This paper introduces a new geometry for the study of dry band formation. Firstly, a thermoelectric simulation of a 69 kV uniformly polluted composite insulator was performed. The results obtained show that thermal stress is greater at the rod surface where current density is maximum. In order to experimentally reproduce the constriction of current density lines on the insulator rod surface, which is the cause of dry band formation, the development of a new simple geometric setup, which was then tested experimentally, was proposed. For this purpose, an ESDD value corresponding to a high level of pollution was used for each polluted sample, and the samples were placed in a climate chamber at constant 90% relative humidity and a constant ambient temperature of 20 °C. Low-voltage tests permitted the determination of the wetting duration, which corresponds to the maximum surface conductance of the polluted layer. The values obtained agree with the 10–40 min duration recommended in IEC 60507. Moreover, the tests performed at a higher voltage demonstrated the efficiency of the proposed setup to simulate the complex process of dry band formation in a reproducible way in terms of leakage current and temperature behavior. The proposed setup is a new and simple method that can be easily used by the electrical industry to develop new material for the next generation of overhead line composite insulators without requiring costly HV equipment.

No abstract

This paper presents an exhaustive study of numerical investigations based on three-dimensional finite-element method modelling of several non-ceramic insulators of 69, 110 and 230 kV having different internal semi-conductive defects in terms of size and position. The internal defects were positioned close to the high-voltage electrode, the ground electrode and at floating potential. The simulations effected on the distortion of the axial and radial E-field components close to the insulator shank between sheds. The results obtained showed that the radial E-field component is more sensitive to the presence of an internal defect as it shows a greater distortion in presence of the defect. It was also observed that the E-field component distortion increases with longer internal defect and that this increase is particularly important for a defect at floating potential. Moreover, it was demonstrated that the length of the insulator, for a defect of constant length, has no significant influence on the E-field component distortion. Finally, the results demonstrated that the presence of a grading ring, as used on the 230 kV insulator, does not have any influence on the E-field component distortion, independently of the defect position.