Pietro Lucio Buccheri

Efficient modeling of a combined overhead-cable line for grounding-system analysis

Simple compact models for combined overhead-cable lines supplying a substation are presented as an extension of a previous paper for grounding system analysis. The overhead line section can be equipped with uniform or combined ground wires, whereas the cable line section can consist of coated metal sheathed cables, with/without intermediate grounding, or uncoated metal sheathed cables in continuous contact with the earth. Besides the calculation of the earth current at the faulted substation, the proposed modeling method allows the evaluation of the leakage current at the transition station, where cables are connected to the overhead line, as well as at critical overhead line towers. In this manner, the effects of the so called ldquofault application transferrdquo phenomenon can be conveniently estimated at the design stage in order to assess the most appropriate safety conditions. Some numerical examples are given by applying a computer program based on the proposed methodology.

An improved MSD-based method for PD defects classification

The new proposed method of pattern recognition is based on the application of multi-resolution signal decomposition (MSB) technique of wavelet transform. This technique has showed off interesting properties in capturing the embedded horizontal, vertical and diagonal variations within an image obtained from the PD pattern in a separable form. This feature was exploited to identify in the PD patterns MSD, relative at various family of partial discharge sources, some detail images typical of a single discharge phenomenon. The classification of a generic PD phenomenon is feasible through a comparison between its detail images and the detail images typical of a single discharge phenomenon. Tests have been performed on specimens having single defects. The obtained results prove that the proposed improved classification method is quite efficient and accurate

Cloud influence in evaluating the electric field of a lightning return stroke

A theoretical model to evaluate the electric field of a lightning return-stroke by taking into account the presence of the cloud, is illustrated. The cloud-lightning channel system is modelled by employing a perfectly conducting sphere placed above a thin-wire vertical antenna excited by a lightning current at the ground level. The current distribution in the channel is derived by a transmission line model found in technical literature. The ground is considered perfectly conductive. Different examples related to various channel lengths and sphere radii are reported in the paper, by stressing the different behaviour with and without the cloud. A comparison with recorded data available in literature, enables to qualitatively validate the results computed by means of the proposed model.