Fault detection method for thrust bearing of submersible motor

Abstract

The present invention relates to the technical field of electrical engineering, and more specifically, to a method for detecting a thrust bearing fault of a submersible motor. First, a two-dimensional model of a submersible motor model in a normal state is established using finite element software, and the output torque and speed of the motor under load are solved in a transient field; secondly, the fault frequency and fault time point are calculated according to the number of thrust bearing sliders and the motor speed in the submersible motor; then, the change in the motor load during the fault is set; and finally, the severity of the bearing fault is detected by comparing the calculated electromagnetic performance results with the actual fault situation. The present invention introduces an impact load at the thrust bearing fault time node in the motor finite element two-dimensional model to simulate the influence of the fault on the motor performance, thereby providing a fault detection method for the thrust bearing fault analysis of the submersible motor and solving the problem of the lack of a thrust bearing fault detection method for the submersible motor.

Description

Technical Field

[0001] The invention relates to a motor fault detection method, in particular to a submersible motor thrust bearing fault detection method. Background Art

[0002] Submersible motors play an important role in water resource allocation, disaster relief and other fields, and thrust bearing failure is one of the main factors causing submersible motor failure, which seriously affects the safe and reliable operation of submersible motors. The thrust bearing is located at the tail of the submersible motor, and there is a layer of water film inside it, which is responsible for bearing the axial force generated when the motor is running. Since the water film inside the thrust bearing is very thin, once foreign matter is mixed into the circulating water inside the motor, it will greatly affect the stability of the water film, causing dry friction inside the thrust bearing, and damaging the thrust slider and disc of the bearing. Therefore, it is of practical significance to study the failure mechanism and diagnosis method of the thrust bearing.

[0003] The mechanism of thrust bearing failure is still unclear, but obtaining actual data through prototype testing not only consumes manpower and material resources, but also some motor parameters are not easy to obtain. There are many research results in the field of bearing fault diagnosis, and data support is also needed to verify the effectiveness of the method. In summary, it is very necessary to design a thrust bearing fault detection method. Summary of the invention

[0004] The present invention provides a method for detecting thrust bearing faults of submersible motors. The simulation model uses the characteristics of electromagnetic performance changes inside submersible motors when thrust bearing faults occur as a detection basis, thereby achieving the purpose of providing a method for detecting thrust bearing faults of submersible motors.

[0005] In practice, when a thrust bearing fails, scratches distributed in multiple concentric circles can be observed on the surface of the bearing slider, and the generation of these scratches will inevitably cause changes in the motor load, providing a basis for the model design method. The solution of the present invention is:

[0006] A method for detecting a thrust bearing fault of a submersible motor comprises the following steps:

[0007] S10: Establish a two-dimensional model of a normal submersible motor using finite element software;

[0008] S20: Setting parameters and solving according to the working conditions in the transient field;

[0009] S30: Calculating the fault frequency and fault time interval according to the motor speed and the mechanical structure of the thrust bearing in S20;

[0010] S40: In combination with the calculation result in S30, the influence of the change of the bearing failure on the motor load is set to obtain a thrust bearing failure finite element model.

[0011] Specifically, in step S20, the simulation time must ensure that the motor reaches a steady state.

[0012] Specifically, in step S20, the mechanical setting of the motor is to couple the load.

[0013] Specifically in actual operation, in step S20, the load size of the coupled load is set according to the working conditions.

[0014] As a specific solution of the present invention, in step S30, the motor speed is the speed corresponding to the coupled load in S20.

[0015] As a specific solution of the present invention, in step S30, the fault time interval includes impact time and friction time.

[0016] As a specific solution of the present invention, in step S30, the thrust bearing fault frequency and fault time interval are calculated according to the following steps:

[0017] S31: Calculate thrust bearing failure frequency:

[0018] The motor shaft speed is n, in rad / min. When a fault occurs inside the thrust bearing, the number of fault points that appear per revolution of the motor shaft should be consistent with the number of bearing sliders, then:

[0019] N f =n c

[0020] The failure time point is:

[0021]

[0022] Then the failure frequency of the thrust bearing is:

[0023]

[0024] Among them, F B is the thrust bearing fault characteristic frequency, n is the motor rotor mechanical speed, n c The number of thrust bearing sliders;

[0025] S32: Calculate the time node of thrust bearing failure:

[0026]

[0027] Among them, T B is the thrust bearing fault characteristic frequency, F B is the thrust bearing fault characteristic frequency, T s Simulate the settling time for the motor model.

[0028] S33: selecting the impact time and friction time of the thrust bearing failure time according to the time node, and selecting q steps of the time node as the impact time according to the simulated failure situation, and the time between two consecutive impact times as the friction time.

[0029] As a specific solution of the present invention, in step S40, the impact and friction of the thrust bearing fault on the motor coupled load vary with the severity of the fault.

[0030] As a specific solution of the present invention, in step 40, the submersible motor thrust bearing fault model is designed according to the following steps:

[0031] S41: setting a thrust bearing fault load variation function according to the fault time interval and the impact and friction caused by the bearing fault;

[0032] S42: adding the thrust bearing fault load variation function to the coupling load of the normal motor model to obtain the thrust bearing fault model of the submersible motor.

[0033] As a specific solution of the present invention, in step 50, the analysis results include changes in the stator current amplitude and the frequency spectrum.

[0034] The submersible motor thrust bearing fault detection method proposed in the present invention has the following beneficial effects compared with the prior art:

[0035] The model can simulate the changes in the electromagnetic performance of the submersible motor when the thrust bearing fails;

[0036] The corresponding mathematical model can be set according to the severity of the thrust bearing fault;

[0037] The effectiveness of thrust bearing fault diagnosis methods and fault-tolerant technologies can be verified. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram of the design process of a finite element model for a submersible motor thrust bearing fault according to the present invention;

[0039] Figure 2 is a bearing fault load variation function in the embodiment;

[0040] Figure 3 A stator current waveform diagram of a thrust bearing fault simulation model in an embodiment;

[0041] Figure 4 is a stator current spectrum diagram of a thrust bearing fault simulation model in an embodiment; DETAILED DESCRIPTION

[0042] The present invention is described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments, and the description of the embodiments is only used to help understand the method and core ideas of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of this patent should be included in the protection scope of the present invention.

[0043] like Figure 1 As shown, a method for detecting a thrust bearing fault of a submersible motor comprises the following steps:

[0044] S10: Use finite element software to establish a normal motor two-dimensional model. The number of thrust bearing sliders is 20, and the motor parameters are as follows.

[0045] This embodiment adopts a submersible motor, and the basic parameters of the motor are shown in the following table:

[0046] Motor parameters Numeric power 75kW Pole pairs 2 Rated voltage 380V Core length 230mm Stator outer diameter 400mm Stator inner diameter 225mm Rotor inner diameter 85mm Groove fit 36—42 Air Gap 1.2mm

[0047] S20: Set parameters and solve the normal motor model in the transient field according to the working conditions. The solution time is 0.5s. The mechanical setting of the motor is a coupled load with a size of 200Nm. At this time, the motor speed is 1490rpm.

[0048] S30: Calculate the fault frequency and fault time interval according to the motor speed and the mechanical structure of the thrust bearing in S20, and calculate according to the following steps:

[0049] S31: In this embodiment, a single-point failure of a thrust bearing is simulated, and the failure frequency is:

[0050]

[0051] Among them, F B =496.7Hz is the thrust bearing fault characteristic frequency, n=1490rpm is the motor rotor mechanical speed, n c =20 is the number of thrust bearing sliders;

[0052] S32: Calculate the time node of thrust bearing failure:

[0053]

[0054] Among them, T B is the thrust bearing fault characteristic frequency, F B is the thrust bearing fault characteristic frequency, T s Simulate the settling time for the motor model.

[0055] The simulation stabilization time of the motor model is 0.4s, F B =496.7Hz, then:

[0056]

[0057] S33: Select the fault time interval according to the time node, and select the 2 steps of the time node as the fault time. In this embodiment, the step size is 0.0002s. Set T s The fault simulation time is 0.2s after that, so the bearing fault impact time is 0.4+N / 496.7±0.0002, where N is 1 to 100, the rest of the time between 0.4 and 0.6s is the friction time, and the simulation time is 0.8s.

[0058] S40: The impact and friction magnitude of the thrust bearing fault on the motor coupling load vary with the severity of the fault. In this embodiment, the impact magnitude is 200Nm and the friction magnitude is 50Nm. The thrust bearing fault model of the submersible motor is designed according to the following steps:

[0059] S41: Set the thrust bearing fault load variation function according to the fault time interval and the impact and friction caused by the bearing fault. The load variation function is as follows: Figure 2 As shown;

[0060] S42: adding a thrust bearing fault load variation function to the coupling load of the normal motor model to obtain a thrust bearing fault model of the submersible motor;

[0061] S50: Analytical model analysis of electromagnetic changes: Figure 3 The figure below shows the stator current waveform of the thrust bearing fault simulation model. The waveform before 0.4 is normal. After 0.4s, the bearing fault load change function is added for 0.2s. It can be observed that the stator current amplitude increases and the waveform is slightly distorted. By performing Fourier decomposition on the faulty stator current, Figure 4 The stator current spectrum of the thrust bearing fault simulation model shows that 50 Hz is the fundamental component, and the current component of 495 Hz can be observed. This is the stator current harmonic component caused by the thrust bearing fault with a fault frequency of 496.7 Hz. The error between them is caused by insufficient acquisition points. The above results verify the effectiveness of the model of the present invention.

[0062] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for detecting a thrust bearing fault of a submersible motor, characterized in that: The following steps are involved: S10: Establish a two-dimensional model of a normal submersible motor using finite element software; S20: setting parameters and solving according to normal working conditions in the transient field; S30: Calculate the fault frequency and fault time interval according to the motor speed and the mechanical structure of the thrust bearing in S20, where the fault time interval includes the impact time and the friction time; S40: setting the influence of the change of the motor load when the bearing fails in combination with the calculation result in S30, and obtaining a finite element model of the thrust bearing failure; S50: comparing the analytical result of the thrust bearing model with the actual situation to detect the bearing status; In step S30, the thrust bearing fault frequency and fault time interval are calculated according to the following steps: S31: Calculate thrust bearing failure frequency: The motor shaft speed is n, in rad / min. When a fault occurs inside the thrust bearing, the number of fault points that appear per rotation of the motor shaft should be consistent with the number of bearing sliders, so: N f =n c The failure time point is: Then the failure frequency of the thrust bearing is: Among them, F B is the thrust bearing fault characteristic frequency, n is the motor rotor mechanical speed, n c The number of thrust bearing sliders; S32: Calculate the time node of thrust bearing failure: Among them, T B is the time node of thrust bearing failure, N is a natural number series, F B is the thrust bearing fault characteristic frequency, Ts is the motor model simulation stabilization time; S33: selecting the impact time and friction time of the thrust bearing failure time according to the time node, selecting q steps of the time node as the impact time according to the simulated failure situation, and the time between two consecutive impact times as the friction time; In step 40, the submersible motor thrust bearing fault model is designed according to the following steps: S41: setting a thrust bearing fault load variation function according to the fault time interval and the impact and friction caused by the bearing fault; S42: adding the thrust bearing fault load variation function to the coupling load of the normal motor model to obtain the thrust bearing fault model of the submersible motor.

2. The method for detecting a thrust bearing fault of a submersible motor according to claim 1, characterized in that: In step S20, the simulation time must ensure that the motor reaches a steady state.

3. The method for detecting faults of thrust bearings of submersible motors according to claim 1, characterized in that: In step S20, the motor is mechanically configured to couple the load.

4. The method for detecting thrust bearing faults of a submersible motor according to claim 3, characterized in that: In step S20, the load size of the coupled load is set according to the working conditions.

5. The method for detecting faults of thrust bearings of submersible motors according to claim 3, characterized in that: In step S30, the motor speed is the speed corresponding to the coupled load in S20.

6. The method for detecting faults of thrust bearings of submersible motors according to claim 1, characterized in that: In step 50, the analysis results include changes in the stator current amplitude and the frequency spectrum.

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