Dynamic Analysis And Optimization Of Thermal Stability For Conduction Cooling Magnet Of SMES System

The thermal stability of the direct cooling magnet of Superconducting Magnetic Energy Storage (SMES) is one of the most important issues in SMES application. When SMES makes power compensation to an electric power system, the dynamic load produced by the magnet and its cooling frame leads to large thermal disturbance to high temperature superconducting magnet, decreasing the stability of the SMES system. In order to increase the thermal stability of superconducting magnet and improve the design of magnet cryogenic system, this paper studies the thermal stability of direct cooling of a superconducting magnet on the basis of its stable and dynamic loads and its thermal transmission properties. With support of the National High Technology Research and Development Program of P.R. China (Project No.2002AA306331-4), the National Science Foundation of P. R. China (Project No. 50176013) and the Research Fund for the Doctoral Program of Higher Education of P.R. China (Project No. 200040487039), the thermal stability of direct cooling of superconducting magnet have been analyzed theoretically and experimentally and optimization research on magnetic thermal stability has been conducted.In order to increase the thermal stability of superconducting magnets and the thermal efficiency of cryogenic systems, this paper calculates the magnetic stable and dynamic loads based on heat transfer theory and electromagnetic theory and studies the magnetic load thermal transmission and its correlation to refrigerator properties. Also, optimization research on the operating condition of direct magnet cooling has proceeded in consideration of the thermal stability of magnet and the perfect degree of cryogenic and thermal systems. It shows that magnet operating temperature is inversely proportional to excitation current velocity and its amplitude.The magnetic dynamic thermal load is nonlinear, coupled and transient when the SMES excitating and demagneting. Mathematical and physical models of magnetic transient-state thermal analysis have been established on the basis of the finite element theory. The element type, its functional and shape function have been determined and the interpolation function has been established. The temperature field matrix has been solved by variational calculation, which provides an effective method to analyze the magnetic dynamic thermal transmission properties. By using finite element analyzing software ANSYS, temperature changes in transient-state have been numerically simulated in the conditions of SMES magnetic direct current-loading, dynamic current-loading and partial thermal disturbance. The magnetic thermal disturbance and transmission properties affected by stable-state load, partial load, discontinuous and continuous excitations have been studied. Magnetic highest temperature and axial temperature difference have been calculated numerically in different running conditions. Magnetic temperature field nephograms and response curves have been obtained in different load conditions. The mechanism of thermal stability has been analyzed and optimal values of excitation current in different running conditions have been obtained. The research on entropy generation minimization and numerical simulation shows that the interface thermal resistance between magnet and its cooling frame increases the temperature of the magnet as well as the power consumption of refrigerator.A SMES cryogenic experiment and its measuring system have been established. The cryogenic property measurement and experimental research have been taken in vacuum insulated experiment, magnet cooldown experiment, constant current source loading experiment and SMES dynamic simulating experiment. Here it is show that the established cryogenic system has good vacuum insulated property. In static cooling phase, the magnet becomes superconducting when the temperature reaches 109K. The lowest temperature of the magnet reaches 13.5K. The maximum current amplitude that constant current source loading can stand is 150A. Excitation dynamic thermal load leads to the increase of magnetic temperature when the SMES compensates the electric power network. The average magnetic temperature increase is 6.7K when the excitation speed is 10A/s. The error of dynamic experiment and numerical simulation result is within 4%. The data provide the evidence for the SMES magnet, cooling frame design and its system safety operation in the future.According to the major factors that influence the thermal stability of direct cooling of the SMES magnet, SMES magnetic thermal performance has been optimally analyzed by using magnetic temperature as an objective function. The method of cooling a superconducting magnet by a heat pipe that we propose has been numerically simulated based on the finite element theory and the ANSYS software. Magnetic cooldown speed, axial temperature difference, and dynamic thermal stability have been improved after the optimization.