High Voltage最新文献

In the detection of multi-component gas based on tunable diode laser absorption spectroscopy (TDLAS), the problem of overlapping interference between the absorption lines of each gas is often encountered. For example, when detecting a gas mixture of sulphur dioxide (SO₂) and thionyl fluoride (SOF₂), the characteristic decomposition components of SF₆, there is overlapping interference in the absorption lines of the two gases, which makes it difficult to detect the concentration of gases accurately. In view of this problem, a novel method based on support vector regression model used for TDLAS is proposed to detect two gases simultaneously. The detection results show that the correlation coefficients between the concentration of SO₂ and SOF₂ and the average value of the second harmonic peak reached 0.992 and 0.993. In addition, through model testing, different concentrations of SO₂ and SOF₂ gas mixture are simultaneously detected, and the resulting maximum errors for measuring SO₂ and SOF₂ concentrations are less than 7.13 × 10⁻⁵ and 0.26 × 10⁻². The maximum errors of the measurement results in the verification test are not more than 6.4 × 10⁻³ and 4.6 × 10⁻². Therefore, with assistance of the novel method, the detection of multiple gases by using a single laser is achieved.

Ionic liquid (IL) as the dispersant can help disperse the organic nanofillers to improve the performance of epoxy resin remarkably. However, the effect of IL on the electrical properties of epoxy composites is not well documented. This comprehensive study consists of the preparation, material characterisation and systematical investigation of electrical properties of 1-Butyl-3-methylimidazole hexafluorophosphate-modified chitin fibre/epoxy composites. The findings show that introducing IL into a chitin/epoxy composite can minimise porosity defects and improve the compatibility between filler and matrix. However, a high concentration of IL induces severe charge injection into chitin/epoxy composites and internal electric field distortion. The addition of 0.75%–1.5% mass fraction IL results in maximum enhancement in the AC breakdown strength of the chitin/epoxy composite (by ∼71%) compared with the non-IL composites. The non-linear conductivity and non-uniform charge injection phenomena of IL-modified composites can be attributed to the movement of radicals and anions due to the decomposition of IL. Through this study, it is highly expected that the organic filler dispersion in the epoxy matrix can be optimised by tuning IL to improve the insulation properties.

In recent years, the ablative discharge of the buffer layer in high-voltage (HV) cross-linked polyethylene (XLPE) cables has become a significant challenge for the operation and maintenance of power lines. However, there is a lack of effective methods to address buffer layer discharge defects. A practical approach is proposed to repair buffer layer defects and mitigate the associated discharge issues. To achieve this goal, the principles of repairing buffer layer defects are analysed by establishing an electrical network model that considers different contact states between the buffer layer and aluminium sheath. Based on this analysis, a method involving the injection of solidifiable rejuvenation fluid between the buffer layer and aluminium sheath is proposed to effectively suppress buffer layer discharge defects. Through simulation calculations, the minimum electrical conductivity and injection volume required to establish a reliable electrical connection between the buffer layer and aluminium sheath is determined. Additionally, a curable rejuvenation fluid containing conductive carbon black silicone rubber is prepared and analysed for its conductivity and flow properties at both the mesoscopic and macroscopic levels. Finally, a real cable office discharge test is conducted to compare the discharge behaviour of defective cables before and after repair. The results demonstrate that when the conductivity of the rejuvenation fluid exceeds 10⁻⁶ S/m, it effectively establishes a conductive channel between the insulation shield and aluminium sheath, thereby reducing the risk of discharge ablation. Furthermore, after injecting the rejuvenation fluid and completely covering the white mark defect, the discharge phenomenon in the buffer layer is significantly suppressed, leading to the restoration of its electrical performance.

Innovative test methods are required to keep up with the increased demand for insulation materials which can withstand the high-frequency square-wave voltages generated by power-electronic equipment. Test systems using high-voltage, high-frequency transformers have proven versatile and easy to realise. The authors investigate the application of amorphous cut cores in such transformers. Analytical and numerical models for the transformer and its frequency response are developed, aiding the design process. An amorphous core-based transformer is designed for 8 kV_pk output at 100 kHz and compared to two previous designs based on ferrite cores. The frequency and pulse response, as well as the high-voltage and thermal performance, are evaluated. The comparison shows that while the low parasitics of the amorphous-based transformer allow for superior frequency response, they are unsuitable for long-duration tests with high pulse repetition frequencies (25–100 kHz) due to increased core losses. The partial discharge inception and flashover voltage are comparable to the ferrite-based transformers.

In response to the time-consuming computational fluid dynamics simulations faced in naturally convective oil-immersed transformers, which result from complex models and a high degree of freedom, an innovative reduced-order digital twin prediction model for transformer temperature fields is proposed. This model facilitates fast predictions of transient temperature distributions. Initially, a comprehensive full-order finite element model of transformer temperature distributions is established. Subsequently, a hybrid approach, combining proper orthogonal decomposition (POD)-Galerkin and data-driven techniques, is proposed to create a reduced-order model (ROM). In this model, a Fourier number is utilised as a criterion to select POD training snapshot sets. Subsequently, the dynamic predictive capability of the proposed model under changing operational conditions is validated. Finally, the ROM is employed for fast predictions of temperature field, and its computational errors and time efficiency are compared across diverse operating conditions with full-order models. The research findings confirm the precision, timeliness, and dynamic nature of the reduced-order prediction model, offering a substantial improvement in prediction efficiency and capabilities, all while preserving the accuracy of the digital twin model.

The authors focus on the impact of melt-free radical grafting with hindered phenolic antioxidants (AO3052) on the electrical properties of polypropylene (PP) for DC cable insulation. The DC conductivity, space charge distribution and breakdown characteristic tests of grafting-modified PP are performed by comparing unmodified PP. The results demonstrate that the grafting of antioxidants can effectively suppress space charge injection, owing to the deeper trap sites at the grafting molecule. The breakdown strength of the grafted PP is significantly enhanced from 30°C to 90°C and especially achieves a 5.3%–6.7% increase after the same DC-prestressed time at 90°C. The surface electrostatic potential and molecular orbitals of the grafted PP are calculated. Simulation shows that the antioxidant introduces multi-level local state traps that can effectively trap the injected space charge, thus decreasing the destruction of molecular chains by electrons and increasing the breakdown strength level. In conclusion, antioxidant grafting modification can improve the breakdown characteristics with or without DC prestress, and thus it appears to be promising in the application of PP-insulated cables.

The electric field distortion caused by the accumulation of space charge in the insulating dielectric is easy to lead to accelerated ageing and even breakdown. In this paper, the space charge characteristics and the interfacial electric field change with time of silicone elastomer under different polarity DC voltages are studied. The results show that the homopolar charge injection is dominant in the silicone elastomer, and the electric field threshold is less than 4 kV/mm. The accumulation of homopolar charge weakens the interfacial electric field, resulting in the reduction of charge injection, and the interfacial electric field and spatial charge distribution gradually stabilise over time. In addition, the electric field at the interface does not decrease to the charge injection field threshold when it reaches stability. A time-varying electric field model of the metal-dielectric interface under a direct current field is derived and a calculation method for the time of charge accumulation to stabilise is proposed, based on the Schottky injection model and the relation between current density and volume charge density. The accuracy of the model is verified by comparing it with the experimental results of the stability time of silicone elastomer. This model is used to estimate the time when space charge accumulation reaches stability by means of the electric field threshold and the interface barrier, which can provide reference for the experimental measurement of space charge.

This study focuses on the degradation behaviour of metallised film capacitors, which are the essential components for the stability of converter valves in flexible ultra-high voltage direct current (HVDC) transmission systems. Through systematic experimentation, we investigated the failure mechanisms of MFCs under HVDC fields with superimposed harmonics, considering both equipment and material perspectives. The experiments subjected capacitors to 500 h of ageing under two conditions: a DC/AC-superimposed field with a constant DC component of 290 kV/mm and an AC ripple rate varying from 12% to 28%, and a control group aged solely under a DC field. Our findings indicate that capacitors aged under the DC/AC-superimposed field exhibited shorter lifespans and more significant capacitance loss than those aged under only the DC field. This difference in performance is primarily attributed to the distinct electrode loss behaviours observed under each ageing condition, which are key factors in the capacitors' capacitance decay. Moreover, the biaxially oriented polypropylene films in the DC-aged samples showed more severe deterioration, characterised by more noticeable molecular chain scission and reduced breakdown strength, compared to those aged under the DC/AC superimposed field. This difference is partly due to the moderate temperature increase caused by harmonics, which benefits the aggregation structure, and partly to the reduced molecular structure damage from the AC field.

The next generation of aircraft, including more electric aircraft and all-electric aircraft (AEA), requires electric power systems with high power density and low system mass specifications. Increasing the voltage of the system to the range of a few kV, medium voltage (MV), is a reasonable approach to achieving high-power-density and low-system-mass EPSs for aircraft applications. Higher voltages, however, pose many challenges for aviation MV power cables such as arcs and arc tracking, partial discharges (PDs), and thermal management. In this regard, thermal management is more challenging since heat transfer by convection is greatly reduced at wide-body aircraft's cruising altitudes due to the reduced air pressure. In this paper, a finite element method (FEM) model is developed in COMSOL Multiphysics for an aircraft bipolar MVDC (±5 kV) power cable. Using the model, the maximum permissible cable current at a low pressure of 18.8 kPa (at an altitude of 12.2 km from sea level, the usual cruising altitude for wide-body aircraft) is calculated. Also, an analytical model is developed based on analytical and proven empirical correlations governing conductive, radiative, and convective heat transfers at the steady state to estimate the ampacity of the bipolar cable system at reduced pressure. It was shown that the proposed analytical model can be used for atmospheric pressure and systems with a larger number of poles, expanding its range of applications. The results of the FEM and analytical models correlate at wide ranges of parameters such as ambient temperature, duct size, distance between the positive and negative pole cables, and the overall diameter of the cables. The influence of horizontal and vertical arrangement of poles is included in the analytical model. The results of this study can be used to design bipolar MVDC power cable systems for the envisaged wide-body AEA.

The linear velocity at the tip of large wind turbine blades can reach 100 m/s, generating static electricity through friction with airborne particles. However, the accumulation characteristics of precipitation static on the blade surface and its impact on the lightning attachment characteristics are rarely reported. The authors constructed a platform for measuring charges on rotating wind turbine blades and employed the electrostatic probe method to obtain the accumulation characteristics of surface charges under different environmental conditions. The experimental results show that positive charges accumulate on the blade surfaces, peaking at 0.69 μC/m² under experimental conditions. The charge density is positively correlated with airborne particle concentration and blade rotation speed, while it is negatively correlated with relative air humidity. Additionally, the authors developed a model of the electric field distribution on wind turbine blades considering the effects of precipitation static. Simulation results indicate that the electrostatic field induced by precipitation static weakens the field strength in the vicinity of receptors, reaching a minimum of only 38% of the original strength, thereby increasing the probability of lightning protection failure. The findings provide an effective supplement to the lightning attachment mechanism of rotating wind turbine blades.