The lightning energy absorption in lightning protection and lightning protection products is mainly zinc oxide varistor and gas discharge tube.
The zinc oxide varistor is a voltage-limiting protection device. When there is no pulse voltage, it exhibits a high-resistance state. Once the pulse voltage is responded, the voltage is immediately limited to a certain value, and the impedance is abruptly changed to a low-resistance state. Compared with the gas discharge tube, its biggest advantage is that when it absorbs the pulse voltage, the residual voltage is higher than the working voltage, it will not cause a short circuit of the power supply, and no freewheeling will occur. The zinc oxide varistor has a faster response time than the gas discharge tube. The breakdown voltage of the gas discharge tube is very sensitive to the rising rate of the pulse voltage. The faster the voltage rise rate, the higher the ignition voltage and the faster the response time. It is possible to correctly select the two types of components, such as varistor and gas discharge tube, and use their respective advantages to combine the power supply arresters, and the overall performance is relatively good. Zinc oxide varistor is required in the power supply arrester and has excellent energy withstand characteristics. The energy withstand characteristic is mainly described by three indicators: rated lightning impulse current, maximum lightning impulse current and energy tolerance. These characteristics are sensitive to zinc oxide. The surface area of ​​the resistor is related to the heat dissipation conditions of the component. The same type of varistor, due to different manufacturers' manufacturing processes and raw material formulations, their energy tolerance will vary greatly.
The gas discharge tube has a strong ability to withstand large energy shocks, but in the specific use, since the residual voltage of the gas discharge tube during discharge is extremely low, which is similar to the short circuit state, it cannot be used alone in the power supply arrester, and the gas discharge tube is used. The flow resistance is related to the pipe diameter. The larger the pipe diameter, the better the flow resistance. The quality problem of the gas discharge tube is mainly characterized by chronic air leakage, reliability problem of long-term use (that is, the DC breakdown voltage value is shifted after suffering multiple lightning impulses), and the photosensitivity effect and dispersion are large. Although the domestic gas discharge tubes have been greatly improved in recent years, the quality is gradually improving, but the overall quality problems still exist, especially the reliability problems and chronic air leakage problems. Therefore, the choice of imported brand-name gas discharge tube in the power supply arrester should be the first choice, and the diameter of the gas discharge tube is better than Ф8mm.
The choice of capacitors and thermal fuses in the power supply arrester is also important. The power supply arrester has been working in the power grid for a long time. There are many cases in which the power supply arrester is damaged due to the quality problem of the capacitor. Therefore, the voltage withstand selection of the capacitor is very important, especially the impulse withstand high voltage. In contrast, foreign products are better than domestic products, Hitachi, OKAYA's capacitor quality is good. The function of the thermal fuse in the lightning arrester is that when the lightning current exceeds the maximum capacity of the lightning arrester, the fuse can be disconnected due to the overcurrent, and the fuse can be disconnected due to the temperature rise of the zinc oxide varistor due to overcutting. It acts as both overcurrent and temperature protection. Due to the normal operating conditions of the power supply arrester, the current is very small, only in the case of lightning shock or pulse voltage shock, under the transient conditions, it is different from the conventional hot-melt fuse, so the power supply arrester Hot melt fuses should have unique properties, ie, blow characteristics under transient conditions.
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