Abstract : This paper discusses the hazards of harmonics from the inability to connect compensation capacitors, analyzes the sources of harmonics, and proposes preliminary suggestions for harmonic mitigation. With the development of the private economy, especially the special steel and chemical industries, the power supply is constantly increasing. In order to achieve the power factor standard, compensation capacitors must be connected. However, the compensation capacitors in substations cannot be connected, and if they are forcibly connected, the capacitor fuses will blow quickly. But according to the operating experience of other substations, under this power factor, the reactive current should not be greater than the fuse blowing current. Why is this? After analyzing the current power supply situation, this is caused by harmonics. The so-called harmonics are that the ideal power system should provide users with a constant power frequency sinusoidal waveform voltage, but due to various reasons, this ideal state cannot exist in reality. Therefore, the content of components with frequencies that are integer multiples of the fundamental frequency obtained by Fourier decomposition of periodic voltage or current is called harmonics. Harmonics are very harmful to the power grid, mainly in the following aspects: 1. Because the power grid is mainly designed according to the fundamental frequency. Due to the presence of LC elements, although resonance does not occur at the fundamental frequency, it may occur at a specific harmonic frequency, potentially amplifying the harmonic current several times or even tens of times. Power grid resonance can cause overvoltage and harmonic overcurrent in equipment, damaging it, especially capacitors and reactors connected in series. Particular attention should be paid to capacitors, as they are capacitive loads and can resonate with inductive equipment on the power grid (most other equipment is inductive). Since their capacitance is inversely proportional to the harmonic frequency, capacitors are more likely to absorb harmonic resonance currents, causing overload, capacitor damage, or fuse blowout. 2. Harmonics cause additional losses (harmonic power) in electrical equipment on the power grid, reducing equipment efficiency. Harmonics also affect normal equipment operation, such as causing severe overheating of transformers, overheating of capacitors and cables, mechanical vibration in motors, aging and deterioration of insulation, and in severe cases, equipment damage. 3. Harmonics can cause relay protection and automatic devices to malfunction or fail to operate, resulting in unnecessary losses. Harmonics can also cause inaccurate measurements by electrical measuring instruments, leading to metering errors. In addition, harmonics can also cause interference to nearby communication systems and other hazards. Given the significant harm caused by harmonics, how are they generated, and how can their impact and harm be reduced? Sources of Harmonics: 1. Induction furnaces and electric arc furnaces are the main sources of harmonics in this region. Analysis of the region's load revealed that the primary reason is the prevalence of the special steel industry, leading to the widespread use of induction furnaces and electric arc furnaces as highly efficient heating sources. Electric arc furnaces utilize the electric arc generated between electrodes to melt metal; therefore, their current waveform is highly irregular, containing various harmonics (2nd to 7th) and interharmonics, making it a major source of harmonics. Induction furnaces, on the other hand, rectify the power frequency current to a medium frequency and then use electromagnetic induction to melt metal, thus generating a large number of high-order harmonics, primarily odd harmonics such as the 5th, 7th, and 11th. This is the main source of harmonics in this region. 2. User transformer groups are a significant source of harmonics in the region. Generally, three-phase transformers have a "sun" shaped core, with the middle phase being half the length of the side phases. Therefore, the asymmetry of the three magnetic circuits causes harmonic components in the transformer's excitation current. So, when voltage is applied to an unloaded three-phase transformer, even without a zero-sequence current path on the receiving side (neutral point ungrounded or delta connection), harmonic components will still be present in the excitation current. Although these harmonic components are small in actual operation, the standardized connection methods of transformer windings and the connections between each winding and each phase of the power grid cause the same harmonics in the excitation current of each transformer to superimpose, forming another important source of harmonics in the power grid. For example, in most distribution transformers, the connection is Y,yn, and the coil corresponding to the middle iron column of the transformer (i.e., the middle phase) is always connected to the B phase. This standardized connection provides a condition for the 3rd, 5th, and 7th harmonics to superimpose. In this region, there are currently 5 35kV user transformers with a total capacity of 400kVA and approximately 800 10kV user transformers with a total capacity of 330kVA. This large group of user transformers has become another significant source of harmonics. 3. Other Sources of Harmonics In fact, harmonics also originate from other sources, such as various industrial electricity consumption (e.g., electroplating, electric pumps) and household electricity consumption (e.g., televisions, computers, fluorescent lamps, etc.) using switching power supplies or other power electronic technologies. Individually, the harmonics generated are very small, but due to their sheer number, they are a significant portion that cannot be ignored. Harmonic Mitigation According to GB/T14549-93 "Power Quality and Harmonics in Public Power Grids," the harmonic voltage occupancy rate of the power grid should not exceed 4% at 0.4kV/10kV/35kV, respectively. Clearly, the power grid in this region is already severely "polluted." In view of the above situation, to reduce the chances of harmonic generation and minimize the harm of harmonics to the power grid, we propose the following suggestions: 1. Mitigate harmonic sources. Following the principle of "whoever interferes, pollutes, and treats," harmonic sources are managed locally. This means installing filters on the low-voltage side of the transformer for users generating significant harmonics. Depending on their operating principle, these filters can be categorized as passive power filters (PPF) and active power filters (APF). Passive power filters utilize the principle of capacitor and inductor resonance to absorb and block corresponding harmonics, thus ensuring a low voltage distortion rate. Generally, appropriate LC parameters are set according to the required harmonic order to be absorbed, and filters are installed accordingly. Some users in this area have already installed such passive filter compensation devices. 5th and 7th order filters are installed, using thyristor automatic switching, which compensates for reactive power while filtering harmonics. However, these passive devices cannot meet the requirements for rapid dynamic compensation of reactive power and harmonics. It is also important to ensure that the LC parameters do not happen to be the resonance parameters of another harmonic while filtering a certain harmonic, thus amplifying that harmonic. An active power filter is essentially a high-power harmonic generator. It collects harmonics emitted from a harmonic source using a harmonic sampling device, then completely replicates harmonics of equal magnitude but opposite direction, and connects them to the power grid to cancel out the harmonics. The generated harmonics vary depending on the harmonic source. It is a new type of filtering device, but it is expensive. 2. Modify some operating and wiring methods to reduce the generation, superposition, amplification, and potential hazards of harmonics. Increase the short-circuit capacity of the power grid and improve the short-circuit ratio of electrical equipment to reduce the impact of harmonics on other equipment on the same power grid. Strengthen real-time control during operation to avoid light load, high voltage operation, thus reducing the impact of excessively high harmonic voltage on system electrical equipment; consciously reconnect the intermediate phase of the distribution transformer to phase A or C to reduce harmonics generated by the transformer group. Where possible, connect in a delta or yn configuration to absorb harmonics on the high-voltage side. 3. In the design process, attention should be paid to avoiding opportunities for harmonic resonance to reduce its impact. According to the "Code for Electrical Design of Civil Buildings" JGJ/T16-923.3.10, "To control the distortion of the sinusoidal waveform of the power grid voltage caused by harmonics generated by various nonlinear electrical equipment within a reasonable range, the following measures should be adopted: When there are multiple voltage options available for transformers of various high-power nonlinear electrical equipment, if a lower voltage cannot meet the requirements, a higher voltage should be selected." In other words, when selecting high-power nonlinear electrical equipment such as medium-frequency furnaces, higher voltages should be chosen as much as possible. In reactive power compensation design, in addition to avoiding resonance between parallel capacitors and system inductive reactance, besides verifying the fundamental frequency, it is also necessary to verify the 3rd, 5th, and 7th major harmonics, avoiding these parameters to prevent resonance of these harmonics. "Harmonic pollution" has become one of the three major public hazards in the power grid. Only when all parties pay attention and take measures to control it can a clean environment be restored to the power grid.