Method for detecting broken bar of asynchronous motor

Abstract

The invention belongs to the technical field of asynchronous motor broken bar detection, particularly relates to an asynchronous motor broken bar detection method, and aims to solve the problem that broken bar detection is difficult in the background technology. A rotational magnetomotive force # imgabs0 # is generated to cut the rotor bars at a relative speed of sns. According to the scheme, the effect of rapidly detecting whether the broken bar fault occurs or not can be achieved by detecting the current harmonic frequency of the machine end, the detection mode is safe and reliable, the fault reason can be effectively positioned, the installation efficiency is improved, when the rotor circuit is asymmetric, the current component with the frequency of (1 + / -2s) fs can be induced in the stator winding, and the fault detection accuracy is improved. The frequency of the asymmetric component added in the stator current is (1 + / -2ks) fs, k = 1, 2, 3..., the asymmetric component frequency can be visually represented from data, the difficulty of broken bar detection is reduced, and a detection mode that abnormity can be found from vibration only after the motor runs is replaced.

Description

Technical Field

[0001] The invention relates to the technical field of asynchronous motor broken bar detection, and in particular to a method for detecting a broken bar of an asynchronous motor. Background Art

[0002] After the aluminum cast rotor is die-cast and centrifugally cast, the probability of missing guide bars has been greatly reduced, but it still has a chance of happening. In addition to the rotor damage that occurs during the production process, the broken bars that may be caused by overspeed testing, and the inspection of the repaired motor, the analysis of broken bars is still an important part of production.

[0003] However, since broken bars are difficult to detect, abnormalities can often only be discovered from vibration after the motor is running. However, since there are many reasons for motor vibration, it is difficult to determine whether the vibration is caused by broken bars. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a method for detecting broken bars of an asynchronous motor, which overcomes the deficiencies of the prior art and effectively solves the problem of difficulty in detecting broken bars.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for detecting a broken bar of an asynchronous motor comprises the following steps:

[0007] Step 1: Under normal circumstances, when the AC power passes through the stator winding, a rotating magnetic motive force is generated. With sn s The relative speed cuts the rotor bars and induces an induced current with a frequency of sf1 in the rotor;

[0008] Step 2: The induced current will produce The same magnetomotive force This in turn generates a current component with a frequency of f1 in the stator winding;

[0009] Step 3: When the asynchronous motor bars are normal, the frequency of the harmonic component in the current is f1;

[0010] Step 4: When the rotor bar of the asynchronous motor is broken, a negative sequence component appears in the rotor magnetic field. This component will establish a magnetic motive force and generate a frequency of (1±2s)f in the stator. s Additional weight;

[0011] The specific expression is:

[0012]

[0013] The expression of ω(t) in the rotor is,

[0014]

[0015] From the perspective of phase A,

[0016]

[0017] Φ A (t) Taking the derivative of t, we get (1±2s)f in the stator. s The expression of induced potential is,

[0018]

[0019] Therefore, the expression of the induced current in the stator due to the broken rotor bar is,

[0020]

[0021] Preferably, the asynchronous motor model is YPTKK4004-2HK2 (900kW 10kV) motor.

[0022] Preferably, the stator and rotor slots of the asynchronous motor are matched in a 48-40 ratio.

[0023] Preferably, the asynchronous motor has a rotation speed of 2979.45 rpm and a slip rate of 0.00685 when outputting rated power.

[0024] The beneficial effects of the present invention are:

[0025] 1. Compared with the detection method of resistance and induction current, the detection method of the asynchronous motor broken bar of the present invention can quickly detect whether a broken bar fault occurs by detecting the harmonic frequency of the machine-end current. The detection method is safe and reliable, and the cause of the fault can be effectively located, thereby improving the installation efficiency.

[0026] 2. The detection method of the broken bars of the asynchronous motor of the present invention is that when the rotor circuit is asymmetric, a frequency of (1±2s)f will be induced in the stator winding. s The current component of the stator current has an asymmetric component frequency of (1±2s)f s , k = 1, 2, 3..., which can be directly expressed from the data, reducing the difficulty of broken bar detection and replacing the detection method that can only find abnormalities from the vibration after the motor is running. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of asymmetric component frequency of a method for detecting broken bars of an asynchronous motor proposed by the present invention;

[0028] Figure 2 A schematic diagram of harmonic statistics results of a method for detecting broken bars of an asynchronous motor proposed by the present invention. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0030] Embodiment 1, refer to Figure 1-2 , a method for detecting a broken bar of an asynchronous motor comprises the following steps:

[0031] Step 1: Under normal circumstances, when the AC power passes through the stator winding, a rotating magnetic motive force is generated. Sn s The relative speed cuts the rotor bars and induces an induced current with a frequency of sf1 in the rotor;

[0032] Step 2: The induced current will produce The same magnetomotive force This in turn generates a current component with a frequency of f1 in the stator winding;

[0033] Step 3: When the asynchronous motor bars are normal, the frequency of the harmonic component in the current is f1;

[0034] Step 4: When the rotor bar of the asynchronous motor is broken, a negative sequence component appears in the rotor magnetic field. This component will establish a magnetic motive force and generate a frequency of (1±2s)f in the stator. s Additional weight;

[0035] The specific expression is:

[0036]

[0037] The expression of ω(t) in the rotor is,

[0038]

[0039] From the perspective of phase A,

[0040]

[0041] Φ A (t) Taking the derivative of t, we get (1±2s)f in the stator. s The expression of induced potential is,

[0042]

[0043] Therefore, the expression of the induced current in the stator due to the broken rotor bar is,

[0044]

[0045] In this embodiment, compared with the method of detecting resistance and induction current, this solution can quickly detect whether a broken bar fault occurs by detecting the harmonic frequency of the machine-end current. The detection method is safe and reliable, and can effectively locate the cause of the fault and improve the installation efficiency. When the rotor circuit is asymmetric, a frequency of (1±2s)f will be induced in the stator winding. s The current component of the stator current has an asymmetric component frequency of (1±2s)f s , k = 1, 2, 3..., which can be directly expressed from the data, reducing the difficulty of broken bar detection and replacing the detection method that can only find abnormalities from the vibration after the motor is running.

[0046] Example 2, refer to Figure 1-2 , a method for detecting broken bars of asynchronous motors. When the rotor circuit is asymmetrical, a frequency of (1±2s)f will be induced in the stator winding. s The current component will induce (1±2s)f in the air gap. s Torque fluctuations and (1±2s)f are generated in the rotor s The additional current component in the rotor continues to induce (1±2s)f in the stator. s By analogy, the frequency of the added asymmetric component in the stator current is (1±2s)f s , k=1,2,3...。

[0047] Take the YPTKK4004-2HK2 (900kW 10kV) motor as an example, the stator and rotor slots match 48-40, the speed is 2979.45rpm at rated power output, and the slip rate is 0.00685. If a broken bar occurs, the asymmetric component frequency should be as shown in the following table:

[0048] k <![CDATA[(1+2ks)f s ]]> <![CDATA[(1-2ks)f s ]]> k＝1 50.685 49.315 k＝2 51.370 48.630 k＝3 52.055 47.945 k＝4 52.740 47.260

[0049] After sampling the asynchronous motor current for no less than one minute, the asynchronous motor current is subjected to Fourier decomposition and statistical analysis is performed on the 47-53Hz part. The statistical results are as follows: Figure 2 As shown, after ignoring the fundamental frequency current of 50 Hz, high points appear near 48.6, 49.3, and 50.7 Hz, especially near 49.3 Hz, where a harmonic current of about 0.9 A appears.

[0050] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0051] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0052] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for detecting broken bars of an asynchronous motor, characterized in that: The following steps are involved: Step 1: Under normal circumstances, when the AC power passes through the stator winding, a rotating magnetic motive force is generated. With sn s The relative speed cuts the rotor bars and induces an induced current with a frequency of sf1 in the rotor; Step 2: The induced current will produce The same magnetomotive force This in turn generates a current component with a frequency of f1 in the stator winding; Step 3: When the asynchronous motor bars are normal, the frequency of the harmonic component in the current is f1; Step 4: When the rotor bar of the asynchronous motor is broken, a negative sequence component appears in the rotor magnetic field. This component will establish a magnetic motive force and generate a frequency of (1±2s)f in the stator. s Additional weight; The specific expression is: The expression of ω(t) in the rotor is, From the perspective of phase A, Φ A (t) Taking the derivative of t, we get (1±2s)f in the stator. s The expression of induced potential is, Therefore, the expression of the induced current in the stator due to the broken rotor bar is, 2. A method for detecting broken bars of an asynchronous motor according to claim 1, characterized in that: The asynchronous motor model is YPTKK4004-2HK2 (900kW 10kV) motor.

3. A method for detecting broken bars of an asynchronous motor according to claim 1, characterized in that: The stator and rotor slots of the asynchronous motor are matched in a 48-40 manner.

4. A method for detecting broken bars of an asynchronous motor according to claim 1, characterized in that: The asynchronous motor has a rotation speed of 2979.45 rpm and a slip rate of 0.00685 when outputting rated power.

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