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Power cables installed underneath the bridge have become vital in the cross-sea power transmission system. The design of grounding system is a decisive factor which determines the safety and reliability of these cables. In this paper, the nodal admittance matrix of the cable system is established considering the influence of the overhead laying condition and the coupled line model is used to improve the calculation efficiency. A matrix solution method, which can greatly reduce the dimension of the nodal equation, is proposed for the steady-state analysis of the grounding system. The grounding system designed for 220 kV cable project of Zhoudai Bridge in Zhejiang Province of China is also investigated. The results show that, compared with the induced voltage, the circulating current is the main factor affecting the ampacity of the cable system. Connecting the impedance at the cable joint can effectively reduce the power loss caused by circulating currents. A guideline for the grounding system design of the power cable lines installed underneath a bridge is proposed in this paper.

Epoxy resin (EP) insulations are widely considered as potential candidates for various applications. However, it is not suitable for high frequency (HF) and high temperature (HT) applications due to its low thermal conductivity. This research presents the tuning of thermal and electrical properties of EP via resin stoichiometry and incorporation of surface-modified hexagonal boron nitride (h-BN) nanofillers. In this research, the curing agent concentration for pure EP is optimized first based on high thermal stability and sufficiently reliable electrical properties. Second, the optimized pure EP is used as a base material to prepare epoxy/h-BN nanocomposites. Various physicochemical, thermal, and electrical characterizations are performed to analyze the properties of prepared materials. Results show that the higher curing agent concentrations offer a good balance between the thermal and electrical performance of the EP. However, the HF and HT stress exhibits detrimental effects on the breakdown strength and dielectric properties of the materials. Also, the addition of nanofillers further enhances the thermal properties while exhibiting sufficient electrical properties. By the control of resin stoichiometry and nanofiller addition, suitable composites for the HF and HT environment can be realized.

Polypropylene (PP) is being considered as a suitable alternative to the cross‐linked polyethylene (XLPE) insulation as the latter is prone to the space charge accumulation when subjected to the voltage polarity reversals in line‐commutated converter high voltage direct current transmission. This novel contribution correlates the space charge accumulation with the trap distribution inside XLPE and PP under the polarity reversal condition. The pulse electro‐acoustic and surface potential decay methods are used to measure the space charge and trap distributions, respectively. These measurements are carried at different poling durations (1 and 6 h at each polarity) and cycles of voltage polarity reversal (one and three cycles) at the electric field of 60 kV/mm. The XLPE shows more homo and hetero charge accumulation than PP. Dominant shallow traps in the XLPE are responsible for the space charge accumulation, whereas deep traps with higher trap density inhibit space charge accumulation within the PP. Furthermore, the positive and negative threshold fields for the space charge accumulation are measured. It is observed that the space charge can be easily accumulated under the negative electric field. Interestingly, the space charge decays rapidly inside the XLPE with the increased number of polarity reversal cycle. A valid theoretical model is developed to explain the space charge accumulation inside the XLPE and PP. The field‐assisted ionization plays a key role in the space charge accumulation inside the XLPE.

This paper presents the influence of thermal ageing on the physico-chemical and electrical properties of 500 kV extra high voltage direct current (EHVDC) XLPE cable insulation. EHVDC XLPE cable sections are placed in a thermal oven and thermally aged at 106 °C (melting peak temperature) for 250, 500 and 1000 h. After ageing, the inner, middle and outer layers of the cable insulation are characterized by Fourier transform infrared (FTIR) spectroscopy, oxidation induction time, X-ray diffraction (XRD), space charge, DC conductivity and DC breakdown measurements. The physicochemical analysis results show that the cross-linking by-products in the cable insulation are difficult to be completely removed during the ageing process, whereas the thermal ageing cannot completely consume the antioxidants in the materials. The space charge measurement results show that the hetero charges are accumulated inside the unaged middle layer samples. However, the space charge accumulation and electrical conductivity of the samples are significantly reduced after 1000 h ageing. Moreover, the DC breakdown strength of the inner and middle layer samples is continually increased with the increase of the ageing time. It is elucidated that the thermal ageing leads to the re-crystallization and re-degassing of samples, improving the space charge behavior and the charge carrier trapping phenomenon. It is proposed that the temperature of 106 °C could be used as a suitable degassing temperature for the EHVDC XLPE cable production.

For high temperature superconducting (HTS) dc cables, one key issue is the necessity of using polymer dielectrics with higher dielectric strength at cryogenic temperature in liquid nitrogen. Nanocomposites have played an important role in improving the dielectric properties of epoxy resin (EP). This article investigates on the dc breakdown strength and the surface potential behavior of the epoxy/Al2O3 nanocomposites (0, 1, 3, 5 wt%) at the room and cryogenic temperatures. Moreover, the trap distributions are analyzed from the surface potential decay (SPD) measurement. The possible effect of the trap distributions on the dc breakdown strength is discussed with the valid results. The measurements show that the dc breakdown strength and the initial surface potential continually increased with the nanoparticle addition up to 3 wt% at both room and cryogenic temperatures, and decreased thereafter. The enhancement of the breakdown strength and the initial potential is also found at cryogenic temperature. Besides, the addition of the nanoparticles decreased the rate of SPD compared with the pure epoxy. It is proposed that the higher trap density and trap level enhances the dc breakdown strength. Interestingly, under the cryogenic environment, the nanoparticles addition significantly affects the trap distributions, which further influences the dielectric strength. The enhanced dc breakdown strength is attributed to the reduced space charge formation, the charge carrier mobility and the energy of the charge carriers within the sample bulk.

The electrical breakdown strength of insulation material is very important for the design of a high-temperature superconducting (HTS) cable. This article investigates the breakdown characteristics of polypropylene laminated paper (PPLP) film samples, which are widely used in an HTS cable. Various test conditions, such as different modes of increasing voltage, voltage types, and ambient temperatures, are used. It is found that the breakdown strength of the PPLP film samples varies greatly with the aforementioned experimental conditions. Based on the existing research, the key reasons for the experimental phenomenon are analyzed. The experimental results provide the reference experimental data for the insulation design of the HTS cable.

This paper presents an estimate for the influence of service time on the conduction current characteristics of a 10 kV AC XLPE. The experimental conduction current results show that the space charge accumulation threshold increases with service time. Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC) experiments show increased thermo-oxidative aging and reduced crystallinity as the service time increases. This results in deeper traps in the XLPE material which can be verified from isothermal surface potential decay experiments. Based on the experimental results, the numerical analysis of thermo-electric fields is carried out for 10 kV AC XLPE cables with different service times under bipolar DC operation mode. It shows that the DC power for 10 kV AC XLPE cable in bipolar DC operation is higher than the AC power, whereas the DC operating voltage and DC power increases with the service time. In order to ensure a safe and long service life of the cables in DC operation, a conductor temperature of 60 °C and DC operating voltage of 11 kV are recommended for 10 kV AC XLPE cables in bipolar DC operation.

This paper presents the mechanism of the surface charge dissipation and flashover voltage of epoxy resin (EP) with nano aluminum nitride (AlN) composites enhanced by dielectric barrier discharge (DBD) plasma treatment in open air. Surface conductivity, surface potential decay (SPD), flashover voltage, Fourier transform infrared (FT-IR) and surface roughness were measured to evaluate the electrical and physicochemical properties of EP/AlN nanocomposite samples before and after the plasma treatments. It is found that surface conductivity is evidently increased with the increase of the plasma treatment time. Moreover, the SPD of the plasma treated samples after positive and negative corona charging are enhanced. However, the positive charge dissipation is influenced more significantly by the treatment. Both the positive and negative flashover voltage are improved after the plasma treatment, and the amplitude of negative flashover voltage is higher than the positive flashover voltage in each case. Physicochemical measurements show that the content of polar groups is improved after the plasma treatment, and the surface roughness is continuously increased with the increment of the plasma treatment time. The calculated trap distribution demonstrates that the amount of both shallow holes trap and shallow electron trap are increased after the plasma treatment. This investigation attributes the enhanced SPD and improved flashover voltage to the increased surface conductivity, the more amount of shallow traps and the improvement of the sample surface roughness.

This paper reports on the effects of four voltage stabilizers, m-aminophenylboric acid, 2-methoxy-5-pyridineboric acid, m-aminobenzoic acid and 4-dimethylaminobenzoic acid, on the insulation properties of polyethylene blends. 1 wt% voltage stabilizers were added into low density polyethylene (LDPE) blend containing 10 wt% high density polyethylene (HDPE) by a solution method. Physicochemical and electrical properties of the blends were analyzed by infrared spectroscopy, thermo-gravimetric analysis, differential scanning calorimetry, electric tree initiation tests, space charge and surface potential decay measurements. The results showed that the addition of the voltage stabilizers had a little effect on the thermal stability and melting properties of the LDPE/HDPE blend. When the voltage stabilizers were included into the blends, the tree initiation voltage (TIV) increased, in particular the blend with m-aminobenzoic acid showed the highest increase of 41% compared to the reference LDPE/HDPE. It was found that space charge accumulations of the blends were apparently suppressed by adding voltage stabilizers. Moreover, the blend with the m-aminobenzoic acid had the least space charge accumulation. The surface potential decay rate of the blends was significantly increased after adding voltage stabilizers. Quantum chemical calculations illustrated that the HOMO-LUMO energy gap was closely related to the TIV of the blends, whereas the m-aminobenzoic acid has the lowest energy gap level and the best effect of restraining the electrical tree initiation. The trap level calculation showed that the trap depth in the blends decreased with the addition of the voltage stabilizers, which was beneficial to suppress the accumulation of space charge in the materials.

This paper reports an enhancement of the nonlinear conductivity, thermal and mechanical properties of micro-silicon carbide/silicone elastomer (m-SiC/SE) composites by adding nano-aluminum nitride (n-AlN) for power module encapsulation applications. The electrical properties (such as nonlinear conductivity characteristics and transient permittivity obtained from polarization current, and trap distributions obtained from thermally stimulated depolarization current) and material properties (including thermo-gravimetric analysis, coefficient of thermal expansion (CTE), and thermal conductivity, tensile strength, strain at break and Young’s modulus) of the pure SE, m-SiC/SE microcomposites, m-SiC/n-AlN/SE hybrid composites are investigated. The effect of the m-SiC fillers and n-AlN fillers on physicochemical properties of the SE matrix is analyzed by FT-IR spectroscopy and crosslinking degree. The measured nonlinear conductivity and transient permittivity are used for electric field simulation under DC stationary and square voltages. It is found that the addition of n-AlN fillers in the SE hybrid composite improves the nonlinear conductivity characteristics and mitigates the electric field under DC stationary and square voltages, compared to the SE microcomposite. Furthermore, the m-SiC/n-AlN/SE hybrid composite has a higher thermal degradation temperature, thermal conductivity, tensile strength, Young’s modulus, and crosslinking degree than the SE microcomposite, whereas their CTE and strain at break are lower. It is elucidated that the m-SiC/n-AlN/SE hybrid composite with enhanced nonlinear conductivity and material properties is a promising packaging material for high-voltage power modules.

Rapid growth in power system has created the opportunity in the field of materials to ensure reliable operation of various equipments throughout their operating life span. Due to the cumulative effects of mechanical, chemical and electrical stresses caused by the partial discharge (PD), insulation gradually degrades. Partial Discharge tests ensure the good quality of cable insulation like cross-linked polyethylene (XLPE) under high voltage conditions. This paper describes the results of a real testing based experiment of Partial Discharge with XLPE cable. Under the application of different voltages, the breakdown level of cable insulation is checked in the laboratory experimental setup. The MATLAB Simulink architecture of test system with PD structure is constructed in correlation with laboratory experiments. The results of both the simulation and the laboratory experiment have been compared in this work. The standard deviation and percentage error are calculated for the simulated and experimental data.