Electric power system; Lightning protection measures; electric transmission line
introduce
Transmission lines and transmission equipment are often installed in the open air to meet the needs of construction, which has a great impact on the natural environment. For transmission lines, the most important weather impact is lightning strike. When the strong current generated by lightning strike is connected to the transmission line, it may cause the transmission line to be damaged, affect the normal operation of the power system, and may also cause a fire or bring corresponding loss of life and property. Due to China's vast territory and large power demand, the installation quality of transmission lines is different due to different environmental, geological and economic factors, resulting in different accidents and causes. Because the reason is not clear, it is relatively difficult to study the lightning protection technology of transmission lines.
The following will be a scientific summary of the causes of lightning strikes on transmission lines in different regions. Only by clarifying the cause of the accident can we analyze the specific problems and put forward further lightning protection measures.
1, Cause Analysis of Lightning Damage
Lightning strike of transmission line is overvoltage caused by Lei Yun discharge, and the discharge channel is established through transmission tower, which leads to insulation breakdown of transmission line. This overvoltage, also known as atmospheric overvoltage, can be divided into direct lightning overvoltage and induced lightning overvoltage. Lightning strike is mainly through the establishment of discharge channels, so that the earth-induced charges neutralize the heterogeneous charges in the thundercloud, so lightning strike is directly related to the integrity of grounding devices.
Transmission lines are basically affected by direct lightning, which can be divided into counterattack and shielding failure, seriously endangering the safe operation of lines. Before making lightning protection measures, we should systematically master the main types of lightning strikes in this area. Only in this way can specific problems be analyzed and lightning protection measures be reasonable and effective.
At the same time, counterattack lightning is also a common phenomenon, which is mainly related to insulation strength and tower grounding resistance, and generally occurs in the weak insulation stage without fixed flashover. Therefore, measures should be taken to reduce the grounding resistance of towers, strengthen insulation and improve the lightning withstand level. Lightning shielding overvoltage is the lightning overvoltage generated when lightning bypasses the lightning conductor and directly hits the conductor. It is mainly related to the amplitude of lightning current, the lightning protection mode of the line, the height of the tower and the special terrain, which mainly occurs on both sides. At present, the main measures taken to shield lightning overvoltage are to reduce the protection angle of lightning rod and install lightning arrester.
Through the accumulation of many years' work experience and the study of relevant data, it can be basically determined that the lightning strike probability is different in different terrain, and the specific types of lightning strike are also different accordingly. For example, affected by terrain factors, the effective height increases, and the shielding failure rate of mountain lines is higher; The route in plain and hilly areas is mainly counterattack. Therefore, different lightning protection measures should be taken according to different terrain.
The probability and types of lightning strikes are caused by many reasons. Only through on-the-spot investigation and analysis of specific data can the types and probability of lightning strike be basically determined, so the staff need to conduct necessary on-the-spot investigation.
2, lightning protection measures
The formulation of lightning protection measures is mainly to reduce the probability of transmission lines being struck by lightning and ensure the safe and effective operation of power system. The probability of transmission lines being struck by lightning varies from place to place. Therefore, the formulation of lightning protection measures is a complex and systematic work, which needs to consider the geological conditions, climate conditions and soil composition of the area where the line passes. Socio-economic conditions and so on. At the same time, the formulation of lightning protection measures should also proceed from the economic point of view, try to reduce unnecessary economic expenditure and save the investment cost of power system. Therefore, in addition to installing the necessary lightning protection devices, we should also pay attention to the following specific links.
2. 1 Reduce the protection angle of external lightning conductor or adopt negative angle protection.
Ignoring the influence of hillside on lightning protection angle will lead to the lightning protection angle of tower not meeting the actual requirements of lightning protection design, increase the number of line flashovers and affect the safe operation of power grid. In view of the situation that running lines in mountainous areas are vulnerable to shielding failure, it is suggested that the effective shielding angle formula be used to calculate and verify the effective protection angle of towers, so as to take corresponding measures in design to reduce the probability of lightning shielding failure under the condition of large protection angle.
2.2 Strengthen insulation and adopt unbalanced insulation.
The number of insulators should be increased in areas with strong lightning activity, large span over towers and many incoming lines. By appropriately increasing the number of insulator pieces and increasing the distance between conductor and lightning rod, the purpose of strengthening insulation is achieved. With the continuous emergence of double-circuit lines on the same tower, when ordinary lightning protection measures can not meet the requirements, unbalanced insulation can prevent double-circuit lines from tripping at the same time when they are struck by lightning. The principle is that the number of insulators in the two circuits is different. When lightning strikes, the line with less insulators flashover first, and the flashover conductor is equivalent to a lightning rod, which increases the coupling effect on another line conductor, improves the lightning withstand level of another line, and keeps it from flashover and maintains continuous power supply.
2.3 Handling of grounding device
A. The lightning withstand level of high-voltage transmission lines decreases with the increase of grounding resistance of towers. In areas with high soil resistivity, the form of replacing grounding grid and the method of replacing soil should be chosen to reduce the resistance. Before the thunderstorm season, the grounding resistance of the tower should be measured in accordance with the methods required by the regulations for the lines in lightning-prone areas; B. The buried depth of grounding device should be greater than 0.6m As the buried depth of grounding device is underground, the staff are required to do anti-corrosion work well, and at the same time, regular inspection should be conducted to ensure that the grounding device is not damaged by human beings. At the same time, the excavation of underground lines also needs corresponding quality supervision. Only those who meet the quality standards can install the next line. For the unqualified excavation work, it should be pointed out in time and rectified within a time limit, and the construction can continue only after the rectification is qualified. C. To reduce the grounding resistance of the tower, it is also necessary to ensure the good connection of overhead ground wire, grounding down lead and grounding grid.
2.4 Installation of Lightning Arrester
The erection of lightning conductor has reduced the induced overvoltage on the conductor to a certain extent, but it has not been completely eliminated. Therefore, it is necessary to install lightning arrester to discharge the lightning to the earth, so as to limit the overvoltage and ensure the safety of transmission lines and equipment.
2.5 Install automatic reclosing device.
Because of the self-recovery performance of line insulation, most lightning flashover accidents can be eliminated by themselves after line tripping. Therefore, the installation of automatic reclosing device has a good effect on reducing the lightning accident rate of lines.
2.6 Strengthen lightning monitoring to eliminate hidden dangers of equipment.
In lightning flashover, single-phase flashover is the most common, and the flashover position is also one tower, but sometimes several bases flashover at the same time or several bases flashover at intervals. Therefore, in the fault inspection, the fault inspection can not be ended only when one fault point is found, but the whole section should be inspected. The lightning location system can be applied to 1 10kV and above transmission lines. Lightning location system is a fully automatic real-time lightning monitoring system. The biggest advantage of the system is that it can realize mechanical automatic lightning monitoring, and can accurately and quickly locate the fault point according to the monitoring results, which improves the work efficiency. At the same time, people can systematically analyze and sum up experience according to the data of automatic monitoring, and the data generated by automatic system has higher accuracy and reliability. Finally, installing automatic monitoring system can reduce the workload of staff and save the labor cost output of power system.
3. Conclusion
To sum up, lightning strike on transmission lines is an objective phenomenon, which can be reduced by itself, but cannot be eliminated. First of all, people should establish a correct awareness of lightning strike and improve their awareness of lightning protection safety. Secondly, they should conduct on-the-spot investigation on transmission lines in different areas and put forward reasonable lightning protection measures. Finally, the installation of lightning protection measures should be carried out under the basic guiding ideology of overall consideration to ensure that lightning protection measures can not only ensure the safe operation of the power system, but also save the capital investment of the power system. This requires the vast number of electric power workers to constantly sum up experience and learn the necessary knowledge and theory. Only in this way can the lightning protection technology of transmission lines be gradually improved.
refer to
[1] Ding Songsheng. Discussion on Lightning Protection of High Voltage Transmission Lines [J]. Scientific and Technological Information in 2007 (10)
[2] Guo Chunyu. Analysis of Lightning Protection Measures for Transmission Lines [J]. Private Science and Technology, 2009( 10)
[3] Mao. Analysis on Lightning Damage of Transmission Lines and Research on Lightning Protection Technology [J]. China Science and Technology Information, 2007( 16)