The influence of harmonics from non-linear loads in the measuring transformers of electrical substations

Abstract

The mainstreams of research papers developed to analysis of electrical systems power quality for non-linear loads are conducted for low voltage feed. This, if in one hand have furnished important results about the performance of power quality provide by installation, in other hand drops off bad quality effects of electrical energy in high and medium voltage distribution net, mainly in effects of harmonics components, in principals apparatus in substations entrance, notably in current and voltage transformers employed to feed protection and measuring systems of installation. This paper explains conclusions of a comparative analysis of voltage and currents behavior and harmonics components between voltage in secondary feed side and primary feed side of a medium voltage substation. In this way, the objective of research is contributed to a better understanding of measurement transformers behavior and his influence in measuring, protection and control, when installed in equipment with predominance of non-linear loads. The objective of paper is identifying the error that can be present in electrical parameters of substation, when measuring in medium or high voltage are used. With this proposal was building an experimental substation in Power Quality Laboratory of Sao Paulo State University. The installation is composite by 2 distribution transformers, 30 kVA, 13,800 / 220 V, connect in substation entry and other in outlet. Between transformers exist 3 current transformers and 2 voltage transformers and also surge arresters and monophase disconnectors. The load was welding machines, resistors and gas discharge high pressure sodium lamps, used in public illumination and industrial installations. The results demonstrate that exist an intense influence of non-linear loads in medium voltage when measuring with current or voltage transformers.