Abstract
Equivalent power system impedance is an important electrical quantity from many points of view. Areas in which this parameter plays an important role include, in particular: Voltage stability analysis, power quality, or fault condition analysis. Power system impedance estimation in real operation conditions can be performed by one of the non-invasive methods described by different authors. This paper aims to investigate and compare seven different methods for power system impedance estimation based on voltage and current variations measurement. After a brief description of selected methods, these methods were applied for power system impedance estimation in the case of two simple simulation tests and then in the case of three real measured data. Voltage and current changes used for power system impedance estimation in real conditions were measured in high voltage (HV) and medium voltage (MV) substations feeding steel mill with the electric arc furnace (EAF) operation. As the results presented in this paper have shown, not all of the methods analyzed are suitable for determining the power system impedance based on the fast step changes of voltage and current that occur, for example, during an EAF operation. Indeed, some of the tested methods were originally designed to determine the power system impedance from changes in voltages and currents recorded at steady state.
Highlights
Measuring and determining the power system impedance in real conditions is an ever-evolving field of research
Different size of power system impedance can be evaluated from the rapid voltage and current change, where subtransient reactances of synchronous machines or reaction of induction motors are included, and a different size of power system impedance can be evaluated from the comparison of steady-state voltage and current changes, where no subtransient reactances of synchronous machines or reaction of induction motors are included
If the interests of power system impedance deals with the power system weakness or with the initial short-circuit current identification, rapid changes of voltages and currents should be used for the analysis
Summary
Measuring and determining the power system impedance in real conditions is an ever-evolving field of research. The first type of TI represents the power system equivalent impedance in the case of steady-state conditions. This type of TI is important to know, for example, for purposes of evaluation of the power system voltage or static stability. The second type of TI represents the power system equivalent impedance in the case of large rapid change in operating conditions, such as in the case of fault occurrence. The difference between these two types of TI depends on the influence of the behavior of synchronous and asynchronous machines as well as of a load in general
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