Voltage Insulation Research Articles

HVDC Surface Flashover in Compressed Air for Various Dielectrics

This study measures the voltage at which flashover occurs in compressed air for a variety of dielectric materials and lengths in a uniform field for DC voltages up to 100 kV. Statistical time lag is recorded and characterized, displaying a roughly exponential dependence on breakdown voltage. Of the materials tested, acrylic is observed to be the most resistant to flashover. These data are intended to facilitate the design of compressed-air insulated high voltage systems as an alternative to SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> insulated systems.

СПОСОБИ МЕТАЛІЗАЦІЇ КЕРАМІКИ, ВИКОРИСТОВУВАНІ ПРИ ВИРОБНИЦТВІ СИЛОВИХ ЕЛЕКТРОННИХ МОДУЛІВ І ЕЛЕКТРОВАКУУМНИХ ПРИЛАДІВ

Power electronic modules are used in engineering related to the need to transmit high-current signals. Typical areas of application of such modules are aircraft navigation systems, elements of switching power circuits and other high-load connections. The central unit of the module is a ceramic base, on which conductive tracks are formed and electronic components are mounted. The finished substrate is often called a switchboard. The substrate performs two main functions: Is the dielectric basis of the printed circuit formed on one or two sides. Provides heat dissipation emitted by semiconductor crystals and circuit elements. Used for substrates non-hygroscopic ceramics, heat-resistant, is an insulating material with high mechanical and dielectric properties. It is relatively easy to manufacture and low cost. In the manufacture of power modules using ceramic substrates of aluminum oxide or nitride with a multilayer metallized coating with a thickness of several microns to several tens of microns (depending on the application), which provides the required degree of adhesion of the coating to ceramics and applied on one or both sides. The main requirements for the finished product are the minimum dimensions and low cost of materials and production process. In addition, the decisive factors are high technical characteristics, resistance to environmental influences and reliability. The design of the finished module must provide minimum values of transient thermal resistances, distributed inductances of power busbars, high insulation voltage. Adhesion strength depends on many factors: coating technology, film material, substrate material; and may decrease during operation of the finished product. During the operation of power modules, they are subjected to thermal and mechanical loads, including vibration. This leads to the destruction of components from overheating and damage to the mechanical damage of the modules. Often the failure occurs in the structure of the substrate-coating conductor. The main reason for this destruction is the low adhesive strength of the metal film to the ceramic base.

Novel dc flashover model for predicting flashover voltage of the iced insulators

Novel dc flashover model for predicting flashover voltage of the iced insulators

A proposal for a lightweight, large current superconducting cable for aviation

More Electric Aircraft (MEA) is one of the most important subjects for designing the next generation of aircraft. Since we cannot ground the electric power systems of a flying aircraft and the air insulation voltage is lower at high altitude, a low voltage, direct current (DC) aircraft electrical system is preferable for a MEA. Since the current must be high to supply high power, we consider high temperature superconducting (HTS) technology because it handles large currents well. We propose a new HTS cable in this paper. The cable uses a stacked conductor, with oppositely directed current in each HTS tape, a structure that has already been shown to be feasible for low voltage cables. It enhances the critical current compared to a single tape conductor, especially for Bi2223 tape. In order to avoid a current imbalance in the stacked conductor, we use the current lead resistance rather than a Roebel conductor design. Then the critical current remains high, and this is confirmed by measurements. The cryogenic pipe will be made of magnesium-lithium alloy, one of the lightest metals available at the present time. We estimate the weight-to-current ratio per unit length to be less than 0.5 kg/A/km at the liquid nitrogen operational temperature of 77 K, lighter than conventional copper cable. If instead we use liquid hydrogen at 20 K, we expect a value less than 0.1 kg/A/km, which is one of the lowest presently achievable values and satisfies the requirements for MEA.

Research of 3.3kV, 60A H-Bridge High-Voltage SiC Diode Modules

The simulation, fabrication and measurement of the high-voltage H-bridge SiC diode module is reported. The SiC module is consisted with 8 self-designed 3.3 kV30 A SiC Schottky diodes (SBDs), in which each bridge arm is connected by double SBD chips to achieve 60A current. Q3D is used to establish simulation model and make network division of the module. Two parasitic parameters, parasitic inductor and circuit resistance, are extracted from the circuits, which are about 37.5 nH and 1.9 mΩ, respectively. By establishing the geometric model and finite element model, finite element analysis software ANSYS is used to calculate steady-state thermal conduction, and the temperature gradient distribution of the formed chips. The results show that the maximum junction temperature of the chip is about 100°C, and the distribution of the temperature field is reasonable. As the lateral conduction of heat increases the effective heat dissipation area, there is no obvious concentration of heat. Under the condition of the test at room temperature and static, the module voltage drop is about 2.1 V, the leakage current is less than 5 uA, and the breakdown voltage is more than 3700 V, respectively. The fabricated 3300 V devices exhibit large safety margin. The insulation voltage exceeds 7000V, thus ensure the safety of the system. The thermal resistance of the chip is about 0.21 K/W, which is basically consistent with the simulation results.

Analysis of the voltage profile in transmission lines operating with injected third harmonic voltages

This paper analyses the voltage profile along a three-phase transmission line whose power transfer capability was increased by an uprating technique based on the injection of a third harmonic voltage component. The superposition of a third harmonic voltage component with the fundamental component at the sending and receiving ends of the line proposes to increase the amplitude of the fundamental voltage component without exceeding the electrical insulation voltage limits, and thus increasing the power transfer capability. However, this uprating technique can affect the voltage amplitudes significantly along the line. In some cases, these amplitudes can be higher than acceptable values. The study was carried out in Simulink/MatLab® software. Two three-phase uprated transmission lines with voltages of 230 kV and 735 kV were represented by the Bergeron’s line model, then voltage profiles and the voltage waveforms in the time domain at the midpoint of each simulated system were obtained. Results have shown that 230-kV transmission lines with lengths of up to 300 km operating under natural to heavy load conditions can be uprated by the THV technique, whereas 735-kV transmission lines have presented overvoltages along its length when operating between light and natural loading, attesting that this technique is not feasible for this system.

Prediction of Critical Flashover Voltage of High Voltage Insulators Leveraging Bootstrap Neural Network

Understanding the flashover performance of the outdoor high voltage insulator has been in the interest of many researchers recently. Various studies have been performed to investigate the critical flashover voltage of outdoor high voltage insulators analytically and in the laboratory. However, laboratory experiments are expensive and time-consuming. On the other hand, mathematical models are based on certain assumptions which compromise on the accuracy of results. This paper presents an intelligent system based on Artificial Neural Networks (ANN) to predict the critical flashover voltage of High-Temperature Vulcanized (HTV) silicone rubber in polluted and humid conditions. Various types of learning algorithms are used, such as Gradient Descent (GD), Levenberg-Marquardt (LM), Conjugate Gradient (CG), Quasi-Newton (QN), Resilient Backpropagation (RBP), and Bayesian Regularization Backpropagation (BRBP) to train the ANN. The number of neurons in the hidden layers along with the learning rate was varied to understand the effect of these parameters on the performance of ANN. The proposed ANN was trained using experimental data obtained from extensive experimentation in the laboratory under controlled environmental conditions. The proposed model demonstrates promising results and can be used to monitor outdoor high voltage insulators. It was observed from obtained results that changing of the number of neurons, learning rates, and learning algorithms of ANN significantly change the performance of the proposed algorithm.

Test Study on Performance of Endothermic Highly Hydrophobic Anti-Icing Materials

In this paper, the solar spectrum selective endothermic coating with CoCuMnOx as the light absorbing pigment is prepared to absorb sunlight efficiently. After optimizing the thickness of the coating, the endothermic coating material with absorptivity of 0.928 and emissivity of 0.198 is obtained. The roughness value of the coating is 0.64 μm, which ensures that the coating has a higher sunlight absorption rate without the need for an antireflection layer. Icing flashover tests were carried out on insulators coated with endothermic highly hydrophobic anti-icing materials. The ice lightning voltage of ceramic insulators (3 pieces) was increased by 13.68%, and that of glass insulators (2 pieces) was increased by 22.96%. Compared with ceramic insulators, glass insulators coated with anti-icing materials have better protection effect.

Temporal and spatial characteristics of soluble salt components accreted on the insulator surface

Due to the differences in typical pollution sources, the soluble salt composition deposited on the naturally contaminated insulators varies with the region. As different soluble salts have different effects on the pollution flashover voltage of insulators, it is necessary to investigate the spatial and temporal distribution of the soluble salt composition deposited on the insulator surface to make the external insulation design more scientifically and reasonably. In this study, an artificial contamination test platform was built to collect the contamination naturally deposited on the specimens. The test results showed that the contamination composition deposited on the specimen was similar to that in the atmosphere, and the inclination angle of the specimen and the duration of pollution deposition had little influence on the contamination composition. After examining the industrial post insulators from actual substations, it was found that the contamination composition was almost the same for different insulator surface materials, insulator shed types, and voltage polarities. It was also found that the deposited contamination was mostly influenced by pollution sources. The results can provide a reference for the studies of pollution distribution of natural insulators.

Forecasting Flashover Parameters of Polymeric Insulators under Contaminated Conditions Using the Machine Learning Technique

There is a vital need to understand the flashover process of polymeric insulators for safe and reliable power system operation. This paper provides a rigorous investigation of forecasting the flashover parameters of High Temperature Vulcanized (HTV) silicone rubber based on environmental and polluted conditions using machine learning. The modified solid layer method based on the IEC 60507 standard was utilised to prepare samples in the laboratory. The effect of various factors including Equivalent Salt Deposit Density (ESDD), Non-soluble Salt Deposit Density (NSDD), relative humidity and ambient temperature, were investigated on arc inception voltage, flashover voltage and surface resistance. The experimental results were utilised to engineer a machine learning based intelligent system for predicting the aforementioned flashover parameters. A number of machine learning algorithms such as Artificial Neural Network (ANN), Polynomial Support Vector Machine (PSVM), Gaussian SVM (GSVM), Decision Tree (DT) and Least-Squares Boosting Ensemble (LSBE) were explored in forecasting of the flashover parameters. The prediction accuracy of the model was validated with a number of error cost functions, such as Root Mean Squared Error (RMSE), Normalized RMSE (NRMSE), Mean Absolute Percentage Error (MAPE) and R. For improved prediction accuracy, bootstrapping was used to increase the sample space. The proposed PSVM technique demonstrated the best performance accuracy compared to other machine learning models. The presented machine learning model provides promising results and demonstrates highly accurate prediction of the arc inception voltage, flashover voltage and surface resistance of silicone rubber insulators in various contaminated and humid conditions.

Design Considerations for High-Voltage Insulated Gate Drive Power Supply for 10-kV SiC MOSFET Applied in Medium-Voltage Converter

High-performance gate drive power supply (GDPS) plays a crucial role in ensuring the reliability and safety of the gate driver for power semiconductor devices. This article focuses on the design of a high-voltage-insulated GDPS for the 10-kV silicon carbide MOSFET in medium-voltage (MV) application. Design considerations, including insulation scheme, high-voltage-insulated transformer design, and load voltage regulation scheme, are proposed. In addition, the performance of the secondary-side-regulated (SSR) GDPS and that of the primary-side-regulated (PSR) GDPS are compared for several aspects, including interwinding capacitance, load voltage regulation rate, conversion efficiency, and hardware complexity. Finally, an SSR GDPS and a PSR GDPS, with an insulation voltage of 20 kV, are built in the lab. The test results demonstrate that the PSR GDPS is more preferable because of lower interwinding capacitance, lower load voltage regulation rate, higher conversion efficiency, and simpler control circuit.

Experimental investigation on composite insulators AC flashover performance with fan-shaped non-uniform pollution under electro-thermal stress

Pollution deposition along with ultraviolet (UV) radiation and electro-thermal stress cause the composite insulators to face with critical conditions. The type of pollution which settles on insulators is not only uniform but also it can be non-uniform and uneven. In this study, the results of the uniform and fan-shaped non-uniform (FSNU) pollution tests on four various types of virgin and aged polymeric insulators under AC voltage are presented. To find the effects of accelerated aging on polymer chains of composite insulators, scanning electron microscopy (SEM) is carried out. Based on IEC 60507, the solid layer method is applied to settle pollution on the insulator surface. The results demonstrate that the flashover voltage of virgin and also aged samples decreased when pollution non-uniformity degree (J) increases from 1 to 13. The flashover voltage of studied insulators is reduced by increasing the occupation ratio (K). However, the impact of K was lesser than J on flashover voltage of the polymeric insulators. Investigated polymeric insulators have been aged up to six weeks (1000 h). Although the influence of two weeks (333 h) accelerated aging on flashover voltage and morphology of the composite insulators was not tangible, therefore flashover strength of the samples is decreased while the aging period time increases. Statistical analysis has been done to estimate the flashover voltage of accelerated aged composite insulators under uniform and FSNU pollution based on virgin insulators. The research aimed to select insulators in windy and sunny areas.

Correction of flashover voltage of catenary insulators based on analysis of soluble salt compositions in saline‐alkali region

AbstractCalcium sulfate and other slightly soluble salts in the natural pollution of catenary insulators could result in differences in flashover voltages between artificially and naturally polluted insulators at the same salt deposition density. Based on the insulator pollution characteristics in saline‐alkali areas and the saturated water absorption of polluted insulators, the equivalent salt deposit density and nonsoluble deposit density of insulators are corrected according to the influence of other coexisting soluble salts on the solubility of calcium sulfate. The correction formula of the insulator flashover voltage is proposed, which considers the equivalent salt deposit density, nonsoluble deposit density and pollution components. The results from the correction formula are compared with the experimental data from the artificial pollution test of the ceramic cap and pin insulator. The results show that salt‐alkali areas are more easy to flashover than other areas. The remaining pollutants can change the conductivity of the pollutant layer by inhibiting or promoting the dissolution of calcium sulfate. Moreover, its effect on the flashover voltage cannot be ignored. The error between the calculated value based on the correction formula and the experimental data is below 6%. A pollution flashover warning mechanism based on relevant meteorological data is proposed. The results can be used as an important reference for the operation and maintenance of catenary insulators in saline‐alkali areas. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

DC pollution flashover performance of HVDC composite insulator under different non-uniform pollution conditions

The non-uniform air flow field and electrical field distributing around insulators cause uneven deposition of pollution particles on different positions and parts of the insulator surfaces. Pollution-induced flashover is a serious threat to the safe operation of the power system, and non-uniform pollution distribution has great influence on flashover voltage of insulators. Towards this, in this study, the solid layer method was used to simulate different non-uniform pollution conditions. Then, DC pollution flashover tests of composite insulators were carried out and the flashover performances were analyzed. The results indicated that the increase of KL/W (from 1 to 15) decreased U50 by 27–32%. While the increase of KT/B (from 1 to 10) increased U50 by 35%, and the increase of KH/M (from 1 to 4) increased U50 by 25%. Where KL/W, KT/B and KH/M are the SDD (salt deposit density) ratio of windward to leeward side, top to bottom surface and high voltage to middle group respectively. Besides, higher proportion of leeward side area will reduce U50. U50 and SDD are still in agreement with the negative power function relationship, non-uniform pollution conditions have great effect on a (constant of power function), but less impact on n (characteristic index of power function). Finally, equations for calculating different non-uniform pollution flashover voltages were established and validated, also the relative errors are acceptable. The results are very important for guiding insulation design and anti-pollution works of operating transmission lines.

Pollution flashover performance of RTV coatings with partial damage

Under conditions of high temperature, high humidity, and strong ultraviolet radiation, RTV coating on the insulators may get aged, powdered and even peeled off. The physical damage of the RTV coating on the insulator surface can result in a reduction in the pollution flashover performance. Therefore, this study investigated the influence of location, lateral length, and longitudinal length of the damage on the pollution flashover voltage of RTV-coated insulators. From the experimental results, it was found that the longitudinal length of the damage along the creepage distance direction was the most influential factor on the pollution flashover voltage. According to the flashover voltage function obtained by fitting, the concept of “effective path” distance was proposed. This concept can be used to analyse the influence of multiple damages on the pollution flashover voltage. To validate the analysis, verification experiments were performed using typical industrial insulator. The results showed that the pollution flashover voltage of the insulator was also in a linear relationship with the proposed “effective path” distance, which confirmed the mechanism analysis.

Construction of microgrooves on the surface of alumina ceramic insulator to enhance its flashover strength

The fabrication method of grooves on the surface of alumina and their influence on the surface flashover characteristics of the alumina insulator were studied in this paper. To prepare grooves with a regular surface structure, the UV laser was applied to carve grooves on the surface of alumina ceramic, and dilute hydrochloric acid was used to corrode and remove the residual materials produced in the laser carving process. By adjusting the laser parameters, periodic grooves were prepared on the surface of a cylindrical alumina insulator with a groove depth of 60 µm and a groove width of approximately 50 µm on the laser spinning carving platform. Then, alumina insulators with different periods were prepared, and their vacuum surface flashover voltages were tested on a short pulsed high-voltage test platform. The test results indicated that the flashover voltages of the alumina insulators with laser carved periodic grooves were increased over 200%, and the improvement did not change much with the groove periods. A further study of the groove parameters showed that several grooves fabricated on the cathode end of the insulators were able to improve the flashover voltage of the alumina insulator to the voltage-withstand level of the fully grooved insulators.

Optimized Design of Multi-MHz Frequency Isolated Auxiliary Power Supply for Gate Drivers in Medium-Voltage Converters

This article presents the design and optimization of a suitable topology for an isolated dc–dc auxiliary power supply with high isolation voltage and low coupling capacitance. The converter consists of a GaN HEMT inverter operating at 6.78 MHz, an LCC resonance tank, and a class-E low d v /d t rectifier. Furthermore, the galvanic isolation is implemented using a coreless planar transformer that enables higher insulation voltage with similar or better converter efficiency compared to designs using a magnetic material. An analytical design methodology is developed, however, SPICE investigations show that optimal designs might lie outside the validity of the design equations. Consequently, a virtual prototyping tool is developed based on a genetic algorithm with numerical simulations, and in turn, is used to optimize the converter. The optimization algorithm maximizes the converter efficiency while minimizing the transformer size. Prototypes are constructed based on the resulting Pareto front. Experimental results show the validity of the simulated results. Prototypes transferring power up to 15 W with a peak efficiency of 81% are shown. The selected topology enables insulating voltages exceeding 40 kV and coupling capacitances below 10 pF.

Improved physical model of electrical lifetime estimation for crosslinked polyethylene AC cable

Inverse power model (IPM), which is a phenomenological model that can predict the electrical life of crosslinked polyethylene (XLPE) insulation, is commonly used to design the insulation and test voltage of cables. Unfortunately, IPM cannot reflect the physical process of electrical aging, and the parameters have no physical significance, which limits the application range and extrapolation accuracy of IPM. Although the physical models of electrical life based on physical and chemical degradation processes exhibiting high accuracy are available, the equations of physical are complex to be popularized in engineering applications. In this paper, a new physical life model for engineering application is presented based on the relationship between transition-state theory and IPM. The proposed model considers the effects of AC electrical stress and thermal stress on aging. The proposed model is fitted to the life data of AC XLPE cable, thus confirming the validity of the proposed model.

Diamond-like carbon coating for effective electrical insulation of Cu and Al wires

The physical and mechanical properties, electrical insulation, chemical resistance, and heat resistance of diamond-like carbon (DLC) films fabricated using the radio frequency plasma-enhanced chemical vapor deposition method (RF-PECVD) on Cu (DLC/Cu) and Al (DLC/Al) substrates were evaluated in this study. The electrical insulation testing results showed that the dielectric breakdown voltage of both DLC/Cu and DLC/Al samples was approximately 145 kV/mm. For assessing the heat resistance, the samples were stored at a high temperature of 200 °C for a fixed time duration, and the changes in the insulation voltage resistance were evaluated. Based on the voltage resistance measurement results of the electrical insulation after heat resistance testing, the study confirmed that the DLC film is heat stable for 7 days of heating. In addition, testing confirmed that the DLC coating remained stable with no deterioration when immersed in both acidic and alkaline solutions, thus indicating high chemical resistance. These findings suggest that DLC is suitable for application as a thin and effective electrical insulation coating, and its properties support the realization of small coil lengths with square wires.

AC Flashover Voltage Model for Polluted Suspension Insulators and an Experimental Investigation in Salt Fog

In recent years, the electrical performance of polluted suspension insulators operating in coastal foggy regions has attracted wide attention because of the occurrence of flashover. Surface wetting by salt fog accretion increases the surface conductivity and degrades the flashover voltage of insulators. Normally, the effect of conductivity under fog condition and pre-contamination on the flashover of polluted insulators are analyzed separately. Therefore, this does not reveal the flashover characteristic in salt fog, which requires further research. This paper describes salt fog experiments with an AC test voltage conducted using suspension insulators in a 110-kV power system. The electrical strength performance of insulators with salt fog treatments is analyzed, and the effects of salt deposit density (SDD) and the fog water conductivity (FWC) on the flashover of three types of suspension insulators are studied. The concept of additional SDD is proposed to quantify analyze the effects of salt fog. The results show that there is less dependence on FWC at higher pollution levels than at lower pollution levels. That is, the effect of FWC on 50% AC flashover voltage ($U_{50}$ ) can be neglected for SDD >0.15 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , whereas FWC has a strong effect on $U_{50}$ for SDD <; 0.15 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . FWC has a greater influence on $U_{50}$ of ceramic insulators than on that of silicone rubber insulator. A model for calculating the critical flashover voltage of insulators is proposed by considering the combined effect of FWC and pre-polluting SDD.