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For lightning protection based protection, to achieve the desired effect, attention should be paid to “appropriate installation of appropriate lightning protection devices in suitable placesâ€. The selection of lightning protection devices is very important.
1. The distribution of lightning currents between various facilities entering the building is as follows: approximately 50 [%] of the lightning current is discharged into the ground via external lightning protection devices, and another 50 [%] of the lightning current will be in the entire system of the metal. Distribute within the substance. This evaluation model is used to estimate the current capability of the SPDs and the metal wire specifications for equipotential bonding at the junction of the LPAOA, LPZOB, and LPZ1 regions. The lightning current at this point is a 10/35μs current waveform. In the case of lightning current distribution among various metal substances: The lightning current amplitude of each part depends on the impedance and inductive reactance of each distribution channel. The distribution channel refers to metal materials that may be allocated to lightning currents, such as power lines, signal lines, Metal pipes and other groundings such as water pipes, metal structures, etc., can generally be roughly estimated only by their respective grounding resistance values. In the case of uncertainty, it can be assumed that the connections are equal in resistance, that is, the metal circuits distribute the current evenly.
2. When a power line is introduced overhead and the power line may be struck by a direct lightning strike, the lightning current entering the protected area within the building depends on the impedance and inductive reactance of the external route, the arrester discharge branch, and the user side route. If the impedance at both ends is the same, the power line is allocated half of the direct lightning current. In this case, a lightning arrester with a lightning protection function must be used.
3. Subsequent assessment models are used to assess the distribution of lightning currents at the junction of the LPZ1 zone after the protection zone. Since the insulation impedance at the user side is much larger than the impedance of the discharge branch of the lightning arrester and the external lead line, the lightning current entering the subsequent lightning protection zone will be reduced, and no special estimation is needed in numerical value. It is generally required that the lightning protection device used in the subsequent lightning protection zone has a current flow capacity of 20 kA (8/20 μs) or less, and no lightning protection device with large flow capacity is required. The selection of surge arresters in the subsequent lightning protection zone should consider the energy distribution and voltage coordination between each level. When many factors are difficult to determine, it is a good choice to use series-parallel lightning protection devices. The serial-parallel type is a concept proposed based on the characteristics of many applications in modern lightning protection and the protection scope level distinction (as opposed to the traditional parallel lightning arrester). Its essence is the effective combination of multi-level discharger and filter technology with energy matching and voltage distribution. Serial-type lightning protection has the following characteristics: Wide range of applications. Not only can it be applied routinely, but it is also suitable for sites that are difficult to distinguish in protected areas. Inducing the partial pressure and delay of the decoupling device under transient overvoltage to help achieve energy cooperation. Reduce the rate of rise of transient interference to achieve low residual voltage and long life and extremely fast response time.
4. The choice of other parameters of the lightning protector depends on the level of the lightning protection zone where each object is protected. The operating voltage of the lightning protector is based on the rated voltage of all the components installed in the pilot circuit. Serial and lightning protectors also need to pay attention to their rated current.
5. Other factors that affect the distribution of the lightning current of the electronic line: The decrease of the grounding resistance at the transformer terminal will increase the distribution current in the electronic line. The increase in the length of the power supply cable will reduce the distribution current in the power line and allow a balanced current distribution in several wires. Short cable lengths and too low neutral impedance will cause current imbalance, causing differential mode interference. Multiple users connected to the power supply cable will reduce the effective impedance, resulting in an increase in the distribution current. In the connected state of power supply, the temporary flow of lightning mainly flows into the power line. This is the reason that most of the lightning damage occurs at the power line.
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