mlsa-iai-msu-lab/ru_sci_bench_zho_cite_reranking huggingface dataset:
Vibration and Audible Noise of Filter Capacitors in HVDC Converter Stations

The filter capacitor stack is one of the main acoustic noise sources in high-voltage DC (HVDC) converter stations. As HVDC systems are built more and more recently, it is significant to research the audible noise of filter capacitors. In this paper, the current situation of research on vibration and audible noise of filter capacitors in HVDC converter stations, which is departed into three partsgeneration mechanism, prediction methods, and reduction measures, is presented and the research achievements are discussed. Scholars have built the model that the alternating electric force caused by the voltage conduces to the vibration, which propagates to the enclosure and radiates audible noise. As a result, the parts contributing most to the generation of audible noise are the top and the bottom of capacitors. In the noise level prediction respect, several methods have been prospected including impact hammer, sweep frequency, impact current, monopole and Kirchhoff formula method, which are suitable for single capacitors or capacitors stacks individually. However, the sweep frequency method is restricted by experiment condition, and the impact current method needs further research and verified. On the other hand, CIGRE WG14. 26 provides three sound reduction measures, but all of them are not so practicable, while MPP absorber and compressible space absorber prospected by Dr. Wu Peng are proved to be effective. The sound barriers are also considered by scholars, and the acoustic directivity performance of capacitors is also researched. Besides, the developing direction of each research field is prospected in corresponding part.
Voltage-sharing Characteristics of Porcelain Insulators for 750 kV AC Substation

Considering the complex environment in 750 kV AC substation, porcelain insulators have particular electric field and voltage distribution in comparison with those used in AC transmission line, meanwhile, the investigation of a typical 750 kV AC substation located in Lanzhou with ultraviolet imager (UVI) demonstrated that the corona discharge of some insulators is serious due to the improper structure design and installation, so research on porcelain insulators used in substation is needed. The three-dimensional finite element method (FEM) 750 kV AC substation calculation model was established to calculate electric field and voltage distribution of insulators, and the voltage distribution curves along insulators which are classified by type and suspension location were obtained using a novel FEM method which can effectively reduce the calculation amount without losing accuracy, meanwhile, the effect of the grading ring for improving voltage distribution of insulators was studied by adjusting the structure parameters of grading ring. Consequently, an optimization structure of rings was proposed by improving the voltage distribution of insulator string and reducing the electric strength of grading ring for the purpose of restricting corona noise, and the on-site observations by UVI showed that the newly manufactured and installed grading ring could obviously avoid the occurrences of corona discharge which validates the optimization design. This paper proposed an effective method combining UVI observation and FEM calculation to study voltage-sharing characteristics of porcelain insulators, and the results can provide experiences and references for the design of 750 kV AC substation.
Equivalency of Artificial and Natural Icing

Climate room is an important instrument to study the icing problems in power networks, and the accuracy of the data from the climate room is under debate. There are many climate rooms in the world, but no standards about the parameters of the climate room such as the room's temperature, the velocity of the wind, and the particle diameters of the water droplets etc. These parameters will influence the icing processes on the lines and insulators. This paper gave a summary of the process and the feature of atmospheric icing of power networks. The speed of the icing on a cylinder rod as a new characteristic quantity was proposed to study the de-icing problems in this paper. For the purpose to analyze the equivalence between atmospheric icing and icing in climate room, a finite element model was made based on a small climate room located in the Graduate School at Shenzhen, Tsinghua University. Through the simulation analysis for the heat transfer and flow issues, the result showed that precooling droplets were cooled into supercooled ones soon after they came into the climate room. Based on the most serious icing-speed in Hengshan, Hunan and a series of experiments, the values of some parameters in studying icing problems were proposed to better simulate the atmospheric icing in climate room.
Experimental and Numerical Study of the Pollution Accumulation on Outdoor Insulators

Flashover on polluted insulators is the most common accident occuring in power system. A great amount of work has been done to study the flashover characteristics on various kinds of insulators with several theoretical models proposed. In these models, the amount and the distribution of the pollution on the insulator is critical to the flashover performance. However, very few simulation works has been carried out to study the pollution accumulation characteristics on the insulators. In this paper, both experimental and numerical efforts were given to study the pollution accumulation characteristics in order to evaluate the flashover probability. Experiments were performed first to have a bird view on the overall pollution distributions considering several crucial influential factors such as the wind speed and wind direction. AC porcelain insulators (XWP_2-160 type) were selected as the experimental samples and the equivalent salt deposit density (ESDD) was measured after the total predetermined amount of pollution was reached. Then, aerodynamic simulation was carried out to study the airflow and velocity distributions on each part of the insulator in clean air with regard to different wind speed and direction. It was found that the amount of the pollution on each section of the insulator has clear connections to the wind speed or air pressure distribution on the insulator surface. These distributions coincide to the pollution distribution obtained from experiments. Besides, the wind speed and air pressure distribution along the insulator chain was also studied. This work has shown that the numerical simulation may predict the pollution distribution on the insulators with practical accuracy. It is also possible to design new insulator shapes to reduce the pollution accumulation on critical areas according to the analysis in this work.
Effect of Exposure to Electrical Discharge on Transformer Oil Properties

Petroleum based oils, the so-called mineral oils, are used for impregnating solid insulations or filling products of very large number of electric materials: transformers, reactors, cables, bushings, circuit breakers, tap changers, etc. In these equipments, oil is exposed to electrical stress and may experience electrical discharges under certain circumstances. Since the electrical stress is unavoidable in power equipments, the ability of oil to resist decomposition under electrical stress is of great importance for the safety of these devices. Electrical stress together with heat and moisture, in the presence of oxygen, oxidises the oil producing free radicals, acids and sludge that are deleterious to the transformer. In this paper, the effect of electrical discharges on oil properties is reported. The results indicate that quality of oil is considerably affected with increasing voltage stress. Comparing oil properties before and after voltage application allows assessing the outcome of random secondary chemical reactions between large oil born free radicals.
Analysis of Trap-controlled Conduction in Modified PTFE

The reasonable conduction property is beneficial to release the deposited charges by conduction current in dielectric space charging environment, thus the level of the deep charging and the pulse discharge can effectively be weakened and inhibited. A traditional method for conductivity measuring under ground circumstance was used, and both the applied voltage and temperature were varied to determine the dependence of volume conductivity in PTFE modified by different filler contents. The results inferred the volume conductivity was significantly affected by the phenomenon of the percolation conduction, as well as the high-field conduction. The shallow and deep charge traps were considered to be a key factor in volume conductivity variation. In this theory, modified by inorganic semi-con-ductive filler, the distribution of trap density and depth in PTFE can be controlled to achieve the ideal temperature-de-pendent conduction property and high-field conduction property, which will finally lead to gentle release of the deposited charges while the electrostatic field reaches the conductivity-variation threshold.
Experimental Investigation on Electrical Tracking of Epoxy Resin Compound with Silicon Rubber

The use of polymer materials as electrical insulators on transmission and distribution lines has been increasing such as epoxy resin. Several advantages of using epoxy resin as an insulating material are its low density, better dielectric properties, and epoxy resin has higher volume resistivity than that of the glass and porcelain. However, epoxy resin has some disadvantages when it is used in tropical areas concerning with the humidity, high ultraviolet radiation, acid rain and effects of contaminants. Consequently, insulator surface will be easily damaged due to electrical tracking, which is indicated by the surface tracking. In this paper, the surface tracking on epoxy resin compound with silicon rubber has been investigated. The test was done based on the method of Inclined Planed Tracking (IPT) IEC 587: 1984 with NH_4Cl as contaminant. The test materials used were epoxy resins based on Diglycidyl Ether of Bisphe-nol A (DGEBA) and Methaphenylene Diamine (MPDA) compound with silicon rubber (SiR) with the dimensions of 50 mm×120 mm and the thickness of 6 mm. The flow rate of contaminant was 0.3 mL/min. The 3.5 kV AC high voltage 50 Hz was applied to the top electrodes. The experimental results show that the contact angle of hydrophobic was affected by compound of silicon rubber. The surface tracking, time to tracking and discharge current were affected by applied voltage, contamination and contact angle. By using micro-cameras, the surface damage was detected. The severest damaged sample surface on a sample had small contact angle. On the other hand, samples with the grea-test contact angle needed longer time to have surface damage in the surface discharge. This shows that it is more difficult for large contact angle samples or more hydrophobic to have surface discharge. Epoxy resin compound with silicon rubber has contact angle of hydrophobic greater than epoxy resin without silicon rubber.
Use of Fourier Transformation for Detection of Faults in Underground Power Cables

An analysis of underground power cables is performed using Fourier analysis with the objective of detecting fault and average life of the cables. Three types of cables are used in this experiment: a normal cable, a shorted cable, and a cable with holes. The impedance in each case is computed and Fourier transformation is applied so that the resulting impedance magnitude and impedance phase can be examined in the frequency domain. Various windowing techniques are applied to the experimental data to eliminate any interference. Fourier analysis is then applied to the impedance data calculated from both the sending end voltage and differential voltage. This analysis reveals differences in the frequency response of the three different types of a cable and can eventually be used as a measure for fault detection. Preliminary results reveal the differences in the frequency response. Accordingly, Fourier type methods can be effectively used as low cost and viable solutions to identify and detect faults in underground cables.
Quality Control of Extruded HVDC Cables: Detection of Critical Flaws Using Low Frequency Voltage Endurance Testing

The main purpose of the work presented here is to evaluare different methods for quality control of polymeric insulated HVDC cables. The insight gained can be used to evaluate proposed test methods for quality assurance of long lengths of polymer insulated power cables. Laboratory experiments were performed using both Rogowski shaped test objects and model cables, insulated with XLPE containing imbedded spherically shaped particles. Tests were performed by stressing the test object with AC (50 Hz), VLF (0.1 Hz) and DC voltages and measuring time to break down at the different voltages. The slope of the voltage-time curve for 0.1 and 50 Hz were found to be parallel showing higher breakdown strength for 0.1 Hz than 50 Hz. The number of periods to breakdown is somewhat higher for 0.1 Hz than for 50 Hz. The breakdown strength for DC was much higher than for both AC 50 Hz and 0.1 Hz. The results indicate that the VLF test voltage needs to be 2 to 3 times higher than at 50 Hz power frequency in order to e-liminate the same defects within a comparable time.
Laboratory Investigation on Lightning Flashes to High Voltage Transmission Lines

This paper presents an investigation on the attractive width of high voltage transmission lines to lightning strikes. In order to design the optimal lightning protection, the estimated number of lightning flashes on the line, which is based on its attractive width, needs to be determined. The investigation was performed using experiments with model tests at the Mississippi State University High Voltage Laboratory. For laboratory experiments, a total of 2, 100 negative and positive switching impulse voltages were applied to transmission line models from a conducting rod, which represented a lightning downward leader. Different tested models of transmission lines on a scale of 1:100 were used. The effects of overhead ground wires, phase conductors, tower structures, and the magnitude and polarity of lightning strokes were also studied. The attractive width increased gradually with the height of overhead ground wires and towers as well as the magnitude of the lightning stroke current. Impulse polarity had an impact on the attractive width, and the attractive width for negative polarity was larger than that for positive polarity. The taller tower had more effect on flash distribution to transmission lines than the shorter one. The experimental results agree with the actual transmission line observations published in literature. The new expressions for the attractive width of transmission lines, based on the experimental results, were established. The accurate estimation of the attractive width can help electric power utilities plan transmission systems reliably and economically. The detailed description of the background problem, proposed method, experimental results, and analysis are presented in this paper.
Calibration of UHF Sensors for GIS: Comparison of Different Methods and Testing of a Calibration System Based on a Conical Antenna

Different methods of calibrating ultra high frequency (UHF) sensors for gas-insulated substations (GIS) were investigated in the past. The first approach was to use strip lines, triplates and TEM calibration cells. These cells had already been in use for years for example to test the electromagnetic compatibility of electronic devices. The smaller the size of the cell, the higher its bandwidth-but the cell should be large enough to not disturb the electric field with the installed sensor under test. To overcome this problem, a calibration procedure using a gigahertz transverse e-lectromagnetic(GTEM) test cell and a pulsed signal source were introduced in 1997. Although this procedure has many advantages and is easy to understand, measurements show several shortcomings of this calibration method. To overcome the disadvantages of the known systems, a calibration cell using a monopole cone antenna and a metallic ground plane were developed and tested. The UHF sensor was placed in a region with minimum distortion of the electric field due to its installation. Experience shows that the new method for calibrating UHF sensors is necessary in order to overcome the limits in the calibration of large sensors and to suppress the propagation of higher order modes and reflections. Due to its surprisingly simple structure, its low price and low overall measurement uncertainty, it is the preferred method for calibrating UHF sensors for GIS applications.
Simulation of Lightning Overvoltage Distribution on Stator Windings of Wind Turbine Generators

This paper analyzes lightning surge on the stator windings of wind turbine generators. The path of lightning in the wind turbines was analyzed. An equivalent circuit model for megawatt direct-driven wind turbine system was developed, in which high-frequency distributed parameters of the blade conducts, tower, power cables and stator windings of generator were calculated based on finite element method, and the models of converter, grounding, loads, surge protection devices and power grid were established. The voltage distribution along stator windings, when struck by lightning with 10/350 μs wave form and different amplitude current between 50 kA and 200 kA, was simulated using electro-magnetic transient analysis method. The simulated results show that the highest coil-to-core voltage peak appears on the last coil or near the neutral of stator windings, and the voltage distribution along the windings is nonuniform initially. The voltage drops of each coil fall from first to last coil, and the highest voltage drop appears on the first coil. The insulation damage may occur on the windings under lightning overvoltage. The surge arresters can restrain the lightning surge in effect and protect the insulation. The coil-to-core voltage in the end of windings is nearly 19.5 kV under the 200 kA lightning current without surge arresters on the terminal of generator, but is only 2.7 kV with arresters.
Mechanism of Arc Discharge in Vacuum Interrupter Based on PIC-MCC Method

With the raise of voltage level in electric power grid, the phenomena of high voltage gas insulation has received extensive attention from all over the world. The research on the breakdown mechanism of vacuum which is the main insulation gas in high voltage level is one of the most important issues. It is also important to the study of vacuum arc in vacuum switch. But for the limitations of available method used in analyzing the breakdown mechanism of vacuum, the main research on vacuum breakdown is macroscopic experiment. The experiments are greatly influenced by environmental factors and high vacuum degree is difficult to be ensured. So the data from the experiments are dispersive and the complex physical change in vacuum breakdown can not be revealed. The purpose of this work is to analyze the mechanism of vacuum breakdown quantitatively by microscopic numerical simulation. The particle in cell and Monte Carlo methods are used here to solve microscopic dynamic equation of gas. Based on the field emission theory in vacuum, electrons produced by the cathode and ions produced by the collision between electron and metal vapor molecule are the objects of this study. The motions of microscopic particles which are at the functions of the applied and self-consistent electric filed are traced in time and two space dimensions. Mont Carlo method is used here to cope with the collisions between electrons and metal vapor molecules. The cross sections of the collision which is related with the energy are all from the experiments. The secondary electron emission, exciting, elastic and ionizing collisions between electrons and metal vapor molecules have been considered in this paper. By the simulation, the number densities of electron and ion are acquired and the microscopic dynamic electric field produced by space charge is also calculated. The effect of vacuum degree on discharge voltage is also discussed here. According to the simulation data, we draw the conclusion that the main reason for vacuum arc formation is metal vapor ionization and large amount of metal gas is from high energy electrons, collision with the anode.
Discharge Diagnosis of Metal-enclosed Switchgear by Using TEV Method

In order to solve the problems of TEV (transient earth voltage) utilization, such as single judgment criterion and low reliability of PD detection in HV switchboard, this paper discussed the method on how to make a better utilization of TEV in PD detection of metal-enclosed switchgears. Through discussing the relationship among the temporal phase, number of pulses and threshold of measuring and extracting the features corresponding to different typical defects, test results showed that the needle discharge distributed in 0°~90° and 200°~340° with low appearance probability above high measurement threshold; internal discharge distributed in 0°~90° and 270°~315°, and showed a similar decreasing trend under increasing of the threshold in the two regions; suspended discharge distributed in 0°~ 135° and 180°~315° where the PD in negative half periods decreased more seriously than those in positive half with increasing threshold. These results followed the doctrine of consistency with the conclusions that were obtained by using the traditional pulse current method. The possibility of using TEV method to make identification of PD defects has been proved to prepare for further research.
Challenges for High Voltage Testing of UHV Equipment

The increase of voltage level for AC and DC transmission systems requires some changes in the high voltage testing for Ultra High Voltage (UHV) equipment. After a short description of the coordination work in the standardization bodies the requirements for UHV equipment are mentioned. The main points concerning high voltage testing of UHV equipment are the impulse shape of standard lightning impulse voltage, the evaluation of the test voltage for impulses with oscillations or overshoot near the peak and the time parameter of switching impulses. The linearity check of the measuring devices, the proximity effect, the wet tests and the atmospheric correction factors are further points to be discussed concerning testing of UHV equipment.
Numerical Simulation of High-current Vacuum Arc in Short Gap

The plasma status of vacuum arc before arc current zero, has a great influence on the interruption performance of the vacuum circuit breakers. In this paper, a vacuum arc model in a short gap was established based on the magnet hydrodynamic (MHD) and a common computational fluid dynamics (CFD) software was utilized to specially investigate the properties of this arc. The spatial distributions of plasma pressure, plasma density, ion axial velocity, and axial current density in front of the anode surface of vacuum arc in this case were obtained. Simulation results indicate that: from the cathode to the anode, both of the plasma pressure and the plasma density increase gradually, and the plasma axial velocity decreases gradually; the axial current density in front of anode has a large radial gradient, and the maximum value is still smaller than the threshold current density for the anode-spot formation, thus, the anode is still passive. The comparison between the plasma density of simulation and the CMOS images taken by the high-speed camera indicates that they are in reasonable agreement with each other and demonstrates the feasibility of the vacuum arc model.