Analysis of Lightning Protection and Grounding Technology of Electric Power Distribution System

Knowledge point: Lightning protection power distribution device

In the construction of power distribution network, lightning protection and grounding protection is an important link. The power distribution network has been exposed to the natural environment for a long time, and its own protection ability is weak. It is easily affected by natural environmental factors and suffers from various operational failure problems. Strengthen the protection of distribution network lines and equipment, set up lightning protection grounding equipment and lightning protection grounding wires respectively, appropriately reduce the grounding resistance of distribution equipment, effectively improve the overall lightning protection performance of the distribution network, and provide a basis for the effectiveness of the distribution network. , reliable and safe operation are guaranteed.

0 1 The importance of lightning protection and grounding in power distribution systems

The power supply coverage of power distribution lines is wide, and the power supply overhead lines are long. If the lightning protection measures are not perfect enough, they are easily damaged by lightning strikes, which will cause multiple distribution lines to trip, causing harm to the safety of the power supply and affecting surrounding areas. The lives of local residents and industrial and commercial activities have caused economic losses to power companies. The above characteristics of power distribution lines also make it difficult to complete on-site repair work in a timely manner. During the construction and maintenance of power distribution lines, great attention must be paid to lightning protection measures to ensure the reliability and safety of the power supply system.

0 2 Lightning protection and grounding technology for power distribution systems

2.1 Grounding and lightning protection of distribution lines

The most commonly used technologies in power systems are still lightning protection wires, lightning arresters and other equipment 011 as the main lightning protection measures. The selection and arrangement of these two lightning protection devices need to be distinguished according to the specific conditions of the specific use occasions. In different situations, Different differences will produce different results, which means that this traditional equipment has certain limitations in materials, which also determines the quality of use of the power distribution system, and the effect is not good.

2.2 New ground rod

The limitations and deficiencies in traditional grounding and lightning protection have stimulated research and innovation in this area. Currently, new grounding rods are actively promoted in China. The new grounding rod is made of copper-plated steel as the main material. The length of a single rod can reach 1.22m. It can be assembled with a threaded connector at will and reaches the national standard grounding value. Moreover, this material has strong corrosion resistance and its electrical conductivity is much higher than that of steel. A large amount of cost is required for the initial installation, but there is no need to spend more money on repairs and maintenance in the later period. The material has good performance, long life, and excellent quality. In addition, its small size and diameter make it easy to install and operate, and the construction difficulty is relatively small. Large-scale construction is required and damage to the surrounding environment is avoided. The use of this high-efficiency ground rod significantly improves the safety and stability of the power distribution system.

2.3 Replace new insulators

In the past, porcelain insulators were often used in the construction of power distribution networks. This is because porcelain insulators are relatively low-cost, but they have problems with zero values. After the zero value appears, it is not easy to find, but it will reduce the resistance of the insulator string. The pressure level is greatly affected by the concentration of natural lightning, resulting in flashover. Technicians need to update the insulator strings in the distribution network and install new glass insulators to improve the insulation level of distribution lines, improve flashover conditions and reduce the frequency of faults. Compared with porcelain insulators, glass insulators have a higher actual detection rate. During the installation process, technicians can more clearly detect inferior products, avoid using insulators with substandard quality, effectively eliminate weak current in distribution network lines, and improve distribution The overall capability of the electrical network lightning protection and grounding protection system.

0 3 Lightning protection and grounding optimization of power distribution system

3.1 Strengthen line arrester protection

For a three-phase power supply system, induced lightning overvoltage exists in the three-phase conductors at the same time, and its amplitude and waveform characteristics are basically the same. In this case, under the action of induced lightning overvoltage, there is a high probability that three phases will flashover to the ground simultaneously. The simulation results show that after installing line arresters, under the action of induced lightning, the overvoltage level along the overhead lines is mainly determined by the installation density of the arresters and the tower grounding resistance. The greater the resistance of the tower line when it is grounded, the smaller the line protection and lightning protection range of the line protection arrester. In order to achieve better line protection and lightning protection effect, it is necessary to increase the installation density of the arrester. When setting up arresters, the grounding resistance of the tower needs to be taken into consideration. The two should maintain a positive correlation, that is, the installation density should increase reasonably as the grounding resistance increases. In addition, when using insulated wires, it is also necessary to appropriately reduce the installation density.

3.2 Improve line insulation level

In order to effectively solve the problem of lightning line tripping, the method of strengthening line insulation can be used. The application effect of this method is relatively obvious and has been widely used in practical engineering fields. From the specific implementation point of view, there are two aspects. One is to increase the number of insulators; the other is to use overhead insulated wires, porcelain cross arms, etc. to directly replace bare wires. Under the same conditions and the same level of lightning strike insulation ability of lines, the use of porcelain cross arms can effectively reduce the probability of tripping caused by lightning strikes on different lines. Improving the technical level of bare insulation of transmission lines can improve the lightning protection performance of lines under direct lightning strikes and induced lightning overvoltages. Referring to relevant simulation experiment data results, enhancing insulation will help improve the lightning protection effect under two overvoltage conditions. Affected by lightning overvoltage, there is a positive correlation between the lightning resistance level and the number of insulator pieces, which will help reduce the occurrence of tripping accidents after the arc building rate is reduced. Research shows that the number of insulator sheets directly affects the line performance, which can generally be described by a linear relationship. Increasing insulators can help achieve a higher lightning resistance level and control the tripping rate at a lower level.

3.3 Do a good job in external grounding work

In the grounding construction of poles and towers of contemporary power transmission lines, workers will connect the main grounding grid of the pole tower to nearby areas with low soil resistivity by connecting the grounding pole trunk lines. This can effectively reduce the grounding of the main power grounding grid. Resistor value. What cannot be ignored is that in the process of using this method, cost issues must still be taken into consideration, and the effect of the resistance of the grounding pole itself on the resistance value of the overall building grounding network must be scientifically analyzed. If there happens to be an area with low resistivity within 100 meters nearby, the effect is quite good by connecting the grounding pole trunk line. If the distance is far away, it is not suitable to connect the grounding pole trunk line to avoid excessive cost.

3.4 Install lightning arrester

Lightning arresters are used to prevent lightning waves under high voltage from entering power receiving areas such as substations or power distribution stations and damaging the protected equipment. There are many specifications and types of arresters. The most common type in the early days was the discharge gap. Due to the existence of these discharge gaps, it is easy to fail to automatically extinguish the arc of all arresters. Later, valve type arresters, tube type arresters, and zinc oxide arresters appeared one after another. Generally speaking, arresters can only protect the tower where they are located. Installing arresters on the entire transmission and distribution line will increase the cost and make maintenance difficult. Therefore, arresters can be selectively installed on lines with high lightning strike risk.

3.5 Carry out inspection and maintenance work

The overall effect of inspection work should be ensured in daily work. As the lightning season approaches, daily inspections should be strengthened and comprehensive inspections of lightning protection devices, high-voltage leads and grounding conditions should be strengthened. If any equipment is found to not meet the requirements, it must be repaired in time. , improve the performance of the equipment, especially the replacement of some failed devices. For the grounding device of the distribution network power line system, periodic grounding potential should be used, which is mainly used to compensate equipment with large capacitance and stable load.

HZCJ-400 Lightning impulse test equipment