Frequency Electric Power Research Articles

Transient voltage performance and protection design of variable frequency ac three-stage generator for more electric aircraft

Abstract Nowadays, variable frequency AC generation system is widely used on more electric aircraft because of their advantages of simple structure, high power density, and high reliability. However, a variable frequency system has a wide range of operating speeds and frequencies, and its exciter field is designed to be highly saturated at low speed. Under the condition of a saturated exciter field at high speed, the generator can produce a very high voltage, which will cause damage to aircraft utilization equipment, leading to catastrophic failures. Therefore, to protect the safety of the aircraft, transient voltage regulation performance and voltage protection design are critical in the system design of variable frequency AC generation. This paper focuses on the design of voltage regulation and protection of variable frequency electrical power systems that can meet airworthiness requirements.

Investigations on a 2.2 K five-stage stirling-type pulse tube cryocooler. Part B: Experimental verifications

In this part, a five-stage Stirling-type pulse tube cryocooler (SPTC) is worked out to verify the theoretical analyses conducted in Part A. The experimental setup is described in detail, and the operating frequency, charge pressure and input electric power of the last two stages are optimized with He-3. Relevant experiments are also conducted with He-4 for comparison. The experimental results show that a no-load temperature of 2.28 K is reached with He-3, and the cooling capacities of 2.5 W at 80 K, 0.15 W at 30 K, 0.05 W at 12 K, 16.9 mW at 6 K, and 12.2 mW at 3.5 K are simultaneously achieved, respectively, with a total system exergetic efficiency of 2.25 %. Satisfactory agreements are observed between theoretical and experimental studies.

Research on the transmission of electric power via the increased frequency coaxial line to a remote low-power load (consumer)

The article gives the analyses of the existing limitations in the transmission of electric power to a remote low-power load (consumer) and the alternative system of an increased frequency electric power supply is offered. The primary parameters of an increased frequency coaxial line are examined at different operating modes. It is shown that in the study progress the influence of the equipotential surface of the Earth’s field on the primary parameters of an increased frequency coaxial line was identified. The calculation methodology of the primary parameters of an increased frequency coaxial line is given taking into consideration the influence of the equipotential surface of the Earth’s field. The obtained results can be used at the designing of increased frequency electric power supply systems for remote low-power loads (consumers).

Magnetic characterization of self-assembled nanostructures in cobalt ferrites using first-order reversal curve (FORC) analysis

Magnetic ceramics are important for numerous technologically relevant applications with a detailed understanding of structure, property, and processing inter-relationships playing a critical role in tailoring magnetic properties. Spinel ferrites are a particularly interesting class of magnetic ceramics of chemical formula AB2O4, with applications including biomedical hyperthermia and high frequency electrical power conversion. In this contribution, we seek to investigate a unique class of Co-ferrites in which spinodal decomposition can produce a ferrite nanocomposite with chemistry and stress state fluctuating within the interior of crystalline grains on the nm-scale, resulting in corresponding fluctuations of intrinsic magnetic properties as well as exchange and magnetostatic interactions. Structural and magnetic characterization of spinel ferrite samples are carried out (1) in the as-milled state prior to thermal processing, (2) after chemical and structural homogenization with a thermal calcination step, and (3) in the spinodal decomposed state following a subsequent annealing treatment within the Co-ferrite miscibility gap. Of note is the formation of a wasp-waisted hysteresis loop which emerges for the spinodal decomposed Co-ferrite sample, indicative of more complex magnetization reversal processes at relatively large applied fields than for homogeneous Co-ferrite samples of similar particle size and identical nominal chemistry. First order reversal curve (FORC) analysis is applied to further characterize the magnetization response, and a conventional interpretation of observed features in the FORC contrast is presented to discuss potential dominant magnetization mechanisms. The work described here represents the first application of FORC to spinodal decomposed magnetic ceramics and provides a strong foundation for future investigations seeking to quantitatively describe the impacts of nm-scale chemical, structural, and magnetic fluctuations on magnetization processes in ferrite spinel nanocomposite systems.

Research on Controlling Limits for Electromagnetic Environment in China

With the remarkable growth of power demand, power transmission and transformation facilities are gradually developing towards the direction of large capacity and ultra high voltage. In China, 500kV EHV AC power grid is mainly used for long-distance power transmission. However, people have panic and psychological pressure for the electromagnetic environment problems caused by high-voltage transmission lines. This paper concentrates on electromagnetic environment control limits around 500kV EHV AC electric power transmission lines in China. The power frequency electric field and power frequency magnetic field of two buildings under the transmission lines are monitored. With the support of objective scientific data, reducing or even eliminating public excessive panic about the electromagnetic environment caused by 500kV EHV AC transmission system.

Highly efficient formation process for functional silicon oxide layers at low temperatures (≤ 120 °C) using very high-frequency plasma under atmospheric pressure

SiO2-like films are deposited with high rates at substrate temperatures in the range of ≤120 °C by means of the developed atmospheric-pressure (AP) plasma-enhanced chemical vapor deposition (PECVD) technology. The AP plasma is excited by using a novel parallel-plate-type electrode system under supplying a 150 MHz very high frequency (VHF) electric power. As the process gases, oxygen (O2) and hexamethyldisiloxane (HMDSO) diluted with helium (He) are used. The electrode system is capable of forming one-dimensional flow of the process gases without any turbulence both inside and outside the plasma zone, which achieves the deposition conditions with no contamination of substrate surface with dust particles. The microstructure and surface roughness of the films are discussed by controlling O2 flow rate (O2/HMDSO source ratio) and VHF power density (PVHF), aiming at the use of the films as the gate insulators of low-temperature thin film transistors (TFTs). Irrespective of the substrate materials (Si wafers or polyethylene naphthalate (PEN) sheets), the films deposited with an appropriate O2 flow rate condition show smooth surface and cross sectional morphologies with no particles being incorporated during the deposition, which lead to the sufficiently good quality to be used as the gate insulator of low-temperature Si TFTs. The capability of forming functional thin films on temperature sensitive substrates will also lead to various applications of AP-VHF plasma as an efficient coating tool for polymer substrates.

Acoustic enhancement of surface reactions

Abstract

Modeling and Control of a 600 kW Closed Hydraulic Wind Turbine with an Energy Storage System

In this paper, an innovative closed hydraulic wind turbine with an energy storage system is proposed. The hydraulic wind turbine consists of the wind rotor, the variable pump, the hydraulic bladder accumulator, the variable motor, and the synchronous generator. The wind energy captured by the wind rotor is converted into hydraulic energy by the variable pump, and then the hydraulic energy is transformed into electrical energy by the variable motor and generator. In order to overcome the fluctuation and intermittence shortcomings of wind power, the hydraulic bladder accumulator is used as an energy storage system in this system to store and release hydraulic energy. A double-loop speed control scheme is presented to allow the wind rotor to operate at optimal aerodynamic performance for different wind speeds and hold the motor speed at the synchronous speed to product constant frequency electrical power regardless of the changes of wind speed and load power. The parameter design and modeling of 600 kW hydraulic wind turbine are accomplished according to the Micon 600 kW wind turbine. Ultimately, time-domain simulations are completed to analyze the dynamic response of the hydraulic wind turbine under the step change conditions of wind speed, rotor speed input, and load power. The simulation results validate the efficiency of the hydraulic wind turbine and speed control scheme presented, moreover, they also show that the systems can achieve the automatic matching among turbine energy, accumulator energy, and generator output energy.

Reignition After Interruption of Intermediate-Frequency Vacuum Arc in Aircraft Power System

Intermediate frequency (IF) electric power supply system has been widely applied in airplanes. Reignition after interruption of 360-850 Hz vacuum arc in axial magnetic field (AMF) is studied in this paper. According to the experimental results, the current interruption ability decreases from 22.4 kA at 360 Hz to 14.0 kA at 850 Hz. With the increase of frequency, the rate of change of current, di/dt, at current zero (CZ) reaches the breaking threshold at a smaller current value. Based on the least squares solution of the Mayr model, the time of decay of arc energy is prolonged when interruption fails, which is disadvantageous to the breaking process. On the other hand, the eddy effect is enhanced by higher frequency, which increases the residual magnetic induction intensity and the hysteresis phase of AMF after CZ. As a result, the diffusion of plasma is blocked. In the experiments, we find that the position of arc reignition always appears at the margin of contacts. It is shown by calculation that the electric field at the marginal area is twice as strong as that inside the contact. The current density is high, where the electric field is strong, leading to the higher probability of field emission. Arc images are analyzed by frame differential method. The sputtering velocity of macroscopic particles is estimated to be 10-20 m/s. The dissipation time of the macroscopic particles is longer than the arc time of IF vacuum arc, and the presence of macroscopic particles leads to the arc reignition. The findings of this paper would be beneficial to the parameter design of IF vacuum circuit breakers, such as the magnetic flux density of AMF, the chamfering of contact margin, and contact materials.

Modeling and Simulation of Variable Speed Variable Frequency Electrical Power System in More Electric Aircraft

The More Electric Aircraft (MEA), Variable Speed Variable Frequency (VSVF) and Electrical Power System (EPS) has lager generating capacity and higher energy efficiency than the conventional Constant Speed Constant Frequency EPS, but the generators of MEA have to working as redundant power supplies to improve the power supply reliability, instead of parallel power supply. To study the steady state operation and power source change strategies under different fault conditions of VSVF EPS, the integrated structure of VSVF EPS is firstly illustrated and operating principles of components are theorized. The key components including variable frequency generators, Bus Power Control Unit, rectifiers and other supplementary elements are then simulated to build a comprehensive VSVF EPS model on the platform of Simulink and the power source change strategies are realized by logic units. Finally, the stability analysis in terms of normal operation is carried out in case studies and power source exchange strategies in different situations are summarized. The results show that the model proposed by the paper can be used to simulate MEA VSVF EPS and analyze its whole operational process effectively and efficiently.

Fluctuation analysis of high frequency electric power load in the Czech Republic

We analyze the electric power load in the Czech Republic (CR) which exhibits a seasonality as well as other oscillations typical for European countries. Moreover, we detect 1/f noise property of electrical power load with extra additional peaks that allows to separate it into a deterministic and stochastic part. We then focus on the analysis of the stochastic part using improved Multi-fractal Detrended Fluctuation Analysis method (MFDFA) to investigate power load datasets with a minute resolution. Extracting the noise part of the signal by using Fourier transform allows us to apply this method to obtain the fluctuation function and to estimate the generalized Hurst exponent together with the correlated Hurst exponent, its improvement for the non-Gaussian datasets. The results exhibit a strong presence of persistent behaviour and the dataset is characterized by a non-Gaussian skewed distribution. There are also indications for the presence of the probability distribution that has heavier tail than the Gaussian distribution.

Dynamic Phasor Modeling of Multi-Generator Variable Frequency Electrical Power Systems

The dynamic phasor (DP) concept has been widely used in modeling electrical power systems. So far, the DP concept has been restricted to modeling systems with one single electrical source at a fixed fundamental frequency, either one generator or an ideal three-phase AC source. This paper aims to extend the DP modeling methodology to a wider application area. Two major achievements have been introduced: 1) application of DPs for multi-source, multi-frequency systems; 2) modeling of systems with time-varying frequencies. These two techniques enable the use of DPs to study nearly all types of electrical power systems (EPS). The developed theory is validated using a twin-generator system from the More Open Electrical Technologies (MOET) project. The accuracy and effectiveness of the developed models is confirmed by comparing the simulation results of detailed switching models and DP models under both balanced and unbalanced conditions.

磁性薄膜電力センサを用いた高周波電力計測

磁性薄膜電力センサを用いた高周波電力計測

Activation of Immobilized Glucose Oxidase Enzyme by Acoustic Wave Resonance Oscillation

Abstract Glucose oxidase enzyme was immobilized on ferroelectric LiNbO3 single crystals that were able to generate acoustic wave resonance oscillations by radio frequency electric power. The generation of the 3.6–14.7 MHz acoustic waves with lattice distortion vertical to the surface caused increases in the enzyme activity for glucose oxidation by decreasing the activation energy of reaction. A mechanism is proposed in which the acoustic waves enhance the interactions between the glucose substrate and the enzyme.

Design and simulation of a PWM rectifier connected to a PM generator of micro turbine unit

In recent years, distributed electrical power generation systems have attracted more attention due to their small scale technologies, lower cost electricity generation and higher reliability and security with fewer environmental consequences, rather than traditional power generators. Different applications such as peak saving, cogeneration, remote power and premium power will make it more and more useful. On the other hand, the permanent magnet synchronous generators, driven by micro turbines, play an important role in the distributed power generation systems. These PM generators produce a high frequency electrical power which needs to be converted to the usual power frequency, 50 or 60 Hz. This conversion is usually done using a back to back combination of rectifier, DC-link and inverter. The main focus of this paper is to present a model for a voltage source rectifier which is connected to a PM generator in a micro turbine unit, where Virtual Flux based Direct Power Control strategy is used to control the mentioned rectifier. The simulation results, using Matlab/Simulink, are presented to show the validity of the proposed model for the PWM rectifier, and to evaluate the performance of the control strategy.

Fabrication of yttrium oxide and erbium oxide coatings by PVD methods

The development of insulating coatings is one of the most important subjects in fusion reactor liquid lithium blanket research and development. The compounds aluminum nitride, yttrium oxide and erbium oxide are considered to be candidate materials for ceramic coatings because of their high electrical resistance and their high compatibility with liquid lithium. In the present study, two types of PVD methods were employed for fabrication of coatings, and their properties were examined. Yttrium oxide and erbium oxide coatings were fabricated by means of radio frequency (RF) sputtering, and erbium oxide coatings were fabricated by arc source plasma assisted deposition. The coatings were all close to their stoichimetric composition, and had higher resistances than that required in the fusion reactor (10 2–10 4 Ωm). The coatings had the crystallinity observed by X-ray diffraction (XRD), which were influenced by fabrication parameters as high frequency electric power or substrate temperature. Annealing after fabrication makes coatings crystallized more while the crystallinity of the coatings fabricated at low temperature were inferior to that of the coatings fabricated at higher temperature.

A micro plasma reactor for fluorinated waste gas treatment

A microreactor based on a micro-structured electrode (MSE) system is presented. With radio frequency electric power applied to the interdigitated, comb-like capacitor structure a homogeneous plasma is driven at atmospheric pressure with low ignition voltages due to small electrode gaps. The MSE is micromachined by plating nickel onto alumina ceramics. A micromachined Foturan ® structure with inlet and outlet channels for the gas flow serves as a reaction chamber. The design of the reactor cell is arranged in a 4×4-array in a multireactor system. The performance of the reactor is modeled with computational fluid dynamics (CFD), used to improve the reactor design. Experiments show that CF 4 decomposition rates of over 70% can be achieved at atmospheric pressure.

Extraordinary Lattice Displacement by Pulse Thickness Extension Mode Resonance Oscillation of Acoustic Wave and Its Effect on the Activity for Ethanol Oxidation of a Thin Pd Film Catalyst

Pulse radio frequency (rf) electric power was applied to a ferroelectric single crystal of z-cut LiNbO3 to generate pulse thickness extension mode resonance oscillation (p-TERO) of bulk acoustic wave, and the effects of p-TERO on the catalytic activity for ethanol oxidation of a Pd catalyst deposited on the crystal were studied. The employment of the pulse method made it possible to introduce several times larger rf power to the catalyst, compared to conventional continuous rf power introduction. The p-TERO remarkably increased catalytic activity for acetaldehyde production, and its effects were particularly great in a high rf power region. A laser Doppler method was developed to monitor lattice displacement caused by p-TERO. The patterns of lattice displacement became nonuniform in a high rf power region by the appearance of extraordinary lattice displacement. Very large activity increases in the region were associated with the lattice displacement. The mechanism of catalyst activation by p-TERO is discu...

Electrical Properties and Melting Treatment Rate of a Continuous Induction Waste Melter.

The continuous induction melter with a graphite-packed bed heat generator has a possible application to a waste melter because of its flexibility regarding waste contents, large treatment rate, and safe performance. This study proposed an analysis scheme for locally matching conditions between a melter and a high frequency electric power generator, and for fluctuation ranges of the frequency and input electric power in the melter. This scheme consisted of estimations of the melter coil inductance and resistance by eddy current loss from analytical solutions of Maxwell equations, which are linked to the locally matching conditions about capacitance and transformer turn number ratio. The measured results in a 100 kW pilot melter were compared to experimental ones. Energy use efficiency of the melter was also obtained by carrying out melting treatment rate measurements regarding two major components included in the wastes, iron and calcium silicate. Numerical results agreed well with the measured ones regarding the local matching conditions (capacitance: 10.4 μF, transformer turn number ratio: 7/15), and the fluctuation widths of the frequency (0.3 kHz) and input power (7 %). The measured melting treatment rates were 135 kg/h for iron and 40 kg/h for calcium silicate, when the respective values of input electric power were 92 and 85 kW. Based on these results, the energy use efficiency of the pilot melter was about 40 %.

Porosity Evolution in Electrosurgical Blade Coatings

AbstractDuring Electrosurgery, Radio Frequency (RF) electrical power is applied to a cutting surface which cauterizes the incision. The desiccation of surrounding tissue results in hemostasis and surgery without bleeding. In the case of localized heavy bleeding, a coagulation process is employed using modulated RF power. However, substantial amounts of desiccated tissue may stick to the blade, undoing the achieved hemostasis, and possibly worsening the situation. To prevent this, various electrosurgical blade coatings have been developed to both permit the flow of RF power through the coating, and prevent desiccated tissue from sticking to it.PolyTetraFluoroEthylene (PTFE) is a commonly used electro- surgical blade coating that undergoes substantial surface morphology changes during use, eventually leading to failure. Highly conductive Diamond-Like Nanocomposite (DLN) electrosurgical coatings have been developed with the requisite non-stick characteristics and enhanced durability.After a brief review of electrosurgical fundamentals, the underlying mechanisms of operation of these two coating materials are compared. In the case of PTFE, establishment and evolution of porosity in the coating is essential to the flow of RF power, yet ultimately leads to long term degradation. Alternate conduction mechanisms for DLN coatings are considered.