2 On the Reliability of Real Measurement Data for Assessing Power Quality Disturbances Alexandre Brandao Nassif Hydro One Inc.,Toronto, ON, Canada 1. Introduction Power quality assessment is a power engineering field that is first and foremost driven by real data measurements. All the power quality assessment applications rely on results from real data processing. Take as an example the art of harmonic filter design, which is an engineering field notoriously known for relying on simulation-based planning; in this technical assessment, data recordings are indirectly used for finding the frequency response (or R-X plots) of the system impedance that is/are in turn used to determine the. | 2 On the Reliability of Real Measurement Data for Assessing Power Quality Disturbances Alexandre Brandao Nassif Hydro One Inc. Toronto ON Canada 1. Introduction Power quality assessment is a power engineering field that is first and foremost driven by real data measurements. All the power quality assessment applications rely on results from real data processing. Take as an example the art of harmonic filter design which is an engineering field notoriously known for relying on simulation-based planning in this technical assessment data recordings are indirectly used for finding the frequency response or R-X plots of the system impedance that is are in turn used to determine the filters tuning frequencies Kimbark 1971 . With so much reliance on the acquired data the quality of such has become a very sensitive issue in power quality. An imperative action is to always employ high-resolution recording equipment in any instance of power quality analysis. Nevertheless high-resolution equipment does not guarantee data usefulness because the measured data may be inherently of very low energy in a variety of ways. Therefore to investigate such cases and to propose methods to identify useful data were the motivations for this research. This chapter proposes methods for data selection to be used in two applications where the reliability issue is crucial the power system impedance estimation and the interharmonic source determination. The network harmonic impedance estimation Network impedance is power system parameter of great importance and its accurate estimation is essential for power system analysis at fundamental and harmonic frequencies. This parameter is deemed of being of great importance for a variety of power system applications such as evaluating the system short-circuit capacity or defining the customer harmonic limits Kimbark 1971 - IEEE Std. 519-1992 . Several methods have been proposed to measure the network harmonic impedance and are available in .