Nowadays, electrical energy has become a basic human need. Electrical energy comes from generators that are distributed through transmission lines to the main substation, the voltage is lowered for electrical energy needs. Inside the main substation there is a transformer (transformer) which is vital equipment in maintaining the stability of the electrical power supply. To support the reliability of the transformer, oil is needed as an insulation system and a cooling system that supports and is of high quality. The non-stop performance of the transformer, the heat generated from the transformer windings and the electrical load that always increases every day can cause the decomposition of hazardous gases to the transformer oil, which can reduce the quality of the transformer oil insulation, fatally it can cause breakdowns in the transformer equipment. So it is very important to test the dissolved gas content in the transformer which is known as the DGA (Dissolved Gas Analysis) test. One of the calculations for the final DGA results is the TDCG (Total Dissolved Combustible Gas) method. Poor DGA test results will reduce the quality of the transformer oil. PT PLN ULTG Cawang monitors the results of DGA tests, routine oil periodically depending on the good or bad results of the DGA test. At the Cipinang Main Substation, the TDCG condition of the DGA test results was found to be high or bad, so oil purification was needed. After oil purification using a purification machine, the results of the
DGA (Dissolved Gas Analysis) test were obtained which improved and had met the
IEC C57 standard, as well as the Decree of the PLN Board of Directors No. 0520
of 2014. We have listed the TDCG method, Roger's Ratio method, Doernenburg
method, Keygas Analysis method. Then finally we analyze it with the fuzzy logic
method using the matlab application to describe the condition of the transformer
oil. Then after purification, researchers obtained data that the transformer oil was also more optimal in cooling the Transformer.
Key words: Transformator, Transformer Oil, TDCG, Roger' Ratio, Doernenburg Ratio, Key Gas, Fuzzy Logic, Matlab, Purifikasi minyak.