The FBG Monitoring Principle Of Transformer Internal Temperature And The Improved Method For Calculation Of The Hot-Spot Temperature

Power transformer serves as one of the most important equipments in the power system. Its reliability is directly related to the safety, efficiency and economy of the power grid operation. Most of the transformers end of life because of the loss of its insulation capability, which is mainly affected by the winding temperature of the transformer in operation. Notably, the temperature in the hottest district of the winding is regarded as the essential constraint on the transformer load. Given this, measuring the internal temperature of the transformer is of great significance for the permissible overload and the operational life assessment.The thesis presents a study on the characteristics of temperature rise with the heat generation and dissipation, which is followed by an analysis of the internal loss principle of the transformer. It also deduces the heating and cooling characteristic equations of winding, iron core and oil as the major components of the transformer, and the characteristic curves are given.Based on the status of the current fiber optic temperature sensor and the specific requirements of the internal temperature measurement of the transformer,researches related to this are conducted, including the design of specific programs for the temperature measuring platform using FBG,selection of the appropriate hardware devices, construction of the measuring platform and acquisition of the data signals. The temperature measuring platform is constructed for the temperature rise experiments of the oil-immersed transformer. The results show that the FBG temperature sensor can be an effective instrument to measure the internal temperature of the transformer with accuracy stability and quick response to the changes in temperature.According to the thermal process of transformer core and winding, this paper analyzes the composition and impacts on the top-oil temperature and hot-spot temperature of transformer core loss and load loss, then it explains the meanings of parameters of hot-spot temperature calculation equation recommended by GB / T 15164-1994 (loading guide for oil-immersed power transformers) from the perspective of physical significance. Base on the analysis of the thermal process, it shows that the heat generated by core loss directly related to the top oil temperature, but the determinants of the hot-spot temperature are the resistance loss and the eddy current loss. Moreover, an improved method for calculation of the hot-spot temperature is given, and it shows higher reliability by compared with the load guide.