Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Pattern Recognition and Machine Learning

Hydrophobic and ice-retarding properties of doped silicone rubber coatings

Superhydrophobic RTV silicone rubber insulator coatings

A fundamental parameter of polluted insulator online monitoring is the leakage current, which has already been shown to be well related with the pollution discharge of insulators. In this paper, in an effort to quantitatively reflect the discharge intensity as well as the discharge status by the leakage current, we carried out an experimental study on artificial pollution discharge of insulators. A high-speed photographic apparatus was utilized to capture the entire process of local arcs on porcelain insulator surface, including the arc generation, the arc development and the flashover, for which the associated leakage current of insulators was synchronously digitized. A comparative analysis of the relation between the two-dimensional discharge image and the leakage current waveform in the process of arc generation and development shows that, if the arc area on insulator surface is relatively small and the leakage current passes through zero, the arc might completely extinct, whereas this phenomena will not occur if the arc area is larger. In addition, the amplitude of discharge arc area is found to be roughly proportional to the square of leakage current over the range of leakage current amplitude from 0 to 150 mA. Our results can provide an important guidance for judgment of the discharge status and the discharge intensity on insulator surfaces using the leakage current of insulators.

Mapping Relation of Leakage Currents of Polluted Insulators and Discharge Arc Area

Polydimethylsiloxane at the interfaces of fumed silica and zirconia/fumed silica

Performance of RTV silicone rubber coatings installed in coastal systems

Condition assessment of naturally aged composite insulators, aiming to better understand the ageing processes involved, is essential for maintaining high reliability in power networks. In this study field-ageing effects on insulating materials (EPDM and VMQ/HCR) of two 150 kV composite suspension insulators are evaluated. The insulators had been in service for 17 years on a coastal transmission network, exposed to seaborne salt spray, windborne soil deposits and intense UV solar radiation. Several diagnostic techniques, including visual inspection, wettability classification, FTIR spectroscopy, SEM and EDX analysis were employed to assess the condition of the insulators. Field-ageing effects were not assessed as critical to dictate insulator replacement. For both insulators morphological and material degradation due to field-ageing was restricted to the upper surface layer of the polymeric housing. The resistance of housing material against tracking and erosion remained unaffected by field-ageing. Surface deterioration of EPDM was more intense than that of VMQ/HCR, despite the fact that the EPDM insulator had been in operation at a site with a lower pollution severity. The EPDM housing was classified as hydrophilic; however, after removing pollutant deposits its hydrophobicity was improved. The hydrophobic properties of the VMQ/HCR housing were only slightly reduced. Field-ageing effects on insulator housing are discussed based on material structural changes caused by ageing stresses.

Evaluation of field-ageing effects on insulating materials of composite suspension insulators

Leakage current (LC) monitoring is a widely employed tool for the investigation of surface electrical activity and the performance of high voltage insulators. Surface activity is correlated to the shape of LC waveforms. Although field monitoring is necessary in order to acquire an exact view of activity and insulators' performance, field waveforms are not often recorded due to the required long term monitoring and the accumulation of data. Instead, extracted values, such as the peak value, charge and number of pulses exceeding predefined thresholds, are recorded, with actual waveforms either being recorded occasionally or not at all. However, a fully representative extracted value is yet to be determined. In this paper, 1540 field waveforms are investigated to acquire a detailed image of the waveforms' shape in the field. Simple classification rules are employed to distinguish between basic groups. Discharge waveforms are further classified based on the duration of discharges. Twenty different features, from time and frequency domain, two feature extraction algorithms (student t-test and mRMR) and three classification algorithms (knn, Naive Bayes, Support Vector Machines) are employed for the classification. Results described in this paper can be used to maximize the efficiency of field LC monitoring.

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Investigation and classification of field leakage current waveforms

The performance of three commercially available room-temperature-vulcanized (RTV) silicone rubber (SIR) coatings was evaluated by means of salt fog testing. Leakage current and contact angle measurements were used in order to monitor the coatings' performance. The measurements indicated that the initial loss of hydrophobicity can be correlated to the surface discharges that develop on the material surface due to the droplets formed. In the case of the silica-filled coating, the considered los.s was observed earlier. Further, lower levels of surface activity and material deterioration were observed for the alumina-trihydrate (ATH)-filled coatings in comparison to the SiO2 filled. The results can be correlated to the filler efficiency and especially to the thermal conductivity achieved. For the considered formulations, the silica-filled coating appeared to have the lowest value of heat conductivity. Finally, for the ATH-filled coatings, additional parameters, such as the particle size, must be considered.

Salt Fog Evaluation of RTV SIR Coatings With Different Fillers

Leakage current (LC) monitoring is widely employed in order to investigate electrical surface activity on high voltage (HV) insulators. Long term field monitoring is required in order to obtain an actual view of the phenomena. Therefore any monitoring system is bound to encounter data size problems. A number of solutions have been proposed to address this problem by extracting different values from the measured waveforms as a performance indication. However, a parameter that is fully representative of the waveform is yet to be determined. Hence, measuring and storing of the actual LC waveform is still required on sites for research and monitoring purposes. In addition, field related noise can result to misinterpretation of the actual activity. In this paper, a number of 26089 waveforms, recorded in a 150 kV Substation on four different post insulators that are part of the grid, are investigated. The monitoring period exceeded six years. Different techniques are applied and evaluated on the data set, employing simple numeric criteria and more advanced techniques such as Fourier and Wavelet analysis. Results are presented towards addressing the problems of noise and data size. The study objective is the incorporation of the results in improved leakage current monitoring systems.

K. Siderakis

Papers

Performance of RTV silicone rubber coatings installed in coastal systems

Evaluation of field-ageing effects on insulating materials of composite suspension insulators

Investigation and classification of field leakage current waveforms

Salt Fog Evaluation of RTV SIR Coatings With Different Fillers

Impact of noise related waveforms on long term field leakage current measurements