Amorphous alloy dry type transformer is a new type of energy saving transformer with a new type of magnetic conductive material (amorphous alloy) making 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.
Amorphous alloy material and characteristics of dry type transformer
The material used for winding and clamping device of amorphous alloy epoxy casting dry type transformer is basically the same as that of ordinary epoxy casting dry type transformer, but the selected core material is very different. A new high-tech product called amorphous alloy is selected. The amorphous alloy is a very thin magnetic material with a thickness of about 0.03mm. It is a certain proportion of alloy raw materials using super rapid cooling technology (cooling rate of 107℃/s), after cooling buoy, cast into the strip sheet. Compared with cold rolled silicon steel sheet, amorphous alloy material has five advantages, but also five disadvantages. These shortcomings bring a lot of difficulties to the design and manufacture of transformers.
The five advantages are as follows:
(1) isotropic soft magnetic materials;
(2) the loss is very low, about 30% of the silicon steel sheet;
(3) high resistivity, about 3 times of silicon steel sheet;
(4) the subsequent processing process is convenient (the subsequent processing can get the required magnetism);
(5) The manufacturing process has good environmental protection.
The five disadvantages are as follows:
(1) The thickness is very thin, the flatness of the material surface is not ideal, and the core filling coefficient is about 0.86;
(2) the hardness is much greater than that of silicon steel sheet, which brings inconvenience to cutting and processing;
(3) annealing must be carried out;
(4) the material is fragile after annealing;
(5) Mechanical stress has a great influence on its performance.
Due to the amorphous alloy strip forming, the section of the core is generally made into a rectangle, and the winding is also made into a rectangle. In one yoke with a break, open the break set winding and close the break. The core adopts the new three - phase three - column structure purchased from outside. Amorphous alloy dry-type transformers have a broad development prospect in distribution market because of the advantages of flame-retardant, high reliability and maintenance-free.
Design and process key points of amorphous alloy dry type transformer
Core shape and magnetic density selection
The shape of the three-pillar amorphous alloy core is shown in Figure 1. The effective cross section of the core is equal to the cross section of the core multiplied by the coefficient, i.e. S1= K ·S, where S1 is the effective cross section, S is the cross section, and K is the lamination coefficient. Products provided by different amorphous alloy core suppliers have slightly different K values. Because the filling coefficient of amorphous alloy core is low, K value is generally about 0.86. When selecting the section of the core, the magnetic flux density should be considered to be about 1.3T, which is lower than that of the core of the silicon steel sheet. This is because the saturation magnetic density of the amorphous alloy is only 1.55T at 25℃, while that of the silicon steel sheet is 2.03T. Moreover, the loss and heating of the amorphous alloy after saturation are very serious, and it is possible to be magnetized in one direction. Core weight GF is equal to the weight of the inner two boxes and the outer one box. The SCBH15-2000/10 product developed by the company adopts magnetic density B=1.153T and unit loss 0.19W/kg.
Comparison of three-column and five-column amorphous alloy cores:
The three-pillar core is 3~5% lighter in weight than the five-pillar core, and the man-hour consumed in the overall manufacturing is less, and the no-load loss is slightly lower. Three-column amorphous alloy transformer is a new type of design, while five-column amorphous alloy transformer is a traditional type of design.
Fig. 1 three - column amorphous alloy core
Process coefficient and no-load loss
When the core frame and winding are assembled in the transformer manufacturing process, it is necessary to open the joint, set the winding and reconnect the joint. These operations that force the core will result in an increase in post-assembly loss and noise compared with the bare core. This added value, the process factor, should be considered in the design. The calculation formula of no-load loss is as follows.
P0 = 1.2 * 1.05 * 1 * 0.19 * GF
1.2 - process coefficient, 1.05 - weight coefficient, 1 - material coefficient, GF - core weight.
The enterprise's assembly tooling is advanced, the assembly level is high, the process coefficient is low, the no-load loss is low.
Rectangular winding
According to the special requirements of amorphous alloy transformers, rectangular windings must be used. There are great differences between rectangular winding and conventional circular winding in design and technology. 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. The low voltage coil is foil resin cast rectangular coil, which increases the ability of short circuit resistance, and the outlet line is completed by copper bar.
Fig. 2 High Voltage Coil (rectangular)
Connection group selection
In the design of the four-frame five-column transformer, DYN11 connection is more appropriate to avoid the phase voltage imbalance caused by harmonics. In the design of three-phase three-column transformer can choose DYN11 connection, or YYN0 connection.
Mechanical strength and resistance to short circuit
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 after being subjected to external stress will increase by about 60%, and the noise will also increase, which seriously affects the performance. Therefore, it is necessary to ensure that the amorphous alloy core is not subjected to external stress. Choose suitable clamping and assembling structure. Force is considered in two respects: static force and dynamic force. The static force takes into account the dead weight of the core and the force exerted during assembly. Dynamic force refers to the impact force of sudden short circuit. Because the winding is quite mature epoxy casting and foil winding used in common epoxy casting dry type transformer, it can fully withstand the impact force of sudden short circuit. The main consideration is to take measures to make the low-voltage winding self-sustaining and transfer the force to the core as little as possible.
Impedance voltage calculation
Direct calculation method for impedance voltage of amorphous alloy transformer with rectangular winding.
Ux = Kx, 5-3.95 x 10, N1I1 (a2L2 + + a1L1 a12L12)/(an EtHx), %
Ua = Pk/(10 x SN), %
Uk= equivalent to a circular impedance voltage calculation method, there are three methods.
Performance data, price cost and economics
The measured values of SCBH15-2000/10 kVA amorphous alloy epoxy casting dry type transformer are shown in Table 2, and the performance data of SCBH15-2000/10 kVA amorphous alloy epoxy casting dry type transformer with the same capacity are compared in Table 3. The winding material is the same, 2605TCA for core amorphous alloy and 30Z130 for silicon steel sheet.
Table 2 Measured values of SCBH15-2000/10 transformer performance
Table 3 Comparison of performance parameters
As can be seen from Table 3, there is little difference in load loss, and the no-load loss of amorphous alloy epoxy casting dry-type transformer has decreased significantly. The core mass of amorphous alloy epoxy casting dry type transformer decreases and the winding mass increases. The market price of 2000KVA single set is about 240,000 RMB (2010) for ordinary epoxy casting dry-type transformer, and 310,000 RMB for amorphous alloy epoxy casting dry-type transformer. The one-time purchase price increased by 70,000 yuan, an increase of about 30 percent.
It is estimated that after 8 years, users will enjoy the economic benefits of low loss.
Let's calculate the total TOC for 8 years.
Market price of electricity is 0.6 yuan /kW·h,
The electricity cost of 8 years of operation K =0.6×8×365×24/1000=42.048 Yuan /W
Common epoxy casting dry type transformer:
The TOC = 240000 + 42.048 x (3060 + 14450) = 976260 yuan
Amorphous alloy epoxy casting dry type transformer:
The TOC = 310000 + 42.048 x (810 + 14910) = 970994 yuan
Through the above comparison of the total use cost, it can be considered that after 8 years, users can enjoy the economic benefits brought by the low loss, while the operating life of the transformer is generally 30 years.
Let's compare energy conservation and environmental protection.
Operating for one year can save electricity:
Electric cost value of one-year operation K =0.6×1×365×24/1000=5.256 yuan /W Annual saving electric cost =[(3060+14450)-(810+14910)]×5.256=9408 yuan
Equivalent to saving electricity meter 15680 kW·h saving coal meter 7841 kg
conclusion
The data of amorphous alloy epoxy casting dry-type transformers described in this paper are compared with the type 10 epoxy casting dry-type transformers which are relatively energy saving in the domestic distribution market. If compared with a large number of distribution oil immersed transformers in use at present, its energy saving and environmental benefits will be more significant. The tracking and testing data prove that the amorphous alloy transformer has stable no-load characteristics. In the current situation of rising prices of silicon steel sheet, the selection of amorphous alloy core for epoxy casting dry type transformer is a good choice for the majority of users and manufacturers. With the implementation of the national energy policy, the reliable operation of the amorphous alloy transformer will be more and more attention and promotion.
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