Aiming at the electrical tree degradation and discharge breakdown of cross-linked polyethylene (XLPE) insulation for high-voltage cables, we prepared XLPE composite materials using photon-trapping voltage stabilizers, including two trifunctional triazine compounds (1,3,5-triallyl cyanurate (TAC) and triallyl isocyanurate (TAIC)) and two hydrogen-capturing phenyl ketones (4-methyl diphenyl ketone (MBP) and 4,4′-di-chlorobenzophenone (DCBP)). The influence rule of photon-trapping voltage stabilizers on the electrical tree degradation of XLPE composite materials was studied, and the photon trapping and excitation properties of the aromatic photon-trapping compounds, and their chemical reaction pathways were analyzed. The inhibition mechanism of the additive types on the electrical tree degradation was explored by using quantum chemical calculations. The results show that the addition of DCBP and TAC with the mass fraction of 1% can increase the initial voltage and initiation time of electrical tree in XLPE insulation. Compared with the pure XLPE insulation under the same voltage, the electrical tree length of DCBP/TAC/XLPE composite insulation decreases by 16.3%, the cumulative damage area decreases by 72.8%, and the maximum amplitude of partial discharge decreases by 29.7%, which shows the best partial discharge suppression and resistance to electrical trees. According to the quantum chemical calculations, MBP and DCBP have strong photon absorption properties, and DCBP can absorb photons with a wavelength of 334 nm, demonstrates a higher reactivity than MBP, and is more capable of capturing photons generated by partial discharge to hinder the damage of photons on the XLPE molecular chain. According to the reaction pathway analysis, DCBP molecure enters excited state after capturing photons, which triggers the proton transfer within the XLPE molecular chains, and promotes the free radical cross-linking reaction between TAC and PE molecular chain, thereby enhancing the local stability of the molecular chain and inhibiting the electrical tree deterioration of XLPE insulation.

The researches on the effect of liquid additives on the improvement of processing characteristics and physical properties of crosslinked polyethylene (XLPE) insulation materials for high-voltage cables are insufficient. In this paper, liquid crosslinking agents and antioxidants were taken as research objects. The effects and mechanisms of liquid additives on the scorch resistance, gel content, crosslinking by-products, thermodynamic and dielectric properties of XLPE were discussed. The results show that the liquid cross-linking agent 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane with a high decomposition temperature and long-chain alkyl groups involved in crosslinking reaction can simultaneously enhance the scorch resistance and gel content of XLPE insulation materials, and reduce the content of crosslinking by-products. Meanwhile, the liquid antioxidants α-tocopherol and sorbitol exhibit excellent compatibility, they can form temperature-dependent proton transfer interactions, which can improve the anti-scorch performance of XLPE without compromising its gel content. Additionally, these liquid crosslinking agent and antioxidants can improve the breakdown performance of XLPE insulation while maintaining its thermodynamic properties. This study proves the feasibility of applying liquid additives to XLPE insulation for high-voltage cable.

To investigate the influence and mechanism of extrusion temperature on the mesoscale crystalline morphology and comprehensive performance of high-voltage cable insulation materials, we prepared three types of insulation materials by controlling the extrusion temperature. Systematic characterization, electrical and mechanical performance testing, and simulation were employed to reveal the structure-property relationship between crystalline morphology and material performance. The results show that at an extrusion temperature of 120℃, the insulation material exhibits densely packed and uniform crystal configuration, and shows optimal crystallinity and crystal size, which is 42.28% and 15.15 μm, respectively. The improvement of crystal morphology can slightly enhance the dielectric constant of insulation materials and maintain extremely low dielectric loss, while can significantly increase the adhesive yield, volume resistivity, electric strength, and elongation at break of insulation materials. According to the mutual verification of simulation and experimental results, it is concluded that complete crystal configuration, larger crystal size and crystallinity can minimize the distortion degree of electric field in the amorphous region, suppressing the occurrence of partial discharge and breakdown, resulting in the electric strength reaching the optimal value (390 kV/mm).

The extrusion process technology of semi-conductive shielding material (SCSM) for high-voltage cables is crucial for the uniform dispersion and distribution of conductive carbon black (CB), as well as the interfacial interaction between CB and matrix resin. To investigate the influence of processing methods and parameters on the structure and properties of SCSM, this study employed twin-screw extrusion granulation and single-screw extrusion sheet processes. The influence of extrusion temperature, screw speed on the microstructure, electrical properties, mechanical properties, and surface smoothness of the SCSM were investigated. The results show that the optimal parameters for the twin-screw extrusion granulation process are 160℃ of extrusion temperature and 120 r/min of screw speed. Under these conditions, the volume resistivity of the shielding material at 23℃ and 90℃ is 9.6 Ω·cm and 265.0 Ω·cm, respectively. In the single-screw extrusion sheet process, when the extrusion temperature and screw speed are 105℃ and 50 r/min, respectively, the CB achieves sufficient shear force and dispersion time, effectively preventing pre-crosslinking of the SCSM. Consequently, there is no protrusions larger than 50 μm in diameter observed on the surface of the shielding material.

The aggregate structure, microcrystalline structure, and surface chemical properties of domestically developed conductive carbon black (CB) were compared with that of international commercial products, and the comprehensive performance of semi-conductive shielding materials prepared by filling CB were studied. The results show that the domestic CB exhibits comparable aggregate structures, microcrystalline dimensions, and carbon content with the imported CB, while the domestic CB contains 0.51% of sulfur elements and demonstrates lower particle size uniformity, alongside a significant variance in the content of various surface functional groups. The semi-conductive shielding material prepared with domestic CB achieves equivalent electrical and mechanical performance to that prepared with imported CB, but its surface smoothness is inferior, which does not meet the industry requirements. It is concluded that the uniformity of particle size, contents of surface functional groups, and the sulfur content are important research direction for structural optimization and performance improvement of domestic conductive carbon black, and surface smoothness is a significant research focus for the development of domestic high-voltage semi-conductive shielding materials.

To improve the thermal ageing resistance of crosslinked polyethylene (XLPE), different contents of anti-ager 2-mercaptothiazole (MB) were blended with PE, and then MB/XLPE sheet samples were prepared through electron irradiation process. The effect of MB content on the crosslinking degree, thermal elongation performance, insulation properties, oxidation induction period, and carbonyl index of XLPE were studied. The results show that with the increase of MB content, the gel content and thermal elongation performance of MB/XLPE composites reduce, while the volume resistivity maintains stable. The addition of MB significantly extends the oxidation induction period and suppresses the carbonyl index growth of XLPE during thermal ageing. When the weight part of MB is 1, the oxidation induction period of MB/XLPE significantly increases from 0.9 min (for pure XLPE) to 80 min; after thermal ageing for 168 h at 165℃, and the carbonyl index of MB/XLPE only increases from 0.04 to 0.06, indicating marked improvement in thermal ageing resistance. Based on the Arrhenius equation, it is concluded that this MB/XLPE exhibits a service life of 76.2 years at 90℃ which is 2.5 times longer than that of conventional XLPE.

To investigate the ageing characteristics and lifetime evaluation methods of graft-modified polypropylene cable insulation materials, accelerated thermal ageing tests were conducted on the samples at different temperature, and the changes in electrical and physicochemical properties of graft-modified polypropylene cables at various ageing stages were studied. The variation of key characteristic parameters, such as melting temperature, relative dielectric constant, and elongation at break with ageing time was analyzed. The results show that the melting temperature, electric strength, and elongation at break are significantly correlated with ageing time, and these parameters can be used as effective indicators for assessing the ageing degree of graft-modified polypropylene cable insulation materials.

To study the internal relationship between space charge transport and polarization/depolarization current of cross-linked polyethylene (XLPE) cable insulation in direct current (DC) field, a space charge-current combined measurement platform was established based on PEA method. The combined measurements were conducted on XLPE cable insulation samples with different ageing time. Parameters such as total charge, carrier mobility, and trap distribution in XLPE samples were evaluated using the combined variation data of space charge and current. The results show that at room temperature and 20 kV/mm, homopolar charges accumulation occurs obviously within the sample, and with the increase of test temperature; the charge polarity changes to the opposite. With the increase of ageing time, the number of accumulated heteropolar charges in the aged samples increases at first and then decreases, and the range of positive charge accumulation expands from near the anode to near the cathode; the decay rates of polarization and depolarization currents in the aged samples decrease, the steady value of polarization current increases, and the depolarization current increases at first and then decreases. With the increase of ageing time, the total amount of charge within the samples increases at first and then decreases, while the conductivity and carrier mobility increase. Notably, the carrier mobility significantly increases when the samples are ageing for more than 10 days, causing the charge accumulation range to gradually extend further from the anode, resulting in a significant reduction in the total amount of accumulated charges within the samples. The trap depth of XLPE samples increases gradually with the increase of ageing time, which is the reason for the reduced decay rate of depolarization current in the aged samples.

To study the ablation mechanism of water-blocking buffer layer in high-voltage cable and reveal its critical conditions, the dielectric performance parameters of water-blocking buffer layer material with different water contents were measured. A three-dimensional non-axisymmetric corrugated aluminum sheath structure cable geometric model was constructed based on gravity effects to conduct electro-thermal-flow multi-physics field coupled finite element simulation. Experimental verification was conducted using a constant current simulated ablation test system, and the voltage and temperature variations during the ablation process were monitored in real-time. The results show that poor contact and moisture are necessary conditions for ablation. When the aluminum sheath is poorly contacted with the buffer layer, electric field concentration occurs near the gaps at the well-contacted positions, and partial discharge can be triggered when the moisture content reaches 5%. In well-contacted areas of buffer layer, capacitive current concentration causes localized temperature rise, and the local temperature would reach the ablation initiation threshold at the water content of 25%. According to the experimental results, ablation only occurs when the aluminum electrode is poorly contacted with the buffer layer, while only electrochemical corrosion is observed under good contact conditions. Electrochemical corrosion initially produces high-resistance white powder, followed by partial discharge, which makes the voltage and temperature rise steadily. With the occurrence of partial discharge, the voltage can reach 147 V, and the temperature can reach 187.8℃, causing partial melting of polyester fibers in the buffer layer, further leading to current concentration, and ultimately causing thermal breakdown of the water-blocking buffer layer material.

To investigate the critical conditions of high voltage cable buffer layer ablation, the types of insulation shielding damage caused by actual cable ablation were summarized in this paper. A three-dimensional asymmetric high-voltage cable model was established by finite element simulation. The ablation development process of high-voltage cables under both dry and wet conditions, as well as the mechanisms of their damage to insulation shielding, were studied separately. The difficulty of ablation under the two conditions was compared and analyzed. The results show that damage under dry condition is attributed to current-induced thermal effects caused by prolonged poor contact. When poor contact extends to 7.5 m, the surface current density on the buffer layer reaches as high as 442 A/m², and the temperature reaches high as 200℃ within the buffer layer. Damage under wet condition arises from current-induced thermal effects caused by the high resistance products from electrochemical corrosion, and these products can penetrate areas where current and temperature are concentrated within the buffer layer. When the coverage rate of white powder reaches 97.9%, the surface current density on the buffer layer is up to 416 A/m². Simulation results align closely with actual dissolution observed in faulty cables affected by ablation, thus validating our analysis findings presented in this paper.