On the Assessment of the Voltage Drop between two Lightning Protection Zones Connected by a Signal Line

The transient performance of a simple communication wire located inside metallic cable tray interconnecting a main Lightning Protection Zone (LPZ) to a second LPZ is analyzed using the electromagnetic field theory approach. The main LPZ is subjected to a lightning strike at one of its aboveground corner. The field theory approach used is essentially an extension to arbitrary frequencies of antenna theory while accounting for the complex electrical characteristics of soil. The computation of transient voltages is carried out using the MultiFields software package. The article focuses on the transient voltage drop along the metallic cable tray that connects the two different systems with the same LPZ level. Comparison are performed between a simple metallic interconnection conductor parallel to the communication wire and two other metallic cable trays. The article shows that the voltage drop along the interconnection cables can be evaluated to determine if Surge Protection Diverters (SPD) are required. Measurements and simulations are compared to validate the computation results, and compare them to the requirement of the pertinent IEC standard.