Surges induced in building electrical systems during a lightning strike

• Influence of lightning current, circuit parameters and connected loads on induced surges is revealed.
• The connected capacitors can reduce surge voltages in a circuit.
• A two-SPD protection scheme can suppress surge voltages effectively.
• An approximate formula was derived for estimating surge currents.

This paper presents an investigation into lightning surges induced in buildings with the FDTD method. When down conductors (DCs) in a building discharge a lightning current, induced surges are observed in adjacent distribution circuits due to electric and magnetic coupling. The induced voltage in an open circuit and the induced current in a close circuit are, respectively, determined by the current surge and voltage surge on the DC. It is found that connected capacitors can reduce the induced surge voltages, but may not be effective. SPDs are then recommended installing at two far ends of a distribution circuit. They are not required to dissipate substantial lightning surge energy observed in the down conductors. The surge currents in SPDs can be estimated using the closed-form formula.