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1. The power line should achieve multi-level protection. The multi-level protection is based on the lightning protection area. The lightning energy is gradually weakened (energy distribution), so that the voltages at all levels are matched with each other, and finally the overvoltage value is limited to the equipment. Within the insulation strength (voltage matching).
Multi-level protection becomes necessary in the following cases: failure of a certain level of lightning protection or failure of a certain lightning protection unit. The residual voltage of the lightning arrester does not match the insulation strength of the equipment, and the cable has a long length in the building.
2. Cable protection in almost all cases should be divided into at least two levels. The same level of lightning protection may also contain multi-level protection (such as series-type lightning protection). In order to achieve effective protection, a lightning arrester can be installed at each lightning protection zone interface. The lightning protection device can be used for a single electronic device, or a space with multiple electronic devices, all passing through the space shield. minefield wires have simultaneous access through the lightning arrester in the interface region. In addition, the protection range of the lightning arrester is limited. Generally, the protection effect is degraded after the distance between the lightning protection device and the equipment line exceeds 10 m. This is because the reflection between the lightning protection device and the equipment to be protected is reflected by the reflection. The voltage, whose amplitude is proportional to the line length and load impedance.
3. In multi-level protection using a power surge protector, if you do not pay attention to energy distribution, you may introduce more lightning energy into the protection zone. This requires that the lightning arrester should be selected according to the aforementioned evaluation mode. SPD has generally by the lightning current, the higher the residual pressure characteristics, flowing through the final stage after the lightning energy distribution lightning current is very small, in favor voltage limiting. Note that it is dangerous to use a lightning arrester that only selects a low response voltage for the final stage protection without considering the voltage matching.
The key to achieving energy distribution and voltage matching is to utilize the inductive reactance of the cable itself between the two-stage arrester. The inductive reactance of the cable itself has a certain hindrance to the burying current and the voltage dividing effect, so that the lightning current is more distributed to the front stage bleed. Generally, the cable length between the two-stage lightning arrester is about 15m, which is suitable for the situation that the protective ground wire is closely attached to other cables or is in the same cable. The length of the branch line on the cable has an impact on the required length of the cable. When the protection ground line has a certain distance from the protected cable (>1m), the cable length is required to be greater than 5m. In some cases where the two-stage lightning protection zone interface is not suitable for the decoupling of the cable itself, or the cable length is short, a special decoupling device can be utilized, and there is no distance requirement.
4. Decoupling devices are important measures to achieve energy distribution and voltage coordination. The following materials can be used as decoupling devices: cables, inductors and resistors.
The series-parallel power supply lightning arrester is a combination of lightning protection devices that considers energy distribution and voltage matching and uses a filter as a decoupling device, and is suitable for various applications.
5. In some extreme cases, the installation of a lightning arrester may increase the possibility of equipment damage and must be eliminated; such a situation occurs. The lightning protection device protects several lines, and the lightning arrester on one of the lines fails or the response speed is too slow. This can cause common mode interference to translate into differential mode interference and damage the device. This requires multi-level protection and attention to the maintenance of the arrester. The lightning protection device is installed without considering the lightning protection zone, energy coordination and voltage distribution. For example, only one lightning protection device is installed at the front end of the device. Because there is no front stage protection, a strong lightning current will be attracted to the front end of the device, resulting in The residual voltage of the lightning arrester exceeds the insulation strength of the equipment. This requires lightning protection must be installed according to the principle of hierarchy.
6. In other cases, incorrect installation will result in the device not being effectively protected. When the lightning protection device is too long and the lightning protection device is working, the voltage caused by the inductive reactance on the connecting line will be extremely high, and the voltage applied to the device will still be dangerous. This problem is more in the application of the final lightning protection device. obvious. The solution to this problem is to use a short connecting line. It is also necessary to use two or more separate connecting lines to share the magnetic field strength and reduce the voltage drop. The single-line thick connecting line has no effect. If necessary, by changing the wiring line to be protected, so that it is close to the equipotential bonding strip (ground point) to reduce cable length.
Mine output line and the input line, a ground line close, laid side by side. This situation has a serious impact on the series-type lightning arrester. When the output line (protected line) and the input line (unprotected line) and the ground line of the series-connected power supply lightning arrester are laid close to each other, a transient surge is induced in the output line, although its intensity is smaller than the original. But it can still be dangerous. The solution to this problem is to lay the input line, the ground line and the output line separately or vertically, to minimize the length of the parallel laying and to open the laying distance.
The lightning arrester grounding wire is not connected to the protected ground of the protected equipment, that is, a separate lightning protection grounding is adopted. This will cause dangerous voltages between the protected line and the equipment protection ground during transients. The solution to this problem is that the grounding of the lightning arrester should be connected to the equipment protection ground.
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