基于小波变换的配电变压器差动保护相位补偿方法

Phase compensation method of distribution transformer differential protection based on wavelet transform

为降低配电变压器故障引起的财产安全损失,提升电力系统运行稳定性,提出了基于小波变换的配电变压器差动保护相位补偿方法。首先,通过计算线模行波电流波动及其梯度绝对值大小,判断配电变压器有无故障,即创建保护启动判据。然后,依据等效线模行波差动电流的能量比确定故障区域,并计算小波变换故障区域的初始模量反向行波差动电流,以获得小波变换模极大值。最后,通过构建故障选极判据获取故障类型,计算故障状态下配电变压器空载合闸时的励磁电流,判断励磁涌流和内部故障电流的变化,并结合保护输出信号的开启和关闭,实现配电变压器的差动保护相位补偿。仿真实验表明,该方法可对区内故障进行有效鉴别,具有很强的可靠性及有效性。负载工况下,该方法相位补偿后电压电流的相位差一致,具有更好的稳定性。

To reduce the safety loss of property caused by a distribution transformer fault and improve the operational stability of power system,a phase compensation method of distribution transformer differential protection based on wavelet transform is proposed.First,considering the fluctuation of line mode traveling wave current and the absolute value of its gradient,it is judged whether there is a fault in the distribution transformer.That is,a protection startup criterion is created.Secondly,it determines the fault area according to the energy ratio of the equivalent line mode traveling wave differential current,calculates the initial modulus of reversing the traveling wave differential current under the fault area of the wavelet transform,and obtains the maximum value of the wavelet transform modulus.Finally,by creating a fault pole selection criterion to obtain the fault type,the excitation current is calculated when the distribution transformer is closed without the load in a fault state.Also the changes of excitation inrush current and internal fault current are judged,and the phase compensation of differential protection of the distribution transformer is realized in combination with the opening and closing of the protection output signal.Simulation results show that this method can effectively identify faults in the area,has strong reliability and effectiveness,and under load conditions,the phase difference of voltage and current after phase compensation is consistent.It also has better stability.