A. Symmetrical components
1. Asymmetric sudden short-circuit in the power system, will inevitably lead to changes in the fundamental frequency component of the current, and produces a DC component free. In addition, asymmetric short circuit will produce a series of harmonics.
2. The flow through the three-phase positive sequence current, three-phase voltage on the positive-sequence voltage components, while flowing through the negative and zero sequence current, the voltage on the component is negative and zero sequence voltage. That is, for symmetrical three-phase components, each sequence component are independent, and only the positive sequence current, negative sequence and zero sequence related.
2. System power element equivalent circuit parameters and sequence
1. The three-phase positive sequence impedance of the transmission line impedance of the transmission line is the steady-state operation. Due to the power transmission member is stationary, the phase sequence change does not alter the mutual inductance phases, so the same negative sequence impedance and the positive sequence impedance.
2. The zero-sequence impedance when flowing through the three-phase line zero sequence circuit, each phase of the equivalent impedance when the same-phase AC current. In this case the three-phase current is not zero, not like the three-phase flow through the positive and negative sequence current as three mutually have another circuit to circuit, a three-phase zero-sequence current.
3. The cable core is small pitch, which line the positive sequence, negative sequence reactance is much smaller than the overhead lines. Its resistance and reactance are usually supplied by the manufacturer.