Category: Issue 31
Publication: 31

According to statistics, the damages of asynchronous motors bearing units make up 15 – 20 % of all other types defects. The bearings damage leads to unevenness the non-magnetic air gap between the stator and rotor, which is the reason for the rotor eccentricity. It is possible in the most severe cases to touch the rotor on the stator inner surface, which may cause mechanical damage. The most commonly known methods for control of unevenness the air gap usually require the disconnection of electric machine from the power supply and to use the external sources of direct or alternating current. For this reason, the method of damage bearings diagnostic eliminates these shortcomings and easy to use is urgent. It is based on an analysis of change the electrochemical induction amplitude values during the operation of an electric machine. In the presence of a bearing defect, the magnetic field in the machine air gap as well as the field pushed out of the gap is changes. So when the sensors are installed directly in the air gap or for convenience on the stator end zone (closer to the rotor) their values will differ on the operating and instantaneous induction, which are measured at the same time. To implement the proposed method in high-voltage asynchronous motors, magnetic field sensors can be set in the form of a wind twisted on the stator tooth. Inductive coils can be used as sensors. It is necessary to set at least two magnetic field sensors in the opposite direction at the pole division of an electric machine. By the magnetic induction value it can be concluded that there is a bearing defect. Measured the two induction values are compared with each other and depending on the degree of development of the defect are found the bearings damage. For each asynchronous motor design, the control points for the set of some sensors should be corrected. Built on a fast Fourier transform analysis allows to compare the spectrum with "reference" and for each peak value determine the tendency of defect development. This tendency is a sensual tool for early recognition of systematic changes. Other methods of electric machines diagnostics have a supporting role. To ensure guaranteed reliability of operation the asynchronous motors is desirable to carry out a comprehensive diagnosis of different physical nature parameters. To speak about a defect can only be compared with the same type asynchronous motor that functions normally. From the rate of distinctions growth can judge with respect to the residual life of bearings, as well as plans real need preventive work. Comparative analysis of results for no defect and defect bearing will allow detecting a set of well-established marks of signal parameters with the reference signal anomalies. Algorithms for automatic finding of the anomalies and appropriate applications for their use as standard can be created after the formal description of the differences in the parameters. Diagnostic method can be improved taking into account its operation at different nuclear power plants.

Keywords: asynchronous motor, sliding bearings, diagnostics.


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