Space Charge Accumulation Research Articles

Charge transport and space charge dynamics in EPDM/2D-nanoclay composite dielectrics

Composite dielectrics with two types of 2D-nanoclays (i.e., Kaolinite and Talc) incorporated in ethylene propylene diene monomer (EPDM) as the polymer matrix exhibit distinctly different electrical performances for high-voltage direct current (HVDC) cable insulations. This study investigated electrical conductivity and space charge as the key electrical characteristics of DC cable insulation in conjunction with dielectric spectroscopies. The findings of this study revealed that the composite dielectric with Talc 2D-nanoclays significantly suppressed space charge and thus minimized electric field distortion to less than 9% under 20 kV/mm at both measured temperatures of 25 °C and 50 °C with thermal gradient. In addition, the activation energy of electrical conductivity for the composite dielectric with Talc 2D-nanoclays is 0.45 eV which is notably lower than that of the composite dielectric with Kaolinite 2D-nanoclays, 0.95 eV. Based on the experimental results, the microstructural characteristics of composite dielectrics were discussed to provide insights into charge transport and space charge dynamics in the composite dielectrics. The charge transport mechanism attributed to the electronic and ionic conduction was explained, and the reasons for space charge accumulation were discussed. The larger interfacial area of 2D-nanoclay particles, the uniform and oriented distribution of 2D platelet-like nanoclay, and the smaller difference between the bandgap of polymer and 2D-nanoclay particles contribute to controlling the charge transport and suppressing the space charge accumulation in the composite dielectrics. Charge dynamics from the dielectric spectroscopy based on the Dissado-Hill model analysis confirms the explained mechanism.

Non–ferroelectric intercalation structure based on Aurivillius phase Bi4Ti3O12: A research arena to achieve high energy storage performance

High density energy capacity is the benchmark of electronic industry, and its improvement is on the way. Here, the BaCaBi4Ti5O18 films present high efficient energy storage trait, which is originated from ferroelectric/non–ferroelectric intercalation structure. The emergent of large gradient elastic energy in ferroelectric/non–ferroelectric intercalation structure not only crushes the ferroelectric domains, but also modulates space charges accumulation. Both factors contribute to the high polarization and intense breakdown strength. The contrast experiments were conducted by single ferroelectric intercalated structure Bi5Ti3FeO15 films, which show almost non ferroelectric energy storage behavior. The finite element simulations are consistent with the experimental evidences. The present results may facilitate a way for structural design of Aurivillius family, which is capable of acting as remarkable energy storage tasks.

Composite Micro-Nanoarchitectonics of MMT-SiO2: Space Charge Characteristics under Tensile State.

Low density polyethylene (LDPE) is a good insulating material which is widely used in cable materials due to its excellent insulation and processability. However, in the DC high voltage environment, pure polyethylene materials still face many problems, the most serious of which is space charge accumulation. The cable will inevitably be subjected to tensile stress during production, installation and operation. Therefore, it is of great significance to study the effect of stretching on the microstructure and space charge characteristics for polymers and their composites. In this paper, MMT/LDPE micro-composites, SiO2/LDPE nano-composites and MMT-SiO2/LDPE micro-nano-composites were prepared by melt blending. Mechanical stretching was carried out on pure LDPE materials and the above three kinds of composite materials. Each material was stretched according to four stretching ratios, which are 0%, 5%, 10% and 20%. The crystal morphology was observed by polarizing microscope (PLM), the crystallization perfection was tested by differential scanning calorimetry (DSC), and the space charge distribution inside each sample was measured by pulsed electro-acoustic (PEA) method. At the same time, the average charge density and apparent charge mobility for samples during depolarization were calculated and analyzed. The experimental results show that when the pure low density polyethylene sample is not stretched, its crystal structure is loose. Tensile stress can make the loose molecular chains align in LDPE and improve its crystalline structure, which is helpful to restrain the accumulation of space charge inside the sample. For MMT/LDPE, SiO2/LDPE and MMT-SiO2/LDPE composites, their internal crystal structure is compact. Stretching will destroy their original crystal structure at first, and then disorder molecular chains inside the three composite materials. With the increase of stretching ratio, the molecular chains begin to orient along the direction of force, the crystallization tends to be perfect gradually, and the space charge accumulation in samples also decreases. From the calculation results of apparent charge mobility for each sample, with the increase of stretching ratio, the trap depth and trap density inside samples firstly increased and then decreased.

Structure – properties relationships of graphene and spinel nickel ferrites based poly(vinylidene fluoride) hybrid polymer nanocomposites for improved dielectric and EMI shielding characteristics

Hybrid polymer nanocomposites with poly(vinylidene fluoride) are prepared based on graphene and spinel nickel ferrites (nFE) nanoparticles to investigate their structure-properties relationships. X-ray diffraction and differential scanning calorimetry confirmed the co-existence of α- and β-crystal phases of PVDF by the incorporation of graphene and nFE whereas solely α- crystal phase formed in neat PVDF. The influence of graphene and nFE on the mechanical properties of PVDF is concentration dependant. The modulus of PVDF is enhanced ∼ 128% from 587 to 1340 MPa at the expense of reduction in failure strain from 18% to 6% in PVDF/graphene nanocomposite whereas in PVDF/graphene/nFE hybrid nanocomposites, the mechanical properties are reduced owing to the embrittlement. On the contrary, graphene-nFE-polymer interfacial space charge accumulation has caused the enhancement of dielectric and EMI shielding characteristics as a function of frequency (1kHz-5 MHz). In PVDF/graphene nanocomposites at 3 wt%, the dielectric constant (ε/) value is increased 16-fold while keeping the dielectric loss (ε//) values equivalent to neat PVDF. Whereas, both ε/ and ε// are increased enormously in PVDF/graphene/nFE hybrid nanocomposites along the whole frequency range. Similarly, EMI shielding (SET) of PVDF/graphene and PVDF/graphene/nFE is ∼ 16 and 22 dB, respectively for a film thickness of ∼0.2 mm. Comparatively, PVDF/graphene nanocomposites exhibited the synergistic balance in mechanical, dielectric and EMI shielding properties over PVDF/graphene/nFE hybrid nanocomposites.

Space Charge Dynamics in Epoxy Based Composites Under DC and Square Pulse Wave of Different Polarities and Frequencies

Space charge dynamics of epoxy based micro-nano hybrid composites under DC and square pulse waves of different polarities and frequencies are investigated. A specially designed high-speed pulsed electro-acoustic (PEA) system is adopted to measure the space charge distributions of the prepared samples under different DC and square pulse voltage with positive and negative polarity. The DC electric field and the square pulse electric field of 20 kV/mm and 40 kV/mm with different polarities and frequencies are used. The results show that the micro-nano filler addition can suppress the space charge accumulation during the polarization. Furthermore, it can facilitate the dissipation of the accumulated charges during depolarization. No polarity effect is found in both samples under DC electric field. More space charges are accumulated in both samples under positive square pulse voltage with lower frequency, whereas the negative square pulse voltage with the higher frequency accelerates space charge accumulation in both samples. Moreover, the negative voltage has a more evident effect than the positive electric field on both samples. The space charge suppression effect of the micro-nano fillers is reduced under the square pulse voltage compared to the DC voltage. It is elucidated that epoxy based micro-nano hybrid composites are potential packaging materials for electronic devices. Still, their performance under the negative square pulse voltage with the high frequency and the positive square pulse voltage with the low frequency needs to be further investigated.

Potential of Epoxy Nanocomposites for Packaging Materials of High Voltage Power Modules: A Validation Using Experiments and Simulation

This paper focuses on the potential of epoxy resin/aluminum nitride (EP/AIN) nanocomposites through experiments and simulation for the packaging material of a 15 kV SiC-IGBT module. For this purpose, space charge, AC breakdown, thermal conductivity and glass transition temperature <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(T_{\mathrm{g}})$</tex> are measured. The electric stress reduction effect in EP/AIN nanocomposites is compared to the traditional packaging material at high-frequency AC and square voltages at 150 °C using the electric field simulation. The experimental results show that the 2 wt% EP/AIN nanocomposite exhibits the least space charge accumulation, highest AC breakdown strength and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$T_{\mathrm{g}}$</tex> amongst the tested nanocomposites. The offset of metallization layers plays a crucial role in the impact of the electrical properties of packaging materials on the electric field of the packaging structure. When the offset of metallization layers is zero, the maximum electric stress in the EP/AIN nanocomposites is lower than the traditional packaging material, both under the AC and square voltages. In the EP/AIN nanocomposites, as the frequency or the nano-AIN content increases, the maximum electric stress decreases under the AC voltages. Traditional packaging materials have a steeper transient electric field variation than EP/AIN nanocomposites, although the transient process is smoother at higher frequencies under square voltages for all the considered materials. A simplified physical model is proposed to explain the electric field distribution variation in the packaging structure under the AC voltages.

Effect of graphene modified semi‐conductive shielding layer on space charge accumulation in insulation layer for high‐voltage direct current cable

Space charge accumulation in the insulation layer of high-voltage direct current (HVDC) cable is one of the key factors restricting the development of HVDC cable. The inner semi-conductive layer as an important structure of cable will affect the charge accumulation characteristics in the insulation layer. This work intends to explore the method of modifying the semi-conductive layer with graphene, to suppress charge accumulation in the insulation layer. First, the semi-conductive layer with different contents of Graphene (G) and carbon black (CB) are prepared. Second, the morphology and surface roughness of the cross section are analysed. Further, the effects of the semi-conductive layer on space charge accumulation of the insulation layer are studied by pulsed electro-acoustic method and thermal stimulation depolarisation current method. The experimental results show that a moderate amount of graphene replacing CB can effectively reduce charge accumulation in the insulation layer and inhibit positive temperature coefficient (PTC) effect at the same time. The surface roughness of specimens decreases with the increase of G content from 0 to 3 phr (parts per hundreds of resin), when the CB content decreases from 25 to 10 phr, the surface roughness of specimen increases. The resistivity test shows that doping G can significantly inhibit the PTC effect of the semi-conductive layer. The volume resistivity of the semi-conductive layer decreases with the increase of G content and CB content. In addition, charge accumulation of the insulation layer rises and then drops under the action of the semi-conductive layer.

Space charge performance of epoxy composites with improved thermal property at high temperature under high electric field

AbstractThis article investigates the high‐temperature space charge dynamics of epoxy composites consisting of micro and nano‐AlN fillers under a high electric field. The test temperatures are selected for the space charge measurement based on the glass transition temperature. An indigenously designed pulse electro‐acoustic system measures the space charge distribution up to 150°C. The stepwise‐increasing field is applied to the test samples from 20 to 100 kV/mm at the rate of 20 kV/mm. The epoxy hybrid composites show negligible space charge accumulation at room temperature and low electric fields, which increases at high temperatures and high electric fields. The hybrid composite with 1 wt% nanoparticle has a dielectric breakdown at 100 and 150°C under 100 kV/mm with an evident amount of accumulated charges. In the hybrid composites with 3 and 5 wt% nanofillers, the breakdown is observed under 80 and 100 kV/mm, respectively, at 150°C. Notably, the micro‐nano filler addition significantly improves the thermal conductivity of the epoxy resin. The uniform dispersion of the fillers affects the electrical and thermal properties of the epoxy. The charge dynamics‐related mechanism is proposed on the basis of morphological characterization and thermal properties of epoxy and its composites.

Behavior of XLPE for HVDC Cables under Thermo-Electrical Stress: Experimental Study and Ageing Kinetics Proposal

The present work deals with the study of the electrical behavior of cross-linked polyethylene (XLPE) used for HVDC cable insulation. The aim is to better understand the influences of electrical and thermal stresses on the insulating material in order to provide useful information for designing HVDC cables. This study was carried out on Rogowski samples made of XLPE insulation with semiconductive electrodes, aged for more than 3 years (1220 days) at three different temperatures (70, 80 and 90 °C) under two DC electric fields (30 and 60 kV/mm). Dielectric loss factor, volume resistivity and space charge accumulation were measured. Results are analyzed and cross-correlated, in order to propose possible ageing kinetics.

Mechanically strong and thermally conductive paper made from aramid nanofiber and fluorinated graphene with excellent dielectric properties

ABSTRACT Dielectric materials with excellent thermal stability, mechanical properties, and thermal conductivity are highly desirable for advanced electronics and electrical equipment. However, it remains a significant challenge to develop a single material with these properties. Here we describe a new strategy to prepare dielectric paper by combining one-dimensional aramid nanofiber (ANF) with two-dimensional fluorinated graphene (F-graphene) through a vacuum-assisted filtration method. The obtained ANF/F-graphene paper exhibits a low dielectric constant of 1.92 at 103 Hz and its electrical breakdown strength is 17.6% higher than that of the neat ANF paper, owing to the presence of F-graphene, which significantly suppresses the accumulation of space charge in the prepared paper. Moreover, high mechanical strength (>200 MPa), thermal conductivity (6.29 Wm−1K−1), and thermal decomposition temperature (>500°C) are simultaneously achieved for the ANF/F-graphene paper. These findings highlight the fabrication of multifunctional dielectric materials and broaden their practical applications in the field of high-temperature electronics and devices.

The characteristics of ion wind thruster based on dielectric barrier discharge in near space

The experimental results show that when the pressure is constant, with the increase of power, the thrust-power ratio of the thruster decreases, and the wind speed and thrust increase, but the increase rate gradually decreases and finally tends to be stable；When the pressure is 5.5 kPa, The rate of increase in thrust decreases the slowest, that is, the thruster has the maximum thrust potential at 5.5 kPa, and when the input power is greater than 75 W, the relative maximum thrust can be generated, reaching 14.8 μN; At the same time, with the increase of input power, the thrust - power ratio increases first and then decreases; When the input power is constant in the range of 15–65 W, as the air pressure increases, the wind speed decreases, and the thrust and thrust-power ratios all have local extremes, that is, when the air pressure is 8 kPa, it reaches the regional maximum, the maximum is 12.7 μN and 0.45 μN/W, respectively, at 16 kPa, it reaches the minimum value of the area, and the minimum is 4 μN and 0.14 μN/W, respectively. By comparing the discharge images under different atmospheric pressures, it can be concluded that the thrust generated by the accelerated collision of particles with a single short-time large current pulse is less than that generated by the accelerated collision of ions with a long-time small high-frequency pulse discharge, and the particle collision probability is the main reason affecting the wind speed; Meanwhile, with the increase of input power, the “virtual electrode” formed by the accumulation of positive ion space charge reduces the increase rate of wind speed and thrust.

Electrochromism of Viologen/Polymer Composite: From Gel to Insulating Bulk for High-Voltage Applications.

Power equipment operates under high voltages, inducing space charge accumulation on the surface of key insulating structures, which increases the risk of discharge/breakdown and the possibility of maintenance workers experiencing electric shock accidents. Hence, a visualized non-equipment space charge detection method is of great demand in the power industry. Typical electrochromic phenomenon is based on redox of the material, triggered by a voltage smaller than 5 V with a continuous current in μA~mA level, which is not applicable to high electric fields above 106 V/m with pA~nA operation current in power equipment. Until now, no naked-eye observation technique has been realized for space charge detection to ensure the operation of power systems as well as the safety of maintenance workers. In this work, a viologen/poly(vinylidene fluoride-co-hexafluoropropylene)(P(VDF–HFP)) composite is investigated from gel to insulating bulk configurations to achieve high-voltage electrical-insulating electrochromism. The results show that viologen/P(VDF–HFP) composite bulk can withstand high electric fields at the 107 V/m level, and its electrochromism is triggered by space charges. This electrochromism phenomenon can be visually extended by increasing viologen content towards 5 wt.% and shows a positive response to voltage amplitude and application duration. As viologen/P(VDF–HFP) composite bulk exhibits a typical electrical insulating performance, it could be attached to the surface of insulating structures or clamped between metal and insulating materials as a space charge accumulation indicator in high-voltage power equipment.

Space Charge Accumulation in Linear Low-Density Polyethylene with Surface Fluorination of the Semiconductive Electrode

Several fluorinated polyethylene surface studies have proved that the fluorination reaction can effectively prevent charge from being injected into polyethylene. Therefore, this paper explores the influence of fluorinated electrode on space charge behavior in polyethylene. In this study, the space charge distribution inside polyethylene is measured by laser-PWP (Pressure Wave Propagation) method while altering electrode fluorination duration and fluorination temperature. The experimental results show that measured homocharge injection is increased in polyethylene to which a fluorinated semiconductive electrode is heat pressed. Attenuated Total Reflectance-Infrared (ATR-IR) spectroscopy and Scanning Electron Microscope (SEM) are also performed, revealing that the fluorinated layer of semiconductive electrode on the interface between polyethylene and electrode block impurities from entering polyethylene. The measured space charge distribution, being the planar average amount, also reveals impurity generation since heterocharge formation is observed. As such impurities are blocked, in the meantime the electrodes' homocharge injection remains un-affected, thereby the measured apparent charge is greatly increased.

Temperature Gradient Affecting Electrical Tree in Silicone Rubber under Impulse Superimposed on DC Voltage

In this paper, the electrical tree growth characteristics of silicone rubber (SiR) are studied under impulse superimposed on DC voltage and a temperature gradient (TG) field. The temperature difference between high voltage (HV) and ground (GD) electrodes varies from -90 to 90 °C resulting in a TG field in the samples. The electrical tree morphology, length and accumulated damage are discussed. Experimental results show that with the increase of absolute value of TG, the electrical tree length and accumulated damage continue to increase, and the tree morphology turns from branch-like tree to bush-branch hybrid tree. The positive TG has a more obvious acceleration effect on the tree growth than does the negative TG. Under the TG, the temperature dependent carrier transport results in space charge accumulation and electric field distortion at low temperature side, which is the main reason for the different growth characteristics of electrical tree. Besides, the accumulated damage of DC superimposed with heteropolar impulse voltage is larger than that under DC superimposed with homopolar impulse voltage. It is concluded that the temperature gradient and impulse superimposed on DC voltage promote the electrical tree growth of HVDC cable accessories insulation.

Space-Charge Accumulation and Its Impact on High-Voltage Power Module Partial Discharge Under DC and PWM Waves: Testing and Modeling

Emerging applications of compact high-voltage SiC modules pose strong challenges in the module package insulation design. Such SiC module insulations are subjected to both high-voltage dc and pulsewidth modulation (PWM) excitations between different terminals during different switching intervals. High <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dV/dt</i> strongly interferes with partial discharge (PD) testing as it is hard to distinguish PD pulses and PWM excitation-induced interferences. This article covers both the testing and modeling of PD phenomena in the high-voltage power modules. A high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dV/dt</i> PD testing platform is proposed, which involves a super-high-frequency (SHF) (SHF >3 GHz) down-mixing PD detection receiver and a high-voltage scalable square wave generator. The proposed method captures SHF PD signatures and determines PD inception voltage (PDIV) for packaging insulation. Using this platform, this article provides a group of PDIV comparisons of packaging insulation under dc and PWM waveforms and discloses discrepancies in these PDIV results with respect to their excitations. Based on these PD testing results, the article further provides a model using the space-charge accumulation to explain the PD difference under dc and PWM waveforms. Both simulation and sample testing results are included in this article to support this hypothesis. With this new model, the article includes an updated insulation design procedure for the high-voltage power modules.

Partial Discharges in HVDC Cables - The Effect of the Temperature Gradient During Load Transients

The paper investigates the role of the space charge accumulation phenomena in the inception of Partial Discharges (PD) in a defect within the bulk of the dielectrics of a High Voltage Direct Current (HVDC) cable. It is widespread accepted that the number of PD occurring in an HVDC cable during its lifetime is largely less than that under AC voltage stress. This is essentially due to higher values of the voltage between the conductor and the screen needed to trigger PD under a steady DC voltage than the same value under AC stress. Nevertheless, due to the dependency of the electrical conductivity of the insulation on the electric field and temperature, PD in HVDC cables is strongly influenced by the temperature distribution and, consequently, on the load current. Thus, the main goal of this research is to evaluate the main parameters of the PD occurring in an HVDC cable during a load transient. Numerical simulations by using Comsol Multlphysics® are validated by the results obtained with an ad hoc experimental setup. A model DC cable, subjected to transient phenomena due to a current step and with an air void defect in the insulation material, is simulated and setup. On the other hand, an experimental setup is used to carry out PD measurements on the same case study. The results of this research show the strong dependency of the PD parameters on the temperature distribution varying over time during a load transient.

Octavinyl polyhedral oligomeric silsesquioxane on tailoring the DC electrical characteristics of polypropylene

This work reports the effect of octavinyl polyhedral oligomeric silsesquioxane (OvPOSS) on tuning the electrical performance of polypropylene (PP). OvPOSS with different content are introduced into PP using the solution method. The microstructural morphology, crystallinity behaviour, breakdown strength, DC conductivity, space charge formation, and trapping level distribution are measured. The results indicate that the OvPOSS nanofiller can be dispersed uniformly with a doping content of 2.0 phr or less. The DC conductivity is decreased, and the breakdown strength of OvPOSS/PP nanocomposites is significantly increased. The space charge accumulation of the OvPOSS/PP nanocomposites is significantly suppressed due to the introduction of deeper traps by the OvPOSS nanofiller. Finally, the experimental results demonstrate that the OvPOSS nanofiller can greatly increase the electrical performance of the base PP and the OvPOSS/PP nanocomposites have much potential for HVDC applications. They further demonstrate that the PP is environmental-friendly due to its thermo-plastic property, which can be recycled after the manufacture.

Large improvement in DC electrical properties of EPDM with 2D platelet nanoclay

Space charge, electrical conductivity and breakdown strength of polymeric insulations are considered to be the most important characteristics for designing DC cable insulation. In this paper, we report the DC electrical properties of ethylene propylene diene polymethylene (EPDM) polymer with two different 2D inorganic clays, one of which shows large improvement of space charge distribution, controlled electrical conductivity and breakdown voltage. The results revealed that compared with the pure EPDM, the space charge accumulation for EPDM filled with Talc was suppressed significantly, especially at 50 °C with thermal gradient. The maximum local electric field enhancement in the volume decreased from 60% for the pure EPDM to 4% for the Talc-filled EPDM under 20 kV mm−1 at 25 °C, while the corresponding value dropped dramatically from 83% to 8% at 50 °C with thermal gradient. Compared with the EPDM, the Talc-filled EPDM showed higher conductivity but with less dependence to electric field and temperature. Microstructure studies suggest the platelet Talc particles distribute in the EPDM matrix homogeneously and make a uniform morphology. This condition consequently causes a desired trap distribution with high density of shallow traps due to the presence of high interfacial area between polymer chains and clay particles which prevents the charge accumulation during the charge carrier transport under DC electric field. Results of the thermally stimulated depolarization current spectra of the samples are in good agreement with the predicted trap distribution based on the experimental results and morphological study.

Charge transport behavior in XLPE-insulated cables under DC and thermal gradient coupling field considering the effects of non-uniform conductivity

The space charge accumulation of cross-linked polyethylene is the primary factor leading to the insulation failure of direct current (DC) cables, and the poor understanding of space charge transport behaviors remains as a bottleneck restricting the development of DC energy transmission technology. In this study, an improved bipolar charge transport model, considering the non-uniform conductivity of the insulation at DC voltage and thermal gradient is developed. The charge transport mechanism is revealed based on the space charge and the electric field distribution. The effects of conductivity on space charge and electric field distribution under DC voltage of polarity reversal is discussed as well. The results show that the space charge and the resulted electric field distribution are significantly affected by the temperature and the electric field gradient. A higher conductivity contributes to suppressing space charge accumulation, and a homogenization of electric field is achieved by an appropriate increase in the conductivity. Besides, the increase in the conductivity does not aggravate the space charge accumulation and distort the electric field after the polarity reversal.

Effect of Heat Exchange Transient Conditions With Moving Water-Air Interface on Space Charge Accumulation in Undersea HVdc Cables

The accumulation of space charge inside the dielectric layer of an HVdc cable is one of the most important issue to be considered in the design stage and during the operating conditions. The separation of space charge is due to several factors including the dependence on temperature of the electrical conductivity of the insulation and the establishment of a thermal gradient under load conditions. This article is focused on the investigation of the effect of an axial heat transmission on the space charge and electric field distributions in an HVdc cable. In order to assess the impact of this phenomenon, a case study involving a cable immersed partly in water and partly in air has been simulated by means of a 2-D thermal and electrical model in time domain. The electric field calculation is based on the quasi-static Maxwell model and the current continuity equation. To simulate the effect of waves, a moving water-air interface is considered, with time varying sinusoidal law. The results show the establishment of an electrical field peak near the water-air interface due to an increased temperature drop over the insulation in this area. The approach and the findings described in this article attempt to improve the knowledge in the relationship between thermal and electrical phenomena in HVdc cables. Moreover, this article focuses on the advisability of appropriately considering the impact of the axial heat transfer in the standards on the thermal rating of HVdc cables.