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Temperature and electric field along the stress grading system of a form wound coil under repetitive impulse voltage are studied using 2D axisymmetric and 3D models in COMSOL¯ 5.3a. The validity of the 3D model is shown by comparing the results with the measured temperature profile along the stress grading system. The evaluation of both temperature and electric field shows that using a stress grading system based on a micro-varistor characteristic reduces the maximum temperature; however, with an increase in the electric field, which can be reduced to an acceptable level. An optimization on the initial conductivity of the micro-varistor characteristic confirms that desired electric field and temperature rise are achievable by selecting an optimized conductivity characteristic. 2D and 3D simulations show that a proposed stress grading system, which is a combination of an optimized stress grading tape conductivity and minimum conductive armor tape length, has a good temperature and electrical performances under repetitive impulse voltage. [ABSTRACT FROM AUTHOR]

Evaluation of thermal and electrical characteristics of a 13.8 kV rotating machine stress grading system shows that a reduced length of conductive armor tape (CAT) from the slot exit reduces the electric field and temperature rise under pulsed voltage. Although, the electric field in stress grading tape (SGT) increased slightly, with a shorter length of CAT during the rise time of the pulse voltage, it decreased during the DC portion of the pulse voltage. The temperature profile of the stress grading system under pulsed voltage at room, elevated room, and near typical operating temperatures are measured and simulated for several CAT lengths; results show lower temperatures for shorter CAT length. The partial discharge inception voltage is unchanged for shorter CAT lengths. A lower temperature rise is desirable as this leads to a longer life in the absence of partial discharges. [ABSTRACT FROM AUTHOR]

The paper addresses the ac modeling and anisotropic dielectric properties of stress grading and conductive armor tapes that are two crucial components in form-wound motor coils. The limitations of the conventional dc conductivity modeling and the necessities of using ac conductivity modeling and anisotropic properties of these materials at high frequencies and high electric field are discussed. The method of measurement of the dielectric parameters at high frequency and high electric field for 2D modeling is also presented. The transient FEM simulations from conventional modeling and the proposed ac modeling are compared to experimentally obtained results. Good agreement is only obtained from the latter modeling. [ABSTRACT FROM AUTHOR]

The paper addresses the temperature and electric field dependence on the conductivity of the conductive armor and stress grading tapes on form-wound motor coils. The temperature and electric field dependence is measured in the laboratory, and the nonlinear dependency is used in transient FEM simulations of the potential distribution on the form-wound coils. The surface potential distribution, for various temperatures and applied voltages, is measured in the laboratory from which the surface electric stress is calculated. Good agreement between the simulated and measured stresses is obtained. A temperature of 155 °C is shown to have little influence on the stress grading, but the electric stress dependence on conductivity is shown to have a major influence on the stress grading of the motor coil examined in this study. [ABSTRACT FROM AUTHOR]

This paper provides an overview of the electric field (E-field) distribution on transmission line composite insulators applied in alternating current applications. Factors that affect the E-field distribution are discussed as well as the influence of the E-field distribution on the short and long term performance. Modeling and measurement methods are reported and examples of calculated E-field magnitudes determined are presented together with corona ring application information. This paper was developed by the IEEE Task Force on Electric Fields and Composite Insulators. [ABSTRACT FROM AUTHOR]

The paper presents the results of the study on the influence of insulator profile on the aging performance of silicone rubber (SIR) insulators in salt-fog. Experiments have been conducted on various two-shed arrangements at 35 V/mm average stress and 0.25 S/m salt-fog conductivity level. The work is also extended to include commercial 15 kV class insulators with different profiles. Shed spacing, shed diameter, alternate shed design and shed shape are the parameters investigated in this study. The low frequency harmonics of the leakage current, early aging period (EAP), and equivalent salt deposit density (ESDD), are used to evaluate the aging performance of different designs. Insulator profile is shown to greatly influence the aging performance of SIR insulators. Shed shape proves to be the most important parameter to be considered in designing non-ceramic insulators profiles. Also, as the shed spacing decreases, the performance of SIR insulators improves. Simulation results using FEMLAB© show that the electric field on insulators is below the corona onset at both dry and wet conditions. Dry band arcing is therefore the main electrical cause for aging in distribution class insulators and it is possible to improve the pollution performance of SIR insulators using appropriate profiles as suggested in this work. [ABSTRACT FROM AUTHOR]

Examines the effect of shed design on the aging performance of silicone rubber insulators in salt-fog. Insulator profiles with shed parameters included in the study; Illustration of the shed parameters of non-ceramic insulators; Calculation of the electric field along the surface of the insulators.

Abstract: Local discharges in the vicinity of the mounting flange of composite bushings due to the electric field enhancement can cause insulating material degradation and finally lead to failure. In this paper, a proposed solution to this problem by employing a resistive silicone rubber coating on composite HV bushings was investigated. Finite Element Method (FEM) analysis of the electric field distribution along the surface of bushings by FEMLAB® simulation and potential measurements by an electrostatic probe (ESP) technique confirmed that the stress grading effect of a 100MΩ resistive coating results in a linear potential distribution and the tangential field is significantly reduced in the region of the mounting flange. [Copyright &y& Elsevier]