The rating current (ampacity) of a conductor erected on a particular overhead line (OHL) structure installed at a specified location is influenced by the conductor, the OHL structure as well as weather and operational parameters. Many studies have been carried out regarding calculating an aerial bare conductor's ampacity at a steady-state conductor temperature, but without considering the OHL structure as part of the system. In this paper, a holistic methodology for calculating the conductor's ampacity and sag at any temperature and power frequency, erected onto a pre-specified OHL structure is developed, considering together the mechanical and electrical parameters of the overall system. This methodology incorporates the conductor's basic material properties allowing the calculations to be applied to newly developed high temperature low sag composite conductors. In this way it becomes possible to identify, at system level, the potential benefits that may result from the improved performance of these conductors as well as to indicate new sizes that may better fit a pre-specified system, optimizing its performance. The methodology is also validated with a real system application, resulting in correct predictions of the performance of a 4-span double line system.

No abstract

A narrow size distribution of irregular aluminium particles was blended into power cable insulation grade polyethylene. Some batches of the resulting material were then melt-filtered to reduce the size of particles present and narrow the distributions further. The failure statistics of the loaded polymers were then determined under AC ramped stress. density of defect can clearly be identified. In addition, for the filtered material, a minimum breakdown field can be associated with a given filter size: a result of commercial importance. Some indications exist to suggest that different modes of failure operate at high and low fields. Candidates for these modes are analysed and discussed in terms of the distributions of defects present. Local field enhancement due to the included flaws were calculated using finite-element techniques.The results are compared with a percolation model of breakdown. Predictions are found to quantify accurately the reduction in the characteristic strength of the material over the narrow range of defect concentrations examined.

The inclined plane tracking and erosion test IEC-60587 is not specified for DC testing. A dc test has been developed from the current ac standard and three formulations of silicone rubber tested. These materials were tested under three voltage levels (2.3, 2.7 and 3.2 kV) for both polarities. Positive dc tests have the highest average and peak leakage current and exhibit a higher degree of surface damage. The observed surface degradation pattern is heavily dependant on polarity. Consistently higher levels of erosion have been observed in the higher voltage positive cases. Erosion of the surface always starts at the bottom electrode, and spreads toward the top electrode. Puncturing of the 6 mm thick samples or deep erosion over more than half the distance between electrodes has only been observed under 2.7 and 3.2 kV positive polarity tests. Results have been analysed using a variety of leakage current analysis techniques going beyond the criteria specified in the original ac standard. The low-frequency behaviour of the leakage current was monitored using a 15 sample per second current recorder. The leakage current magnitude is investigated in a case study and is shown to follow a normal distribution. Reversing the polarity of tests shows the leakage current seen in a test is largely independent of the surface degradation pattern present, but the surface degradation pattern over the first three hours may dictate the morphology of ensuing deep erosion

A holistic computational methodology is employed in this paper to present an analysis of the widely used aluminum alloy conductors (AAAC) performance on a 33-kV wood pole structure. This analysis highlights the basic system properties that influence its mechanical and electrical performance. A comprehensive comparison of the performance of the common AAAC and aluminum conductor steel reinforced (ACSR) conductors erected on the structure is presented, including the study of the increase in operating temperature on the losses, ampacity and sag, in order to identify the most appropriate conductor for the pre-specified structure. Some recently developed high temperature low sag (HTLS) composite conductors are also studied in terms of power transfer uprating on distribution overhead lines. Their performance is examined at normal temperatures instead of the high operating temperatures for which they are specifically designed for, in order to evaluate the benefits they may offer at distribution level voltages. Index Terms-Aluminum alloy conductors (AAAC), aluminum conductor steel reinforced (ACSR), ampacity, high temperature, high-temperature low sag (HTLS), reconductoring, sag.

Electrical treeing is one of the main mechanisms of degradation in polymeric high voltage insulation, a precursor of power equipment failure. Electrical trees have been previously imaged mostly using two-dimensional imaging techniques; thereby loosing valuable information. Here we review the techniques that have been previously used and present the novel application of X-ray computed tomography (XCT) for electrical tree imaging. This non-destructive technique is able to reveal electrical trees, providing a threedimensional (3-D) view and therefore, a more complete representation of the phenomenon can be achieved. Moreover, taking virtual slices through the replica so created brings the possibility of internal exploration of the electrical tree, without the destruction of the specimen. Here, laboratory created electrical trees have been scanned using XCT with phase contrast enhancement, and 3-D virtual replicas created through which the trees are analyzed. Serial Block-Face scanning electron microscopy (SBFSEM) is shown to be a successful complementary technique. Computed tomography enables quantification of electrical tree characteristics that previously were not available. Characteristics such as the diameter and tortuosity of tree channels, as well as the overall tree volume can be calculated. Through the cross-section analysis, the progression of the number of tree channels and the area covered by them can be investigated. Using this approach it is expected that a better understanding of electrical treeing phenomenon will be developed.

No abstract

No abstract