Characteristics and performance analysis of amorphous alloy

Amorphous alloy transformer is a new type of energy saving transformer which uses a new type of magnetic conductive material - amorphous alloy to make a core. Compared with the transformer with the silicon steel sheet as the core, the no-load loss decreases by more than 70%, and the no-load current decreases by about 80%. It is a distribution transformer with better energy-saving effect at present, especially suitable for the rural power grid and the developing areas where the load rate is low.

 

 

 

Since the first amorphous alloy transformer came out in the United States in the 1980s, amorphous alloy materials and amorphous alloy distribution transformers have developed very rapidly. Up to now, there are about 2 million amorphous alloy transformers in operation all over the world.

The characteristics of amorphous alloy material and dry type transformer

 

 

 

The amorphous alloy is a special soft magnetic material with a thickness of only 0.03mm. It is a banded metal formed from a certain proportion of alloy raw materials in the melting state after super rapid cooling (cooling rate of 10-7℃/S). Compared with the cold-rolled silicon steel sheet, the amorphous alloy material has the following characteristics: (1) isotropic soft magnetic material; (2) Low unit iron loss, 70%~80% lower than that of silicon steel sheet; The thickness is very thin, only 0.03mm, low filling coefficient; ④ high resistivity, small eddy current loss; The manufacturing process is greatly simplified, energy saving and pollution-free; High hardness, high cutting requirements; ⑦ annealing treatment must be carried out, fragile; ⑧ sensitive to mechanical stress, the force will affect the performance.

 

 

 

As amorphous alloy material has the characteristics of very low loss, it is especially suitable to be used as the core of distribution transformer to reduce its no-load loss. However, in order to avoid the influence of the force on the performance of the amorphous alloy core, special design should be carried out in the structure, which is different from the conventional transformer.

 

 

 

Amorphous alloy transformers can be divided into two types: oil-immersed and dry. Amorphous alloy dry type transformer and epoxy casting type and open type 2 types, to epoxy casting type.

 

 

 

The amorphous alloy core is a rectangular section with an open coil core that has a break at one yoke position. The break is closed by opening the winding of the break package. The core is generally three - phase four - frame five - column structure. The high and low voltage windings are made into rectangles accordingly. The low voltage windings are generally foil-wound and the high voltage windings are wire-wound and cast with epoxy resin. Amorphous alloy dry type transformer is a new type of low loss dry type transformer, because of inherits the traditional dry type transformer flame retardant, high reliability, maintenance free and other advantages, so amorphous alloy dry type transformer in the distribution transformer market has broad development prospects.

 

 

 

Design and process requirements of amorphous alloy dry type transformer

 

 

 

2.1 Selection of magnetic density

 

 

 

The magnetic density design plays a decisive role in the cost, performance and noise level of amorphous alloy dry type transformers, and is the most critical parameter in the design of amorphous alloy transformers. Due to the particularity of amorphous alloy material, its saturation magnetic density is less than 1.5T, which is much lower than that of cold-rolled silicon steel sheet (about 2.0T). The loss and heating of the amorphous alloy after saturation are very serious, and it is possible to be magnetized in one direction. Therefore, the working magnetic density must be reasonably selected in the electromagnetic design. In addition, the noise of the transformer mainly comes from the vibration of the core caused by the magnetostriction of the core material, and the magnetostriction degree of the amorphous alloy is about 10% higher than that of the silicon steel sheet. In order to reduce noise, the amorphous alloy core must have the same or similar magnetostrictive properties as the cold-rolled silicon steel sheet core. Therefore, the selected working magnetic density of the amorphous alloy dry type transformer is required to be lower than that of the cold-rolled silicon steel sheet. The section of amorphous alloy core increases by about 50% and the core mass increases by about 40%, which increases the transformer noise and cost to a certain extent.

 

 

 

The study shows that the no-load noise increases by about 2dB for every 0.05T increase in magnetic density, and the noise increases by about 3dB if the transformer is made into finished products. Therefore, the selection of appropriate magnetic density is the key to the design of amorphous alloy dry type transformer. The influence of magnetic density on noise and the restriction of magnetic density on material cost should be taken into account, and the amount of iron core should be reduced as far as possible under the premise of meeting the noise requirements. According to the current manufacturing experience and manufacturing level of amorphous alloy dry type transformer, it is more suitable to select the core working magnetic density below 1.3, but it must be combined with the enterprise's own technological level to comprehensively consider.

 

 

 

2.2 Process coefficient

 

 

 

In addition to the unit loss W/kg, another important parameter for the design of amorphous alloy core is the unit magnetization capacity VA/kg. Reducing the unit magnetization capacity VA/kg of amorphous core can also achieve the purpose of noise reduction. Due to the restrictive relationship between the unit magnetization capacity VA/kg of amorphous core and the unit loss W/kg, the lower unit magnetization capacity VA/kg must be determined by combining with the technological level of the enterprise. In the transformer manufacturing process, 4 or 8 core frame and winding assembly, need to open the opening joint, package winding and reconnection joint, etc. These operations that force the core will result in an increase in post-assembly loss and noise compared with the bare core. In the design, we should consider the added value, namely the process coefficient, which is related to many factors such as the combined assembly mode of core and winding and the level of tooling. The enterprise's assembly tooling is advanced, the assembly level is high, the process coefficient is low and the no-load loss is low. By selecting a higher unit loss W/kg to obtain a lower unit magnetization capacity VA/kg, that is, under the premise of meeting the requirements of no-load loss, the redundant "loss performance" into "magnetization performance", so as to achieve the purpose of noise reduction. Only after a long time of exploration and manufacturing, can we get the accurate process coefficient consistent with the enterprise itself.

 

 

 

2.3 Rectangular winding

 

 

 

According to the special requirements of amorphous alloy transformers, rectangular windings must be adopted. There are great differences between rectangular winding and conventional circular winding in design and manufacturing technology. Because the wire is less fit to the rectangular mold than the circular winding, the radial size of the rectangular winding should be controlled well. Appropriate winding margin should be selected in the design, and fixture integral type should be adopted in the process. The radial dimension of the rectangular winding should be well controlled.

 

 

 

2.4 Connection group selection

 

 

 

Because the amorphous alloy core adopts three-phase, four-frame and five-column type, in order to avoid the formation of the loop on the side columns for the third harmonic wave, Dyn11 is used in the connection group.

 

 

 

2.5 Process control

 

 

 

Process control is an important factor in the design and manufacture of amorphous alloys. At present, for amorphous alloy dry type transformer three-phase five-column assembly design mainly has two kinds of assembly methods: flip type and mount type. The way of assembly affects the quality of the joint of the amorphous alloy core, and the quality of the joint of the core directly affects the noise of the product. Generally speaking, the paperback type has the least damage to the opening of the amorphous coil core, the best joint quality, and the effective prevention of debris falling into the winding, but the relative process requirements are higher.

 

 

 

The treatment of the open joint of the amorphous alloy core generally follows the following principles: (1) the lap length of 12~16mm, not less than 8mm; (2) lap surface smooth, no burr, sharp corners; (3) special glue (3M glue) or high temperature resistant glue can be used after lapping to prevent core debris and reduce the vibration at the joint.

 

 

 

2.6 Mechanical strength

 

 

 

The structure of amorphous alloy dry type transformer is different from the traditional dry type transformer. Because of the particularity of amorphous alloy material, the loss will increase by about 60% after being subjected to external stress, and the noise will also increase, which seriously affects the performance. Therefore, the amorphous alloy core must be protected from external stress. In order not to make the core too stressed, the core is suspended on the winding, the core only bears its own mass, no other compression force. Structure, around the machine body adopts Ω shape curved plate structure parts assembly structure, winding and iron core is supported by structure. Therefore, the bearing strength of the upper and lower clips has become the key to structural design.

 

 

 

Through mechanical analysis, the bending plate thickness and bending size of the clip are selected reasonably to ensure the maximum stress of the clip

 

Less than the allowable stress of the clip steel.

 

 

 

2.7 Short-circuit resistance

 

 

 

Because the amorphous alloy core can not be subjected to external force, the structural particularity determines that the force of amorphous alloy dry type transformer is not as good as that of traditional transformer. Therefore, the sudden short circuit test has become the technical "threshold" for the production and marketing of amorphous alloy dry type transformers.

 

 

 

Due to the particularity of amorphous alloy strip, the rectangular section of amorphous alloy transformer core is chosen. Considering the cost and insulation distance, the high and low voltage windings are also designed into rectangles. When the transformer short circuit occurs, it bears the repulsion force of the high voltage winding radial outward and the low voltage winding radial inward when the short circuit electric force occurs. The force of rectangular winding is not as uniform as that of circular winding, and it is easy to be stressed and deformed when it bears short circuit electric force. In addition, the particularity of amorphous alloy dry type transformer structure is that the winding axial load-bearing structure is adopted instead of the traditional design scheme of using the core as the main load-bearing structure. Thus, the axial and radial short-circuit electrical force test of the rectangular winding is more severe than that of the circular winding.

 

 

 

Because the winding is pressed axially between the upper and lower clips through the pad, the high-voltage winding is a rigid body structure cast with epoxy resin, which is sufficient to withstand the mass of the iron core and the axial electric force generated by short circuit. The calculation and verification of the axial electric force are the same as those of the circular winding. The low voltage winding is copper foil winding, oven curing, its rigidity is not as good as resin casting. Therefore, the radial electrical force of the foil winding with rectangular cross-section shrinking inward when the low-voltage winding bears short circuit becomes the most severe point when the amorphous alloy dry type transformer bears short circuit.

 

 

 

The structure and stress state of amorphous alloy dry transformer windings are different from circular windings in bearing radial short circuit electric force, so the empirical formula of circular windings cannot be used to calculate and verify it. The finite element analysis of the winding of the rectangular structure can be carried out by using the structure simulation analysis software. It can be concluded that the radial deformation of the rectangular winding in the direction of the long side is the most serious when the rectangular winding is subjected to short-circuit electric force. Therefore, the rectangular winding should be designed as close to the square as possible, in this case, the force deformation is minimal. During the assembly process, support blocks can be added in the long and wide directions to enhance their strength.

 

 

 

3. Economic and social benefits

 

 

 

China is a country with the fastest growing energy consumption in the world, and it is also a country in short of energy. Energy conservation is an essential national policy for China to build a conservation-oriented society. In order to meet the needs of social sustainable development and ecological environment protection, the National Development and Reform Commission has listed amorphous alloy transformers as the key power-saving products. At present, there are many methods for economic analysis of amorphous alloy transformer, and the analysis Angle is not the same. According to the electric power industry standard DL/T 985-2005 the distribution transformer for technical and economic evaluation of energy efficiency to provide the distribution transformer calculation method of the technical and economic analysis of energy efficiency in the Total Cost method TOC (Total Owning Cost) concept, to a comprehensive, fully express the purchased transformer comprehensive Cost, it integrated the initial Cost of the transformer and the equivalent present value of the Cost of loss.

 

 

 

 

 

 

 

Where, is the comprehensive energy efficiency cost of distribution transformer, yuan; CI is the initial cost of distribution transformer equipment, yuan; PO is the rated no-load loss of transformer, kW; Pk is the rated load loss of transformer, kW; For A unit

 

The equivalent initial cost of no-load loss, yuan /kW; B is the equivalent initial cost of unit load loss, yuan /kW.

 

 

 

Take the machinery enterprise as an example, assuming that the service life is 20 years, the discount rate is 8%, the annual charging time is 8760h, the unit monthly capacity cost is 20 yuan /kW, the electricity charge is 0.65 yuan /kW, the annual maximum load time is 5500h, the load rate is 0.75, then

 

 

 

 

 

 

 

Taking 315kVA as an example, the performance comparison of SCBH15 amorphous alloy dry type transformer and SCB9 ordinary dry type transformer is shown in Table 1.

 

 

 

 

 

 

 

 

 

Compared with SCB9 ordinary dry type transformer, the price of SCBH15 amorphous alloy dry type transformer should be higher than about 20000 yuan (reference price). Thus, the TOC difference between the two can be calculated

 

 

 

 

 

During the life period, the amorphous alloy dry-type transformer is used to replace the ordinary dry-type transformer with the same specification, and the cost can be saved 19170 yuan. The operating life of the general dry transformer is 30 years, and the economic effect is better. In summary, the amorphous alloy dry type transformer has remarkable economy.

 

 

 

In today's increasingly tense energy, people will pay more attention to energy conservation and rational use. During the 11th Five-Year Plan period, one of the main targets for China's economic and social development is to reduce energy consumption per unit of GDP by about 20 percent. Not long ago, the National Development and Reform Commission formulated a medium - and long-term energy conservation plan, stipulating that starting from 2006, mandatory energy efficiency standards, energy conservation certification and energy efficiency labeling will be implemented on electrical equipment, which shows that the work of energy conservation is urgent.