Abstract: This paper analyzes the core structure, no-load loss, noise, short-circuit withstand capability, and technical and economic aspects of amorphous alloy distribution transformers. The paper argues that amorphous alloy distribution transformers offer significant energy savings and good economic benefits, and should be widely adopted. It also suggests adopting some preferential policies from foreign countries to encourage the development and promotion of amorphous alloy distribution transformers in China; and that measures should be taken as soon as possible to address issues such as irregular bidding processes and local protectionism in some areas, and to prevent substandard products from entering the power grid. Keywords: power distribution system; transformer; amorphous alloy core transformer; no-load loss; noise; short-circuit withstand capability 0 Introduction Since China began large-scale urban and rural power grid construction and renovation in 1998, measures such as promoting S9 type energy-saving distribution transformers, ceasing production of S7 type transformers, and phasing out the "64" and "73" series high-energy-consuming transformers in the power grid have played a positive role in reducing power grid line losses. Statistics show that the national line loss rate decreased from 8.52% in 1996 to 7.59% in 2004. However, compared with developed countries, it is still 1.5 to 2 percentage points higher, equivalent to an additional 15 to 20 billion kWh of electricity loss annually. This shows that the task of reducing energy consumption is arduous, but the potential is also considerable. In 2005, the National Development and Reform Commission and the Ministry of Science and Technology jointly drafted the "Outline of China's Energy Conservation Technology Policy" (draft for comments), which clearly stated: "Promote the production and application of S11 type and amorphous alloy core type low-loss transformers, low-energy-consumption conductors, fittings, and other energy-saving power distribution equipment and accessories. Before 2010, eliminate the S7 type and '73' and '64' type high-energy-consumption transformers currently in service with the power grid." Amorphous alloy distribution transformers, as a power distribution technology and equipment with significant energy-saving effects, have been gradually accepted by manufacturers and users in recent years. 1. Amorphous alloy core (1) The thickness of the amorphous alloy core sheet is extremely thin, only 0.025mm, less than 1/10 of that of commonly used silicon steel sheets; the lamination factor is low, only 0.86; the strip has three widths: 142, 170, and 213mm. Source: http://tede.cn (2) The saturation magnetic flux density of amorphous alloy is low. Single-phase transformers generally take 1.3 to 1.4T, and three-phase transformers generally take 1.25 to 1.35T. Therefore, product design is limited by materials. (3) The hardness of amorphous alloy is relatively high, 5 times that of oriented silicon steel sheets. Therefore, processing and shearing are very difficult, and the requirements for equipment and tools are high. Generally, the edge shearing is heated to obtain a good shearing surface. The core column is rolled from amorphous alloy strip of the same width, so the core cross-section is rectangular, and the corresponding high and low voltage windings are rectangular. (4) During the rapid cooling and winding of the core in the forming process of amorphous alloy, stress will be generated. In order to obtain good loss characteristics, the amorphous alloy core must be annealed under certain magnetic field conditions after forming. The annealing process is relatively complex and has high requirements. (5) The brittleness of the amorphous alloy core material after annealing (easy to generate debris) is also an issue that needs to be considered in the design and manufacturing, and certain process measures need to be taken. (6) Amorphous alloy core material is very sensitive to mechanical stress. Both tensile stress and bending stress will affect its magnetic properties. Therefore, the core loss will increase with the increase of pressure. This needs to be fully considered in the design scheme of the transformer body structure. (7) The core structure of a single-phase amorphous alloy core transformer is generally "frame" shaped, as shown in Figure 1; the structure of a three-phase transformer is composed of 4 "frames" combined into a similar three-phase five-column structure, as shown in Figure 2; when the capacity is large, a structure of 8 core frames stacked together is used. Figure 1 Schematic diagram of single-phase amorphous alloy core structure Figure 2 Schematic diagram of three-phase amorphous alloy core structure 2 No-load loss of amorphous alloy core transformer after operation The hysteresis loss and eddy current loss of amorphous alloy sheets are significantly lower than those of oriented silicon steel sheets. Therefore, the no-load loss of amorphous alloy core distribution transformer is only 40% of that of S11 type distribution transformer, or even less [1]. However, some people believe that the no-load loss of amorphous alloy core transformer after operation will show an increasing trend. This problem was considered as early as during the development of amorphous alloy transformers. In 1982, the first amorphous alloy core transformer was put into operation in the United States. In 1983, the Electric Power Research Institute (EPRI), GE, and New York State Electric Power Company considered this problem, and in 1985, 1,000 25 and 15 kVA pole-mounted transformers that had been manufactured were sent to 90 EPRI member units for a two-year field test. The test data of the field test showed that after two years of operation, its no-load current and no-load loss were very close to those at the time of delivery test [1]. Tokyo Electric Power Company, Takao Electric Company, and Hitachi Electric Company in Japan conducted in-depth and detailed research on the long-term reliability of amorphous alloy transformers. Starting in 1991, they conducted accelerated aging, field operation, short-circuit, and impact tests on 200 amorphous transformers of different capacities, and also tested the effects of load and vibration on the transformer's no-load characteristics. The results showed that the no-load characteristics were stable and the operation was reliable within a 30-year lifespan [2]. my country has also conducted research on this issue. In 1995, the Beidao District Power Bureau of Tianshui City, Gansu Province, as the trial operation unit for amorphous alloy distribution transformers, tested 10 amorphous alloy transformers that had been connected to the grid for two months, according to the requirements of the Ministry of Metallurgical Industry and the Ministry of Electric Power regarding the testing of key experimental projects. The test results were consistent with the test values ​​before operation [3]. After the core material is formed, it has undergone annealing treatment at a high temperature of approximately 400℃, which is high enough for the normal operating temperature and short-circuit thermal stability temperature. Therefore, there is no need to worry about the material changing due to temperature within a 30-year lifespan. Therefore, amorphous alloy transformers do not exhibit increased no-load losses during operation. 3. Noise of Amorphous Alloy Transformers Studies show that the hysteresis of the core laminations is the main cause of transformer noise, which is related to the core size and magnetic flux density. At the same magnetic flux density, the degree of hysteresis in amorphous alloys is about 10% higher than that of traditional grain-oriented cold-rolled silicon steel sheets. However, the saturation magnetic flux density of cold-rolled silicon steel sheets is higher, approximately 2.03T, while that of amorphous alloys is lower, approximately 1.5T. Because the rated operating magnetic flux density of amorphous alloy core transformers (1.25–1.35T) is much lower than that of cold-rolled silicon steel core transformers (1.63–1.73T), their actual hysteresis is similar. However, compared to traditional core transformers of the same specifications, amorphous alloy core transformers have a core mass that is about 40% larger and an effective cross-sectional area that is more than 50% larger, which to some extent increases transformer noise. In addition, the core's structure and manufacturing process also have a certain impact on noise. The surface of the amorphous alloy core is coated with epoxy resin. Poor resin coating, resin shedding due to poor resin quality or improper mixing ratios, or uneven seam stacking can all increase transformer noise. Therefore, it is necessary to implement vibration reduction measures such as painting seams and adding sound-absorbing pads for the core and transformer body during product design. Thus, the sound level of amorphous alloy core transformers is difficult to control. The industry standard JB/T 10088—2004, "Sound Level of 6-500kV Power Transformers," also states: "The sound level limits specified in this standard do not apply to amorphous alloy core transformers; the sound level limits for amorphous alloy core transformers shall be determined through negotiation between the manufacturer and the user." However, its noise is not uncontrollable. Under current technological conditions, with careful attention and control during the design, manufacturing, and use of amorphous alloy transformers, the sound level of amorphous alloy core transformers can reach the level of traditional core transformers. However, for applications with strict noise requirements, careful consideration is advised. 4. Connection Group Since the three-phase amorphous alloy distribution transformer adopts a three-phase four-frame five-limb core structure, each phase winding is wound on two adjacent frames with independent magnetic circuits. In addition to the fundamental magnetic flux, each frame contains a third harmonic flux. The percentage of the third harmonic flux in the fundamental sinusoidal flux depends on the selected rated flux density during operation. The third harmonic flux in the two core frames of one winding is exactly opposite in phase but equal in magnitude; therefore, the phasor sum of the third harmonic flux in each winding is zero. When the high-voltage winding of the transformer uses a D connection, the third harmonic current forms a loop within the delta configuration of the high-voltage winding, and there will be no third harmonic voltage component in the induced secondary voltage waveform. Of course, the no-load loss in each frame is still affected by the second harmonic flux within its respective frame; therefore, its connection group generally uses a Dyn connection. Users should pay attention to this when selecting products. Source: Power Transmission and Distribution Equipment Network 5. Short-Circuit Withstand Capability As mentioned above, the losses of amorphous alloy cores increase rapidly with increasing pressure. If a transformer experiences a short circuit, the resulting impact electrodynamic force, if directly applied to the amorphous alloy core, would be unbearable. Therefore, the traditional design scheme of using the core as the main load-bearing structural component cannot be adopted in the transformer body structure. The low-voltage winding should be self-holding. Generally, the low-voltage winding is wound on a rigid cylinder, and the high-voltage winding is directly wound on the low-voltage winding. During assembly, the windings are supported on a separate winding support system and pressed firmly. This prevents the core from being subjected to pressure, reducing the radial inward or outward expansion of the transformer during a short circuit, thus effectively ensuring the transformer's short-circuit withstand capability. This structure has been proven through actual short-circuit withstand capability tests. 6. Technical and Economic Efficiency of the Product The energy-saving effect of amorphous alloy transformers has been widely recognized, and its technical and economic feasibility has been reported. Under the current market conditions, through a comparative analysis of the economics of the SH15 type three-phase oil-immersed amorphous alloy core distribution transformer and the S11 type three-phase oil-immersed distribution transformer, in terms of investment payback period, the electricity cost savings of the amorphous alloy core distribution transformer can make up for the investment difference in more than 4 years, after which users can benefit in the long term [1]. 7 Application and Development The promotion and application of amorphous alloy core transformers not only has good energy-saving benefits, but also environmental benefits. Energy saving is equivalent to reducing power generation or building fewer thermal power plants, thereby reducing the emissions of CO2, SO2 and nitrogen oxides from power plants. Amorphous alloy core distribution transformers have long been used abroad and have achieved successful experience. More than 1 million amorphous alloy core distribution transformers are connected to the grid in the United States; 350,000 are in operation in Japan, and the world's largest 5,000 kVA amorphous alloy transformer is also in operation; it is also used in EU countries; and amorphous alloy transformer manufacturing plants exist in Asian countries such as India, Bangladesh, South Korea, and Thailand. my country began producing and applying amorphous alloy transformers in the early 1990s, but development has been slow and the promotion has not been very successful. Compared with the S11 type three-phase oil-immersed distribution transformer, the three-phase oil-immersed amorphous alloy core distribution transformer consumes more effective materials and requires more labor time to manufacture, resulting in higher costs. Based on current material prices, the former is approximately 1.3 times the price of the latter. This price is still acceptable to both supply and demand sides compared to previous years, which is conducive to widespread application. Furthermore, when purchasing transformers, price should not be the sole consideration; the total cost (TOC) should be evaluated to determine if it is the lowest possible over its lifespan. This is also an internationally accepted method. In June 2005, the Rural Electrification Department of the State Grid Corporation of China included this method as an appendix to the standards for amorphous alloy transformers during discussions. At present, in addition to oil-immersed amorphous alloy core distribution transformers, a variety of amorphous alloy core transformer products have been launched according to market and user needs: amorphous alloy core dry-type transformers, amorphous alloy core underground transformers, high-flammability oil amorphous alloy core transformers, amorphous alloy core combined transformers (i.e., American-style box-type transformers), prefabricated amorphous alloy substations (i.e., European-style box-type transformers), etc., and their application scope is becoming wider and wider. 8 Conclusion (1) Amorphous alloy core distribution transformers have significant energy-saving effects and good economic performance. The part of the additional investment compared with S9 and S11 type transformers can be recovered within the years stipulated by the policy. If the investment is made in one go, repeated investment in the short term can be avoided. The promotion and application of amorphous alloy distribution transformers are in line with the national policy orientation of energy conservation. The product manufacturing technology is basically mature, the product reliability is guaranteed, and it can fully meet the needs of users and can be widely promoted and applied. (2) According to the current situation, in addition to planning and guidance, the state should improve the standards for energy-saving products as soon as possible, standardize management methods, and introduce specific preferential policies to encourage the use of amorphous alloy transformers. For example, learn from the preferential policies adopted by foreign governments for energy-saving projects, such as encouraging scientific research, production subsidies, tax reduction or refund, investment subsidies for purchasing energy-saving products, and low-interest loans, and increase the financial and credit support for the energy-saving industry. (3) Since the processing and manufacturing process of amorphous alloy cores is relatively special and complex, it is advisable to adopt a professional and centralized large-scale production model to facilitate quality control and assurance. Transformer manufacturers can order according to their own requirements and only use the formed cores to manufacture amorphous alloy transformers. (4) Users should correctly view the issues of no-load loss, noise, connection group, and manufacturing technology of amorphous alloy distribution transformers. When selecting products, the manufacturing level, quality assurance capabilities, and after-sales service of the manufacturer should be comprehensively considered. Price should not be the sole basis for product selection. (5) At present, there are significant differences in the production scale, production conditions, and process level of domestic manufacturers of amorphous alloy transformers. Due to the lack of standardization in the bidding market and local protectionism in some places, products from some small-scale and low-quality enterprises may enter the market. Therefore, it is recommended to take measures as soon as possible to change this situation and prevent inferior products from entering the power grid during the promotion process. 9 References [1] Zheng Guopei, Liu Zhong, Chen Xing, et al. Technical and economic analysis of SH15 amorphous alloy core distribution transformer. Transformer, 2005, (6). [2] Chen Yuguo, Ma Xiaokun, Zhang Yongsheng, et al. Overview of research and development of amorphous alloy core transformer. Rural Electrification, 2001, (2). [3] Zhu Yonghui. Analysis of the effect of grid-connected operation test nodes of amorphous alloy transformer. Rural Electrification, 1999, (5).