arrester (AR)
Surge arresters (ÜSA), Arrester, are passive electrical components used in high and low voltage networks to discharge overvoltages. They are also found in power supplies of equipment and systems to protect electronic components against damage. The surge problem is particularly relevant in telecommunications equipment because transmission lines can absorb transient surges caused by lightning or switching surges.
A surge arrester is a spark gap between two metal electrodes that are routed to the outside via wires and spaced according to the overvoltage. The electrodes can be arranged in a ceramic or glass tube filled with air or inert gas. If a surge arrester works with air, it is called an air spark gap; if it is filled with inert gas, it is called a gas-filled surge arrester (ÜSAg) or gas discharge arrester.
Functioning of surge arresters
In normal operation, the spark gap is extremely high impedance with an insulation resistance greater than `10^10` ohms and an extremely low capacitance of a few picofarads (pF). When the ignition voltage is exceeded, the gas in the gas discharge gap ionizes and forms a conductive arc across which the overvoltage is dissipated. The gas discharge is caused by ionization of the noble gas and occurs in a few hundred milliseconds.
In addition to the response time, which can be a few nanoseconds, other characteristic values include the rated response voltage, which can be less than 100 volts up to a few kilovolts (kV), the rated leakage current and the rated leakage surge current. Surge arresters, which are referred to as surge limiters in DIN 0845, are divided into load classes with respect to the rated leakage impulse current. There are a total of six load classes between with rated discharge impulse currents between 2.5 kA and 100 kA.
In addition to the surge arrester discussed here, there are various components for surge protection such as varistors, capacitors, Zener diodes, transil diodes, surge protection diodes or suppressor diodes, multilayer varistors and simple electronic circuits that protect against overvoltage.