Research On Problems Of Losses And Temperature Rise For Stator Transposition Bars In Turbo-generators

Turbo-generators are the key electromechanical energy conversion devices of the nuclear power plant. In the background that the safe and efficient nuclear power is developing rapidly in China, the design and research of turbo-generators has become an important issue in the development of nuclear power industry. With the increase of the turbo-generator unit capacity, the losses and temperature rise of stator bar will increase. In order to effectively control the losses and temperature rise of the stator bar, the weaving transposition and parallel connection structures are usually used in stator bar strands in large turbo-generators. The appropriate design of transposition types depends on the accurate calculation of losses and temperature rise for stator bars with different transposition structures. In this dissertation, a mega-kilowatt class nuclear turbo-generator is taken as the research object, and the problems of the leakage magnetic field, circulating current losses, eddy current losses and temperature rise of its stator transposition bars are studied.The two-dimensional transient time-stepping finite element model for researching the slot leakage magnetic field of stator bar and the three-dimensional transient time-stepping finite element model for researching the end leakage magnetic field of stator bar are established respectively, and the slot and the end leakage magnetic field of stator bar are calculated. The influence of the rotor main pole magnetic field on the slot leakage magnetic field of stator bars and the influence of the end structure components on the end leakage magnetic field of stator bars are discussed. The assumptions of the stator bar slot and end leakage magnetic field distribution in traditional calculation methods for losses of stator transposition bars are amended.The mechanism of circulating current losses in stator transposition bars is researched, and the circuit network method for calculating circulating current losses is proposed, which can calculate circulating current losses of stator bars with all kinds of transposition types rapidly. The universal equivalent circuit network model of stator transposition bars suitable for all kinds of transposition types is established, and the calculation method of leakage reactance parameters in the circuit network model is proposed based on the principle of discrete integral. The strand current and circulating current losses of stator transposition bars in the mega-kilowatt class nuclear turbo-generator are calculated. Aimed at the characteristics of stator bars in mega-kilowatt class nuclear turbo-generators that there are four stacks strands in one stator bar, the optimal structure of stator bar is proposed to reduce circulating current losses effectively.The mechanism of eddy current losses in stator transposition bars is researched, and the conductor segment method for calculating eddy current losses is proposed, which can consider both the actual transposition structure and the end leakage magnetic field. The slot and end conductor segment models are established respectively and their calculation methods are proposed. The slot and end eddy current losses of stator transposition bars in the mega-kilowatt class nuclear turbo-generator are calculated. The influence of the strand transposition structure and the number of conductor segments on calculation results of eddy current losses in stator transposition bars is discussed.The three-dimensional fluid temperature coupled network method for calculating temperature rise is proposed, which can consider both the actual transposition structure and the actual heat source distribution. The three-dimensional fluid temperature coupled network model of stator transposition bars suitable for all kinds of transposition types is established and its calculation method is proposed. The calculation methods of thermal resistance and heat source parameters in fluid temperature coupled network model are proposed. The temperature rise in stator global domain of the mega-kilowatt class nuclear turbo-generator is calculated and the influence of stator bar transposition structure on the calculation results of stator temperature is discussed.The finite element method is adopted to validate the proposed circuit network method for calculating circulating current losses, the proposed conductor segment method for calculating eddy current losses and the proposed fluid temperature coupled network method for calculating temperature rise. Furthermore, the calculation method of losses in stator transposition bars is validated by the experiment using the single slot auxiliary laboratory testing platform for stator transposition bar.