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Absfract-The tnherent differences in the accuracy of measunnglmonitoring power quality (PQ) instrumentation has led the Brazilian Transmission Independent System Operator (ONS -Brazilian ISO) ONS to conduct a comprehensive field campaign and laboratory tests. These tests have allowed for evaluation of the accuracy and measurement methodology for a large number of commercially available instruments. This paper presents the laboratory test results for the performance of the different instrumensts. AN of the instruments were simultaneously fed the same voltage signal. Lab tests were conducted which included most commom power quality indices such as: steady state voltage, frequency variation, unbalance voltage, voltage fluctuation and short duration voltage variation (sag).

This paper presents the results and inconsistencies concerning the accuracy of harmonic measurement instruments, particularly under harmonic timevarying conditions. Several instruments were fed simultaneously with different voltage signals and harmonic distortion results compared for each case. Significant differences among the several instruments tested were found. Index Terms:Harmonic distorion, harmonic measurement and instrumentation, time varying harmonics, harmonic measurement methodology. .O-IntroductionFrom the very beginning of its activities, ONS (The Brazilian Transmission ISO) has heen working with extreme diligence to establish performance standards in the Main Transmission Network as well as create the measures necessary to monitor their compliance.ONS is aware that the technical and philosophical aspects associated to the performance standards adopted by the Main Transmission Network, as well as the processes utilized to manage these standards are in a state of constant evolution. As such, intense on-going debates and discussions are underway both in Brazil and in the exterior. Besides this, when considering the environment of technological possibilities, some or all of these questions might be asked:When, where and how should performance standards he evaluated;What accuracy should be demanded of equipment and measuring systems (measurement protocols);What results should he made available to agents and society in general to reflect the principles of the range, transparency and relevance of information in order to characterize power quality in the Main Transmission Network and facilitate decision making;To what extent must the agents in the sector be involved in the management of power quality performance standards? This paper focus some issues concerning the accuracy of the measurement instruments for harmonic distortion evaluation. 2.0-BackgroundThe process to establish standard values for the transmission system performance indices should he preceded by measurement campaigns in order to verify the actual performance of the system. Specifically in the case of harmonic distortion, the Brazilian IS0 (ONS) has decided, before to begin the measurement campaigns, to evaluate the performance of the available measurement instruments.The aim of the tests was to verify the compliance of the instruments one with respect to the others. No judgment related with accuracy or measurement methodology was done. All the instruments were fed simultaneously with the same voltage signal. In the case of the tested instruments present different results the next step will be to go to a controlled environment (laboratory) in order to evaluate their accuracy and characteristics, including the measurement methodology.Instruments were tested considering two non-linear load characteristics. The first one corresponds to an arc furnace load and the second one to a rectifier load.A summary of the getting results for the twomeasurement campaign is presented in the following two item.The indices utilized to evaluate the instrument...

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