Polypropylene (PP) exhibits excellent insulation properties, high thermo-stability, and recyclable nature, thus expected to be the next-generation insulation material for HV cable application. Chemical grafting modification is an effective technology to improve the electrical properties of polypropylene. In this paper, we develop and report a new-type grafted PP insulation material by water-phase grafting technology. The comprehensive properties including electrical, thermal, and mechanical of it are tested and compared with traditional cable insulation material—crosslinked polyethylene (XLPE). The results show that the grafted PP holds superior thermal properties and enough mechanical flexibility. The electrical properties are of significant advantages, including resistivity enhanced by nearly two degrees of magnitudes, AC/DC breakdown strength raised by over 20%, and obviously suppressed space charge accumulation. These results indicate that grafted PP is very suitable for application in HV cable systems, either AC or DC. This research lays a foundation for the research and development of the next-generation recyclable polypropylene cables at higher voltage levels.

Polypropylene (PP) is regarded as an environmentally friendly cable insulation material to replace cross-linked polyethylene owing to its thermoplastic nature, high-temperature resistance, and outstanding dielectric characteristics. Grafting modification was applied to satisfy the demand for a higher-voltage power grid, and it was proved to be effective in enhancing the insulating performance of PP. The electrical tree is a common cause of cable insulation failure. This study examines the electrical tree initiation and growth characteristics of methyl methacrylate (MMA) grafted PP under different temperatures. Our results indicate that high temperature can promote the electrical treeing process, while grafting modification can hinder the process. The trap characteristics show that more deep traps are introduced in the grafted materials that can limit the motion of electrons and, thus, restrict the electrical tree initiation process. The crystallization morphology shows that the size of spherulites increases and the boundaries of the spherulites become blurry with higher MMA content. The compressed amorphous region and the tortuous boundaries of the crystalline can hinder the electrical treeing process. High temperature may improve charge carrier mobility and enhance the molecular chain relaxation, thus enlarging the free volume and finally accelerating the treeing process. The findings of this study would serve as a reference for designing grafted pP insulation for power cables.

To reduce the damage from the power frequency follow current of distribution lines, a multi-fracture compression airflow arc-extinguishing structure is studied. The structure is mainly composed of a compression tube, a metal electrode, and metal connection fittings, and the multi-fracture compression airflow arc-extinguishing body is formed by the combination of packaging and insulation fittings. The body and the air gap are parallel to both ends of the insulator. When lightning strikes, the internal short gap of the main body and the air gap break down, and the lightning arc enters the arc-extinguishing body through the breakdown channel. In the structure, the arc is compressed by force to form internal and external gradients of temperature and to produce jet airflow. The jet airflow acts on the subsequent power frequency follow current arc, which is suppressed and extinguished. In this paper, a model coupling an arc and a compressed jet airflow in a multi-fracture compression airflow arc-extinguishing structure is established theoretically and simulated by simulation software. Finally, a power frequency follow current interruption test is carried out. The simulation results show that a high-speed airflow of 600 m/s is formed around the fracture at approximately 0.99 ms, and the airflow is proportional to the rate of temperature variation. The test results show that the power frequency follow current of 1.289 kA is cut off within approximately 3 ms without a reburning phenomenon. The effect of power frequency follow current interruption is obvious in the structure.

To avoid the restriction of the arc energy on the energy quenching of an arc and rapidly quench the arc to restore the insulation characteristics of the gas, the process of arc quenching by an explosion air shock wave is studied in this paper. The interaction between an explosion air shock wave and an arc is considered inside a cylinder structure so that concentrated pressure and airflow velocity can be produced. First, a coupling model of the explosion air shock wave and arc is developed theoretically. Second, according to the model, the explosion air shock wave and arc are simulated by finite element simulation software. It is found that the interaction between the explosion air shock wave and arc is most intense at 0.04 ms, the arc is driven out of the cylinder at 0.087 ms, and then, the arc is gradually quenched. Finally, the test results show that the arc is completely quenched at approximately 0.80 ms, and the value of the peak current is 1 kA. Although there is error between the simulation and test results, the effectiveness of the explosion air shock wave in quenching the arc is still verified, and the arc is quenched over a time scale of milliseconds.

The increasing demand for polymer dielectrics in different scenarios, such as electrical insulation cable, requires elevated electrical and mechanical properties. In order to understand the relationship between mechanical properties and the structure of grafted monomers in a grafted polypropylene (PP) system, a design framework based on the transfer-learning method has been proposed for designing grafted side chain structure in PP system. 22 samples of polypropylene-grafted polymer are synthesized. Through a well-trained multi-layer perceptron model for predicting glass transition temperature (Tg), mechanical properties of the grafted PP have been well predicted by the transfer-learning method. Meanwhile, the grafting group structures are divided into nine substructures. By assembling these substructures, the chemical space is established for prediction. Moreover, candidates with satisfied deep traps and flexible mechanical properties are screened out for reference. This work turns qualitative understanding into a quantitative analysis based on mathematical models and broadens the application of polymer materials design with a small dataset.

Polyurethane (PU) materials are extensively utilized in power equipment. This paper introduces a comprehensive evaluation method that combines electromagnetics and computational chemistry based on the Density Functional Theory (DFT) to elucidate the impact of external electric fields on the molecular structure of PU during electrical contact. The study focuses on the microstructural and molecular energy changes in the hard (HS) and soft (SS) segments of PU under the influence of an electric field of uniform intensity. Findings indicate that the total energy of HS molecules decreases markedly as the electric field intensity increases, accompanied by a significant rise in both the dipole moment and polarizability. Conversely, the total energy and polarizability of the SS molecules decrease, while the dipole moment experiences a slight increase. Under the influence of a strong electric field, HS molecules tend to stretch towards the extremities of the main chain, leading to structural instability and the cleavage of hydroxyl O-H bonds. Meanwhile, the carbon chain of the SS molecules twists towards the center under the electric field, with no chemical bond rupture observed. At an electric field intensity of 8.227 V/nm, the HOMO-LUMO gap of the HS molecule narrows sharply, signifying a rapid decline in the molecular structure stability, corroborated by infrared spectroscopy analysis. These findings offer theoretical insights and guidance for the modification of PU materials in power equipment applications.