GIS is defined as a metal-enclosed switchgear that uses all or part of a gas instead of air at atmospheric pressure as an insulating medium. It is a high-voltage power distribution device composed of a circuit breaker, a busbar, an isolating switch, a voltage transformer, a current transformer, a lightning arrester, and a casing. The high-voltage power distribution device is called a gasinsulated substation. GIS uses sulfur hexafluoride (SF6) gas with excellent insulation and arc extinguishing properties as insulation and arc extinguishing medium, and seals all high-voltage electrical components in the grounded metal cylinder, so compared with the traditional open-type power distribution device. GIS has the advantages of small floor space, complete sealing of components without environmental interference, high operational reliability, convenient operation, long maintenance period, small maintenance workload, rapid installation, low operating cost and no electromagnetic interference. After more than 30 years of research and development, GIS technology has developed rapidly and is rapidly being applied to power systems worldwide. At present, with the development of the global power system itself and the increasing requirements for the reliability of the system operation, GIS technology will continue to develop and will become the mainstream of the development of high-voltage electrical appliances in this century.
First, the installation of GIS
I have discussed several technical aspects of GIS installation and testing. In order to ensure the smooth implementation of GIS installation, designers need to seriously consider the following two aspects during the construction design stage. Otherwise, it will bring many difficulties to the installation of GIS. .
The first is the way GIS is lifted. At present, most of the load conditions for installation and lifting of indoor GIS use electric single girder bridge cranes. There are two speeds for crane lifting, and the low speed is mainly used for adjustment when the equipment is in place. Two files coordinated application. Such as the Gongbo Gorge 330kV GIS project, the cotton beach 220kV GIS project and some power stations with higher voltage levels have adopted this lifting method, which has proved to be effective.
Second is the pre-buried method of GIS equipment foundation. Usually the load conditions, retention holes and pre-buried requirements of the GIS are provided by the manufacturer, but the basic pre-buried method is determined by the designer according to the basic information provided by the manufacturer. At present, the most commonly used basic embedded parts are channel steel and bolts. The construction of the pre-embedded bolt is simple, but the adjustability is poor. If the bolt encounters the slab reinforcement, the bolt position needs to be adjusted, and the hole is re-opened on the equipment bracket that needs to be connected and fixed, and then the venting is performed on the opening. However, the above problems are not present in the pre-buried channel steel, so there are many applications in the installation process.
The above two aspects should be noted in the design. During the installation of the GIS, the designer's representative is often required to be on site. At this point, the designer should understand the three major elements of the GIS installation process: cleanliness, tightness, and vacuum. Because the structural characteristics of GIS determine the installation process itself is the last critical stage to control the quality of GIS after operation.
A large number of installation practices have proven that ensuring cleanliness is the most important task in GIS final assembly and on-site installation. The site of the domestic GIS installation site is usually inferior. In order to prevent dust, water should be sprinkled on the installation site and cleaned with water before installing the GIS equipment. The installation is started after the air is stationary for 48 hours. The aluminum tube as the electrode will inevitably have surface burrs and aluminum chips during the processing. These particles are the source of discharge in the pressure test, so special attention should be paid to the cleaning of the aluminum conductor. This requires on the one hand to strengthen the cleaning inspection of the conductor processing process to prevent the occurrence of dead zones; on the other hand, before the final assembly, the manufacturer should increase the new means of cleaning the conductor vibration, try to clean out the residual corners of the hollow body, or The conductors before installation were subjected to a partial discharge test to check for residual aluminum chips and wires. Due to the lack of management of some domestic GIS products, there are still debris left in the GIS at the time of shipment. In addition, many installation sites are not well managed, and the dust is cloudy, which increases the difficulty of ensuring cleanliness. Therefore, it must be strictly required and carefully constructed. Wanjiazhai GIS is caused by the GIS internal debris caused by three discharges during the test, and has to be dismantled for local cleaning, which not only increases the workload, but also affects the construction period. This lesson deserves to be taken as a warning.
Sealing is the key to GIS insulation, and SF6 gas leakage can cause fatal failures in GIS. Therefore, the seal inspection should be carried out throughout the entire manufacturing and installation. The sealing effect mainly depends on the welding quality of the tank, followed by the manufacture and installation adjustment of the sealing ring.
In addition to the above two key factors, the vacuum requirement is the third controlling factor in the final assembly and installation process. It is an important guarantee for controlling the water content of SF6. It can not only reduce the moisture of the SF6 gas itself, but also reduce the inside of the tank. The moisture contained in other objects (insulators, seals) is generally required to reach 133 Pa before filling with SF6 gas, and then continue to vacuum for 30 min. The key to the influence of moisture on the operation of GIS is that if the SF6 gas is not controlled below 0 °C, condensation will form on the surface of the insulator when the temperature changes, and the attached water droplets react with the SF6 arc product to form low fluoride such as HF. This results in deterioration of the insulating material and the metal surface along the surface. If the allowable value of the SF6 dew point is controlled to a lower value, it is not water droplets but ice crystals which condense on the surface of the insulator when the temperature changes, and it has little effect on the insulation performance. Therefore, both IEC and international regulations stipulate that the new gas charged into GIS should not exceed -5 °C at the rated density.
Second, the test of GIS
GIS tests include type testing, factory testing, and field testing. The type test is to verify the correctness of the product and verify the performance of the GIS device; the factory test is carried out at each interval to check whether there is a defect in the processing; the field test is to check the GIS power distribution device in the packaging and transportation. Whether or not an abnormal phenomenon occurs during storage and installation is an effective monitoring method that must be carried out before the GIS is put into operation, and the first two tests cannot be replaced.
A large number of field test results show that: (1) parts in the insulation test often loosen, fall off, and scratches on the conductive surface; (2) strong vibration causes cracking of the insulator; (3) electrode surface defects caused by misalignment; (4) Conductive particles are allowed to enter during the installation process; (5) the tool is forgotten in the device due to negligence; (6) The conductive particles that were originally lurking in the device were not detected during the factory test, and were later oscillated during transportation and installation. Or float in the device, etc. These factors can cause insulation failure. These insulation defects are generally divided into two categories: one is the insulation accident induced by free particles and dust, called the active insulation defect (Class A); the other is the fixed insulation defect (Class B) due to accidents during installation and transportation.
According to relevant statistics, 2/3 of the insulation accidents of SF6 equipment occurred on equipment that was not subjected to on-site withstand voltage test. The operational experience of the Ontario Water and Electricity Authority of Canada shows that GIS accidents occur not only in equipment that has not been tested for on-site insulation, but also in the first four months of operation after installation. These accidents account for about 67% of the total accidents. . The first year accident rate was 0.53 times/year and interval, followed by 0.06 times/year and interval. According to the survey report in North America, the accident rate in the first year after GIS operation was 4 times/years, and 0.1 times/years after one year. Therefore, after the GIS is assembled, transported and installed on site, it is necessary to conduct insulation tests before commissioning.
Third, the GIS shell grounding problem
There are two types of GIS grounding methods, one is one-point grounding and the other is multi-point grounding. One point of grounding is to insulate one end of each segment of the GIS housing, and the other end is grounded at one point. Structurally, the series-connected housings are generally insulated between the flanges and insulated from the ground at the housing support. The advantage of this grounding method is that since there is no case current passing for a long time, even if the current rating is large, the temperature rise of the outer casing is low, and the loss is small; since no current flows into the base portion, there is no temperature rise in the civil steel reinforcement. . Of course, its shortcomings are also very prominent, that is, the grounding voltage of the outer casing is higher at the time of the accident, and the external magnetic field is also strong. When the current flowing through the conductor is large, the outer steel bar tends to be heated, because there is only one grounding wire. Therefore, the reliability is poor. At present, domestic GIS design generally does not use this case grounding method.
The multi-point grounding method is to connect the outer casing and the earth with a conductor in a certain section of the GIS, and to use more than two points of multi-point grounding. Generally, the structure is not insulated between the flanges in series, the support of the equipment is not insulated, and is fixed by a fixing bolt, and the grounding wire is also installed in the casing. There are many advantages of multi-point grounding: less external magnetic leakage and low induced overvoltage; since the GIS housing has more than two grounding points, it can greatly improve its reliability and safety; it does not require the use of insulating layers such as insulating flanges. Convenient; the outer casing and conductor currents are almost offset, so the external magnetic field is small, so that the steel structure generates heat and the induced current flowing through the control cable sheath is small. Due to the inductive current flowing through the housing, the temperature rise and loss in the housing is greater than the one-point grounding method. However, the casing loss in the GIS project of the power station itself is not large, so the replenishment can be neglected in the project. For example, the power loss of the GIS casing of the Guangzhou Pumped Storage Power Station is 2.43~3.79W/(m·ph), which can be omitted.
Fourth, the work to be improved in GIS design
According to the extensive experience of GIS engineering in various power stations in recent years, I believe that there are still some blank points in design standardization that need to be resolved. Because the design criteria are the basis for the entire design process, the device interface standard is the manufacturer's manufacturing basis.
The first is the setting of the expansion joints, especially the technical requirements for the expansion joints when using imported GIS equipment. The expansion joint is mainly used to absorb the thermal expansion and contraction of the GIS busbar, the displacement of the foundation expansion joint, the installation adjustment between the equipment, and the displacement caused by the earthquake and operation. Therefore, it is mainly arranged in the busbar and each equipment, the transformer incoming line, and the line outlet. Connect to other locations. In the power plant of the hydropower station, there are many expansion joints between the dam and the expansion and contraction of each expansion joint can not be accurately measured. Therefore, in the bidding design of GIS, high requirements should be put forward for the expansion joint.
If imported GIS equipment is used, foreign manufacturers have different views on the expansion joints. Some manufacturers think that they can fully meet the horizontal displacement and vertical displacement of the design requirements, while some manufacturers believe that the civil construction expansion joints have little relationship with the expansion joints.
China's national standard stipulates that "the manufacturer shall select the structure of the expansion joint according to the purpose of use, the amount of displacement allowed, etc.", "The corresponding displacement (uneven sinking) allowed between the separate bases of GIS shall be agreed by the manufacturer and the user. ". In order to ensure that there is evidence in the technical negotiations with foreign companies, and to ensure the safety and reliability of GIS equipment operation, quantitative calculations and requirements for expansion joints should be added in China's standards.
Followed by the material and size of the GIS grounding wire. This is often a problem that is discussed more in the negotiations with GIS foreign investors. Foreign manufacturers all agree that the GIS room uses copper grounding grid and copper grounding lead. Because copper has better conductivity and corrosion resistance than steel, but because of its high cost and high welding cost, most of the power stations in China use steel grounding grid and steel. Ground wire. At present, domestic ultra-high voltage GIS uses copper grounding leads. The connection between the copper lead and the steel grounding grid is to be carried out in a special way to prevent chemical corrosion of the steel from direct contact with the copper.
In addition, foreign manufacturers calculate the grounding line section according to the GIS's thermal stable current, and have specific calculation formulas and curves. The calculated parameters include the grounding short-circuit current, the duration of the fault, and the corresponding allowable temperature rise of the grounding wire. The corresponding allowable temperature rise value of the fuse is decisive. Some manufacturers use a allowable temperature rise of 100 ° C, so that the selected ground wire cross section is smaller, and some manufacturers use a allowable temperature rise of 200 ° C, so the selected ground wire The section is larger. China's specifications require the use of short-circuit current flowing through the grounding wire, the thermal stability coefficient of the conductor, and the duration of the fault to calculate the cross-section of the grounding conductor. Therefore, it is often the case that the grounding cross-section does not meet the manufacturer's requirements. In this country's specifications, relevant provisions should be made on the specifications and dimensions of the grounding wire.
The above problems are inevitable in the GIS design process, and they need to be improved. Only by formulating corresponding standards as soon as possible can we ensure the design quality and product quality, and minimize the imperfections in the design and the hidden dangers in the operation. Before the standard is formulated, it is hoped that the majority of designers can understand these problems, fully consider them in the design process, and learn from the solutions of other power stations to ensure the design quality as much as possible, so that it can be widely applied and can operate safely.
We've been around for over 16+ years. We make sure our sound is The Best Sound.
Manufacturing high-quality products for customers according to international standards, such as CE ROHS FCC REACH UL SGS BQB etc.
wholesale earbuds, earbuds in bulk, earbuds custom, true wireless earbuds
TOPNOTCH INTERNATIONAL GROUP LIMITED , https://www.micbluetooth.com