High Voltage最新文献

Accurate surface charge inversion can guide the research on surface modification of insulators in GIS/GIL. The current inversion algorithms have disadvantages of high computational cost and low accuracy. Based on that, the integral equation method (IEM) is proposed to calculate the transformation matrix. Compared with the traditional analytical method (AM), IEM has a simple calculation process. The calculation speed of IEM is much faster than that of AM. To suppress the numerical divergence in IEM, the Tikhonov regularisation method is introduced and Tikhonov-IEM is proposed. For square insulators, compared to IEM, the peak-mean square error (PMSE) is reduced by about 40 percent. However, Tikhonov-IEM is not suitable for basin insulators. Therefore, the least square method (LSM) is introduced and the LSM-IEM is proposed. For basin insulators, compared to IEM, the PMSE is reduced by about 30 percent. Finally, the accuracy of the algorithms is verified by physical tests.

In the past three years, a number of oil-immersed ultra-high-voltage shunt reactors have experienced discharge defects when being put into operation, resulting in an overload of acetylene. However, detecting and identifying these discharge defects caused by switching impulse voltage is challenging under steady-state conditions. This poses unpredictable and difficult-to-assess safety risks for the longterm operation of the equipment and subsequent transient processes. Hence, comprehending the discharge behavior of oil-pressboard (PB) insulation under switching impulse voltage and devising a method to identify defects becomes crucial. This study focuses on investigating the frequent arc reignition (FAR) pattern exhibited by typical defects under both standard and oscillation switching impulse voltages. The objective is to uncover the mechanism behind FAR and propose a defect recognition strategy suitable for transient processes. The study reveals the FAR process will occur at least once during the breakdown process; the FAR phenomenon is the weakest in the surface defect with a weak vertical electric field. The average recovery voltage percentage and the average discharge interval of the FAR process decrease with increasing impulse amplitude or oscillation frequency. Additionally, the average number of discharges decreases with higher oscillation frequency, while it initially increases and then decreases with increaseing amplitude. Based on the analysis of the number of FAR processes and their variation in terms of amplitude or discharge interval, a method for recognizing oil-PB defects during switching transient processes is developed and successfully applied to a case study involving acetylene overload in a 1000 kV shunt reactor.

The strain clamps and leading wires are important components that connect conductors on overhead transmission lines and conduct current. During operation, poor contact between these components can cause abnormal overheating, leading to electric failures and threatening power system reliability. Recently, the use of unmanned aerial vehicles equipped with infrared thermal imagers for strain clamp and leading wire maintenance has become increasingly popular. Deep learning-based image recognition shows promising prospects for intelligent fault diagnosis of overheating faults. A pre-treatment method is proposed based on dynamic histogram equalisation to enhance the contrast of infrared images. The DeepLab v3+ network, loss function, and existing networks with different backbones are compared. The DeepLab v3+ network with ResNet101 and convolutional block attention module added, and the Focal Loss function achieved the highest performance with an average pixel accuracy of 0.614, an average intersection over union (AIoU) of 0.567, an F1 score of 0.644, and a frequency weighted intersection over union of 0.594 on the test set. The optimised Atrous rates has increased the AIoU by 12.91%. Moreover, an intelligent diagnosis scheme for evaluating the defect state of the strain clamps and leading wires is proposed and which achieves a diagnostic accuracy of 91.0%.

As a typical failure phenomenon in transformers, sulfur corrosion has garnered significant attention in the field of high-voltage engineering. Grain boundary character distribution (GBCD) copper windings have been introduced to enhance sulfur corrosion resistance by slowing down intergranular corrosion. In this study, the sulfur corrosion behaviour and mechanisms of the GBCD copper windings under various temperatures were experimentally and theoretically studied. Results show that GBCD can enhance the corrosion resistance of copper in liquid environments. With the increase in temperatures, the insulating properties of oil and papers in traditional copper windings experience notable degradation, while GBCD copper windings show more stable insulating behaviours. In addition, modelling of grain boundary energy indicates that the grain boundary structure of GBCD copper windings has a lower average interface energy of 0.170 eV/Ų. Calculations of reaction thermodynamics show that GBCD copper windings possess a higher failure temperature (135.2°C) and inhibition degree (activation energy) of the sulfur corrosion (32,557.62 J/mol), revealing the stability and enhanced sulfur corrosion resistance at elevated temperatures.

Surface flashover is a crucial issue for the miniaturisation of electronic facilities in military, industrial, and aerospace engineering. The oriented hexagonal boron nitride (hBN) composites, due to excellent thermal and electrical insulating properties, show a potential application in high-voltage power equipment, while the surface flashover performance of hBN composites dependent on oriented hBN texture is rarely reported. The effects of hBN orientation and contents on the surface flashover performances of oriented hBN composites are investigated. The isothermal surface potential decay of the oriented hBN composites was also studied. It is found that the charge transportation could be adjusted by the hBN orientation, thus regulating surface flashover strength. The DC flashover voltage of the in-plane oriented hBN composites with a thickness of 15 μm reached the maximum of 27.6 kV at the hBN loading of 20 wt%, 14.5% higher than that of the pure resin. The carrier mobility of out-of-plane oriented hBN composites is about three times greater than that of the in-plane oriented composites, indicating that the charges are easily transported along the hBN basal plane. The larger carrier mobility causes charge dissipation in composites near the electrode at the hBN basal plane parallel to the axis of electrodes and inhibits the distortion of the surface electric field on the composites, thus enhancing the surface flashover. Consequently, developing oriented insulators for high-voltage applications and enabling an optimum insulation design would be beneficial because of the compactness and high reliability of power apparatus for use in power grids.

A simulation analysis and an experiment are carried out to investigate how the gap difference between the breaks of a direct current vacuum circuit breakers with multi-breaks (MB-DC VCB) caused by the mechanism dispersion of the breaker influences the distribution of TRV among the breaks. An interruption model of MB-DC VCB, combining the continuous transition model, is established to analyse the rising rate of transient recovery voltage and the dielectric strength recovery speed of the breaks for MB-DC VCB under different gap difference conditions. Based on the experimental platform of dual break DC vacuum circuit breaker breaking, the correctness of the simulation model is verified on a DC VCB with the double-breaks interruption experimental platform. Moreover, a model is applied to the non-synchronous interruption simulation of a DC VCB with three-breaks. The relationship between the TRVs of the breaks under different gap difference conditions is analysed using the comparative analysis method, obtaining the maximum gap difference at the moment of breaking failure. The results of this study show that large-gap breaks have a higher TRV than small-gap breaks (the fracture of the action delay module), with double fractures reaching 1.4 times and triple fractures reaching a maximum of 1.52 times; the ability of small-gap breaks to withstand TRV is weak, giving rise to re-breakdown or even interruption failure; as the number of fractures increases, the maximum gap difference also increases. Improving the synchronous interruption ability of the MB-DC VCB is conducive to improving the interruption performance and interruption success rate of this type of a circuit breaker.

An arc is the high-temperature discharge plasma produced in the opening process of mechanical switches, which directly affects the breaking capability of a hybrid DC circuit breaker. According to the physical mechanism of an electric arc, the construction of an arc model for simulation analysis is an important technical means in the electrical field. In this study, based on the theory of magneto hydrodynamics (MHD), a gas mechanical switch model of a natural commutation DC circuit breaker with a compound gap is established. The arc motion process under different conditions is simulated and calculated. The influence of different initial pressures, different opening speeds, and different striking currents on the arc voltage characteristics is analysed. The results show that the larger the gas pressure, the smaller the arc volume and the higher the arc voltage. The faster the opening speed, the longer the arc and the higher the arc voltage; with the increase of the current, the arc voltage increases rapidly at a low current, while the arc voltage increases slowly at a high current.

Accurate simulation of lightning-induced overvoltage for overhead distribution lines is helpful to prevent lightning trip accidents. An electromagnetic return-stroke model was used to represent lightning and then a 3D finite-difference time-domain (FDTD) method was adopted to simulate the lightning-induced overvoltage on a distribution line without a field-line coupling model. How lightning-induced overvoltage behave for different ground conductivity and varying distance between the distribution line and the lightning channel was analysed. The results showed that the overvoltage waveforms at the centre point of the line corresponding to lightning strikes on the lossy ground and an ideal ground (σ = ∞) were similar; however, the peak amplitudes of the waveform were affected by soil conductivity at a close distance. The relationship between magnitude of the overvoltage and distance can be described by a second-order exponential decay equation. Finally, the overvoltage calculated using the proposed model was compared with those obtained based on Agrawal's model and measurements made using the newly developed intelligent insulator on site. From these comparisons, it could be concluded that the FDTD method with the electromagnetic return-stroke model produces reasonably accurate results of the attenuated oscillation waveform, which can better reproduce the overvoltage on operational distribution lines.

During the operation of high-voltage cables, external stress and residual stress can affect the aggregated structure of insulating materials and lead to significant deterioration in their electrical performance. To investigate the evolution characteristics of the electrical properties of cross-linked polyethylene (XLPE) under mechanical stress, this paper explains the relationship between the aggregated structure of XLPE and its electrical properties and proposes a method for improving insulation performance under mechanical stress. The results show that metallocene polyethylene used as a nucleating agent can promote crystallisation through heterogeneous nucleation and increase Young's modulus by non-uniform nucleation, increasing crystallinity and reducing interplanar spacing, resulting in more complete crystal forms and reduced damage to the aggregated structure during the tensile process. After nucleating agent modification, the XLPE crystallisation becomes more uniform, and interfacial adhesion forces increase. The weakened interface damage process between the amorphous and crystalline regions under tensile stress effectively inhibits the process of molecular chain polarisation turning and reduces trap density. The modified XLPE crystal structure shows a tendency towards densification and enhanced molecular chain interactions, which can reduce the damage to the aggregated structure under tensile stress, while the reduced free volume inside the material and the shortened average free path of carriers can weaken the damage of high-energy electrons to molecular chains, thereby inhibiting the process of electrical tree degradation. The results show that nucleating agents have great potential for maintaining the stable operation of XLPE cables under mechanical stress.

Wang, P., et al.: Impact of air pressure variations on electrical vehicle motor insulation. High Voltage. 8(5), 1011–1019 (2023). https://doi.org/10.1049/hve2.12346

The authors wish to bring to the readers' attention the following error in the article by Peng Wang, Chaofan Yu, Shakeel Akram, Ziyuan Fan, Wenhuan Zhao, ‘Impact of air pressure variations on electrical vehicle motor insulation’.

We apologise for this error and any confusion that it may have caused.