Development Of Comprehensive Insulation Testing System For Stator Bar Of Large Generator

The factory inspection of stator bar insulation of large generator is an important means to ensure its quality.At present,most of the insulation inspection items of stator bar of generator are carried out separately at home and abroad,which results in low efficiency and high cost of insulation inspection.Therefore,according to the actual needs of manufacturers,this paper develops a comprehensive automatic testing system for stator bar insulation of large generators.According to the function and index requirement of generator stator bar insulation test,this paper designs the system structure of large generator stator bar insulation comprehensive test system,including fixture electrode,AC high voltage generator,dielectric loss factor measurement unit,surface resistivity measurement unit and test center control unit,which can complete AC withstand voltage test of large generator stator bar,and automatic measurement of dielectric loss factor and surface resistivity of stator bar.In order to eliminate the influence of leakage current on dielectric loss factor at the end of the stator bar,this paper adopts a double protection electrode test scheme with automatic voltage feedback tracking,which can accurately measure dielectric loss factor at the linear section of the stator bar without destroying the insulation structure at the end of the generator,and uses quasi-synchronous algorithm to eliminate the influence of non-integral period sampling and harmonic wave on the measurement.On this basis,the hardware circuit of the dielectric loss factor measurement system is designed,including analog signal extraction circuit,multi-channel analog signal conditioning circuit,data acquisition circuit,system correction circuit,central control circuit,step-up and step-down control circuit and communication circuit.In order to accurately measure the surface resistivity of generator stator bar insulation,a four-electrode measuring system is used to measure the surface resistivity of generator stator bar.The corresponding hardware circuits are designed,including switching circuit,signal pre-conditioning circuit,data acquisition circuit,central control and communication circuit.In this paper,the above hardware is debugged in the laboratory,and the upper computer software and the lower computer software systems are designed respectively to achieve the comprehensive control of the measurement system.The whole system debugging results show that the integrated testing system designed in this paper can meet the requirements of various testing functions,realize the automatic control of AC withstand voltage of generator stator bar,and realize the automatic measurement of dielectric loss factor of generator stator bar during boosting process.The measurement accuracy of dielectric loss factor can reach 0.03% and surface resistivity can reach 1%,which meets the accuracy requirements of the measurement process of insulation parameters of generator stator bars.