Distribution transformer silicon steel selection

Distribution transformer silicon steel

With the improvement of environmental protection requirements, the energy efficiency level of distribution transformers has also been improved. There will be an increase in material costs associated with distribution transformers, especially the raw material for transformer silicon steel.

According to the current market price of materials, in the cost of main materials of distribution transformers, the cost of core materials accounts for about 25%, the cost of copper materials accounts for about 65%, and the cost of other materials accounts for about 10%.

How to reasonably select silicon steel transformer core materials and improve product cost performance has become a topic of widespread concern for manufacturers.

In this paper, the author compares and analyzes different schemes for the new energy-efficiency distribution transformers of grade 1 and grade 2, and obtains the corresponding relationship between the price difference of adjacent grades of electrical steel and the proportion of product cost reduction, and proposes the key points of the application of thin strip oriented silicon steel transformer core, which are as follows: Provide reference for your purchase of distribution transformers.

Table of Contents

How to choose transformer silicon steel for distribution transformer?

Taking a new energy efficiency class 2 distribution transformer with a capacity of 100kVA as an example, the grades B23R080, B20R075 and B20R070 transformer silicon steel sheets are used for electromagnetic scheme design, which are defined as Scheme I, Scheme II, and Scheme III in turn.

The iron core column and the winding section adopt an elliptical structure, considering the influence of the thickness of the silicon steel transformer core sheet paint film and shear quality on the lamination coefficient f, the 0.23mm electrical steel sheet f is selected as 0.96, and the 0.2mm silicon steel sheet f is selected as 0.95.

Because thin-strip transformer silicon steel is sensitive to mechanical stress, the performance loss during shearing and stacking has a great influence on the no-load loss additional coefficient K value. Based on the empirical formula for the no-load loss additional coefficient of distribution transformers, and here On the basis of fine-tuning: the K value of the additional air loss coefficient of scheme I is selected according to 1.25, the K value of scheme II and III is selected according to 1.33, the weight and See Table 1 for costs.

Except for the price of transformer silicon steel in Table 1, the prices of other materials are the same.

From the cost comparison of the three schemes, it can be seen that the material cost is significantly reduced by using the higher grade oriented silicon steel to make the same type and performance of the new energy efficiency grade 2 distribution transformer.

Material cost comparison of the three schemes

It can be seen from the comparison results of scheme I and scheme II that when the price difference between adjacent grades of silicon steel transformer core is 78.5 usd per ton-1, the material cost can be reduced by 4.4%;

When the price difference between adjacent grades of silicon steel transformer core is 157 usd per ton-1, the material cost can be reduced by 3.72%;

When the price difference between adjacent grades of electrical steel is 235.7 usd per ton-1, the material cost can be reduced by 3.05%.

Comparison result of scheme II (1) and scheme III: when the price difference between adjacent grades of silicon steel is 78.5 usd per ton-1, the material cost can be reduced by 4.43%;

When the price difference between adjacent grades of silicon steel is 157.1 usd per ton-1, the material cost can be reduced by 3.72%;

When the price difference between adjacent grades of silicon steel is 235.7 usd ·ton-1, the material cost can be reduced by 3.02%.

When the price difference between adjacent grades of silicon steel is in the range (0~1500) yuan·ton-1, the 3 nodes in Table 1 are extended to 300, 500, 800, 1000, 1200 and 1500 yuan·ton-1, a total of 6 nodes , calculated in this way,

The cost reduction ratio of each node is shown in Table 2 (the cost reduction ratio in Table 2 is the average of two comparisons).

It has been verified that the performance indicators of the prototype produced by the three schemes meet the requirements of the standard, the measured values of empty, load loss and impedance voltage are consistent with the design values, and the noise sound power is less than 40dB.

Comparison of carbon emissions from distribution transformers

Different grades of oriented silicon steel are used to make new energy-efficiency grade 2 distribution transformers. Due to the different consumption of raw materials of the transformers, the carbon emissions generated in the production process are also different. According to the calculation method of the carbon emission index of low-carbon products of distribution transformers, the material consumption of three schemes The resulting carbon emissions are shown in Table 3.

Transformer model

Plan

Silicon steel grades

Carbon emission/kg CO2e·k VA-1

S20-M-100/10-NX2

I

B23R080

14.82

 

II

B23R075

14.76

 

III

B23R070

14.72

High-efficiency energy-saving transformers that meet the energy efficiency standards of Grade 1 and Grade 2 in GB20052-2020 will increase the proportion of power transformers operating on the grid by 10%. According to the three-year grid-connected operation capacity of the distribution transformer of 480 million kVA, of which the level 2 energy efficiency accounts for 70%, or 340 million kVA, the plan III (B20R070 silicon steel sheet) is selected to make a new energy efficiency class 2 distribution transformer, which is the same as the plan I. (B23R080 silicon steel sheet), the carbon emission can be reduced by 3.4×104 tons. The calculation formula is shown in formula (1).

E=Ec X P (1)

Among them, Ec is the carbon emission difference between Scheme I and Scheme III, kg CO2e/k VA; P is the three-year grid-connected operation capacity of a class 2 energy-efficiency distribution transformer, k VA.

New Energy Efficiency Grade 1 Distribution Transformer Silicon Steel Selection

silicon steel transformer

Selecting different grades of grain-oriented silicon steel to develop new energy efficiency class 1 distribution transformers

Taking a 100kVA energy efficiency class 1 distribution transformer as an example, B20R075, B20R070 and B20R065 silicon steel sheets are used for electromagnetic scheme design, which are defined as Scheme IV, Scheme V, and Scheme VI in turn. The core column and the winding section adopt an elliptical structure, the lamination factor f of the 0.2mm silicon steel sheet is selected as 0.95, and the value of the additional air loss factor K of the three schemes is selected as 1.31. The main material weight and cost of the three schemes are shown in Table 4.

From the cost comparison of the three schemes, it can be seen that the material cost is significantly reduced by using a higher grade oriented silicon steel to make a new energy efficiency grade 1 distribution transformer of the same type and performance.

According to the cost comparison principle in 2.1, compare plan IV with plan V, plan V (1) and plan VI. When the price difference between adjacent grades of silicon steel is in the interval (0~1500) yuan·ton-1, 6 nodes are also selected. , the cost reduction ratio of each node is shown in Table 5.

Carbon Emissions Comparison

According to the carbon emission comparison principle in Section 2.2, the carbon emissions generated by the consumption of materials in the three schemes are shown in Table 6.

According to the three-year grid-connected operation capacity of the distribution transformer of 480 million kVA, of which the first-level energy efficiency accounts for 30%, that is, 140 million kVA, the plan VI (B20R065 silicon steel sheet) is selected to make a new energy-efficiency first-level distribution transformer, and Compared with scheme IV (B20R075 silicon steel sheet), the carbon emission can be reduced by 3.92×104 tons, and the calculation formula is the same as formula (1).

Application key points of thin strip oriented silicon steel

Design Ideas for Distribution Transformer Core

1) Compared with the 0.23mm silicon steel sheet commonly used in the industry, the 0.2mm thin strip silicon steel paint film accounts for a relatively large proportion. In addition, considering the influence of shear burrs during processing, the core lamination coefficient in the electromagnetic calculation scheme is somewhat different. Decrease, the value is generally 0.95~0.955. Because thin strip silicon steel is sensitive to mechanical stress, considering the performance loss during shearing and stacking, the selection of the additional coefficient of no-load loss should leave a certain margin.

2) In order to reduce the influence of residual stress on the overall performance during the shearing process of thin strip silicon steel, it is recommended that the minimum sheet width of the iron core be selected as ≥50mm.

3) The iron core adopts five-level full miter joints. In order to improve the production efficiency, it is recommended to use the “321” stacking method for the stacking method: the main and secondary layers are stacked in a single piece, and the other stages are stacked with 2 and 3 pieces in turn.

4) In order to further reduce the no-load loss of the iron core, the section of the iron yoke can be increased to 1.05 times the section of the core column.

Process control (mainly shear burr control)

1) Slitting: The tool end jump is controlled by ≤0.015mm, the tool gap is controlled between 0.01mm and 0.015mm, and the coincidence of the upper and lower tools is controlled between 0.18mm and 0.2mm. When the strip is wound, the pressing force of the take-up device should be appropriately adjusted to avoid deformation of the silicon steel sheet caused by excessive pressure.

2) Horizontal shear: The width of the feeding guide rail should be adjusted according to the width of the strip +0.2mm ~ 0.3mm to prevent the silicon steel sheet from being pulled too tightly.

3) During the assembly process, the clamping force of the iron core is controlled at 0.25MPa ~ 0.3MPa, and the no-load loss and noise are the best at this time.

Conclusion

High grade thin strip oriented silicon steel is used in new energy efficiency distribution transformers, and the effect of cost reduction and efficiency increase is remarkable.

When the market price difference between adjacent grades of silicon steel sheets is within a reasonable range, the use of high-grade oriented silicon steel to produce new energy-efficient distribution transformers has less material consumption, smaller transformer volume, higher cost performance, and carbon emissions from material consumption. less.

Because thin strip silicon steel is sensitive to mechanical stress, the performance loss during processing has a great influence on the additional coefficient of no-load loss, so a certain margin should be reserved in the design and calculation.

When the silicon steel sheet is sheared, the key parameters such as the amount of tool clearance and the amount of overlap should be adjusted reasonably according to the thickness of the sheet to reduce the performance loss during the processing.

The selection of high-grade, low iron loss oriented silicon steel in high-efficiency and energy-saving distribution transformers can reduce material consumption, reduce carbon emissions, and improve product cost performance. Green development and other aspects have positive promotion significance.

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