THE STUDY ON MEASURING TECHNIQUE OF PARTIAL DISCHARGE IN GAS INSULATED SWITCHGEAR USING ULTRA HIGH FREQUENCY METHOD WITH EXTERNAL SENSORS

Objective In order to find early latent faults and prevent catastrophic failures, diagnosis of insulation condition by measuring technique of partial discharge(PD) in gas insulated switchgear (GIS) is applied in this paper, which is one of the most basic ways for diagnosis of insulation condition. Methods Ultra high frequency(UHF) PD detection method by using internal sensors has been proved efficient, because it may avoid the disturbance of corona, but the sensor installation of this method will be limited by the structure and operation condition of GIS. There are some of electromagnetic (E-M) waves leak from the place of insulation spacer, therefore, the external sensors UHF measuring PD technique is applied, which isn't limited by the operation condition of GIS. Results This paper analyzes propagated electromagnetic (E-M) waves of partial discharge pulse excited by using the finite-difference time-domain (FDTD) method. The signal collected at the outer point is more complex than that of the inner point, and the signals' amplitude of outer is about half of the inner, because it propagates through spacer and insulation slot. Set up UHF PD measuring system. The typical PD in 252kV GIS bus bar was measured using PD detection UHF technique with external sensors. Finally, compare the results of UHF measuring technique using external sensors with the results of FDTD method simulation and the traditional IEC60270 method detection. Conclusion The results of experiment shows that the UHF technique can realize the diagnosis of insulation condition, the results of FDTD method simulation and the result UHF method detection can demonstrate each other, which gives references to further researches and application for UHF PD measuring technique.

Analysis of Excitation Characteristics of Ultra High Frequency Electromagnetic Waves Induced by PD in GIS

The understanding of the excitation mechanism of ultra high frequency (UHF) electromagnetic waves (EW) is essential for ap- plying UHF method to partial discharge (PD) detection. Since the EW induced by PD in gas insulated switchgear (GIS) contains not only transverse electromagnetic (TEM) wave, but also high-order transverse electric (TE) and high-order transverse magnetic (TM) waves, we analyzed the proportions between the TEM wave and the high order waves, as well as the influence of the PD position on this proportion, using the finite different time domain (FDTD) method. According to the unique characteristics of the waves, they are separated only ap- proximately. It is found that the high-order mode is the main component, more than 70%, of the electric field around the enclosure of GIS, and that with the increasing distance between PD source and inner conductors, the low frequency ( below about 800 MHz) component of EW decreases, but the high frequency component (above 1 GHz) increases, meanwhile the proportion of high-order components in EW could reach 77% from 70%. It concluded that the closer the PD source to the enclosure is, the easier high order EW may be excited.

SIMULATION OF TEMPERATURE FIELD IN ULTRA-HIGH FREQUENCY INDUCTION HEATING AND VERIFICATION

An experimental and numerical study on the temperature field induced in the ultra-high frequency induction heating is carried out.With an aim of predicting the thermal history of the workpiece,the influence factors of temperature field,such as the induction frequency,the dimension of coil and the gap between coil and workpiece,are investigated considering temperature-dependent material properties by using FLUX 2Dsoftware.The temperature field characteristic in ultra-high induction heating is obtained and discussed.The numerical values are compared with the experimental results.A good agreement between them is observed with 7.9% errors.

A Diagnostic Study on the Relationship between the Assembling of Low Frequency Waves in the Pacific Ocean and the Abnormality of the Subtropical High

By use of the filter analysis technique, the Complex Empirical Othogonal Function (CEOF) method and the ECMWF/WMO 2.5°×2.5°grid data of the geopotential heights during the summer months in 1988, an interseasonal process that the western Pacific subtropical high (WPSH) was anomalously far to the north in the first and second ten days of July is studied. It has been found that in the western Pacific subtropical region in the first and second ten days of July,it is the continuous assembly of low frequency geopotential waves (LFGWs) that leads to the abnormality of WPSH. This abnormality emerges with the enhancement of wave assembling and ceases while the wave assembling situation disappears. The structure of the low frequency assembling waves corresponds to the structure of subtropical high in its abnormal period. The effect of the assembling waves on the abnormality of subtropical high can be considered as the accumulation of disturbance energy carried by the low frequency waves from different directions in the western Pacific region.

Investigations of high-frequency induction hardening process for piston rod of shock absorber

The microhardness of piston rods treated with different induction hardening processes was tested. The experimental results reveal that the depth of the hardened zone is proportional to the ratio of the moving speed of the piston rod to the output power of the induction generator. This result is proved correct through the Finite Element Method (FEM) simulation of the thermal field of induction heating. From tensile and impact tests, an optimized high frequency induction hardening process for piston rods has been obtained, where the output power was 82%×80 kW and the moving speed of workpiece was 5364 mm/min. The piston rods, treated by the optimized high frequency induction hardening process, show the best comprehensive mechanical performance.

The Principle and Practice of the Deviation of Power Frequency Component Relay on High Voltage Transmission Line

The research and development of ultra high speed protective relay of transmission line has got great interest and attention of protective relay engineer over the world. Several versions and schemes of ultra high speed relay have been studied and designed in recent twenty years. But only a few of them have got actual apiication in the power system. The relay based on the deviation of power frequency component (DPFC) can get very high reliability with ultra high speed so it has got wide application in Chinese power system. Thousands relay sets have been applied and its operation experience verifies their excellent performance. This paper summarizes the course of the development of the uItra high speed protective relay and compares the merits and defects of the main schemes which have been developed. The principle and successful pratice of the ultra high speed protection based on DPFC reIay are introduced.

EXPERIMENT AND SIMULATION FOR THICK-PLATE BENDINGBY HIGH FREQUENCY INDUCTOR

In order to produce thick plates with complicated curved surface, a prototype bending machine by the use of high frequency inductor was developed. The bending mechanism is based on the localized stresses which are induced from the difference of temperature in thickness by the high frequency inductor. The operating speed and the thickness of plate were examined from the experiment, and the variation of the temperature was measured. Finite element analysis was carried out in the second part based on the experimentally obtained temperature distribution. The so-called Mindlin plate element was used in order to perform the simulation efficiently. The strategy to produce such curved surface in the practical process was discussed and further perspective of the production system was described. (Edited author abstract) 6 Refs.

Structure optimization of connection frames based on frequency sensitivity in macro-micro motion platforms

High-performance connection frames are of great significance for ultra-high acceleration and ultra-precision positioning in macro-micro motion platforms. This paper first takes the connection frame as a research object,builds a finite element model(FEM) of the natural frequency of the frame, and then verifies the correctness of this model. The frequency sensitivity method is then used to perturb the structural parameters of the FEM of the connection frame, and the sensitivities of the first-order natural frequency and mass of the corresponding structural parameters are obtained by calculation and analysis. The design variables are also determined. The natural frequency is used as the optimization objective, and the design parameters and mass of the connection frame are constrained. The structural parameters of the connecting frame are obtained through optimization, and the model is built and verified by experiments. The results show that the first-order natural frequency of the connecting frame is effectively improved by the frequency sensitivity method, avoids resonance between the connecting frame and the voice coil motor, and realizes the lightweight design of the connection frame. This research provides a reliable basis for the stable operation and ultra-precision positioning of ultra-high acceleration macro-motion platforms.

Development of a Fast and Facile Analytical Approach to Quantify Radiometabolites in Human Plasma Samples Using Ultra High Performance Liquid Chromatography

Introduction: Conventional metabolite analyses often require manual sample preparation, generating variability of measurements. This study describes a new method to quantify radiometabolites in blood, combining ultra high performance liquid chromatography (UHPLC) and turbulent flow chromatography, an alternative fully automated process allowing analyte’s extraction. Methods: A new radiotracer for dopamine transporter imaging, namely LBT-999, was used to demonstrate the method’s robustness. Matrix effect, Turboflow column loading, linearity, specificity and precision were evaluated with in vitro samples of LBT-999 in human plasma. Radiodetector sensitivity and preliminary evaluation were respectively determined by analysis of calibrated samples of [18F]LBT-999 and blood samples from 4 healthy subjects injected with [18F]LBT-999, withdrawn at 5, 15, 30 and 45 min pi. Results: With three sequential loadings (3 × 100 μL) of the Turboflow column, mean coefficients of variation were 1%, below 2%, 2% and 30.9% for matrix effect, specificity, repeatability and intermediate precision, respectively. Correlation coefficients for linearity were superior to 0.97. Limits of detection and quantification of the radiodetector were fixed at 3 and 9 c/s. Retention times for [18F]LBT-999 and the two radiometabolites detected by radio-UHPLC were 6.5, 4.8 and 9.6 min. Forty-five min after the injection, parent fraction was still predominant with 57.8% ± 25% of the total radioactivity. Conclusions: An innovative approach, allying UHPLC and Turboflow column, was developed and its sensitivity, linearity, specificity and repeatability validated. Preliminary results of the clinical trial are in accordance with literature data, demonstrating its efficiency in radiometabolites quantification.

A Data Transmission Method Using a Cyclic Redundancy Check and Inaudible Frequencies

This paper describes a data transmission method using a cyclic redundancy check and inaudible frequencies.The proposed method uses inaudible high frequencies from 18 k Hz to 22 k Hz generated via the inner speaker of smart devices.Using the proposed method,the performance is evaluated by conducting data transmission tests between a smart book and smart phone.The test results confirm that the proposed method can send 32 bits of data in an average of 235 ms,the transmission success rate reaches 99.47%,and the error detection rate of the cyclic redundancy check is0.53%.

Ultra-high-field magnetic resonance:Why and when?

This paper briefly summarizes the development of magnetic resonance imaging and spectroscopy in medicine.Aspects of magnetic resonancephysics and-technology relevant at ultra-high magnetic fields as well as current limitations are highlighted.Based on the first promising studies,potential clinical applications at 7 Tesla are suggested.Other aims are to stimulate awareness of the potential of ultra-high field magnetic resonance and to stimulate active participation in much needed basic or clinical research at 7 Tesla or higher.

Preparation and Properties of Ultra-fine Chromium Carbonization of High Performance Mechanical Activation

The preparation of hydroxyl chromium oxide by hydrogen reduction of disodium chromate and particulate hydroxyl mechanical activation features were studied. Then with self-made hydroxyl chromium as the raw material, a direct reduction and carburization process was used to prepare ultra-fine chromium carbonization. Through SEM and XRD, the high performance mechanical activation, key coefficients, microstructure, hardness and wear-resisting property were investigated. The results reveal that suitable mechanical activation and carbon reducing carbonization temperature, carbonization time, carbon content are beneficial to obtaining ultra-fine chromium carbonization. Typically, when the time of high performance grinding is 5 min, the carbon reducing temperature is 1100 ℃, the carbon reducing time is 1h, the carbon content is 28%, and finally the particle size of chromium carbide powder is 1 μm. Under this condition of preparation of ultra-fine chromium carbide, both the hardness and wear resistance are better than those in the industrialization of chromium carbide coating.

The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy

The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy are systematically studied.The results show that fatigue fracture still occurs above the cycle of 10~8 for tests carried out at the frequency of f=20 kHz and stress ratio R =-1,so the traditional fatigue limit at cycle of 10~7 is not appropriate for fatigue design.Fatigue fracture surfaces are perpendicular to stress axis for cylindrical and plate specimens,and the fatigue cracks originate from the extra surface of the specimens.Fatigue crack is apt to propagate from cutting direction to forward direction,which occurs mainly in the second propagation stage at higher stress amplitude. There is an obvious frequency effect for DZ125 superalloy.The higher the test frequency is,the more serious the effect of frequency on fatigue behaviors of the alloy.After the frequency correction,the ultra-high cycle fatigue S-N curve well coincide with the traditional fatigue S-N curve.

A Novel Method of Newton Iteration in Complex Field and Lattice Search for Locating Partial Discharges in Transformers

在变压器局部放电特高频定位的多传感器时间差测量中不可避免地存在误差,这往往导致时间差方程组在实数域内无解。为了得到时间差方程组的最优近似解,提出了复数域牛顿迭代网格搜索方法。该方法在复数域内进行迭代;当迭代结果为实数时就将其作为定位结果;当迭代结果为复数时,以其实部为中心点坐标,在该点周围局部区域内采用网格搜索法计算最优近似解。通过在变压器上开展试验检验了该方法的可行性和准确性。研究表明,在一定时间误差下,在实数域采用牛顿迭代法计算时不收敛,而在复数域可以收敛,平均定位误差为0.20 m。复数域牛顿迭代网格搜索方法能够在一定时间误差下求解时间差方程组,给出最优近似解,实现局部放电定位。

Mesoplasticity Approach to Studies of the Cutting Mechanism in Ultra-precision Machining

There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.

A DIAGNOSTIC RESEARCH OF THE SEASONAL NORTHWARD BEATING OF THE SUBTROPICAL HIGH

Diagnostic techniques of CEOF, power spectrum and bandpass filter wave are applied in this paper to analyze the seasonal northward beating of the northern subtropical high using day to day geopotential fields of 2.5 ×2.5 at 500 hPa May through July in 1988 and 1991. It is concluded that it is globally observed that the subtropical high has northward beats that propagate westward; the source of beating mainly lies in the region of Arabian Sea and central Pacific and the sink in eastern Pacific; the seasonal beating is dominated by effects of the disturbance field; low frequency oscillation plays a key role in the beating and the westward propagation so that the difference in the latter in individual years is caused by the varying source of disturbance and the low frequency waves it excites.

Analysis of prospecting polymetallic metallogenic belts by comprehensive geophysical method

This paper is based on the analysis and research on the silver-lead-zinc polymetallic ore in New Ballyhoo Banner in southern Manzhouli of Inner Mongolia.Because metal mineralization brings rock formations,the geophysical features such as low resistivity,high polarization rate and uneven distribution of magnetization,the comprehensive geophysical methods are adopted including high-precision magnetic measurement,high-power induced polarization,IP field middle gradient and controlled source audio-frequency magnetotellurics.In the survey work of multi-metal ore deposits,from surface sweeping to single point measurement,and from single point to section going deeper layer by layer,the resolution of measurement is continuously improved,and various geophysical methods support and complement each other,so explorers can successfully predict the direction,scale and volume of the metallogenic belts in conjunction with geochemical exploration,geological survey and drilling.It has provided a strong basis for completing the exploration task of predicting the reserve volume of ore bodies.The research conclusions of this exploration case have thus a high reference value in the same type of exploration work.

Ultra-Wideband Log Periodic Dipole Antenna (LPDA) for Wireless Communication Applications

This paper proposes a printed log-periodic dipole antenna (LPDA) for ultra wide bandwidth (UWB) applications. The antenna comprises of cascading four U shaped elements of different line lengths with balun circuit to improve the antenna impedance matching. The proposed antenna dimensions are 50 × 50 mm2 with FR4 substrate thickness 0.8 mm. Full-wave EM solver HFSS (High Frequency Structure Simulator) is used for modeling the proposed antenna. The pulse distortion is verified by the measured the proposed antenna performance with virtually steady group delay. The simulation and experimental results show that the proposed antenna exhibits good impedance matching, stable radiation patterns throughout the whole operating frequency bands, acceptable gain and stable group delay over the entire operating band. An UWB extended from 1.85 GHz to 11 GHz is obtained, and the average antenna gain is about 5.5 dBi over the operating band with peak gain around 6.5 dBi and 70% average radiation efficiency.

A High Frequency Boundary Element Method for Scattering by Convex Polygons with Impedance Boundary Conditions

We consider scattering of a time harmonic incident plane wave by a convex polygon with piecewise constant impedance boundary conditions.Standard finite or boundary element methods require the number of degrees of freedom to grow at least linearly with respect to the frequency of the incident wave in order to maintain accuracy.Extending earlier work by Chandler-Wilde and Langdon for the sound soft problem,we propose a novel Galerkin boundary element method,with the approximation space consisting of the products of plane waves with piecewise polynomials supported on a graded mesh with smaller elements closer to the corners of the polygon.Theoretical analysis and numerical results suggest that the number of degrees of freedom required to achieve a prescribed level of accuracy grows only logarithmically with respect to the frequency of the incident wave.

Multi-Valued Solution and Level Set Methods in Computational High FrequencyWave Propagation

We review the level set methods for computing multi-valued solutions to a class of nonlinear first order partial differential equations,including Hamilton-Jacobi equations,quasi-linear hyperbolic equations,and conservative transport equations with multi-valued transport speeds.The multivalued solutions are embedded as the zeros of a set of scalar functions that solve the initial value problems of a time dependent partial differential equation in an augmented space.We discuss the essential ideas behind the techniques,the coupling of these techniques to the projection of the interaction of zero level sets and a collection of applications including the computation of the semiclassical limit for Schr¨odinger equations and the high frequency geometrical optics limits of linear wave equations.