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Protection mode of signal SPD

In order to ensure the safe and reliable operation of the electronic information system, the interference that occurs in the electronic information system must be limited to below the interference limit of the equipment. However, interference and damage limits for equipment are largely unknown. In order to prevent information technology equipment from being disturbed or even damaged, the signal SPD must limit the interference effect to below the surge immunity value of the protected equipment. Compared with the selection of protectors in the power system, the voltage and frequency of the signal SPD in the 220/380V system are fixed, while the signals transmitted in the information system have different types. Every electrical parameter of the transmitted signal contains the information actually transmitted, so the installation of the power SPD and the signal SPD in the electronic information system cannot affect the signal transmission.

   Two protection modes for signal SPD:

   1. Parallel pair

   Generally, the two signal lines of twisted pair and parallel line pair are completely balanced to the ground, so their lightning protection requirements are exactly the same, and the principle of lightning protection of multiple pairs of parallel lines is exactly the same as that of a pair of parallel lines, as shown in Figure 2 -1 shown. For a pair of parallel communication lines, it is generally required that any pair of wires should be considered for lightning protection to the ground and between wires. For those parallel wire pairs that connect precision equipment and require high lightning protection, multi-level lightning protection circuits should also be considered.

Decoupling Current Limiting Components

Figure 2-1 Parallel pair SPD principle

2. Coaxial cable

   Ordinary coaxial cables only have a metal core wire and a metal sheath layer. The lightning protection of this type of coaxial cable is mainly concentrated between the core wire and the metal sheath layer. Some coaxial cables also have a grounding shielding layer outside the core wire and the metal sheath layer. The lightning protection of this coaxial cable needs to take protective measures between the sheath and the shielding layer in addition to the core wire and the outer sheath layer. . Figure 2-2 shows the lightning protection principle of the coaxial cable.

(a) Principle of coaxial lightning arrester circuit with shielded ground wire

(b)  Principle of coaxial lightning arrester circuit without shielded ground wire

Figure 2-2 Principle of coaxial lightning protection circuit