Stress Analysis Of Field Winding Leads And Inter-Pole Connections In Pumped Storage Generator

At present and for a considerable period of future time,pumped storage is a relatively mature and commonly used method of ultra-large-scale energy storage,and it functions irreplaceably in the safe operation and the new energy absorbing of the power grid.Compared with the ordinary hydro-generators,the pumped storage generator used in pumped storage power plants require more frequent start,shutdown and switching between generating and motoring operations,resulting in large variation of the mechanical stress on the rotor components.The inter-pole connection of field winding is an important part of the magnetic pole in a hydro-generator.The leads of magnetic pole coil are connected with the inter-pole connections.Field winding leads are a structure between the slip ring and the first magnetic pole and between the slip ring and the end magnetic pole,and they provide the field current for the magnetic poles.In recen t years,the inter-pole connections and field winding leads in the domestic pumped storage generators have frequently failed,which seriously threatened the safe operation.This suggests that the influence of complex mechanical and electrical conditions on the reliability should be fully considered in the structural design of the inter-pole connection and field winding leads,the weak parts in the structure should be identified,and corresponding measures should be taken in the design and assembly to avoid the risks.This benefits the efficient and reliable operation of pumped storage units.In this thesis,by using mechanical and electromagnetic finite element models the dynamic stresses of three typical structures of inter-pole connection and two typical structures of field windin g lead in three pumped storage generators are calculated fully considering the influences of the structural components and the operating conditions on the boundary conditions and the mechanical loads.The overall idea is to use finite element commercial software to make electromagnetic and mechanical models of different structures of inter-pole connection and field winding lead under different operating conditions,and to calculate the stress,strain and fatigue loss considering the effect of temperature change.This thesis presents the following specific work.A two-dimensional time-stepping electromagnetic finite element model of the entire pumped storage generator,including the stator core,armature winding,rotor core,damping winding and field winding,is created according to the design parameters and drawings.For some operating conditions without monitoring data,e.g.,three-phase sudden short circuit,the waveforms of the armature current and the field current are calculated by using the two-dimensional electromagnetic time-stepping finite element model.Three-dimensional electromagnetic models of the inter-pole connection,the field winding leads and the surrounding structure are made and fed with the field current to calculate the electromagnetic stress.For the operating conditions with monitoring data,the model is directly fed with the measured field current;for the operating conditions without monitoring data,the model is fed with the field current calculated from the two-dimensional model.The calculated electromagnetic stress is compared with the calculated centrifugal stress to evaluate the influence of the electromagnetic force on the operating life of the inter-pole connections and the field winding leads.The centrifugal stress caused by the rotation is calculated by using three-dimensional mechanical models of inter-pole connection and field winding lead.The speed and the boundary conditions are set according to the different operating conditions and structural characteristics.Under different operating conditions the previously calculated electromagnetic stress and mechanical stress of the inter-pole connection and field winding lead are superimposed to obtain the total stress.The change of total stress under different temperature conditions is considered,and the safety of the inter-pole connection and field winding lead is evaluated.On the basis of the above work,the key structural parameters of the inter-pole connection are changed to calculate the stress of different geometry,and the fatigue loss of one typical geometry is calculated.The thesis suggests some improvement of the structural parameters according to the evaluated stress and fatigue loss.Considering the different operating characteristics with the different structures,operating conditions,speeds and rated capacities/powers of pumped storage generator this thesis proportionally scales the models of three typical inter-pole connections and applies them to 16 different pumped storage generators for their different stress distribution.The applicability of these inter-pole connection structures to different types of pumped storage generator is analyzed based on the calculated stress distribution.