To prevent tripping due to the fault of transmission line is one of the important topics in the current industrial power transmission power transmission and security. Line insulator string flashover, lightning wave intrusion substation caused by power outages caused by lightning, in the southern provinces of China has accounted for 60% of the flashover accident of transmission line, especially of 110kV transmission line, the plain area of the lightning strike rate is 0.1 ~ 0.5 per 100km - year, mountainous area of up to 1 ~ 4 times per 100km in [1]. Adding line lightning arrester (MOA) is one of the effective ways to prevent lightning accidents and reduce the trip rate [2].
Japan, the United States, Russia has a number of applications Zinc Oxide lightning protection devices to prevent lightning flashover success story. Japan in 1990s has more than 30000 phase 77~500kV line surge arrester in the system, the installation of line lightning arrester has achieved good results [3].
The research in this field started late in our country, the application of silicone rubber composite coat technology in the lightning arrester can not start late. Up to now, has been studied and manufactured a variety of types of 110~500kV line surge arrester, a total of 7610 phase in the system running, received good results. The line arrester in our country is divided into two series: series gap and no gap. The difference with the international is currently no gap line surge arrester accounted for more than 50%.
Zero gap of line arresters successful applications benefit from the silicon rubber composite, it replaces the original porcelain coat, so that the quality of 220 kV lightning arrester is reduced to below 50 kg from 260kg, in order to achieve on the tower suspension mounting. The lightning arrester with series gap circuit is composed of a lightning arrester body and an outer series gap. Ontology and the ordinary composite coat lightning arrester is a connected gap (GAP) by two ring - ring or rod - rod type discharge electrode.
The two ends of the lightning arrester body are sealed with metal flanges, and the inner part is provided with a nonlinear ZnO resistance piece and the epoxy glass fiber cloth is pressed by a spring. In this way, the arrester greatly reduced due to the "leak" and bring about the problem of moisture.
On the flange design, the classic ball head, ball and socket are respectively connected with the high voltage and grounding terminal. In 2003, China's natural bridge - Guangzhou line into the use of 500kV gap line arrester design, in addition to adhering to the technical basis of the lightning arrester, but also must address the following 8 key technical issues:
(1) silicone rubber composite coat with excellent performance
The lightning arrester composite coat which is made of silicon rubber and other organic insulating materials must possess excellent properties such as weather resistance, ultraviolet resistance, corrosion resistance and so on. Compared with the porcelain bushing, the silicone rubber compound coat has a great advantage in weight and stain resistance, as shown in Table 1. Composite coat can be selected materials, a lot of variety.
(2) with the durability of bonding technology
Zinc Oxide lightning arrester in the years to withstand the use of wire tension, Xian Zhen, wind, snow, etc.. The bonding part between the upper and lower flange and the epoxy glass fiber cloth is the transmission area of the arrester load force and the weak link of the sealing technology. The author believes that the use of high temperature, high strength epoxy mixture and inverted cone structure is one of the most successful design, the practice has proved this point.
(3) the sealing technology of the interface
Sealed silicon rubber compound coat, connecting flange to the epoxy glass cloth tube outer package is the appearance the arrester strengthen good sealing, but also to prevent the electrical erosion and effective measures. At present, many foreign similar products in the process has not been able to achieve such a package, but must ensure that the silicone rubber and flange of a variety of metal materials and heat treatment after the coating has a good adhesion. In addition, a small groove structure can be added on the flange to enhance the mechanical stress of the silicone rubber without the appearance of the rubber.
(4) explosion proof technology
In order to obtain good explosion-proof performance, the epoxy glass fiber cylinder can be processed into a long trapezoidal groove before the mould pressing and curing umbrella skirt is made. Trapezoidal groove in the lightning arrester failure, the exhaust effect, wedge block to ensure that the injection of silicone rubber into the epoxy glass fiber cloth tube cavity. The length, quantity and the explosive force of the trapezoidal groove must be calculated by strict calculation and experiment. The lightning arrester in China and Russia through the 40kA and 800A short circuit current test.
(5) absorption energy check
A gap line arrester is composed of a lightning arrester body and an outer series gap. Under normal operating conditions, the charging rate of the lightning arrester body is less than 10%, which is mainly subjected to lightning over-voltage, so its other technical requirements are greatly reduced. Lightning arrester resistance to withstand lightning over-voltage ability is extremely strong, the diameter of the 50mm resistance of the film that can withstand the 4/10ms, 100kA large current impact.
(6) calculation and adjustment of electric potential distribution
The outstanding technical problem of 500kV and 330kV line lightning arrester is that the electric potential distribution is not uniform. And porcelain bushing type arrester is different, it is hanging in the air, must use the three-dimensional electric field, with the finite element method to calculate the potential distribution [5]. Due to the structure can not be used outside and capacitance of the pressure. Lightning arrester height of more than 5m, if not to take measures, the potential distribution of uneven coefficient will reach 1.2, the charge rate of 98%. This will accelerate the aging of electrical resistance at high field strength. Therefore, through the SolidWorks 3D design and improvement of potential distribution design, and through change of grading ring number, size, placed position and the depth of ptosis and other measures to make the 500kV zero gap line lightning arrester (5.4m) potential distribution non-uniform coefficient restrictions at 10.4% the following.
(7) the internal negative pressure of arrester
In the whole process of mould injection of silicon rubber, all parts of the lightning arrester are in a state of being heated (above 100 degrees Celsius). When the compression molding is complete (i.e., the arrester is sealed), low pressure is formed inside the cooling. Known by the "baszyn curve", this time sheet resistance surface flashover voltage high to decline and possible damage of lightning arrester at low voltage. This is the production factory is easy to ignore the technical problems.
(8) the factors affecting the stability of gap discharge
Discharge gap voltage stability is the lightning protection performance standards, rod - rod pure air gap and ring ring insulator support gap discharge characteristics itself has the difference. The former is very non-uniform electric field, and the latter is slightly non-uniform electric field; the former discharge voltage is slightly low, scattered small, the latter not only scattered large and insulator performance effect obvious, when the pollution caused by the leakage current and reaches a certain value, it with the lightning arrester body leakage current formed a "divider", obviously change the electric potential distribution of lightning arrester, improve the value of discharge voltage of arrester, which is designers must be given full consideration.