As the key component of modern energy conversion systems, high-frequency transformer (HFT) directly affects the reliability of the system, and the design parameters of HFT, such as power density, loss, and temperature rise, are coupled with each other. Therefore, optimizing the design of HFT while considering multiple parameters has important engineering significance. In order to reduce the operating temperature rise without compromising the optimization outcomes, this article establishes a coupled design model of HFT and heat dissipation fins, and proposes a multi-objective optimization design method for HFT considering heat dissipation based on multi-objective particle swarm optimization (MOPSO). Finally, a 10 kHz/20kVA litz-wire HFT prototype is designed, and the proposed optimization design method is verified through modeling simulation and experimental testing.

Establishing an accurate renewable energy unit model is the basis for researching impact of large-scale renewable energy access on system. However, only black-box model of manufacturer can be obtained in actual modeling work. Multi-manufacturer models and multi-control modes of renewable energy units (REU) also bring difficulties to simulation modeling and analysis. First, the rationale for a structured model is analyzed. Combination strategies of "switching control" and "transient control" are put forward, and it is pointed out high voltage ride-through (HVRT) and low voltage ride-through (LVRT) control mode of REU has analytical consistency. Then, taking doubly-fed induction generator (DFIG) as an example, based on a large number of HVRT and LVRT response characteristic curves of the DFIG and detailed fault response stage division, fault ride-through characteristics are analyzed. An equivalent model of "switching control" with multiple response periods combined with multiple control modes is constructed. The electromagnetic transient model of the whole working condition is established on the basis of general fault ride-through equivalent "switching control" and "the steady-state power control","transient control" of the DFIG. Finally, simulation and error analysis verify the proposed model's effectiveness and applicability.

Grid-forming converters (GFMs) possess the capability of actively supporting grid voltage and frequency, and are expected to become key equipment for ensuring the stable integration of renewable energy in future power systems. However, due to their flexible control strategies and inherent overcurrent limitations during grid faults, the short-circuit current calculation becomes significantly more complicated, making traditional calculation principles and methods no longer applicable. This paper investigates the intrinsic characteristics of GFMs, summarizes their current-limiting behavior and control-loop configuration, reviews recent research progress on saturated current-limiting methods and virtual-impedance-based limiting strategies, analyzes the impact of different control schemes on short-circuit current response characteristics, and finally presents several insights and recommendations for advancing short-circuit current calculation methodologies for GFMs.

Ultrasonic-based partial-discharge (PD) detection has attracted considerable attention in the power industry. When the ROOT-MUSIC algorithm is used to detect PD sources in switchgear, the angle search can only be performed within the plane of a one-dimensional linear array, resulting in a limited direction-finding range and angular blind zones. To address these limitations, a 3D-ROOT-MUSIC algorithm is proposed. By adopting a dual dimensionality-reduction strategy, the proposed 3D-ROOT-MUSIC algorithm decomposes a three-dimensional polynomial into three one-dimensional polynomials, thereby overcoming the difficulty of solving the 3D rooting polynomial and enabling applicability to three-dimensional arrays. Simulation results based on 100 Monte Carlo trials and root-mean-square error (RMSE) evaluations under different signal-to-noise ratio (SNR) conditions indicate that the proposed algorithm achieves high direction-finding accuracy, a wide angular coverage, and strong interference robustness. Finally, a 27-element cubic array was built using IM73D122V01 digital microphones to conduct PD-source detection experiments in a switchgear scenario; across 11 direction-finding test groups, the azimuth and elevation residuals fall within −0.3° to 0.4°, and the RMSE remains stable between 0.3° and 0.5°, which verifies the effectiveness and accuracy of the 3D-ROOT-MUSIC algorithm for PD-source detection in switchgear.

Dry-type air-core reactors are crucial equipment for inductive reactive power regulation in ultra/extra-high voltage substations. In recent years, multiple incidents of equipment failure and fire faults have occurred, posing significant challenges to grid stability. Focusing on a 2024 fire fault involving a 35 kV dry-type air-core reactor in an ultra-high voltage substation, this study conducted a disassembly analysis of both the faulted phase and a reference phase, performed comprehensive diagnostic testing and verification, and carried out failure analysis. By combining these findings with existing detection methods for dry-type air-core reactors, the study identifies limitations in current detection approaches. This work offers valuable insights for the industry regarding fault diagnosis, analysis, and the advancement of detection technologies for dry-type air-core reactors.

ABSTRACT The lack of active power support capability in power systems with large‐scale renewable energy integration has become a significant constraint on stability. This paper proposes a variable speed condenser (VSC) control strategy based on a doubly fed machine. The rotating rotor shaft can provide inertia support for the system and participate in primary frequency regulation of wind farms or PV stations by adjusting the rotor speed. The stator of the VSC is directly connected to the grid. During short‐circuit faults, the principle of flux linkage conservation can provide short‐circuit current support for the system, suppressing transient overvoltage phenomena. Meanwhile, the fully controlled power electronic converter can provide rapid voltage regulation capability for the system. Simulation and field test results indicate that the VSC can provide stable inertia support, short‐circuit current support, primary frequency regulation and rapid voltage regulation. It can be installed in PV stations and wind farms to enhance the grid‐connection performance of renewable energy power plants.

This study investigates the bidirectional interaction between mechanical stress and magnetic properties in transformer cores. Grain-oriented silicon steel is employed to analyze the influence of stress on magnetization characteristics. Based on experimentally measured secant relative permeability data under various stress levels, the secant relative permeability is formulated as a bivariate function of magnetic flux density and stress. To overcome the limitations of conventional predefined empirical models, an analytical constitutive model for stress-dependent secant relative permeability is formulated using symbolic regression (SR), providing a highfidelity mathematical representation for complex magneto-mechanical behaviors. The model is integrated into a magneto-mechanical bidirectional coupling framework, enabling the dynamic updating of magnetic properties based on local stress states. A 110 kV three-phase three-winding oil-immersed transformer is analyzed to compare unidirectional and bidirectional coupling strategies. Results show that stress feedback modifies magnetic flux distribution and core loss characteristics, reducing peak magnetic flux density by 1.75% and peak core loss by 5.81%, while capturing local nonlinear and stress-sensitive regions. The proposed framework improves the physical consistency of flux redistribution and loss evaluation, providing a refined analytical approach for the electromagnetic-structural coupled analysis of transformer cores.

Oil-paper insulation is the main insulation system for oil immersed power equipment. Accurately evaluating its aging status is crucial for the power grid operation and maintenance department to formulate maintenance strategies. To clarify the influence of testing excitation amplitude and testing temperature on the variation law of dielectric characteristics of oil-immersed power equipment, and to improve the accuracy of evaluation results based on curve characteristics, wide - temperature and wide-frequency dielectric response experiments were conducted on oil-paper insulation systems ( pressboard-oil gap-pressboard) with different aging degrees under various excitation amplitudes. The test results show that as the test temperature increases, the characteristic frequency range of non-linear changes in the loss factor curve shifts towards high frequencies. For the oil-paper insulation model in the later stage of aging, due to the synergistic effect of ion alternating oscillation process and positive and negative ion composite motion in the transformer oil gap, the loss factor curve exhibits different nonlinear changes in the high and low frequency ranges. Meanwhile, a calculation method for critical field strength and critical frequency was proposed based on the oscillation model. The influence of different testing temperatures and aging on the critical frequency and critical field strength of oil-paper insulation systems was revealed. The research results of this paper provide certain theoretical support for conducting on-site diagnosis and analysis of insulation status of oil-immersed power equipment based on frequency domain dielectric response detection technology.

The "15th Five-Year Plan" period represents a critical phase for China to achieve its landmark carbon peaking target. With the development of new energy power generation exceeding expectations, power grid planning faces unprecedented challenges and opportunities. This paper examines the technical characteristics of power grids during this period, including the normalization of high-proportion new energy output, the dynamic process coupling of transmission and distribution networks, and the weakening effect of system scale growth on stability improvement. To address these characteristics, the paper proposes key research directions for security and stability analysis in grid planning during the "15th Five-Year Plan" period, which include: screening typical scenarios for stability analysis, load modeling incorporating distributed generations, load capacity of power electronics-dominated generation systems, and comprehensive short-circuit current management. In technological innovation, the paper suggests such scenario-specific studies as application of grid-forming technologies，optimal selection of transmission technology solutions, etc.

With the continuous increase in the proportion of new energy generation capacity, the stochastic nature and weather-coupled characteristics of its output pose significant challenges to power system supply-demand balance. Traditional methods struggle to quantify risks associated with numerous extreme scenarios and insufficiently characterize low-probability, high-impact scenarios such as long-term low output of new energy and "extreme heat and windless" weather. This paper proposes a supply-demand balance state assessment method that constructs an 8760-hour full-scenario set through stratified sampling and achieves scenario reduction using an improved clustering algorithm. On this basis, extreme scenarios are supplemented to form a specific scenario set. Combining with a time-series production simulation algorithm for sources-grids-loads-storage, a four-level assessment system is established based on power deficit magnitude and duration. Validation using 2030 development planning data of a regional power grid demonstrates the feasibility and effectiveness of the proposed model and method, providing an efficient quantitative assessment tool for supply-demand analysis in high-proportion renewable energy power systems.

This paper investigates the vibration and noise characteristics of high-frequency transformers (HFTs) with Litz wire windings. Despite the numerous advantages of high-frequency transformers, the analysis of vibration and acoustic noise in high-frequency transformers remains a challenging issue. A comprehensive analysis framework is developed to study these characteristics of HFT. First, an electromagnetic force model is established to analyze the high-frequency vibration mechanism. The magnetic properties of nanocrystalline cores are characterized through experimental measurements. Then, a multi-physics coupling model incorporating electromagnetic, mechanical, and acoustic fields is then constructed. To enhance computational efficiency, a simplified 2D multi-physics coupling model is proposed based on HFT load force analysis. The model’s effectiveness is verified through comparative studies under both sinusoidal and square wave excitations. Finally, experimental validation is performed using a specially designed high-frequency vibration and noise testing platform. The measured results demonstrate good agreement with the theoretical predictions, confirming the model’s accuracy. The research provides theoretical and data support for the optimization design of high-frequency transformers considering vibration and noise factors comprehensively.

The ground electrode line is the circuit connecting the neutral point on the DC side of the converter station to the ground electrode in a DC transmission system. Under high-current modes such as monopolar operation, the conductor experiences significant heating. Once a conductor breakage fault occurs, the current path is disrupted. If, for instance, one circuit of a double-circuit line on the same tower breaks, the current originally shared by both circuits transfers entirely to the remaining circuit, causing its current to double instantly. This leads to a rapid and sharp increase in conductor temperature. The conductor may experience reduced strength due to overheating, and in severe cases, even melt. This paper focuses on the ground electrode conductor, establishes a temperature calculation model, performs computations for both transient and steady-state temperatures, and analyzes the current-carrying temperature rise characteristics. It calculates the maximum allowable operating time and maximum allowable operating current for the conductor under extremely high current conditions, providing crucial data support for system dispatch. As time increases, the conductor temperature initially rises rapidly. After increasing to a certain extent, the rate of temperature rise gradually decreases, and the conductor temperature increases slowly until it reaches the steady-state temperature. As the current-carrying capacity increases, the conductor temperature gradually rises, and the relationship between them approximates a linear relationship with the square of the current. The temperature declines rapidly at lower wind speeds but gradually stabilizes as the wind speed continues to rise. The thermal-resistant aluminum alloy conductor steel reinforced used for grounding electrodes demonstrates a higher allowable current-carrying capacity than aluminum conductor steel reinforced.

In ultra-high voltage converter stations, the phenomenon of flashover along the outer insulation of dry hollow reactors made of epoxy (EP) /glass fiber (GF) composites poses a potential threat to the stability of the power system. To enhance its flashover performance under varying complex conditions, it is necessary to conduct in-depth research on the flashover mechanism of this material under different voltage forms. This study conducted tests on the flashover voltage, surface space charge distribution, and partial discharge (PD) parameters under varying AC-DC ratios and AC frequencies, and exploring their relationships. The results show that the DC content in the AC-DC ratio decreases, the flashover voltage decreases, the apparent total discharge of PDs increases, and the maximum surface space charge density decreases. The main influencing factor is the increase in the number of seed charges involved in gas ionization. Increasing the AC frequency, the flashover voltage decreases, the apparent total discharge increases significantly, and the surface charge density remains basically unchanged. The main reason is that the change in the number of alternating cycles further increases the number of seed charges. This study reveals the flashover mechanism of EP/GF composites under different voltage forms, which provides theoretical support for subsequent material modification.

Partial discharge test of transformers is an essential part of equipment factory testing and an important means of assessing the overall insulation performance of transformers. Taking the disassembly analysis and handling method of partial discharge test abnormalities during the factory test of a 500kV transformer as an example, this article elaborates on the background and method of induction withstand voltage test with partial discharge measurement, and describes in detail the handling of partial discharge abnormalities. In the process of identifying the cause of the abnormality, the starting position of the fault was accurately determined through disassembly inspection, simulation calculation, physical and chemical analysis of the insulation cardboard, and X-ray inspection of the formed parts. The discharge traces left on the body were identified, and the discharge path was determined to accurately determine the cause of the fault. At the same time, a repair plan for the subsequent transformer was provided, and two partial discharge tests were conducted to verify that the transformer's handling measures were reasonable and effective, ensuring zero defect operation of the equipment.

The dynamic characteristics of transmission conductors under actual operating conditions, such as aeolian vibration, are jointly influenced by multiple factors including tension, vibration amplitude, vibration frequency, and conductor type. The internal relationships among these factors typically exhibit significant nonlinear characteristics, posing considerable challenges to traditional modeling methods. This paper constructs a data-driven prediction framework for conductor dynamic characteristics based on experimental data, employing three models—Random Forest (RF), Support Vector Regression (SVR), and Multilayer Perceptron (MLP)—for comparative analysis. The research results indicate that the deep neural network model outperforms traditional machine learning models in terms of nonlinear fitting capability and generalization performance under multi-feature conditions, enabling more effective capture of the complex mechanical response characteristics of conductors under various operating conditions. The method proposed in this paper provides a feasible and efficient technical approach for the rapid assessment and intelligent modeling of conductor dynamic behavior.

The increasing penetration of wind power poses a significant challenge to power system frequency stability, making it vital to enable wind turbine generators (WTGs) to participate in the frequency response of power grids. Considering the frequency response ability of WTGs is closely related to their operation status, how to fully utilize the frequency response ability of WTGs and select appropriate time to exit frequency support according to system frequency characteristics is a key point in designing an effective frequency response method for wind turbines. This paper proposes a two-stage adaptive frequency control method for wind power, through which, the frequency support power of WTGs can be adaptively adjusted according to frequency variation and the operation status of WTGs in frequency support stage, and WTGs can provide maximum frequency support power when the frequency reaches its security constraint. In the rotor speed recovery stage, the proposed method allows the WTG to adaptively exit from the frequency support according to the rate of change of frequency (RoCoF), thus avoiding large power dips and improving the secondary frequency dip (SFD). Meanwhile, through the proposed method, WTGs can provide sufficient frequency support power to respond to subsequent disturbances during rotor speed recovery. The modified IEEE 39-bus system is used to verify the effectiveness of the proposed method.

With the rapid development of China's national economy and the sharp increase in power demand, the rapid growth of the number of transformers makes the requirements for equipment quality control and equipment evaluation methods urgently need to be further improved. This paper carries out research on transformer technical conformity assessment, which can realize data storage, data mining and correlation analysis. The digital twin constructed can convert data into assets, and then establish a complete set of digital management service system of transformer equipment, which is conducive to improving the intelligent level of technical conformity assessment of main equipment. The technical conformity evaluation database was established and the data differentiation analysis was completed. An early warning mechanism for key data of transformer technical conformity assessment is proposed, a digital platform for data management and analysis of conformity assessment is established to further improve the efficiency of technical conformity assessment, fully mine and analyze technical conformity assessment data, and improve equipment quality.