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Surge protective device (SPD)

Surge protective device (SPD), also known as surge protective device (SPD), is a kind of surge protective device
An electronic device whose circuit provides security protection. The electrical appliances used to limit the manic overvoltage and discharge the surge current include at least one nonlinear element.
Composition, principle and classification of surge protective device
The basic components of surge protective device are: discharge gap, gas filled discharge tube, varistor, suppression diode, choke coil, etc. According to its operation principle, it can be divided into voltage switch type SPD, voltage limiting type SPD and combined type SPD. Its working principle is to protect the protected equipment or system from damage caused by impact by introducing the transient over-voltage limiting equipment of power line and signal line into the range that can bear, or introducing strong lightning current into the ground.
Main performance and index of surge protective device
Voltage protection level (Up)
The voltage protection level is a parameter representing the voltage performance between the surge protection terminal blocks, which shall be greater than the maximum value of the limiting voltage.
Nominal discharge current (In)
It flows through the surge protector and has a current peak value of 8/20ys waveform. It is used for the class II test of surge protector and the pretreatment test of class 1 and class 1 tests.
Impulse current (limp)
The current defined by the three parameters of current peak value Ipeak, charge quantity Q and specific energy W/R is used for the class experiment of surge protective device. The typical waveform is 10/350us
Classification of lightning protection grade and lightning stroke risk assessment
In the ordinary design, the lightning protection grade is mainly determined according to the importance, use nature and value of the electronic information system.
Selection of surge protective device
Installation position of surge protective device
The distribution line often used in the design is TN-S system, and the installation position of surge protective device in this system is highlighted.
Determination of Impulse Current and Nominal Discharge Current of Power Line Surge Protector
Generally, our design is mainly based on the lightning protection level of building electronic information system, and is determined by referring to Table 2 below.
Selection of Stamping Resistance Rating of Power Distribution System
In the selection of surge protective devices, we should pay special attention to the fact that the distribution box for the equipment room and the electronic information equipment requiring special protection are actually in the position of the distribution line. For example, the distribution box we often distribute power to the strong motor room is a class I load in many buildings, which supplies power directly to the power transformation and distribution substation. According to Table 3, it should be the location of the distribution box, and then combined with 4.2, 4.3 It is required to correctly determine the parameters of power line surge protector. If the lightning protection office in some areas has special requirements, it shall also meet the requirements of the local lightning protection office.
Installation requirements and precautions
1. When the power line surge protector is installed at each position, its connecting wire should be short and straight, and its total length should be less than 0.5m, so that the effective protection level Up/f is less than the equipment impulse withstand voltage rating Uw The first level surge protector shall be installed close to the total equipotential of the incoming line as much as possible, and the second and third level surge protectors shall be installed near the protected equipment as much as possible.
2. If the line length between the first level power surge protector at the entrance and the protected equipment is greater than the value of Lpo or Lpi, the surge protector shall be added at the protected equipment or at the distribution box of the distribution line. If the line length between the power supply surge protector and the protected equipment at the distribution box is greater than Lpo or Lpi value, a tamper protector shall be added at the protected equipment. When surge protector is added at the protected electronic information equipment, Up shall be less than the rated value of equipment impulse withstand voltage Uw, with a 20% margin.
3. In order to improve the reliability of surge protective device, multi-level coordination can be carried out, or coordination with other equipment can be carried out. For example, coordination with RCD can effectively prevent the occurrence of personal safety accidents; It can ensure the continuity of power supply when used together with over-current protector.
4. If the surge protective device is installed on the interface where the power line passes through the lightning protection zone, the number of surge protective devices installed shall also match the number of lightning protection zones divided. In multistage SPD protection, the installation number should be accurately calculated and the installation location carefully selected, so that the installation location and the installation number can be accurately matched, so that the lightning current can be shared according to the energy tolerance of each SPD, and the lightning can be guided to the ground, so that the original threat value of lightning can be reduced below the damage immunity of the protected equipment, and the effect of protecting the electronic system can be achieved.
5. If there is no shielding measure for the overvoltage protection level between information equipment in the building, the induced voltage circuit shall be designed. If 80% of the overvoltage withstand level of the protected equipment exceeds the specified 10%, the voltage amplitude shall be increased.
6. If there is no lightning protection device in the building, when the building with information system needs to be equipped with SPD protection, the lightning protection network should be used to shield the building.
epilogue
With the application of surge protector in electronic information products, electronic equipment is protected from the damage of lightning electromagnetic pulse, which improves the security and reliability of electronic information equipment and facilities in the power supply system, and promotes the implementation of smart grid

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