Because of the elements which run under nonideal linearity and unentire symmetry in the power system , the loads which are different and change randomly , the methods which adjust and control the system faultily and operate improperly , the disturbance and the malfunction which happen somewhere , the current and voltage in the supply system are distorted seriously and thus large amount of harmonics are produced 但是，由于电力系统元件运行的非理想线性或非完全对称、负载的性质各异且随机变化、调控手段的不完善以及错误操作、外来干扰和各种故障的存在，供电网中的电流(电压)发生畸变，产生大量谐波。
