Principle and application of lightning arrester in power system - News - Global IC Trade Starts Here Free

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Lightning consists of high-energy low-frequency components and highly permeable high-frequency components. It mainly adopts two forms, one is to directly transmit lightning-induced damage equipment through metal pipelines or ground lines; the other is lightning electromagnetic pulse of lightning passage and discharge passage to sense metal pipeline or ground line to generate waves in various coupling ways Inrush damage device. Most of the lightning loss is caused by this induction. For electronic information equipment, the hazard mainly comes from the coupling energy of the lightning electromagnetic pulse caused by lightning, and the transient surge generated by the following three channels. This paper mainly analyzes the application of lightning protection devices in power systems.

First, the basic principle of lightning protection Lightning and other strong interference on the communication system damage and the consequences are serious, lightning protection will become necessary. Lightning consists of high-energy low-frequency components and highly permeable high-frequency components. It mainly adopts two forms, one is to directly transmit lightning-induced damage equipment through metal pipelines or ground lines; the other is lightning electromagnetic pulse of lightning passage and discharge passage to sense metal pipeline or ground line to generate waves in various coupling ways Inrush damage device. Most of the lightning loss is caused by this induction. For electronic information equipment, the hazard mainly comes from the coupling energy of the lightning electromagnetic pulse caused by lightning, and the transient surge generated by the following three channels. Metal pipeline channels, such as water pipes, power lines, antenna feeders, signal lines, aviation obstacle light leads and other surges; ground channels, ground power counterattack; space channels, electromagnetic energy of the electromagnetic group.
The surge of the metal pipeline channel and the ground potential counterattack of the ground channel are the main causes of the damage of the electronic information system. The most obvious form of damage is the lightning loss caused on the power line, so it needs to be the focus of anti-expansion. Lightning protection will be a systematic project due to the intrusion of lightning into the electronic information system. The central content of lightning protection is venting and balancing.
1. Venting is to discharge the energy of lightning and lightning electromagnetic pulses through the earth, and should conform to the hierarchical principle, that is, as much as possible and as far as possible, the excess energy is discharged into the ground before being introduced into the communication system; Lightning energy is weakened according to the level of protection of lightning protection. The lightning protection zone, also known as the electromagnetic compatibility zone, divides the environment into several zones according to the different sensing strengths of lightning and lightning electromagnetic pulses by people, objects and information systems: LPZOA zone, all objects in the zone may be directly struck by lightning. Therefore, all the special bodies may guide away all lightning currents, and the electromagnetic field in this area is not attenuated. In the LPZOB area, it is impossible for each object in the area to be directly struck by lightning, but the electromagnetic field in this area is not attenuated. In the LPZ1 area, it is impossible for each object in the area to be directly struck, and the current flowing to each conductor is further reduced than the LPZOB area. The electromagnetic field attenuation and effect depend on the overall shielding measures. Subsequent lightning protection zones (LPZ2 zone, etc.) should further introduce the subsequent lightning protection zone if it is necessary to further reduce the guided current and electromagnetic field. The requirements of the lightning protection zone should be selected according to the environmental zone required by the system to be protected. condition. The higher the protected area number, the lower the expected interference energy and interference voltage. In the modern lightning protection technology, the setting of the lightning protection zone is of great significance, and it can guide us to implement the technical measures such as shielding, grounding, and connection of electricity.
2. Equilibrium is to keep the potential difference of each part of the system not enough to cause damage, that is, the potential of all metal conductors in the environment where the system is located and the system itself remains substantially equal in the transient phenomenon, which is essentially based on equalization equipotential bonding. A potential compensation system consists of a reliable grounding system, a metal conductor for equipotential bonding and an equipotential bonding device (lightning protection). This potential compensation system can be quickly protected in the short time of transient phenomena. An equipotential is established between all of the conductive components in the area in which the system is located, and these conductive components also include active conductors. With this complete potential compensation system, an equipotential region can be formed in a very short time, and this region may have a potential difference of several tens of kilovolts with respect to the distance. It is important that there is no significant potential difference between all conductive components within the area where the system to be protected is located.
3. The lightning protection system consists of three parts, each part has its important role, there is no substitute. The external protection consists of the lightning receptor, the down conductor and the grounding body, which can directly discharge most of the lightning energy into the underground vent. Transition protection consists of reasonable shielding, grounding, and wiring to reduce or block the induction introduced through each intrusion channel. Internal protection, consisting of equalizing equipotential bonding and overvoltage protection, can equalize the system potential and limit the overvoltage amplitude.
Second, the role of lightning arrester and technical parameters lightning arrester, also known as equipotential connector, overvoltage protector, surge suppressor, surge absorber, lightning protection, etc., lightning protection for power line protection It is called a power surge protector. In view of the current lightning damage characteristics, lightning protection is especially in lightning protection and rectification, and the lightning protection protection scheme is the simplest and most economical lightning protection solution. The main function of the lightning arrester is to keep the potential at both ends consistent or limited to a range when transferring transients, and transfer excess energy on the active conductor.
Entering the underground venting is an important part of achieving equal pressure equipotential bonding. Some main technical parameters of the lightning arrester: rated working voltage, rated working current, and current carrying capacity of the special batch type parallel power supply lightning arrester. Throughflow capability, the ability of the lightning arrester to transfer lightning current, in kiloamperes, is related to the wave open type. The lightning arrester can be divided into a lightning protection device capable of preventing direct lightning strikes and a lightning protection device for preventing lightning. Lightning protection against lightning strikes is usually used for line protection that may be struck by direct lightning strikes, such as the protection of the LPZOA area and the LPZ1 area. The current waveform is tested and expressed with a 10/35 μs current waveform. Lightning protection against lightning is usually used for line protection that cannot be struck by direct lightning strikes, such as the protection of the LPZOB area and the LPX1 area and the LPZ1 area. Using 8/20μs current waveform test and indicating its current-capacitance response time, the time required for the lightning arrester to control the transient phenomenon is related to the waveform property. Residual voltage, the voltage limiting capability of the lightning arrester for transient phenomena, related to the magnitude and waveform properties of the lightning current.
Third, the choice of lightning protection device based on the protection of the lightning protection device to achieve the desired results, should pay attention to "reasonably install the appropriate lightning protection device in the right place", the choice of lightning protection 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 of the lightning protection device 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 10/35μs 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 struck by a direct lightning strike, the lightning current entering the protected area 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.
3. The subsequent evaluation mode is used to evaluate the distribution of lightning current 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 numerical value. It is generally required that the power supply lightning arrester used in the subsequent lightning protection zone has a flow capacity of less than 20 kA (8/20 μs), 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. The serial-to-parallel is a concept based on many applications in modern lightning protection, and the protection level is differentiated (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. The series-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 and 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 operating voltage is based on the rated voltage of all components installed in the circuit. Serial-type lightning arresters also need to pay attention to their rated current.
5. Other factors affecting the distribution of lightning current on the electronic line: a reduction in 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. When the power supply cable is connected to multiple users, the effective impedance is reduced, and the distribution current is increased. 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.
Fourth, the installation of lightning protection 1. Power line should achieve multi-level protection, multi-level protection is based on each lightning protection zone, the lightning energy is gradually reduced (energy distribution), so that the voltage limits of each level match each other, and finally Limit the overvoltage value to the insulation strength of the device (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. The wire in the minefield is connected to the lightning protection zone at the same time. 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 child's lightning device, if you do not pay attention to energy distribution, you may introduce more lightning energy into the protection area. This requires that the lightning arrester should be selected according to the aforementioned evaluation mode. Generally, the lightning arrester has the characteristics of higher lightning current and higher residual voltage. The lightning current flowing through the non-level lightning arrester after energy distribution is extremely small, which is beneficial to voltage limitation. 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 arresters is about 15m, which is suitable for the 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, it is not suitable to use the cable itself for decoupling. Special decoupling devices can be used, 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 that the lightning arrester must be installed in a hierarchical manner.
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, reduce the length of the cable by changing the wiring of the protected wire to the equipotential bonding bar (grounding point).
The output line of the lightning arrester is close to the input line and the ground line, and is 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 protection device should be connected to the equipment protection ground.