Moisture Transfer Rule Of Oil-paper Insulation And Its Impact On The Ageing Characteristics During Thermal Ageing Process

Oil-paper insulation degradation is the main reason leading to transformer fault. It is caused by the long-term combined effects of various factors, in which temperature plays a dominant role, and generally considered that the transformer insulation life depends on the thermal aging life of cellulose insulation material; Moistrue has been considered as the'number one enemy'except temperature to oil-paper insulation because it can severely reduce the electrical strength of oil-paper insulation, accelerate oil-paper insulation aging, and short the insulation life. But, the combined effect of temperature and moisture to oil-paper insulation degradation is short of systematically study at home and abroad. Therefore, it is very important to make the assessment transformer insulation sate and fault diagnosis that study on moisture transfer rule of oil-paper insulation and its impact on the aging characteristics during thermal aging process.This paper designed a aging test, in which the insulating papers with the initial moisture contents of 1%, 3% and 5% were aged in mineral oil at 90℃, 110℃and 130℃respectively. Then, this paper systematically studied the variation trends of moisture content in paper, in oil and total moisture content of oil-paper insulation system during the aging process and their mutual relations; Analyzed the the moisture transfer law accoding to the moisture distributed condition of among layers inside paper and the variation trends of total moisture content of oil-paper insulation system. This paper also studied on the influence of moisture on the oil-paper insulation deteriorate rate by analyzing the variation of the degree of polymerization of insulating paper; Finally, discussed the moisture content and its transfer rule on the impact of the thermal aging characteristic parameters including furfural content in oil, acid content in oil, frequency domain dielectric spectroscopy of insulating paper.The main research results:①According to the global moisture content varying trend of in oil, in paper and the total oil-paper insulation system, this paper proposed the idea which based on the global fluctuations characteristic of moisture content varying trend of in oil, in paper and the total oil-paper insulation system to make the assessment transformer insulation ageing sate and moisture levels. And fonud that the fluctuation amplitude of moisture content in oil can be used as a characteristic parameter to make the assessment of moisture levels.②Obtained the influence mechanism of different initial moisture content on water transfer law of oil-paper insulation system during the aging process, and found that the level of initial moisture content play a decisive role to the water transfer law of oil-paper insulation system.③Found that the effect of moisture and temperature on oil-paper insulation ageing is not a simple superposition, but showed mutual coordination, mutual restraint.④The moisture content and its transfer inside oil-paper insulation system have a great influence on the trends of aging characteristic parameters such as furfural, acid in oil and frequency domain dielectric spectroscopy of insulating paper. Therefore, to make the assessment transformer insulation sate and fault diagnosis based on these characteristic parameters more accurate, this paper suggests that the moisture of oil-paper insulation should be taken into full account of consideration.