Guest Editorial: Research Progress and Technology Development of HVDC Cable: Part I

Giovanni Mazzanti reviews the existing testing techniques for HVDC cable systems, considers development tests, pre-qualification tests, extension of qualification test, type tests, routine tests, sample tests and after installation tests. An example of an innovative sea trial testing procedure is shown, which is the outcome of a fruitful partnership between a cable manufacturer and the national transmission system operator in Italy. Gian Carlo Montanari et al. present a theory-driven and measurement-based procedure, having the purpose to minimise partial discharge (PD) inception risk. This procedure is based on stepwise voltage application during cable energisation. The fundamental idea behind the proposed approach stems from considering that the jump voltage is the trigger of PD occurrence. It is shown that compared with the conventional energisation consisting of rapidly increasing voltage, the stepwise approach can reduce the risk of PD inception and related extrinsic ageing, even for the steady state voltages larger than PDIVDC. Cheng Zhang et al. propose a PD vibration diagnosis methodology using the embedded fibre based on the heterodyne interferometric phase-sensitive optical time domain reflectometry (φ-OTDR) and Hilbert demodulation, to detect the PD of HVDC submarine cable. The proposed method is verified by PD experiment with pre-set defects in 220 kV submarine cables under DC voltage. Shengtao Li and Shihang Wang et al. propose and substantiate the concept of regulating the high-temperature stabilities of crosslinked polyethylene (XLPE) insulation by the synergistic effects of antioxidants and crosslinking agents. This study illustrates the positive effect of antioxidants on the antiscorching characteristic, thermal elongation and oxidation induction time of XLPE insulation is related with the dicumyl peroxide content. Jinghui Gao and Lisheng Zhong et al. investigate the fundamental mechanisms of charge accumulation and the associated homo-junction effect in homo-bilayer XLPE (H-XLPE). The findings provide experimental evidence and theoretical clue for elucidating the role of the interface area on the charge accumulation that affects reliability and stability of submarine cable systems. Chong Zhang and Lisheng Zhong et al. develop an extra-low frequency (ELF) dielectric analysis method based on time-dependent polarisation current for nondestructive detection of byproducts in XLPE. The proposed ELF dielectric analysis method enables the nondestructive detection of byproducts in cables, opening a new avenue for cable degassing effect evaluation. Yuanxiang Zhou et al. incorporate the voltage stabiliser anthrone into XLPE and enable field-driven adaptive migration and charge trapping, thereby dynamically regulating local electric fields. This method inhibits charge injection and transport, significantly reduces internal field distortion and results in a negative electric-field coefficient effect. Isabella Nett and Willem Leterme investigate the impact of lubricant on charge dynamics at macroscopic interfaces in HVDC cable joints. The findings highlight that lubricant diffusion affects both the bulk properties and charge accumulation at the interface, and underline the large effect of the type of lubricant. These results are crucial for understanding the long-term performance of cable joints and insulating materials in HVDC cable systems. Zhonglei Li et al. propose a nondestructive optical imaging-based three-dimensional (3D) reconstruction method to analyse electrical tree propagation in polypropylene (PP) cable insulation under mechanical bending. The technique combines focus-stacked optical imaging with a feature fusion algorithm to segment in-focus regions across depth layers, enabling 3D reconstruction of electrical trees in PP homopolymer (PPH), block copolymer (PPB) and elastomer-blended (PP/TPE) samples. Man Xu et al. investigate elastomer-toughened PP insulation to meet the application requirements for green noncrosslinked PP cables in HVDC transmission. It focuses on the formation of β-crystals in isotactic polypropylene (iPP) by adding a β-nucleator and improves the DC characteristics at elevated temperatures. In conclusion, this special issue presents the latest advancements in advanced testing methods of HVDC cable and improved insulating materials. We hope readers find this collection insightful, educational and inspiring. We sincerely thank all contributing authors and reviewers for their invaluable efforts in ensuring the quality and timeliness of this special issue. Special appreciation is extended to Professor Weijiang Chen, Editor-in-Chief of High Voltage, and the editorial office for their generous support throughout the publication process. No datasets were generated or analysed. Shengtao Li: Professor. His research interests include dielectric theory, electrical materials and their applications in power equipment, insulation technologies under extreme conditions. Lisheng Zhong: Professor. His research interests include insulating materials, structural design, and engineering applications for power cables. Davide Fabiani: Associate Professor. His fields of research are mainly related to nanostructured materials for applications in electrical and electronic apparatus, HV apparatus diagnosis, evaluation of the effect of non-sinusoidal waveforms on reliability of components and insulation systems, electrical conduction mechanisms and ageing processed in high voltage insulation systems. Chong Zhang: Professor of Engineering. His research interests include design, development and application of electrical materials for power equipment. Shihang Wang: Associate Professor. His research interests include high voltage cable insulation, novel cable insulation, and their polymer physical and electrical properties. Jinghui Gao: Professor. His research interests include physicochemical mechanisms in the manufacturing and application of power cables, insulation technologies and dielectric theories in clean energy utilisation, sensing mechanisms of functional dielectrics and their applications in the Energy Internet of Things. Roland D. Zhang: Professor of Engineering. His research interests include cable engineering, quality assurance and cable dimensioning for different offshore cable projects and interconnectors, especially for DC underground cables and submarine cables.