ABSTRACT The incorporation of nanocellulose‐doped insulating paper into the material composition of a given structure has been demonstrated to enhance the material’s mechanical properties and retard the development of cracks. However, the effects of different length‐to‐diameter ratios of nanocellulose are different. In this paper, multi‐scale doped modified insulating paper with different mass fractions were prepared. The modification mechanism of multi‐scale doped modified insulating paper and its advantages were analysed in terms of the dynamic reorganisation of hydrogen bonding during the fracture process of the insulating paper, fibre bridging during the development of microcracks, and the interfacial and agglomeration effects of microfibrillated/nanocellulose, modified paper retains insulating properties while enhancing mechanical properties. At the same time, based on the Halpin–Tsai model, introducing the fibre orientation factor and incorporating the calculation of agglomerate and interfacial phases was also undertaken. This approach enabled the prediction of Young’s modulus for multi‐scale doping system and single‐scale doped modified insulating paper, and the optimal ratio of multi‐scale mixed fibre doping is derived based on the modified mechanical model. The experimental findings demonstrate that the modified mechanical model exhibits numerical stability and universality in terms of Young’s modulus prediction error, with a maximum error of 6.07% and a minimum error of 0.7% across different batches of insulating paper. The multi‐scale doped modified insulating paper and the mechanical quantitative model hold significant potential in enhancing the mechanical properties of insulating paper and its prediction.

ABSTRACT Power lines in synthetic‐aperture radar (SAR) images are reflected as point signatures, which fluctuate annually in both the azimuth and range directions. A novel framework is proposed in this paper to evaluate the four‐dimensional dynamic status of power line sag using those point signatures in time‐series SAR images. An inversion model is proposed to reconstruct the three‐dimensional power line sag profile based on the point signature positions and power line suspension points in the SAR coordinates. By combining the elevation function and the power line parabolic function derived in the SAR image, the 3D geometry of power line sag can be reconstructed using the range–Doppler model. A sag–temperature model is proposed to evaluate the 4D dynamic status of power lines in time‐series SAR images. The results show that the proposed model has been able to identify one of the power line sag failure events in the study area, which occurred around September 2016, with an approximate 2.54‐m line sudden sag downward. This case study shows the potential of spaceborne SAR for real‐time power line sag monitoring, particularly under extreme weather conditions.

ABSTRACT Boron nitride (BN), characterised by its wide band gap and robust dielectric properties, has emerged as a promising filler for polymer‐based dielectric composites. Nevertheless, its practical implementation in polymer matrices has been hindered by poor dispersibility and inadequate interfacial adhesion. This study addresses these challenges by developing hyperbranched polymer (HBP)‐functionalised BN (HBP‐BN) and fabricating HBP‐BN/cellulose nanofiber (CNF) composite films via vacuum‐assisted self‐assembly. The HBP‐BN/CNF films demonstrate a low dielectric loss (tan δ < 0.016) and significantly improved volume resistivity (10 9 Ω·m) and high thermal stability (55.36% residual mass at 800°C). Notably, the surface flashover voltage is elevated from 13.82 to 15.61 kV, demonstrating superior insulation capability. All these results highlight the promising potential of HBP‐BN/CNF composite films for use as advanced dielectric materials, providing a novel approach to develop eco‐friendly high‐performance materials for high‐voltage insulation systems in next‐generation electronics and electrical devices.

ABSTRACT This study examines transient overvoltage phenomena in 525 kV high‐voltage direct current (HVDC) onshore cable systems, with particular emphasis on the influence of grounding configurations in two joint types: straight‐through and screen‐separated. Transient overvoltages arising from wave propagation and reflections are analysed, highlighting the impact of joint types, bonding cable configurations (coaxial vs. noncoaxial) and bonding cable length on the resulting overvoltage magnitudes. The necessity of modelling screen‐to‐earth representations of sectionalised cables at grounded joint locations in the vicinity of faults is emphasised, whereas simplified representations of ungrounded and grounded straight‐through joints are identified as sufficient for system‐level simulations. To address the computational challenges of detailed electromagnetic transient simulations, a stand‐alone simplified circuit is proposed to analyse grounded joint transients and to mitigate errors caused by insufficient time‐step resolution. The results provide practical insights for insulation coordination, supporting the reliable integration of HVDC technology into long‐distance cable‐based transmission networks while enhancing system resilience.

ABSTRACT In gas‐insulated high‐voltage direct current (HVDC) devices, micro partial discharges (PD) caused by micro‐protrusions or surface roughness on conductors or enclosures may not cause immediate insulation system failure due to their weak discharge intensity. However, the continuous charging of carriers generated by the discharges to the insulator is one of the potential triggers of surface flashover of insulators. This work investigates the micro PD characteristics in SF 6 at 0.1–0.7 MPa, which is below the lower limit of conventional detection methods, via a highly sensitive micro‐discharge measurement platform. The experimental results show that the micro PD exhibits a strong polarity effect. With increasing pressure, the mean amplitude and mean repetition rates exhibited an extremum at 0.3 MPa. As the applied voltage increased, the mean amplitude shifted from negative polarity dominance over positive polarity to positive polarity dominance over negative polarity. Time‐resolved PD (TRPD) and pulse sequence analysis (PSA) patterns indicate that the micro PD is characterised by clustered bursts and amplitude stratification. Furthermore, the negative polarity micro PD is more stable than the positive polarity counterpart. The results of this work can provide references to guide the optimized design of gas‐insulated HVDC devices.

ABSTRACT Modern high‐voltage electrical equipment operates in complex environments where surface conditions are subjected to multifaceted influences from electric fields, thermal gradients, contaminants, irradiation and other extreme environmental factors. Under high‐voltage conditions, surface flashovers frequently initiate at the gas–solid interface of insulators, jeopardising the operational reliability of industrial systems. To address flashover challenges in practical electrical equipment, this review systematically analyses the impact of environmental variables—including gaseous media, voltage waveforms, contaminants and high‐energy irradiation—on surface flashover characteristics. Subsequently, we comprehensively synthesise the mechanisms, contributing factors, suppression techniques and enhancement strategies for surface flashover in four critical equipment categories prone to this phenomenon: high pulsed power systems, spacecraft operating in vacuum environments, gas‐insulated switchgear/transmission lines (GIS/GIL) and outdoor insulators. The environmental dependencies of flashover behaviour in these systems are rigorously examined. Furthermore, to advance flashover prevention in next‐generation industrial applications, this study identifies 25 fundamental scientific questions and 25 technical questions to guide future research directions. By establishing an integrated theoretical framework and methodological foundation for engineering‐oriented flashover studies, this work provides actionable insights and mitigation approaches to enhance the surface insulation of modern industrial infrastructure.

ABSTRACT This paper presents a simplified equivalent circuit model (ECM) for the post‐arc sheath stage in DC vacuum circuit breakers and outlines the method for calculating circuit parameters using the particle‐in‐cell Monte Carlo collision (PIC‐MCC) method. The post‐arc sheath is modelled as a parallel combination of a variable resistor and a variable capacitor. Based on a specific DC experimental case, the PIC‐MCC simulation provides essential parameters of charged particles and electric field data for calculating equivalent resistance and capacitance. The total current through the circuit components is calculated by applying the transient recovery voltage (TRV), and the resulting post‐arc current (PAC) waveform is compared with experimental results to validate the simplified ECM and the proposed parameter calculation approach. Further simulations study the impact of the initial drift velocity of charged particles on equivalent circuit parameters and PAC traces, showing that higher drift velocities increase capacitance and decrease resistance, leading to higher PAC peaks. The comparison with experimental data indicates that considering the drift velocity contributes to the simulation accuracy.

ABSTRACT In order to meet the needs of mechanical properties of cable insulation, polypropylene (PP) needs to be blended with low modulus materials to achieve toughening and softening. However, the compatibility between two or more resins can significantly affect the electrical properties of the composites. To solve this problem, the styrene–ethylene/butylene–styrene block copolymer (SEBS) with high heat resistance is selected as the blending elastomer, and grafted polypropylene (GPP) is prepared to be as basic resin. The morphological structure, thermal properties, mechanical properties and high temperature DC electrical properties of PP, GPP, PP/SEBS and GPP/SEBS are studied. The results demonstrate that compared with PP/SEBS, GPP/SEBS has significantly refined ‘island phase’ structure, further reduced storage modulus and slightly increased tensile strength and elongation at break and higher viscosity at low shear frequency. Electrical properties test results show that the grafted composite exhibits obvious suppression effect on space charge and conductance current, and enhances the DC breakdown strength. The introduction of the grafted material not only effectively improves the compatibility of the composites but also significantly improves the electrical properties of the material. This result can provide a reference for the development of eco‐friendly high voltage cable materials.

ABSTRACT Cross‐linking byproducts in the cross‐linked polyethylene (XLPE) cable insulation material significantly affect the insulation properties of XLPE, and the non‐destructive detection method for cross‐linking byproducts during cable degassing process still faces great challenges. This work develops an extra‐low frequency (ELF) dielectric analysis method based on time‐dependent polarisation current for non‐destructive detection of byproducts in XLPE. The effects of single byproduct of acetophenone and cumyl alcohol on the ELF dielectric properties of XLPE are studied separately. The ELF associated static permittivity and the dielectric loss of XLPE rise as the content of the single byproduct increases, and the α relaxation (10 −4 –10 −3 Hz) and β relaxation (10 −3 –10 −2 Hz) of XLPE are observed. Ionisation of acetophenone occurs above electric field strength of 20 kV, whereas ionisation tends to saturate above 50 kV. The optimal field strength for ELF dielectric testing of XLPE is determined to be 20–50 kV. Furthermore, the degassing factor is proposed to accurately determine the removal of byproducts. Based on these, the non‐destructive detection of degassing of XLPE cable is achieved. The proposed ELF dielectric analysis method enables the non‐destructive detection of byproducts in cables, opening a new avenue for cable degassing effect evaluation.

ABSTRACT The high‐voltage cable is one of the key equipment for power transmission, and its reliable operation depends on the crosslinked polyethylene (XLPE) insulation. The XLPE insulation not only requires excellent dielectric performance but also remarkable high‐temperature stabilities, including the antiscorching characteristic during the extrusion process evaluated by the torque curves, antioxidation properties measured by oxidation induction time (OIT) and the thermal elongation determined by the hot set method. In general, the high‐temperature stabilities are significantly influenced by the additives. This paper proposes and substantiates the concept of regulating the high‐temperature stabilities of XLPE insulation by the synergistic effects of antioxidants and crosslinking agents. Specifically, the positive effect of antioxidants on the antiscorching characteristic, thermal elongation and OIT of XLPE insulation is related with the dicumyl peroxide content. This study illustrates the intricate correlation between the high‐temperature stabilities of XLPE insulation and the additives, thereby offering valuable guidance for the formulation design of XLPE insulation for better performance.