Method of estimating overheating temperature of oil-immersed electric appliance

A method of estimating an overheating temperature of an oil-immersed electric appliance in which ester oil is used as insulating oil, the method comprising:

• extracting sample gas from the ester oil, wherein the sample gas is dissolved in the ester oil;
• measuring, by a gas separation device, a plurality of gas components in the extracted sample gas;
• estimating, from the extracted sample gas, the overheating temperature based on a first concentration ratio representing a concentration ratio between two types of gas components contained in the ester oil and a second concentration ratio representing a concentration ratio between two types of gas components, at least one of which is different from the two types of gas components in the first concentration ratio, contained in the ester oil;
• and
• determining whether to perform a safety measure responsive to an occurrence of an overheat abnormality based on the estimated overheating temperature, wherein
• when the ester oil contains acetylene, the first concentration ratio and the second concentration ratio are selected from:
• a concentration ratio of acetylene to ethane,
• a concentration ratio of acetylene to hydrogen,
• a concentration ratio of acetylene to methane, and
• a concentration ratio of acetylene to ethylene, and
• when the ester oil does not contain acetylene, the first concentration ratio and the second concentration ratio are selected from:
• a concentration ratio of ethylene to hydrogen,
• a concentration ratio of ethane to hydrogen,
• a concentration ratio of ethylene to methane, and
• a concentration ratio of methane to ethane.