1. Power line should be multi-level protection, multi-level protection is based on the level of each lightning protection zone, the gradual reduction of energy of lightning (energy distribution), so that the limits of voltage at each level with each other, and ultimately limit the value of over-voltage equipment insulation Within (voltage coordination).
In the following cases, multi-level protection becomes necessary: ​​one grade of lightning protection device fails or one of the lightning protection devices fails. The residual voltage of the lightning arrester does not match the insulation strength of the device, and the length of the cable in the building is long.
2. In most cases, the cable protection should be divided into at least two levels. The same level of lightning protection device may also include multiple levels of protection (such as serial and lightning protection devices). In order to achieve effective protection, lightning protection devices can be installed at the interfaces of lightning protection zones. The lightning protection devices can be used for a single electronic device or a space equipped with multiple electronic devices. All of the protection devices are usually shielded from space. The conductors of the minefield are connected with lightning arresters at the same time through the lightning protection zone interface. In addition, the protection scope of the SPD is limited. Generally, the protection effect will be degraded when the distance between the SPD and the equipment circuit exceeds 10m. This is because of the oscillation caused by reflection on the cable between the SPD and the device to be protected. Voltage, its magnitude is proportional to line length and load impedance.
3. In multi-stage protection using a powered child's lightning device, if attention is not paid to energy distribution, more lightning energy may be introduced into the protected area. This requires that the surge protector should be selected according to the aforementioned evaluation mode. Generally, the lightning arrester has the characteristics of higher lightning current and higher residual voltage. After the energy distribution, the lightning current flowing through the unshielded lightning arrester is extremely small, which is favorable for voltage limitation. Note that it is dangerous to select only low-response voltage surge arresters for final protection without considering voltage matching.
The key to achieving the energy distribution and voltage matching lies in the use of the intrinsic inductance of the cable between the two levels of surge arresters. The intrinsic inductance of the cable has a certain effect on the impediment of the buried current and the partial pressure, so that the lightning current is more distributed to the pre-stage discharge. It is generally required that the length of the cable between the two lightning arresters is about 15 meters, which is suitable for the situation where the protection ground wire and other cables are laid close to each other or in the same cable. The length of the branch line on the cable affects the required cable length. When the protection cable has a certain distance (>1m) from the cable to be protected, the cable length must be greater than 5m. In some cases where it is not suitable to use the cable itself as a decoupling measure, such as the two-level lightning protection zone near the interface or the cable length is short, special decoupling devices can be used, and there is no distance requirement.
4. Decoupling devices are important measures for energy distribution and voltage matching. The following materials can be used as decoupling devices: cables, inductors, and resistors.
Serial-type power supply lightning protector is a combination of lightning protection device that considers energy distribution and voltage matching and uses a filter as a decoupling device, and is suitable for applications in various occasions.
5. In some extreme cases, installing lightning arrestors will increase the possibility of equipment damage and must be eliminated; such situations occur. The lightning protector protects several lines, and the lightning arrester on one line fails or responds too slowly. This may cause common mode interference to be converted into differential mode interference and damage the device. This requires the implementation of multiple levels of protection and attention to the maintenance of lightning protection devices. Irrespective of the lightning protection zone, energy coordination and voltage distribution, the lightning protection device is installed casually. For example, only a lightning protection device is installed at the front of the device. Because there is no protection at the front stage, a strong lightning current will be attracted to the front of the device. The residual voltage of the surge protector exceeds the dielectric strength of the device. This requires that lightning protection devices must be installed in accordance with the principle of hierarchy.
6. In other cases, the wrong installation will prevent the device from being effectively protected. When the surge protector's connection line and the lightning arrester work too long, the voltage caused by the inductive reactance on the connection line will be extremely high, and the dangerous voltage will still be added to the device. This problem is even more serious in the application of the last stage surge arrester. obvious. The solution to this problem is to use short connection lines, but also to use two or more separate connection lines to share the magnetic field strength, reduce the pressure drop, single line thickening the connection line is no effect. If necessary, the length of the connecting wire can be reduced by changing the wiring of the protected wire so as to be close to the equipotential connection row (grounding point).
Lightning protector output line and input line, grounding line close, side by side laying. This situation has a serious impact on serial-type lightning arresters. When the output line (protected line), input line (unprotected line), and ground line of the series-type power supply surge protector are laid close to each other, a transient surge will be induced in the output line, although its strength is smaller than the original. But it can still be dangerous. The solution to this problem is to lay the input line, ground line, and output line separately or vertically, minimizing the length of parallel laying, and pulling away the distance of laying.
The grounding wire of the SPD is not connected to the protection ground of the protected equipment, that is, a separate lightning protection grounding is adopted. This will cause a dangerous voltage between the protected line and the equipment protection ground during transients. The solution to this problem is to connect the lightning protection device to the equipment protection ground.
In the following cases, multi-level protection becomes necessary: ​​one grade of lightning protection device fails or one of the lightning protection devices fails. The residual voltage of the lightning arrester does not match the insulation strength of the device, and the length of the cable in the building is long.
2. In most cases, the cable protection should be divided into at least two levels. The same level of lightning protection device may also include multiple levels of protection (such as serial and lightning protection devices). In order to achieve effective protection, lightning protection devices can be installed at the interfaces of lightning protection zones. The lightning protection devices can be used for a single electronic device or a space equipped with multiple electronic devices. All of the protection devices are usually shielded from space. The conductors of the minefield are connected with lightning arresters at the same time through the lightning protection zone interface. In addition, the protection scope of the SPD is limited. Generally, the protection effect will be degraded when the distance between the SPD and the equipment circuit exceeds 10m. This is because of the oscillation caused by reflection on the cable between the SPD and the device to be protected. Voltage, its magnitude is proportional to line length and load impedance.
3. In multi-stage protection using a powered child's lightning device, if attention is not paid to energy distribution, more lightning energy may be introduced into the protected area. This requires that the surge protector should be selected according to the aforementioned evaluation mode. Generally, the lightning arrester has the characteristics of higher lightning current and higher residual voltage. After the energy distribution, the lightning current flowing through the unshielded lightning arrester is extremely small, which is favorable for voltage limitation. Note that it is dangerous to select only low-response voltage surge arresters for final protection without considering voltage matching.
The key to achieving the energy distribution and voltage matching lies in the use of the intrinsic inductance of the cable between the two levels of surge arresters. The intrinsic inductance of the cable has a certain effect on the impediment of the buried current and the partial pressure, so that the lightning current is more distributed to the pre-stage discharge. It is generally required that the length of the cable between the two lightning arresters is about 15 meters, which is suitable for the situation where the protection ground wire and other cables are laid close to each other or in the same cable. The length of the branch line on the cable affects the required cable length. When the protection cable has a certain distance (>1m) from the cable to be protected, the cable length must be greater than 5m. In some cases where it is not suitable to use the cable itself as a decoupling measure, such as the two-level lightning protection zone near the interface or the cable length is short, special decoupling devices can be used, and there is no distance requirement.
4. Decoupling devices are important measures for energy distribution and voltage matching. The following materials can be used as decoupling devices: cables, inductors, and resistors.
Serial-type power supply lightning protector is a combination of lightning protection device that considers energy distribution and voltage matching and uses a filter as a decoupling device, and is suitable for applications in various occasions.
5. In some extreme cases, installing lightning arrestors will increase the possibility of equipment damage and must be eliminated; such situations occur. The lightning protector protects several lines, and the lightning arrester on one line fails or responds too slowly. This may cause common mode interference to be converted into differential mode interference and damage the device. This requires the implementation of multiple levels of protection and attention to the maintenance of lightning protection devices. Irrespective of the lightning protection zone, energy coordination and voltage distribution, the lightning protection device is installed casually. For example, only a lightning protection device is installed at the front of the device. Because there is no protection at the front stage, a strong lightning current will be attracted to the front of the device. The residual voltage of the surge protector exceeds the dielectric strength of the device. This requires that lightning protection devices must be installed in accordance with the principle of hierarchy.
6. In other cases, the wrong installation will prevent the device from being effectively protected. When the surge protector's connection line and the lightning arrester work too long, the voltage caused by the inductive reactance on the connection line will be extremely high, and the dangerous voltage will still be added to the device. This problem is even more serious in the application of the last stage surge arrester. obvious. The solution to this problem is to use short connection lines, but also to use two or more separate connection lines to share the magnetic field strength, reduce the pressure drop, single line thickening the connection line is no effect. If necessary, the length of the connecting wire can be reduced by changing the wiring of the protected wire so as to be close to the equipotential connection row (grounding point).
Lightning protector output line and input line, grounding line close, side by side laying. This situation has a serious impact on serial-type lightning arresters. When the output line (protected line), input line (unprotected line), and ground line of the series-type power supply surge protector are laid close to each other, a transient surge will be induced in the output line, although its strength is smaller than the original. But it can still be dangerous. The solution to this problem is to lay the input line, ground line, and output line separately or vertically, minimizing the length of parallel laying, and pulling away the distance of laying.
The grounding wire of the SPD is not connected to the protection ground of the protected equipment, that is, a separate lightning protection grounding is adopted. This will cause a dangerous voltage between the protected line and the equipment protection ground during transients. The solution to this problem is to connect the lightning protection device to the equipment protection ground.
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