5 rules for lightning protection
In order to achieve the desired effect based on the protection of the lightning arrester, it should be emphasized that "the appropriate lightning arrester is properly installed in the right place", and the choice of the lightning arrester is very important.
1. The distribution of lightning current between various facilities entering the building is as follows: about 50% of the lightning current is discharged into the ground by an external lightning protection device, and another 50% of the lightning current will be in the metal material of the whole system. Make an assignment. This evaluation mode is used to estimate the flow capacity and the specification of the metal wire for the equipotential bonding at the junction of the LPAOA zone, the LPZOB zone and the LPZ1 zone. The lightning current at this location is a 10/35 s current waveform. In the case of distribution of lightning current in each metal substance: the amplitude of lightning current of each part depends on the impedance and inductive reactance of each distribution channel, and the distribution channel refers to metal substances that may be distributed to lightning current, such as power lines, signal lines, Metal pipe grades and other groundings such as water pipes and metal frames are generally estimated only by their respective grounding resistance values. In the case where it is not certain, it can be considered that the resistance is equal, that is, the metal lines are evenly distributed.
2. When the power line is introduced overhead, and the power line may be hit by a direct lightning strike, the lightning current entering the protection zone of the building depends on the impedance and inductive reactance of the external lead line, the lightning arrester branch and the user side line. If the impedance of the inner and outer ends is the same, the power line is distributed to half of the direct lightning current. In this case, a lightning arrester with direct lightning protection must be used.
Subsequent evaluation models are used to assess the distribution of lightning currents at the junction of the protected area in the LPZ1 area. Since the insulation resistance of the user side is far greater than the impedance of the lightning arrester branch and the external lead line, the lightning current entering the subsequent lightning protection zone will be reduced, and no special estimation is needed in the value. Generally, the power supply lightning protection device used in the subsequent lightning protection zone has a flow capacity of 20 kA (8/20 s) or less, and does not require a lightning protection device with a large flow capacity. The selection of lightning protection devices in the subsequent lightning protection zone should consider the energy distribution and voltage coordination between the various stages. When many factors are difficult to determine, it is a good choice to use a series-connected power supply lightning arrester.
3. The serial-parallel type is a concept proposed according to the characteristics of many applications in modern lightning protection and the level of protection scope (compared to the traditional parallel lightning protection device). Its essence is an effective combination of multi-stage arrester and filter technology through energy matching and voltage distribution. Serial-type lightning protection has the following characteristics: it is widely used. Not only can it be applied as usual, but also suitable for places where the protected area is difficult to distinguish. The partial pressure and delay of the induced decoupling device under transient overvoltage to help achieve energy coordination. Slows the rate of rise of transient disturbances to achieve low residual voltage and long life with extremely fast response times.
4. The other parameters of the lightning arrester depend on the level of the lightning protection zone where each protected object is located. The working voltage is based on the rated voltage of all components installed in the lead circuit. Serial-type lightning arresters also need to pay attention to their rated current.
5. Other factors affecting the distribution of lightning current of the electronic line: the reduction of the grounding resistance of the transformer terminal will increase the current distributed in the electron line. An increase in the length of the power supply cable will result in a reduction in the distribution current in the power line and a balanced current distribution among the several conductors. Too short cable lengths and too low neutral impedance will cause current imbalance, causing differential mode interference. Connecting the power supply cable to multiple users will reduce the effective impedance, resulting in an increase in the distribution current. In the continuous power supply state, the temporary flow of the lightning mainly flows into the power line, which is the reason why most lightning losses occur at the power line.
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