Aprofundamento em técnicas de levantamento de resposta em frequência de TPs

Abstract

With the increasing use of non-linear equipment, there is also concern about the behavior of the electrical power system in the face of possible harmonic distortions caused by these loads and their respective effects. Thus, studies are developed regarding techniques for measuring and quantifying these harmonic distortions in the context of campaigns to measure Power Quality indicators. When dealing with measurement systems, it may be necessary to use voltage transducers (VTs), depending on the voltage level to be measured. However, it is known that some types of VTs may not present a linear response in the frequency spectrum. Since the inductive voltage transformer is a device widely used for this purpose, studies to obtain the frequency response of this element are of great importance, as it is known in the literature that harmonic distortions may have impact on its accuracy of measurements. As there are several proposed procedures to perform the frequency response test, the present work intends to perform two out of these procedures found in Brazilian regulations, in order to analyze the main differences between the test procedures, and the results obtained from them. In this context, the first procedure consists in applying the VT primary with harmonic voltage lower than its rated value. On the other hand, the second procedure is characterized by the applying rated fundamental voltage plus harmonic components. After carrying out the tests, the frequency response curves were drawn, it was verified that the results obtained by the tests differed from each other, and that the VT response from the test with the fundamental voltage plus harmonic components showed non-linear characteristics, violating the limits for higher precision instruments suggested by IEC/TR 61869-103 for some harmonic orders. The test with a voltage lower than the rated remained within the suggested limits. Therefore, it is concluded that it is necessary to perform the test that considers the presence of rated fundamental voltage despite its greater difficulty in carrying out it in the field, since it leads to more accurate results along the harmonic spectrum, showing the real impacts of non-linearity of inductive voltage transformers.