Dual Modulation of Space-Charge Dynamics in LDPE: Coupled Effects of Moisture Uptake and Electrode Interfacial Symmetry Resolved by PEA

This work presents the first experimental study that integrates, within a unified physical and methodological framework, the coupled effects of absorbed moisture and the chemical symmetry of semiconductive electrodes on the dynamics of space charge in low-density polyethylene (LDPE) subjected to extreme DC electrical stress. Using the pulsed electroacoustic (PEA) technique with micrometer-scale resolution, we characterized injection, transport, volumetric saturation, and field-distortion processes under controlled humidity conditions (0–12 h of vapor exposure) and across four interfacial configurations representative of commercial cable architectures (ISL-LDPE-OSL, OSL-LDPE-ISL, ISL-LDPE-ISL, and OSL-LDPE-OSL). The results show that moisture reduces the effective depth of dominant trap states and enhances effective carrier mobility, lowering transit times by up to a factor of two. At fields above 75-80 kV/mm, moisture induces nonlinear transport regimes governed by volumetric trap saturation and the formation of multipacket charge frontsnonlinear transport regimes governed by trap-saturation-induced electrostatic feedback and multipacket charge-front emission. In parallel, asymmetric interfaces amplify charge injection and generate intense, strongly distorted profiles, whereas symmetric configurations suppress net charge accumulation by more than an order of magnitude and stabilize the internal field. Integrating both dimensions reveals a dual-modulation mechanism: moisture governs the volumetric physics of transport, while interfacial symmetry regulates boundary injection. This unified framework provides direct implications for the engineering of polymeric insulation in HVDC cables and for the development of multiscale predictive models under realistic operational conditions.