The existence of moisture in transformer oil will reduce the insulation performance of oil and accelerate the oxidation degradation of oil

resulting in major accidents like the transformer insulation breakdown. Firstly

based on the existence and harm of micro-water in oil

the research progress in on-line monitoring methods of micro-water content in transformer oil at home and abroad was summarized. The emphasis was put on several online monitoring methods in detail

such as capacitance sensor analysis of micro water in oil

microwave sensor analysis and infrared spectrum analysis. Moreover

the effects of the micro water content on the physical and chemical properties of oil were generally analyzed. The results show that the capacitive sensor on-line monitoring method of moisture content in oil used widely is easily affected by the environment

and the measurement precision is low. Microwave sensing analysis is not suitable for the measurement of moisture. Infrared spectrum monitoring technology can be used for on-line monitoring and quantitative analysis of moisture content in oil. A single physical or chemical property of oil is mainly utlized in the monitoring methods of oil moisture

thus the methods have the problems of incompleteness and redundancy. Therefore

we put forward a new online monitoring method

which is the multivariate information fusion method of the spectrum characteristic of physical-chemical properties of oil

to solve key problems of the micro-water content in transformer oil online monitoring comprehensively. The new proposed technology helps to construct a scientific and reasonable on-line monitoring system of oil by using multi-variable infrared spectrum characteristics. It has a good application prospect for solving the problem of oil reuse abandoned due to water pollution in China

and it provides a theoretical support for the accurate monitoring of water content in oil.