Selection procedures for surge protective devices according to the probability of damage

Surges due to lightning are the main cause of damage to the electrical equipment and the systems of surge protective devices (SPD) are the most widely used measures of protection. For practical applications, the probability PSPD that an apparatus, protected by a given SPD system, will be damaged is a key point for its proper selection and installation. The paper proposes practical procedures for the selection of SPD systems able to protect, with a given probability, electronic and electrical equipment within a structure against lightning surges. Examples of application of such procedures to different types of SPD systems are shown in the worst cases of direct lightning stroke to the structure or to the connected low voltage overhead line; also the cases of lightning stroke to ground nearby the structure or the connected line are considered.