Sphere Gap Research Articles

Study on the triggered discharge characteristics of sphere gaps for protecting transformer neutral point

Study on the triggered discharge characteristics of sphere gaps for protecting transformer neutral point

Sphere Gap Breakdown Voltage Prediction Based on ISSA Optimized BP Neural Network and Effective Electric Field Feature Set

Electric field distribution is a determinant factor of air gap breakdown voltage. This paper defined an effective electric field zone between the sphere gaps for feature extraction, and 29 parameters were extracted from this zone to reflect the electric field distribution. A data mining model was established by back propagation neural network (BPNN) for sphere gap breakdown voltage prediction, taking the electric field features as inputs. The maximum information coefficient (MIC) method was used to select features strongly correlated to the breakdown voltage, and a multi‐strategy improved salp swarm algorithm (ISSA) was applied to optimize the BPNN parameters to enhance the prediction performance. The standard sphere gaps provided in IEC 60052 were taken as training set and test set, which were divided according to the electric field nonuniform coefficients. The breakdown voltage prediction results of test sample sphere gaps demonstrate good agreements with the experimental values. With input features selected by the MIC method, the ISSA optimized BPNN model has a mean absolute percentage error of only 0.83% and a maximum relative error of 5.86%. By constructing the nonlinear mapping relationship between the effective electric field features and the insulation strength, this study provides a new approach to predict air gap breakdown voltage. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Electrostatic Field Feature Selection Technique for Breakdown Voltage Prediction of Sphere Gaps Using Support Vector Regression

This article proposes a methodology for air gap breakdown voltage (BV) prediction based on support vector regression (SVR), taking various features extracted from the electrostatic field calculation results as input variables. The genetic algorithm (GA) is applied for feature selection to improve the performance of the SVR model. A case study on sphere gap BV prediction is reported to demonstrate the validity of the proposed technique. This study provides a reference for dielectric strength prediction by artificial intelligence algorithms, thus to guide the optimal design of air insulation structures.

Simulation and Experimental Analysis of an Impulse Voltage Generator

This paper presents the simulation and experimental analysis of an impulse voltage generator (IVG) used for atmospheric discharge voltage tests. The electrical equivalent circuit of the IVG was simulated using the electromagnetic transients program EMTP-VR. Besides the simulation of the generator operation, it was necessary to make a detailed revision of the IVG components and determine their working condition to carry the laboratory experiments. The lack of a high DC voltage source to feed the IVG led to developing a high-voltage dc supply. Although the IVG was designed and built in February 1982, this equipment was out of operation due to its DC power supply failure. Due to the interest in rehabilitating the equipment to perform high voltage experiments, and with the need to characterize insulation materials and electrical equipment subject to electrical stress, it was decided to put it back into operation. Capacitor tests were carried out for each IVG stage to determine if they fulfilled the electrical charging function. Other components were also repaired, such as damaged resistances and sphere gaps. The impulse generator was configured with a maximum of six stages which is half of the original design. Before doing an experiment with the IVG, a simulation analysis was made to study the IVG. The simulation results allow evaluating before the experimentation whether the impulse generator is working correctly; the model allows to analyze the charge and discharge of each capacitor and the electrical currents at each branch of the IVG equivalent circuit. Performance Simulation and experimental results are presented to demonstrate the IVG functionality. The IVG will be used for carrying out insulation tests made by power engineering graduate students.

Experimental, analytical and numerical analysis of voltage distribution along the cap-and-pin insulators

This paper deals with the experimental, analytical and numerical analysis of voltage distribution along the cap-and-pin insulators. Five different insulators strings are analyzed, consisting of two, three, four, five and six cap-and-pin U40BL glass disc insulators. Experimental measurements are performed in the high voltage laboratory at the Faculty of Electrical Engineering East Sarajevo. Measurement of the voltage distribution along the disc insulators is performed by using measuring sphere gap. Analytical calculations are performed by using mathematical model which considers parasite self-capacitances of disc insulators, as well as their parasite capacitances to the earth and to the phase conductor. Calculations of the parasite capacitances values are performed and optimum values which lead to the minimum difference between measured and calculated results are suggested. Numerical analyses of the non-linear voltage distribution are performed by using electrostatic field model in software Comsol Multyphisics. 2D axisymmetric models of the cap-and-pin insulators are developed. Despite the measuring configuration is not suitable for numerical analysis, relatively good agreement between the measured results and results calculated by using specialized software are achieved.

Design and Implementation of Van de Graaff Generator

The paper proposes a design and implementation of Van de Graaff generator whose output voltage is 80.28 KV. To calculate the generated output voltage we have use the sphere gap method. A Van de Graaff generator is an electrostatic generator as it works on a principle of electrostatics. A Van de Graaff generator is used to generate a high DC voltage. It was first developed by Robert Jemison Van de Graaff in 1929, in USA and carries his name along 1931. This generator uses a moving belt to build up very high voltages on a hollow metal globe which is located on top of the generator. The potential difference that is developed in modern Van de Graaff generator reach about 5 megavolts. A Van de Graaff generator that we design and built that is intended to be used in schools and colleges for teaching the basics principles of Electrostatics and Electromagnetics as well as many other applications. Nowadays many schools and colleges laboratories and many museums use this type of generators for electrostatics demonstrations.

Calculation of Breakdown Voltage of Gas Gaps With Weakly Nonuniform Field: Sphere and Donut Gaps

Breakdown voltage (BDV) is calculated for two electrode structures, namely, sphere and donut gaps, operating in air at atmospheric pressure. The calculation is based on the streamer BD criterion. COMSOL software package is used for field analysis and calculation of critical number of electrons by assessing integrals of the efficient ionization coefficient along field lines. Thus, also lengths of critical avalanches that can propagate from both electrodes were obtained. First, simulations were performed for sphere gaps at conditions standardized by IEEE to derive critical number of electrons for highly reliable experimental data. It was shown that these numbers deviate greatly from the widely accepted 108 number, and that clear tendencies for the deviations exist depending on the gap to sphere diameter ratio. This assisted us in the second part of this work, which is a description of a spark gap (SG) formed by two donuts. Such gaps are compact and can serve as closing switches, and as a crude HV measurement means. Experimental results and comparison to calculated BDVs are reported. These two examples illustrate a simple and effective method of BDV calculation in arbitrary geometries with weakly nonuniform field for well-characterized gases at moderate pressures; it can be used with industry-standard software in HV practice.

Design and realization of a nearby lightning-electric field environment simulator

Objectives Lightning can be extremely harmful to ships on the open seas. Especially with the large-scale application of electronic and electrical equipment and closed integrated masts, the lightning indirect effect on ships is becoming increasingly serious. In order to effectively carry out the lightning indirect effect test for shipborne electrical and electronic equipment, Methods a kind of nearby lightning-electric field environment simulator based on the principle of Marx generator was designed and realized in this paper. The simulator realized the peak cut-off of the impact high voltage by using the adjustable single chopping sphere gap, and established a simulated nearby lightning-electric field environment through the high voltage plate and the conductive ground plane. Results The test results show that the device has a cut-off time of less than 2 μs and a drop time of less than 0.09 μs, which can produce a pulsed electric field environment that meets the requirements of GJB 1389A-2005. Conclusions This paper can provide equipment support for the research on the indirect effect of the nearby lightning strokes on system electronic and electrical equipment based on GJB 8848-2016.

A Feature Set for Structural Characterization of Sphere Gaps and the Breakdown Voltage Prediction by PSO-Optimized Support Vector Classifier

Air insulation strength relates closely to the electrostatic field distribution of the gap configuration. To achieve insulation prediction on the basis of electric field (EF) simulations, the spatial structure is characterized by a feature set including 38 parameters defined on a straight line between sphere electrodes. A support vector classifier (SVC) with particle swarm optimization (PSO) is used to establish a prediction model, whose input variables are those features. The EF nonuniform coefficient f of each sample gap is calculated and used for training sample selection according to the ranges off values. Trained by only 11-sample data, the PSO-optimized SVC model is employed to predict the power frequency breakdown voltages of 260-sphere gaps with a wide range of structure sizes. The predicted values coincide with the standard data given in IEC 60052 very well, with the same trend and minor relative errors. The MAPEs of the five predictions with different training sets are within 2.0%. The model is also effective to predict the breakdown voltages of Φ9.75-cm sphere-Φ6.5-cm sphere gaps, whose MAPEs are within 2.6%. The results demonstrate the effectiveness of the EF feature set and the generalization ability of the SVC model under the case of limited samples. This paper lays the foundation for estimating the dielectric strength of other air gaps with similar structures.

Research on key technologies in ±1100 kV ultra‐high voltage DC transmission

Based on completely mastering ±800 kV transmission technologies, the first ±1100 kV direct current (DC) transmission demonstration project is being constructed in China. Combining theoretical analysis and a large number of experiments, the margin of switching overvoltage in converter stations, the configuration scheme and performance of lightning arresters, the shielding angles of ground lines under different geographical conditions, and the maximum air gap of lines have been determined. The switching impulse flashover characteristics of equipotential sphere and typical rod-plane air gaps are also provided. The external insulation is designed differently for light, medium, and heavy pollution areas. For the ±1100 kV project, if the 8 × 1250 mm2 conductors are applied, the pole gap is 26 m and the height of the line is 25 m, all the electromagnetic parameters will meet the requirement of international electromagnetic standards. The key design points of ±1100 kV converter transformers, smoothing reactors, converter valves, and wall bushings are researched and the 75 mH smoothing reactors, ±1100 kV/5000 A converter valves, and ±1100 kV/5523 A wall bushings are successfully made. The optimised hierarchical connection modes and coordination control measure of the ±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.

Analysis of Electric Field and Current Density for Different Electrode Configuration of XLPE Insulation

The most important aspect influencing the circumstance and characteristics of electrical discharges is the distribution of electric field in the gap of electrodes. The study of discharge performance requires details on the variation of maximum electric field around the electrode. In electrical power system, the insulation of high voltage power system usually subjected with high electric field. The high electric field causes the degradation performance of insulation and electrical breakdown start to occur. Generally, the standard sphere gaps widely used for protective device in electrical power equipment. This project is study about the electric field distribution and current density for different electrode configuration with XLPE barrier. Hence, the different electrode configuration influences the electric field distribution. This project mainly involves the simulation in order to evaluate the maximum electric field for different electrode configuration. Finite Element Method (FEM) software has been used in this project to perform the simulation. This project also discusses the breakdown characteristics of the XLPE. The accurate evaluation of electric field distribution and maximum electric field is an essential for the determination of discharge behavior of high voltage apparatus and components. The degree of uniformity is very low for pointed rod-plane when compared to other two electrode configurations. The non- uniform electric distribution creates electrical stress within the surface of dielectric barrier. As a conclusion, when the gap distance between the electrodes increase the electric field decrease.

平等電界領域における大気中球ギャップのULD現象低電位依存性

To the present, the ultraviolet radiation linear discharge (ULD) phenomenon was found in the sphere gap of the uniform electric field region. This phenomenon is the phenomenon which generates the linear discharge of the ultraviolet radiation region with the spark discharge. It became clear that ULD had the close relation for the phenomenon known until now as spark delay and irregular discharge phenomenon only.

平等電界領域における大気中球ギャップの不整放電現象の要因

By the present, uniform electric field region of the sphere gap is utilized for the high tension proofreading. Generally, the discharge voltage is difficult to get stabilized discharge voltage, when spherical electrode is used. Especially, beginning of use is discharged low-voltage, when there was long-time unused hour of spherical electrode, since there is a position which is easy to discharge the electron. Such discharge is known as an irregular discharge phenomenon. Therefore, pre-discharge, etc. is done near in the use.

A prediction method for breakdown voltage of typical air gaps based on electric field features and support vector machine

Breakdown voltage of the air gap is of vital importance for the design of the external insulation in high-voltage transmission and transformation projects. In this paper, a new prediction method for the breakdown voltages of typical air gaps based on the electric field features and support vector machine (SVM) was proposed. According to the finite element calculation results of static electric field distribution, the electric field values in the whole region, discharge channel, surface of the electrode and the shortest path were extracted and post-processed, which constituted the electric field features characterizing the gap structure. Then, the breakdown voltage prediction model of the air gap was established by using electric field features as the input parameters to SVM, and whether the gap breakdown would happen as the output parameters of SVM, which changing the regression problem to a binary classification problem. This model was applied to predict the power frequency breakdown voltages of different short air gaps including sphere-sphere gaps, rod-plane gaps, sphere-plane gaps and sphereplane- sphere gaps. The power frequency breakdown voltages of longer air gaps which are affected by corona, and the 50% positive switching impulse breakdown voltages of long sphere-plane gaps and rod-plane gaps were predicted as well. The predicted results agree well with experimental values and simulated results of the published models, which validate the effectiveness of the proposed model. This method supplies a new possible way to obtain the breakdown voltage of air gaps.

The Measurement of the Voltage Distribution along High Voltage Suspension Porcelain (5-6-7 Insulator)/String in Case of Clean Condition

The operational voltage or the voltage distribution along porcelain insulator string is affected by stray capacitances, which causes a non-uniform voltage distribution. The recital of insulator sometimes depends on the amount of insulator/string. In order to explain these activities and phenomena clearly in this research, an equivalent circuit that takes the insulator material properties and the stray capacitances is implemented in the TINA program package to analyze the voltage distribution along the insulator string with and without guard ring under power frequency voltage. Finally, the simulation results of voltage distribution have been compared with experimental results, which were obtained in the KKU High Voltage Research Laboratory. To investigate the voltage along across each (5, 6, 7) insulator/string in clean condition, the string efficiency has been measured by sphere gap method. From the simulation results, the voltage across (5, 6, 7 clean and contaminated insulator/string) with and without guard ring were simulated by the TINA program. From this simulation results, we found that the string efficiency of clean string insulator condition which the insulator consists of 5, 6, 7 insulator/string without guard ring equals 66.92, 58.45 and 53.71%, respectively. The string efficiency which the insulator consists of 5, 6, 7 insulator/string with guard ring equals 90.42, 87.03 and 78.35%, respectively. In the experiment, the sphere gap was used to measure the voltage along insulation string. In case of the clean string insulator condition, the string efficiency which the insulator consists of 5, 6, 7 insulator/string without guard ring equals 69.12, 62.67 and 57.04%, respectively. The string efficiency which the insulator consists of 5, 6, 7 insulator/string with guard ring equals 76.36, 66.69 and 59.76%, respectively.

Design and numerical investigation of A HVDC vacuum switch based on artificial current zero

With the fast development of multi-terminal high-voltage direct-current (HVDC) transmission technology, there is an urgent demand for the HVDC interruption technique. In this paper, an interruption scheme for HVDC based on artificial current zero is proposed with its main circuit breaker consisting of modularized vacuum switch in series. A triggered sphere gap is adopted as the commutation switch to achieve bidirectional DC interruption. The interruption process, particularly, the most important two commutation processes, is simulated based on a circuit model. The residual current and its influence after current commutation, which might exist due to the weak arc extinguishing capacity of the sphere gap, are analyzed. It is proposed to use back-up circuit breakers to interrupt the residual current. Furthermore, the influence of the frequency of the countercurrent on the interruption process, particularly, on the integral of i <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> t in the triggered sphere gap due to the residual current, is discussed.

Peak Voltage Measurements Using Standard Sphere Gap Method

The paper presents a measurement system of peak value of high voltage (H.V.) using 150 mm diameter sphere gap, disposed in vertical position. Experimental breakdown results have been compared with standard values at atmospheric reference conditions STC (20°C, 101.3 kPa, or 760 mmHg). The main experimental and theoretical characteristics are presented.

Reduce the Amount of Transformer Oil using Air Mixtures in Sphere Gap Electrodes and Proposed Composite Insulating Liquid

Reduce the Amount of Transformer Oil using Air Mixtures in Sphere Gap Electrodes and Proposed Composite Insulating Liquid

Measurements of characteristics of electromagnetic radiation caused by electrostatic discharges in metal sphere gap at voltages less than 1 kV

In this study, the characteristics of Electromagnetic (EM) radiation caused by Electrostatic Discharges (ESDs) from metal spheres charged to voltages less than 1 kV are examined experimentally. Our experimental system consists of a pair of spherical electrodes of different diameters, a 1-18 GHz-band-width horn antenna and a 20-GHz-bandwidth digitizing oscilloscope. Polarization, waveform duration and peaks of antenna-received voltages from the EM field radiation are measured in order to clarify the EM radiation mechanism. The ratio of the received voltages between the antenna arrangements of the field polarization parallel and perpendicular to the spark pass is 18 to 20 dB. The polarities of the antenna-received voltages are the same as those of the charge voltages across the gap. Moreover, the waveform duration and the first peaks increase with an increase in the diameters of the spherical electrodes. Consequently, we find that the polarization, waveform duration and first peaks of the EM field radiation can be explained by a dipole antenna structure, which makes the spark part of the spherical electrodes a feeding point on the straight line passing through the centres of the two spheres.

Simulation and measurement of the voltage distribution on high voltage suspension Porcelain insulator string under pollution condition

Satisfactory operation of suspension insulator strings is intimately related to the voltage distribution of the string. At operational voltage, the voltage distribution along insulator string is affected by stray capacitances, which causes a non-uniform voltage distribution. In addition, the performance of insulator changes by the accumulation of environmental pollution over its surface that will deteriorate by absorption of moisture sharply. In order to explain this dilemma clearly, a full equivalent circuit, which takes into account the insulator material properties and the stray capacitances, is derived from the Finite Element Method Based Software, which is implemented in the EMTP-ATP package to calculate the voltage distribution, power loss and the leakage current, flowing through the string with and without pollution under power frequency voltage. Finally, the simulation results of voltage distribution have been compared with experimental results, which were obtained in the High Voltage Laboratory. In experimental procedure, an attempt to form the pollution on the surface of the insulator has been carried out. For this investigation the dry pollutant on the insulator surface has been approached according to IEC60507, which has led to the resistance of pollutants. Then, the voltage distribution of clean and polluted insulator strings has been measured by sphere gap method.