Study Of Electric Machine Shaft Voltage And Current Detection Method

The principle of electric machine is law of electromagnetic induction and law of electromagnetic force.The shaft voltage of electric machine is caused by dissymmetry magnetic circuit around the electric machine.If the shaft voltage exceed the limited value,shaft current will be created by breakdown bearing insulation.And it will break bearing.For safety operation,it will be measure the shaft voltage and current during electric machine test.This test item is hard to examining.Because shaft voltage are seriousness waveform distortion and poor repeatability & symmetry,and it lead to big data deviation.This thesis research the shaft voltage and current measure principle to design the feasibility way for motor test application.And develop a shaft voltage online detector equipment and it is used on site.There is unbalanced magnetic flux linkage on the shaft caused by stator during motor operation.Then it will generate induced electromotive force between the two sides of shaft.It is shaft voltage.It is caused by unbalanced flux;ultra-harmonics;electrostatic induction;external power source intervening.The voltage lead to shaft current.Firstly,research the formula and method referenced standard and design a High internal resistance voltmeter direct measurement.It is a method that read the voltage and current through the high internal resistance voltmeter by touch the test contact on both side of shaft during motor operation.This way measured the root mean square value of voltage and current.It is an integral in spell.Design a use oscilloscope measurement for measure the peak value about shaft voltage and current.It used oscilloscope transform the signal given by sensor to waveform image.The peak value can be got by analysis the image.We improve it by base on time window measurement for more fit to workshop environment after experimental study.After that,a kind of shaft current and voltage online measuring equipment was be developed based on these research.This equipment was be applied in power plant area.Then,a low power consumption long distance wireless transmission scheme by n RF401 is protocoled to equipment upgrading.This thesis proved the effectiveness and feasibility of the high internal resistance voltmeter method.The test result show the RMS value is fit to theory inference.The result can support the shaft voltage and current test scheme which will used on motor final test.Base on time window oscilloscope measurement is an improvement form oscilloscope measurement scheme.The peak value measuring is solved by it.Developed online measuring equipment can be used for motor operation monitoring and it has been approved available.