【作者】 张皓；

【导师】 赵伟；

【作者基本信息】 清华大学 ， 电气工程， 2007， 硕士

【摘要】 在实际的三相制电力系统中,外部电流对电流互感器误差性能的负面影响不容忽视。为了检测电流互感器在实际工作环境中的实际误差,国内权威部门提出一种在被检电流互感器铁心上局部缠绕一次绕组的所谓非均绕等安匝检定方法。然而,目前国内外在对该方法物理机理的研究上存在空白。因此,对该方法的物理机理进行深入研究,无论对电流互感器检定的科学合理性还是对指导大功率电流互感器的优化设计,均具有重要的理论意义和实用价值。本文首先采用等值电路,结合实例,分析由外部电流产生的杂散磁场对电流互感器误差性能的影响。之后,分别利用分离变量法和电磁场有限元方法求解外部电流产生的杂散磁场。经与实测值比较发现,三维磁场计算机数值仿真结果较为准确。研究表明,外部电流对电流互感器的影响程度,主要取决于杂散磁场的大小,其与电流互感器的主磁场合成后,若电流互感器铁心仍保持工作在线性区内,则外部电流对其误差性能的影响可忽略不计;而一旦合成磁场足以使电流互感器铁心达到饱和,其误差性能将严重恶化。其次,结合实例,对非均绕一次绕组电流产生的泄漏磁场对电流互感器误差性能的影响进行分析,并对泄漏磁场进行三维有限元仿真计算。研究结果表明,与杂散磁场相仿,泄漏磁场对电流互感器误差性能的影响程度,也取决于其与主磁场合成后电流互感器铁心是否饱和;而且,完全可通过改变一次绕组在电流互感器铁心上的覆盖角度,得到大小不同的泄漏磁场。最后,为满足用户需求,还利用径向基函数网络对杂散磁场、泄漏磁场的仿真结果进行了数据拟合。为使检定结果合理反映电流互感器的实际误差性能,从检定时和实际工作环境中电流互感器铁心局部最高磁通值相等出发,根据推导出的合成磁场表达式,将两个径向基函数网络结合,实现了对不同工作环境中的被检电流互感器,选用不同覆盖角度非均绕的等安匝检定方法,并以实例证明了所采用计算方法的合理性。更多还原

【Abstract】 In three phase system, the serious influence of external currents on the current transformer’s accuracy shouldn’t be ignored. Domestic authorities presented the uniformly-distributed equal ampere-turns verification method, which concentrates the primary turns on one part of the current transformer’s core, to measure the error of current transformer in actual working environment. However, there’s few or no special research on this verification method at home and abroad up to now. Therefore, the research on the theory of this method will be valuable and significant for verification, design and improvement of current transformer.Firstly, this paper uses equivalent circuit to analyze the influence of external current’s stray magnetic field on the error of current transformer. Then, this stray magnetic field is solved with separation of variables and finite element method separately. Compared with actual measured value, the numerical computation result of three-dimensional magnetic field proved accepted. It indicates that the influence quantity of external currents on current transformer depends on the magnitude of stray flux. If the resultant flux of stray and working flux of current transformer is big enough to make the current transformer’s core saturated, the accuracy of current transformer will consequentially get bad. Otherwise, the change of current transformer’s accuracy could be ignored.Secondly, this paper takes an example to analyze the influence of concentrated primary turns’leakage magnetic field on the error of current transformer. Also, this leakage magnetic field is solved with finite element method. Like the stray flux, the influence quantity of leakage magnetic field on current transformers depends on whether the current transformer’s core is saturated in the resultant magnetic field of leakage and working magnetic field. The change of primary turns’concentrated angle on current transformer’s core could change leakage magnetic field.The radial basis function neural network is used to fit the numerical computation results of stray flux and leakage flux separately. Then these two radial basis function neural networks are combined to give concentrated angle of primary turns on the current transformer’s core to ensure that flux maximum of the core under verification equal to flux maximum in actual working environment. The measurement result is the error of current transformer in actual working environment consequently. An example is taken to prove that computational method is rational.更多还原