A lightning protection system protects a structure from damage due to lightning strikes, either by safely conducting the strike to the ground, or preventing the structure from being struck. Lightning protection systems are commonly installed on structures, buildings, trees, monuments, bridges and water vessels to protect from lightning or electrical discharge damage. Lightning protection systems are also used to protect appliances, machinery, electrical systems and electronic equipment from lightning or electrical discharge damage. Most lightning protection systems are composed of a network of lightning rods and/or lightning arrestors (surge protectors), metallic cable conductors, and ground electrodes designed to provide a low impedance path for the lightning to travel through to the ground.
A lightning rod is a metal strip or rod with a conductive cable or other low-resistance path to ground. A lightning rod, which is usually installed on a rooftop, provides a point well above the structure to be protected with a very good, earthed connection. Because of its position, shape, and conductivity, the lightning rod may draw energy (current) from a lightning discharge and diverts the energy to ground via the conductive cable to ground, thus preventing damage to the structure. FIG. 1, which is adapted from Tesla U.S. Pat. No. 1,266,175, shows an early lightning rod.
A lightning arrestor is a device, which is typically used for protecting electronic or electrical equipment from lightning by diverting any surges of high-voltage electricity caused by atmospheric discharges to ground. The lightning arrestor includes an “active” element, which switches from a non-conductive state to a conductive state in response to a surge in voltage. The active element in its conductive state provides a short i.e. a path for the high voltage to go to ground, bypassing the electronic or electrical equipment to be protected. In other words, the active element acts as an over-voltage release valve. The active element of a lightning arrestor may, for example, be a metal oxide varistor, a transient suppression diode, a gas discharge tube, a spark gap, a crowbar (circuit) using a Zener diode driving the gate of a silicon-controlled rectifier (SCR) latch, or any other suitable device. For convenience in description, both lightning rods and lightning arrestors may be referred to as lightning arrestors herein.
Consideration is now being given to improving traditional lightning protection systems.