In this article dissolved gas in 132kV/33kV 15MVA power transformer is analyzed using the Kelman Kit (Transport-X) through Duval's triangle method and Roger's Ratio method. Under the impact of electrical, thermal and environmental stresses, the equality of mineral insulation oil deteriorates in a gradual manner, electrical failures such as hot spots and partial discharges occurs in the insulating oil. Dissolved Gas Analysis (DGA) technique detects incipient failures in the transformer. DGA is considered as most important test for insulating liquid in electrical apparatus throughout the world. In this technique, an oil sample will be taken at anytime from the transformer valve for testing the oil. This paper intends to show the gassing of oil is a more complex phenomenon. Different types of gasses causes faults like thermal, internal failures, etc in the transformer. To detect the type of fault two major methods are adopted i.e Roger's ratio method, Duval triangle method.