Proposed three ratios technique for the interpretation of mineral oil transformers based dissolved gas analysis

Dissolved gas analysis (DGA) of oil is one of the major diagnostic tools that are used to detect the incipient faults of oil-immersed transformers through the correlation between the dissolved gases content in transformer oil and a particular malfunction. There are several techniques of DGA to interpret the incipient transformer faults such as Doernenburg ratio, Rogers's ratio, IEC ratio and Duval triangle techniques. This study presents a new proposed technique for transformer fault diagnosis using a new three gas ratios concentration of DGA to overcome the conflict that takes place in the traditional interpretation techniques. The accuracy of the proposed diagnosis technique is verified using practical DGA data obtained from 688 samples that have been collected from different transformers of different rating and different lifespan reported by Egyptian Electricity Holding Company, IEC TC10 and related databases surveyed from actual incident cases. The comparison with traditional DGA techniques showed that the proposed DGA ratio technique has good diagnosis accuracy. It is found that the suggested three ratios technique method has 99.86% accuracy as compared with 85.67% for Duval, 75.08% for Doernenburg, 47.34% for IEC and 39% for Rogers when testing 688 cases.