中文摘要：

微分方程算法采用集中参数的电阻和电感串联模型,可以实现快速动作。线路故障后的暂态期间,由于受到电压、电流互感器传变特性和线路分布电容等因素影响,微分方程算法计算出的阻抗会在实际值上下频繁波动,影响保护的可靠动作。针对这一问题,提出采用希尔伯特—黄变换（HHT）处理微分方程算法计算结果的方法。通过经验模态分解将代表高次谐波的固有模态函数分离出来,得到具有单调变化趋势的＂残差＂,再由此计算出故障线路阻抗。仿真结果表明,该方案能在线路故障后快速估算出具有较高精度的阻抗值。

英文摘要：

The differential equation algorithm（DEA）based on the resistive-inductive model of a fault loop circuit can be used to make rapid tripping decisions.However,effected by various factors,such as the transient response characteristics of voltage and current transformers,the distributed capacitance,etc,the result of DEA fluctuates up and down around the actual value frequently after a fault occurring.It may lead to relay operating incorrectly.In order to overcome this problem,a scheme in which Hilbert-Huang transform（HHT）is used to extract high-frequency components of the results of DEA,is presented. Through empirical mode decomposition（EMD）,the intrinsic mode functions（IMF）of high frequency harmonics can be separated out,and the residue which has monotonic trend and useful for evaluating the impedance of fault line can be obtained. Simulation results show that the proposed scheme can evaluate the impedance with high accuracy.