Experimental Modeling Investigation Of Large Four Poles Generator Cooling System

As the rapid development of economy in our country, electricity is widely used invarious fields in the society, including economic activity and daily life; the demand forelectricity in every walk of life is growing, and the construction scale of grid is alsoconstantly developing. Because of the low material consumption, low operation cost, aswell as short production cycle for unit capacity of the large capacity generator, theeconomic benefit of large capacity generator is quite promising. Nowadays, thedevelopment of generator is pointing at large capacity, but the main obstacle of capacityincreasing of generator lies in cooling techniques of the generator. The study on thecooling techniques of large capacity generator is significant.Based on the similarity theory and dimension analysis, similarity numbers ofcooling model for sub-slot of large capacity generator, including flow, pressure, rotationas well as heat transfer, are determined; also, the static and dynamic modelingexperiments are carried out based on these similarity numbers, and the operatingparameters of the modeling experiment correspond to those of the prototype. Bycarrying out experimental investigation using the modeling experiment system, it isfound that the static pressure distribution in the rotor sub-slot from inlet of rotor sub-slotto the center of rotor is consistent with the outlet velocity distribution of the radialventilating grooves, with decreasing first and then increasing under different coolingflow rates. The coil wall temperature at different locations are basically consistent, andthe wall temperature as well as temperature rise increases along with the increasingexcitation current. It is also found that the relationship between the temperature rise andthe ratio of present current to rated current is basically quadratic. After analyzing theexperimental data, a rotor heat transfer model based on a revised D-B equation isproposed, and the predicted result of revised Nusselt number (Nu’) agrees well with theexperimental one, with an uncertainty less than20%. Meanwhile, this heat transfermodel is used to predict the average coil wall temperature with different workingconditions, and it is found that the predicted result agrees well with the experimentalresult with an uncertainty less than7%.In order to study the evaporative cooling system applied in large generator, the heattransfer characteristics of natural circulation boiling flow in vertical experimentalsection is investigated. It is found that the heat transfer coefficient increases with the decreasing inlet subcooling. When the inlet subcooling is less than a certain value, theheat transfer coefficient fluctuates. The heat transfer coefficient increases withincreasing heat flux. Furthermore, the heat flux has great influence on the flow rate ofnatural circulation. Due to the size of flow channel in the evaporative generator is small,a visual experimental study is carried out to investigate the influence of bubble behavioron two-phase flow pressure drop, which happens in rectangular hollow conductors withvertical narrow channel in the generator. It is found that the relationship between theexperimental section pressure drop and the inlet subcooling is not monotonic with theother working conditions identical, including system pressure, mass flux-rate and heatflux. In the narrow channel, the bubble grows easily to an equivalent size of the channelgap, and coalesce between bubble happens to form bigger bubble or steam clusters,which causes blockage in the channel and the pressure drop increases. However, thegravity pressure drop decreases with the increasing void fraction.The result of present study has great significant in the design and manufacture ofventilation cooling system and evaporation cooling system which are used in largecapacity generator.