| Machine eccentricity is the condition of unequal air gap that exists between the stator and rotor. It is a common type of motor fault. The survey shows that 80% of motor mechanical faults are associated with eccentricity. When the degree of eccentricity is small, the performance of motor will decline. However, if the eccentricity becomes severe, the rotor would rub the stator and the motor would break down eventually. The submersible motor plays an important role in people’s daily lives, agriculture, industry and other applications. It is entrusted with responsibilities of the national security prevention and control of water. Due to limitations of the work environment, some submersible motors with an elongated structure, such as working in well, are more easily fails in eccentricity fault under the combined influence of gravity, unbalanced magnetic pull, rotor deflection, etc,. Once the submersible motor breaks down due to the eccentricity fault, it not only brings economic losses, even endangers people’s life. Therefore, it is significant for reducing people’s lives and property to research the eccentric failure mechanism of submersible motor and find appropriate detection methods.Using the motor current signature analysis and monitoring vibration signals are the most commonly methods to detect eccentricity at present. However, the applicable range of motor current signature analysis method is limited since only a particular combination of motor pole pairs and rotor slot number will give rise to significant components of stator current. As for the vibration detecting method, it needs high precision measuring equipment and the diagnosis error is larger. The eccentricity fault firstly gives rise to the change of air-gap magnetic field. Therefore, in this paper, the distribution characteristics of air-gap magnetic field are analyzed firstly in submersible motor under eccentricity fault. Then the detecting method of eccentricity fault based on air-gap magnetic analysis is proposed. This method owns wide applicable range and strong anti-interference ability. In this paper, the main work is expounded as follows:(1) The air-gap magnetic field is calculated by analytic method. Firstly, the air-gap permeance model is established considering the slotting effect when the motor is under eccentricity condition. Then based on the MMF and permeance wave approach, the magnetic field is obtained. Finally, the new magnetic field harmonics due to the eccentricity are determined. They are chose as characteristic signals to detect eccentricity fault;(2) The difference between the stator current and the air-gap magnetic field is analyzed, and their difference is determined;(3) The influence of rotor slot number on the detection signal and the amplitude of the signal are analyzed;(4) The method of measuring the air-gap magnetic field indirectly is proposed by placing the search coil in the stator tooth part of the motor. The effectiveness of the method is verified by the finite element simulation;(5) Proposing the method that detecting eccentricity by using the stator slot leakage flux and stator yoke magnetic field characteristic signals, and carrying on the simulation verification;(6) Proposing multi-point magnetic field characteristic detecting method based on the stator slot leakage flux and stator tooth magnetic field, respectively. And the placement of the search coils is introduced in detail. The method can not only diagnose the type of eccentricity fault, but also determine the position of the minimum air gap.The problems that need to be solved and the next work about eccentric detection of submersible motor are described at the end of the paper. |
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