Simplified HV tower grounding system model for backflashover simulation

In this paper the authors present and discuss the application of a lumped parameter model, based on a simple π-type network, which is advantageously usable in lightning performance studies of a typical HV European overhead lines (OHLs). This simplified model is able to simulate tower grounding systems also accounting for non-linear ionization phenomena. The behaviour of the simplified grounding system model is compared with the results provided by using a full circuit model, formerly validated by comparison with experimental tests and with simulation results yielded by field models available in literature. Numerical results show a good agreement between the two models; in addition, the proposed π-network model drastically reduces the computational resources (i.e., memory occupation and execution time) required when complex power systems must be studied in transient and non-linear conditions.

Introduction

As well known, the steep-fronted current impulses injected by lightning strokes in OHL tower peaks or shield wires can cause backflashover of line insulation. In order to prevent back-flashes, complex grounding arrangements (i.e. involute geometries) and/or large spatial extension (i.e. counterpoises) are commonly used for OHL towers built on medium-to-high resistivity soils. The aim is the reduction of the tower grounding impedance, mainly due to relaying performance concerns and lightning withstand. The numerical simulation of such spatially extended grounding systems may be advantageously carried out by means of circuit models [1]–[4], able to provide accurate results even for complex scenarios [5]–[11]; however, the main drawback of such models, especially when complex power systems must be simulated and non-linear soil ionization phenomena must be taken into account [12]–[16], is the large request of computational resources in terms of occupation memory and execution time.