Factors influencing the probability of an apparatus damage in an extended earthing arrangement

In the present paper lightning overvoltages on apparatus bonded to an extended earth arrangement are investigated. A case study of a large earthing grid (200m × 200m) covering an industrial plant is considered where a stand-alone power supply system (no connection to external lines) is supplying apparatus powered by a secondary board, earthed to a different point from the main distribution board. The values of the stressing voltage on the apparatus due to resistive coupling, the protection measures to be adopted according to the different characteristics of the lines connecting the distribution boards, and the probability of apparatus failure are evaluated. The analysis, performed by several simulations by means of the transient software EMTP-RV, show that protection against lightning of structures and of industrial plant may require the adoption of technical solutions that, even if in accordance with standards [1-4], need a particular study.