ANALISIS PENGUJIAN ISOLASI PADA TRANSFORMATOR DI GARDU INDUK 150 KV SERANGDiniAustia PratiwiauthorIn Indonesia, there are two main types of transformers: step-up and step-down transformers, which increase and decrease voltage. This system serves as the primary link between the electrical energy produced and the energy consumed by consumers. Insulation resistance testing is crucial to ensure the performance and quality of the transformer, ensuring it experiences no power loss. Several potential issues may affect the insulation resistance, such as leakage current, weather conditions, and the age of the transformer. This testing was carried out using several methods. The first method, Polarization Index (PI), serves to assess the condition of the transformer winding. The second method, tangent delta, is used to measure electrical losses in the transformer. The third method, breakdown voltage (BDV) testing, is conducted by sampling the transformer oil. This testing was performed over a two-year period, in 2022 and 2024. Based on the research, the insulation resistance in the 2022 PI test showed a value of 1,21 on the primary to ground side, which is questionable, while the tertiary to ground value of 1,66 indicates good condition. The 2024 PI test showed a primary to ground value of 0,97, which is below the accepted standard, and a value of 1,92, which is the highest and considered good. The tangent delta test in 2022 showed a maximum value of 0,2%, which is within the good standard, while in 2024 it recorded a lower value of 0,7%, indicating degradation. The BDV (Breakdown Voltage) test produced an average difference of 23 kV which is still considered good.TK Electrical engineering. Electronics Nuclear engineering2026-04-18Fakultas Teknik Universitas Sultan Ageng Tirtayasa;TEKNIK ELEKTROThesis