Development, Manufacture and Application of S11 Volume Core Transformer
Abstract: To reduce the loss of transformers and improve the efficiency of power supply and distribution systems is a problem that is concerned by countries around the world. In the entire power supply system, distribution transformers account for the largest proportion, improve their performance, reduce the loss index, have an important significance for the power system to save energy, improve system reliability. Because the coil core transformer has its unique structural advantages, compared with the traditional laminated core transformer, it has the advantages of light weight, small size, small no-load loss, low noise, and excellent mechanical and electrical performance. Therefore, in the future, In the construction and transformation of power grids, wound core transformers will be gradually used.
1 The origin of S11 coil core transformer
(1 Overview:
Reducing the loss of transformers and improving the efficiency of power supply and distribution systems are issues of concern to countries around the world. In the entire power supply system, distribution transformers account for the largest proportion, especially in rural power grids, which are almost all distribution transformers. Therefore, improving their performance and reducing loss indicators is of great significance for energy saving of power systems and improving system reliability. Because the coil core transformer has its unique structural advantages, compared with the traditional laminated core transformer, it has the advantages of light weight, small size, small no-load loss, low noise, and excellent mechanical and electrical performance. Therefore, in the future, In the construction and transformation of power grids, wound core transformers will be gradually used.
In the late 1980s, the United States, Germany, and Japan successively developed coil core transformers, which were first used on electronic transformers as high-end electronic products and medical products such as copiers, computers, karaoke machines, game consoles, etc., and gradually shifted to power transformers. on. The coil core is made of continuous unrolled silicon steel sheet, and there is no seam on the sheet to reduce noise. At the beginning, there were only single-phase iron cores, which were later expanded from single-phase coil core technology to three-phase coil core production. As long as two closed rectangular cores are used, a rectangular three-phase three-column core can be made by winding a rectangular core around an electrical steel strip. It consists of two identical inner boxes and outer boxes. Compared with a single phase, three-phase wound core transformers have insufficient losses and a reduction in noise, but they have many advantages over stacked core transformers.
The single-phase wound core transformer has only one frame. After the core is annealed, the process coefficient is only 1.05. The three-phase coil core transformer generally adopts the form of a three-phase three-column inner core. After the core is annealed, the process coefficient can reach 1.15 to 1.2.
Roll core transformer manufacturing process is mainly composed of silicon steel sheet slitting, core coiling, core vacuum annealing, coil winding, body insulation assembly, product assembly and other processes.
(2) The status of domestic S11 coil core transformers:
In the mid-1990s, China developed coiled iron core tooling equipment and manufacturing technology. In the late 1990s, some Chinese manufacturers imported coiled iron core tooling equipment and technology from Japan, Sweden, and other countries.
The core of the coil core transformer is a cold-rolled silicon steel sheet having a thickness of 0.3 mm or less, and is slit into strips of different widths, continuously rolled (with no joint in the middle) into a rectangular frame, and due to the width of the silicon steel sheet The shape is different, and the cross-section is not the same after it is formed. This can be divided into two kinds of roll core: ladder type and R type.
Ladder-type coil core transformers and R-type coil core transformers have the advantages of coil core transformers. However, there are differences between them, such as the use of silicon steel, trapezoidal than the R-type, magnetic trapezoidal than the R-type larger, the volume of the R-type than the trapezoid slightly smaller, as All other aspects are not good enough to be generalized, and it is necessary to further improve the tooling equipment, improve the production process, improve the design ideas, and gradually show their respective advantages.
At present, there are only a dozen or so manufacturers that produce S11 coil core transformers in China. Most of them are production ladder manufacturers, but there are only a few R manufacturers. In addition to supplying domestic customers, the products of coil core transformers have been sold abroad.
Roll core transformer production, China's current focus on 10kV voltage level, the maximum capacity of 800kVA has passed the identification, 1250kVA, 1600kVA has been successfully trial production.
At present, the volume transformers purchased by the power sector are mostly 315kVA and below.
(3)Comparison of the no-load loss indicators of coil core transformers in China with foreign products:
Compared to Japan's Mitsubishi Transformer: No-load loss reduced by 21.8%
Compared to Japan's Osaka transformer: no-load loss reduced by 10.3%
Compared to Toshiba's transformers in Japan: 30% reduction in no-load losses
Than the Italian transformer: no-load loss reduced by 39.6%
Compared to Norwegian Transformers: 36.5% reduction in no-load losses
Than Belgium Transformer: No-load loss reduced by 21.2%
Compared to German Transformer: No-load loss reduced by 11.6%
From the above, we can see that China's current production of S11 coil core distribution transformers has a leading position in the international no-load loss.
2 S11 coil core transformer structural features and processes
(1) Roll core transformer structure features and processes:
The core structure of the three-phase coil core transformer is composed of two rectangular cores that are inwardly convex in section and cores that are externally convex and that are surrounded by two cores. In order to avoid the transitional damage of the silicon steel sheet during rolling, the corners of the core window should be rounded (usually the fillet radius is larger than 4mm).
Roll core transformers slit cold-rolled silicon steel sheets (thickness ≤ 0.3 mm) into strips of different widths and roll them on a core winder.
Ladder-type coil core operation process: The different widths of reel strips needed to be tensioned on the rack, pull down the last stage through the tension device to be used. Fix the mold on the winder shaft to ensure that the die section jumps within the allowable tolerance range. Take the first stage of the film fixed on the mold, adjust the tension properly, slow rotation after two weeks and put down the pressure roller on the head, it can be automatically wound. After the first level is finished, the first stage piece is cut, the second stage piece is centered on the first stage, and the second stage title is pressed with the first stage and the last two weeks for winding. Repeat the above operation until the single frame iron core is completed. When the three-phase outer iron core is wound, the two rolled inner iron cores are combined and fixed, and after the measurement dimensions meet the requirements, the outer core is wound on the winding machine.
After the core roll is formed, in order to prevent high-temperature deformation during annealing, the core is shaped and clamped with a special tool and put into an annealing furnace (preferably a vacuum nitrogen filling annealing furnace) according to a set procedure. The computer controls the temperature curve to automatically reduce the no-load loss. The maximum annealing temperature is 860°C. During the annealing process, nitrogen should be charged at an appropriate temperature to prevent oxidation of the iron core. After the coil core is well annealed, it can completely eliminate the internal stress, there is no high magnetic resistance everywhere in the magnetic circuit, so the no-load current can be greatly reduced, the process coefficient is only about 1.05.
(2) coil structure characteristics and processes:
The coil core transformer high and low voltage coils are directly wound on the iron core. Therefore, only layer or spiral coils can be used. The coil is generally not impregnated with lacquer, so all the insulation between the layers is made by Lingge dispensing paper. The main oil passage between the high and low pressures adopts the semi-oil curtain curtain strut structure to ensure uniform oil clearance.
In the winding process of the coil, firstly, the qualified core of the coil is fixed on a dedicated winding machine, and a tight belt is wound on the core. Then, the two half gears are installed on the iron core column, and the positioning of the gear copper sleeve and the iron core is fixed; the two driving gears and the winding gear are adjusted by the handle so as to make the meshing optimally, and the gear spacing between the two ends is ensured. Winding axial size requirements.
Winding a three-phase coil core transformer on a vertical winding machine generally begins with the uppermost core A column (item). First, wrap the inner paper tube, then use a white cloth tape to tighten the paper tube and fix it on the boss of the two-end winding gear. The winding machine should be flexible. The low voltage flat copper wire is wound according to the design requirements, wrap the head insulation (note the winding of the coil), and fix the coil head on the gear. At the beginning of the winding, the ordinary coil “8†word binding method is used to bind the initial bar end insulation, and 4 to 5 axial tension tightening belts are uniformly added and placed along the circumference. When the system is wound, the shrinking belt and the turn are alternately positioned up and down, and the edges are tightened so that the turns are tightly formed. When winding the last point of the end of the system, it is necessary to determine the starting position to move the vehicle backwards. Use the same method as the initial method to wrap the insulation, and use the “8†method to tie the end insulation and the end of the cable. The length is pressed against the reserved end insulation). After the low-voltage coil is wound, the outer diameter of the coil should be measured to see if it meets the requirements. Then, according to the requirements of the drawings, place the insulation between the high and low oil channels and continue to wind the high voltage coil. The high-voltage coil winding method is basically the same as the laminated coil winding method, and will not be described here. After the A-column (phase) coil is wound, the core is moved up and the B and C-phase coils are sequentially wound. After the entire coil is wound, the body is placed on the assembly platform with a special spreader, the head and the end are withdrawn, and the end is insulated and pressed. Lift the iron core by means of a spreader, install the iron yoke insulation, put on the iron core clamp, and press the coil axially (note that the iron core should not be pressed too tightly, otherwise it will increase the core loss). The core body of the wound core transformer is assembled into a solid body that can withstand the electromechanical forces caused by strong short-circuit currents. In addition, in order to prevent the coil from getting wet, the body assembly should be performed in time after winding the coil. From the coiled coil to the overall assembly process, the annealed iron core should be handled with care, equipped with necessary tooling spreaders, etc. to ensure that the iron core is not subject to large vibrations, and iron is not to be avoided during the assembly process. Core loss increases.
(3) Roll core transformer process performance:
Use special clips for body assembly to ensure better resistance to short-circuits of the laminated core. Roll cores are rolled on the production line without the need for cross-cutting equipment, eliminating quality fluctuations caused by manual lamination, stacking, and insertion of iron yoke. The coil does not require a set process, and the body assembly requires only the coil shaft to be fastened and does not require the assembly and fastening of the iron core. The process is greatly simplified. In terms of coil core transformer production process, it can reduce 5 to 6 processes compared to producing the same stacked core transformer. Therefore, the production efficiency is higher, the quality is more stable and reliable, and it is rarely affected by human factors.
3 Technical characteristics of S11 coil core transformer The S11 transformer coil core breaks the traditional laminated core structure. Roll core transformer is a low-noise and environment-friendly, high-efficiency and energy-saving distribution transformer. Compared with the traditional laminated transformer, it has the following seven significant characteristics:
1 Continuous rolling of silicon steel sheet, iron core seamless, greatly reducing the magnetic resistance, no-load current reduced by 60% to 80%, increased power factor, reduced power line loss, improved power supply quality of the power grid.
2 Continuous winding makes full use of the orientation of the silicon steel sheet, reducing the no-load loss by 20% to 35%.
After the 3 cores are annealed, their magnetic properties can be restored to their original levels before machining.
The 4-volume iron core structure is naturally fastened without the need for clamps. This avoids deterioration of core performance and increased losses due to core tightening forces.
The 5 roll iron core itself is a seamless, compact structure that reduces the noise level during operation to 30 to 45 dB, protecting the environment. Therefore, it is suitable for installation and use in buildings and living areas.
6-core iron core processing material, silicon steel sheet without cross-cutting process, less scrap corner material, material utilization rate higher than the S9 type iron core transformer, at the same capacity, the weight of the iron core is reduced by about 10%, saving raw materials, The performance price ratio has been greatly improved.
The 7-volume iron core has a high degree of mechanization in production and processing, and the production efficiency is about 2 times higher than that of the laminated iron core.
The disadvantages of the coil core transformer: First, the core annealing process requires a higher level; second, core winding and coil winding require special equipment; third, the core and winding maintenance is more difficult.
At present, domestic coil core transformers purchased are mainly 315 kVA and below.
In 2000, the National Electric Power Company's rural power work department, complete sets of equipment department, and electric power machinery bureau jointly held the Symposium on the application of S11 core transformers. It was clarified that all localities could promote their use according to actual conditions.
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