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

Abstract

Summary 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.

Whole‐line fault analysis method for unbalanced distribution networks with inverter interfaced distributed generators

“…Cho et al [6] proposed a shunt fault analysis method to improve the distribution automation, using the bus impedance matrix. The loads effect was considered in short-circuit analyses and a fault current algorithm was developed by Kim [9] based on the Newton-Raphson power-flow calculation, sequence, and superposition methods.…”

“…Nevertheless, research shows that the distribution network contains numerous buses and constructing the whole bus impedance matrix needs more efforts, which is not suitable for distribution network [7][8][9][10][11]. The bus-oriented methods need to be improved in DMS.…”

A new load flow and short‐circuit analysis for unbalanced modern distribution system

“…This method has also not introduced the DGs and various transformer models in the short‐circuit calculations. A sequence component based short‐circuit analysis methods for distribution grid along with IBDGs and unbalanced load models are introduced in References 26 and 27. In the method proposed in Reference 26, a current control strategy based inverter model has been considered during the short‐circuit current calculation.…”