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This research presents a dynamic modeling approach to predict flashover voltage (FOV) of polymer insulators. Pre-flashover conditions can be used to represent analytical formulations for different stages of dry band arcing activities on the surface of polluted insulator. In this study, experimental results of pollution flashover tests are used to develop a circuit model of pollution arcs based on Obenaus model. Estimation of circuit values is done by use of intelligent algorithm with no dependency on profile of insulators which is also more beneficial than typical analytical calculations. Then, separation and investigation of discharge and pollution voltage is done and proper classification is made. This classification is later used to predict pre-flashover conditions and pollution flashover. Gaussian model is used to make fitness of voltage of pollution layer and voltage of discharge on the surface of insulator. Gaussian representation of each stage in pollution flashover contains critical signals leading to complete discharge. Based on the obtained model, a flowchart is presented to predict dynamic stages of flashover. Comparison to various experimental data shows close correlations with the results of proposed model. An online monitoring system can be developed according to obtained results in order to prevent pollution flashover.

Free metallic particles are the main factor inducing flashover incidents and threatening the safety of gas-insulated switchgear (GIS) and gas-insulated transmission line (GIL) devices. Acoustic diagnosis is widely used to detect free metal particles due to its high sensitivity, but it generally fails under multiple particle conditions because of the overlap of acoustic signals. This paper proposes a new method of acoustically recognizing multiple free metallic particles. The pattern of t-Normalized N that can be used to distinguish single/multi-particles is determined first. Second, each particles neighboring collision signals are extracted from raw data by the established physical relation between adjacent collision signals. Finally, the free metal spherical double-particles mass and density values are calculated as per the numerical connection between adjacent collision signals. The proposed method is validated in a scale concentric hemisphere platform. The results of this work may provide a workable reference for GIS free metal multi-particle monitoring.

This paper studies the AC pollution breakdown characteristics of the EGLA and broaden current knowledge of pollution flashover. Compared with the flashover of the normal insulator, three kinds of specificity of the EGLA were found. Firstly, the pollution flashover process can be divided into three categories. Secondly, the wet flashover voltage, Uf _wet, of the novel insulator is higher than the dry flashover voltage, Uf _dry. Thirdly, the piecewise fitting methods with aESDD^-b+d and aESDD^-b+ cESDD^-d are more suitable for fitting the empirical formula of flashover voltage. Furthermore, to explain specificity, the electric potential and electric field distribution are calculated based on the finite element method. Calculated results indicate that when the EGLA is covered with a 0.5mm water film, the maximum electric field intensity decreased from 2.17 kV/cm to 1.99 kV/cm. Also, U_arrester (the withstand voltage of the insulation section) was obtained from the tests and it presents a discontinuous and random increasing trend until flashover occurs, which is considered to be one of the important reasons for the specificity. Besides, based on the Obenaus model and Hampton's criterion, we further analyzed the arc development process by a simplified plate model

The surface voltage of an insulator assumes importance for understanding tracking and flashover characteristics. Until now, determination of surface voltage of insulating surfaces is left to simulation software and such simulations are left unverified experimentally, leading to uncertainty of the results, which may sometimes be erratic with improper choice of boundary or initial conditions or inaccurate material properties, nonlinearities etc. The paper presents a novel method, using which the surface voltage of any insulating surface such as insulator strings or transformer bushings can be measured. Unlike a conducting surface, the measurement of insulating surface voltage using voltage dividers would be erratic as the measuring arrangement itself will vary the voltage division due to the local unknown impedance between the insulated surface and hv conductor. Recently a method for measurement of surface voltage of an insulated conductor using cylindrical strips was reported. In this paper, based on analytical derivations, a more generalized method of measurement, applicable to any point on an insulating surface of arbitrary geometry is proposed using circular-disc strips. The proposed experimental method is applied to insulator strings and transformer bushings and validated by simulation of the entire systems. The simulation and experimental results are in excellent agreement.

For decades it has been known that spacecraft charging-induced electrostatic arc discharge on solar arrays can cause cell degradation and damaging secondary arcs. While discharging on large-area so...

Insulator pollution flashover occurs frequently and is harmful to the power transmission and distribution network. But the randomness of the pollution flashover and the complex influencing factors make it difficult to be predicted. The objective of this paper is to study the mechanism of the discharging on insulator surfaces and design a the calculation method which derives flashover probability. By calculating the distorted electric field in the initial streamer discharge quantitatively and combining it with the equivalent circuit of the insulator surface, the initial discharge voltage is derived. By analyzing the change in power input and dissipation in the process of the arc discharge, we propose the criterion on arc development and extinction, and the critical flashover conductivity of the insulator is obtained. Based on the probability density function, the behavior of the factors on the critical flashover conductivity is described, and the probability of insulator pollution flashover is calculated under different environmental conditions. In the validation experiment, the measured initial discharge voltage and pollution flashover ratio are close to the calculated values. The methods proposed in this paper could be used in the quantitative calculation of the initial discharge voltage and the prevention of the pollution flashover on insulators.

The current lead insulation of the high temperature superconducting DC current limiter is in the terrible working environment of strong electric field and temperature gradient field from room temperature to liquid nitrogen (LN2) temperature. Bisphenol F epoxy resin, as a common terminal insulation material, is prone to surface flashover during equipment operation, which leads to premature failure of insulation. In order to improve the reliability of the terminal insulation system, epoxy resin/γ-Al2O3 nanocomposites were prepared. The dielectric constant, DC conductivity, trap distribution, partial discharge characteristics and DC surface flashover voltage of the nanocomposites at room temperature and in LN2 were measured and analyzed. The results show that with the increase of γ-Al2O3 nanoparticles content, the DC surface flashover voltage of the nanocomposites first increases and then decreases, and the partial discharge inception voltage generally increases. Appropriate γ-Al2O3 nanoparticles doping can effectively inhibit the generation and development of surface discharge.

Generally accepted industry standards, such as National Fire Protection Association (NFPA) 70E-2018, require arc-flash incident energy analysis to be updated when changes occur in the electrical power distribution system, and the analysis shall be reviewed for accuracy at least every five years. NFPA 70E also requires the data used for creating equipment labels, which contain arc-flash energy information, to be reviewed at least every five years, and, if the review identifies a change that renders the arc-flash energy label inaccurate, the equipment label must be updated.

The flashover along epoxy spacer installed in 1 MV DC GIL caused by the excessive concentration of electric field threatens the safe operation of the ITER NBI (neutral beam injector). A spacer with surface conductivity gradient has been proposed to optimize the electric field distribution. In this paper, a simplified model of transmission pipeline with spacer is established. It is found that the electric field is mainly concentrated on the high voltage triple junction and the turning position of spacer. The surface conductivity gradient distribution on the spacer is designed by an iterative method. Results indicate that surface conductivity gradient can weaken the electric field distortion on both sides of spacer, especially the electric field strength of turning position of the concave surface is decreased obviously compared with that of the conventional spacer.

This study determines the voltage across insulators after a direct lightning strike to an overhead ground wire on a 24 kV pole structure for different grounding distances of overhead ground wire, to calculate the maximum ground resistance required to avoid disruption of the distribution line system using ATP-EMTP software. The results show that when a 40 kA lightning current, the average lightning current in Thailand, strikes a 24 kV pole structure, the maximum ground resistance should not exceed 4 Ω for a 40 m grounding distance of overhead ground wire, based on an existing critical insulator flashover of 205 kV. However, because the average ground resistance in Thailand is approximately 10 Ω, this study proposes increasing the insulation level from 205 kV to 300 kV to reduce the likelihood of power outage. The cost-effectiveness of such an investment is assessed in terms of net present value (NPV), internal rate of return (IRR), profitability index (PI), and discounted payback period (DPP) using existing economic tools. Results show that when the critical insulator flashover is increased from 205 kV to 300 kV for a 40 m grounding distance of overhead ground wire, the project is likely to have a DPP of 15.12 years, NPV of 143,321.87 USD, IRR of 12%, and PI of 1.15. On the other hand, grounding distances greater than 40 m for overhead ground wire result in negative NPV, although the back flashover rate can be reduced by 1.51–5.71% with grounding distances of 80–200 m compared to the situation in the absence of grounding.

The partial arc is a destructive discharge phenomenon for HVDC insulators under icing conditions, leading to flashover incidents. This study sets up a calibrated Schlieren system to examine the DC arc's thermal characteristics on an ice surface. The theoretical analysis shows that the plasma component changes significantly between 2000 K to 2882 K, which is the characteristic temperature of arc formation. Experimental results show that the temperature characteristics in the time domain depend on the discharge stages. A temperature jump appears at the spark discharge and then increases exponentially with the leakage current during the arc formation. However, the temperature in the corona and brush discharge is almost unchanged. Results also show that higher water conductivities increase the spark temperature and promote arc formation, but do not affect corona and brush discharge, which take place in the air gap. In the arc channel, the gas near the core comprises molecules, atoms, electrons, and ions, while the gas in other regions is mainly composed of neutral molecules. This study provides findings that might enhance our basic understanding of the ice surface's partial arc formation process.

A stochastic lightning attachment model for evaluating the lightning performance of overhead transmission lines is introduced. The proposed model considers the stochastic nature of lightning attachment by taking into account the lightning discharge branched and tortuous behavior. It integrates physical criteria on leader inception by adopting the Petrov and Waters model, as well as leader discharge progression considering also the competing interaction of multiple upward leaders. A generalized methodology combining stochastic modeling of lightning incidence with an electromagnetic transients (EMT) simulation model is proposed so as to estimate the backflashover and shielding failure flashover rates of HVDC overhead lines; an application to a monopolar −400 kV line sheds light on the basic parameters that affect the lightning performance of HVDC lines. The probability of shielding failure is higher than that obtained by the deterministic lightning attachment models. The stochastic nature of lightning attachment and the effect of lightning peak current distribution should be considered for the design and evaluation of the lightning performance of the emerging HVDC systems.

Aiming to improving the insulator resistance in the polluted media, a new proposed model consisting of an insulating surface coated by a non-linear conductive film has been studied. There are two important roles of the non-linear film. At low voltage gradient, a very small current passes. This low leakage current tends to raise the surface temperatures slightly above the ambient and retards dew deposition, which contributes to many flashovers. At high voltage gradient, i.e. the condition of dry zones formation; the leakage current increases sharply under the discharge across the dry zones, so this discharge diminishes. To investigate the effect of this non-linear film on the surface diacharge and flashover, the electrical characteristics of non-linear film has been studied, and both theoretical model and experimental work, which has been carried out with simple model are discussed. It has been found that the chance of the formation of local surface discharges, and the critical flashover voltage has increased due to the existence of this non linear film. The mathematical expressions of the electric field in the discharge column and pollution layer were deduced for computing the critical flashover voltage.

The present experimental work reports an investigation of the effect of artificial pollution on the performance of suspension ingulators. It was found experimentally that the greasing of suspension insulators by silicone grease improve their performancos oven undor heavy pollution conditions. A silicono grease layer of comparatively small thickness reduces the effect of dirt accumulation and increase the flashover voltage. The leakage current of greased insulators is very lower than that of ungreased insulators. It was found also that the flashover mschanism of polluted insulators under both d.c. and a.c. voltagos depends mainly on the formation of dry-bands, formed by the leakage current. As the applied voltage is increase, these bands extend in width causing partial sparkings across them and leading finally to a totally flashover over the insulator.

Due to wind and uneven distribution of the field along the insulator, a kind of non‐uniform contamination is deposited on the insulator surface as fan‐shaped and longitudinal pollution. This paper investigates such non‐uniform pollution from theoretical and experimental points of view. For this aim, the residual resistance of the pollution layer is formulated based on the geometry of fan‐shaped and longitudinal non‐uniform pollution. Also, the arc current is formulated using the arc Obenaus's equivalent circuit for a constant arc voltage in terms of arc length propagation. Finally, the AC dynamic theoretical model of pollution flashover is proposed that can estimate flashover parameters for different values of the fan‐shaped density degree (J), extension degree (K) and longitudinal non‐uniform pollution density degree (Z) considering instantaneous variables in arc progression. It results that with increasing Z, the flashover voltage increases, while by increasing the J and K, the flashover voltage decreases. To validate this model, the experimental tests are performed on the sample silicone rubber (SiR) insulator that show acceptable accuracy of theoretical model. Furthermore, based on experimental results, a new correction coefficient is proposed under fan‐shaped and longitudinal pollution that varies in the range of 0.85–1.62.

Charge trap characteristics of epoxy spacer insulating material due to surface flashover are important for improving the stable operation of GIS. In this work, magnesium oxide (MgO) filled epoxy nanocomposite material is proposed as the spacer material and its performance is compared with pure epoxy. The surface properties of spacer materials were altered using surface flashovers generated due to standard lightning impulse (LI) and steep fronted lightning impulse (SFLI) having front time of 0.1 µs, using rod plane electrode setup. The impact of surface flashovers on charge trap characteristics were analysed through surface and space charge studies. The surface charge behaviour was estimated by surface potential decay and their trap characteristics, space charge accumulation was measured using pulsed electro acoustic technique. SFLI flashover voltage was lower compared to LI voltages and MgO filled epoxy nanocomposite had higher flashover voltage compared to pure epoxy. The space charge density of MgO filled epoxy nanocomposite was less compared to pure epoxy after treating with LI/SFLI flashover voltages. MgO filled epoxy nanocomposite had enhanced surface potential decay and reduced trap energy after surface flashover. Due to the superior insulating properties, MgO filled epoxy nanocomposite can be used as the spacer material in GIS components.

Under rain conditions, the sliding water droplets on the insulator’s surface shorten the air insulation distance between the sheds and even cause a flashover. In order to study the mechanism of air gap breakdown with rain droplets, the breakdown process was recorded by a high-speed camera and the influences of rain water droplets (conductivity, volume, and position) were studied. The experimental results show that the impact of the water droplets on the direct current (dc) breakdown voltage is related to the air gap length. The shorter the air gap, the greater the drop of the flashover voltage. Although water conductivity does not affect the breakdown voltages, the arc development path is related to it. This research has significance for revealing the rain flashover mechanism of insulators.

This paper presents the surface discharge characteristics with changes in gas pressure under a sphere-plane electrode with a Teflon dielectric in N 2 /0 2 mixed gas (80:20) and focuses on interpreting the surface discharge mechanism at both high pressure (0.3-0.6 MPa) and low pressure (0.1-0.2 MPa). The partial discharge and surface flashover voltages are measured under AC high voltage between 0.1 and 0.6 MPa of the N 2 /0 2 mixture gas. It is clearly observed that two surface discharge paths are revealed with the pressure change in the N 2 /0 2 mixed gas. In the high pressure case, the surface discharge path develops from the cathode-triple junction to a Teflon surface, and in the low pressure case, the path passes through the bulk gas at the sphere-electrode surface away from the triple junction and then advances to the Teflon surface. Surface discharge models for these two patterns are proposed based on surface discharge mechanisms including electron avalanche, photoionization, photoemission, electron attachment, electron detachment, and dielectric charging.

As power distribution systems become increasingly interconnected and concentrated with distributed energy resources (DER) and high potential equipment, effectively avoiding the medium-low voltage caused safety risk, drawing more attention. Therefore, the accurate, fast, and reliable preemptive arc detection and location method is essential to be developed. However, due to the issues such as low sensitivity, delayed detection, complex structure, and susceptible to interference by other sources, the traditional approaches are not up to the detection and location job, for weak system source and high arcing resistance featured medium-low voltage arc flash. To overcome the limitations, this article explores a novel arc flash preemptive detection and location mechanism. With the application of geometric distribution analysis on magnetic density flux and current density, mathematical modeling incorporated magnetohydrodynamic approach is developed. With a series of actual cases incorporated simulations were performed, the criterion of arc initiation and concisely numerical model on arc fault location estimation is derived, which shows a good ability to catch the transient dynamics of arcing current in the early initiating stage, and also proves the reliability and accuracy on fast detection and location uses. These results offered valuable information for medium-low arc fault mitigation and hazard prevention.

In this article, the influences of outgassing and flashover on the performance of a novel multipacting cathode are numerically investigated by using particle in cell-Monte Carlo collision (PIC-MCC) method, including the conditions of weak, medium, and strong outgassing. The numerical results demonstrate that under the condition of weak outgassing (0.1 Torr), multipacting is hardly influenced by gas ionization. Multipacting dominates the entire physical process. Due to the further improved output current by additional electrons generated from ionization, the weak outgassing can help cathode performance enhancement. Under the condition of medium outgassing (1 Torr), gas ionization first boosts multipacting developing and then tends to suppress multipacting process. During the initial stage, multipacting dominates the entire physical process. When multipacting tends to saturate, gas ionization will dominate the whole physical process. The rapidly increased output current will finally decrease gap voltage and induce the diode breakdown. Under the condition of strong outgassing (1 atm), multipacting is suppressed by gas ionization from beginning to end. Gas ionization dominates the whole physical process all the time. The strong effect of ionization collision will finally induce streamer discharge and diode breakdown.

In this study, to allow the flashover to occur, combustion tests were conducted by setting the conditions of a fire source using a large-scale compartment and changing the opening condition. As a result, the inside temperature of the compartment was measured under the fire source conditions. Moreover, according to the “Handbook on Design Calculation Methods of Fire Behavior” by the Architectural Institute of Japan, the validity of the heat release rate required for the flashover to occur was verified through the correlation between QFO/Qvmax and AT(kpc)1/2/cP0.5AH1/2.

In this work, effect of the oscillation frequency on the oil surface flashover characteristics under lightning impulse voltage is experimentally studied. Four lightning impulse (OLI) waves with different oscillation frequencies and 1.2/50 µs standard lightning impulse (SLI) wave are used in this study. The experiment results show that flashover voltages under OLI are larger than those under SLI and the flashover time lags under OLI are longer than those under SLI. Additionally, the flashover voltage tends to increase and the time lag tends to be shorter as the oscillation frequency increases. According to the experimental results and the discharge theory of liquids, we believe that the waveform oscillation frequency affects both the effective electron generation time lag and the formative time lag. This work provides a reference for the waveform selection of the on-site withstand voltage test and explains the physical mechanism of the oil flashover discharge from the perspective of impulse waveform oscillation.

The demand for DC gas-insulated switchgear/gas-insulated transmission line (GIS/GIL) becomes more and more urgent in recent years owing to the rapid development of high voltage direct current (HVDC) transmission systems. Insulators in DC GIS/GIL could easily accumulate a large number of charges on its surface during long-term operation, which might lead to overstressing of polymeric insulation or surface flashover. Therefore, it is of great significance to propose an effective method for dissipating extra surface charges. However, achieving charge dissipation without opening the tank is still a great challenge to SF 6 -insulated equipment for a long time. In this paper, a novel method, which is named X-ray based non-contact charge dissipation method (XNCDM) for insulators in SF 6 -insulated equipment, is proposed. The effects of X-ray irradiation on the charges dissipation and the influences of irradiation dose were experimentally investigated in SF 6 . The mechanisms underlying are discussed in detail. Results show that surface charges on the insulator can be almost completely dissipated after short-time X-ray irradiation with enough dose, owing to the significant enhancement of electric conduction along the insulator surface and charge neutralization by gas ions near the gas-solid interface. This paper provides a novel technique for realizing rapid surface charge dissipation on the insulator, which is of great significance for a variety of engineering applications of DC GIS/GIL.

It is usually seen that DC flashover voltage of the water droplet on the surface of silicone rubber (SIR) composite insulator is lower than AC flashover voltage. It is necessary to study the mechanisms and influencing factors of the surface properties. In this article, experiments are performed to study the moving processes of the water droplet and the influences of its dynamic behaviours on flashover voltage under DC/AC electric field. Besides, an electrohydrodynamic coupling method is employed to establish the simulating model. Moreover, the theoretical physical model is established to reveal the mechanisms of dynamic behaviours of a droplet. It is indicated that the simulation results are in good consistency with the experimental data. The elongation behaviours of a droplet on the surface of a composite insulator can influence the homogeneity of the electric field distribution along the sample's surface. It is shown that the different dynamic behaviours and flashover performances for a single water droplet on the SIR surface are both affected by the volume of the droplet and the type of voltage applied.

Purpose. To develop methods and conduct force tests under loading, full-scale fire tests of a reinforced concrete monolithic slab as part of an experimental fragment of a framing building, to obtain experimental data on relative deformations and displacements during force tests, temperature distribution in the fire chamber, in structural sections, slab displacements during fire exposure and to assess the damage. Methods. Force tests of reinforced concrete slab using inventory loads, a set of deflection meters and strain gauges; full-scale fire tests of a reinforced concrete monolithic floor under load using a hydrocarbon fire load, a complex of thermoelectric converters and a displacement measurement system. Findings. A methodology has been developed and strength tests of a reinforced concrete cast-in-place slab as part of an experimental fragment of a frame building under a load of 675 kg / m2 have been carried out. The slab deflection in the span was no more than 1/1000. The relative compressive strains of concrete in the maximum values did not exceed 0.36 ‰, the relative tensile strains of concrete in the maximum values were 0.89 ‰, which indicates the elastoplastic work of the structure. A technique was developed and full-scale fire tests of a cast-in-place slab as part of an experimental fragment of a frame building under a load of 675 kg / m2 were carried out. With the use of 2405 liters of waste engine oil and 1.8 m3 of wood, a thermal fire rate close to the standard was created. The temperature on the heated surface reached 1000 °С, while on the unheated side the temperature was not higher than 40 °С, which led to significant deformations of the slab, in total between the center and the console edges it was about 300 mm, or 1/30th of the slab geometric length. As a result of tests on the 69th minute from the beginning of the flashover fire, unexpected destruction of the reinforced concrete centrifuged columns occurred. After the fragment collapsed, two linear plastic hinges were found in the span at a distance of 1.5 m from each support at the point where additional reinforcement has been cut. Application field of research. The research results can be used to assess the fire resistance of reinforced concrete cast-in-place flooring, in the development of design methods and in the modeling of reinforced concrete cast-in-place structures under force loading and at fire, as well as in the development of methods for full-scale fire tests of reinforced concrete structures.

The objective is to compare the electrical performance of a tubular barrier made of silicone and glass protecting an air gap with an alternating electric field. This investigation is focused on rod–rod and rod–plane electrode systems with variable interelectrode distance. An experimental device consists of wooden support in U shape. The air space disruption tests of the two systems with tubular barriers were supported by a visualization of the path of their electrical rupture. A disruption model of a non-uniform electric field air gap was developed in this study. Using the experimental results of dielectric breakdown of the considered systems, this model characterizes the flashover voltage as a function of the barrier insulation’s nature. In addition, it allows an easy comparison of its electrical insulation capacity under these conditions. Under pollution, no protection is provided by a glass barrier to the two systems due to the highly conductive behaviour of the pollution layer covering its surface. On the other hand, that offered by a tubular silicone barrier is by far the best because of the flashover discharge’s presence on its surface under these conditions. In a clean and dry atmosphere, the electrical insulation power of the systems is more efficient with a silicone barrier than with a glass one, because of its more advantageous dielectric properties and its lightness.

To support the safe operation of the novel three-element mixed insulation oil (TEMO) transformer, gas generation behaviors of the TEMO oil–paper insulation system under overheating faults and discharge faults were investigated. Results show that that the content of H2 and C2H6 generated by TEMO–paper insulation system is much higher than that in conventional mineral oil (MO)–paper insulation system under different overheating temperatures. Under partial discharge fault, the content of H2 dissolved in oil changes distinctly, while the content of C2H2 also increases with the discharge time. Under surface flashover breakdown, AC breakdown and lightning impulse breakdown fault, the content of H2 and C2H2 changes greatly compared to other gases, while the concentration of total hydrocarbon gases in TEMO–paper insulation system is smaller than that in MO–paper insulating system after the same breakdown times. The diagnosis model of overheating and discharge faults for the TEMO–paper insulation system was proposed based on the oil dissolved gas analysis, while H2, C2H2 and C2H4 were chosen as the characteristic gases and the boundary settings were determined. The verified result for the low-temperature overheating, lightning impulse and surface flashover fault for the TEMO–paper insulation system presents that the new diagnosis model is effective.

The first two parts in this series gave full analysis and discussion of five high temperature insulation materials, i.e. PTFE, FEP, ETFE, PEEK, and PI over aspects of space charge behavior, conduction property as well as partial discharge, respectively. In this part, the degradation and surface breakdown properties are investigated and the related mechanism is discussed. The results showed that due to stable formation of C-F structures, PTFE and FEP melted locally during arc erosion test, with no carbon element being precipitated. At 25 °C, PI showed the best surface anti-arc erosion property among ETFE, PEEK and PI. However, compared with other samples, the arc withstand property of PI can be much more influenced at higher temperature and in case of surface contamination. Compared with the results measured at 25 °C, the surface flashover voltage decreased for all samples when measured at 150 °C, which can be explained by the expansion of “analogous ineffective region”. FEP has the highest surface flashover voltage at both 25 °C and 150 °C, which is due to higher surface roughness. The content of this paper provides a reference for aging characterization and evaluation of high temperature materials for DC cable and circuit board insulation.

In this paper, through the application of 3D printing technology, insulators with different surface microstructures are prepared. Surface flashover test of the printed insulators shows that surface microstructures have a strong influence on the surface flashover voltage. This indicates that through proper surface microstructure design and the application of 3D printing technology insulators with high surface voltage withstand strength can be prepared. The influence of gas release characteristics, with and without thermal treatment, on the surface flashover voltages is studied. The results indicate that insulators with lower gas release rate own higher voltage withstand strength.

In this paper, the pollution flashover performance of a superhydrophobic surface with different coating strategies are studied. The results show that a superhydrophobic coating is effective in preventing pollution flashover under high voltage. The superhydrophobic coatings show increased pollution flashover voltage when compared to room temperature vulcanized silicone rubber and to an uncoated glass substrate. A novel suppression mechanism of the superhydrophobic coating is proposed which is driven by the electrostatic force produced by the applied voltage. The coalesced slippery slurry droplets and the expanded dry area on the superhydrophobic surface contributes to increased flashover voltage on the superhydrophobic surface. The superhydrophobic coating promises to be a prospective application in anti-pollution performance of insulators.

In this paper, the influence of surface charges is quantitatively analyzed based on the study of surface charge distribution under DC voltage and flashover characteristics of insulators under superimposed voltage of DC and lightning impulse. It is found that when DC and impulse voltage are in the same polarity, surface charges weaken the electric field along the insulator surface and flashover voltages under superimposed voltage increases. When DC and impulse are in the opposite polarity, surface charges enhance the electric field along the insulator surface, and flashover voltages will decrease. The calculation results of the electric field along the flashover path show that the changing rate of the maximum field strength is approximately equal to the changing rate of flashover voltage, which proves that the influence of surface charges on flashover characteristics of insulators mainly depends on their distortion of the electric field.

Characterising the risk of the fire spread in informal settlements relies on the ability to understand compartment fires with boundary conditions that are significantly different to normal residential compartments. Informal settlement dwellings frequently have thermally thin and leaky boundaries. Due to the unique design of these compartments, detailed experimental studies were conducted to understand their fire dynamics. This paper presents the ability of FDS to model these under-ventilated steel sheeted fire tests. Four compartment fire tests were modelled with different wall boundary conditions, namely sealed walls (no leakage), non-sealed walls (leaky), leaky walls with cardboard lining, and highly insulated walls; with wood cribs as fuel and ISO-9705 room dimensions. FDS managed to capture the main fire dynamics and trends both qualitatively and quantitatively. However, using a cell size of 6 cm, the ability of FDS to accurately model the combustion at locations with high turbulent flows (using the infinitely fast chemistry mixing controlled combustion model), and the effect of leakage, was relatively poor and both factors should be further studied with finer LES filter width. Using the validated FDS models, new flashover criteria for thermally thin compartments were defined as a combination of critical hot gas layer and wall temperatures. Additionally, a parametric study was conducted to propose an empirical correlation to estimate the onset Heat Release Rate required for flashover, as current knowledge fails to account properly for large scale compartments with thermally thin boundaries. The empirical correlation is demonstrated to have an accuracy of ≈ ± 10% compared with the FDS models.

Minor physical defects can decrease the dielectric efficiency of epoxy resin and severely threaten the electrical device’s dependability. Self-healing may be considered an effective method to preserve the electrical and mechanical properties of the epoxy resin. Besides, self-healing significantly decreases the influence of small physical destruction on the power system. In this research, epoxy resin incorporated with various concentration of microcapsules was prepared. The polyurea formaldehyde (PUF) microcapsules were treated using a silane coupling agent (KH550) to enhance dispersion. Moreover, the self-healing performance of the epoxy resin incorporated with microcapsules was analyzed by FTIR, SEM, and DC Flashover in air and vacuum. In addition, trap energy and trap density were obtained from measurements of surface potential decay (ISPD). The SEM results indicate that in comparison with pure epoxy resin, the microcapsule/epoxy resin composite has an improved self-healing performance. The DC Flashover of epoxy resin in air and vacuum was found relatively higher after incorporation of microcapsules than pure epoxy resin. The distribution of trap energy and trap density measured by surface potential decay measurements confirms that 5 wt% have deeper traps and the highest trap energy levels.

There is a relative lack of research on the development of creepage discharge in aged oil-paper insulation subjected to AC-DC combined voltage in converter transformers. In this study, based on the physical and chemical properties of oil-paper, we propose a sphere-plate electrode model to study the creepage discharge parameters and characteristic spectra of aged oil-paper subjected to AC-DC combined voltage. The results show that the creepage discharge inception voltage of aged oil-paper is related to the AC voltage component of the AC-DC combined voltage. However, when the DC voltage component is 60 kV, the flashover phenomenon was found to occur in one of the severely aged samples before the AC voltage was applied. Despite being subjected to the same DC voltage, the flashover phenomenon did not occur in three other samples aged to different degrees. Large-amplitude discharges were found to appear earlier in the severely aged samples. At the same creepage discharge stage, as the aging time of the oil-paper increased, the number of large-amplitude discharges was found to rapidly increase, and the time interval between adjacent discharges was found to gradually decrease. At each stage of the creepage discharge, the small-amplitude discharge has a “hump” shaped distribution. The larger the DC voltage component, the shorter the endurance time of aged oil-paper, and the more severe the damage to the oil-paper. The DC voltage component was found to have an accelerating effect on the development of creepage discharge in aged oil-paper insulation.

The metal particles’ movement in DC GIL can easily result in gas-gap breakdown or insulator surface flashover, which will seriously reduce GIL’s insulation performance. To suppress the particle movement and discharge, the authors manufactured the colloidal PI/TiO2 nanocomposite film by the in-situ polymerization method and coated the film on the electrode surface. This paper characterized and tested the film’s physicochemical properties and analyzed its influence on the lifting voltage and movement activity of spherical, linear, sheet metal particles. The results show that TiO2 nanoparticles disperse evenly in the polyimide matrix with excellent compatibility between inorganic and organic phases. As nanoparticles’ content increases, the composite film’s mechanical performance and electrical strength decrease, and the corona resistance time increases first and then decreases. Nanocomposite films can significantly increase the lifting voltage of metal particles. The lifting voltage is almost the same, whether it is the bottom-electrode coating or dual-electrode coating. Voltage polarity does not affect the lifting voltage; however, as the film thickness increases, the lifting voltage increases. After coating, the metal particles’ movement decreases and gradually the particles lie on the bottom electrode’s surface. In the meanwhile, the gas-gap discharge process also stops. There is an obvious polarity effect for the movement of metal particles. The bottom-electrode coating method should be adopted for DC positive voltage, while the dual-electrode coating method should be adopted for DC negative voltage.

This article proposes a new adaptive commissioning methodology for arc flash mitigation in steel manufacturer users considering the Tap-to-Tap varying current consumption. This process is achieved through adaptative protection settings computed to reduce the total clearing time of relays adding the restriction of the incident energy. The proposed methodology carries out the detection of abrupt changes in current consumption to detect Tap-to-Tap change in operation stages of electric arc furnaces. The application of this methodology is performed on a steel manufacturer user and shows the reduction of the incident energy values according to Tap-to-Tap operation cycle.

In the usual practice, the evaluation of overvoltages due to direct lightning strikes to overhead power lines is focused on the representation of the effects of the lightning current injection, whilst the effects of the coupling between the conductors and the lightning electromagnetic pulse (LEMP) is disregarded. Motivated by recent results obtained for the case of a medium voltage line configuration with a shield wire, this paper extends the analysis to assess the contribution of the LEMP on the lightning performance of an overhead distribution line with and without periodically grounded wires and surge arresters. Moreover, the paper deals with the LEMP effect on the occurrence probability of flashovers on different phases, which is an important information on the service continuity of networks with isolated or compensated neutral earthing. A validation of the results is obtained by comparing the overvoltages calculated by the electromagnetic transient program including the model of the line illuminated by the LEMP and those obtained by a three-dimensional finite difference time-domain approach.

Many factors have an influence on the development of compartment fire notably on its heat release rate as well as on its capability to propagate and become a flashover situation. The main element which rapidly conveys fire from a compartment to another is hot smoke flowing out through openings of the compartment source of fire. The present work aims to experiment the impact of the variation of heat release rate of the source on the behaviour of fire. So, five fire tests with different heat release rates were thus carried out in a reduced scale room. Temperature of burned gases inside the room, were measured during tests by sensors connected to a data acquisition system. Results revealed that temperature of burned gases as well as its content in carbon monoxide, evolves differently according to two ranges of the incoming air/outgoing gases ratio. The first range of which the ratio is lower than 2, corresponds to the case where both parameters decrease rapidly. The second range of which the ratio is higher than 2, corresponds to the case where both parameters decrease moderately. The transition from the first to the second range, points out the passing from the ventilation-controlled fire to the fuel-controlled fire. A relation expressing the variation of the mass flow rate of outgoing burned gases according to the heat release rate of the fire source has been given.

NFPA 70E and IEEE 1584 are defining standards for arc flash hazard analysis. Both assume three-phase faults for calculations since three-phase power distribution is predominant in utility and industrial applications; however, arc flash in single-phase systems is excluded. Single-phase faults to neutral or ground or single phase-to-phase faults can occur in a variety of circumstances. Such events may have the potential to produce arc flash and blast that would pose a significant safety concern. This paper describes a recent doctoral research investigation of arc flash in one single-phase configuration. Experiments were sponsored by UL and performed at the Schneider Electric High-Power Laboratory in Cedar Rapids, Iowa. This facility provided a test article; a full suite of voltage, current, and temperature instrumentation; and high-speed video recording. Experimental work revealed incident energy values less than 0.2 cal/cm2 for 240-volt single-phase arc fault events though there was still significant flash and splatter of molten wire residue. 480 V single-phase events produced an order of magnitude greater heat energy, and at 22 kA sustained arcing until interrupted by the test cell controller. Results suggest that 240 V single-phase panels and equipment common in residential and light commercial applications may be at very low risk of yielding arc flash burn-related injuries. However, 480 V single-phase faults can produce levels of incident heat energy known to cause burns, flash, and blast pressure at available fault currents between 10 and 22 kA.

In this article, a new method is proposed to identify the health condition of composite insulators through investigating the leakage current (LC) along with the electric potential (EP) and electric field stress (EFS) profiles. In this regard, variations of the LC harmonics and the distribution profiles of the EP and EFS are investigated through a series of experimental and simulation analyses conducted on composite insulators under various environmental and pollution conditions. Fast Fourier transform (FFT) and a COMSOL-multiphysics environment are utilized to analyze this variation. The results reveal a strong correlation between the LC harmonics and the insulator health condition. A new diagnostic criticality index based on the third to the fifth harmonic ratios of the insulator LC is proposed to quantify the composite insulator criticality and predict the likelihood of flashover occurrence. The EP and EFS analyses can be used to provide a complementary diagnosis of the insulator’s health state under severe pollution and humidity conditions. The proposed analysis enables the transmission line network operator to get an insight into the insulators’ functional status, thus improving the network reliability through avoiding insulator failure and adopting a proper condition-based maintenance scheme.

In the alpine region, there are many flashover failures of ethylene-propylene rubber (EPR) cable terminations due to cavity discharges in China high-speed railways (CHRs). The cable termination with cavity defects is used as test samples and a low-temperature PD test system is set up to study the characteristics of partial discharge (PD) of cavity defects in cable termination in those regions. Influences of the different temperatures on internal discharge in EPR insulation at −40°C and 20 °C have been analyzed. When the applied temperature dropped to −40°C, the PD initiation voltage and extinction voltage decreased by 31% and 28%, respectively, and the discharge pulse appeared at both positive and negative half-cycles. The results showed that, at 20 °C, the discharge was mainly caused by the internal discharge of the gas-filled cavity. Apart from the internal discharge of the gas-filled cavity, a marked trace of surface discharge was also detected at −40°C. Besides, the characteristics of PD development at −40°C are closely related to the discharge phase distribution and the asymmetry of the spectrum. The research can further reveal the development and evolution of PD of the gas-filled cavity and provides a basis for judging the severity of termination at low temperature.

Knowing more about insulator pollution is of guiding significance to the development of anti-pollution strategies. Traditional methods can be used to determine only the pollution degree of insulators. However, the pollution distribution also has a substantial influence on the flashover voltage of insulators even under the same equivalent salt deposit densities (ESDD). In this article, an ESDD spectral density method and a visualization method based on hyperspectral technology are proposed. The proposed method presents the ESDD distribution using hyperspectral images. A detection model based on characteristic wavelengths is established with partial least squares regression to detect the insulator ESDDs. Based on the ESDD detection results, the features of the ESDD spectral density process, including the building of the ESDD probability graph, the overall ESDD, and visualization of the ESDD, are presented. Example analyses of field-operating insulators were conducted, revealing that the ESDD spectral density can be used to track the pollution distribution of insulators and that the pollution degree can be calculated from the overall ESDD. The error of the overall ESDD calculated by this method is within 10%. In addition, visualization of the pollution distribution can more intuitively record the degree of pollution and the nonuniform distribution characteristics. Both the pollution degree and distribution can be obtained by this method. Therefore, hyperspectral technology can overcome the limitations of traditional methods and convert the ESDD results into an image to determine the ESDD distribution. These research results provide theoretical instruction for guiding insulation design and anti-pollution strategies for operating transmission lines.

The adulteration on bushing is tranquil of different actinic element, which threats the firmness of superficial insulation and also infects the interior conductor by carrying a lofty voltage current down a grounded circumvallation. Therefore adulteration pernicious and exploit the bushing. An aim to learn the adulteration condition of bushings which are blighted by nitrates and sulphates such as Ca (NO3)2, KSO4, MgSO4 and CaSO4, unnatural pollution study on three different voltage ratings of bushings were carried out. In that leakage current and arc flash voltage was noted then conductivity has been measured and finally ESDD have been calculated using mathematical formulation, hence the results are compared. Later, by using support vector machine (SVM) the percentage error have been obtained by using gaussian and polynomial kernel function, after that the result have been compared by using hybrid SVM with GA (Genetic algorithm). The fast finding scrutiny conclude that, firstly salt concentration get shoot up then ESDD and conductivity will also get shoot up with dwindle in arc flash voltage and leakage current, comparative analysis babble that hybrid SVM with GA exhibit preferable outcome when compared to SVM.

Ethylene–propylene rubber (EPR) cable is the most commonly used type in high-speed railway. Several flashover accidents take place in cable termination in an extremely cold environment. In this study, EPR cable terminations were tested in a simulated low-temperature system with varied applied voltages. The results showed that the differences in elastic modulus and free space volume between EPR insulation and stress control tube (SCT) in a frigid environment would lead to structural defects between them. Damages on the EPR insulation occurred in the form of flashover point when the ambient temperature declined to −30°C and below, with the growth rate of discharge and resulting extent of damage across the EPR/SCT interface being non-linearly related to ambient temperature. Besides, the partial discharge (PD) initial voltage and PD extinction voltage under low-temperature conditions reduced by >40% compared with those at 20°C. The flashover probability of EPR terminations increased significantly, and the shape characteristics of PD patterns have also changed obviously at low temperatures. It can be verified that under the high-voltage and low-temperature conditions, the EPR/SCT interface is prone to organisational mismatch, which will lead to the PD phenomenon and seriously affect the stable operation of EPR cable terminations.

Water droplets on the surface of insulators can distort the electric field and cause the generation of surface partial discharge or flashover. In this study, the inception and the development of surface partial discharges on a 110 kV composite insulator were evaluated by using a solar-blind ultraviolet imager. Several experiments were conducted by using water droplets differing in volume, conductivity, and position on an insulator housing. The results showed that the corona inception voltage decreases with the increasing volume of the water droplets. The relative permittivity of the water droplet decreases with the increase of the conductivity and then reduces the electric field intensity and increases the corona inception voltage. Installing the grading ring can increase the value of the corona inception voltage by 38% at most. To investigate the influence of the water droplets on the corona inception characteristics of the insulator, the sheath and shed models were proposed according to the feature of the electric field distribution. By changing the parameters of the water droplets, the corona inception voltage, discharge position, and electric field were analysed. Furthermore, the flashover voltage of the water droplets is influenced by its conductivity, while the corona inception voltage by its relative permittivity.

This study aims to predict the flashover voltage (FOV) of silicone rubber (SiR) insulators. Accordingly, it benefits from two methods, including an artificial neural network (ANN) model and a FOV gradient fitting model. The FOV and leakage current (LC) tests are carried out on one un-aged and three aged specimens under uniform and longitudinal non-uniform pollution circumstances. The proposed ANN model is designed based on equivalent salt deposit density (ESDD), pollution non-uniformity degree, aging time, LC first harmonic magnitude I 1 , and total harmonic distortion. Furthermore, a FOV gradient model is proposed based on ESDD, I 1 , and creepage distance. To validate the proposed models, the FOV and LC tests are conducted on two different types of SiR insulators. Then, the predicted FOV from the ANN model and calculated FOV from the voltage gradient model are obtained. The results indicate that the relative errors of the ANN model and FOV gradient fitting model are