Unbalanced source identification at the point of evaluation in the distribution power systems

Abstract

SummaryThree-phase unbalance is one of the most important power quality problems in the power system. When the system is working under unbalanced conditions, more losses and heating effects will be induced, and the system will become less stable, which is harmful to both utilities and customers. The most important thing for a seriously unbalanced system is to find out the main unbalanced source to take proper measures to mitigate the problem. In this paper, a method is proposed to indentify the main unbalanced source at the point of evaluation (POE) in the distribution power systems. Two extreme cases are analyzed in the paper by assuming that the unbalanced source to be totally from the POE upstream network or downstream network. Therefore, 2 corresponding analytical formulas are derived to reveal the relationship between the POE voltage unbalance factor (VUF) and the current unbalance factor (CUF). A method is then proposed to determine the contribution of the unbalanced source at the upstream and downstream networks based on the comparison between the derived VUFs and the actual VUF. Sensitivity analysis is implemented to show the robustness of the proposed method. The effectiveness and validity of the proposed method is illustrated by the IEEE 13-bus test system and IEEE 37-bus test system. It is shown that the estimation error of the proposed method is generally within 5%.

Determining the Responsibility of Three-Phase Unbalanced Sources Based on RICA

“…The three-phase current and voltage at the PCC can be obtained by measurement, and the collected information is subjected to Fourier analysis to obtain the fundamental frequency component of the voltage and current. By calculating the symmetrical component method, the phase component can be converted into the sequence component, as shown in Equations (5) and (6).…”

“…As one of the main power-quality problems, voltage unbalance has caused widespread concern among power sellers and consumers [1][2][3][4]. Voltage unbalance refers to the phenomenon that the voltage amplitude of the fundamental frequency is not equal, or that the phase is offset in a three-phase power system [5,6]. In a power system, voltage unbalance is the result of a combination of numerous unbalanced sources.…”

“…At present, the research on voltage unbalance mainly focuses on the division of unbalanced responsibility, unbalanced source location, calculation of node unbalance [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], and research on voltage unbalance mitigation measures. The assessment of the contribution of unbalanced sources at the point of common coupling is the premise of responsibility division and governance.…”

“…Mahyar Abasi proposed to establish a model in the n-node radial distribution network to analyze the impact of loads, lines, and sources on the system unbalance, but the topology of the system needs to be known [4]. According to circuit topology, Sun Yuanyuan has derived the general formula for the division of unbalanced sources responsibility, which only requires knowledge of the voltage and current at the PCC [5,6]. In [8], the three-phase power flow method was used to evaluate the effects of unbalanced sources and loads on the unbalance factor.…”

A practical approach for distribution network load balancing by optimal re‐phasing of single phase customers using discrete genetic algorithm

“…Load unbalance is one of the conventional problems in the distribution networks . It is caused by inappropriate distribution of demands among network phases, variety of customers usages, existence of unbalanced three‐phase loads, and distribution networks nonsymmetrical impedances.…”