Analysis of distributed generation operation modes using new effective voltage stability index in radial system

Abstract

SUMMARY This paper presents detail assessment of the impact of renewable energy type distributed generation operation modes on the voltage stability indices. Most of renewable distributed energy sources are capable of operating in two modes, which are constant voltage and constant power modes. Different simulation results were obtained for voltage stability index (VSI), which serves as indicator of stability. Furthermore, this study has also considered charging station (CS) as a load, that is, gradually increased at the selected bus until the system attains instability state. The persistence of the instability can lead to voltage collapse, and VSI value can give an indication of the collapse as well. In this paper, the concept of active power voltage stability index (P‐VSI) is introduced with the aim of predicting the voltage collapse as a result of incremental CS loading in the network. Based on the analysis conducted in radial networks with multiple distributed generation units, the P‐VSI gave better indication for the voltage collapse much more than reactive power voltage stability index. The analysis was conducted on 33 bus distribution system. Copyright © 2013 John Wiley & Sons, Ltd.

A comprehensive assessment to propose an improved line stability index

“…However, in real systems, P and Q may flow in opposite directions. In such conditions, the above‐mentioned indicators may not properly evaluate the stability status, which has not considered in research works . To clarify this problem, in the network shown in Figure , the L index is calculated in the following operating points: Case P Load = 600 MW, Q Load = 200 MVAr. In this case, since P and Q are flowing from bus 1 to the other one, bus 1 is considered as the SB.…”

“…In this regard, these indicators may seem to be a proper tool for voltage stability assessment. Nevertheless, in the sequel, it will be shown that these indices have a major drawback, which is not considered in the literature . To explain this drawback, consider the simple network shown in Figure A, which includes three transmission lines connected in series.…”

A new approach for static voltage stability assessment in distribution networks

“…In the following literature, using a two‐bus equivalent circuit, researchers have presented indices such as L mn , L P , line collapse proximity index (LCPI), line voltage stability index (LVSI), simplified voltage stability index (SVSI), power stability index (PSI), L 1, and new voltage stability index (NVSI) based on the bus voltage levels, the maximum transferrable power, and line characteristics. These indices have low computational demand and can easily calculate the stability level of all network buses.…”

Optimal location of step-up transformer in radial distribution networks to enhance static voltage stability

“…Safety in a power system is usually representative of its capability in maintaining stability against fluctuations and malfunctions . The phenomenon of voltage stability, as one of the restricting factors in power system operation in various sectors including generation, transmission, and distribution, has been received many researchers' and power companies' attention . It is approved that voltage stability can be used as a suitable criterion in order to assess the security level of power systems .…”

“…4 The phenomenon of voltage stability, as one of the restricting factors in Nomenclature: Indices: 1, the downstream network of the step-up transformer; 2, the upstream network prior to the step-up transformer Variables and parameters: a, the voltage ratio of the step-up transformer; I L , load current, pu; l, the length of the line, km; p, the real power of load, MW; P, the real power of load, pu; Q, the reactive power of load, pu; R, line resistance, pu; S, load apparent power, pu; V, voltage magnitude at the receiving end of the feeder, pu; V S , voltage magnitude at the sending end of the feeder, pu; X, line reactance, pu; χ, the horizontal axis of xy bidimensional space; Y, the vertical axis of xy bidimensional space; Z, line impedance, pu; φ, the inverse cosine of load power factor; δ, the angle of the line impedance; Δ, the discriminate (delta) of quadratic equation; ΔV, voltage drop across the line; λ, the percentage of the length of the feeder that is located between the sending end and step-up transformer power system operation in various sectors including generation, transmission, and distribution, has been received many researchers' and power companies' attention. [5][6][7][8][9][10] It is approved that voltage stability can be used as a suitable criterion in order to assess the security level of power systems. 1112 claim that power system is a nonlinear dynamic system, and the most important discussion of this system is that of voltage stability.…”