Why should surge protective devices be classified?

- Oct 19, 2020-

Surge protective device (SPD) is divided into several levels, which are also called in many ways, such as T1 SPD and T2 SPD, class 1 test and class II test, class I surge protective device (SPD), secondary surge protective device (SPD), etc? What's the effect?

Class 1 surge protective device

Its main function is to discharge current, with a waveform of 10 / 350 μ s. It is mainly used at the boundary between lpz0 and lpz1 (general distribution box, low-voltage transformer incoming cabinet), so as to protect the system equipment from the surge current damage caused by lightning strike on the line.

It is generally required that the surge protective device (SPD) of this level power supply has large impulse capacity, and the required limiting voltage is less than 2.5KV, which is called class I power SPD. These lightning protection devices are specially designed to withstand large lightning current and absorb high-energy surge.

Because class I SPD mainly absorbs large surge current, they can not completely protect the sensitive electrical equipment inside the power supply and distribution system.

Class 2 surge protective device

Its main function is to limit the voltage. It limits the residual surge voltage of level 1 surge protective device to 1.5kv-2.0kv, and its waveform is 8 / 20 μ s. It is used at the boundary between lpz1 area and lpz2 area or later lightning protection boundary (floor distribution box, ammeter box or terminal box) to prevent transient surge voltage caused by intermittent lightning stroke or switch operation.

As the secondary protection, the surge protective device (SPD) should be voltage limiting type, and its lightning current capacity should not be less than 20KA. It should be installed in the key or sensitive electrical equipment to absorb the remaining surge. It has good suppression effect for transient overvoltage, which is called class II SPD. Generally, the power supply and distribution system can meet the requirements of equipment operation if the secondary protection is achieved.

Class 3 surge protective device

Its main function is voltage clamping, which can reduce the residual surge voltage to less than 1.0kv, which is suitable for the further protection of the electrical equipment at the end of the line. When the SPD installed at the incoming end of the electronic information equipment is used as the third level protection, it should be a series voltage limiting power supply SPD, and its lightning current flow should not be less than 10kA.

For more precise protection, a built-in power supply SPD can be selected in the internal switching power supply part of the electrical equipment, so as to completely remove the target of micro overvoltage. It is required that the high impact capacity is 20KA or less per phase, up < 1KV, and it can also protect the electrical equipment from the transient overvoltage hazard generated in the system.

For the rectifier power supply used in optical fiber communication equipment, base station communication equipment and radar detection equipment, depending on the protection requirements, DC SPD matching with its working voltage can be used as the final protection.

Class 4 surge protective device

If the withstand voltage level of the equipment is low, four or more levels of protection may be required, and the lightning current capacity shall not be less than 5ka.

A good lightning protection design and selection can ensure the safety of the protected equipment, and at the same time, it can achieve good protection effect with a small amount of money to prevent the equipment from being damaged by surge voltage and surge current. Lightning protection is a technical work. Once the design and installation are unreasonable, it can not play its due role, but may bring destructive consequences.