Advanced Dissolved Gas Analysis Method With Stray Gassing Diagnosis

Dissolved gas analysis (DGA) is the oldest and most reliable method to identify any fault within a power transformer. Existing DGA can identify as many as 6 types of fault, but is not able to identify stray gassing, which refers to unusual generation of gas from insulating oil, or often provides wrong diagnosis, making accurate identification of the cause of a fault difficult. To address such a shortcoming, we developed a new advanced DGA to identify stray gassing by conducting 62 cases of simulation, collecting relevant data (75 units under Cigre Brochure 296) into a database and analyzing them along with existing faults (122 under IEC TC 10). As part of analysis of the database and, ultimately, accurate diagnosis, we identified gas limits and the percentage of gas for each fault to provide distinction between existing faults and stray gassing. This study describes how the advanced DGA for identifying dissolved gas has been developed and how to verify its accuracy.