Modeling Turn Insulation Thermal Aging Process for Traction Substation Transformer

Abstract

Power transformers of traction substations operate under conditions of significant daily, monthly, and annual load imbalance. For example, the greatest load per hour of intensive traffic in the presence of increased weight trains can exceed the average daily load by 2-3 times or even more. Ambient temperature also varies widely. When designing traction substations, the transformer rated power level is selected lower than the maximum daily or hourly power to ensure its best use, taking into account its overload at various time periods. A condition for systematic overloads and increased load is the preservation of the transformer insulation standard service life. Under the influence of temperature and a number of other factors, the physicochemical properties of solid insulation undergo changes over time, which causes the insulation brittleness. During the irreversible process of aging, the electrical strength of the insulation almost does not decrease, but after a certain time, it becomes unable to withstand mechanical stresses from vibrations or short circuits. The aging rate depends on temperature, and the achieved degree of aging depends on the temperature and time of exposure. Moisture, atmospheric oxygen, and other factors also affect the rate and achieved degree of aging of insulation, the strict accounting of which is not possible. The transformer effective service life is largely dependent on impacts such as overvoltages, short circuits in the network and emergency overloads. The load and/or temperature of the cooling medium exceeding the rated values cause accelerated wear of the transformer and are the main risk factors.