A practical approach of lightning protection measures for power receiving facilities in telecom building

In this paper, we present a summary of lightning protection measures aimed at securing a more reliable power supply for a telecom building. Based on an analysis of the entry paths of lightning surges into telecom building, we implemented lightning protection measures for the power receiving facilities by strengthening the equipment's tolerance to overvoltage surges. This was achieved by using a multistage lightning arrester (LA) to suppress the inflow and outflow of surges, and by introducing surge protective devices (SPDs) in the signal paths. To cover the eventuality of relay equipment damage caused by a lightning strike, we also implemented measures such as redundant undervoltage relays and potential equalization by connecting the earth electrodes together. Of these measures, this paper discusses an example of lightning countermeasures for relays that are at high risk from lightning strikes due to them being directly connected to signal lines from the outside, yet are responsible for important functions such as switching between the mains power supply and emergency backup generator. Since a relay's lightning surge breakdown voltage is relatively low, it can be impossible to protect with a commercial surge protector device (SPD). We therefore tried to suppress lightning surge voltages by using a lightning protection unit consisting of an SPD combined with an inductor. A relay has two types of wiring — the zero-phase voltage measurement line between the relay and the pole-mounted air switch (PAS) at the demarcation point between the commercial mains system and the customer equipment, and the −48 V DC control power supply lines between the rectifier and relay. These have two different earthing systems routed to the protective earth and to the −48 V DC earth wire, so we installed lightning protection units at both ports. To verify the effects, we measured the voltage applied to the electronic components inside the relay when a 10 kV lightning surge was applied to each port. As a result, we confirmed that these voltages were below the impulse breakdown voltage of the electronic components, and that the relay was able to continue operating normally.