正序、负序、零序的出现是为了分析在系统电压、电流出现不对称现象时，把三相的不对称分量分解成对称分量（正、负序）及同向的零序分量。只要是三相系统，就能分解出上述三个分量（有点象力的合成与分解，但很多情况下某个分量的数值为零）。对于理想的电力系统，由于三相对称，因此负序和零序分量的数值都为零（这就是我们常说正常状态下只有正序分量的原因）。
The appearance of positive sequence, negative sequence and zero sequence is to analyze the three-phase asymmetric component decomposed into symmetrical component (positive and negative sequence) and zero sequence component in the same direction when the voltage and current of the system are asymmetrical. As long as it is a three-phase system, the above three components can be decomposed (a little like the synthesis and decomposition of force, but in many cases the value of a component is zero). For an ideal power system, because of three-phase symmetry, the values of negative sequence and zero sequence components are zero (which is why we often say that only positive sequence components exist in normal state).