Inclined Plane Tracking Research Articles

Functional behaviors of electric field grading composite materials

Non-linear resistive field grading materials (FGM) are used in different high voltage applications e.g. cable terminations, joints and rotating machines, where the electric stress is critical. It is already established that the use of FGM is an improved stress grading technique compared to conventional geometric methods. There is a constant endeavor within the electric power industries to extend these concepts to other power equipment. In order to achieve a wide spread use of FGM, they need to satisfy several functional requirements e.g. fire safety, tracking resistance, hydrophobicity, high thermal conductivity, besides certain dielectric properties e.g. field dependent conductivity, permittivity and low dielectric losses. In the present study ZnO filled silicon rubber (SiR) composite with different functional fillers, in total six different material compositions, are evaluated with respect to several important functional behaviors. Further, stress grading behavior of these six materials are demonstrated by finite element simulations on a generic electrode geometry and by performing inclined plane tracking test. Suitability of these material compositions to industrial applications are discussed.

Examination of Surface Tracking on Polyurethane Foam Insulators

In this research, life time of foam insulation materials was tested and surface degradation of foam insulators was investigated ASTM D2303 test conditions. Surface tracking on organic solid insulators is one of the main reasons for failure in high voltage systems. Due to various factors, such as humidity, pollution, ice load, increase in local voltage, it is hard to estimate the lifetime of an insulator. To determine the model parameters, several tests are performed according to the ASTM D2303 accelerated inclined plane tracking test method by investigating the breakdown times of polyurethane foam under various external conditions generated artificially in the laboratory. Foam insulation materials have to suffer several degradation mechanisms throughout their service life under high voltage. Surface tracking is one of these severe mechanisms which can lead to a total breakdown of the insulator.

DC inclined-plane tracking and erosion test of insulating materials

The paper reviews previous work on the DC inclined plane test and suggests equivalent DC voltage levels in parallel to AC voltage in the ASTM inclined plane tracking and erosion test. The aim of this work is to provide a basis for standardizing the inclined plane test for DC voltage. Round robin tests done in five laboratories on five specimens of a silicone rubber material were done with the purpose of establishing appropriate ratios by which the equivalent DC voltages can be determined with respect to the corresponding AC voltages. These levels were determined as 67% and 87%, for +DC and -DC respectively, of the AC initial tracking voltage, and for practical purposes, these levels are rounded to 70 and 90%.

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.

Effects of thermal conductivity on dc resistance to erosion of silicone rubber/BN nanocomposites

Silicone rubber (SiR) is widely employed as an insulating material in transmission lines because of its excellent electrical properties and superior performance under wet and polluted conditions. However, the discharges that occur during operation can cause electrical erosion on the surface of silicone rubber insulators. The thermal conductivity of insulators has a correlation with the resistance to tracking and erosion. This study attempts to clarify whether the addition of boron nitride (BN) particles can improve the resistance to tracking and erosion of SiR by increasing its thermal conductivity. Before the tests, specimens were prepared by dispersing nano-BN particles into room temperature vulcanizing (RTV) silicone rubber at different loadings. In this paper, the dc test has been developed from the current IEC 60587 inclined plane tracking and erosion test to compare the phenomena occurring during the tests. Temperature distribution was observed by an infrared thermal imager. The experimental results indicate that the filled specimens have a lower degree of surface damage than the unfilled specimens. In addition, with the increase in content of fillers from 0 to 7 wt%, the thermal dissipation is improved and both the erosion depth and the weight loss show a decreasing trend, which proves the resistance of silicone rubber to tracking and erosion is improved.

Comparison of laser ablation and inclined plane tracking tests as a means to rank materials for outdoor HV insulators

As the popularity of polymeric composites for outdoor high voltage (HV) use continues to increase, surface degradation through electrical discharge activity is becoming a more serious issue. In order to design composites offering improved resistance to degradation, and hence improved component lifetimes, tests need to be performed under controlled conditions in order to rank different materials. Inclined plane tracking tests are often used to determine the relative performance of various material formulations used in their construction. An alternative approach is to employ a high power laser to deposit known amounts of energy at a known rate to the sample surface. In this paper a variety of material formulations were subjected to inclined plane tracking tests as well as to laser ablation testing. The results indicate that the two test methods compare favorably and that laser ablation offers a quick and cost effective way of screening candidate material formulations, prior to more detailed study.

Erosion resistance of electrospun silicone rubber nanocomposites

This paper presents the results of an examination of the erosion resistance of two-part room temperature vulcanizing (RTV) silicone rubber (SiR) nanocomposites. The SiR composites were filled with 7 nm size fumed silica and 1.5 μm size micro-silica. Separate samples were prepared using conventional mechanical mixing and an electrospinning technique, and their erosion resistances were compared. The electrospinning technique allows for a higher volume fraction of nanofiller and micro-filler in the composites as compared to the conventional samples. The erosion resistances were tested using both an infrared-laser-based source and the ASTM D2303 standard inclined plane tracking and erosion method (IPT). The experimental results for the eroded mass, tracking voltage, and tracking time show that the erosion resistances of electrospun samples are much greater than those of conventional samples. Scanning electron microscope (SEM) images and variable tracking patterns of the conventional samples after the IPT tests suggest an improvement in the dispersion of the fillers within the electrospun samples compared to the conventional samples. Power analysis during the IPT tests also shows that more power is required to track and erode electrospun samples before sample failure occurs than is needed for conventional samples, which suggests improved bonding between the fillers and the silicone rubber matrix. These findings also are supported by the results of thermo-gravimetric analysis.

Impact of Ultraviolet Radiation on an Artifi cially Polluted Silicone Rubber during Inclined Plane Tracking Test

This paper presents experimental results obtained on tracking and erosion resistance of Silicone rubber (SIR) with and without pollutants. The IEC-60587 Inclined Plane Tracking and Erosion Test method combined with UV radiations of different intensities was employed to assess two different formulations with same base polymeric material (SIR). The hydrophobicity recovery property of silicone rubber formulations before and after inclined plane tracking test was studied besides the effect of corona. Some of the physical, thermal and electrical properties were compared before and after inclined plane tracking test. It is inferred from the analysis carried out on the experimental results that the intensity of UV radiation plays a major role in deteriorating the surface characteristics of the material. It is also found that the introduction of UV in the test method has helped in distinctly evaluating polymeric materials. The effect of two different pollutants was not the same on formulations considered for the study, which implies that the additives play a dominant role in the overall performance of the material than the base polymer. The study also revealed that a formulation with a better performance under a certain pollutant need not have to behave the same way under a different pollutant. Presently, CIGRE Working Group (WG D1.14) is active in standardization of material aspects besides developing suitable methodology for the testing of polymeric materials for outdoor insulation application; the inferences appear to be an useful input to both CIGRE working group and International Electro technical Committee (IEC TC 15 PT 2).

Laser ablation of silicone composites

Silicone rubber based composites are widely used to produce outdoor insulators. In adverse weather conditions these can be damaged by surface discharge activity resulting in deterioration of their dielectric properties and an eventual need for replacement. Inclined plane tracking tests are frequently used to determine the relative performance of different material formulations used in their construction. An alternative approach to characterisation is to use an infra-red laser to deposit known amounts of energy at a known rate to the sample's surface allowing comparative ranking of different materials. In this paper several silicone based composites have been ranked using a laser ablation technique and the results were then compared to those obtained from tracking tests on the same materials. The comparison indicates that laser ablation ranks the materials in the same order as the tracking tests and may therefore constitute a quick and cost effective method for the routine characterisation of outdoor insulation components.

Use of image analysis in DC inclined plane tracking tests of nano and micro composites

Leakage current magnitude is used as one of the failure criteria in the tracking and erosion test IEC 60587. The 3rd harmonic is also often used to identify periods of arcing activity. This technique is not available for the equivalent dc test. This paper presents the use of a machine vision camera alongside measurements of leakage current to identify discharge activity during dc testing and so enable determination of arc intermittency. This simple image processing technique is shown to add significant value to the existing leakage current analysis techniques and can provide an understanding of the process of degradation and its dependence on voltage polarity. Tests are reported on a commercial silicone rubber compound, a micro-filled epoxy resin, and the same epoxy resin system with nano particle fillers at 5% by weight. It is shown that the technique is applicable to this wide range of materials. It is also shown that changes to the performance of the epoxy compound by the addition of nano filler is due to more than just improving discharge resistance, reported elsewhere. The wettability of the samples is seen to be important, controlling moisture flow during a test. For this reason, in the case of the top electrode being positive, the nano filled material failed the test earlier than the standard material, with reduced erosion but increased leakage current.

Erosion resistance of alumina-filled silicone rubber nanocomposites

This paper deals with the experimental studies on the erosion resistance of low weight % alumina-filled nanocomposites and highly filled microcomposites. Erosion resistances of 2.5 % and 4 % by weight alumina-filled silicone rubber nanocomposites and 5 %, 10 %, 15 %, 20 % and 30 % by weight ATH filled microcomposites have been compared. For the performance comparison, inclined plane tracking and erosion resistance tests have been done on the silicone rubber samples. The results obtained indicate that the performance of 4 % by weight nanocomposite is comparable to that of the 30 % by weight ATH composite. Thermo gravimetric analysis shows that the thermal stability of the nanocomposite is better than the microcomposite even at low concentration of the nanofillers studied. The above encouraging results can be mainly attributed to the better thermal stability of the nanocomposite due to the large increase in the number of nanofillers, significant quantity of polymer chains with restricted mobility at the interface between the polymer and the fillers and better physical bonding between the nanofillers and the polymer matrix. Interestingly, formation of entirely different types of physical micro structures, viz., lump type and honey comb type have been observed at the degraded portions of the microcomposites and the nanocomposites respectively which also supports the above observation. It is also noticed that the ratio of r.m.s to average leakage current is a reflection of the degree of erosion of the sample which in turn seems to be a good indicator to assess the degradation performance of materials.

Tracking and erosion resistance of high temperature vulcanizing ATH-free silicone rubber

Traditionally aluminum trihydrate (ATH) is added to high-temperature vulcanized (HTV) silicone rubber for outdoor insulation applications to improve flame retardancy and the electrical tracking and erosion performance. In this work, the flammability of ATH-free HTV silicone rubber formulations were evaluated by the UL94 vertical burning test. The most promising candidates, as well as reference formulations filled with silica or silica/ATH only, were then evaluated by the inclined plane tracking and erosion test at 4.5 kV. The best result was obtained by silicone rubber containing 100 phr silica and 15 phr melamine cyanurate. It was suggested that this was a result of the arc quenching ability of the melamine hence extinguishing the electrical arc. If the filler level was too high, resulting in poor dispersion, the resistance to tracking and erosion was significantly reduced. Thus formulating a HTV silicone rubber with good tracking and erosion resistance is a balance between having a high enough filler content, while still maintaining a good dispersion of the particles in the polymer matrix, as well as good bonding between the particles and the matrix.

Performance of silicone rubber in DC inclined plane tracking tests

The inclined plane tracking and erosion test IEC-60587 is not specified for DC testing. A dc test has been developed from the current ac standard and three formulations of silicone rubber tested. These materials were tested under three voltage levels (2.3, 2.7 and 3.2 kV) for both polarities. Positive dc tests have the highest average and peak leakage current and exhibit a higher degree of surface damage. The observed surface degradation pattern is heavily dependant on polarity. Consistently higher levels of erosion have been observed in the higher voltage positive cases. Erosion of the surface always starts at the bottom electrode, and spreads toward the top electrode. Puncturing of the 6 mm thick samples or deep erosion over more than half the distance between electrodes has only been observed under 2.7 and 3.2 kV positive polarity tests. Results have been analysed using a variety of leakage current analysis techniques going beyond the criteria specified in the original ac standard. The low-frequency behaviour of the leakage current was monitored using a 15 sample per second current recorder. The leakage current magnitude is investigated in a case study and is shown to follow a normal distribution. Reversing the polarity of tests shows the leakage current seen in a test is largely independent of the surface degradation pattern present, but the surface degradation pattern over the first three hours may dictate the morphology of ensuing deep erosion.

Inclined-plane tracking and erosion test according to the IEC 60587 Standard

The present IEC 60587 IEC standard needs several improvements which would help manufacturers of power equipment and material suppliers to assess outdoor polymeric materials in a more reliable way.

ANALISIS SIFAT HIDROFOBIK PERMUKAAN HDPE BERDASARKAN NILAI TOTAL HARMONIC DISTORTION

Polymer material has been developed to replace the porcelain insulator material and glass. When it is used as outdoor insulator, environmental conditions have a significant influence to the value of surface discharge current, especially for the coastal area and industry. Salt, dust and chemicals contaminant are suspected as the causes of initial current of surface discharge and the insulator surface degradation which lead to a flashover. To analyze the performance of the insulator surface when the leakage current occurs, the Total Harmonic Distortion (THD) is needed to be determined. The value of THD leakage current indicates the hydrophobic characteristic of surface material. This paper analyzes the results of leakage current measurement in laboratory-scale based on IEC 587:1986 with Inclined-Plane Tracking (IPT) method to the High Density Polyethylene (HDPE) polymer material which is provided in smooth and rough surface. The testing voltage is 50 Hz AC. Data of leakage current magnitude values cover its maximum average as a function of time and the result of FFT to the wave form of the leakage current. As the result, the value of percentage THD decrease as the function of time. The smooth surface material has THD value 43.42% and the rough surface has 15.89%.

Erosion resistance of nano-filled silicone rubber

The paper presents the experimental results obtained on the erosion resistance of silicone rubber (SIR) filled with 12 nm size fumed silica (nano filler) to those filled with 5 /spl mu/m size silica filler (micro filler). The ASTM 2303 inclined plane tracking and erosion test was used in the comparison as well as an infrared laser as the source of heat to erode the SIR samples. The erosion resistance of the SIR materials increased with increasing percentage of the fillers, and it was observed that 10% by weight of nano-filled SIR gives a performance that is similar to that obtained with 50% by weight of micro-filled SIR. The low frequency components of leakage current and the eroded mass are used to evaluate the relative erosion resistance of the composites and the third harmonic component of the leakage current shows good correlation to the measured eroded mass. The paper discusses the possible reasons for the improvement in the erosion resistance of nano-filled silicone composites.

Electrical tracking performance of LLDPE-natural rubber blends by employing combination of leakage current level and rate of carbon track propagation

Electrical tracking develops from surface discharge activity associated with the flow of leakage current on insulator surface under wet and contaminated conditions. Arcs created from this surface discharge phenomenon burn the polymer insulator material and create carbonized tracks in the long run. This paper reports on electrical tracking performance through the observation of leakage current and carbon track development of blends of linear low-density polyethylene with natural rubber (LLDPE/NR) either filled with or without alumina trihydrate. An electrical tracking and erosion test using the inclined-plane tracking method is conducted to study the overall performance of surface tracking properties. The combined effect of leakage current level and carbon track propagation rate is used as a new technique for describing the level of electrical tracking performance based on the proposed normalized degradation index. Morphological analysis is also carried out to investigate the surface microstructure before and after the tracking test. The experimental results show that different material compositions affect the leakage current and carbon track development. In addition, the calculated normalized degradation index has shown some correlation with the degree of surface deterioration.

Analysis of the insulation capability of polyester insulator

The lifetime of polyester resin samples has been determined with the ASTM D2303 inclined plane tracking test method (IPTTM) for different environmental effects. Most of the external factors have a unique degradation effect, hence the tracking image observed on polyester resin highly depends on these factors. The structure and topography of the tracking patterns generated on the surface of polyester resin have been examined using the fractal dimension model. The accuracy and success of the fractal dimension model can significantly improve the possibility of determining the variety of aging processes that an insulator has been subjected to over a long time period. In order to verify the results, the structures have also been analyzed by using Markov random fields (MRF) and cellular neural networks (CNN).

Thermal conductivity of filled silicone rubber and its relationship to erosion resistance in the inclined plane test

Silicone rubber samples having various concentrations and mean particle sizes of either alumina tri-hydrate or silica filters, prepared by room temperature and heat cured under pressure (hot pressed), are tested for erosion resistance in the ASTM D2303 inclined plane tracking and erosion test. Their corresponding thermal conductivities are determined using a transient temperature technique in which an infrared laser is employed as the heat source and a thermal imaging camera as a temperature detection device. Scanning electron microscope observations show greater filler bonding to the silicone matrix in the hot pressed samples than in the room temperature vulcanized samples leading higher thermal conductivity and increased resistance to erosion, for both ATH and silica filled samples. The correlation study shows a strong relationship between the erosion resistance and the thermal conductivity of the tested samples, highlighting the importance of an outdoor insulating material to have high thermal conductivity in order to withstand dry band arcing. The results can be used to provide guidance on filler selection for silicone rubber compounding for outdoor insulation applications.

The role of inorganic fillers in silicone rubber for outdoor insulation alumina tri-hydrate or silica

A systematic study to understand how alumina tri-hydrate (ATH) and silica fillers improve the erosion resistance of silicone rubber during dry band arcing showed that the thermal conductivity of the resulting composite material is the main criterion governing material erosion. The thermal conductivity of the composite material is dependent on the thermal conductivity, concentration, particle size, and bonding of the filler particles to the silicone matrix. In this context, either filler can be shown to perform better than the other, depending on the formulation, in the ASTM inclined plane tracking and erosion test. Therefore, the industry perception that ATH filler imports better erosion resistance than silica in silicone rubber can be misleading. The release of water of hydration from ATH appears to have a secondary effect that may be more relevant in silicone compositions having a low concentration of a filler.