Surge protection device (SPD) is also called surge protector, is used to limit transient overvoltage and leakage protection devices on the guidance of nonlinear surge current of charged system, rush or to protect the low voltage level of electrical or electronic systems against lightning and lightning electromagnetic pulse operation over-voltage. In recent years, electronic information systems (such as television, telephone, communications, computer networks, etc.) have developed rapidly, and electronic information equipment has emerged and popularized in large numbers. This kind of system and equipment are expensive and important. Its working voltage and voltage level are very low and it is easy to be damaged by lightning electromagnetic pulse. Therefore, SPD is required to be used as over-voltage protection.

Classification of surge protection device

SPD is an indispensable device of lightning protection of electronic equipment, its function is to enter into the instantaneous power lines, signal transmission line overvoltage can withstand voltage range in the equipment or system, or a powerful lightning flow into the earth to protect the protected equipment or system is not affected by the impact of.

According to its working principle, SPD can be divided into voltage switch type, voltage limiting type and combination type.

(1) Voltage switch type SPD. When there is no instantaneous overvoltage, a high impedance is produced, and once the lightning transient overvoltage is exceeded, the impedance is changed to low impedance, allowing lightning current to pass through, also known as a short-circuit switch type SPD".

(2) Voltage limiting type SPD. When there is no instantaneous overvoltage, it is high impedance, but the impedance will decrease as the surge current and voltage increase, and the current and voltage characteristics are strongly nonlinear, sometimes called the "clamp type" SPD".

(3) Combination type SPD. It is composed of voltage switch type component and voltage limiting type component, which can be displayed as voltage switch type or limited voltage type or both, which is decided by the characteristic of voltage added.