Although electric power and electrician manufacturing are traditional industries, with the application of new technologies and new materials, like some emerging industries, there will be major technological breakthroughs with qualitative leap, and products and technologies will be upgraded with high voltage and insulation technology. For example, in the past 40 years, technological progress has been closely related to the development of materials science. For example, the SF6 gas-insulated switchgear (GIS), which was introduced in the mid-1960s, has been widely used, changing the design and layout of substations; The metal oxide surge arresters that were developed in the early 1970s have replaced the use of decades-old silicon carbide valve arresters, completely changing the design, manufacture and application of arresters; the cross-linked polyethylene cables developed in the early 1960s are not only The power distribution grade replaces the traditional viscous impregnated oil-paper cable, and has been able to compete with oil-filled cables at high voltage and ultra-high voltage levels; the rapid development and application of silicone rubber composite insulators has greatly replaced the trend of traditional porcelain insulators. The power system has also made some breakthroughs in recent years. For example, flexible (flexible) AC transmission systems with only more than 10 years of history and light HVDC transmission technologies that have been eliminated in recent years to eliminate expensive converter stations are based on power electronics. The rise of distributed power generation in recent years has been greatly related to the development of new energy applications, advances in the manufacturing technology of solar photovoltaic cells and fuel cells, and research on micro gas turbine generators and new wind turbines. tutor.
The success of the system has greatly promoted the rapid development of distributed power generation. In addition, the breakthrough of basic research will also cause major changes in the electrical industry. For example, the research and development of superconducting equipment in recent years has been successful. The above is due to the discovery of high-critical temperature superconducting materials 15 years ago. It should be pointed out that today people pay attention to the important role of interdisciplinary research in promoting scientific and technological progress, but often ignore the achievements of this subject in a certain product. Applied to other products to achieve technological breakthroughs In order to clarify this point of view, this paper introduces ABB's successful combination of cable technology and generator transformer manufacturing technology in recent years, using cable windings to manufacture high-voltage generators and new dry-type transformers, and achieved technology. The breakthrough in this technological innovation has great economic benefits, and it is worthwhile for China's electrician manufacturing industry to learn from the advantages of using high-voltage generators with cable windings to improve the output voltage of generators. It is obvious that conventional generators for meters (generator voltages generally < 20kV) and high voltage generators when comparing the main wiring of the power plant. It can be seen from the figure that when a high-voltage generator is used, a step-up transformer and a generator breaker with a large rated current are not required, thereby reducing the equipment cost and reducing the floor space of the electrical equipment, and the latter is extremely expensive for the earthwork excavation project. Expensive hydropower stations have great economic benefits (in the case of high-voltage generators, there is no need to excavate the caverns where the step-up transformer is placed and the generator house to the busbar culvert of the transformer). In addition, due to the reduced stator current of the generator, The mechanical force on the end of the stator winding is reduced, and the copper loss of the stator winding is also reduced.
Use the main wiring of conventional generator (a) and high voltage generator (b) to compare 1-generator; 2-generator breaker; 3-arrestor; 4-boost transformer; 5-line breaker in the last century Many researchers have been working on the development of high-voltage generators. However, since the insulation technology used in the developed products is not easy to implement in the products, the working voltage of commercial generators never exceeded 30kV before 1998, which is in line with today's transmission voltage. It has become quite disproportionate to have an UHV P1000kV) rating. In 1998, ABB developed a high-voltage generator with cable windings and brought it to market. The registered trademark name is Powerformer. It is obviously composed of half of the English term of the generator (PowerGenerator) and transformer (Transformer). The first unit (45kV, 11MVA) indicating that it is a booster transformer was installed in a hydroelectric power station in northern Sweden in the spring of 1998; the second (136kV, 42MVA) was installed in the west of Stockholm in 2000. A cogeneration heat power plant 3 at 100km uses a cable winding to make sub-windings in the generator. It was actually studied more than half a century ago, but the prototype voltage did not exceed 36kV, and no product was formed. The XLPE cable with good performance is completely solid insulation, and the insulation layer can be made very thin, which enables ABB to solve the technical difficulties that were difficult to overcome before and realize the high-voltage generator with the voltage transmission level.
ABB's history of producing ultra-high voltage XLPE cables is not long. It began to produce 400kV grades in 1995 and 500kV products in 2000. In 1973, the company produced a field strength of only 6kV/mm when producing 123kV XLPE cable. Now the design field strength of 15kV/mm in 525kV products is extrapolated according to ABB's measurement data, and the XLPE cable is hit by long-term voltage. The field strength is quite close to 50kV/mm(), so the company believes that the design field strength of UHV cables can be > /mm in the near future, that is, the insulation thickness can be further reduced by taking ABB's 136kV high-voltage motor as an example. The design field strength of the XLPE cable winding of the XLPE cable used in the relationship between the breakdown field strength and the applied voltage time (the solid line is the measured value, the dotted line is the extrapolated value, and the 0 is the measured withstand value) is 10kV/mmP. It is the winding insulation design value of conventional motor that is more than three times the field strength value of 3kV/mm (conventional motor adopts rectangular section winding, the field strength of the plane part is 3kV/mm, the field strength at the groove angle is - the high voltage without the step-up transformer is made) Since the generators have different ground potentials in the stator windings, ABB uses three different sizes of cables to make the sub-windings, that is, the diameter of the circular slots of the stator core near the rotor is small, and the insulating layer is used. Thin cable; while far In the larger diameter circular groove at the rotor, the cable using the thicker insulation cable as the stator winding is a conventional XLPE cable, but without the outer skin (outer sheath), that is, the outermost layer is the outer half of the cable. Conductive layer: Since the outer semiconducting layer is at ground potential, the cable winding does not exhibit the discharge of the air gap in the slot and the corona discharge of the winding at the slot as in the conventional motor winding.
3 Dry-type transformers with cable windings The current leading products of transformers are still traditional oil-immersed transformers, that is, mineral oil is used as insulation and cooling medium, which does not meet the requirements of fire and explosion protection, and oil leakage will also cause environmental damage. The pollution, so this product needs to be replaced by a non-combustible or flame-retardant transformer. In recent years, with the development trend of high-voltage power grids entering cities and the long-term power supply needs of urban high-rise buildings, the need for urban disaster-proof transformers is more urgent. Because of the technical immaturity of non-combustible liquid medium transformers, flame-retardant liquid media such as organic liquids The medium is currently in high prices in China and therefore not much application, so the urban disaster-proof transformers are mainly dry-type transformers and SF>gas-insulated transformers. The leading product of dry-type transformers so far is epoxy-casting and insulating transformers, which have been obtained at the distribution level. widely used. However, the epoxy casting transformer has poor heat dissipation conditions and low overload capability; and the performance against short-circuit impact is not ideal, which is easy to cause insulation cracking, which makes it difficult to manufacture high-voltage and large-capacity epoxy casting transformers. "35kV, capacity 20MVASF gas-insulated transformers have mature technology in the world. Toshiba, Mitsubishi and Hitachi, Japan have successfully developed 275kV 100MVA gas-insulated transformers with different cooling methods, which can be used together with GIS. The whole gas-insulated but sub-gas insulated transformer manufacturing process, especially the cooling method of large-capacity high-voltage transformers, is much more complicated than conventional transformers. So far, some developed countries in Europe and America have not introduced such products.
Based on the experience of developing high-voltage generators, ABB introduced a new type of dry-type transformer using XLPE cable windings, and named the product as Dryformer, apparently condensed by the dry-transformer English phrase DryTransformer. . The first cable winding transformer was 20MVA, 140 / 6.6kV, which was put into operation in December 1999; the second was 25MVA, 78A1kV, which was put into operation in May 2000. Because the windings have different ground potentials, the cable winding is Wrapped with XLPE cables of several different insulation thicknesses. This dry-type transformer uses strong wind cooling and is designed to have a spare fan volume of 100%, allowing the transformer to operate for a short period of time with a few hours of overload.
Since the outer semiconducting layer of the cable winding is at ground potential, the part other than the transformer winding does not have partial discharge and corona discharge like the normal transformer. In addition, the neodymium insulation of the new dry type transformer has the same insulation level as the main insulation. Therefore, it is not necessary to take measures of electric field adjustment at the winding ends like a conventional transformer to achieve protection of the longitudinal insulation.
Another important advantage of using a cable-wound dry-type transformer is that it can reduce the line loss of the power grid and achieve significant economic benefits. This can be seen from an example. Since the rated voltage of a conventional dry-type transformer is lower than 69kV, it must be The oil-immersed transformer is used to reduce the 69kV to 24kV power supply about 5km away from the user. When the new dry-type transformer is used, the 69kV cable can be directly used to supply the high-voltage dry-type transformer located beside the user 5km away, so that the line loss can be reduced by 28 per year. <104kW.hABB said that the company has been able to manufacture cable winding transformers with voltages up to 145kV and 150MVA. It can be seen that this kind of transformer has a good application prospect. 4 Discussion Whether in the generator or in the transformer, the outer semi-conductive layer of the cable winding should be at the ground potential, so that the electric field can be completely confined within the cable insulation to prevent the cable. Partial discharge occurs in the portion other than the winding. Therefore, the resistivity of the outer semiconducting layer must be within an appropriate range. If the resistivity is too high, the outer semiconducting layer is not at the ground potential, and the resistivity is too low in the semiconducting layer. Caused a large loss It is reported that the outer semi-conductive layer of the transformer cable winding has a resistivity of about 40.cm. The oil-free transformer of the transmission voltage level is an urgently needed product for GIS, which can make the entire substation more environmentally friendly. Cable winding dry-type transformers with conventional dry-type transformers (a) and new dry-type transformers (b) are required to have a unique advantage in this case, which can reduce fast transients. Voltage (VFTO) threat to transformer longitudinal insulation GIS isolation switch operation will cause VFTO, because the front edge of this overvoltage wave is very steep (nanosecond level), often connected to GIS Since the winding insulation of the cable winding has the same insulation level as the main insulation, it is expected to solve the threat of VFT0 to the longitudinal insulation of the transformer. This is an internationally unsolved technical problem. 5 Conclusion Academically, cable windings are used for generators and The transformer does not seem to have much innovation. However, from the point of view of industrial application, this move has great technical and economic value. It can be considered as an important technological innovation suggestion that China's cable industry and generator transformer manufacturing cooperate. , carry out research and development work
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