The application effect of line arrester manufacturers in line lightning protection
In order to reduce the damage caused by lightning strikes to transmission lines, installing line arresters in vulnerable sections of transmission lines can improve the lightning resistance level of the lines. In view of this, the basic principles of lightning protection of line arresters and the preparations before installation are introduced. We also tracked and analyzed some of the lightning arresters that have been connected to the network in recent years. Since the original lightning-struck pole towers were installed with line-band series gap arresters, no lightning tripping has occurred in the towers so far.
In order to reduce the impact of lightning strikes on the safe operation of transmission lines, a variety of lightning protection measures are usually taken, mainly including: reducing the ground resistance of the tower; erecting lightning protection wires; improving the line insulation level; installing coupling ground wires, etc. However, there is still no effective solution to the problem of preventing the impact of shielding lightning on lines and the lightning protection of line poles and towers with high soil resistivity. For this reason, there is an urgent need to take some new technical measures to improve the lightning resistance level of line poles and towers to reduce the lightning tripping rate.
With the application and development of synthetic insulation materials in lightning protection technology, many countries, such as the United States and Japan, install lightning arresters in vulnerable sections of transmission lines to improve the lightning resistance level of the lines and reduce the lightning tripping rate.
1. Basic principles of lightning protection with line arresters
For poles of average height, the lightning resistance level of the line is mainly related to four factors: 50% discharge voltage of the line insulator; whether there is an overhead ground wire; lightning current intensity; and the grounding resistance of the pole. The 50% discharge voltage of the insulator is certain, and the lightning current intensity is related to the geographical location and climatic conditions. When lightning arresters are not installed, to improve the lightning resistance level of transmission lines, it is often necessary to use overhead ground wires and reduce the ground resistance of the tower. In mountainous areas, it is very difficult to reduce the grounding resistance, and shielding is easy to occur. This is why the lightning tripping rate of transmission lines in mountainous areas is high.
Line arresters are connected in parallel with line insulators. When the arrester operates during a lightning strike, the residual voltage of the arrester is lower than 50% of the discharge voltage of the insulator string. Even if the lightning strike current increases, the residual voltage of the arrester only increases slightly, and the insulator will still not flashover. After the lightning current passes, the power frequency freewheeling current flowing through the arrester is only milliamp level. The power frequency freewheeling current flowing through the arrester goes out at the first zero crossing, the circuit breaker will not trip, and the system returns to normal state. Figure 1 illustrates the relationship between the volt-second characteristics of the line arrester and the volt-second characteristics of the insulator. During shielding, the volt-second characteristic of the arrester is more than 15% lower than that of the insulator, and during counterattack, it can be more than 20% lower.
2. Preparation work before installation of line arrester
Line arresters are mainly used to reduce the lightning tripping rate of power transmission lines, rather than to limit operating overvoltage. Therefore, line arresters should be of the type with series gaps, and preparations must be made before installation.
2.1 Carry out specified electrical tests
The arrester manufacturer should conduct specified electrical tests before installation and operation. Measure its insulation resistance, voltage U1mA at DC 1 mA and leakage current at a voltage of 75% U1mA. The measurement results should be compared with the factory data without significant changes, and should comply with the regulations. During the installation process, the series gap must be installed as required. After installation and operation, the action of the counter must be checked and recorded so that other lines can be analyzed and compared in the future.
2.2 Fixed-point principles for installing line arresters
a) Line operating experience. Analyze the operation status of the line since it was put into operation to determine the poles and towers that are susceptible to lightning strikes, and analyze and determine whether it is a bypass or a counterattack.
b) The terrain, landforms and adjacent impacts that the line passes through. On-site survey of the sections that the line passes through, especially the lines that pass through fish ponds, rivers, and mountains, etc., is important to analyze, and record the sections where the line poles and towers may be struck by lightning due to terrain and geomorphological conditions. Generally, the poles and towers passing through this section will be given priority.
c) Grounding resistance of towers and spacing between adjacent towers. Based on the grounding resistance requirements and actual grounding resistance values of the towers designed when the line is put into production, towers that do not meet the design requirements for grounding resistance are identified and modified. Priority is given to towers that cannot meet the requirements due to geological conditions.
d) Based on the above factor analysis and traffic conditions, determine the best location for line arrester installation.
Yichang Hengyuan Technology Co., Ltd. specializes in the production of European-style cable joints, plug-and-pull heads, cable branch boxes, American-style elbow joints, high-voltage vacuum circuit breakers, high-voltage load switches, arresters, zinc oxide arresters, tank arresters, over-voltage protectors, counters, monitors, heat-shrinkable cable accessories, Manufacturer of cold shrink cable accessories, T-heads, wall bushings, European cable accessories, American cable joints, transformer neutral point protection devices, fuses, isolating switches, PT cable heads, elbow cable joints, 10kV outdoor terminals, switch cabinets, cable intermediate joints, cable accessories and other products
