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Study on Estimating Method of Hottest Spot Temperature in Oil-immersed Transformers

Author: JiangTaoSha
Tutor: SunCaiXin
School: Chongqing University
Course: Electrical Engineering
Keywords: Hottest spot Temperature Top oil temperature Bottom oil temperature Short-circuit Test
CLC: TM411
Type: Master's thesis
Year: 2009
Downloads: 229
Quote: 8
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Abstract


Power transformer serves as one of the most important equipments in the power system. Its end of life is due to the loss of its insulation capability. The hottest spot temperature, which is the highest temperature in the insulation inside a transformer, is the key factor of limiting the loading ability of the transformer. Thus it is of great significance for the permissible overload and the operational life assessment to monitor the hottest spot temperature. After research on literatures, this thesis conducted the estimating method of hottest spot temperature in oil-immersed transformers based on analysis of temperature distribution inside transformers and the data analysis of temperature rise experiment. The thesis conducted the following work:First of all, by studying the characteristics of temperature rise with the heat generation and dissipate, which is followed by an analysis of the internal loss principle of the transformer and a discussion of the influence of its no-load and load loss on winding hottest spot temperature, the heating and cooling characteristic equations of winding, iron core and oil as the major components of the transformer are given, Also, the characteristic curves of these parts are given .The analysis indicates that the hottest spot temperature appears in the windings of the transformer.Moreover, based on heat transfer theory and the analysis of the temperature distribution in the transformers, by comparing different thermal circuits and their drawbacks, bottom oil temperature is chosen as the feature temperature to calculate the hottest spot temperature using electrical thermal circuits. Comparisons of the results from the thermal circuit based on bottom oil temperature with the other two methods are given, and it shows that the estimating method suggested by this paper is more accurate.Meanwhile, to acquire data for comparison, researches including the design of an instrument transformer, the selection of temperature measuring system are conducted. All the data in this paper is from the measurement of electrical thermal couple. To confirm the accuracy of this measuring method, fiber optic sensors are employed to provide the comparison. All the results show that electrical thermal couple can do a satisfactory job.Furthermore, the features of hottest spot temperature are studied using the data acquired from the short-circuit temperature rise experiments. Hottest spot temperature is found to be stable in position, and the temperature distribution in the winding area where hottest spot temperature occurs has turbulence. Supporting theoretical analysis are given to support the findings.

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CLC: > Industrial Technology > Electrotechnical > Transformers, converters and reactors > Power transformers > Oil-immersed power transformers
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