Analysis and Application of Lightning Protection Measures for 10kV Distribution Lines
The 10 kV distribution line is very complicated. Once a lightning incident is encountered, it is difficult to maintain and manage the power grid, which often results in significant economic losses. Lightning is a common natural phenomenon, and people cannot predict the exact time of its occurrence, thus causing great harm to 10 kV distribution lines. A large number of studies have shown that lightning accidents are mainly caused by the influence of induced lightning overvoltage on the line. Therefore, it is extremely urgent to take lightning protection measures for 10 kV distribution lines to ensure the safe operation of the power grid.
1. Factors affecting 10 kV distribution lines
1. Inductive lightning overvoltage
Induced lightning overvoltage refers to the lightning overvoltage caused by lightning around overhead distribution lines. Although the line is not directly hit by lightning, a lot of electric charges that are opposite to the nature of thunderclouds are induced on the wires. Facts have proved that the number of lightning accidents caused by induced lightning overvoltage accounted for 90% of the total number of faults in the distribution line, and has become the chief culprit in the failure of the 10 kV distribution line. Literature studies have shown that if the wire of a 10 kV distribution line is 10 meters away from the ground and the lightning strike is 50 meters away from the wire, a lightning current of 100 kA will be generated. If the line does not take any lightning protection measures, it will produce a lightning current of 100 kA. The maximum lightning overvoltage can reach 500 kV. If the insulation effect of the 10 kV distribution line is not good, it is easy to be broken down by lightning overvoltage, or even broken.
2. Insulation level
The failure rate caused by the explosion of the insulators in the distribution lines is also very high. The normal operation of the insulator determines the safety of the distribution line, because the insulator determines the insulation level of the 10 kV distribution line. Therefore, the insulator must be maintained well. In the case of long-term operation of 10 kV distribution lines, if the insulators are not regularly inspected, repaired or replaced, once the line is aging, the insulation level of the entire distribution line will be greatly reduced and increased. Probability of lightning accidents.
3. Lightning protection installation
① Installation of transformer. Once the lightning overvoltage reaches more than ten times the rated voltage, it will break down the insulating protective layer around the neutral point of the transformer. At present, most of the lightning arresters of transformers in China are installed on the high voltage side, and the lightning protection on the low voltage side is very weak. The lightning protection of the transformer can be installed in front of the main fuse or in front of the appearance of the distribution line. During the installation process, the low-voltage end of the arrester must be grounded. Since the neutral line behind the current-type protector cannot be grounded repeatedly, otherwise once the protector loses its working ability, the entire line cannot be protected against lightning. Therefore, the grounding line of the low-voltage arrester should be installed on the neutral line of the transformer. Head end.
②Pole switch and knife switch. If a pole switch and a knife switch are installed in a 10 kV power distribution line, the safety and reliability of the line can be greatly improved. But in fact, many lines do not have lightning protection for pole switches and knife switches.
③ Lightning protection for switch cabinets and other units. The 10 kV distribution line contains many units, and each unit is critical. Lightning arresters can be installed in each unit, or they can be installed selectively. Obviously, although the installation cost of the former is high, the safety performance is also high.
2. Analysis of lightning protection measures for 10 kV distribution lines
1. Reduce the probability of explosion and flashover of insulators and improve the insulation level of distribution lines.
If the voltage change is too large, it will adversely affect the operation of the distribution line. In order to improve the lightning protection effect of 10 kV distribution lines, U50% discharge voltage insulators should be used. Because the distance between the loops on the same pole is very small, once it is broken down by lightning overvoltage, the loop grounding phenomenon is easy to occur, which greatly affects the power supply reliability of the 10 kV distribution line. Therefore, all wires must be insulated, and insulation must be set between the insulator and the wires to improve the reliability of the distribution line.
2. Selectively put into operation automatic reclosing
As long as a lightning failure occurs on a 10 kV distribution line, it is difficult to completely repair it. In order to avoid further expansion of lightning failure, automatic reclosing should be installed at certain positions in the line. If the distribution lines are all cables, in this case, automatic reclosing is not required. If the distribution lines are overhead, it is recommended to use automatic reclosing to improve the safety performance of the line. If it is a mixed line of cables and overhead insulated conductors, and the cable accounts for more than 40% of the entire line, you can ignore the installation of automatic reclosing at this time. If it is a cable and overhead bare wire mixed line, and the length of the cable reaches more than 50% of the entire line, automatic reclosing may not be considered.
3. Install a special lightning arrester
The lightning arrester is an important lightning protection device in the 10 kV distribution line, which can play a good role in protecting the entire line. There are many kinds of lightning arresters, the common ones are gap-free arresters and zinc oxide arresters. Under the combined action of power frequency voltage, freewheeling and lightning overvoltage, the gapless arrester is prone to aging, which makes the lightning protection function invalid and greatly affects the power supply reliability of the distribution line. Zinc oxide lightning arrester does not need to be repaired, and can be specially installed to protect the weak links in the distribution line. If the pole switch and the knife switch are also installed with the arrester, the distribution line can be fully protected. Therefore, it is best to install zinc oxide lightning arresters in the 10 kV distribution lines.
4. Install parallel gap insulators
When the insulator flashover occurs, do not let the arc contact the surface of the insulator. If the gap cannot withstand the operating overvoltage, the fault of the distribution line will be enlarged. If a parallel gap is installed in the line, the parallel gap can protect the insulator string. In addition, the operation and maintenance of the parallel gap are extremely convenient and can be directly observed with the naked eye.
5. Reduce equipment grounding resistance in 10 kV distribution lines
The relevant documents stipulate the grounding resistance of power distribution equipment as follows. If the capacity of the power distribution transformer is not greater than 100kVA, the ground resistance of the equipment should not be greater than 10 ohms; if the capacity of the power distribution transformer exceeds 100kVA, the equipment’s ground resistance The grounding resistance should be no more than 4 ohms. When installing the lightning arrester in the weak link of the power distribution line or the switch and switch on the pole, the grounding resistance should be controlled below 4 ohms. There are generally two measures to reduce the resistance of power distribution equipment: One is to use a horizontal grounding body. The disadvantage of this method is that it is easily corroded and the service life is not long. The second is to add a resistance reducing agent. Adding high-efficiency bentonite, which can reduce resistance and prevent corrosion, next to the horizontal grounding body is very effective and can greatly reduce the resistance of the pole. Which method is used to reduce resistance should be selected according to the actual situation.
6. Overvoltage protection
At present, my country has many kinds of lightning protection technologies. Although many technologies have obvious advantages, their disadvantages are also obvious. As a protection technology for overhead distribution lines, overvoltage protection can meet the needs of my country's power grid development. Overvoltage protection for distribution lines can protect the distribution lines from lightning overvoltages, flashover voltages, and power frequency increases, thereby greatly improving the safety of the line's operation.
Yichang Hengyuan Technology Co., Ltd. is a professional manufacturer of European-style cable connectors, plug connectors, cable branch boxes, American elbow connectors, high-voltage vacuum circuit breakers, high-voltage load switches, lightning arresters, zinc oxide arresters, tank arresters, overvoltage protectors, Counters, monitors, heat-shrinkable cable accessories, cold-shrinkable cable accessories, T-shaped heads, wall bushings, European cable accessories, American cable connectors, transformer neutral point protection devices, fuses, isolation switches, PT cable heads, elbows Manufacturers of type cable joints, 10kV outdoor terminals, switch cabinets, cable intermediate joints, cable accessories and other products
