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Improvement of electrical performance for porcelain insulators using silicone rubber coating

This work presents the improvement of electrical performance for porcelain insulators using silicone rubber coating, which can affect the porcelain insulators performance or properties.

porcelain insulators using silicone rubber coating

Abstract:
This work presents the effect of room temperature vulcanized (RTV) silicone rubber coating on cap and pin type porcelain insulator under ac (50Hz) flashover voltage (KV). Describes experimental results obtained for improvement of porcelain insulator removed from 33kV overhead transmission line at Aswan, Egypt after 28 years of service. Also, this study briefly surveys the environmental contaminated surface of porcelain insulator. The flashover voltage have been measured for insulator under various contaminated materials such as ; (cement – sand – silica fume – phosphate ). This work concluded that RTV silicon rubber coating register good electrical performance under dry, wet and wet with 5% , 10% NaCl conditions

Introduction:
High voltage insulator plays an important role in an electrical power system including generation, transmission, and distribution of electricity. In addition to the mechanical support of the conductor their electrical role is to isolate the metal structure of the tower from the conductor which carries the power to be transmitted and distributed. As a result, many pollutants from different sources such as dust from industrial factories, saline from the sea and sand storms, may be deposited on the surface of the insulator. Contaminated high voltage insulator in presence of humidity due to fog and rain leads to leakage current, dry band arcing, and ultimately may cause full flashover, which result in power outage and associated cost. Inorganic materials such as porcelain have been used in outdoor insulators for a long time.
Porcelain is still the most widely used outdoor insulating material for high voltages. Porcelain is an inert and stable material that can take substantial amount of arcing without serious surface degradation, because of their capacity to withstand the heat of dry band arcing. However, these materials are highly wet table when exposed to wet conditions, like fog, dew, and rain, because of their high surface energy. The main problem with porcelain high voltage insulators is that water readily forms a continuous film on their surface. In the presence of contamination, leakage current then develops which may lead to flashover that could be followed by an outage of the power system. In order to reduce the incidence of insulator flashover, room temperature vulcanizing (RTV) silicone rubber is being widely used to coat insulators to enhance their electrical Performance.
RTV silicon rubber coating is applied increasingly for porcelain and glass insulators or bushings this method is an efficient replacement for the above the operation mechanism is the same as greasing except NSDD affectivity. There are RTV coatings with different performances the key point in their performance is their ingredient the coatings that lost their water repellency by environmental factors have short life and inefficient performance in convenient application is another advantage that affect significantly on cost. Wetting characteristics of various kinds of insulators has been studied. It can be found anti-contamination insulators on the wetting characteristics, such as, polymer and room temperature vulcanized silicone rubber coated insulators having superior hydrophobicity, and semiconducting glaze insulators having drying effect by leakage current in the glaze, have been developed. However, such superior performances of these insulators cannot be always expected.
Hydrophobicity of silicone rubber and drying effect of semi conducting glaze may not be fully effective under some wetting conditions. Higher surface resistances were confirmed on RTV silicone rubber coated and semi conducting glaze insulators compared with normal porcelain insulators under clean surface conditions due to hydrophobicity or drying effect in an artificial fog chamber. Higher resistances were measured on RTV SIR coated insulators compared with normal insulators. So, under moderate wetting conditions hydrophobicity may be effective for improving surface insulation.

This study briefly surveys the polymeric materials RTV silicone rubber coating of porcelain insulator to with stand the flashover ac (50Hz) voltage. Four types of environmental contaminated materials have been introduced on the surface of coated porcelain insulators, such as; sand, cement silica fume and phosphate at dry and wet conditions.

 

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