Application Fundamental Research On Lowering Temperature Of Electrical Equipment By Coolant Phase-Change

With the rising of living standard day by day, the requirement of electric power is more and more, and saving energy and high efficiency becomes the aim to concentrate. To increase effective utilization ratio of electrical equipment in power system, it is important that lower their temperature. In general, the electrical equipment are cooled by gases and water. Owing to their intrinsic properties, the capacity and efficiency of electrical equipment are limited. Scientists in many countries have been studying and finding better kind of cooling methods in nearly years. Phase-change cooling shows special high efficiency. This method can keep lower and uniform wall temperature. Meanwhile, it is safe and reliable, and will have a great future on application of large electrical equipment. Our country has made great progress in the research and manufacture of evaporative generator. Because it is a new area, and relate to other subject, there are many theoretic and experimental questions need to solve. The thesis combined with the research of national "95 "major industry project —400MW evaporative cooling turbogenerator at LiJiaXia born by Institute of Electrical Engineering of Chinese Academy of Sciences, and the HeBei province key subject—Evaporative cooling transforms. It gave some theoretical exploration and derived some heat transfer calculated methods. Author studied and analyzed the feasibility of using evaporative cooling method in 400MW generator, and did some basic experiment. The contents of every chapter and main results are as follows: 1. Heat transfer study on oil-cooling transformer: On the basic of analysis to traditional oil-cooling transformer heat transfer, some calculated methods have been given systematically. They consist of the flow rate in a self -circulation transformer, heat transfer coefficients, the temperature distribution in oil and windings. This paper mentioned that the winding's position will effect on self convection of transformer oil. These analyses and calculated methods supply theoretical basis for the design and experiment studying of evaporative cooling transformer. 2. Theoretical study on evaporative cooling transformer: Analyzing and comparing thermal and electric property of coolants, the R-113 and R-30r has been determined for the research. From the mechanism of heat transfer by phase-change, author gave firstly the calculated relationship between heat load and temperature of windings when the coolant is in case of self convection, nucleation and film boiling respectively. Thus, the theoretical calculation methods of heat transfer on evaporative cooling transformer has been put out. 3. Two-phase flow calculation on evaporative cooling generator: The coolant self circulation heat transfer is the key in evaporative cooling generator. Based on the theory of two-phase flow and heat transfer, thesis gave out the calculated methods of flow resistance, flow power, cycle flow rate, coolant temperature distribution, heat transfer mode between liquid and wall in different flow state. It is constructive for the theoretical research on two-phase flow of evaporative cooling generator. 4. Temperature distribution research on evaporative cooling generator stator: After gave the calculated methods of temperature distribution in the hollow conduction, the paper derived numerical calculated methods in arbitrary section of winding. It analyzed the temperature distribution of 400 MW turbogenerator winding in different conditions. Three-dimension numerical calculated method of core was established. The probable position where the temperature is highest was given. It is helpful for generator design and ensures running safety. 5. Experimental study on evaporative cooling generator: An experimental system has been established for certification that evaporative cooling methods is reliable in generator and the theoretical calculation is correct. Comparing with the 400MW turbugenerator hollow conductor experimental results, the theoretical calculated method is very precise. Every factor effecting on coolant flow and heat transfer is analyzed by changing power and cooling water flow rate. On the basic of experimental study, the relationship between power and circulated flow rate, the largest power and the longest length and the smallest diameter of hollow conductor were gained. It gave the reference range that chooses the proper hollow conductor and working area when design an evaporative cooling generator.