In this paper a prediction model is proposed for estimation of furan content in transformer oil using oil quality parameters and dissolved gases as inputs. Multi-layer perceptron feed forward neural networks were used to model the relationships between various transformer oil parameters and furan content. Seven transformer oil parameters, which are breakdown voltage, water content, acidity, total combustible hydrocarbon gases and hydrogen, total combustible gases, carbon monoxide and carbon dioxide concentrations, are proposed to be predictors of furan content in transformer oil. The predictors were chosen based on the physical nature of oil/paper insulation degradation under transformer operating conditions. Moreover, stepwise regression was used to further tune the prediction model by selecting the most significant predictors. The proposed model has been tested on in-service power transformers and prediction accuracy of 90% for furan content in transformer oil has been achieved.

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.

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.

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%.

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.

Evaluating the electrical tracking and erosion resistance of polymeric housing materials is an essential task performed in the development of outdoor insulators. “Tracking” means the formation of a surface carbonaceous path, and “erosion” means weight loss of the housing material. An absolute measurement of the tracking and erosion resistance is not possible; only relative ranking of composites can be achieved using the standard tracking and erosion tests. During the early use of organic insulating materials, failure due to tracking was a major concern, and therefore standard screening methods were proposed to evaluate the tracking rather than the erosion resistance. Erosion has become more important following the development of tracking resistant composites containing high levels of inorganic fillers.