Power Transformer Hot Spot Temperatures Estimation based on Multi-attributes

摘要

Operational thermal stresses due to dynamic loading and changing environmental conditions enhance the weakening of the power transformer insulation system. During the operation of power transformers, insulation hot spot temperature is a critical parameter that needs to be held under recommended threshold. This is because, amid other factors, cumulative effect of insulation aging depends on time change of hot spot temperatures. In this paper, a multi-parameter based thermal model established upon a thermal-electric circuit scheme to estimate transformer hot spot temperatures is proposed. The model includes the effects of solar irradiation, varying ambient temperatures, dynamic loading and the nonlinear thermal resistance of oil-paper insulation. Moisture effect is considered in estimating the thermal resistance of cellulose, whilst in calculation of oil insulation nonlinear thermal resistance, a universal thermal model is proposed which uses some transformer design-dependent variables and considers different heat transfer modes inside a transformer. The multi-parameter model is validated using data collected from in-service mineral oil immersed transformers. Simulated results of the proposed thermal model are in agreement with the on-site measured values with good model accuracy.