【作者】 温惠；

【导师】 谭震宇；

【作者基本信息】 山东大学 ， 电工理论与新技术， 2011， 硕士

【摘要】 随着我国电网负荷密度和总体容量的增长,系统的短路电流越来越大。基于氧化锌避雷器(Metal Oxide Arrester, MOA)的串联谐振经济型故障限流器,由于其较好的短路电流限制能力,运行可靠性高、技术经济性能好、无需外加控制而实现自动投切等明显优点,可望在高压电网中首先获得实用。发生短路故障时,巨大的短路能量注入到MOA中,金属氧化物压敏电阻(Metal Oxide Varistor, MOV)上有大量短路电流流过,导致其温度快速升高。为保证MOA的可靠运行,延长其使用寿命,需要尽快散热降温。因此,MOA冷却结构的设计和了解MOV阀片柱的温度分布非常重要。本文首先分析了MOA热传递的过程,介绍了包括Tominage模型法、等值热路图法、有限差分法、有限单元法在内的几种热分析方法的主要原理；讨论了氧化锌电阻片在小电流段、转折区的工频电流段、标准操作冲击电流段和标准雷电冲击电流段的功率损耗特性；在总结了傅立叶定律和导热微分方程等传热学理论的基础上,阐述了用有限单元法计算温度场的基本原理和过程,并给出了应用有限元软件ANSYS求解场问题的一般步骤。然后在传统MOA散热结构的基础上提出了一种新型MOA散热结构,即通过在两个ZnO阀片间叠加铝垫块,并在铝垫块上加工冷却通道的方法来改善MOA的散热效果。分别对传统和新型的MOA温度场问题建立了三维有限元模型,并利用ANSYS进行瞬态温度场的仿真计算,得出了相应的温度场分布规律和散热规律。系统地计算分析了冷却通道的条数、直径等几何因素对于通风道内传热特性和MOA散热特性的影响,提出了使散热效果更好的优化的结构参数(冷却通道的条数和直径),结果表明：MOA散热能力随冷却通道直径不同而变化,通道直径存在约为10mm的最优值,此时冷却结构散热效果较好,四条冷却通道比两条冷却通道具有更好的散热效果。计算并给出了MOA在长期运行后达到稳定平衡态时MOV的温度场分布,结果表明温升在允许范围内,MOA在该短路故障下仍能安全可靠运行。分析了残压变化时,MOA的发热和散热规律,计算了MOA可以承受的连续故障发生的最小时间间隔以及连续两次短路故障时MOA的散热特征。本文所做的工作为MOA的冷却结构设计和散热分析提供了理论依据和数据支持。更多还原

【Abstract】 As the increase of the load density and capacity of the power network, the short-circuit current becomes larger and larger. Owing to its strong ability of the limitation on short-circuit current, good reliable in operation, good technical and economic performance, and the auto-switching realization without additional control, economic type of the fault current limiter based on Metal Oxide Arrester (MOA) is expected to be applied in high-voltage system.When short circuit happens, tremendous short circuit energy enters into MOA and there is strong short-circuit current on Metal Oxide Varistor (MOV), leading to the rapid temperature increase of MOV. In order to insure the reliability of MOA operation and extend its service life, the temperature of MOV need to be reduced as soon as possible. Therefore, both the design of cooling structure with the excellent cooling efficiency and the knowledge for the temperature distributions are very important.In this thesis, the process of heating transformation of MOA is analyzed, the main principle of some thermal analysis methods, such as Tominage Model Method, Equivalent Thermal Circuit Diagram Method, Finite Difference Method, Finite Element Method (FEM), are introduced, and the power loss property of ZnO resistor in the different current regions which including low current section, turning area section, operation impulse current section and lightning surge current section are discussed. Also, the heat transfer theories such as Fourier’s law and conduction differential equations are summarized, the calculation principles of temperature field based on finite element method are briefly described, and the general steps for solving temperature field problem by using ANSYS are given.In order to improve the cooling effect of the cooling structure in MOA, a novel cooling structure is suggested. In this structure, special aluminum pad is added between two ZnO valve plates, and cooler channels are made on aluminum pad. The 3-D FEM model is established to solve the temperature field of the traditional and novel MOV, and the transient temperature field is simulated by using ANSYS code. Accordingly, the distribution characteristics of the temperature field and heat dissipation law are obtained. The systematical calculations and analyses on the influences of the diameter, numbers and distributions of the cooling channels on the heat transfer are performed, and the optimized geometric parameters with better cooling effects is presented. It is shown that the efficiency of the cooling structure can be changed by changing its diameter, there is an optimum diameter of 10 mm, where the good cooling efficiency is obtained, and the efficiency of cooling structure with the four channels is better than those with the two channels. In addition, the temperature distributions of MOV are calculated when the environment temperature is higher under stable equilibrium state after a long period running of MOA. The calculated results shows that the risen temperature is within the allowable range and MOA can reliably run in the short circuit fault. Finally, the heating and cooling properties of MOA are analyzed under different residual voltages, and the minimum time interval of two continuous faults and heating of MOA for two continuous faults are calculated.The goal of this thesis is to provide the theoretical evidence and data support for cooling structural design and heat dissipation analysis of MOA.更多还原