Compared with the porcelain jacket zinc oxide surge arrester, the composite jacket zinc oxide arrester has a series of advantages such as small size, light weight, good explosion-proof and sealing performance, large creepage distance, pollution resistance, simple manufacturing process and compact structure, so it is popular among users. However, there are also aging and electrical erosion defects of the jacket material. In this field, in addition to studying how to improve the characteristics of zinc oxide varistor, it also studies the aging resistance and electrical corrosion resistance of jacket insulation materials, as well as improving the internal insulation structure and material properties to compensate for the shortcomings of organic composite materials.
I. Principle Zinc Oxide ZnO arrester is a new type of arrester developed in the 1970s. It is mainly composed of zinc oxide varistor. Each piece of varistor has its own switching voltage (called varistor) when it is made. Under normal operating voltage (ie less than varistor voltage), the varistor value is large, equivalent to the insulation state, but in Under the impact voltage (greater than the varistor voltage), the varistor is broken down at a low value, which is equivalent to a short circuit condition. However, the varistor is restored and recoverable; when the voltage above the varistor voltage is removed, it returns to a high impedance state. Therefore, after installing a zinc oxide lightning arrester on a power line, when a lightning strike occurs, the high voltage of the lightning wave causes the varistor to break down, and the lightning current flows into the earth through the varistor, so that the voltage on the power line is controlled within a safe range, thereby Protect the safety of electrical equipment.
Structure of composite jacket zinc oxide surge arrester
Second, the composite jacket zinc oxide arrester is generally composed of the following main components:
a. a series of zinc oxide varistor pieces (or valve sheets) constitute a valve core;
b. Internal insulation and mechanical strength materials composed of glass fiber reinforced thermosetting resin (FRP);
c. Hot vulcanized silicone rubber outer cover material;
d. Silicone sealant and adhesive;
e. Inner electrode, external terminal and fitting.
However, various manufacturers choose different production processes and product structures according to different production and technical conditions. According to the internal insulation structure between the resistive sheet of the composite jacket zinc oxide surge arrester and the outer insulating umbrella sleeve, the author selects four representative structures in China for comparative experimental research to obtain composite jacket zinc oxide of different structures and processes. The difference in the performance of the arrester in electrical and physical machinery, the four typical arrester structures are shown in Figure 1.
Here, A-type, B-type, C-type and D-type are respectively used to represent epoxy glass prefabricated tubes, resin glass composite winding, resin glass composite winding and resin potting, heat shrinkable plastic sleeve and resin potting. In addition to these four types, there are also SMC hot-molding, high-temperature curing epoxy resin casting, etc., which will not be studied here. The outer sleeves of the above-mentioned four kinds of arresters can be prefabricated, so that after the high temperature two-stage vulcanization, the outer sleeve material can achieve optimal electrical and physical properties, and the prefabricated umbrella sleeve is finally bonded and sealed with the core. In addition, the above-mentioned four types of A and B types can be directly molded or injection molded on the outer sheath of the core body, but the vulcanization temperature and the vulcanization time have certain limits, otherwise the characteristics of the inner insulating material and the resistive sheet are easily caused. A change has occurred.
In order to improve the contrast, the four structural samples are first made into a resistor core (rod), and then tightly bonded to the prefabricated silicone rubber jacket by an adhesive, and the ends are sealed with a shield end cap to form a lightning arrester sample. And a proportional unit, wherein the A-shaped core body is a resistor sheet, an electrode and a spring are encapsulated in the epoxy glass fiber tube; the B-type core body is obtained by winding and heating and curing the electric resistance sheet and the electrode with an epoxy-impregnated alkali-free glass ribbon; The C-shaped core body is also obtained by first winding the electric resistance sheet and the electrode with an epoxy-impregnated alkali-free glass ribbon, heating and solidifying, and then pouring and curing with an epoxy resin; the D-shaped core body is first heat-shrinking the resistor sheet and the electrode. The plastic sleeve is fixed, then cast with epoxy resin and heat cured. The size of the resistor sheet is 34 x 20.5 mm.
In addition, in order to study the inner and outer insulation properties of the arrester, an insulator test piece was prepared by replacing the resistor piece with an insulating rod to form an "equal shape" arrester.
III. Performance Test and Analysis of Composite Jacket Zinc Oxide Arresters For the structure of the above four composite jacket zinc oxide surge arresters, what are the differences in physical and electrical properties? How big is the difference? This is the problem that the author wants to study and solve.
Referring to the relevant standards of the composite jacket zinc oxide surge arrester, it is found that only the following items are associated with the internal structure of the above-mentioned arrester in all the test items, and the remaining items are not related to or closely related to the structure of the arrester. Therefore, only the following test items are selected for testing here.
four. 1 4/10 high current impact test For the 34×20.5mm resistors used in composite jacket zinc oxide surge arresters, the 4/10μs high current impact level has always been the target of China's IEC standard (ie, reaching 65kA) and foreign advanced level impact. At present, some of China's production plants are still not fully satisfied.
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