Fundamental Research Of Open Channel Evaporative Cooling Technique For Rotor Of Large Turbine-generator

Heat generated in the electrical machinery interior has already become the bottleneck that limits generator to large capacity. Applied to cooling of generator, the evaporative cooling technique is effective, safe, has simple structure and is easy to maintenance, so it has been more and more valued by electric power department and electrical manufacturing by now. The evaporative cooling technique of hydro-generator has been fully-fledged enough to be applied to hydro-generators in the Three Gorges, and there are also certain research results of cooling of turbine-generator stator. With developing demand of internal cooling technique in large capacity electrical machinery, fundamental research of evaporative cooling technique in the area of rotor cooling is urgently needed. Open channel evaporative cooling technique for rotor has large cooling potential and no special request to the pressure resistance, so it has very much market prospect and the superiority is especially more obvious on large capacity turbine-generators. Study object of the paper is open channel evaporative cooling system of the turbine-generator's rotor winding. The research is focused on the temperature measurement system of the rotor, developed for the model experiment, the flow characteristic of coolant in the open channel, the model experiment, the design of open channel rotor.In the process of new cooling structure development of evaporative cooling turbine-generator rotor, it's very important that measuring the temperature distribution on the rotor, not only for the improvement of the rotor cooling structure, but also for the guarantee of safe and reliable run and so on. In order to coordinate with the model experiment of rotor, three rotor temperature measurement systems are developed in the paper. System No.1 transfers temperature signal through slip rings. Multi-channel switch circuit is installed on the rotor and changes multi-channel input into one-channel output, thus multi–channel temperature signal can be transferred through less slip rings than the common solution. System No.2 is wireless rotor temperature measurement system based on MSP430 monolithic processor and nRF401 wireless communication module, using thermal couple as temperature sensor. Hardware structure, function of main device and software architecture is introduced in detail in the paper. Service condition indicates that the system is simple and easy-to-use and temperature signal is stable and reliable. The paper also presents discussion to some related technical detail. Besides, system No.2 is open and modular. With suitable modification to signal gathering part, this system can also use thermal resistance as sensor. The paper introduces system No.3, which is wireless temperature measurement system using PT100 thermal resistance as sensor. Three systems introduced above are mainly suitable for the model experiment. With some modification, they are also available for temperature measurement of hydro-generator and turbine-generator. Two wireless temperature measurement systems are also available in other non-contract measurement.Coolant evaporates in the open channel on the rotor and the cooling effect mainly depends on flow rate through the open channel. Flow rate depends on pressure and flow resistance. Flow analysis and computation of coolant in the open channel is involved with evaporation of heated coolant in the rotor. First, the paper presents analysis of evaporation of heated coolant in the open channel rotating around horizontal axis. Computational method of flow resistance of heated coolant under high centrifuge field (a g ) is presented. Law of coolant velocity changing with rotational speed is achieved and influence of rotational speed to the cooling system is estimated in the paper.The paper has completed open channel rotor model and loss simulation experiment with current has been finished on this model. Influence of current density, coolant flow rate and rotation speed on cooling effect is analyzed in the paper.Experiment results indicate that coolant flows smoothly in the open channel, temperature distribution is even in the radius direction of rotor winding and temperature rise conforms to related national standards of turbine-generator. Based on theoretical analysis and model experiment, design of open channel rotor is presented in the paper. The following is included: overall design of system, coolant feed and discharger beside the axis, design of rotor winding, overflow, steam exhausting way in the channel and so on. At present, open channel evaporative cooling technique applied to turbine-generator rotor is at the start stage. The paper presents analysis of some technical difficulty which is discovered during model experiment and forecast the developmental direction of open channel evaporative cooling technique.