The electric field at the edge of the power capacitor plate is an extremely uneven electric field, and its calculation is a difficult problem. Decades ago, some scholars challenged this problem and announced their research results. There are many methods for calculating the electric field in the literature that can be used to calculate the electric field at the edge of the capacitor plate, including the conformal transformation method, the finite element method, etc. However, their calculations are too complicated and inconvenient to use. So far, in conventional projects for power capacitor design and calculation, only the operating field strength (i.e. average field strength) is calculated, and the marginal field strength №J is not calculated. Due to the lack of suitable calculation tools, the issue of the marginal electric field of power capacitor plates has received little attention and is basically still at a loss. People, especially professional designers and researchers, hope to find an “ideal” simple method to calculate the marginal electric field of the plate, so as to study the relationship between the shape scale of the component structure and the electrical and physical parameters of the medium and the marginal electric field of the plate. It also provides practical tools for increasing the calculation of marginal field strength in routine projects of power capacitor design and calculation. The so-called “ideal” simple calculation method should be: the physical model based on the calculation is basically consistent with the reality, so it can express its basic rules and allow some details to be ignored to prevent the model structure from being too complex for analysis.
Complex and complicated; the derived calculation formula is simple and easy to use frequently, concise and easy to understand, concise and easy to remember; the calculation results are logical and can provide theoretical guidance for the structural design, performance analysis and manufacturing process of capacitors.
Based on the above guiding ideology, various explorations have been conducted on relevant issues and some results have been accumulated. Applying it to the design and calculation of power capacitors is very helpful for analyzing the performance of capacitors and comparing and optimizing design plans. Part of the results are now announced and experts are invited to comment and make corrections.
Differences in plate edge insulation: Modern high-voltage parallel capacitor components use oil-immersed polypropylene film as the inter-electrode medium and aluminum foil as the plate. One end of the plate protrudes outside the medium, and the other end is folded and recessed in the medium. The structural advantages of this protruding and folded plate are: it improves the electric field distribution at the edge of the plate, significantly improves the partial discharge performance, greatly reduces the plate resistance and plate loss, reduces the temperature rise, and improves thermal stability It is widely used because it is flexible and can use protruding plates to connect components, simplifying the structure and manufacturing process, saving man-hours, etc.
This article uses a simplified circuit model to solve the electric field distribution in the edge insulation of the plate, focusing on the protruding and folded plate structures commonly used in modern power capacitors. It also provides some concepts for expressing the edge electric field and some formulas for calculating the electric field distribution. It also provides The calculation formula of plate marginal capacitance is given. The electric field distribution in the insulation at the edge of the plate is extremely uneven, and the maximum field strength appears on the surface of the edge of the plate. Its value is equal to the product of the average field strength and the electric field distortion coefficient. As the distance from the device to the edge of the plate increases, it quickly decays to zero according to the rules of the exponential function. These concepts and formulas are helpful for understanding and understanding of the marginal electric field, and can provide theoretical guidance for the structural planning, functional analysis and manufacturing process of capacitors.
Conclusion 1) The weakest part of the marginal insulation of the capacitor plate is its oil gap. The electric field in the oil gap is an extremely non-uniform electric field. The maximum field strength appears on the edge surface of the electrode plate, and its distribution is an exponential function that rapidly decays. The maximum field strength in the oil gap is equal to the ratio of the component voltage to the characteristic thickness6. 6 is also the attenuation constant of the plate marginal potential or field strength distribution. Through a 6 thickness potential or field strength, the attenuation is 0.368. The attenuation is 0.018 3 through the thickness of 46, and the electric field outside our thickness has actually attenuated to zero. Equation (12) can be used to calculate it very conveniently. 6 is approximately half of the total thickness of the interpolar medium. 2) The maximum field strength in the oil gap can be obtained by multiplying the uniform field strength and the electric field distortion coefficient Kqh.The electric field distortion coefficient can be calculated very conveniently using equation (13A)