Surge, also known as voltage surge or surge, is a common phenomenon in power systems, usually referring to sudden current or voltage fluctuations. Such fluctuations may be caused by lightning strikes, grid failures, switch operations or other reasons. Power surges can cause serious damage to power equipment and electronic equipment, and even lead to safety issues such as fire. Surge protection devices are electrical appliances used to limit transient overvoltages and discharge surge currents. They mainly ensure power safety by reducing the damage caused by surges to power equipment and electronic equipment.

The core components of surge protection devices are generally varistors, gas discharge tubes and graphite gaps. According to the core components, they can be divided into three categories: voltage switch type SPD, voltage limiting type SPD and composite type SPD. Their commonality is that when lightning current invades the system, they can timely discharge lightning current to the ground, limit lightning overvoltage and the entire process is in nanoseconds and will not affect the normal power supply of the equipment.