a synchronous motor depends on the size of the mechanical load on the motor, while reactive power depends on the magnitude of the excitation current in the rotor. In an under-excited state, the stator winding "absorbs" reactive power from the grid; in an over-excited state, the stator winding "sends" reactive power to the grid. Therefore, by adjusting the motor's excitation current to an over-excited state, the synchronous motor can "send" reactive power to the grid, reducing the reactive power supplied to industrial and mining enterprises and thus improving their power factor. Synchronous operation of an asynchronous motor involves appropriately connecting the three-phase rotor windings of the asynchronous motor and applying a DC excitation current, causing it to operate like a synchronous motor. This is known as "synchronization of asynchronous motors." Therefore, by adjusting the DC excitation current of the motor to an overexcited state, reactive power can be output to the grid, thereby improving the power factor of the low-voltage network. 3-8 Reasonable selection of transformer capacity and improvement of transformer operation: For transformers with low load rates, methods such as "removal, replacement, paralleling, and shutdown" are generally adopted to increase their load rate to the optimal value, thereby improving the natural power factor of the grid. Through the above descriptions of improving the weighted average power factor and natural power factor, we may have gained a deeper understanding of the simple electrical term "power factor." Knowing the profound impact of improving the power factor on power companies, we will now briefly introduce the methods of artificial compensation for electrical equipment and the method for determining the compensation capacity. 4. Artificial Compensation of Power Factor The power factor is a representative and important indicator of the usage and utilization level of electrical equipment in a factory, and it is also a major indicator for ensuring the safe and economical operation of the power grid. Power supply companies can no longer meet the power factor requirements of factories simply by improving the natural power factor. Factories also need to install compensation devices to manually compensate for the power factor. Methods for manually compensating electrical equipment include: 4-1. Static capacitor compensation. When a company has many inductive loads, the reactive power they draw from the power supply system is lagging (negative) power. If a set of capacitors is connected in parallel with the inductive loads, the reactive power required by the capacitors is leading (positive) power. If the capacitor C is chosen appropriately, and QC + QL = 0, the company no longer needs to draw reactive power from the power supply system, and the power factor is 1, reaching the optimal value. (1) Determination of capacitor compensation capacity (2) Parallel compensation phase-shifting capacitors should meet the following voltage and capacity requirements: Ue.c ≥ Ug.c nQg.c ≥ QC Where Ue.c——rated voltage of capacitor (KV) Ug.c——operating voltage of capacitor (KV) n——total number of capacitors in parallel Qg.c——operating capacity of capacitor (KVar) QC——compensation capacity of capacitor (KVar) 4-2. Dynamic reactive power compensation Dynamic reactive power compensation is generally applied to large steel enterprises with large power consumption, rapid load changes in the production process and repetitive impacts. This kind of dynamic reactive power fluctuates frequently, rapidly and with large amplitude. Compensation by synchronous condensers or fixed capacitors is far from meeting the requirements. At present, the new type of dynamic reactive power compensation equipment generally used is the static var compensator. It has the advantages of stabilizing system voltage, improving power grid operation performance, rapid dynamic compensation response, and superior regulation performance. However, the most obvious disadvantage is that the investment is large, the equipment size is large and the footprint is large. 5. Conclusion This paper focuses on the impact of power factor on power supply companies and the economic and social benefits of improving power factor. It introduces the main factors affecting power factor and general methods for improving it. It also discusses how to determine the reactive power compensation capacity and two specific methods for applying manual reactive power compensation.