Water Trees In Polyethylene Research Articles

Effect of Physico-Chemical Factors on the Propagation of Water Trees in Polyethylene

The action, type, and concentration of salts in solution in water on the propagation of water trees in polyethylene has been studied using the water needle method and a visualization system allowing measurements under electric stress. Some possible mechanisms for the action of the salts are discussed: effect of salt concentration on the conductivity of the solution, effect of by-products from electrochemical reactions at the electrode, and the effect of polyethylene oxidation at the water-polymer interface.

Water Absorption during Water Treeing in Polyethylene

The amount of water in water trees has been measured as a function of tree length. It is roughly proportional to the volume of the water tree and the fraction of the tree volume filled with water is of the order of several percent. This water content in water trees is approximately proportional to the applied electric stress.

Water Absorption during Water Treeing in Polyethylene

Water Absorption during Water Treeing in Polyethylene

Effect of Frequency on the Growth of Water Trees in Polyethylene

The effect of frequency on the growth of water trees in polyethylene has been investigated using the water needle test. An accelerating effect was observed up to a maximum between 4 and 8 kHz with both NaCl solution and deionized water. This phenomenon cannot be ascribed to a frequency dependence of the electrical behavior of the trees. It results from the mechanical properties of the polymer itself and can be interpreted by analogy with environmental stress cracking. The frequency dependence of the growth rate appears to be a consequence of the existence of a mechanical absorption peak in polyethylene located at about 30 kHz at room temperature.

Water Treeing in Polyethylene - A Review of Mechanisms

A literature survey on the mechanisms of water-treeing electrical cables is presented. The survey provides an introduction, some background, and examples of current research on water-treeing mechanisms. The mechanisms of water-treeing have been broken into three categories: chemical, electrical, and mechanical. Along with discussion on the types of mechanisms, methods are discussed for reducing tree growth by fillers, additives, or structural changes in polyethylene. Some interesting new theories have been proposed which may help to explain the appearance and growth of water trees in electric cables.

Growth of Water Trees in Polyethylene and Silicone Rubber by Water Electrodes

In this paper, various experimental results are described of water trees obtained in polyethylene and silicone rubber, using the water electrode method. The mechanisms of initiation and growth of water trees are discussed. The growth of water trees depends upon the applied voltage, the frequency, and the water resistivity below 10 k?·cm. No differences in the growth of water trees were found among NaCl, KC1 and BaC12 solutions having equal resistivity. It is concluded that Maxwell stress, exerted on polyethylene or silicone rubber by applying an alternating voltage, forms micro-cracks in the material. Water permeates into the polymer, because the dielectric constant of water is higher than that of polyethylene or silicone rubber. With a high electric field and a high frequency, vaporization of water due to dielectric heating may occur: vapors may permeate into the amorphous region, and micro-cracks are formed by the vapor pressure.

A Study of Inception and Growth of Water Trees and Electrochemical Trees in Polyethylene and Cross Linked Polyethylene Insulations

This paper presents an experimental investigation into the effect of different factors, such as contaminants, humidity content, temperature, field strength and frequency on water treeing in polyethylene (PE) and cross linked polyethylene (XLPE). For this investigation, model test specimens have been used to supplement cables for testing. Colored trees and their points of initiation have been analyzed for their content of impurity elements and always are found to contain sulfur and some metal. The results show that the relative humidity in the insulation must exceed approximately 70% to produce a significant number of water trees. The average size of the trees shows a very small dependence upon time and temperature and a slight decrease with increasing field strength. An increase in frequency from 50 to 5000 Hz approximately doubles the average size of the trees. The trees appear during the first 300 hours of voltage application, but since no growth rate can be observed at either frequency, it is not justified to establish a frequency acceleration factor in general.

ポリエチレンの水トリーに関するモデル試験

ポリエチレンの水トリーに関するモデル試験