Towards Recyclable Insulation Materials for High Voltage Cables

The preferred material for modern extruded high voltage transmission cables is cross-linked polyethylene (XLPE). This material has excellent thermo-mechanical and dielectric properties, however it is not easily recycled at end of use, raising questions as to its long term sustainability [1]. Therefore research work at Southampton has sought to identify suitable recyclable alternatives to XLPE. Such candidate materials need to have low temperature flexibility and high temperature mechanical stability combined with a sufficiently high electrical breakdown strength

Raman Microprobe Analysis of Electrical Treeing in Silicone Rubber

Previous papers have identified Raman microprobe analysis as a useful tool in the chemical analysis of electrical trees and have successfully applied the technique to trees grown in polyethylene. This paper comprises a detailed spectroscopic study of electrical trees grown in silicone rubber. A selection of trees of varying fractal dimensions were exposed using cryogenic microtomy and then the individual tree channels were subjected to surface specific Raman microprobe analysis. It was found that although some trees show that few chemical changes have occurred, some trees (including some where complete breakdown has occurred) show evidence of the presence of silica and carbon, the latter possibly originating from the side groups of the polymer chain. After this, some of the samples were then analyzed using scanning electron microscopy (SEM) to provide an alternative method of analysis and to reinforce the conclusions made. Results are discussed in comparison to previously published results from a similar analysis on trees in polyethylene

Electrical Treeing in Silicone Rubber

Electrical treeing has been widely studied in a range of polymeric materials. In these investigations, the morphology and PD patterns associated with the growth of electrical trees in a model transparent silicone rubber were investigated using a new system recently developed at Southampton. With increasing voltage the trees became more complex in appearance but nevertheless grow more rapidly. As the tree evolves the PD pattern becomes more intense which may provide a method of monitoring the extent of treeing in opaque samples. Raman studies indicate that treeing and breakdown channels are hollow, carbonaceous entities, a finding consistent with other studies

Aging behaviour of dodecylbenzene in the presence of copper and dibenzyl disulfide (DBDS)

Copper sulfide deposition remains a serious issue in high voltage power transformers and can result in equipment failure. In order to understand the chemistry of this process, dodecylbenzene was used as a model oil system. Copper and dibenzyl disulfide (DBDS) were added in controlled amounts and accelerated aging was then performed. It was found that copper sulfide (CuxS) could be formed (i.e. the included copper sheets were blackened) even under non-oxidative conditions but only when DBDS was present in the oil. The reaction was accelerated in the presence of oxygen and competes for available copper with the parallel copper carboxylate producing reaction. The AC breakdown strength was reduced after aging, but exhibited a more catastrophic reduction in oils containing DBDS, confirming the detrimental effects of CuxS on breakdown performanc

Effect of aging on the physical, chemical and dielectric properties of dodecylbenzene cable oil

In high voltage transformers a liquid dielectric,such as mineral oil, serves both as an electrical insulator (in conjunction with paper) and as a coolant. Similarly, in paper/oil cables mineral oil or dodecylbenzene in conjunction with paper serves as the electrical insulator. In such systems, the oil serves as a convenient medium for sampling to indicate plant health. In the current study dodecylbenzene was aged at elevated temperatures in the presence of air and copper. A battery of tests was then performed to assess the changes in physical, chemical and electrical properties. After aging the oils were yellowed and oils aged with copper showed oxidation, increased water content and the formation of a precipitate, whilst those aged in the absence of copper showed much less aging. Changes in electrical properties were noted such as increased dielectric loss, increased electrical conductivity and decreased dielectric breakdown strength. It was found that the presence of the precipitate did not affect the electrical properties of the oi

Differential effects and temporal course of attentional and motivational training on excessive drinking

Background. Two cognitive-motivational variables that help to solidify drinkers’ intentions to drink are their alcohol attentional bias and their maladaptive motivation. Objective. The Alcohol Attention Control Training Programme (AACTP) was designed to rectify the former, and the Life Enhancement and Advancement Programme (LEAP) was designed to rectify the latter. Method. The present study used a factorial design to compare the individual and combined effects of the two interventions on mean weekly drinking and atypical weekly drinking of 148 harmful drinkers (49% males, mean age = 28.8 years). A variety of other cognitivemotivational and demographic measures were also taken at baseline, and the drinking measures were reassessed at post-treatment and 3 and 6 months later. Results. In comparison to LEAP, the effects of AACTP were less enduring. Combining AACTP and LEAP had few incremental benefits. Conclusions. These results suggest that AACTP would be more effective for achieving short-term reductions in drinking, whereas LEAP would be more effective for alleviating problematic drinking

A Comparison of Polymeric Cable Insulation Properties Following Lightning Impulse Ageing

LDPE and HDPE are common materials used within high voltage insulation systems. These materials will be aged after working under high voltage for a long time. The ageing process of these materials may be affected by external factors. The application of repetitive lightning impulse over-voltages is one of these factors and will be considered in this paper. This paper includes the sample preparation process, the ageing of samples under identical conditions and finally the analysis of electrical properties after the ageing process. The obtained results are used to compare the effect of repetitive lightning impulses with these two materials. These results are also used to highlight the possible mechanisms behind the lighting impulse ageing process