Talking about the Five Rules of Selecting Lightning Arrester
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For lightning protection based protection, to achieve the desired effect, attention should be paid to “arranging suitable lightning protection devices in a suitable placeâ€. The selection of lightning protection devices is very important.
1. The distribution of lightning currents between various facilities entering a building is as follows: about 50% of the lightning current is discharged into the ground via an external lightning protection device, and another 50% of the lightning current will be within the metal material of the entire system. Assign. This evaluation model is used to estimate the current capacity of the SPDs and the metal wire specifications for equipotential bonding at the junction of 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 and metal structures 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 hit 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, lightning arrester discharge branch, and user side line. If the impedance at both ends is the same, the power line is allocated to half of the direct lightning current. In this case, a lightning arrester with a lightning protection function must be used.
Subsequent assessment models are used to assess the distribution of lightning currents at the junction of the LPZ1 zone at the later time. 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-type 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 features: 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 coordination. Reduce the rate of rise of transient interference to achieve low residual voltage and long life and extremely fast response time.
4. The selection of other parameters of the lightning protection device depends on the level of the lightning protection zone where each protection object is located. The operating voltage of the lightning protection device 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 wire: The reduced grounding resistance of the transformer will increase the distribution current in the electronic wire. 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 the power supply, the temporary flow of the thunder mainly flows into the power line, which is why most of the lightning damage occurs at the power line.