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 installa-tion.  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 under-standing  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 installa-tion 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 installa-tions. The results demonstrate that exist an intense influence of non-linear loads in medium voltage when measuring with current or voltage transformers.