arresters

Arresters, or surge arresters, are protective devices used in electrical power systems to limit overvoltages caused by lightning, power faults, or switching events. They divert surge currents to the ground, reducing overvoltage across equipment. In normal operation they present high impedance, but at elevated voltages their conductivity increases dramatically, clamping the voltage to a safe level.

Common types include metal-oxide varistor (MOV) arresters, gas discharge tube (GDT) arresters, and older spark-gap arresters. MOV arresters contain zinc oxide based varistors in a protective housing; they respond quickly and clamp surges, dissipating energy. GDT arresters use a gas-filled tube that ionizes to form a conductive path when a high voltage appears, then extinguish when current falls; they can handle large surge currents but may require a follow-up arrest for sustained faults. Spark-gap arresters rely on an open air or sealed gap that arcs at a threshold and are simple and robust.

They are rated by nominal discharge current IN, maximum continuous operating voltage (MCOV), and energy rating; the devices are coordinated with fuses and breakers to ensure proper disconnection in case of failure. MOVs are electronically non-linear, and their clamping voltage depends on current; GDTs have high insulation until breakdown at peak voltages. In many systems, multiple arresters are placed at substations and along distribution lines.

Maintenance concerns include degradation under repeated surges, moisture ingress for polymer-housed arresters, fire risk, and eventual replacement after a surge event. They are essential for protecting transformers, switchgear, feeders, and communication circuits, and play a critical role in ensuring system reliability.