I. Overview
China's distribution transformers usually refer to power transformers whose voltage is 35kV and 10kV and below, and whose capacity is 6300kVA and which directly supply power to end users. At present, the total power loss of the distribution transformers operating on-line across the country is approximately 41.1 billion kWh , accounting for approximately 3.16% of the total generation in 2000 . Although distribution transformers are highly efficient equipment (95-99%) , due to their large number and fixed no-load power consumption, even small improvements in transformer efficiency can result in considerable energy savings and greenhouse gas reductions. The emissions, therefore, have their own huge potential for energy savings.
In the late 1990s, China's distribution transformer industry developed rapidly. Since 1997 , due to the urban and rural power grid renovation project, the power transformer industry has maintained a good momentum of development. In 1999 , the output of power transformers increased by 24.81% . In 2000 , the output of power transformers increased by 15.88%, and the proportion of distribution transformers increased. In 1999 , the proportion of distribution transformers increased from 34.72% in 1998 to 39.51% , an increase of 5 percentage points ; the proportion of distribution transformers in 2000 was 36.89%. . ( The output of transformers of 10kV 6,300kVA and below is 304,099 sets, 41,778kVA , 35kv 6,300kVA and the following transformers output is 7,821 sets, 9316.4kVA) . The oil-immersed distribution transformer equipment selected for the urban-rural power grid renovation project has all been transformed from the S7 model to the S9 model.
With the development of market economy and continuous advancement in science and technology, continuous application of new materials and new processes, new low-loss distribution transformers have been successfully developed. Many transformer manufacturers in China have invested a lot of money in the introduction of foreign advanced manufacturing technology and equipment, and continuously research and develop low-loss transformers and transformers in various structural forms. For example, oil-filled transformers have emerged as S10 and S11 series that are more energy-efficient than the new S9 series. The SC9 series of new dry-type transformers and low-loss products such as amorphous alloy cores all show the energy-saving potential of distribution transformers in China.
In addition, older transformers with less than 20 years of inefficiencies in distribution transformers running on the Internet account for approximately 10% or more of the estimated capacity of approximately 240 million kVA. These transformers are designed according to the standard of the 1960s and 1970s. Very high, if you spend a certain amount of investment to replace old transformers with S9 , you will certainly get great economic benefits. According to the calculation of different capacity, the investment return for replacing the old transformer with the S9 transformer is generally only 2 to 3 years (the condition of the old transformer return charge and disassembly fee is not counted ) , and its potential for energy saving is huge.
Second , transformer development trends and product characteristics
After continuous efforts in China's distribution transformer industry, it has made breakthroughs in the past after the 1990s . Transformer performance is not only an improvement in the material quality of core silicon steel sheet, but also a breakthrough in the capacity structure and manufacturing process, thus reducing energy consumption. Great progress has been made in reducing no-load currents and noise.
1. The development trend of energy-saving distribution transformer products in recent years
1.1 Volume Distribution Transformer (S11 type ) This type of transformer has been adopted by some developed countries as early as the 1960s and has been gradually promoted in China in recent years. Roll core transformer advantages:
Reduce transformer no-load losses. About 10 ~ 25% , according to the transformer capacity and reduce the no-load current, generally 50% of the laminated core noise level of the transformer is significantly reduced, small transformers can be 37 ~ 42dB, reducing noise pollution to the town.
1.2 The use of single-phase distribution transformers (D10 type ) Many countries in the world, such as the United States, have long been used in residential single-phase three-wire systems for low-voltage distribution, which is of great significance for reducing the loss of low-voltage power distribution. The transformers are mostly on-column and are easy to install and close to the load center. They are usually less maintenance sealed. Compared with the three-phase transformer with the same capacity, the no-load loss and load loss are small, the amount of effective materials is also less, the price is lower 20~30% . Our country has been welcomed by users after trial and reform in individual places.
1.3 Amorphous Alloy Distribution Transformer Since the invention of non-wafers by U.S. Allied Corporation in 1979 , it has been used as a sample for research and production in small quantities around the world. The no-load loss of amorphous alloy distribution transformers is reduced by 70 to 80% compared to silicon steel. However, the fundamental reason why the use has not been fully promoted is that prices are higher. In 1998 , Shanghai Credit Co., Ltd. introduced the manufacturing technology of amorphous alloy core transformer from GE of the United States. The SH-M amorphous alloy core-sealed transformer produced has a rated capacity of 50 to 2,500 kVA and a no-load loss of 34~. Between 700W , the load loss is between 870~21,500W , the no-load current is between 1.5~0.5% , and the short-circuit resistance is between 4~4.5% .
1.4 Dry-type distribution transformers are widely used in places with high requirements for safe operation due to their simple structure, convenient maintenance, fire-retardant, and dust-proof features. In the past, dry-type distribution transformers were used in small quantities and have developed rapidly in recent years. At present, they have accounted for 3 to 5% of the total distribution transformers, and some large cities accounted for 50% .
   Epoxy dry-type transformers have made great progress in China. At present, China can produce epoxy resin dry-type transformers with a maximum voltage of 35kV and a maximum capacity of 20,000kVA . SC9 is a new type of dry-type energy-saving transformer. The loss is much lower than that of the old products. Compared with the old SC8 dry-type transformer, the average no-load loss is 87.52%, and the average loss of load is 10.27%. Compared to S9 , the average load of the oil-immersed no-load is reduced by 17.34%. The average decrease is 23.88% . In addition, the transformer noise level is also significantly reduced. China and Europe use this type of dry-type transformers.
Impregnated dry-type transformer (or nomex paper type) is the earliest type of dry-type transformer application. It has been developed as an open-air dry-type transformer ( OVDT ). Polyester fiber paper or Poly- Fan is used for winding interlayer and turn-to-turn insulation. Amine synthetic paper ( NOMEX paper). The windings of this structure are sufficiently withstand short-circuit capability after being processed by vacuum pressure impregnation ( VPI ) process. Because Nomex paper temperature class C ( 220 °C) is a high-temperature insulation material, with flame retardant, moisture-proof and excellent environmental characteristics, allowing large overloads for a long time, high operating reliability. It accounts for 85% of dry-type transformers in the US market.
1.5 box-type transformers, also known as high and low voltage prefabricated substations , most of the functional components and transformer body are immersed in the transformer box, produced by the transformer manufacturer. Substations close to the load center can reduce line losses and are also among the energy-saving distribution transformers.
2 . Energy-saving distribution transformer material issues
In the development of new distribution transformers , the role of magnetic and conductive materials is very important, and both of these areas are relatively backward, and there have been no major breakthroughs over the years . Silicon steel sheets are almost entirely imported.
2.1 Historical Review of Magnetic System Development
Most of China's 64 , 73 standard transformers use hot-rolled silicon steel sheets as the core's magnetically permeable material. Because the hot-rolled silicon steel sheets have no directionality, the three-phase iron cores use direct seams. Both the material of the magnetically conductive material and the core structure determine the no-load loss and no-load noise. Japan 1964, invented high-permeability grain-oriented silicon steel sheet cold-rolled, after 80 years, the volume of imported materials such silicon steel sheet, to promote the structural improvement of magnetic systems, due to the cold rolled silicon steel sheet directional; iron There is no longer a joint on the stem, the lamination positioning method is improved, no holes can be provided in the stem and the yoke, and the no-load loss is greatly reduced.
In the 1990s , the world developed a cold-rolled grain-oriented silicon steel sheet with a thickness of only 0.23 mm , such as laser irradiation or plasma treatment, which is the lowest unit loss of silicon steel sheet products, 50 Hz and 1.7T . The unit loss is only 0.9W/kg . The latest structure of the 45-degree joints of the core structure is also present, which reduces the no-load loss and no-load noise once again, which further reduces the loss of the distribution transformer by 60 %. .
In 1974 , the U.S. Lien Company developed an iron-based amorphous alloy. In 1978 , the U.S. GE company measured a unit loss of 0.44 W/kg at 6 OHz and 1.5 T. In 1980 , the company launched the 15kVA amorphous core distribution transformer for the first time. Later, the GE company made a 2500kVA amorphous core distribution transformer. The no-load loss is reduced by 70% compared with the laser-treated high-magnetic-permeability grain-oriented cold rolled silicon steel sheet. China also developed a batch of amorphous iron core distribution transformers in 1994. Some plants already have the ability to mass produce amorphous core distribution transformers.
From the above review of development history, we can see that the development of magnetic materials, the modernization of processing equipment for magnetic materials, the improvement of iron core structure, and the significant reduction in no-load loss and no-load noise, allow the transformer to be installed near residential areas. .
2.2 Historical Review of Winding Development in Conductive Systems
In the history of the development of distribution transformers in China, aluminum conductors have also been used. Although they can meet the performance requirements, domestic users do not welcome aluminum transformers. Aluminum transformers are no longer being produced.
In order to reduce the load loss, from the material, the domestic use of oxygen-free copper wire; in addition to flat wire, round wire, but also the use of copper foil. Because the oxygen-free copper has a low resistivity and its surface is bright, the load loss can be low.
In the development of the winding structure, attention is paid to the improvement of the heat dissipation performance, and the longitudinal heat dissipation oil gap is used as far as possible; at the same time, the fastening structure of the winding guarantees the mechanical strength of the short-circuit current.
2.3 Other Structural Improvements
The traditional distribution transformers are used in the midpoint insulation 10kV system, so the winding group is selected Yyn0 , with the growth of non-linear load, the choice of coil core structure, winding the connection group in the transition to Dyn11 .