Influence of the surrounding medium on the dielectric strength measurement of LLDPE/clay nanocomposites

Abstract

This paper evaluates dielectric breakdown measurements according to the ASTM D149-09 standard for various specimen thicknesses and surrounding media. This study was performed on LLDPE/nanoclay with three different surrounding media. Pre-breakdown partial discharge activity was monitored and the electrical field in the breakdown area was computed by FEM modeling.It was observed that the variations of the dielectric breakdown values from the neat polymer to the nanostructured polymers strongly depends on the surrounding medium, a situation which could lead to non-valid conclusions if appropriate care is not taken to select the optimal experimental procedure. Also, the results underscore the influence of the pre-breakdown partial discharge gas generation on the electrical field distribution and the influence of the surrounding medium degradation.To conclude, the ASTM D149 Standard shows a lack of normalization in terms of the surrounding medium parameters and the sample thickness, even though a certain amount of normalization is needed in order to compare breakdown results from one experiment to the other and to improve the understanding of the solid dielectric breakdown phenomena.

Dielectric Properties of PE/Clay Nanocomposites

“…The calculated estimatorŝand̂of the Weibull parameters obtained from the statistical analysis of 13 different samples are given in Table 3 with the confidence bounds for the scale parameter (or at the 63.2 percentile). Since the breakdown strength, when measured using the ASTM short term test, is largely affected by the chosen procedure, such as rate of rise, type of electrodes, specimen thicknesses, and the type of surrounding medium, we must be extremely careful before assessing an improvement (or not) of this property for a particular material over another [30]. Accordingly, the breakdown measurements were conducted in two different Figure 10: (a) Modeling of the dielectric response of a 97/0/3 nanocomposite using (17) and (18) with two H-N relaxation peaks; (b) corresponding relaxation time distribution for the interfacial peaks.…”

“…However, when the same procedure was repeated for a thinner specimen (0.53 mm), no improvement in the breakdown strength was observed. This can be explained by the inception of an intense partial discharge activity prior to breakdown, leading to a very fast erosion and failure of the tested specimens [30]. Another set of measurements were conducted on the same thin samples using different mineral oil with a higher dielectric strength, and a slight improvement of the dielectric strength was observed for the clay containing composites [30].…”

A Novel Oil-Immersed Medium Frequency Transformer for Offshore HVDC Wind Farms

“…Depending on the relative permittivity of the materials [65], the electrical field in the medium around a solid insulation material under a test can be higher than the electrical field within the test object. This causes surface discharge and partial discharges near the test object (see Figure 3-22) which deteriorates the material around the electrode corners and can affect the breakdown voltage of the test setup [105]. During application of voltage, by placing the sample inside a suitable oil as a surrounding medium, there will be no external discharge at the edges of the electrodes, and an ACBD will happen inside the insulation material any discharge over the surface of the sample will be avoided.…”

Effects of stearic acid and thermal treatment on morphology and dielectric properties of UHMWPE/POSS composites prepared by ball milling

“…They consist of a polymer matrix within which a nanofiller which can be clay [2], boron nitride [3], etc. is dispersed.…”