The Study Of Novel Method To Measure Moisture Content In Transformer Oil Based On Terahertz Technology

Moisture content is an important parameter which can indicate the state of insulating material. Especially for power transformer, its insulation structure is consist of pressboard and insulating oil. In the aging processing of insulating materials, the moisture will be generated and distributed in the paper or insulating oil according to a certain proportion. As the materials aging, the moisture content will increase and itself can also accelerate the speed of material's aging. So it is necessary to measure and obtain the moisture content in insulating material including oil and paper. Traditional method to obtain the moisture content is not suitable to measure on site. THz radiation offers a high sensitivity for water and THz technology has become a fast and nondestructive test method for detecting the micro-water content of substances. So THz-TDS (terahertz time domain system) is introduced to measure the moisture content in insulating oil. In this paper, oil sample with different moisture content are prepared through saturated water absorption carried out in the natural environment. And moisture content of samples are determined by using the titration. Before testing by THz-TDS, oil samples are put into fluid container. In the experimental processing, the response signals of time domain are obtained. Also the absorbance spectrum of terahertz waves in frequency domain is calculated. The results show that moisture in oil will caused absorption phenomenon even if its content is extremely low. When the moisture content of sample is higher, the power of transmitted waves is lower and phase delay is more. Then response signal of time domain is fitted using linear equation. And absorbance spectrum in frequency domain is fitted using equation of Beer-Lambert law. Results of these two fitting are compared and. show that equation of Beer-Lambert law has a better fitness in moisture content. It is proved that THz techniques can be a potential field test method to detect the moisture content in insulating oil and has an extensive application prospect in the field of insulation state detection.