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# Why is the zero line current greater than the live current?

1. Three-phase sinusoidal symmetrical alternating current. When the three-phase symmetrical load is balanced load, since the current vectors are equal in magnitude, the direction is 120 degrees out of phase, and the vector sum is zero, that is, its zero-sequence current is zero.
2, three-phase sinusoidal symmetrical alternating current, in the case of three-phase asymmetric load, that is, unbalanced load, because the current vector size is not equal, the direction, that is, the phase difference is not exactly 120 degrees, and the vector sum is not zero, that is, its zero-sequence current is not Balance current, but less than either phase current.
3. Three-phase sinusoidal symmetrical AC power supply. In the three-phase load, due to the existence of nonlinear components such as diodes, when there is a DC component in the three-phase load current and a high-order harmonic of three times the integer, the zero-sequence current is its arithmetic sum. That is, the zero-sequence current may be greater than the phase line current, such as a three-phase half-wave rectification circuit, and any phase current is 1/3 of the load current, and the load current is a zero-sequence current.

4. However, in the three-phase bridge rectifier circuit, since there are currents in the positive and negative half cycles of the alternating current, and the positive and negative half cycles are symmetrical within one week, the three phases are symmetric, that is, the direct current component and the third integer. The higher harmonics do not exist, so the vector sum of the three-phase currents is zero, that is, the zero-sequence current is zero.
5. In the single-phase bridge rectifier circuit, since there is current in the positive and negative half cycles of the alternating current, and the positive and negative half cycles are symmetrical within one week, the direct current component of the single-phase current and the triple integer multiple of the harmonics The wave does not exist.
6. If the three-phase load is a load such as a single-phase bridge rectifier circuit, although the balance is not balanced, the vector sum of the three-phase current is not zero, that is, the zero-sequence current is not zero, and the neutral current is not greater than the phase line. Current.

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