Research On Transformer Aging Character And Analysis Aging Mechanism

Power transformer is one of the most important equipments in power grid. Whether the transformer work normal is directly related to power grid can be safe, efficient and economical operation. Insulation fault is mostly the main reason of accidents occurred in transformer. The age of the oil-immersed transformers is depending on the life of insulation . Reseaching the aging characteristics and mechanisms of the insulating oil-papers of transformers and establing the aging models of insulators are valuable on academics and productions for the identification of the aging degree of the insulators, the prediction of the lifetime of equipments, the reduction of power accidents, the improvement of the reliability of transformers.In this paper No.25 and No.45 pure oils and their oil papers were used on aging tests of the insulator of the transformer, and according to some related standards measureing methods for aging characteristic parameters were improved. These methods were employed to measure the thermal aging characteristic parameters such as acid value, volume resistivity, micro-water content, viscosity, aggregating value and so on of these oils and oil-papers at 120℃, 100℃and 80℃respectively. The relationships witnin characteristic parameters had been discussed. The lnear regression of the degree of polymerization and multiple aging parameterswere analyzed by multiple linear regression analysis modle; Gases dissolved in transformer oil during aging process were analyzed through GC-900-SD gas chromatograph according to DL / T722- 2000 standard, such as the content of the aging product of carbon monoxide and hydrogen, methane and ethane, etc. The relationship between the aging degree of the insulator and CO2/CO were studied. The heat aging process were studied by Shimadzu LC-10AT high-performance liquid chromatography and Avatar360 Fourier infrared spectrometer. The cellulosic molecule model were established by Accelrys Materials Studio 4.0. The cellulosic molecule aging process at 120℃had been simulated by quantum chemistry molecular dynamics module(DMol3 /Dynamics). Combining the research results and relevant knowledge of chemistry, the the aging mechanism of oil-paper is discussed. And the main conclusions are as follows: (1) Many materials are produced during the aging process. As part of the products, carbon monoxide and carbon dioxide are mainly come from insulation paper cracking of aging.The experiment result shows that there is close relationship between insulation paper aging stage and the trend with the aging time of CO2/CO or micro water. So the aging parameters of CO2/CO and micro water can be used to evaluation the insulation paper aging degree.(2) The multiple regression model of the degree of polymerization and multiple aging parameters can be drawed as : Y=B0+B1x1+B2x2+B3x3+ B4x4+B5x5+B6x6. It is useful to judge the insulation aging degree and trend of the transformer. In order to findequipment safety conditions, furfural test should be carried for those equipments whoes insulation aging note values increase obviously. Then the rational track test plan is formulate to avoid transformer fault.(3) The correlation between the parameters as followed, there is a negative exponent relationship between volume resistivity and acid value,ρv = ae ?cm+b; there is index relationship between the degree of polymerization and acid value, DP = Aex /b+c; there is correlation between micro water content and degree of polymerization, DP = A+Bx+Cx2; there is correlation between CO2/CO and degree of polymerization, DP = A+Bx+Cx2.(4) The aging of oil and oil-paper is closely related with the temperature. The higher the temperature, the faster ageing rate of oil and oil-paper . At the same aging conditions, the aging rate of oil-paper is faster than theat of pure oil. The corresponding parameter of oil-paper also change faster. It is explained that the ageing rate of oil-paper is faster than that of the oil, and insulation aging is promoted by the oil-paper.(5) The infrared spectroscopy of the insulating samples shows that, The absorption peaks of the aldehyde is at 1720cm-1, and the characteristic absorption peaks of telescopic vibration is at 2900cm-1,and the absorption peaks between 3500 cm-1 and 3300cm-1 is significant changed. The structural changements of paper cellulose molecules during aging process can be found. That the furfural produced during the aging process is confirmed by HPLC and IRC.(6) The aging mechanisms of insulating paper as followed: the 1,4-β-nucleoside key ,which connect glucose forms cellulose chain, is the easiest fracture key during insulation aging process. Large amounts of D-single glucose monomers and lots of small molecules free radicals are generated due to the fracture key. Then during the aging later, part of the pyranoid ring within the glucose monomer open-loop fracture, and half acetal hydroxyl followed fracture. The carbon dioxide,carbon monoxide, hydrocarbons and furfural are generated with the key broking.At a certain temperature, water and oxygen will accelerate the degradation of insulating cellulose.