What Is a Lightning Arrester?
A lightning arrester is a device that protects electronic equipment from lightning damage.
The role of lightning arresters is to protect electronic equipment by limiting transient overvoltage caused by lightning strikes and diverting excess current. They are also known as Surge Protective Devices (SPDs).
The electronic equipment we use must be operated at the proper voltage. However, when a building or other structure in which electronic equipment is used is struck by lightning, the equipment is subjected to overvoltage as a lightning surge. The excessive voltage is called surge voltage, and electronic equipment is momentarily subjected to high voltage at levels it should not be at, causing damage.
A lightning arrester is a device that suppresses the momentary abnormal voltage that occurs when lightning strikes or when a switch is opened or closed. It protects electrical equipment from the application of abnormal voltage. A similar term to lightning arrester is lightning rod, but lightning rods protect buildings and people from lightning strikes, and simply installing a lightning rod does not protect electrical equipment.
Uses of Lightning Arresters
Lightning arresters are used at the point of entry from overhead power lines. In particular, the installation of lightning arresters is required by the national technical standards for electrical equipment at the entry points from high-voltage overhead power lines.
Lightning arresters are also installed in buildings, especially those that handle a lot of electronic equipment. As one of the measures to protect the entire building from lightning damage, lightning arresters are installed on the main power distribution board, on the distribution boards installed on each floor, and on each electronic device. To protect important electronic equipment from lightning damage, it is important to use multiple lightning arresters depending on the installation location.
Principle of Lightning Arresters
The principle of lightning arrester is based on the workings of nonlinear resistance, which allows electronic equipment to act as an insulator at the voltage at which it is used and to carry excess current when excessive voltage is generated. A lightning arrester consists of a gap, called a discharge gap, and a nonlinear resistance whose voltage is not proportional to the current.
When electrical equipment is connected to the power line, lightning arresters are installed between the power line and ground so that they are in parallel with the equipment. When the applied voltage is at a normal level, the nonlinear resistance in the lightning arrester is high, and because of the air gap, no current flows, and the lightning arrester is the same as an insulator that does not conduct electricity.
However, when an abnormal voltage is generated by lightning or open/close surges, voltage is applied to the air gap, and the nonlinear resistance instantly becomes low resistance, allowing the surge current to flow to the ground side and preventing overvoltage from being applied to the electrical equipment. After discharge, the nonlinear resistance becomes high again and no follow-on current from the power supply voltage flows. The starting voltage for lightning arrester operation should be higher than the operating voltage of the electrical equipment and lower than the withstand voltage of the electrical equipment.
After the lightning arrester operates, residual voltage may occur, and this residual voltage must be taken into account when selecting the lightning arrester. Semiconductor devices such as metal oxide varistors (MOVs), avalanche break diodes, surge protective thyristors, and gas-filled discharge tubes are used as nonlinear resistors.
Types of Lightning Arresters
There are two main types of lightning arresters. One is lightning arrester for power supply and the other is dedicated lightning arrester for communication and circuits. Each type of lightning arrester is classified according to the application, and is standardized by the IEC (International Electrotechnical Commission). The JIS is also standardized according to the IEC.
IEC 61643-1/JIS C5381-1 (required performance and test methods for surge protective devices connected to low-voltage power distribution systems) defines the classification of lightning arresters for power supplies. They are classified into Classes I-III, which are used according to the location where lightning arresters are installed.
IEC 61643-21/JIS C5381-21 (required performance and test methods for surge protective devices connected to telecommunications and signal lines) classifies lightning arresters for telecommunications and lines. This standard divides lightning arresters for telecommunications and signal lines into 10 categories. Unlike lightning arresters for power supplies, the categories are not used according to the location of the equipment, but rather to allow a variety of test methods to be performed on a single lightning arrester.