How to improve the reliability of 10kV vacuum swit

2022-08-08
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How to improve the daily reliability of 10kV vacuum switch

vacuum switch is one of the most promising switching appliances with medium voltage, and it is also the switching appliance that can fully meet the requirements of modernization at present. At the same time, the vacuum switch takes the extremely excellent insulation performance and arc extinguishing ability as well as the vacuum with completely closed contacts as the insulation medium. The extremely excellent insulation performance of vacuum makes the contact opening distance of vacuum switch very small (the contact opening distance of 10kV vacuum circuit breaker is only 8mm-12mm), and the required opening and closing speed is not high. Therefore, the operation power consumption of vacuum switch is small, and the vibration and noise during operation are small. At the same time, vacuum has strong arc extinguishing ability, high dielectric strength after arc, recovery speed, low vacuum arc voltage and low arc energy. The arcing time of vacuum switch is short. Within the wide current range from small current to rated short-circuit breaking current, the arcing time remains stable and can withstand the recovery voltage with high rising speed. The vacuum interrupter has a very long mechanical and electrical life. With a long-life operating mechanism, the vacuum switch also has a very long mechanical and electrical life. The vacuum arc extinguishing chamber does not need to be repaired, and it is impossible to repair. The operating mechanism can also be repaired less or free. Therefore, the maintenance workload of vacuum switch is very small, and the maintenance cycle is very long. It is a kind of switch with less or no maintenance. Vacuum switch can not only cut off power frequency current, but also high-frequency current. The arc of the vacuum switch burns in the sealed vacuum arc extinguishing chamber, and high pressure and toxic gas will not be generated during arc burning, so the vacuum switch has no explosion risk, will not cause the combustion and explosion of surrounding flammable and explosive substances, and will not pollute the environment. Vacuum switch is the safest and cleanest switch. The main disadvantage of vacuum switch is that the material testing machine has the phenomenon of current cutoff, which will produce high operating pressure in some occasions. In addition, the price of vacuum circuit breaker is much higher than that of traditional oil circuit breaker (but lower than SF6 circuit breaker). With the progress of contact materials and the improvement of the design and manufacturing process of vacuum interrupters, the operating overvoltage of modern vacuum switches has been greatly reduced, the price has also been significantly reduced, and its shortcomings have become less and less obvious. Therefore, it is especially welcomed by the power system and has been widely used, and its operation reliability is also recognized by the majority of users. As early as 1997, the seven substations under the headquarters of our bureau have all realized oil-free l0kV switches, and all of them use vacuum switches. From the operation and maintenance experience in the past few years, the following aspects of its operation reliability are summarized, and I hope to study with you

2 gains and losses of split vacuum switch in the transformation of old equipment

the use of vacuum switch has been relatively mature in technology in recent years, and now the economic reasons hinder its large-scale promotion and application. There are millions of oil switchgear in 10kV power system in China. Although some users have also suffered from many oil switches and realized the advantages of vacuum switches, it is very difficult to completely replace oil switches with vacuum switches. At the same time, it is not only a pity, but also unrealistic and economically unbearable to scrap so many oil switch cabinets. According to this situation, only the form of sub packaged vacuum switch can be reformed. The so-called split vacuum switch is to replace the original oil less switch with a vacuum switch, leaving most of the original switch. The secondary circuit does not need to be changed, the primary wiring only changes the part connected with the switch, and the rest such as current transformer, disconnector, electromagnetic operating mechanism and control power supply do not need to be changed. This not only retains all the advantages of the vacuum switch, such as simple maintenance, suitable for frequent operation, safety, no explosion hazard, but also has the advantages of rapid installation, no impact on normal production, and can be completed by daily maintenance. In the past, all substations under the headquarters of our bureau used oil less switches, and the annual switch overhaul took several months. In the process of overhaul, it is often found that the switches that cut off the short-circuit current due to fault tripping, and their moving contacts, static contact fingers, arc extinguishing blades and other serious burns must be replaced. This greatly increases the loss rate of switchgear, and has to spend a lot of money to buy switch spare parts, which greatly wastes human and material resources. As it is an oil filling equipment, there is oil leakage, which will become the main obstacle for us to achieve "double standards". At the same time, because our bureau has sufficient funds for production in recent years, under such a climate, the Bureau headquarters will replace all the original low oil switches with vacuum switches. These include: (1) zn50-10, zn9-10 and znll-30 of Henan Xinyang high voltage switchgear plant; (2). ZN28-10 type of Zhujiang high voltage switchgear plant; (3). Znl9-10 type of Foshan Electric Appliance Factory; (4). Zn-10 type of Shandong Zibo High Voltage Switchgear Factory; (5). Znll-10 Ⅲ type of Sichuan Electric Appliance Factory; (6). Vk-10j25a-1 of Guangzhou Nanyang Switchgear Factory, in addition to our best technology, vk-10j25a-1 and znll-10 Ⅲ switches use spring mechanism, but there is also a ring stiffness tester for cement pipes, which is mainly used for the detection of other mechanical properties. It is equipped with CD-10 Ⅱ and cdl0 Ⅲ electromagnetic mechanisms. Because the opening and closing speeds required by the oil less switch and the vacuum switch are different, the speed requirements of the vacuum switch are not high. For the operation of the equipped, select a batch of leading enterprise actuators with strong representativeness, great industry influence, strong production and operation strength and high management level, which do not need a lot of closing work. After the transformation, the electromagnetic operating mechanism equipped with the original oil less switch is retained as the operating mechanism of the vacuum switch, and the electromagnetic mechanism has a large closing current, When it is used as the operating mechanism of vacuum switch, providing large closing work will produce strong mechanical impact and vibration, lengthen the closing bounce time, and change the stroke and overtravel. If the contact opening distance of the vacuum switch increases, the breaking capacity of the switch will be reduced, and the mechanical life of the arc extinguishing chamber of the switch will be reduced; If the contact opening distance becomes smaller, the breaking capacity and withstand voltage level of the switch will be reduced. Keeping the contact stroke (i.e. overtravel) within the allowable range can ensure that the contact can still maintain a certain contact pressure after a certain degree of electrical wear and ensure reliable contact; Provide buffer when the contact is closed to reduce bounce; When the contact is opened, the contact can obtain a certain initial acceleration, pull off the welding point, reduce the arcing time, and improve the medium recovery speed. The travel and overtravel of the vacuum switch are changed due to the electromagnetic operating mechanism. We often encounter such examples in the actual production process. For example, in the annual pre-test of the 10kV vacuum switch equipped with the electromagnetic operating mechanism in the 110kV West substation, through the re measurement of the travel and over travel of the vacuum switch, we found that almost all the values of the vacuum switch have changed, beyond the range of the allowable standard. This is very dangerous. Because the stroke and overtravel of the vacuum switch are important parameters to ensure reliable operation, if they are unqualified, the working performance of the whole switch will be affected, and in serious cases, the switch may explode because it can't disconnect the short-circuit current. Therefore, in order to ensure the reliable operation of the vacuum switch, the following measures should be taken:

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