Experiences and Analyses of Reconstruction and Commissioning of Medium Voltage Substation

Abstract The paper will present experiences in the reconstruction of the transformer station, which supplies the industrial factory. The previous version of the medium voltage (MV) substation with oil-filled transformers, and the new MV substation with dry and more energy efficient transformers, will be presented. An analysis of the operation and maintenance methods of oil transformers will be given. As oil transformers have many disadvantages, the reason, choice and cost-effectiveness of replacement with new dry transformers will be presented. Tests and measurements of insulation resistance of the winding and transformer protection during commissioning will also be presented. PT100 probes, which are connected to the thermostat, are installed in each low voltage winding of the dry transformer. Testing of this thermal protection of the transformer will be presented as well. Since transformers supply industrial consumers, mostly nonlinear ones, it is important to analyse the losses and life span of transformers. Nonlinear consumers lead to early aging of winding insulation, premature failures and reduction of transformer life. The newly designed and installed MV substation with Ring-main unit is ABB type SafePlus, and its installation and operating instructions will also be presented. The MV is equipped with a protection terminal, so settings and measurements of this terminal in transformer cells will be done. After the commissioning of the transformer station, the most important are diagnostics and periodic tests. Methods of periodic testing of MV substations will be presented in this paper.