| At present, the short-circuit fault seriously threatens the security and stability of power system & large-scale power supply. The fault current limiter (FCL) installed in these systems is one of main measures. And this technology is already successful application in AC power system. Development of high voltage DC power system requires DC FCL also. As a consequence, research on key theory and measure of high voltage DC power system has become the leading edge for power system research.A snubber with function of DC FCL is proposed in this paper. The theory, topology, eddy current loss and magnetic hystersis loss of the snubber have been studied, and a minitype sunbber has been manufactured. Then, 3.5nF/100kV snubber has been simulated and tested. The conclusions are as follows:The analysis of the equivalent resistance for snubber considering magnetic saturation is presented in this paper. Using Ampere's law, the eddy current and the thickness of saturated regions can be deduced in each core tape referring to Fink-Baker method. The equivalent resistance of the snubber is obtained. The transient eddy current model based on the stray capacitance and the equivalent resistance is analyzed. The solving process is listed in detail with variable substitution. Parameters, which are exponential time constant and arc current and peak current of the arc current, are obtained. The equivalent resistance of snubber and the decay time of arc are been obtained when some core tape just fully saturated.The core material of the snubber has been confirmed. From analytical method of ferromagnetic material, several kinds of ferromagnetic material have been compared, and suitable one has been chosen. The relation between the controlling parameter and the dimension of the snubber has been analysed. And results show that the snubber should be slightness. The inside radius and outer radius are determined referring to the dimensions of transmission line, and the length of snubber is confirmed.A simulation model consisting of a parallel resistance and inductance is been presented and set up. The two parameters can be directly calculated according to the work condition, dimensions and material characteristics of the snubber. And simulation study has been researched. The simulation results show that saturation threshold voltage of snubber can be enhanced with secondary resistor, and also show that the capacity of limitting current and absorbing stored energy can be improved. The theoretic analysis laid theory base for snubber test model manufacture and high voltage, high capacity snubber research.Minisnubber was constructed for Experimental Advanced Superconducting Tokamak (EAST) neutral beam injector (NBI) referring to the simulation design scheme. A sequence of experiments has been completed. And results show that snubbers have good ability of current-limiting function. Exponential time constant and peak current of the arc current are approximately the same as measured ones. The validity of the analytical method is validated.The 3.5nF/100kV snubber of EAST NBI has been manufactured. We conducted a sequence of tests on the EAST NBI experimental system. And the results show that a very good agreement between the experimental test results and the simulated ones. Because the stray capacitance of test stand is much larger than its expectation value, EAST NBI system should introduce two 3.5nF/100kV snubber prestnted in this paper.A snubber proposed in this paper has the advantages of low voltage loss under steady state, high limiting resistance, fast dynamic response, satisfied current limiting effect and powerful ability of absorption stored energy. It is a promising apparatus as the NBI system protection. Experimental study on the minisnubber validated the theory analysis and proposed simulation model are validity in this paper, which make a ready for research and designing International Thermonuclear Experimental Reactor (ITER) snubber. |
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