Dry Band Arcing Research Articles

Discharge behavior and dielectric performance of artificially polluted hydrophobic silicone rubber

Flashover voltage and discharges behavior were investigated with silicone rubber (SiR) polluted with fog, red clay or carbon particles. For a SiR polluted with carbon, partial discharges occur between water droplets and form interspersed dry bands. For a SiR polluted with red clay, the leakage current induces uniform dry bands and dry-band arc discharges. Because flashover occurs through the dry bands, the noticeable difference in flashover voltage between the polluting materials is not seen. The pollution deposit changes the surface state and causes partial discharges which lead large leakage current, however, the partial discharges don't significantly lower insulation performance.

Enhancement of tracking and erosion resistance of silicone rubber with platinum/amino-silane by modulation of crosslinking density

Tracking and erosion resistance of silicone rubber with N-[3-(trimethoxysilyl)propyl]aniline (NTSPA) and Karstedt catalyst (Pt) was improved significantly by increase of crosslinking density through incorporation of polymethylvinylsiloxane with high vinyl content of 2.93 mol% (HPMVS). Silicone rubber with 15 phr of HPMVS passed the incline plane test (IPT) at 4.5 kV with eroded mass of merely 0.65 wt%, whereas silicone rubber without HPMVS failed the test. TGA and TG-FTIR results indicate that increase of crosslinking density facilitated radical crosslinking reactions induced by Pt/NTSPA at elevated temperature. Residues from silicone rubbers after IPT were characterized via Raman spectroscopy, 29Si NMR and SEM. The results reveal that highly crosslinked network promoted formation of a compact silicon oxycarbide ceramic barrier to protect inner material from further degradation during dry band arcing. Moreover, conductive graphitic carbon in the residue decreased remarkably, thereby inhibiting the formation of conductive path.

Effect of mixing sequences of γ-piperazine propylmethyl dimethoxysilane on the tracking and erosion resistance of silicone rubber

γ-Piperazin propylmethyl dimethoxysilane (HD-110) was introduced into silicone rubber containing platinum catalyst to enhance the tracking and erosion resistance by two mixing sequences:adding HD-110 in the preparation of silicone rubber masterbatch (SR-1) or silicone compound (SR-2). The effects of HD-110 and its mixing sequence on the thermal stability, tracking and erosion resistance, and mechanical properties of silicone rubber were investigated by rubber process analyzer (RPA), transmission electron microscopy (TEM), extraction resistance test, thermogravimetric analysis (TGA) and inclined plane (IP) test. It was indicated that HD-110 could significantly improve the thermal stability and tracking and erosion resistance of silicone rubber. Especially, SR-1 could pass the IP test at 4.5 kV with a eroded mass ratio of 0.35 wt%, which was much less than the 5.34 wt% of SR-2. SR-1 also had better mechanical properties. RPA, TEM and extraction resistance test revealed that HD-110 in SR-1 could easily condense with the Si-OH groups of silica to make HD-110 stable in the silicone rubber matrix and improve the interfacial interaction between silica and silicone rubber. Therefore, under the continuous elution of conductive solution and the heat stress generated by dry-band arcing, HD-110 was stable enough to enhance the tracking and erosion resistance of silicone rubber.

The Development of Low-Current Surface Arcs Under Clean and Salt-Fog Conditions in Electricity Distribution Networks

Electricity distribution networks are built to deliver increasing amount of electricity from distributed energy resources (DERs) such as offshore and onshore wind and solar farms. Aging of network assets through low-current surface discharges is becoming a great concern for the security and reliability of the distributed energy supply. In particular coastal conditions can present a challenge for overhead line insulators through the environment of salt fog. Also, onshore areas may expose power lines to clean fog and agricultural or industrial pollution. In this paper, experimental studies are conducted to investigate electrical arc formation and growth on insulators, following the testing standards in accordance with IEC 61109. Dry-band arcs in both clean-fog and salt-fog environments are compared. It is identified that arcs are much faster to develop and have greater energy in salt-fog environments, due to the lower surface resistance and resulting higher leakage current. The time from a first arc to strike, to the situation where the arc is stable on the insulator surface is identified as a potentially critical parameter in controlling aging of an insulation surface. The time from initial appearance of an arc to full stability is eight times shorter in a salt fog of 16,000 $\mu \text{S}$ /cm compared to a clean fog of $600~\mu \text{S}$ /cm. This means the very existence of a stable low-current arc is much more likely in polluted conditions. Accumulated arc energy and heat dissipation have been calculated for both fog conditions. It is concluded that aging by low-current electrical arcs tends to be more severe in salt-fog environments, so that great care needs to be taken when designing overhead lines and insulators in such areas.

Study on Acceleration Factor at 5000 h Multiple Stress Test and Aging Evaluation of EVA Insulator

SUMMARYThe authors carried out an outdoor exposure test and the 5000 h multiple stress test to ethylene vinyl acetate (EVA) polymer composite insulator used for 22 kV distribution line and an attempt was made to estimate the acceleration factor of the 5000‐h multiple stress test corresponding to the climate condition of the Kyushu area. By comparing dry band arc cumulative charge of leakage current at 5000‐h multiple stress test with that in the outdoor exposure test, the authors estimated the acceleration factor of the 5000‐h multiple stress test to be about 20 times. The acceleration factor was found to almost agree with the evaluation result of the absorption of hydroxyl group by FT‐IR analysis and the surface roughness of the insulator, respectively. Finally, for the electrical property, the expected life of EVA insulator that the authors developed was confirmed to be more than 40 years.

Fault development upon water ingress in damaged low voltage underground power cables with polymer insulation

Developments in the electricity sector, related to integration of sustainable energy, not only affects the medium voltage but also the low voltage infrastructure. Condition monitoring of Low Voltage (LV) underground power cables becomes of increasing interest to safeguard reliable power delivery. Since the start of phasing out oil-paper insulated cables, polymeric insulation is most widely applied. As phenomena associated with high electric field stresses are not expected, little is known about the degradation mechanism of LV cables with polymeric insulation. External damage is known to be a major cause of defects, which directly causes a failure or initiates degradation resulting in a failure later on. To study the degradation mechanisms, short cable sections with artificial damage have been subjected to periodic water exposure in the laboratory. This shows that dry-band arcing is a major mode of degradation, with accumulation of pollutants due to chemical decomposition. Several factors such as water conductivity, presence of oxygen, soil type and insulation material have been investigated. Strong dependencies upon these parameters are observed. However, it may be hard to quantify the degradation process in practical situations. The presence of a water film that can sustain dry-band arcing will occur only in certain situations and for limited amount of time. However, the accumulation of these events, mainly caused by periods of precipitation, will eventually lead to breakdown at the damaged spot.

Investigation of the tracking and erosion resistance of cured liquid silicone rubber containing ureido-modified MQ silicone resin

Ureido-modified MQ silicone resin (DIPUPES-MQ) was prepared by the hydrolytic condensation of tetraethoxysilane (TEOS), (γ-diisopropylureidopropyl) triethoxysilane (DIPUPES), hexamethyldisiloxane and divinyltetramethyldisiloxane. Subsequently, DIPUPES-MQ was employed to improve the resistance to tracking and erosion of addition-cure liquid silicone rubber (ALSR), and it showed that DIPUPES-MQ could significantly enhance the tracking and erosion resistance as well as the mechanical properties of the ALSR. When the content of DIPUPES-MQ was 3.75 phr, all the test samples passed the inclined plane tracking and erosion (IP) test at 4.5 kV. The thermogravimetry (TG), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) and FTIR results showed that the striking enhancement in the tracking and erosion resistance of the ALSR was probably ascribed to the decomposition of the ureido groups. In the pyrolysis process, the ureido groups of DIPUPES-MQ could generate isocyanic acid to hinder the “unzipping” depolymerization through reacting with Si-OH groups, so that the amount of cyclic dimethylsiloxanes inducing intense and continuous dry-band arcs was decreased.

複合加速劣化試験における加速係数の検討とEVAがいしの劣化評価

The authors carried out an outdoor exposure test and the 5000h multiple stress test to ethylene vinyl acetate (EVA) polymer composite insulator used for 22kV distribution line and an attempt was made to estimate the acceleration factor of the 5000h multiple stress test corresponding to the climate condition of the Kyushu area. By comparing dryband arc cumulative charge of leakage current at 5000h multiple stress test with that in the outdoor exposure test, the authors estimated the acceleration factor of the 5000h multiple stress test to be about 20 times. The acceleration factor was found to almost agree with the evaluation result of the absorption of hydroxyl group by FT-IR analysis and the surface roughness of the insulator, respectively. Finally, for the electrical property, the expected life of EVA insulator that the authors developed was confirmed to be more than 40 years.

Suppression of silicone rubber erosion by alumina trihydrate and silica fillers from dry-band arcing under DC

This paper describes the suppression of dry-band arcing erosion of silicone rubber by alumina tri-hydrate and silica fillers in the DC inclined plane test, employing the wavelet based multiresolution analysis of leakage current. The third detail component of the leakage current as decomposed by the wavelet-based multiresolution analysis is shown to be an indicator of the effectiveness of the filler type in suppressing erosion by dry-band arcing. The addition of alumina tri-hydrate or silica filler to silicone rubber increases the thermal conductivity of the composites, retarding the development of the eroding temperature, and thus the evolution of the third detail. Additional effect is also obtained for the dehydration enthalpy, of alumina tri-hydrate in silicone rubber at a filler level of 30 wt%, in impeding the development of hot spots on the tested surface. A reduction in the magnitude of the third detail is evident with filler level, indicating that the increasing volume of silica or alumina tri-hydrate reduces the temperature of the dry-band arcing plasma. Comparable levels of the leakage current third detail is found between 30 wt% alumina tri-hydrate and silica filled composites which suggests the water of hydration plays a minor role in diluting the SiR but at 58 wt% an internal oxidation mechanism that produces gases diluting the arcing phase appears to suppress erosion.

The DC inclined-plane tracking and erosion test and the role of inorganic fillers in silicone rubber for DC insulation

The first polymer insulator for AC transmission lines was developed in the late 1950s. This insulator consisted of a flexibilized epoxy resin weathershed cast onto a fiberglass rod, and field trials on a 138-kV line took place in 1959. Insulators failed almost immediately on energization due to severe tracking and erosion of the bisphenol-A epoxy material, which was later, through inclined-plane tests, shown to be inherently unsuitable for use in outdoor insulation [1]. This article describes a study of the DC dry-band arcing mechanism as a foundation for the development of a standard DC inclined-plane test and its employment in the evaluation of silicone-rubber housing composites for outdoor DC insulation.

Fractal analysis of nano-reinforced silicone rubber insulators evaluated on a tracking wheel

The increased use of polymer insulators on the overhead electrical power system has led to many designs of insulators, with many profiles and materials, but the performance has not always been stellar, particularly in polluted and wet environments, and degradation by tracking and/or erosion has been the main reason for this. In tests, such as the tracking wheel, visual inspection of tracking and erosion is subjective and can be misleading in establishing a quantitative measure of the damage to insulators. In this article fractal analysis is used to analyze the leakage current that develops on polymer insulators when subjected to pollution and electrical stress. Leakage current manifests itself by dry-band arcing leading to erosion and possible tracking of the polymeric material. Leakage current obtained from continuous monitoring of insulators under test is subjected to a methodology based on fractal analysis.

Effect of urea-containing anti-tracking additive on the tracking and erosion resistance of addition-cure liquid silicone rubber

Three novel urea-containing anti-tracking additives were prepared and used to enhance the tracking and erosion resistance of addition-cure liquid silicone rubber (ALSR). The suppression effect and mechanism of the additives on tracking and erosion were investigated by the inclined plane (IP) test, thermogravimetry (TG) and thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR). It was found that the anti-tracking additives not only significantly improved the tracking and erosion resistance but also enhanced the mechanical properties of the ALSR. When using 2 phr of the anti-tracking additive, all the ALSR samples could pass the 4.5 kV level in the IP test. This might be mainly attributed to the arc-quenching capability of the urea group and the formation of a ceramic barrier to protect the underlying materials from further degradation during the dry band arcing. The TG and TG-FTIR results revealed that the urea-containing anti-tracking additives could prevent the radical decomposition of the ALSR below 400 °C. Hence, it considerably improved the initial thermal degradation stability of the ALSR and prolonged the time to track.

Investigation into the eroding dry-band arcing of filled silicone rubber under DC using wavelet-based multiresolution analysis

This paper describes an investigation into the dry-band arcing mechanism leading to erosion of filled silicone rubber in the DC inclined plane test. Good correlation is obtained between the formation of surface residue, hotspots and the eroding dry-band arcing. The hotspots detected by infrared camera correlates well with the temperature of degradation determined by thermogravimetric analysis and differential scanning calorimetry. To characterize the physical mechanism of dry-band arcing, wavelet-based multiresolution analysis up to seven levels of resolution is applied to the leakage current waveforms. The analysis shows that both stable and intense discharges characterize the eroding dry-band arcing. A time-to-eroding parameter is proposed to determine the relative resistance to the formation of residue. Faster accumulation of residue is evident under -DC than +DC. Earlier inception of erosion is obtained for the silica filled- as compared to the alumina tri-hydrate filled- silicone, in which the release of the water of hydration is postulated to suppress the residue formation.

Erosion of silicone rubber composites in the AC and DC inclined plane tests

In this paper, the performance of silicone rubber composites containing 0, 10 and 30 wt % loading of silica filler is investigated in the initial-tracking voltage test method of the inclined plane test under AC and DC showing the most inferior erosion class under +DC followed by -DC and then AC. DC as compared to AC dry-band arcing characteristics are analyzed by conducting leakage current measurements prior to and after the inception of dry-band arcing. At high test voltages, instability of the contaminant rivulet is found to be an important factor in the development of dry band arcing and, consequently, biasing the test outcomes when equal voltages of rms AC and DC are selected. The initial tracking voltage in ASTM D2303 is, therefore, proposed as a reliable approach by which +DC and -DC test voltages can be reliably selected. A coefficient of variation parameter is also proposed as a useful mean of selecting the equivalent DC voltages, and the validity of the parameter is verified experimentally using the initialtracking voltage test method. Erosion in the constant voltage method is investigated under DC by applying the equivalent voltages and compared to AC. Based on this methodology, it is suggested that an improvement in silicone rubber compositions is needed for DC. Moreover, the need to select the creepage distance of polymer insulators designed for AC, yet to be used under DC, with reference to tracking/erosion performance is highlighted.

Evaluation of Discharge Ignition by Composite Pollution Test with Silicone Rubber

Application of polymeric materials for electric power apparatus is spreading worldwide. However, the aged deterioration is anxious because of dry band arc discharges generated on the surface of the polymer materials. In this paper, we carried out composite pollution tests and measured the discharge ignition time of silicone rubber. The results showed that there was no large difference in the discharge ignition times obtained between ac and dc voltage applications. Additionally, it was shown that the difference of the discharge ignition was influenced by hygroscopic property of the pollution material.

Leakage current analysis, FFT calculation and electric field distribution under water droplet on polluted silicon rubber insulator

In this paper, an experimental test results on silicon rubber insulator with voltage of 20 kV have been shown. Artificial aging on insulator has been done using solid layer methods according to IEC60507 standard. Leakage current waveforms during the experimental studies were measured. Normally Fast Fourier transform method used to find the harmonic spectrum in the leakage currents. Three states of analysis are considered. In the first state, it is done with nominal voltage and without arc. In the second state, it is done in the presence of dry band arcing and corona discharge and in the last case, continuous arc is investigated and in each state harmonic analysis is performed. It is observed that in second state the third harmonic components increase rather than in the first state. Artificial aging on insulator has been done using solid layer methods according to IEC60507 standard. Leakage current waveforms during the experimental studies were measured. Eventually, to distinguishing pollution intensity, equivalent salt deposit density calculations are implemented. At the end, finite element method has been investigated for the results of water droplets existing on the surface of silicone rubber materials and electric field distribution along the surface of insulator.

Long Wire Antenna-Like Behavior of Uninsulated Overhead Distribution Cables

Uninsulated overhead distribution cables are evaluated in terms of their propagation and radiation behavior when excited by a partial-discharge (PD) pulse. Low attenuation levels at high frequency and a traveling-wave radiation pattern are observed for a single aluminum cable. The dominant radiated frequency components of surface discharge and dryband arcing are experimentally evaluated, and a high level of activity is observed in the 400-600-MHz and 900-1000-MHz bands. High directivity values at specific angles are also recorded at 400 and 900 MHz for single- and three-cable distribution systems. These findings show that a PD signal will travel for a significant distance along a cable and leak radiation predominantly in a specific direction, thus assisting the design of the RF-based discharge detection and localization system.

DETECTION OF CORONA AND DRY-BAND ARC DISCHARGES ON NANO-COMPOSITE EPOXY INSULATORS USING RF SENSING

RF radiation due to corona and dry-band arc discharges have been observed using an antenna. Variations in radiated energy were observed due to change in the distance between two water droplets, the contact angle and the volume of the droplets, and the condition of the insulator surface. Changes in the frequency spectrum within the 800MHz{900MHz and 1.25GHz{1.4GHz frequency bands have been used to identify the transition from corona discharge to dry- band arc discharge. The 800MHz{900MHz emission band has also been used to monitor the condition of the insulator. These flndings highlight the potential for RF sensing in the identiflcation of partial discharges and insulator condition monitoring.

Analysis of frequency characteristics of electrical arcs on the insulating sheath of the ADSS fiber optic cables

The insulating outer-sheath of ADSS (All dielectric self supporting) cables used on high voltage transmission lines are often subjected to various environmental effects. The ageing process of cable sheath can be investigated by using the dry-band arcing test method under laboratory conditions. Dry-band arcing is the most common technique to determine the ageing period of insulating materials. Environmental effects such as rain, humidity, dew and ice produce various amounts of wet regions on the cable surface. Electrical arcs and hence degradations are occurred on the cable surface due to the enhanced electrical field with formation of wet regions. In this study, the ageing process of ADSS cables was investigated by using the dry band arcing test method (IEEE 1222 Electrical surface degradation). Rainfall intensity determines the wet regions on the cable surface which affects the ageing process of the cable. During tests electrical arc signals were investigated by analyzing wet region scope versus amplitude and frequency spectrum variations via the FFT method. It is possible to claim that the proposed FFT analysis clearly identifies the ageing period of the ADSS cable which was subjected to different rainfall intensities by monitoring frequency spectrum of the arc signals.

Increased energy in stable dry-band arcs due to length compression

The occurrence of dry-band arcs on outdoor composite insulators can degrade the polymeric materials¿ surface and ultimately may lead to insulator failure. The degradation processes are generally considered as aging effects occurring over long periods of time, from years to decades. In this paper, it is shown that if a stable dryband arc is physically compressed in length by external forces, such as electrolyte deformation due to wind or gravity, the arcing activities will become more severe. This in turn, may accelerate the degradation into a short time-frame hazard. A series of experiments are carried out to investigate the electrical characteristics of the arcs as they become compressed. In this case experiments are performed on silicone rod insulators at controlled angles to the horizontal. Rapid aging is observed after such events. Measurements of arcing period, peak current, and arc resistance during the arcing compression process are analyzed. Based on the experiments, a `Double Sinusoidal Model¿ is developed to simulate the current-voltage characteristics of dryband arcing during its compression. Both experiment and simulation show that arc power, arc energy and corresponding energy density will dramatically increase if arc compression occurs, which may lead to more rapid and serious damage on composite insulator surfaces than is experienced otherwise. It is suggested that aggressive erosion events may occur in short periods of time within extended test regimes or entire service histories.