As long as the relay protection tester is a three-phase system, these three components can be decomposed. They are used to analyze the three-phase asymmetric phase separation into symmetrical components when the system voltage and current are asymmetrical. Negative sequence) and zero-sequence components in the same direction. Under normal circumstances, the relay protection tester will only have a positive sequence component. When the system fails, the three phases become asymmetrical, and the negative sequence and zero sequence components with amplitude can be decomposed. There is only one of them. By detecting the two components that should not appear under normal conditions, you can know what is going wrong in the system. Through a series of related data, we can analyze the general situation of various system failures as follows:
Draw a vector diagram of the system's three-phase current (the current and voltage are the same); find the algorithm for each component:
1) Find the zero sequence component: add and sum the three vectors. That is, phase A does not move, and the origin of phase B is translated to the top of phase A (arrow). Note that phase B is only translational and cannot be rotated. The same method translates phase C to the top of phase B. At this point, the vector from the A-phase origin to the top of the C-phase (in this case, the arrow-to-arrow) is the sum of the three-phase vectors. Finally take the one-third of the magnitude of this vector, which is the magnitude of the zero-sequence component, the direction is the same as this vector.
2) Find the positive sequence component: The original three-phase vector diagram is first processed as follows: phase A does not move, phase B rotates clockwise by 120 degrees, and phase C rotates counterclockwise by 120 degrees, thus obtaining a new vector diagram. According to the above method, the vector diagram is three-phase summed and taken in one-third, which results in a positive-order A phase, and the two phases of B and C are respectively drawn by the amplitude of the phase-A vector by 120 degrees. This leads to the positive sequence component.
3) Find the negative sequence component: Note that the processing method of the original vector image is different from the normal sequence. The A phase does not move, the B phase rotates 120 degrees counterclockwise, and the C phase rotates 120 degrees clockwise, thus obtaining a new vector diagram. The following method is the same as the positive sequence.
Draw a vector diagram of the system's three-phase current (the current and voltage are the same); find the algorithm for each component:
1) Find the zero sequence component: add and sum the three vectors. That is, phase A does not move, and the origin of phase B is translated to the top of phase A (arrow). Note that phase B is only translational and cannot be rotated. The same method translates phase C to the top of phase B. At this point, the vector from the A-phase origin to the top of the C-phase (in this case, the arrow-to-arrow) is the sum of the three-phase vectors. Finally take the one-third of the magnitude of this vector, which is the magnitude of the zero-sequence component, the direction is the same as this vector.
2) Find the positive sequence component: The original three-phase vector diagram is first processed as follows: phase A does not move, phase B rotates clockwise by 120 degrees, and phase C rotates counterclockwise by 120 degrees, thus obtaining a new vector diagram. According to the above method, the vector diagram is three-phase summed and taken in one-third, which results in a positive-order A phase, and the two phases of B and C are respectively drawn by the amplitude of the phase-A vector by 120 degrees. This leads to the positive sequence component.
3) Find the negative sequence component: Note that the processing method of the original vector image is different from the normal sequence. The A phase does not move, the B phase rotates 120 degrees counterclockwise, and the C phase rotates 120 degrees clockwise, thus obtaining a new vector diagram. The following method is the same as the positive sequence.
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