Today Transformers 300 MVA in use of Electricity Generating Authority of Thailand Metropolitan Electricity Authority and private companies were active in the power transmission system. To increase the efficiency and security of the countrys energy systems after using it for a while it requires annual maintenance such as checking and testing of various power. However the problem of leakage of transformer oil is a common problem and affects the environment. This is caused by the malfunctioning equipments which affect the performance of the transformer. The solution will require more time and money. We have to find a way to fix the leak of the transformer oil by reducing the amount of oil and the temperature of the oil in order to reduce the time and cost -savings.HoweveriIt does not affect the performance of the transformer