New Class of Additives to Inhibit Tree Growth in Solid Extruded Cable Insulation. Final Report

摘要

Ferrocene (5%) inhibits treeing and raises the needle-plane breakdown voltage by approximately 100%. However, it is unstable (oxidizes) both in air and in the presence of dicumylperoxide. None of the antioxidants investigated stabilized ferrocene. The effectiveness of ferrocene is not due to an increase in intrinsic dielectric stength, or electron scavenging properties, but seems to be related to the low ionization potential of the compound. The mechanisms are discussed. Nine other related compounds have been found to be ineffective or oxidatively unstable. Low-frequency dielectric studies indicate that the lack of effectiveness of most of the ionic compounds investigated previously was due to an unexpected frequency dependence of field-enhanced dissociation. A new ionic compound, alpha -bromolauric acid, has been found to be effective in steel-needle breakdown tests at 60 Hz. Although it is oxidatively stable, results suggest that its performance may be specific to systems where field enhancement occurs at iron imperfections. Long-term tests at room temperature show a large improvement in breakdown voltage; however, at 85 exp 0 C reactions involving iron result in the formation of large voids that completely bridge the needle-to-plane test gap. The most important result of the two studies into additives for inhibiting tree growth in solid extruded cable insulation has been the finding, backed by supporting information on the mechanisms involved, that one can significantly inhibit treeing and raise the breakdown stength. Unfortunately, the materials identified have all suffered from thermal and oxidative instability. (ERA citation 05:002956)