Study On Thermal Aging Of Traction Transformer Insulation Under Impulse Loads And Its Effect On Moisture

Traction transformer is the heart of traction power supply system,and it is the most critical and expensive power supply equipment in electrified railway.Its operating state determines the safe and stable operation of traction power supply system.The life of the traction transformer is mainly determined by the insulation life,the speed of the insulation aging rate determined by temperature,and the moisture will also accelerate the insulation aging,which is the "number one enemy" in addition to temperature.Due to the low average load rate of the traction transformer,the winding’s temperature will rise instantaneously when the train passes,and the internal temperature field distribution will be extremely non-uniform.Under a long-term impulse loads the oil-paper insulation aging rate distribution is extremely non-uniform.The moisture distribution in the oil-paper insulation is also non-uniform.Therefore,in this paper,the temperature field and thermal aging characteristics of traction transformers are studied for impulse loads,and the effect of aging on moisture diffusion is of great engineering significance for better assessment of the remaining life of traction transformers.Firstly,based on the structural characteristics of test transformer windings,a twodimensional numerical simulation model of low-voltage windings was established.The simulation model is compared with the test transformer,which verifies the validity of the model.The distribution characteristics of winding temperature field under different impulse conditions were studied.The effect of load rate,lasting time and time interval on the hot-spot temperature rise of the winding is analyzed.Secondly,an accelerated impulse thermal aging test was designed,and an accelerated impulse thermal aging test platform was constructed.The degree of polymerization of the insulation paper was tested during the test.The effect of impulse loads on the thermal aging rate and service life was determined,and the objective weight evaluation of the aging rate by impulse conditions was determined.Finally,the transient moisture content and equilibrium moisture content in insulation paper at different temperatures,different degrees of aging,and different thicknesses were tested.And the diffusion factors and equilibrium time constant for moisture diffusion in oilpaper insulation under different conditions were obtained by combining with finite element simulation models.The effect of aging on the diffusion of oil-paper insulation moisture was analyzed.