Air-core Transformer Research Articles

Nikola Tesla-Father of Our Energy Systems.

Nikola Tesla (1856-1943) was an American-Croatian electrical engineer who studied at Graz and Prague. He emigrated to the USA in 1884, where he worked for Thomas Edison. After a period of time, apart from having differences of opinion, Edison did not pay him the promised remuneration, so he left the job and set up on his own. Soon, Tesla promoted alternating current (AC) and invented his AC induction motor, which eliminated commutator and sparking brushes needed for direct current (DC) motors favored by Edison. During the early years of electricity, there was one problem: DC was not easily converted to higher or lower voltages. Tesla believed that AC could be converted to different voltages relatively easily using a transformer. He also made substantial improvements in the field of AC power transmission and generation, realizing that it could be generated and transmitted far more effectively than the commonly used DC. He patented his inventions and set up a partnership with George Westinghouse. His interest then shifted to developing a high-frequency and high-voltage Tesla coil with an air-core transformer, and he achieved this in 1899. He even made a device that could transmit power without intervening wires by using the earth as a transmitting oscillator. He was increasingly interested in transmitting power over large distances.

Design and Optimization of Air-Core HTS Pulse Transformer for Series-Type Hybrid Circuit Breaker (S-HCB)

Design and Optimization of Air-Core HTS Pulse Transformer for Series-Type Hybrid Circuit Breaker (S-HCB)

Real-Time Detection Method for Saturation Speed of Air-Core Coil Current Transformer

Traditional methods generally rely on a fixed threshold to determine whether the current transformer is saturated. However, this threshold based judgment method is difficult to adapt to different working conditions and changes in current waveforms. In view of the different characteristics of current transformer and the diversity of working environment, it may not be accurate to judge its saturation state only by relying on a fixed threshold. In order to improve the efficiency of current transformer speed saturation detection and reduce the error, a new type of air core coil current transformer speed saturation real-time detection method is proposed. Based on the working and current characteristics of the fast saturation current transformer, the discrete Fourier algorithm is used to suppress power frequency interference signals, with the fundamental frequencies set to 45 Hz and 55 Hz respectively, in order to separate the signal from power frequency interference and reduce the interference intensity of the power frequency interference signal; Identify all faults and saturation points, and extract effective data segments. The wavelet transform characteristics of the secondary current waveform of current transformer in saturated and unsaturated states are deeply studied. By analyzing the changes of different operating conditions and current waveforms, more discriminant features are extracted by using the characteristics of wavelet transform, so as to realize the real-time and accurate detection of saturation state. The results indicate that after adopting the proposed method, the highest accuracy of data segment extraction reached 97%; The maximum detection error is only 4%. The detection time is only 1.31 s. This indicates that the proposed method improves the detection performance and is practical.

Design method for high-power high-frequency magnetic-resonance air-core transformer

PurposeThe purpose of this paper is to study the multi-objective optimization design method of high-power high-frequency magnetic-resonance air-core transformer (ACT).Design/methodology/approachFirst, this paper studies the interleaved winding technology, the process of modeling and simulation, the calculation method of high-frequency loss of Litz wire and the design of magnetic shielding in detail. Second, the multi-objective optimization design process of high-frequency magnetic-resonance ACT is established by parametric scanning method and orthogonal experiment method.FindingsAn ACT model of 2 kV/100 kW/81.34 kHz was designed. The efficiency, weight power density and volume power density are 99.61%, 21.6 kW/kg and 5.1 kW/kg, respectively. Finally, the multi-physical field coupling simulation method is used to calculate the port excitation voltages and currents and temperature field of ACT. The maximum temperature of the ACT is 95.5 °C, which meets the design requirements.Originality/valueThe above research provides guidance and basis for the optimization design of high-power high-frequency magnetic-resonance ACT.

A 1-MHz GaN-Based $LCLC$ Resonant Step-Up Converter With Air-Core Transformer for Satellite Electric Propulsion Application

A gallium nitride (GaN)-based resonant step-up converter is proposed for the application in the satellite electric propulsion (EP) system. This converter consists of a full-bridge inverter, a resonant tank, and a multistage Cockcroft–Walton voltage multiplier to provide a high voltage gain. Additionally, the air-core transformer is introduced due to the megahertz switching frequency allowed by the GaN device. Thus, the limited magnetizing inductance of transformer and the remarkable junction capacitance of diode have to be carefully considered in the resonant tank design, especially after considering that this converter normally operates at the light load in the EP system. In this work, the fourth-order <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ LCLC$</tex-math></inline-formula> resonant converter is investigated. The recommended parameter selection for the fourth-order resonant tank is also provided. A 1.2-MHz, 23-V/2.5-kV, and 6-W prototype is demonstrated. It achieves a low harmonics distortion and a low power loss with the zero voltage switching.

NUMERICAL SOLUTION FOR THE DISTRIBUTION OF THE ELECTROMAGNETIC AND THERMAL FIELDS OF AN AIR-CORE TRANSFORMER

The article presents a numerical solution for the distribution of the electromagnetic and thermal fi elds of an air-core transformer using the fi nite element method. The distribution of the magnetic fi eld is determined for the dynamic steady state and magnetic nonlinear core characteristics. The model presented facilitates the establishment of criteria for optimizing transformer operation under various load conditions, environments as well as in the case of failures. Thus, the transformer can operate at maximum capacity while, at the same time, the probability of faults due to overheating is reduced to a minimum.

A Compact Repetitive High-Power Pulse Generator Based on Air-Cored Pulse Transformer

A Compact Repetitive High-Power Pulse Generator Based on Air-Cored Pulse Transformer

Geometrical Optimization of Medium-Frequency Air-Core Transformers for DCX Applications

This article analyzes the potential of air-core transformers (ACTs) for realizing medium-voltage high-power isolated dc–dc converters. ACTs, i.e., transformers without magnetic cores, are particularly interesting for their simple construction and reduced weight. However, the reduced magnetizing inductance, the reduced magnetic coupling, and the stray fields are challenging aspects for the design of ACTs. A comprehensive model of the ACT (e.g., magnetic field patterns, skin and proximity losses, shield’s eddy currents, harmonics, insulation constraints, and thermal limit) is proposed and verified with measurements obtained with a prototype. Afterward, a complete multiobjective optimization of a series resonant converter (SRC) operating as a dc transformer (DCX) between two 7 kV buses with a rated power of 166 kW is conducted. Two different geometries are considered for the ACT: concentric cylindrical coils and planar spiral coils. As a result, the optimal ACT (operated at 162 kHz) features extreme power densities of 7.5 kW/dm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and 31 kW/kg, which confirms the superiority of ACTs regarding the gravimetric power density. The calculated efficiencies are 99.5% and 98.7% for the ACT and the complete dc–dc converter, respectively. Finally, the different tradeoffs are highlighted and analyzed, e.g., mass, volume, efficiency, switching frequency, part-load behavior, and insulation distance.

A New 7 kW Air-Core Transformer at 1.5 MHz for Embedded Isolated DC/DC Application

This paper presents the study of air-core transformers for electric vehicles, developing them for medium-power (tens of kWs) converter applications specifically used at a high frequency. Air-core transformers have the advantage of lacking magnetic saturation and iron losses, making them suitable for high-frequency applications. We designed and manufactured a transformer for a determined frequency and inductance value. The design of this passive component aims to both keep the magnetic field inside the transformer and manage the thermal energy efficiently. The electrical, magnetic, and thermal properties are simulated and then verified by experiments with a specific test bench. The transformer reaches high performances for a higher frequency than usual for an equivalent power transfer in automotive applications.

Analysis of the Performance Limits of 166 kW/7 kV Air- and Magnetic-Core Medium-Voltage Medium-Frequency Transformers for 1:1-DCX Applications

Solid-state transformers (SSTs) are employing compact high-power medium-voltage (MV) medium-frequency transformers (MFTs) and enable the power transfer between galvanically isolated DC systems. Considering a typical SST isolation stage, i.e., a 166 kW unregulated series-resonant DC–DC converter acting as a DC transformer (DCX) with equal input and output MV DC voltages of 7 kV (1:1-DCX), we derive component- and system-level performance limits of air-cooled realizations with either an air-core transformer (ACT) or with a magnetic-core transformer (MCT). We describe the design of two fully rated MFT prototypes in detail and provide a comprehensive experimental characterization to validate the derived performance limits, including the dielectric losses and the analysis of stray magnetic fields. The realized ACT and MCT prototypes achieve measured efficiencies of 99.5% and 99.7% at gravimetric power densities of 16.5 and 6.7 kW/kg, respectively. Considering 10 kV SiC MOSFETs, calculated system-level efficiencies of the ACT-based and MCT-based 1:1-DCX result in 99.0% and 99.2% at the nominal operating point, with similar part-load efficiency characteristics. This article concludes with an application-oriented qualitative evaluation of the two concepts.

A 10 MHz DC/DC Converter With Zero-Phase Difference Synchronous Driving Signal

In this article, a 10 MHz dc/dc converter based on three-dimensional air core transformer with zero-phase difference synchronous driving signals is designed. By using the characteristics of no leakage inductance in the inner winding of the nested toroidal air core transformer, the phase difference between the output voltage of the inverter and the input voltage of the rectifier can be regarded as zero, so that the rectifier and the inverter can use the same driving signal, which simplifies the control of the synchronous rectifier switches, and realizes the reliable and efficient synchronous rectification control at 10 MHz. The prototypes with primary and secondary compensation are proposed and the experimental results verify the feasibility of the proposed control method and numerical design method.

Development of an Advanced-Fuel Nuclear Fusion Experiment

As a first step to exploring the possibilities of D-3He plasmas, a deuterium-tritium burning plasma experiment at high field and plasma densities, which can be much closer to the required parameters than present-day experiments, is particularly attractive. Compact high-field experiments were the first to be proposed in order to achieve fusion ignition conditions based on existing technology and the known properties of high-density plasmas. In previous studies, a feasibility study of a high-field D-3He experiment of larger dimensions and higher fusion power than Ignitor, but based on Ignitor technologies, was brought to the proposed Candor fusion experiment. Unlike Ignitor, Candor would operate with values of poloidal beta around unity and the central part of the plasma column in the second stability region. The toroidal field coils are divided into two sets of coils, and the central solenoid (air core transformer) is placed between them in the inboard part. In this paper, a revised design of Candor is proposed, based on the new technologies. This tokamak is capable of reaching D-3He ignition on the basis of existing technologies and knowledge of plasma, without any optimistic extrapolation.

Experimental and numerical study of high frequency superconducting air-core transformer

Although many researches on superconducting air-core transformers have been carried out, it is mainly on the power frequency situation. The high-frequency characteristics of superconducting air-core transformers are still unclear. In this paper, we applied experimental and finite element simulation approach to study the operation and loss characteristics of high frequency superconducting air-core transformer made by YBa2Cu3O7−δ (YBCO) tapes. The numerical model established is based on the H formula and the E–J power law, and the edge degradation and anisotropy of the critical current density of the tape are considered in the model. The results show that the operating characteristics of superconducting transformers are significantly different from those of conventional transformers, and their operating characteristics have strong frequency and power dependence. The obtained findings can provide a theoretical basis for the design of high-frequency resonant transformers.

Preliminary demonstration on JET of an ITER neutron environment-compatible quadrupole mass-spectrometer✰

Strict limits recently imposed on neutron exposure to electronics for critical diagnostic systems on ITER, the fusion reactor demonstration facility under construction in the south of France, has led to the development of a quadrupole mass spectrometer with an exceptionally long cable. An 80 m cable exceeds the last state-of-the art limit of 15 m, imposed by the normally required proximity of the RF supply to the analyzer, and will allow locating the electronics in a neutron safe environment. This breakthrough, a joint development of ORNL with Hiden Analytical Ltd., was enabled by the use of an intermediate, RF-matching unit, free of silicon-based electronics, and using only vacuum tubes and an air-core transformer, rendering it resilient both to ionizing radiation and to fringing magnetic fields. After successful testing of the prototype unit, both at ORNL and Hiden's laboratories, the unit was installed on the JET tokamak, as part of a multi-sensor, divertor effluent gas analysis system, similar to one also under design for ITER. As such, the prototype will be tested both before and during the next nuclear (D-T) operation of JET, planned for mid-2021. In this paper, the prototype development, laboratory testing and first results from non-nuclear plasma pulse testing on JET are presented. The latter include not only successful detection of fusion fuel cycle and impurity species, but also improved resolution and stability over the state-of-the-art, 15m-cable units on the same analysis station.

Dynamic Wireless Power Transfer in Electric Vehicles

An Electrical vehicle can utilize a force move framework to charge the on-board Rechargeable Energy Storage System (RESS the battery) or to give the capacity to the electric engine. It is additionally conceivable to utilize remote force move to charge the batteries while fixed, using charging pads. Both of these arrangements are satisfactory for assessing at home or in-vehicle parking, yet at the same time, require the vehicle to stop in a proper area to charge the battery. We propose an eco-friendly wireless charging system for electric vehicles, which enables wireless charging of the vehicle while running on the highways. The proposed approach is also used for the charging of cars in the shopping malls and other parking places. Moreover, the proposed charging system may require electrical energy from the solar PV systems and wind turbines, installed along the highways. The solar PV system and wind turbines are connected to form a Microgrid system and feed generated electrical energy to the wireless charging system. The surplus electrical energy may be either fed back to the primary grid or used for highway illumination. The wireless charging system also consists of an air-core transformer with its primary winding below the highway surface and secondary mounted on the vehicle. The ac power from secondary passes through a rectifier and dc-dc conversion stage to produce suitable dc voltage and current for the charging of the battery unit.

Error Analysis of Air-Core Coil Current Transformer Based on Stacking Model Fusion

Air-core coil current transformer is a key piece of equipment in the digital substation development. However, it is more vulnerable to various faults when compared with the traditional electromagnetic current transformer. Aiming at understanding the effect of various parameters on the performance of the air-core coil current transformer, this paper investigates the influence of these factors using the maximum information coefficient. The interference mechanism of influencing factors on the transformer error is also analyzed. Finally, the Stacking model fusion algorithm is used to predict transformer errors. The developed base model consists of deep learning, integrated learning and traditional learning algorithms. Compared with gated recurrent units and extreme gradient boosting algorithms, the prediction model based on stacking model fusion algorithm proposed in this paper features higher accuracy and reliability which helps improve the performance and safety of future digital substations.

Series-DC connection of Offshore wind generating units - modeling, control and galvanic isolation.

This work proposes an air-core DC-DC solid state transformer to connect the wind turbines of an offshore wind farm in series with a DC transmission link. This emerging layout does not use a power transformer to increase the voltage from the offshore collector network to the transmission level, nor does it require a rectifier station to convert the electrical energy to DC. The diode-clamped rectifiers, connected to each permanent-magnet generator, are controlled to drain sinusoidal currents from the generators in order to extract the maximum power from the wind turbines. The air-core transformer, designed by means of a finite element software, ensures the galvanic isolation between the wind generator and the HVDC link. From the generator side, a single-phase full-bridge three-level inverter feeds the primary coil of the transformer, whereas the secondary coil is wound using by means of an XLPE-insulated cable. This paper also presents a strategy for designing the controllers that regulate the output voltage of each wind conversion unit. Results from digital simulations, obtained with PSCAD/EMTDC, are presented to validate the technical feasibility of the proposed DC-DC solid-state transformer scheme, as well as to demonstrate its performance under different operational conditions.

Design and Experimental Analysis of 166 kW Medium-Voltage Medium-Frequency Air-Core Transformer for 1:1-DCX Applications

The galvanic isolation of solid-state transformers (SSTs) is typically realized with a medium-frequency (MF) magnetic-core transformer (MCT). Previous demonstrations indicate that achieving highly power-dense and lightweight MCTs imposes several challenges on the design because of stringent requirements related to insulation and cooling. This work investigates the achievable efficiency of an optimized 166 kW/7 kV air-core transformer (ACT), which is a core part of a dc transformer (DCX), i.e., an unregulated dc–dc SST with a voltage scaling defined by the transformer turns ratio. The ACT features relatively low complexity of the construction, comparably high coupling values, and high efficiency. Modeling, optimization, and construction of the realized ACT are explained and guidelines regarding insulation, cooling, and shielding of the magnetic stray flux are discussed in detail. Furthermore, the prototype is experimentally validated to demonstrate its full functionality. In the investigated DCX, which is based on a series resonant converter (SRC) topology, the realized ACT is found to achieve a full-load efficiency of 99.5% and an unprecedented gravimetric power density of 16.5 kW/kg. With the use of 10 kV SiC MOSFETs, the complete DCX is estimated to reach an efficiency of 99% at 166 kW output power.

Computational and experimental study of air-core HTS transformer electrothermal behaviour at current limiting mode

The paper provides the results of the experimental and computational study of the processes occurring in high temperature superconducting transformer windings while secondary winding is short-circuited. The obtained mathematical simulation matches closely with the experimental results. The temperature variation curves for superconducting windings were analysed, and conclusions were made on the necessity of changes in HTS transformer design, namely the necessity of windings heat-insulation from each other and adding a high-resistance coating material for HTS wire in HTS transformer primary winding.

A novel methodology for high‐frequency lumped equivalent circuit of an isolated transformer winding construction based on frequency response analysis signal morphology interpretation

A novel auto-synthesis method is proposed to construct the mutually coupled equivalent circuit of an isolated air-core transformer winding based on the signal morphology interpretation of its measured frequency response analysis (FRA) only. Therefore, this approach aims to determine the model parameters from the frequency sub-bands (low, medium and high frequency), each of which reflects its dominant parameters, where the parameter identification procedure is done from their corresponding sub-band separately. Besides, the optimisation algorithms have difficulties in estimating the nearly unique lumped circuit parameter in a large search space. For this reason, based on analytical simplifications, two novel dynamic autonomous methods have been proposed to restrict the search space bounds of the inductances and the capacitances. Finally, real case studies were used on actual air-core windings to validate the ability of the proposed method to perform an automated synthesis. Consequently, a nearly unique equivalent circuit model has accomplished automatically with high accuracy.