Integrating renewable energy resources such as wind farms is an increasingly prominent trend for future power grids. However, the wind generator tower is consistently at risk of lightning strikes, putting the wind farms’ transformer at risk of damage by lightning transients traveling through the system. Various harmonic contents of the lightning transient can excite the transformer’s resonance frequencies, resulting in both terminal and internal overvoltages (OVs). To effectively safeguard transformers against resonance OVs, it is imperative to first identify the resonance points of the transformer. Following this, a protective method must be implemented to mitigate harmonic content magnitudes that contribute to resonance. This paper introduces a series-protection device comprising an air core reactor and suppressor resistance designed to protect the transformer. The research aims to provide solutions to safeguard wind farm transformers from both terminal and internal resonance OVs caused by lightning transients. The effectiveness of the protection device is assessed through analysis, simulation, and experiments conducted in a high-voltage laboratory setup.

Capacitance plays a crucial role in high dv/dt situations, making the accurate estimation of parasitic capacitance essential. This paper introduces an improved method of moments (MoM) for calculating the capacitance of round conductors, with or without insulation layers. The proposed method combines MoM with an analytical solution based on Laplace's equation. Compared to the original MoM, the proposed method does not require consideration of polarization charges on the surface of the insulation layer, which reduces the matrix size. Additionally, the proposed method can provide asymptotic formulas for capacitance calculation. The proposed method is compared with the 2D finite-element method (FEM), MoM and measurements. The results demonstrate that the proposed method aligns well with both the FEM simulations and the actual measurements. The proposed method uses less than half the time to calculate the same cases compared to the original MoM.

This paper presents the prototype development and performance evaluation of a three-stage flyback-based Input Series Converter designed as an Auxiliary Power Supply (APS) for a Modular Multilevel Converter (MMC)-based Arbitrary Waveform Generator (AWG). The APS is connected across the submodule capacitors of the MMC and converts the capacitor voltage to 24V, providing power to the gate drivers and control units within each submodule. The proposed converter features integrated active Input Voltage Sharing (IVS), a scalable architecture, and wide-input voltage operation. A multi-winding flyback transformer ensures high-voltage insulation between the submodule capacitor and the APS output while facilitating active IVS for balancing input capacitor voltages. A transformer prototype has been developed and tested in an open-loop converter configuration. The system’s performance has been evaluated at an output power of 30W across an input voltage range of 300V–3600V.

As the voltage levels of solid-state transformers (SSTs) increase using medium-voltage switches, high-frequency transformers (HFTs) used inside SSTs are subjected to increased electrical stress. This stress, characterized by high voltage, high-frequency pulsewidth modulation (PWM) voltage, can cause insulation partial discharge (PD) and potentially lead to failure of the HFT insulation system. While PD behavior under power-frequency sinusoidal voltage has been extensively studied, the behavior of HFT insulation under PWM square pulse conditions is less well understood. To address this gap, a high voltage high-frequency PWM voltage PD test platform is developed and high-frequency current transformer (HFCT) and ultra-high-frequency (UHF) antenna are used for PD signal detection. PD tests are performed under a variety of PWM conditions including PWM frequency, rise time, voltage amplitude, and different insulation layers to thoroughly investigate the HFT insulation behavior. The PD characteristics of repetitive PD inception voltage and phase-resolved PD patterns at different PWM conditions are recorded and analyzed under PWM conditions. In addition, this article explores the underlying PD mechanisms of the HFT insulation under high-frequency PWM stress, providing insights to explain the observed test results. The findings from this research provide essential references and lay a solid foundation for future advances in optimal design, health monitoring, reliability analysis, and lifetime prediction for HFTs in power electronics applications.

Polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), and polyimide (PI) are widely used in aerospace due to their excellent properties. Understanding their aging behavior is essential for long-term performance in extreme environments. This study examines the effects of thermal oxidative aging (at 250°C over varying periods) under humid conditions on their chemical, structural, thermal, mechanical, and dielectric properties. In PEEK, aging led to solidification and crosslinking phenomenon which resulted in increased tensile strength and storage modulus, while elongation at break and tan δ decreased. Dielectric permittivity, polarization charge density, and leakage current also declined with aging, while AC breakdown strength increased by 1.6% in PEEK. PTFE exhibited surface oxidation, thermal degradation, and a decrease in storage modulus, with an increase in loss tangent. Breakdown strength slightly decreased, while dielectric loss and leakage current increased over aging time. PI underwent severe mechanical degradation, with tensile strength reduced by 54% and elongation by 16%, along with oxidation-induced discoloration. Low-mass polar molecules generated in PI during thermal degradation which contributed to the deterioration of its dielectric properties, lead to increased permittivity, polarization, leakage current, and a lower breakdown strength observed after aging. These findings provide insights into degradation mechanisms, aiding aerospace material selection for extreme environments.

The effective prediction of dynamic cable ratings (DCR) in the HVDC cable is pivotal for enhancing transmission efficiency and maximizing electricity sales in offshore wind farms. Due to complex wind conditions, traditional machine learning methods, such as support vector machines, struggle to provide accurate long-term DCR predictions and express prediction uncertainties. To address these challenges, this article proposes a novel deep learning framework for dynamic cable rating prediction based on encoder–decoder networks, in which the encoder utilizes Bidirectional extended-long Short-Term Memory networks to encode contextual information from the input data. The decoder introduces an additive attention mechanism, which allows the network to focus on relevant features in the input sequence. In addition, to capture the uncertainty for DCR prediction, a Bayesian neural network approximation method based on the Monte Carlo dropout method is introduced. Finally, this paper introduces a thermal risk estimation method by considering both the maximum conductor temperature limit and the temperature gradient limit. Results demonstrate that the proposed method not only improves electric field distribution but also achieves superior economic benefits.

This paper studies the power density limits of propulsion motor for electric aircraft considering thermal aspects and breakdown voltage reduction of insulation. The study em-ploys multi-objective optimization (MOO) to explore various mo-tor cooling options and filter configurations. The results show that motors with direct winding heat exchanger (DWHE) can reach higher specific power, while those equipped with water jacket cooling (WJC) offer a moderate design with simpler structure. Furthermore, the impact of sine wave and dv/dt filters on electric motors design is studied. The findings demonstrate that dv/dt filters enable designs with higher overall specific power compared to sine wave filters. Through simulations, this study identify the challenge faced by aviation motor design in significantly increased insulation thickness, necessitating advanced insulation materials with a minimum thermal conductivity of 5 W/(m.K) to facilitate a high specific power design. Based on this assumption, a preliminary design of 9.6 kW/kg with an efficiency of 98% is presented.

Resonant converters are popular in power electronics due to their soft-switching capabilities, which enhance efficiency and prolong component lifetime. Three- phase resonant converters are particularly noteworthy for their higher power density and reduced ripple, making them ideal for demanding applications. A critical aspect of optimizing three-phase LLC resonant converters is the design of a transformer with adequate leakage inductance required for the resonance circuit. This paper compares two distinct transformer designs for such converters: a five-limb shell-type transformer and a symmetrical triangular transformer. Both designs are evaluated in terms of their performance, efficiency, and suitability for integration into the converter architecture. A detailed design procedure using Finite Element Method (FEM) analysis is presented to guide the development of these transformers. The practicality of this approach and its effectiveness are demonstrated through the implementation of a 3.4 kV to 60 V, 50 kVA prototype. This work provides a comparative analysis of transformer designs and introduces a validated methodology for improving the performance of three-phase LLC resonant converters through optimized transformer design.

The energy transition involves integrating numerous pieces of equipment that undergo frequent switching operations and face the risk of lightning strikes. Consequently, power systems are exposed to fast transient switching and lightning surges, necessitating enhanced protection solutions for power equipment. Over the past decade, viable solutions have emerged to mitigate fast transients and safeguard transformers in the form of a ring-core parallel inductor and resistor circuit (R-PIR). Although this device effectively protects medium-voltage transformers from fast transients, a precise and comprehensive model for this component is still lacking, especially considering the importance of refining the R-PIR for broader applications. This paper introduces a detailed model of the R-PIR as a protective device, validated by electromagnetic transient simulations and finite element methods, which are also confirmed by experiments. The main goals of the research work are to investigate the performance and design features of the R-PIR comprehensively and demonstrate how the designed R-PIR protects transformers against fast transients. The research work is validated by experiments conducted in a lab environment. It is concluded that designing the R-PIR within an appropriate frequency range can considerably suppress transient overvoltages to which the transformer is exposed.

The evolution of electrical power systems demands an increasing reliance on unpredictable renewable energy resources (RES). However, integrating these resources poses challenges, as their intermittent nature introduces transient events that can significantly impact power transformers. These transient phenomena may initiate energy oscillations in the form of weakly-damped resonances between system elements, i.e., transmission lines and cables, transformers, and the grounding system. Such conditions may impose stresses beyond the tolerance of insulating materials, leading to fast lifetime degradation and, eventually, the failure of critical components in the network, such as the costly power transformers. The impedance of the grounding system can limit the dissipation of surges, hence, causing severe overvoltages upon transient phenomena. By employing detailed transient models of crucial system components, this research puts forward a comprehensive analytical study of the transient interactions. In this regard, an analytical high-frequency transformer winding model based on lumped elements, and wideband frequency-dependent models for cables and the grounding system derived by applying electromagnetic theory are presented. These models, integrated into electromagnetic transient software, enable the identification of vulnerabilities and examination of case studies involving lightning strikes and switching events. Furthermore, the details of a novel protection method applied to safeguard the transformer are discussed in this paper. The presented protection method consists of a ring toroid core and a resistive suppressor on the secondary side of the core. This protection component is connected in series with the transformer to decrease the harmonic content and magnitude of the transient signals. The design procedure of the series protection device against voltage transient signals is presented and elaborated.

Traditional methods such as Steinmetz's equation (SE) and its improved variant (iGSE) have demonstrated limited precision in estimating power loss for magnetic materials. The introduction of Neural Network technology for assessing magnetic component power loss has significantly enhanced accuracy. Yet, an efficient method to incorporate detailed flux density information—which critically impacts accuracy—remains elusive. Our study introduces an innovative approach that merges Fast Fourier Transform (FFT) with a Feedforward Neural Network (FNN), aiming to overcome this challenge. To optimize the model further and strike a refined balance between complexity and accuracy, Multi-Objective Optimization (MOO) is employed to identify the ideal combination of hyperparameters, such as layer count, neuron number, activation functions, optimizers, and batch size. This optimized Neural Network outperforms traditionally intuitive models in both accuracy and size. Leveraging the optimized base model for known materials, transfer learning is applied to new materials with limited data, effectively addressing data scarcity. The proposed approach substantially enhances model training efficiency, achieves remarkable accuracy, and sets an example for Artificial Intelligence applications in loss and electrical characteristic predictions with challenges of model size, accuracy goals, and limited data.

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 the production of green hydrogen, electrolyzers draw power from renewable energy sources. In this paper, the design of Solid State Transformer (SST) for large-scale H ₂ electrolyzers is benchmarked. The three most promising topologies are chosen for design and comparison, including Modular Multi-level Converter (MMC) based SST, Modular Multi-level Resonant (MMR) based SST, and Input-Series-Output-Parallel (ISOP) based SST. The distance between converter towers for insulation and maintenance, the insulation system of the transformer, and the cooling system are designed with practical considerations in order to have an accurate estimation of the volume and weight of the SST. Losses in the switches are calculated based on equations, and losses in passive components are calculated based on FEM simulation. The operating frequency for each topology is optimized to minimize loss, weight, and volume. The best of each topology is then compared with each other to identify the most suitable one for large-scale H ₂ electrolyzers.

As the integration of renewable energy sources into the grid increases, the insulation systems of grid components such as transformers and switchgear encounter significant challenges due to the transients and harmonics generated by power-electronic-based converters. A test generator capable of replicating these component stresses is essential to accurately evaluate these insulation systems under real-grid conditions. This paper proposes a modular cascaded H-bridge-based high-voltage arbitrary waveform generator, prototyped with three stages to generate customized waveforms (triangular, sawtooth, pulse, and complex) up to 8 kV. The H-bridge modules are designed using Si MOSFETs with a maximum blocking voltage of 4.5 kV. The input to the HV H-bridge module is provided by a 10 kV medium-frequency transformer, whose design is described with a focus on the insulation system and winding configuration. This transformer is driven by a zero-voltage switching driver. This arbitrary waveform generator excels in several aspects, including a straightforward design procedure, compact size, high voltage capability, ease of integration, and cost.

In electron optics, calculation of the electric field plays a major role in all computations and simulations. Accurate field calculation methods such as the finite element method (FEM), boundary element method and finite difference method, have been used for years. However, such methods are computationally very expensive and make the computer simulation challenging or even infeasible when trying to apply automated design of electrostatic lens systems with many free parameters. Hence, for years, electron optics scientists have been searching for a fast and accurate method of field calculation to tackle the aforementioned problem in the design and optimization of electrostatic electron lens systems. This paper presents a novel method for fast electric field calculation in electrostatic electron lens systems with reasonably high accuracy to enable the electron-optical designers to design and optimize an electrostatic lens system with many free parameters in a reasonably short time. The essence of the method is to express the off-axis potential in an axially symmetrical coordinate system in terms of derivatives of the axial potential up to the fourth order, and equate this to the potential of the electrode at that axial position. Doing this for a limited number of axial positions, we get a set of equations that can be solved to obtain the axial potential, necessary for calculating the lens properties. We name this method the fourth-order electrode method because we take the axial derivatives up to the fourth order. To solve the equations, a quintic spline approximation of the axial potential is calculated by solving three sets of linear equations simultaneously. The sets of equations are extracted from the Laplace equation and the fundamental equations that describe a quintic spline. The accuracy and speed of this method is compared with other field calculation methods, such as the FEM and second order electrode method (SOEM). The new field calculation method is implemented in design/optimization of electrostatic lens systems by using a genetic algorithm based optimization program for electrostatic lens systems developed by the authors. The effectiveness of this new field calculation method in optimizing optical parameters of electrostatic lens systems is compared with FEM and SOEM and the results are presented. It should be noted that the formulation is derived for general axis symmetrical electrostatic electron lens systems, however the examples shown in this paper are with cylindrical electrodes due to the simplicity of the implementation in the software.

This paper introduces an innovative Magnetic Switch (MFS) designed to control and alter magnetic flux within energy system components, offering an alternative to conventional power electronic devices. The MFS comprises a low-current control coil, a control core, and a high-density magnetic flux-carrying main core combined with a main coil energy system. In this novel magnetic configuration, when a low-power current excites the control coil, the magnetic flux in the main core (supplied by the main coil) decreases to nearly zero. Conversely, when the control coil disconnects from the power source, the magnetic flux within the main core attains its maximum value. This operation positions the MFS as a groundbreaking concept within magnetic-based energy systems, akin to transistors in power electronics. The main outcomes of the MFS concept are that it can vary the magnetic flux of the main core in the large range, and it is a fast magnetic switch with a simple and low power loss control circuit and an independent control coil from the main coil. Analytical studies thoroughly elucidate the performance and advantages of this proposed magnetic switch, substantiated by Finite Element Method simulations and experimental prototype outcomes.

More and more printed circuit boards (PCBs) will be used in electric aircraft to achieve higher power density of the on-board electric system, while PCBs in aircraft are more likely to generate partial discharges (PDs) due to external factors such as compact structure and low air pressure. Therefore, this article proposes a fluorescent fiber-based method for detecting and evaluating PDs on PCBs. The detection method is effectively immune against the presence of the electromagnetic, acoustic, and vibration interference. Based on the optical detection, the evolution regularities of PCB surface appearance changes, optical PRPD patterns, and optical pulses during the aging process of PCB under different air pressure are analyzed in this article. Then, 12 assessment features are extracted for the PD aging process, and the contribution of these 12 features to the severity assessment at different air pressures is obtained using the minimal-redundancy-maximal-relevance (mRMR) algorithm. Finally, different numbers of PD features are tested for PD severity assessment by the support vector machine (SVM) algorithm. The evaluation results show that the severity assessment method proposed in this article can achieve an assessment accuracy of at least 91.1% and up to 94.4% under all three air pressures, which has good application and guidance value.

Litz wires, which are utilized to suppress eddy current, often have complex structures. This paper presents a partial element equivalent circuit (PEEC)-based 3D model for Litz wires with round conductor. The model accounts for both transverse and longitudinal magnetic fields. The discretization of the Litz wire is based on cylindrical elements resulting in a reduced number of elements. Cylindrical element analysis is based on a 2D analytical method. The proposed model is compared with 3D FEM, which shows the model has good accuracy and fast computational speed. It is promising to facilitate Litz wires optimization.

This article presents a 3-D numerical impedance calculation method based on cylindrical elements. It can be used to model the Litz wire and further air-core coil wound by the Litz wire. The discretization is based on cylindrical elements, resulting in a small amount of elements. Cylindrical element analysis is based on a 2-D analysis and its analog to 3-D. The analysis considers both transverse and longitudinal magnetic fields applied to elements. The proposed method is applied to several Litz wires and compared with 3-D finite element method (FEM), which validates that the method has good accuracy and fast computational speed. The effectiveness of the method for the air-core coil is validated by measurements. The proposed method is promising in facilitating coil optimization.

This paper discusses the prototype development and testing of a load invariant, high voltage gain DC power supply using inductive power transfer. The developed supply is intended to power the submodules of the CHB based arbitrary waveshape generator for testing high voltage components and materials. Using the Series Parallel topology, a load invariant voltage gain of 15 is obtained from a 350 V input DC Bus, with an efficiency of 88% and a load regulation of 18%. The obtained 5 kV output can conduct DC breakdown of dielectrics with a damping resistor and can test insulation aging, breakdown under high frequency AC.