Study On Key Design Technology For High-power Gear Variable Speed Device

Large gear variable speed transmission device is a new equipment incorporated with mechanics, electricity and hydraulics as a whole, the technology of its design and manufacturing is a sophisticated and integrated technology. For the reason of foreign technology blockade restrictions to China and lacking of systematic research, design, production and experiments, only minor products are imitated in a few companies nowadays, while large-scale high-parameter device is still basically dependent on imports. In particular, high-power gear variable speed devices used for boiler feed water pump in the thermal power is fully imported from abroad, which are over6000kW and5000rpm to6650rpm, supporting600,000kilowatts or1000,000kilowatts of supercritical generator sets or even ultra supercritical generator sets. In this dissertation, with high-power gear variable speed device as the study object, applying modern design calculation methods, a comprehensive study about the internal shaft system with high power density, the hydraulic drive system of the impeller’s working chamber and the control system of displacement of scoop tube, inlet oil of working chamber and outlet oil of scoop tube is fulfilled. The key design and manufacturing technology of large gear variable speed transmission device consisting of high-power, high-speed gear transmission, hydraulic transmission and control system are basically mastered, high-speed and heavy duty hydraulic adjustment speed transmission device used for supercritical or ultra-supercritical coal-fired generating units is developed. The research contents of this dissertation involve the basic characteristics of the commissioning and the working match relationships in the device, the shaft system model buliding and the sliding bearing capacity calculation, the flow field numerical simulation and analysis in the working chamber of the impeller and the working hydraulic control system. Main research and conclusions are as following: (1) Based on the transmission structure of the large gear speed control system, the shaft system dynamics model is established and model calculations about gear shaft, pump shaft, turbine shaft and the coupling state of gear shaft and pump shaft are respectively accomplished. From the calculation results, it can be concluded that the system is safe while working. Based on two methods of incomplete liquid lubricated bearing capacity calculation and liquid lubrication hydrostatic bearing capacity calculation, the load capacity calculations of ten sliding bearings including radial sliding bearings and thrust sliding bearings of the device are finished. Also the suggestion methods to increase the load capacit of sliding bearingy are proposed.(2) Based on the hydraulic transmission characteristics of flow field in the working chamber of the impeller, three-dimensional numerical simulation method of inner flow field is determined. Fluid blocks of adjacent three blades are selected as the research subjects and fluid analysis software FLUENT is used, the pressure, speed and liquid phase distribution are analysed, in which the rated power is7334kW, the input speed is1490r/min for gear speed device at three representative operating conditions such as braking, traction and nominal speed, where the filling rates are40%,80%and100%respectively. After calculating the torque coefficient, the output external characteristic curve can be predicted. By contrast, it is the ideal characteristic curve.(3) On the basis of three-dimensional model of the impeller, the liquid forces of the impeller are analyzed. Aiming at the pump wheel and the assembly body of the pump wheel and turbine wheel sleeve, different finite element analysis softwares are applied to analyse the impeller, then the stress and displacement distribution on the impeller housing acted by the liquid are obtained, and the maximum stress point in the impeller is found. The maximum stress occurs at the location connected by the impeller blade root and the cavity. The calculations of turbine impeller sleeve connector body also show that the turbine sets stress has a great effect on the stress of inner wall, occurring at the center circle of vortex sets which are most likely destroyed throughout the impeller. (4) Based on the oil control system theory, the formula of the speed device’s working oil mass can be derived and then its calculation method is got. Taking the large gear variable speed transmission device with a rated power of7334kW for example, by calculating the required working oil mass under different ratios, it is found that the gear adjusting device’s maximum power loss is about16percent of working mechanical power when the ratio is0.667. From the curve drawn between working oil and ratio, it can be seen that when the output speed is adjustable between20%-97%, the maximum required working oil mass is approximately5.25times the minimum oil mass. By analyzing the oil passing area of the inlet oil control valve, the location of displacement of scoop tube spoon tube and the filling rate, the precise control for the spoon tube and hydraulic system can be achieved.