Transformer Coils Research Articles

Finite element solution of nonlinear eddy current problems with periodic excitation and its industrial applications

An efficient finite element method to take account of the nonlinearity of the magnetic materials when analyzing three-dimensional eddy current problems is presented in this paper. The problem is formulated in terms of vector and scalar potentials approximated by edge and node based finite element basis functions. The application of Galerkin techniques leads to a large, nonlinear system of ordinary differential equations in the time domain.The excitations are assumed to be time-periodic and the steady-state periodic solution is of interest only. This is represented either in the frequency domain as a finite Fourier series or in the time domain as a set of discrete time values within one period for each finite element degree of freedom. The former approach is the (continuous) harmonic balance method and, in the latter one, discrete Fourier transformation will be shown to lead to a discrete harmonic balance method. Due to the nonlinearity, all harmonics, both continuous and discrete, are coupled to each other.The harmonics would be decoupled if the problem were linear, therefore, a special nonlinear iteration technique, the fixed-point method is used to linearize the equations by selecting a time-independent permeability distribution, the so-called fixed-point permeability in each nonlinear iteration step. This leads to uncoupled harmonics within these steps.As industrial applications, analyses of large power transformers are presented. The first example is the computation of the electromagnetic field of a single-phase transformer in the time domain with the results compared to those obtained by traditional time-stepping techniques. In the second application, an advanced model of the same transformer is analyzed in the frequency domain by the harmonic balance method with the effect of the presence of higher harmonics on the losses investigated. Finally a third example tackles the case of direct current (DC) bias in the coils of a single-phase transformer.

Design Optimization of MEMS Based LLC Tunable Resonant Converter for Power Supplies on Chip

In this paper, a novel MEMS based LLC converter is proposed for on chip power supplies. The design is optimized based on commercially available Metal MUMPs process for fabrication. The resonant frequency is optimized at 20MHz and MEMS based variable capacitor is fabricated on the chip to tune the peak resonance frequency of circuit which varies due to the load variations. The Design is simulated in FEM based numerical software COMSOL and Intellisuite. According to analysis the magnetizing inductance of 42nH and leakage inductance of 40nH has been achieved from 16 mm2 rectangular coil transformer. The total capacitance of 1500pF has been achieved from parallel plate capacitors and variation of 3pF has been achieved from variable capacitor.

Postmortem Investigation of Power Transformers—Profile of Degree of Polymerization and Correlation With Furan Concentration in the Oil

In this paper, postmortem aging investigations on insulation material of power transformers are presented. A methodology for taking paper samples in a systematical manner and a scheme for calculating an average degree of polymerization (DP) for the entire transformer out of the DP values of the individual paper samples will be shown. The typical DP profile in the axial direction of transformer coils will be explained using calculated distribution of losses within the coils of a 740-MVA generator stepup transformer. Further, correlations between the furan (2-FAL) concentration in the oil and the average DP of the investigated German GSU transformers and grid transformers are derived and compared with existing correlations.

Study on signal intensity of low field nuclear magnetic resonance via an indirect coupling measurement

We carry out an ultra-low-field nuclear magnetic resonance (NMR) experiment based on high-Tc superconducting quantum interference devices (SQUIDs). The measurement field is in a micro-tesla range (∼10 μT−100 μT) and the experiment is conducted in a home-made magnetically-shielded-room (MSR). The measurements are performed by the indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements using a commercial room temperature amplifier. The results show that in a wide frequency range (∼1 kHz−10 kHz) the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils.

New magnetically ordered phases in YbRh2Si2

AbstractYbRh2Si2 is a widely studied heavy Fermion system with a variety of interesting properties, among them a quantum critical point at 60 mT for B // a,b‐plane 1. At low temperatures we previously found a new magnetically ordered phase below 2.2 mK 2 taking place in the well known antiferromagnetic phase which starts at 70 mK 3. In addition to this “A” phase, we now observe a second, weaker phase transition below 14 mK and 5 mT which we named B phase. To study these phases of YbRh2Si2 at the lowest possible temperatures, we measured the DC magnetization in magnetic fields up to 60 mT using a home made rf SQUID magnetometer. The A phase is very robust and extends at least up to a magnetic field of 23 mT. Above this field, it is suppressed to below our detection limit of 1 mK. The A transition is characterized by a reduced magnetic susceptibility in the ordered state and there is zero magnetization in the limit B → 0. From these findings, we expect it to be an antiferromagnetic ordered state. The experiments were performed in our low temperature cryostat at the Walther Meissner Institute in Garching which includes a 0.9‐mole PrNi5 nuclear demagnetization stage with a final temperature of 400 µK. The temperatures of the nuclear stage were measured by pulsed NMR on a Cu rod thermally anchored to it. YbRh2Si2 single crystals of very high quality have been grown in an Indium flux at the MPI CPfS Dresden. The samples were clamped in a 5 N Ag rod screwed to the nuclear stage and extending into the pick‐up coil of a conventional flux transformer. Their temperatures were always close to that of the nuclear stage. In addition, we performed specific heat measurements with the semiadiabatic heat‐pulse method.

Design and Analysis of Impregnation Chamber Used In Vacuum Pressure Impregnation Process

The simple explanation is that in nature and in manufacturing, things leak. Vacuum impregnation stops leak. The ultimate goal of vacuum impregnation is to seal leak/migration paths without impacting the functional, assembly or appearance characteristics of a part. The impregnation chamber which is used in VPI process operates maximum up to 80 to 150 psi.it is important to analyse and design the pressure vessel that will provide safety, durability and serviceability to the company. Accomplishing this task will require a very good understanding of behaviour and a good knowledge of parameters that affecting the pressure vessel due to varying loads, pressure and thickness of shell element. The most important one is that the given geometry of pressure vessel must be analysed to assure it should meet the design standards. Vacuum impregnation as an industrial process has been in commercial use for more than 60 years. For the world's largest manufacturers, it continues to be the preferred process through which to guarantee the pressure-proof, leak-proof, and corrosion-proof requirements of parts and components in critical operations. The ultimate goal of vacuum impregnation is to seal leak / migration paths without impacting the functional, assembly or appearance characteristics of a part. Functional characteristics include the ability for fluids or gasses to flow only where needed in order to enhance in-service performance of the components' design. Assembly characteristics, which must be maintained, include performance of tapped holes; the integrity of mating and sealing surfaces, the elimination of residual internal contamination in water jackets, sockets, surfaces and dimensional areas. Appearance characteristics include oxidation and discoloration. Vacuum impregnation is governed by military standard MIL-STD-276A as well as numerous proprietary and customer specifications. The vacuum component of the process removes the air that occupies the migration path commonly known as porosity in cast or pressed metals. The impregnation component of the process fills the void with a durable and stable material suitable for field of use. These materials can be silicate or epoxies. (7) During normal operation, transformers are subjected to the failure of the insulation system. How long an insulation system will be serviceable depends on the materials chosen and the service environment. Thermal, mechanical, voltage and environmental stresses all combine to reduce the service life of the transformer. Solid- state Controls, Inc. (SCI) manufactures all of its transformers using the Vacuum Pressure Impregnation (VPI) process. This system strengthens the insulation system and extends the service life of the transformer. The VPI process is the most advanced system in use today. The VPI process is the most effective way known to eliminate the dead air spaces that cause hot spots within the transformer coils. These hot spots can be 20 0 higher than the average coil temperature. The VPI process, along with a good resin, provides a low thermal resistance path that lowers the average operating temperature of the transformer.The resin seals the transformer against environmental conditions and bonds all components of the insulation system together for good mechanical strength. This is very effective in reducing mechanical vibrations. This greatly reduces the audible noise level of the transformer. The VPI process and resin also enhances the dielectric capability between windings and between the windings and ground. This allows the transformer to survive higher voltage stress levels without failure. The general VPI process contain following parts In the impregnation chamber (also known as an autoclave, pressure vessel or vacuum vessel) air is evacuated from the leak path in the part by using a deep vacuum. The evacuated leak path is filled with sealant by covering the part with the sealant and applying pressure. More energy is required to penetrate the porosity with sealant than to evacuate the air. In the recovery station (also known as drain station, centrifuge) excess sealant is recovered for reuse. In the wash/rinse station (also known as surge station, rolling rinse or pump over station) residual sealant is washed from the part's internal passages, taps, pockets and features where sealant is undesirable. In the cure station (also known as standing, rolling cure or pump over station) the sealant, impregnated into the walls of the part, is polymerized in the leak path. In general, vacuum impregnation includes four steps.

Development of New Intelligent High Potential Therapeutic Apparatus with Intelligent Materials

The article represents the design of new type intelligent High potential therapeutic apparatus, using Atmega1280 as controller. High potential therapeutic apparatus is a kind of potential therapeutic apparatus exerting negative high voltage electric field around the body, which is curative for shoulder pain, headache, insomnia, chronic constipation. The design reduces voltage from 220V ac to 110V ac and constitutes different circuits with relays. To get different treatment waveform, inductances of various value is used in different circuits. Generate appropriate treatment voltage with the transformer booster. In order to achieve various values of treatment voltage, circuit connects to various primary coils of local treatment transformer and systemic transformer. Simultaneously, compose the corresponding control software. Finally achieve the hardware and software design of the high potential therapeutic apparatus. Results of experiment show that a new high potential therapeutic apparatus is successfully designed. Local treatment mode and systemic treatment mode are can produce the treatment effect of the obvious through actual testing and using.

Control Method for Wireless Inductive Energy Transfer Systems With Relatively Large Air Gap

Recent improvements in semiconductor technology make efficient switching possible at higher frequencies, which benefits the application of wireless inductive energy transfer. However, a higher frequency does not alter the magnetic coupling between energy transmitter and receiver. Due to the still weak magnetic coupling between transmitting and receiving sides that are separated by a substantial air gap, energy circulates in the primary transmitting side without being transferred to the secondary receiving side. This paper introduces an energy control method that reduces energy circulation in the primary to zero. The method makes use of the fact that energy can be stored in a magnetic field by the primary side and absorbed by the secondary side. Furthermore, the secondary side converter topology is modified in order to boost the damping as seen by the primary converter at required times. Essentially, the control method realizes an energetic coupling factor of one between the air coils of the wireless transformer. The working principle of the control method has been verified with an experimental setup.

Electrical and dielectric characteristics of magnetic ceramics of Mn1−xNixFe2O4 spinel nanoferrites

Ceramics materials of the class of spinel nanoferrites of Mn1−xNixFe2O4 (x = 0·00, 0·025, 0·50, 0·75 and 1·00) of 13–25 nm particle sizes have been investigated for their electrical and dielectric characteristics. The dc electrical resistivity was measured and found to decrease with an increase in x to follow the Verwey mechanism because of the increase in electron hopping between the Fe2+ tetrahedral site (A site) and the Fe3+ octahedral site (B site). In addition, the resistivity of ferrites was observed to decrease with an increase in temperature, confirming their semiconductor characteristics. The dielectric constant and the dielectric loss factor were found to decrease as the frequency increased, following the Maxwell–Wagner interfacial type of polarisation. The study of the electrical properties of the prepared ferrites suggests their usefulness in important applications in electronic devices in reducing power losses due to an increase in conductivity caused by the increment in Ni concentrations in various electronic circuitries, such as those in computers and transformer coils.

Analysis of electromagnetic forces in high voltage superconducting fault current limiters with saturated core

This paper presents a three-dimensional numerical analysis of the electromagnetic forces within a high voltage superconducting fault current limiter (FCL) with a saturated core under short-circuit conditions. The effects of electrodynamic forces in power transformer coils under short-circuit conditions have been reported widely. However, the coil arrangement in an FCL with saturated core differs significantly from existing reactive devices. The boundary element method is employed to perform an electromagnetic force analysis on an FCL. The analysis focuses on axial and radial forces of the AC coil. The results are compared to those of a power transformer and important design considerations are highlighted.

Occupational hand dermatitis caused by benzoyl peroxide in transformer coil binding tape

Occupational hand dermatitis caused by benzoyl peroxide in transformer coil binding tape

Compact atmospheric pressure plasma self-resonant drive circuits

This paper reports on compact solid-state self-resonant drive circuits that are specifically designed to drive an atmospheric pressure plasma jet and a parallel-plate dielectric barrier discharge of small volume (0.5 cm3). The atmospheric pressure plasma (APP) device can be operated with helium, argon or a mixture of both. Equivalent electrical models of the self-resonant drive circuits and discharge are developed and used to estimate the plasma impedance, plasma power density, current density or electron number density of three APP devices. These parameters and the kinetic gas temperature are dependent on the self-resonant frequency of the APP device. For a fixed switching frequency and APP device geometry, the plasma parameters are controlled by adjusting the dc voltage at the primary coil and the gas flow rate. The resonant frequency is controlled by the selection of the switching power transistor and means of step-up voltage transformation (ferrite core, flyback transformer, or Tesla coil). The flyback transformer operates in the tens of kHz, the ferrite core in the hundreds of kHz and Tesla coil in the MHz range. Embedded within this work is the principle of frequency pulling which is exemplified in the flyback transformer circuit that utilizes a pickup coil for feedback control of the switching frequency.

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The one way of heat removal intensification from the transformer coils by means of laminar intermediate layer destruction by an ultrasonic irradiation is described. The basic merits and demerits of ultrasound application for transformers irradiation are shown

503 変圧器コイルの簡易モデルの構築手法

503 変圧器コイルの簡易モデルの構築手法

Design of a Contactless Energy-Transfer System for Desktop Peripherals

This paper presents an approach to design a contactless energy-transfer system to supply desktop computer peripherals. Energy is transferred using coreless transformers from an array of primary coils (placed on a table) to one or several secondary coils (placed under the peripheral). Knowing the geometrical structure of the coils of a coreless transformer, accurate calculations allow predicting the power that can be transferred to a load. By applying these calculations to one basic energy-transfer cell, it is then possible to design a whole table that is able to supply many consumers at any location. The main problem with such systems is that the energy transfer is not constant along the surface and may not be even enough to supply an electronic device. This paper proposes several solutions to solve this problem.

Development of a Compact Measurement System of Transport Characteristics in HTS Conductors by Using an HTS Current

In order to realize HTS power machines and devices with high performance, it is important to evaluate the characteristics of HTS conductors quantitatively. We developed a compact system to measure the transport characteristics of HTS conductors under various experimental conditions. This system enables us to measure the transport characteristics of straight HTS conductors up to a current capacity of 1 kA class at 77 K, 66 K, and 4.2 K. The measurement of transport current losses is done by the Poynting vector method. The distribution of Poynting vectors around the sample conductor can be obtained by using many sets of both potential leads and pickup coils. An HTS current transformer (HTS-CT) is used to feed current to the sample conductor for the measurement. A secondary current of about 1 kA at 77 K can be induced when the primary current is 40 A. The sample conductor is connected to the secondary coil of this transformer. As a sample conductor, we used a conductor consisting of 16 parallel Ag-sheathed Bi-2223 multifilamentary tapes. The joint method between the HTS-CT and sample conductors is also examined. Based on these results, the usefulness of this measurement system is discussed.

Over-current characteristics of model coil using Y-based multi-filament wire for superconducting power transformers

In the Japanese national project to develop superconducting power applications using Y-based coated conductors, the present focus is on various aspects of technological development of superconducting power transformers. Since Y-based multi-filament wire contributes to reduction in AC loss of superconducting transformer coils, a 5mm-wide long-length multi-filament, between the filaments of 3 and 5, has been developing by a laser scribing method. In the case of the project target, a 66kV/20 MVA power transformer coils require a Y-based multi-filament wire between the lengths of 200m and 300m. It also must withstand over-current of about seven times the rated current, which is generated when a power system fault occurs. In this paper, over-current characteristics of model coil using Y-based 3-filament wire were evaluated.

An ultralow noise current amplifier based on superconducting quantum interference device for high sensitivity applications

An integrated ultrahigh sensitive current amplifier based on a niobium dc superconducting quantum interference device (SQUID) has been developed. The sensor design is based on a multiturn signal coil coupled to a suitable SQUID magnetometer. The signal coil consists of 60 square niobium turns tightly coupled to a superconducting flux transformer of a SQUID magnetometer. The primary coil (pick-up coil) of the flux transformer has been suitably designed in order to accommodate the multiturn input coil. It has a side length of 10 mm and a width of 2.4 mm. In such a way we have obtained a signal current to magnetic flux transfer coefficient (current sensitivity) as low as 62 nA∕Φ(0). The sensor has been characterized in liquid helium by using a direct coupling low noise readout electronic and a standard modulated electronic in flux locked loop configuration for the noise measurements. Beside the circuit complexity, the sensor has exhibited a smooth and free resonance voltage-flux characteristic guaranteeing a reliable and a stable working operation. Considering a SQUID magnetic flux noise of S(Φ)(1∕2) = 1.8 μΦ(0)∕Hz(1∕2) at T = 4.2 K, a current noise as low as 110 fA∕Hz(1∕2) is obtained. Such a value is about a factor two less than the noise of other SQUIDs of the same category. As an application, Nyquist noise measurements of integrated test resistors using the current sensing noise thermometer technique are reported. Due to its high performance such a sensor can be employed in all applications requiring an extremely current sensitivity like the readout of the gravitational wave detectors and the current sensing noise thermometry.

The cryogenic system for ITER CC superconducting conductor test facility

This paper describes the cryogenic system of the International Thermonuclear Experimental Reactor (ITER) Correction Coils (CC) test facility, which consists of a 500 W/4.5 K helium refrigerator, a 50 kA superconducting transformer cryostat (STC) and a background field magnet cryostat (BFMC). The 500 W/4.5 K helium refrigerator synchronously produces both the liquid helium (LHe) and supercritical helium (SHe). The background field magnet and the primary coil of the superconducting transformer (PCST) are cooled down by immersing into 4.2 K LHe. The secondary Cable-In-Conduit Conductor (CICC) coil of the superconducting transformer (SCST), superconducting joints and the testing sample of ITER CC are cooled down by forced-flow supercritical helium. During the commissioning experiment, all the superconducting coils were successfully translated into superconducting state. The background field magnet was fully cooled by immersing it into 4.2 K LHe and generated a maximal background magnetic field of 6.96 T; the temperature of transformer coils and current leads was reduced to 4.3 K; the inlet temperature of SHe loop was 5.6 K, which can meet the cooling requirements of CIC-Conductor and joint boxes. It is noted that a novel heat cut-off device for High Temperature Superconducting (HTS) binary current leads was introduced to reduce the heat losses of transformer cryostat.

Analysis of Specific Absorption Rate and Current Density in Biological Tissues Surrounding Energy Transmission Transformer for an Artificial Heart: Using Magnetic Resonance Imaging-based Human Body Model

The transcutaneous energy transmission system used for artificial hearts is a transmission system that uses electromagnetic induction. Use of the TETS improves quality of life and reduces the risk of infection caused by percutaneous connections. This article reports the changes in the electromagnetic effects of TETS that influence a human body when the locations of the air-core coils of the transcutaneous transformer are changed. The specific absorption rate and current density in a model consisting of a human trunk that included 24 different organs are analyzed using an electromagnetic simulator. The air-core coils are located on the pectoralis major muscle near the collarbone in model 1, whereas they are located on the axillary region of the serratus anterior muscle, which overlies the rib in model 2. The maximum current densities in models 1 and 2 are 5.2 A/m(2) and 6.1 A/m(2), respectively. The current density observed in model 2 slightly exceeds the limiting value prescribed by International Commission on Non-Ionizing Radiation Protection (ICNIRP). When the volumes of biological tissues whose current densities exceed the limiting value of current density for general public exposure are compared, the volume in model 2 (156.1 cm(3)) is found to be larger than that in model 1 (93.7 cm(3)). Hence, it is speculated that the presence of the ribs caused an increase in the current density. Therefore, it is concluded that model 1 satisfies the ICNIRP standards.