HV composite polymeric insulators are being accepted increasingly for use in outdoor installations by the traditionally cautious electric power utilities worldwide. They currently represent -60 to 70% of newly installed HV insulators in Nortb America. The tremendous growth in the applications of non-ceramic composite insulators is due to their advantages over the traditional ceramic and glass insulators. These include light weight, higher mechanical strength to weight ratio, resistance to vandalism, better performance in the presence of heavy pollution in wet conditions, and comparable or better withstand voltage than porcelain or glass insulators. However, because polymeric insulators are relatively new, the expected lifetime and their long-term reliability are not known and therefore are of concern to users. Additionally they might suffer from erosion and tracking in the presence of severe contamination and sustained moisture. This leads to the development of dry band arcing that under certain circumstances could lead to failure of polymer insulators. In this paper a review is presented of the recent performance experience of HV composite polymeric insulators in outdoor service, testing methods, aging, the ranking of the materials, the role of fillers, the role of low molecular weight components present in the insulators, the mechanisms responsible for the loss and recovery of hydrophobicity, one of the most important properties of polymers, the mechanisms of failure, detection of faults, type and quantity of natural contaminants, effects of exposure to rain, hydrocarbons, stationary air and wind, various methods to optimize the electrical performance and a relatively new method for evaluating the performance status of polymeric insulators in the field.

Outdoor HV composite polymeric insulators

New insights into the vertical distribution and microbial degradation of microplastics in urban river sediments.

Aging of polymeric and composite materials is reviewed mainly from the standpoint of their interfacial performance. Insulating materials can be divided into simple polymers and composites. Polymers for power cables, transformers, insulators and rotating machines consist of thermoplastics such as PE, PET and PPS, elastomers such as silicone, EPR and EPDM, and thermosets such as epoxy. Composites for GIS, rotating machines and insulators comprise epoxy/glass, epoxy/silica/alumina, and epoxy/mica systems. Aging processes are complicated in general, and take place under simultaneous multiple stresses such as electrical, thermal, mechanical and environmental stresses. Some of the phenomena covered in this paper are associated with the degradation by tracking and erosion and the loss of hydrophobicity in case of surface properties, and with PD, electrical treeing, water treeing and combined phenomena. The quality of cable insulation such as XLPE has been improved extensively from the standpoint of design electric strength. Interfacial problems will emerge for modification of cable joints. It is expected that polymers for outdoor use and filled epoxy resin systems should be improved from their environmental stability and from their design stress enhancement, respectively.

Aging of polymeric and composite insulating materials. Aspects of interfacial performance in aging

A study of the loss of hydrophobicity of high temperature vulcanized (HTV) silicone rubber (SIR) after immersion in saline solutions as a function of time (0 to 3000 h) at different temperatures is reported. The hydrophobicity is determined by measuring the static contact thetas between the tangent to the droplet of distilled water and the horizontal surface of the HTV SIR. The conductivity of the saline solution was varied from 0.005 to 100 mS/cm and the temperature from 0 to 98 degC. The contact angle which gives a measure of the hydrophobicity of the surface decreased sharply during immersion. The contact angle decreased from the original value of 100plusmn4.6deg to low value of 15deg after 3000 h of immersion at 98 degC in a solution of 0.005 mS/cm. The lower the conductivity, the larger was the decrease in the contact angle. The changes in the weight of the HTV SIR due to the uptake of water and the average surface roughness (ASR) are determined during the immersion. The increase/decrease in the weight and surface roughness of the HTV SIR are correlated with the contact angle and hence with the loss of hydrophobicity. The surface free energies gammasd, gammash and gammas, the interfacial energy of HTV SIR and water gammasl, and the energy of adhesion Wsi of water on HTV SIR are determined as a function of time during the immersion and related to the loss of hydrophobicity.

Effects of saline water and temperature on surface properties of HTV silicone rubber

This paper describes water diffusion into and electrical testing of unidirectional glass reinforced polymer (GRP) composite rods used as load bearing components in high voltage composite (non-ceramic) insulators. The tests were performed following ANSI standard C29.11 Section 7.4.2 that can be used to evaluate electrical properties of composites. The unidirectional composite rod materials based on either E-glass or ECR-glass fibers with modified polyester, epoxy and vinyl ester resins were investigated. Two types of ECR-glass fibers were considered, namely high and low seed (voids). The effects of composite surface sandblasting, mechanical pre-loading and nitric acid exposure on the electrical properties of the composites were studied. In addition to the required data of the ANSI standard, the specimen mass gain was also measured after boiling for 100 h. Most importantly, there was no correlation found between the mass gain and the leakage current for different composites. The materials with high seed ECR-glass fibers had much higher leakage currents and they absorbed less moisture than the composites based on either the low seed ECR-glass fibers or E-glass fibers. It was shown in this work that different types of sandblasting, as well as mechanical preloading with and without acid exposure had a negligible effect on the leakage currents and water mass gain of the composite specimens.

Water diffusion into and electrical testing of composite insulator GRP rods

Polymeric materials are used increasingly in both outdoor and indoor insulation and it has become imperative to find a convenient and a practical method to evaluate the performance of the insulation in situ. The hydrophobicity of a polluted surface particularly in the presence of moisture, determines the level of the leakage current which may result in a flashover and an outage of the power system. However, it is difficult to measure the hydrophobicity of insulators in the field, and therefore the measurement of the electrical surface resistance in situ has been suggested as an alternative method that might give information on the surface state. In the present study, polyvinylchloride (PVC) was used to study the characteristics of the surface resistance, the change of the hydrophobicity and the relationship between both of them in the presence of salt-fog. The dependence of the surface resistance on factors such as the duration of the wetting in salt-fog, the recovery during drying time, the length of the specimens, the level of the applied dc stress used to measure the resistance and the ac stress is reported. The surface free energy per unit area of PVC, during exposure to salt-fog, was calculated using the harmonic-mean method and was found to be consistent with the changes in both the surface resistance and the hydrophobicity of the surface. The surface tension /spl gamma//sub s/, increased from 43.1/spl times/10/sup -3/ J/m/sup 2/ for the virgin specimen to 76.8/spl times/10/sup -3/ J/m/sup 2/ after complete wetting in un-energized salt-fog. The diffusion coefficients of a saline solution having a conductivity of 1 mS/cm into the pvc were found to increase from 2.8/spl times/10/sup -15/ m/sup 2//s at 74/spl deg/C to 1.6/spl times/10/sup -14/ m/sup 2//s at 98/spl deg/C.

Electrical surface resistance, hydrophobicity and diffusion phenomena in PVC

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Electrical surface resistance, hydrophobicity and diffusion phenomena in PVC