Lightning Arrester Working | Lightning Arrester Principle & Types
⚡Their primary purpose is to safeguard equipment from transient overvoltages, which can have various sources. Notably, they are named for their role in protecting against overvoltages caused by lightning strikes.
⚡For instance, when lightning strikes a transmission line, the resulting discharge typically travels to the ground through the tower. However, if the ground connection is faulty due to issues like a broken cable or a raised tower foot resistor the overvoltage can damage transmission line insulators and flow through the conductive cables.
⚡This type of overvoltage, characterized by a rapid wavefront and high voltage levels (depicted as the Vp wave), exceeds what substation equipment can withstand. As the overvoltage reaches the substation, the lightning arrester is the first line of defense, absorbing most of the energy from this wave. This reduces the voltage seen by the remaining equipment to a safer residual level (represented by the Vr wave). For this reason, it is critical to position the lightning arrester at the forefront of substation bays, ahead of vital equipment such as transformers.
⚡All substation equipment must be designed to endure the residual voltage (Vr) from lightning strikes, a requirement verified through insulation coordination studies.
⚡Modern lightning arresters are composed of zinc oxide blocks, also known as Metal Oxide Varistors (MOVs). These blocks, made of zinc oxide and doped with other metals, exhibit semiconductor properties. Under normal system voltage, they act as an open circuit, allowing only a minor leakage current.
⚡However, during an overvoltage event, they become a short circuit, enabling the discharge current to pass through, thereby protecting the system.
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