Research On Detection Method Of Broken Rotor Bar Fault For Induction Motor At Time-varying Loads

The induction motors are widely used in industrial and agricultural fields because of their simple structure,low price,and convenient maintenance.However,due to the long-term operation and harsh working conditions,motor failure frequently occurs.Once the failure of the motor is light will destroy itself,heavy will bring huge economic losses.Therefore,it is particularly important to perform early fault detection on the motor to ensure its safe and reliable operation.Rotor broken bar(BRB)fault is a common fault of induction motor,accounting for about 10% of all faults.At present,the research on the detection of BRB fault for induction motor at constant load is becoming increasingly mature,while the research on the detection of BRB fault at timevarying load is relatively less and has some deficiencies.In addition,the disturbance of the load will also interfere with the detection of BRB fault,which will easily cause the confusion of the detection results.Therefore,how to realize the collaborative detection of load disturbance and rotor broken bar fault is another problem to be solved urgently.Based on these,the main research content of this paper is as follows:(1)In order to detect the BRB fault of induction motor at time-varying loads,an envelope extraction algorithm based on short-time sliding Fourier transform(STSFT)is proposed to extract the envelope of stator current,and then judge whether the rotor is fault or not according to the evolution of envelope.The entire performance of the algorithm was tested by simulation,and its shortcomings were analysed.Then,the spectrum correction technology was introduced to improve it,and a new detection method based on short-time sliding correction Fourier transform(STSCFT)was then developed.Finally,the feasibility and universality of the algorithms were verified by testing experiments of two induction motors with different powers(1.1 k W and 2.2 k W).(2)In order to achieve a good distinction between load disturbance and BRB fault,and avoid confusion in the detection results.A method based on extracting the envelope of instantaneous active current and reactive current was proposed,and the distinction between them was realized according to the different performance of load disturbance and BRB fault in the envelope.Meanwhile,in order to improve the accuracy of envelope extraction,another new envelope extraction method based on short-time sliding Prony(STSP)was proposed.The whole performance of the algorithm was analysed by simulation and compared with STSCFT.Finally,the effectiveness and feasibility of the proposed method were verified by experiments.(3)In order to better apply the methods proposed in this paper to practice,a set of BRB fault on-line detection system for induction motor based on Lab VIEW was designed and implemented.The design and implementation of the hardware and software system were described in detail.Finally,the reliability and feasibility of the system were verified by the relevant test experiments of a Y90s-4 induction motor.68 figures,4 tables and 86 references are included in this thesis.