With the rapid development of vacuum switch technology, vacuum interrupters continue to be miniaturized, and the reasonable design of the insulation level inside the vacuum interrupter has become particularly important, and has become a research direction in the field. Vacuum interrupter interior electric field The distribution is the key to the design of the internal insulation level, and the analysis of the internal electric field is an extremely complex dynamic insulation problem, which is based on the study of the electrostatic field inside the vacuum interrupter. Here only from the static electric field of the vacuum interrupter to analyze, in the miniaturization of the vacuum interrupter design and improvement process, with the help of the electrostatic field analysis function of Ansoft Maxwell software can be different shapes of the various components of the vacuum interrupter chamber Electrostatic fields at different locations are analyzed and continuously adjusted according to the analysis results. Ultimately, the internal electrostatic field is evenly distributed, thereby improving the internal insulation level of the miniaturized vacuum interrupter.
1. Ansoft Maxwell Software IntroductionAnsoft Maxwell software is a popular large-scale universal limited software package. It is a powerful electromagnetic field simulation tool and is mainly used in the calculation and analysis of electric fields, magnetic fields, eddy current fields, and thermal fields.
Ansoft Maxwell software is a complete Window program, friendly user interface, intuitive and convenient to use. This software has the following advantages over other finite element analysis software:
(1) has a powerful data processing function.
(2) Simultaneously has the model input port while having the simple and easy drawing function, may facilitate to introduce the model which the other drawing software forms.
(3) In the process of splitting, manual splitting and automatic splitting can be performed. The shape and density of the grid are flexible and various, and the energy error can be reduced to any specified value.
(4) Various types of linear and nonlinear analysis can be performed.
2. The application of Ansoft Maxwell software in miniaturized vacuum interrupter insulation optimization designThe interior of the vacuum arc-extinguishing chamber is mainly composed of contacts, conductive rods, shields, bellows, etc. There are many factors affecting the internal insulation level, but the rational design of the internal structure can effectively achieve the capacitance balance between the internal gaps, internal The electric field intensity is distributed evenly, thereby increasing the internal insulation level. The following is the author's work in the use of Ansoft Maxwell two-dimensional software on the miniaturization of the vacuum arc chamber interior structure and electric field analysis and optimization of some methods and experience for my colleagues to discuss.
2.1 The establishment of a vacuum interrupter calculation model
Ansoft Maxwell's two-dimensional electrostatic field analysis mainly includes three parts: pre-processing module, analysis module and post-processing module. The main process is to establish models, set boundaries, define materials, assign boundary conditions and loads, dissect, solve and post-process.
The vacuum interrupter is a typical axisymmetric structure, and its internal electric field can be considered as an axisymmetric electric field. Therefore, only half of the structure diagram can be drawn when building the calculation model. This can be simplified as a two-dimensional axisymmetric problem. Reduce the amount of post-processing calculations. The model can be created in Ansoft Maxwell, or it can be drawn in other drawing software and imported into the model via the input port. The author proposes to build a model in AUTO CAD or CAXA, import it into Ansoft Maxwell, and then use it, and rotating the body can be considered as the solution object. The structural model is shown in Figure 1:
Fig.1 Diagram of vacuum interrupter calculation model
After the model is established, it is critical to set the boundary conditions. In fact, the solution of the electric field of the vacuum interrupter belongs to the open field problem. Here, in order to reasonably determine the unbounded calculation area of ​​the electric field of the vacuum interrupter, we usually take the equivalent of the arc-extinguishing chamber. Five times as much distance as the boundary of the open field field, the outside can be regarded as an infinity space, as shown in Figure 2:
Fig. 2 Full field electric field calculation model field partition of vacuum interrupter
1—Vacuum interrupter 2—Air 3—Infinity calculation area 4—Open field boundary
2.2 Calculation of Static Electric Field
Before computing, various materials are assigned according to the structural design, and the infinite boundary is defined as the balloon boundary. The calculation conditions are: the potential of the movable contact and its connected metal parts is set to zero, the potential of the static contact and its connected metal parts is set to 10 kV, the shielding cover is set to floating potential, and the boundary of the balloon at infinity is set to voltage, here The setting of the dynamic and static terminal voltage conditions can also be reversed. According to the set conditions, Ansoft Maxwell software uses adaptive meshing technology to automatically generate segmentation elements for finite-element electric field analysis, as shown in Figure 3. The calculation error can be reduced to any given value. The energy error in this paper is less than 1%.
Figure 3 Adaptive dissection result
Ansoft Maxwell software has a powerful post-processing function that can analyze a variety of problems in the electric field, such as electric field strength, power line distribution, inductance, capacitance, etc. This article mainly analyzes the electric field strength at a particular point and the distribution of power lines along the surface of the porcelain shell.
2.3 Miniaturization of vacuum interrupter interior structure optimization design
After the miniaturization of the vacuum interrupter, the size, shape, and mutual positional relationship of the internal structural components have a great influence on the internal insulation level. The following analysis is performed on several different structures. The structural schematic is shown in FIG. 3.
The difference between Fig. 3-a and Fig. 3-b lies in the different direction and position of the shield;
The difference between Fig. 3-c and Fig. 3-b is the arrangement of the static shield.
Figure 3 Different design structures
Using Ansoft Maxwell software to analyze and calculate the three kinds of programs, the results obtained under the same load conditions are very different.
2.3.1 Distribution of Power Lines
The breakdown point of the vacuum interrupter is shown on the porcelain shell. The porcelain shell itself has a certain dielectric strength. However, if the structure of the arc extinguishing chamber is unreasonable, the distribution of the electric field along the surface of the porcelain shell is not even, and it may be in the dynamic electric field. Under the effect of the partial breakdown of the porcelain shell.
After calculating the three structures, the resulting power line distribution pattern is shown in Figure 4: a, b, and c are static pressure and high pressure; a1, b1, and c1 are high pressure and dynamic pressure.
a a1
b b1
c c1
Figure 4 Power Line Distribution [Analysis]In Figure 4-a, the distribution of power lines is obviously non-uniform, and the intermediate potential line is biased towards the static end. This increases the potential gradient along the porcelain shell near the static end. When a high voltage is applied at the static end, it can easily lead to near the static end. The breakdown occurs along the surface of the porcelain shell; in Fig. 4-a1, the situation when the high voltage is applied at the moving end is slightly better, but the middle potential line is also biased towards the static end, which also causes the potential gradient along the surface of the porcelain shell to be uneven, so this solution Can not be considered.
In Figure 4-b, Figure 4-b1, Figure 4-c, and Figure 4-c1, the distribution of the power lines along the surface of the porcelain shell is basically uniform, and the intermediate potential line is basically at the middle of the surface of the porcelain shell. The potential gradient change will be more uniform, which is conducive to reducing the breakdown rate along the surface of the porcelain shell. Especially after the endshield is added in the structure c, although the static end is not very obvious when the high voltage is applied, it becomes dynamic. When the high voltage is applied to the terminal, the middle potential line is basically located in the middle position along the surface of the porcelain shell, so that the potential gradient along the entire surface of the porcelain shell will not abruptly increase, and the insulation level along the surface of the porcelain shell will be increased. Therefore, the end shield cover is added. Structure c is better than the other two structures.
2.3.2 Analysis of Electric Field Strength
Another key point in the vacuum interrupter insulation design is the strength of the electric field at the three-phase junction between the vacuum and the insulating housing and air. The large volume of vacuum interrupters can be improved by the provision of end shields, pressure equalization shields, etc., but the miniaturized vacuum interrupters are not easy to start from this aspect, and can only be modified continuously by the shape of the internal components. With a reasonable arrangement and verification of the electric field strength, the design scheme for the uniform distribution of the internal electric field and the small electric field strength at the three-phase junction is optimized.
Using the same setting conditions, the calculated electric field intensity distribution diagrams for the above three structures are shown in Figure 5: a, b, and c are the static end plus high pressure conditions; a1, b1, and c1 are the dynamic end plus high pressure conditions.
a ESD at the three-phase boundary of the static end: 5.33 e+004kV/m a1 Emax at the three-phase boundary of the static end: 4.27e+004kV/m
Moving three-phase junction Emax: 1.86 e+004kV/m Moving three-phase junction Emax: 2.66e+004kV/m
b Three-phase boundary at static Emax: 3.73e+004kV/m b1 Three-phase boundary at static end Emax: 3.32e+004kV/m
Moving end three-phase junction Emax: 2.4 e+004kV/m Moving end three-phase junction Emax: 2.4e+004kV/m
c Three-phase junction at the static end Emax: 3.46e+004.kV/m c1 Three-phase boundary at the static end Emax: 3.2e+004kV/m
Three-phase junction at the moving end Emax: 2.33e+004kV/m Three-phase junction at the moving end Emax: 2.4e+004kV/m
Figure 5 shows the electric field intensity distribution
ã€analysis】The values ​​shown in the figure are measured with respect to certain set parameters.
Structure a: The values ​​shown indicate that the electric field strength at the three-phase junction of the static end is significantly higher than that at the three-phase junction of the moving end regardless of whether the high voltage is applied at the stationary end or the high voltage is applied at the movable end, so it is easy to be close to the static Insulation damage occurs at the end, which is consistent with the above power line analysis results.
Structure b: The electric field strength at the three-phase boundary of the dynamic and static ends is lower than that of the structure a, and the difference in the electric field intensity at the dynamic and static ends is reduced when a high voltage is applied, and the insulation level of the structure a is optimized.
Structure c: After the end shield is added at the static end, the electric field strength at the three-phase junction of the static end is reduced to a smaller value, and the dynamic end is not changed significantly, which makes the insulation level of the arc extinguishing chamber further optimized. Therefore, the three structures are relatively comparable, and the structure c is optimal.
From the above two analysis situations, the results of insulation optimization in the arc extinguishing chamber are consistent.
In the above, only a limited number of scenarios have been optimized and analyzed to introduce the specific application of Ansoft Maxwell software. In the optimization of insulation design for miniaturized vacuum interrupters, optimization analysis is also needed from many aspects, such as the thickness, radius, radius of curvature of the contacts, the transition between the contacts and the cup holder, and the shape and curvature of the port of the shield. The radius, the distance between the contact and the shield, the distance between the static and dynamic contacts, etc. We must also consider the analysis of the power line and the analysis of the electric field strength. Although this optimization process is cumbersome, after a series of optimization analysis, we can help us to reasonably design the size of each component and reasonably arrange the position of each component. , It can effectively improve the electric field distribution in miniaturized vacuum arc chamber and increase the insulation level of miniaturized vacuum interrupter.
3ã€Conclusion1) The application of Ansoft Maxwell software has provided scientific design basis for designers in the field, greatly shortened the design cycle and provided us with competitive conditions.
2) With the miniaturized vacuum interrupter optimized by Ansoft Maxwell software, the internal insulation level can be greatly improved, thereby further adapting to the market's demand for miniaturization of high voltage products.
3) The calculation method discussed in this paper is only a bit of experience in the work of the author, and it is only applicable to the qualitative analysis of two-dimensional electrostatic fields, and more applications have yet to be further discussed by colleagues.
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