A short-circuit analysis algorithm capable of analyzing unbalanced loads and phase shifts through transformers using the Newton-Raphson power-flow calculation, sequence, and superposition methods

摘要

Load in short-circuit analyses is usually neglected because the short-circuit current magnitude that flows from conventional rotating machines is significantly greater than the short-circuit current magnitude changed by the loads. However, as distributed loads unbalanced in phases have been connected to a grid, the current that flows from them affects the magnitude and angle of the short-circuit current. Thus, the objective of this study is to develop a short-circuit algorithm able to analyze the effect of unbalanced loads and phase shifts through transformers on the short-circuit current. For this purpose, this study adds the steady-state short-circuit models of loads unbalanced in phases to the sequence network. To determine the accurate short-circuit current, this study proposes the superposition principle that superimposes the contribution of pre- and post-fault conditions. To calculate the pre- and post-fault voltages, this study also combines the three-phase Newton-Raphson and sequence methods. In addition to the superposition principle, this study takes phase shifts through three-phase transformers in the sequence network into account. The case studies indicate that the proposed method could be more accurate because of not ignoring loads unbalanced in phases and the phase shift through transformers.