Insulators have always represented important equipment used for electric energy production, transmission, and distribution of electrical power system. In general, their main role is to isolate equipment or parts of it that are grounded from the ones that are energized. Also, they may often be mechanically loaded, depending on their purpose.
Historically, glass insulators have been in service for more than a century and their prior use was as telegraph insulators, though improvements were necessary for exploitation in electrical power system. Through many generations, glass insulators have been taken to another level for reliable and representative service, namely due to their good resistance against aging under environmental influence. Main upgrades were in glass as dielectric material – toughening, adjusting shape of the glass shell for better performance in demanding environment, achieving hydrophobic properties by polymer coating of glass insulators, etc. Through decades, transitions to higher voltage levels were demanded and glass insulators had to be longer to withstand applied voltage, therefore their weight had increased, and they had loaded towers significantly. Alternatively, the idea of polymer insulators would not only solve the problem regarding weight but would also propose other dielectric properties that glass insulators are in lack of.
Composite polymer insulators, which have been in service for around 50 years, in the beginning were not users’ preferable choice, due to lack of experience of their unpredictable ageing degradation. Yet, improvement of materials and outcome of manufacturing process led to highlighting their ability to meet strict demands of service in polluted areas. Other benefit of introducing composite polymer insulators was in possibility of different construction known as cross arm, which opened opportunities such as transition to higher voltage level on already existing towers, while simultaneously increasing all clearance distances: phase to cross arm, phase to shield wire, and phase to ground.
Both types of insulators have specific advantages and valuable properties that, if designed and manufactured properly, will fulfill requirements for a certain area. Although mechanical aspect is not considered in this thesis, influence of mechanical loading of insulators is time dependent, and taking it into account according to standard SIST EN 5041-1:2013 and should not be negotiable for any designer and manufacturer. Regardless of type and material, insulators are exposed to electrical and mechanical stress during exploitation. Focusing on electrical stress, which is caused by unequal potential distribution from energized to grounded part of insulator and corona discharge, it must be studied in advance.
Electric potential and electric field calculation is based on theory of electromagnetism and Maxwell’s field equations. For analysis of electric potential and electric field distributions on insulators, calculation of both is done in the manner of electrostatics.
When it comes to modeling complex geometry and shapes, reliable and precise methods must be used, since calculations and results rely on method’s preciseness. One of popular methods with these benefits is Finite Element Method. Since laws of physics are mainly described with partial differential equations, making them demanding for analytical calculation, this method proposes discretization of geometry and shapes into small subdomains, called finite elements. Once the domain is divided into small elements, it allows to approximate desired quantity, for example electric potential, by simple functions (linear, quadratic, or cubic function). This means that the more precise discretization of geometry and, consequently, approximation of partial differential equation are, the more precise results of this method are achieved. Finite element method is powerful due to its ability to deal with arbitrary shapes and inhomogeneous media. For both composite and glass types of insulator 3D models have been created in COMSOL Multiphysics software, based on FEM, and used for analysis in areas such as electromagnetics, structural mechanics, acoustics, fluid flow, heat, and mass transport. As the most important part of modelling, preprocessing is done in such manner to provide mesh preciseness and accuracy of results.
Analysis of electric field distribution, when talking about electrical stress, is done with varying corona rings dimensions and position for both insulators. After achieving desirable distribution, length of both insulators has been changed to keep the arcing distance according to standardized requirements.
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