Electromagnetic Field In End Region Of Large Scale Air-Cooled Turbine Generator With Generator-Grid System Transient Operation

In the end of 2016,National Development and Reform Commission and National Energy Administration proposed The 13th Five-Year Plan for the energy development and put forward that optimizing the energy structure,improving the energy utilization efficiency,achieving the clean and low-carbon development are the essential requirements for promoting the energy revolution.Gas-steam combined cycle generation using natural gas is high efficiency and low pollution power generation pattern.It has the advantages of maximizing saving the coal,and great economic and environmental benefits.Now,it is planned to build large gas-steam combined cycle power station with high power supply efficiency,low investment,short construction cycle,high automation and less pollution in Beijing-Tianjin-Hebei,Pearl River Delta and Yangtze River Delta.As the main equipment in power production,the large air-cooled turbine generator is comparable to the heart of gas-steam combined cycle power station.The design technology,operation characteristics and fault characteristics are the key research directions of international academia and engineering circles.With the quickly and frequently starting and stopping performance,simple cooling system and easy to maintain,the air-cooled turbine generator is especially suitable for gas turbine in combined cycle system.Because of the favorable peak load regulation performance,gas-steam combined cycle generator units are generally used as the peak load regulation generator units,which require the generator operating with the quickly and frequently starting and stopping performance.During the frequently starting and stopping process,the generator may occur various short circuit fault,or even cause the out-of-phase synchronization fault.The faults have a great impact on the stability of the generator and power grid operation.In some serious cases,the generator will lose synchronization and generate large power oscillation in the system.When the fault occurs,the large impulse current flow through the stator and rotor windings,which accelerates the insulation aging of the stator and rotor windings and causes the thermal deterioration of the insulation materials.On the other hand,the mechanical vibration caused by the electromagnetic force on the stator end winding or the stator end core in the process will lead to insulation worn out and fatigue breakage,which will lead to safety accidents.Therefore,in order to reduce the economic losses caused by the faults,some theoretical basis for further study on above problems.The main contents of this dissertation are as follows:The time-stepped finite element mathematical model,taking into account the saturation of magnetic field and non-linear factors for dynamic analysis of generator-grid,is built.It can include the interaction of electromechanical coupling and a multi-mass module spring system model,which takes into account the transmission torque,damping torque and the different changes of rotational speed of each mass block.With the established model,the supersaturation at the stator and rotor core and the time varying physical quantities can be studied under synchronizing out of phase.By using the magnetic conductivity of rotor wedge on longer slots and changing rotor slot indexing number,the nonuniform level and the saturation degree on rotor pole can be improved.Because the stator end winding of the turbine generator is very long and its structure is very complex,it is vulnerable in the fault.Therefore,a multi-regional nonlinear transient electromagnetic field generator-grid coupling model is proposed.It could not only consider exactly the nonlinear effect of magnetic field saturation and distortion,but also solve the complicated end leakage magnetic field,the eddy current field and the electromagnetic force distribution under special working conditions.By using the proposed method,the distribution of the axial leakage magnetic flux in end region at no-load condition and steady short-circuit condition are analyzed,and the calculation values on measured positions are compared with the measured values,which can prove that correctness of the proposed theoretical method.With the established model,the time-varying electromagnetic field under synchronizing out of phase fault and short circuit fault can be investigate.The quantitative of electromagnetic force with the time varying on the stator end winding can be calculated under different faults.The electromagnetic force distribution at different locations of the end winding is analyzed,and the maximum magnetic flux density drift and attenuation with the increase of fault time on the stator end core is revealed.The research provides technical support for the design of large capacity air-cooled turbine generator.In order to reduce the eddy current loss on the end components of the air-cooled turbine generator and the axial leakage flux entering in the stator core,using different components material compound of iron and copper instead of the traditional composite structure with copper shield,magnetic shield or both copper shield and magnetic shield is proposed in this paper.Based on the numerical calculation method,the eddy currents on the end components and the axial magnetic flux leakage in the end region with different electromagnetic characteristics schemes shielding material are studied.By adjusting the components of different elements of copper-iron alloy and changing the electromagnetic characteristics of copper-iron alloy,the electromagnetic characteristics of copper-iron alloy materials with different components are analyzed in detail.The mechanism of the relationship between the total loss at the end region and the loss on various structural parts is revealed.The strategy of restraining the eddy current loss at the end region is put forward,and the copper-iron alloy materials with different components are studied.In order to ensure the safe and stable operation of air-cooled tuebine generator,the material can restrain the magnetic flux leakage in different depths leading phase operation.According to the shielding effect of metal shield on axial magnetic leakage and the flow path of the axial magnetic leakage enters the metal shield,in order to ensure the shielding effect of metal shield on axial magnetic leakage and reduce the eddy current loss on the metal shield,through theoretical analysis of the flow path and penetration depth,an optimized set of metal shielding with multi-thickness and diverse structure is constructed to ensure its effectiveness.On the guarantee of shielding effect,the thickness and shape of metal shielding optimization can not only reduce the eddy current loss on the metal shielding,but also increase the heat dissipation area on the metal shielding,and reduce the temperature on metal shielding.In addition,aiming at the serious problem of magnetic gathering on the stator end core,a new type of conical stator end core structure is proposed,which reveals the distribution law of stator leakage under this structure,and raises the design of generator end structure from the guidance of practical engineering experience to the prediction design by numerical calculation method.