Talking about How to Improve the Operation Reliability of 10kV Vacuum Switch

1 Introduction

The vacuum switch is one of the most promising switching appliances for medium voltage, and it is also the most widely used switchgear for modernization. At the same time, the vacuum switch is excellent in insulation performance and arc extinguishing ability and the vacuum of the contact is completely enclosed as the insulating medium. The excellent insulation performance of the vacuum makes the contact distance of the vacuum switch small (the touch of the 10kV class vacuum circuit breaker) The head opening distance is only 8mm to 12mm), and the required branching and closing speed is not high, so the operation power consumption of the vacuum switch is not large, and the vibration and noise during operation are small. The vacuum has both strong arc-extinguishing ability and high post-arc medium strength, recovery speed, low vacuum arc voltage and low arc energy. The vacuum switch has a short arcing time. From a small current to a wide current range of rated short-circuit breaking current, the arcing time remains stable and can withstand a recovery voltage with a high rising speed. The vacuum interrupter has a very long mechanical life and electrical life. With a long-life operating mechanism, the vacuum switch also has a long mechanical life and electrical life. The vacuum interrupter does not require maintenance and cannot be repaired. The operating mechanism can also be repaired or repaired. Therefore, the maintenance work of the vacuum switch is extremely small, and the maintenance cycle is long, which is a switch with less maintenance or maintenance-free. The vacuum switch can not only interrupt the power frequency current, but also break the high frequency current. The arc of the vacuum switch is burned in the sealed vacuum interrupter. When the arc is arced, no high pressure and toxic gas are generated. Therefore, the vacuum switch has no danger of explosion, and will not cause combustion and explosion of surrounding flammable and explosive substances, nor will it pollute. surroundings. The vacuum switch is one of the safest and most "clean" switches. The main disadvantage of vacuum switches is the phenomenon of shut-off, which in some cases produces higher operating pressures. In addition, the price of vacuum circuit breakers is much higher than traditional oil circuit breakers (but lower than SF6 circuit breakers). With the advancement of contact materials and the improvement of vacuum interrupter design and manufacturing process, the operating overvoltage of modern vacuum switches has been greatly reduced, and the price has also been significantly reduced. Its shortcomings have become less and less obvious. Therefore, it is particularly popular with the power system, and has been widely used, and its operational reliability has been recognized by the majority of users. The seven substations under the headquarters of our bureau have all achieved l0kV switch oil-free in 1997, and all use vacuum switches. From the experience of operation and maintenance in the past few years, the following aspects have been summarized for its operational reliability, and we hope to study with you.

2 The difference between the replacement and the vacuum switch in the old equipment transformation

The use of vacuum switches has matured in technology in recent years, and it is currently mainly for economic reasons that hinder the widespread application of them. In China's 10kV power system, oil switch cabinets account for millions of units. Although some users have suffered from many oil switches, they also recognize the advantages of vacuum switches. However, it is difficult to replace the oil switch with a vacuum switch. At the same time, it is not a pity to scrap up so many oil switch cabinets. I can't afford it economically. According to this situation, only the modification of the sub-packaged vacuum switch type is carried out. The so-called split-type vacuum switch only replaces the original low-oil switch with a vacuum switch, retaining most of the original switch, the secondary circuit does not need to be modified, the primary wiring only changes the part connected with the switch, and the rest is like current transformer, isolation. The switch, electromagnetic operating mechanism, and control power supply do not have 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, etc. It also has the advantages of quick installation, no impact on normal production, and daily maintenance. In the past, all substations under the headquarters of our bureau used oil-less switches. The annual switch overhaul took several months, and during the overhaul process, the switch that cuts the short-circuit current due to fault trip is often found. Serious burns such as static fingering and arc extinguishing tablets must be replaced. This greatly increases the loss rate of the switchgear, and has to spend a lot of money to buy switch spares, which greatly wastes human and material resources. Because it is an oil-filled equipment, there is a leakage of oil, which will become the main obstacle for us to create a "double standard". At the same time, due to the abundant funds used in production in recent years, in this climate, the headquarters has replaced all the original oil-less switches with vacuum switches. Among them are: (1) ZN50-10, ZN9-10, ZNll-30 of Henan Xinyang High Voltage Switch Factory; (2) ZN28-10 of Zhujiang High Voltage Switch Factory; (3) ZNl9 of Foshan Electrical Appliance Factory -10 type; (4). ZN mouth type 10 of Shandong Zibo high voltage switch factory; (5). ZNll-10III type of Sichuan Electric Appliance Factory; (6). VK-10J25A-1 type of Guangzhou Nanyang Switch Factory, etc. In addition to the VK-10J25A-1 and ZNll-10III switches, the spring mechanism is used, and the others are equipped with CD-10II and CDl0III electromagnetic mechanisms. Since the switching speeds required by the oil switch and the vacuum switch are different, the speed requirement of the vacuum switch is not high, and the operating mechanism used does not require a large closing work, and the original oil switch is modified after the transformation. The electromagnetic operating mechanism used is reserved as the operating mechanism of the vacuum switch. The electromagnetic mechanism provides a large closing work when used as a vacuum switch operating mechanism due to the large closing current, which will generate strong mechanical force. Impact and vibration, the closing bounce time is lengthened, and the stroke and overtravel changes. If the contact opening distance of the vacuum switch becomes larger, the breaking capacity of the switch will decrease, and the mechanical life of the switch interrupter will be reduced. If the contact opening distance becomes smaller, the breaking capacity of the switch will be caused. Reduced pressure level. The contact stroke (ie, the overtravel) is maintained within the allowable range to ensure that the contact maintains a certain contact pressure after a certain degree of electrical wear, ensuring reliable contact; providing cushioning when the contacts are closed, reducing bounce; When the head is opened, the contact obtains a certain initial acceleration, breaks the fusion welding point, reduces the arcing time, and improves the medium recovery speed. The stroke and overstroke of the vacuum switch are changed due to the use of the electromagnetic operating mechanism. We often encounter such examples in the actual production process. For example, in the 110kV West Substation, the 10kV vacuum switch with electromagnetic operating mechanism is used in the annual pre-test. By retesting the stroke and overtravel of the vacuum switch, we found almost all vacuum. The value of the switch has changed beyond 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 fail, it will affect the performance of the whole switch. In severe cases, the switch may explode due to the short-circuit current. Therefore, in order to ensure the reliable operation of the vacuum switch, it is recommended to take the following measures:

(1) Combine the annual preventive test to measure the stroke, overtravel, closing time, switch contact resistance and other parameters of the vacuum switch. If any unqualified data is found, it should be adjusted immediately to meet the manufacturer's standard. And record the data before and after the test, write a test report, as a reference for the next year's annual pre-test.

(2) Perform vacuum measurement of the vacuum interrupter to check whether the vacuum interrupter is intact.

(3) It is recommended to contact the manufacturer of the vacuum switch to explain the difference between the closing work of the electromagnetic mechanism and the spring mechanism, whether it can meet the technical performance requirements of the vacuum switch, and whether the long-term operation will reduce the reliability and shorten the vacuum switch. Mechanical life, if it does exist, please provide a solution.

In addition, some routine maintenance checks are required on the vacuum switch:

(1) The vacuum switch should be kept clean frequently. Pay special attention to clean the dust of the insulator, the insulating rod and other insulating parts in time, and wipe the dust on the insulating shell of the vacuum interrupter with a clean dry cloth.

(2) All parts of the friction should be kept clean, so that the operating mechanism is flexible and reduces mechanical wear.