Lightning or the operation of large-capacity electrical equipment generates surges inside and outside the power supply system. Its impact on the power supply system (China low-voltage power supply system standard: AC50Hz220V/380V) and electrical equipment has become a concern. focus. External surges in low-voltage power supply systems mainly come from lightning discharges, which consist of one or several separate lightning strikes. Each lightning strike carries several high-amplitude, short-duration currents. A typical lightning discharge will consist of two or three lightning strikes, each occurring approximately 1/20 of a second apart. Most lightning currents fall within the range of 10~100Kade, and their duration is generally less than 100μs.
Today’s common arresters can be divided into four categories according to their structure: air gap, zinc oxide, silicon carbide, discharge tube and zinc oxide combination.
(1) Air gap arrester
The main characteristics of air gap arrester are: large flow rate. This kind of lightning protection product is mainly used in LPZOB area, or is a deformed derivative product. The form is used as a lightning protection protector for overhead lines in power systems. According to the different applications of air gap arrester products, they are divided into air discharge tubes and inert gas (such as hydrogen) discharge tubes. The latter is mainly used for overvoltage protection in signal transmission, and its flow rate is generally 10~20kA. In Figure 1, the product with the structure in (a) is suitable for TT systems. The flow rate of this series of products is 50kA and is suitable for use in lightning protection systems with a maximum flow rate of 100kA. However, due to the structural characteristics, attention should be paid to the installation back when installing. The board has enough space for sparks to escape to avoid causing fire, so it is not very suitable to use this product in the distribution box of general buildings. However, in large distribution rooms and the installation environment permits, this product is still more suitable as Class B. Lightning protection products; (b) The product is suitable for various power grid structures. Since it is also an open design, attention must be paid to the fire protection requirements of the power distribution environment during installation; (c) The product in the picture is mainly used in TT power grid Power supply lightning protection. The main feature of this structure is the bridge structure. There will be arc creeping phenomenon instead of high current spark discharge. Therefore, more attention should be paid to the safety distance during installation: (d) The product in the picture is The current that the closed gas discharge tube can withstand depending on the distance between the discharge electrodes is equivalent to the first three structures. The biggest advantage of products with this structure is that there is no need to consider the safety fire distance during installation, so it is suitable for use in general buildings. It is used in power distribution environments with high physical and safety levels.
The main component of the air gap discharger is the material of the discharge electrode. At present, air gap dischargers mainly rely on imported products. The main problem of similar products made in China is that the discharge electrode will It is impossible to ensure that the discharge spacing remains unchanged and that metal vapor is not produced to cause metal plating in the discharge chamber and affect the flow of the arrester.
(2) Zinc oxide arrester
Zinc oxide arrester is the lightning protection overvoltage device with the highest application rate since its invention in Japan in the 1980s. At present, single-substrate zinc oxide arresters and double-substrate zinc oxide arresters are mainly used in the LPZI area, but multi-substrate zinc oxide arresters are also used in the LPZOB area. The biggest feature of zinc oxide arresters is their fast response time (can be at the ns level). At present, the maximum flow rate of a single-substrate zinc oxide arrester does not exceed 80kA (8/20μs). From this aspect, considering multi-substrate zinc oxide arresters, it is makes up for this shortcoming. However, in order to achieve a larger flow rate, multiple substrates must be used in parallel, which leads to an energy distribution problem. If 3 or more substrates are used in a zinc oxide arrester, then each of them The startup voltage and internal resistance of the substrate must be very similar. Because under high voltage and high current conditions, even a resistance difference of lΩ will cause uneven energy distribution on the zinc oxide substrate. Then one piece will be damaged while the others will not be damaged or will be rarely damaged. However, even so, there will be One piece of damage will also affect the entire power arrester or short-circuit a phase to ground, causing a power supply accident. Zinc oxide arresters have the widest range of applications. Single/double-chip zinc oxide arresters are suitable for use in multi-level lightning overvoltage protection after Class C and D in any power distribution system. Multi-substrate zinc oxide arresters can be used under certain circumstances. It is also suitable for use in power supply level B lightning protection. Since the capacitance of zinc oxide arrester is relatively large, it will affect its application in high frequency and ultra-high frequency fields.
(3) Silicon carbide arrester
Silicon carbide arrester is mainly used for lightning protection of high-voltage electrical equipment in substations. It is characterized by large flow rate, but the reaction time is relatively long. Currently, it is also The most common high-voltage lightning protection product for power systems.
(4) Combined lightning arrester
The advent of combined lightning arresters fundamentally solves the problem of high residual voltage, slow reaction time and oxidation of gas discharge tube (gap) arresters. The disadvantage of zinc arrester is its small flow rate. The arrester with this structure generally adopts the structural form shown in Figure 2. In this way, the flow rate of the single-chip zinc oxide arrester is greatly increased, and the residual voltage is reduced to a lower level.
Depending on the combination method, the arrester of this structure can be used in the B/C level lightning protection of NPE distribution structures and other distribution structures