High Voltage最新文献

With the widespread application of composite insulators in transmission lines, exploring the accumulation mechanism of pollution particles on composite insulator surfaces is of importance to ensure the safe and steady operation of the power system. Addressing the current theoretical shortcomings, this study categorises the accumulation process of particles on the insulator surface into three stages, namely ‘spatial motion’, ‘surface collision’, and ‘surface motion’. The motion and rotation velocities in a multi-physics field are calculated in the spatial motion stage. In the surface collision stage, a parameter called ‘neck height’ is introduced to determine the optimum mechanics theory, and the normal deposition criterion is established. For the surface motion stage, the sliding displacement and rolling displacement on the surface are calculated based on the rotation speed of the particles. A dynamic pollution accumulation model of the composite insulator is established based on the normal deposition criterion and tangential displacement. Finally, numerical simulations are performed by using the finite element method. Simulation results show that the proposed model agrees with the actual insulator pollution accumulation, and the deposition model is still applicable for various types of composite insulators operating in different applied voltages. The deposition probability of particles increases with the increasing particle size. In the surface motion stage, particle displacement increases with particle size and wind velocity.

A high-temperature superconducting (HTS) dynamo flux pump can inject DC currents into closed-loop HTS magnets without contact. It enables the realisation of current-lead-free or even through-wall charging systems for high-field applications such as nuclear magnetic resonance/magnetic resonance imaging (MRI) magnets, fusion reactors and accelerators. Researchers have proposed many simulation models to understand the working principle of HTS dynamos, few of which are in 3D because of converging problems. Therefore, the influences of many key 3D parameters in the HTS dynamo are scarcely reported. The authors propose an efficient 3D modelling method of the HTS dynamo based on the T-A formulation. The rotating magnets are modelled by a ring-shaped permanent magnet with space-time-variant remanent flux density to avoid moving meshes. This, together with the T-A formulation, makes the 3D model efficient and universal. The accuracy of the model is verified by the experimental instantaneous and time-integrated dynamic voltages. Using this model, the authors present systematic case studies to thoroughly explore the influences of the key parameters of a dynamo flux pump on the dynamic voltage and losses. The proposed modelling method and results could significantly benefit the design and optimisation of HTS dynamos for high-field magnets.

In order to accurately predict the content and variation trend of dissolved gas in transformer oil and guide the condition maintenance of power transformers, a combined prediction model based on multi-information fusion is proposed and its effectiveness is analysed. First of all, based on the possibility of pathological and missing historical sample data, a detection and filling method based on variable weight combination samples is established. Second, the authors propose two models. Aiming at the non-linear and non-stationary characteristics of gas content, a univariate decomposition prediction mode HBA-VMD-TCN which based on the Honey Badger algorithm, variational mode decomposition and time convolutional network (TCN) is established. Then the multivariate Informer prediction model is established for gas content affected by multiple variables. Third, the cross-entropy theory is used to determine the weight coefficients of the two models, and the multi-information fusion combined prediction model is formed. Finally, on the basis of the above, a method to determine the time step and the position information of the transition point adaptively in the process of prediction is proposed to further improve the prediction accuracy. The results show that, through a series of simulation experiments of model comparison and transformer anomaly prediction, the accuracy and effectiveness of the combined prediction model are verified.

Developing low-carbon gas insulated transmission and distribution equipment is essential to achieve the ‘carbon peak, carbon neutralisation’ or ‘net-zero’ in the power industry. Scholars have carried out various research on the eco-friendly insulating gas (such as C₄F₇N, C₅F₁₀O) and next-generation SF₆-free equipment to gradually reduce the utilisation of strong greenhouse gas SF₆.

The cover of this issue is inspired by the allusions of the “Year Beast” in Chinese traditional culture. It is said that in ancient times, every New Year's Eve there would be a murderous “Year Beast” attacking the world, and the people drove it away with firecrackers. These habits have gradually become the customs of the New Year. Coinciding with the Chinese Lunar New Year, the authors compare the “discharge” that threatens the safety of gas insulated equipment to the “Year Beast”. The traditional insulating gas SF₆ incarnates as an ‘immortal’ to protect the insulation safety of equipment for a long time. However, due to the greenhouse effect of SF₆, its use is gradually limited. At the same time, the eco-friendly insulating gas is like the ‘pupil’ that gradually jointly resist the discharge with SF₆ to ensure the safe and stable operation of power equipment.

In the future, the development of eco-friendly insulating gases and SF₆-free equipment will further ensure the safety of the power grid and protect the lights of all households. On the occasion of the Spring Festival, we wish all scholars and readers a happy New Year!

Transformers may suffer multiple short-circuit impacts during long-term operation, and axial instability is one of the typical types of serious accidents caused by short-circuit faults. The axial instability form of the winding-block structure is analysed, and the dynamic solution of the winding short-circuit electromagnetic force is obtained by establishing the three-dimensional magnetic-circuit-force multi-physical field coupling simulation model. The influence of strain rate on the cushion block constitutive equation is corrected, and the modified model is verified by short-circuit impact test and quasi-static test. The research results show that for 110 kV 31.5 MVA transformers, the maximum electromagnetic axial resultant force of winding is 363.16 kN, and the ultimate tilt force is 1214.2 kN. The pre-tightening force configuration is accordingly recommended to range from 363.16 to 608.28 kN, which is narrowed by 18.49% compared with the static calculation method; Meanwhile, adding a logarithmic strain rate correction term to the classical constitutive equation of the cushion block can achieve a good correction of the stress-strain relationship with the coefficient of determination above 0.99, and the cushion block has a larger elastic modulus under high strain rate load. The research results provide an important theoretical reference for the axial stability structure of transformers.

A novel control scheme is presented to eliminate the negative effects of communication disturbances, which introduces active disturbance rejection control (ADRC) in the control strategy design to achieve the objectives of the restoration of the bus voltage and the sharing of the power even in the presence of disturbances and delays in communication. Simultaneously, its dynamic disturbance decoupling feature is used to realise the decoupling between power and voltage, so that the proposed controller only exchanges power information with its neighbours, reducing the communication burden and simplifying control structure. The control performance of the strategy is verified by employing steady-state analysis. The impact of controller parameters is studied by establishing a small signal model. Finally, both simulation cases and experimental tests prove the feasibility of this scheme.

The eco-friendly insulating gas perfluoroisobutyronitrile (C₄F₇N) is potentially used in gas-insulated transformers (GIT) to replace sulphur hexafluoride (SF₆). However, evaluation of the long-term insulation reliability and gas–solid interface discharge decomposition characteristics of the gas–solid film insulation structure in GIT is indispensable. The authors simulated the gas–solid film insulation structure in GIT and explored the interface partial discharge (PD) characteristics of C₄F₇N/CO₂ gas mixture with polyethylene terephthalate (PET). The effect of gas pressure, mixing ratio on gas–solid interface gas decomposition, PET degradation was investigated, and the interaction mechanism was analysed. It is found that the interface PD generated three degradation regions on a PET film. The gas–solid interface reaction in the electrode contact region and the discharge development trace was significantly higher than that of halation region. The content of gas decomposition products decreases with the increase of gas pressure and the PD intensity of SF₆-PET is inferior to that of C₄F₇N/CO₂ under the same condition. Relevant results provide reference for the development and application of C₄F₇N/CO₂ based GIT.

The insulation performance of oil paper insulation is significantly affected by moisture such that monitoring moisture content is important. However, it is difficult to obtain the moisture content accurately due to its dynamic change under multi physical fields. Studying the moisture transportation in oil paper insulation under multi physical fields becomes a vital method in solving the problem. A multi physical model describing moisture migration was proposed, which considered the effects of temperature on moisture in different existing states in oil-immersed paper (OIP). The temperature distribution formed a vapour pressure gradient to drive moisture migration and affected migration speed. Then, experiments and simulations of moisture migration were performed, which showed that the experiments were in good agreement with simulation. The results revealed that the temperature gradient caused uneven moisture distribution and the increased temperature reduced OIP moisture content. The established model could fully characterise moisture migration under temperature gradient, which provided a theoretical reference for predicting the risk of partial dampness and evaluating insulation performance.

Condition monitoring of the insulating system within power transformers has a massive importance according to the electrical utilities. Dissolved gas analysis (DGA) is frequently used for this purpose. However, DGA lacks the necessary level of accuracy to identify all equipment faults, particularly in their initial stages of degradation. Also, it does not have the capability for real-time monitoring and relies on manual sampling and laboratory testing, causing potential delays in fault identification. Additionally, the interpretation of DGA data necessitates specialised expertise, which may pose difficulties for smaller entities that have limited access to resources. Therefore, the contribution of this research is to use infrared spectroscopy measurements as a new effective technique substituting the DGA method for fault diagnosis in insulating oil. The inception faults that were considered in this study were the electrical fault (discharges of high energy) and the thermal fault (300°C < Temperature < 700°C). Regarding that, two test cells were crafted especially for serving the simulation processes inside the laboratory for both types of inception faults. Subsequently, six samples of pure paraffinic mineral oil were taken to be degraded in the laboratory. Following that, all of them besides another sample that were not subjected to any kind of faults were taken to be examined by Fourier transform infrared (FTIR) spectroscopy to obtain an overview of the oil's behaviour in each fault case. After that, the FTIR analysis was initially verified utilising the DGA method. Then, for further affirmation, the dielectric dissipation factor (DDF) for all samples was measured. In the final analysis, the verification tests provide experimental evidence about the outperformance of this new optical technique in detecting the transformer's inception faults in addition to proving its potential for being a superior alternative to the well-known traditional diagnostic techniques.

Outlet short circuit on the low-voltage (LV) side and winding inter-turn short circuit faults are hazardous to transformer operation. To investigate the formation mechanism of winding insulation faults of distribution transformer, ANSYS Maxwell was used to build a coupled magnetic field-circuit model with the same structural dimension as the actual distribution transformer. An outlet short circuit and winding inter-turn insulation faults were set by using the voltage-controlled switch in the external circuit of the model. Subsequently, the differences in the electromagnetic characteristics and the electrodynamic force distributions of the windings under three operating conditions, namely, nominal load, three-phase outlet short circuit on the LV side and inter-turn insulation failure were studied, respectively. The results show that compared with the rated load, in the cases of outlet short circuit and inter-turn insulation faults, the amplitude of winding current increases by 20 and 50 times, the magnetic field strength grows by 20 and 17 times, and the electrodynamic force rises by 400 and 230 times, respectively. Outlet short circuit fault is more likely to cause the winding instability and deformation, and inter-turn short circuit fault can easily burn out winding insulation. Therefore, corresponding preventive measures were proposed.