Practical application and development of the hotte

2022-09-22
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Practical application and development of power transformers

power transformers are mainly used for metering (such as power consumption records and electric energy transactions), protection (such as protection relays and system protection) and load monitoring (such as economic management of industrial loads). According to different purposes of use, there are great differences in the design and construction of power transformers. For the transformer used for measurement, it is required to have high accuracy under the normal voltage and current, while for the transformer used for protection, it is required to have good linearity within a wide range of voltage and current

in case of system fault or instantaneous overvoltage (surge or spark) that disturbs electricity, the output of power transformer can still be used by taking appropriate measures through protective relay. By opening or closing the circuit breaker, or reconfiguring the system, the influence of disturbance can be reduced, so that the rest of the system can still be protected. Power transformer is the most commonly used and economical means to monitor this disturbance. This kind of transformer must be able to achieve its original performance even in the face of various harsh outdoor environments, such as ultraviolet radiation, pollution, humidity, rain, temperature changes and salt fog. In order to ensure good operation in these extremely harsh environments, abb often checks the materials used to protect these power transformers

in the late 1960s, butyl rubber was once the most widely used dry insulation material for medium voltage (to 40 kV) power transformers. Butyl rubber for outdoor use with appropriate formula is a very good insulator. Some power transformer manufacturers still use butyl rubber with patented formula until today. The molding and curing of rubber requires a high processing pressure (more than 15 times higher than the atmospheric pressure), but it is not conducive to accurately maintaining the dielectric gap and the geometric shape and size of the core coil group, which is essential to ensure the normal performance of the transformer 1), as shown in Figure 1. This limits the application of this material, but also promotes the further research on better insulation materials for outdoor power transformers

after evaluating the liquid pouring resin, it is found that it is a good insulating material to replace butyl rubber. Its initial raw materials can be pumped, measured, mixed and distributed. If the vacuum casting process is adopted, only a moderate vacuum degree is required, or in the automatic pressure solidification (a the audience and citizens can indulge in interactive experience PG) process, a slightly higher die-casting force (about twice the atmospheric pressure) is adopted. The pressure in the curing stage can be slightly higher than the atmospheric pressure (two to three times the atmospheric pressure). These more relaxed process conditions can better maintain the precise space size and the geometric shape of the iron core coil group unchanged, and always produce high-quality products

among these resins, cyclic aliphatic epoxy resin (CEP) was first used as outdoor insulator in the late 1970s. It has good performance in preventing aging and leakage corrosion, and can withstand outdoor humidity, ultraviolet radiation, various pollution and chemical erosion. Globally, CEP is the most widely used insulator material for outdoor medium voltage equipment

in the 1980s, it was found that the outdoor grade polyurethane (PUR) elastomer (elastic polymer) is an economically effective alternative material for the insulator of medium voltage electrical equipment. This resin is mainly processed by the vacuum liquid casting process, which is the least disturbed process for all liquid casting resins. It has a lower molding temperature and a shorter production cycle than other epoxy resin vacuum casting processes, Fully cured outdoor grade pur elastomer is easy to manufacture, with good insulation properties and high outdoor performance

advanced outdoor insulation

due to its light weight, high voltage resistance, and excellent performance in highly polluted environment, silicone rubber has become the main insulating material widely used outdoors. Its good outdoor performance is mainly due to its hydrophobicity (i.e. its water repellency)

small water droplets on the surface of hydrophobic insulating materials will make conductive pollutants flow away from the surface

hydrophilic (absorbing water) insulating materials in a humid environment, the surface often forms a continuous film, so that conductive pollutants suspended in the atmosphere (such as salts, inorganic acids and organic acids) gather and dissolve on the film, thus forming a conductive film. This film with electrolyte will directly lead to dry band arc2). If the insulator is polymer, a high arc temperature (1000 C) will gradually degrade the thermal properties of the polymer, causing corrosion of the insulation surface, resulting in an increase in leakage. With the passage of time, the drying zone will gradually expand, followed by the expansion of arc length, and finally lead to flashover. Therefore, the selection of packaging insulation materials will have a significant impact on the long-term performance of outdoor equipment. Hydrophobic insulating materials can prevent the formation of a thin water film on the surface, so the small droplets formed by water particles will flow away from the surface, and also take away the pollutants that can conduct electricity. This self-cleaning characteristic of hydrophobic surfaces reduces dry zone arc accidents, thereby extending the service life of outdoor equipment. This is also the main reason why the type, diameter, connection mode and other factors of selecting valves for high-voltage outdoor insulators affect the connection mode between hydrostatic testing machine and products with silicone rubber. At the beginning of this century, a more advanced hydrophobic CEP material, known as hydrophobic cyclic aliphatic epoxy resin (hcep, its trademark name is hydrophobicaraldite), was introduced into the electrical insulation resin market. Hcep manufacturers have reported that compared with CEP, hcep has enhanced hydrophobic properties. If it is placed in an aggressive outdoor environment for a long time, hcep can still maintain the hydrophobicity of the surface, and also maintain good electrical, chemical, thermal conductivity and corrosion resistance (CEP material is corrosive). According to the report, hcep has been identified as the best commercial outdoor insulation material for the development of a new generation of outdoor vacuum shutter (ovr)

through in-depth research and development of hcep advanced design tools and production processes, a new generation of ovr has been developed, with hcep embedded electrodes and vacuum circuit breakers. This hcep embedded electrode meets the fire and smoke standards required by the French railway authorities, and has been applied in the vacuum circuit breaker used in railway power supply

at Koeberg insulator pollution test station (kipts) near Cape Town, South Africa, ovr passed the outdoor exposure test for up to one year, thus obtaining the certification of Eskom, the South African Electricity Authority. It is reported that the climate in this region is world-famous for its severe degree. Ultraviolet radiation is harmful, and various industrial and marine pollutants and a large number of sediments are very serious

excellent design and production

the development of ovr using hcep insulating materials is very successful. At the same time, the combination of advanced design tools and the best commercial dielectric materials is also a promotion for the development of a new generation of power transformers (oits) with the same technology. At the end of 2003, abb launched the research and development of a new generation of oits to enable it to have better performance in the outdoor heavily polluted environment. Using simulation software to optimize the development strategy of OIT design can avoid increasing costs due to multiple trial production of machine samples

advanced simulation software can predict and measure the electric field stress distribution inside and on the surface of electrical equipment castings. Various electric field stress distributions can be simulated to optimize the design of dielectric gap geometry of insulating materials

simulation software can be used to evaluate various OIT designs and predict the distribution of electric field stress. Different insulating materials with unique dielectric properties produce different electric field stresses. In addition, the environmental conditions around the three-dimensional model of the device can be changed to simulate various environmental conditions and their effects on the electric field stress (see Figure 3). The optimal design to reduce the distribution of electric field stress must also meet the requirements of convenient manufacturing and improving mechanical stability, so that the instrument can withstand the extreme temperature changes that may be encountered on site. ABB uses its proprietary simulation tool ramzes (zero defect solution for feedback molding) to optimize process and mechanical design. Ramzes can be used to analyze the three-dimensional model of the instrument and the preliminary design of its related insulation mold. This scheme can optimize process parameters, such as mold temperature distribution, mixing temperature, casting speed and curing shape required in resin casting, curing and cooling cycles. As the device gradually cools to the ambient temperature, synthetic mechanical stress and strain will be generated in the solidified casting device, which can be measured by ramzes. These stresses and strains can be minimized by optimizing casting and curing parameters

improve process technology

even with the best material and design, the product performance may not be guaranteed. The reliability and long-term performance of the product can be guaranteed only if the hydraulic system is a load adaptive oil inlet throttle speed regulation system with manufacturing conditions that ensure controllable and repeatable production. In the early stage of resin casting technology, the most commonly used process is vacuum packaging process. This process with low pressure requires only the least mechanical reinforcement for the iron core coil group, which is different from the situation of high-pressure mold and cured butyl rubber. However, the disadvantage of this process is that the processing cycle is relatively long, and it usually takes several hours from injection molding, curing to mold removal. The liquid injection filling epoxy resin process was introduced in the 1980s. Using advanced and mature control methods, the process is automated and further optimized to obtain consistent results. At present, the automatic pressure solidification (APG) process can effectively shorten the whole production cycle in less than 90 minutes, so it has become one of the processes selected for epoxy resin at present

abb's new OIT is packaged with excellent insulating material hcep, which can be protected from the adverse outdoor environment and ensure good mechanical properties

horizontal tensile testing machine adopts constant load control device

in the process of producing reliable power transformer, advanced manufacturing technology is the guarantee of excellent products. Advanced APG casting process equipment and advanced automatic mixing and distribution system are the most important production equipment for manufacturing required parts. When there is a need, they can be used to mix and process mixed epoxy resins with different components. By combining the two devices, the core coil group can be poured, filled with epoxy resin, and its flow condition can be optimized in the subsequent curing process. Finally, a consistent high-quality finished product is achieved

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