| New energy development, energy-savings and emissions reduction were emphasized and listed as priorities in the"The Outline of the National Program for Long- and Medium-Term Scientific and Technological Development". These industries will generally be planned by the State. Metrology Science is closely connected with the national strategy and provides powerful support for metrology calibration and traceability. This allows for development and sustainability of the economy and society, and innovation in scientific research.High amperage direct current measurement technology is widely used in industries such as metallurgy, chemical engineering, electroplating, electrical vehicle charging station, DC power transmission, and many others. High-accuracy measurement of high amperage direct current can provide the basic data for energy-savings and emissions reduction. It is also critical to measure, control, and calibrate high amperage direct current in scientific research of nuclear physics and high energy physics. Research and development for a high-accuracy high amperage direct current ratio national standard is the critical technical basis of high amperage direct current and ratio traceability in industries and sciences in the country. In this research, the self-calibration method and apparatus of the high-accuracy Direct Current Comparator (DCC) under working state, that is working and leakage megnetomotive forces, are developed. The research was funded by the project of"Research in Measuring High Amperage Direct Current"(Contract No. 0404GY-2), the sub-project of"Setup and Improvement of Electrical National Standard and Calibration System"(Project No. 2003DIA7J035), that is a basic research project under the Ministry of National Science and Technology.In the research, the theory and method of the DCC self-calibration, magnetic shielding, bus layout, performance testing, and uncertainty budget were developed, a set of theory of designing and self-calibrating the high-accuracy high amperage DCC, which is named of a method of distributed and uniformized space magnetomotive force, was self-renovation proposed and applied to the development and calibration of a series of DCCs. A self-calibration apparatus of high amperage direct current ratio was developed, with ranges of 10 A: 1 A to 5 kA: 5 A. The measurement uncertainty (k=2) of self-calibration is from 1×10-8 to 2.6×10-7, which is the best specifications according to the mastered information. The problem of ratio self-calibration of high-accuracy DCC under rated magnetic potential and working state was solved successfully.The research focused on the accurate ratio self-calibration of high amperage DCC under working states, and highly fruitful results are summarized as follows:1. The theory of designing, fabricating and self-calibrating the high-accuracy High Amperage DCC, a method of distributed and uniformized space magnetomotive force, was first put forward, and the strong magnetic interference introduced by large current buses is reduced. The experiment results on a developed apparatus confirmed that the theory is correct and effective.2. A new series and parallel method using primary windings with the same nominal turns connected in series or parallel for DCC high-accuracy self-calibration was proposed. The ratio equation of"series and parallel"method was deduced. It is proved that the relative deviation limitation is smaller than the product of the maximum difference among equivalent turns of windings (producing equivalent magnetic potential) and the maximum difference among the current over parallel windings. By combing with rigid-fixed bus bars and uniformized parallel currents technologies, the high-accuracy self-calibration of high amperage DCC under magnetic leakage was accomplished.3. A theoretical equation to calculate the effectiveness of magnetic shielding with air gap was deduced based on magnetic circuit method. It is concluded that magnetic shielding effectiveness in the vertical direction is worse than that in the horizontal direction; the comprehensive magnetic shielding effectiveness is determined by the thickness of the air gap and not affected by the thickness of magnetic shielding and permeability. The good agreements between the electromagnetic numerical simulation value and analytical value were achieved by using the 5kA:5A DCC developed as an example.4. Through electromagnetic numerical analysis based on the Astatic Structure Principle, it is proposed that using even and symmetrical eccentric buses and returning conductors can uniformly distribute space magnetomotive force inside of the detecting cores and magnetic shielding, and reduce dramatically the influence of magnetic leakage in the basis of simulating and analyzing the magnetic leakage characteristics produced by an eccentric bus in the detecting magnetic core. Furthermore, the bus layout, structure and parameters design were optimized after the influences of bus winding number, window radius, and shapes were analyzed.5. Using the series and parallel method and combining the optimized technologies of bus design, air gap control, and double magnetic shielding, high amperage DCCs with"series and parallel"structure in their buses were developed and high-accuracy series and parallel ratio self-calibration under working states was carried out.6. Through analyzing the magnetic leakage of the buses in the detecting core under different series connections using FEM analysis method, it is concluded that the method of"one by one in opposed series"is better for evaluating the influence to the uncertainty due to magnetic interference introduced by the buses.7. A mathematical model for the uncertainty budget of DCC self-calibration using series and parallel method was established. In the basis of practically measuring the non-linearity on magnetic potential and influence of magnetic leakage et al, the measurement uncertainty was estimated and verified.
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