Improved three-phase load flow using phase and sequence components

Abstract

The single-phase load flow is efficiently optimised for the rapid solution of power flow and voltages in large systems. The three-phase load flow, at present treated simply as an extension of the single-phase load flow, is primarily used to calculate asymmetry at fundamental frequency throughout the transmission system. A new three-phase load flow, radically different from the single-phase load flow, is proposed. The new load flow is more suited to the analysis of power quality problems in the transmission system. A mixed combination of sequence and phase component mismatches is used, with emphasis on robust convergence rather than speed. It is shown that the three-phase load flow will find one of two solutions at each load busbar, one of which corresponds to abnormal levels of zero sequence voltage. The abnormal solution can be avoided by ensuring a path for zero-sequence current from the load.