Influence of frequency on water treeing in polyethylene

Water treeing depends on many parameters, especially frequency. We have reviewed the literature for water trees grown in polyethylene soaked at room temperature in distilled water and various NaCl solutions. All existing data obtained with water needle electrodes (Ascraft cells) obey one single relationship between water-tree length and the number of field cycles, i.e. the frequency×time. The upper frequency limit of this process appears to be in the 30 kHz range. The effect of ion concentration is more influential for a large number of field cycles (above 10⁸ cycles), but is not as significant as the frequency effect. The field calculated at water needle defect, ranging from 80 to 600 kV/mm, has little influence on water tree length. The practical impact of these observations is briefly discussed