What are zero sequence voltage and zero sequence current?

The emergence of positive sequence, negative sequence and zero sequence is to analyze the asymmetry of the system voltage and current, and decompose the asymmetric components of the three phases into symmetric components (positive and negative sequence) and zero sequence components in the same direction. As long as it is a three-phase system, the above three components can be decomposed (a bit like the synthesis and decomposition of forces, but in many cases the value of a certain component is zero). For an ideal power system, due to three-phase symmetry, the values ​​of the negative sequence and zero sequence components are both zero (this is why we often say that there are only positive sequence components in the normal state). When the system fails, the three phases become asymmetrical, and then the negative sequence and zero sequence components with amplitude can be decomposed (sometimes only one of them). Therefore, by detecting these two components that should not appear normally, you can know that something is wrong with the system (especially the zero sequence component when a single phase is grounded).

1) Find the zero sequence component: Add three vectors to find the sum. That is, phase A does not move, and the origin of phase B translates to the top of phase A (arrow). Note that phase B only translates and cannot rotate. Use the same method to move phase C to the top of phase B. At this time, draw a vector from the origin of phase A to the top of phase C (sometimes arrow to arrow). This vector is the sum of the three phase vectors. Finally, take one-third of the amplitude of this vector. This is the amplitude of the zero sequence component, and the direction is the same as this vector. 2) Find the positive sequence components: First do the following processing on the original three-phase vector diagram:: Phase A does not move, phase B rotates 120 degrees counterclockwise, and phase C rotates 120 degrees clockwise, so a new vector diagram is obtained. Add the three phases of this vector diagram according to the above method and divide it into one-third, thus obtaining the positive sequence A phase. Use the amplitude of the A phase vector to draw the B and C phases with a difference of 120 degrees. This gives us the positive sequence components. 3) Find the negative sequence components: Note that the processing method of the original vector diagram is different from that of finding the positive sequence. Phase A does not move, phase B rotates 120 degrees clockwise, and phase C rotates 120 degrees counterclockwise, so a new vector diagram is obtained. The following method is the same as in positive sequence

Can we understand that zero sequence current is the product of an analysis method? It is not something that actually exists, just like welfare is also analyzed

Yes, ordinal networks are originally used for system analysis, right?