Arrester

An arrester is a protective device in electrical systems that limits overvoltages by diverting surge currents to ground or neutral. The most common form is a surge arrester, installed on power networks, transformers, and switchgear to limit transient voltages caused by lightning or switching operations.

There are several technologies used in arresters, including gas discharge tube (GDT) arresters, metal-oxide varistor (MOV) arresters, and air-gap (spark-gap) arresters. GDT arresters contain a sealed gas-filled chamber that ionizes when the voltage exceeds a breakdown threshold, forming a low-impedance path to ground. MOV arresters use nonlinear metal-oxide blocks whose resistance drops sharply at higher voltages, clamping the voltage to a safe level. Air-gap arresters rely on a controlled gap that conducts when external voltage is large enough to bridge it, directing surge current to ground.

Operation is simple: under normal conditions the arrester presents high impedance and draws only leakage current. When a surge occurs, the device becomes conductive and shunts the surge away from protected equipment, then returns to high impedance after the event.

Installation and coordination require connection between the protected line and earth (or line to neutral), with proper grounding, creepage distances, and coordination with upstream protection devices to minimize nuisance operation while ensuring effective protection.

Applications span power transmission and distribution networks, substations, distribution transformers, switchgear, telecom lines, and buildings, where arresters help prevent insulation damage and equipment failure from lightning and switching transients.

Typical specifications include voltage rating, nominal discharge current, residual voltage (protection level), and energy capability. Regular inspection and periodic testing are recommended, with replacement after severe surges or detected degradation.