Current standard practice in EHV/HV Italian substation design: Oriented modelling and simulation of lightning protection system for improving design criteria

This paper addresses the issue of the protection of power substations towards the effects of transient overcurrents/overvoltages of atmospheric origin. The activity is developed in the framework of a research project recently promoted by the Italian Transmission System Operator (TERNA S.p.A.), aimed at investigating the response of its power infrastructures to lightning disturbances and simulating effective overvoltages affecting interconnection components. In particular, an electromagnetic model of an EHV/HV Italian standard substation is set-up in order to re-discuss the current design practice, in term of type and location, for the relevant protection devices. The developed model and the relative analysis procedure are based on high frequency equivalent circuits to represent all the committed components when subjected to lightning phenomena. To this regard, a simulation campaign was preliminary performed in order to fit model parameters with rated characteristics and experimental tests available by manufacturers. The models are implemented and tested into the widely adopted PSCAD/EMTDC electromagnetic environment. Simulations are devoted to investigate the effectiveness of the protection provided by the combined use of surge arresters and spark gaps towards lightning disturbances. In particular, current utilization of metal oxide surge arresters in the Italian transmission grid is basically limited to autotransformer protection, as close as possible to the machine windings. This paper aims at suggesting preferable adoption and placement of additional LSAs at line end terminals, proposing comparison of different design solutions. With concern to this point, effects of present installation of spark gaps at line terminals are modelled and criticized with regard to LSAs, also promising for their significant cost reduction in the last decade.