Ricerc@Sapienza

The lightning performance evaluation of overhead lines (OHLs) is a very important task, since the vast majority of line outages are due to backflashover caused by a direct lightning stroke. The paper presents results concerning the lightning performance evaluation of existing Italian 150 kV OHLs. An ATP-EMTP Monte Carlo procedure is used to assess the OHL backflashover rate (BFOR): main feature of the procedure is a simplified pi-circuit model able to simulate the transient grounding system behavior with high accuracy and very low computational effort.

A significant majority of overhead transmission lines' (OHLs) outages is due to backflashovers caused by direct lightning strikes: the realistic assessment of the lightning performance is thus an important task. The paper presents the analysis of the lightning performance of an existing 150kVItalian OHL, namely, its backflashover rate (BFOR), carried out by means of anATP-EMTP-based Monte Carlo procedure.

The probability of flashovers due to indirect lightning on overhead lines is us ually calculated assuming a statistical distribution for the induced voltages, and a deterministic and specified value for the insulation level of the line. However, more accurate practices of insulation coordination suggest a statistical treatment for the insulation level too, in order to relate the probabilistic nature of both electrical stress (induced voltage) and the electrical strength (insulation level).

We study the shielding performance of shield wires in overhead power lines. We propose a novel chain matrix formulation, that employs longitudinally symmetric transmission-line cells to more efficiently, and correctly, simulate the propagation behaviour over the line accounting for the periodical grounding. The analysis is performed in the frequency domain and results in time domain are obtained through inverse Fourier transform. In the case of direct lightning, we can easily compute overvoltages across insulator strings for insulation coordination purposes.