Lightning Transients in Low-Voltage Installations Inside Different Types of Class II Lightning Protection Systems

This paper presents a numerical electromagnetic analysis of loop-termination voltages inside an outer lightning protection system (LPS) resulting from direct and indirect lightning strikes. The method of moments is combined with the transmission-line model and employed to model the whole structure in three dimensions and the lightning channel, respectively. Three distinct types of class II LPS are modeled with one- and three single-phase parallel vertical loops of the TN-S system inside the LPS. All cases are simulated by using the negative subsequent stroke current with linear-rising front at lightning-protection level II. The connected equipment at the loop terminals is considered in the offstate to simulate the worst condition. The results reveal that for the three-loop configurations, the middle-loop termination voltages of all floors are always higher than those of the outer loops and the frequency of oscillations of the middle loop is roughly twice that of the outer ones. In addition, the midedge strike case gives higher loop-termination voltages for all floors than those of the corner strike case. For the slender LPS, the effect of the strike location dominates in the case of high surge impedance of the feeder only.