A method and device for detecting a dynamic inter-turn short circuit fault of a generator stator winding

Abstract

The application discloses a kind of generator stator winding dynamic interturn short circuit fault detection method and device, it is related to generator state monitoring and fault diagnosis technical field, comprising: real-time measurement generator rotor vibration signal;Utilize fast fourier transform and transform vibration signal from time domain signal into frequency domain signal;The time domain signal and the frequency domain signal after transformation obtained by acquisition are compared with the spectrum component of vibration signal under normal condition, to judge whether generator occurs winding dynamic interturn short circuit fault.The application identifies whether generator occurs stator winding dynamic interturn short circuit fault by detecting the rotor vibration of generator.The application is simple and easy to operate, makes up the deficiency of the winding dynamic interturn short circuit fault detection at present, the feature of detection is obvious, and the effect is better, provides reference for the detection and diagnosis of generator stator winding dynamic interturn short circuit fault.

Description

Technical Field

[0001] This invention relates to the field of generator condition monitoring and fault diagnosis technology, and more specifically to a method and device for detecting dynamic inter-turn short-circuit faults in generator stator windings. Background Technology

[0002] Currently, generator stator windings have insulation defects due to insulation aging and prolonged exposure to complex mechanical and thermal stresses. These defects manifest as cracks and wear. When direct connections exist between copper wires in different turns, stator winding inter-turn short-circuit faults occur. Most current research describes stator winding inter-turn short circuits as steady-state faults, where the insulation fault point is permanently connected. However, in reality, under electromagnetic forces, intermittent or periodic contact can occur between the short-circuited turns, resulting in a dynamic stator winding inter-turn short circuit. Specifically, in dynamic stator winding inter-turn short circuits, the fault is not continuous. During certain periods, the stator winding is normal and no short circuit occurs; during other periods, the short-circuited turns come into contact, causing a short circuit. Dynamic stator winding inter-turn short circuits are an early form of inter-turn short circuit faults and are often difficult to detect during major generator overhauls. After prolonged operation, a generator may develop a steady-state stator winding inter-turn short-circuit fault, leading to an imbalance in the generator's three-phase current, significant vibration in the stator winding, and the generation of a large amount of heat that raises the temperature of the faulty coil. This can eventually cause insulation failure, affecting more coils and causing serious consequences such as generator shutdown.

[0003] In summary, early detection and handling of faults can reduce economic losses caused by downtime and other issues. Therefore, how to detect dynamic inter-turn short-circuit faults in generator stator windings is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides a method and apparatus for detecting dynamic inter-turn short-circuit faults in generator stator windings, in order to solve the problems existing in the background art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for detecting dynamic inter-turn short-circuit faults in generator stator windings includes:

[0007] Real-time measurement of generator rotor vibration signals;

[0008] The vibration signal is transformed from a time-domain signal to a frequency-domain signal using the Fast Fourier Transform.

[0009] The collected time-domain signal and the transformed frequency-domain signal are compared with the spectrum components of the vibration signal under normal conditions to determine whether the generator has experienced a dynamic inter-turn short-circuit fault in the stator winding.

[0010] Optionally, the real-time measurement of the generator rotor vibration signal specifically includes:

[0011] An acceleration sensor is installed on the bearing housing of the generator rotor to measure the rotor vibration signal.

[0012] Optionally, determining whether a dynamic inter-turn short-circuit fault has occurred in the generator stator winding specifically includes:

[0013] The air gap magnetomotive force of the generator under normal operation and under dynamic inter-turn short-circuit fault of the stator winding, as well as the air gap permeability per unit area, are obtained.

[0014] The air gap magnetomotive force is multiplied by the air gap permeability per unit area to obtain the air gap magnetic flux density of the generator.

[0015] Calculate the magnetic pull force per unit area based on the air gap magnetic flux density of the generator; and integrate the magnetic pull force per unit area over the entire circumference to obtain the unbalanced magnetic pull force on the rotor.

[0016] When the unbalanced magnetic pull on the rotor is zero, the generator is in normal condition.

[0017] When the unbalanced magnetic pull on the rotor is not zero, the generator experiences a dynamic inter-turn short circuit fault in the stator winding.

[0018] Optionally, the air gap magnetomotive force is specifically manifested as follows:

[0019]

[0020] In the formula, ω is the electrical frequency, t is time, I0 is the excitation current of the generator, and K = 2qw c k wl τfL, q is the number of slots per pole per phase, w c qw represents the number of turns of the coil. c k is the total number of turns in the parallel branches of the stator winding. wl τ is the fundamental winding factor, f is the stator winding pitch, L is the generator frequency, and γ is the stator core length; γ is the harmonic order, γ = 1, 3, 5, 7; η is the coefficient of stator magnetomotive force relative to rotor magnetomotive force; Ψ is the generator's internal power factor angle, determined by load characteristics; α m β1 is the circumferential position angle of the air gap; β2 is the angle between the resultant magnetomotive force of the air gap and the rotor magnetomotive force when the stator winding is in normal operation; I is the angle between the resultant magnetomotive force of the air gap and the rotor magnetomotive force when the stator winding is dynamically short-circuited between turns. fd1 and Ifd2 These are the amplitudes of the first and second current harmonics generated in the excitation winding under a dynamic inter-turn short circuit in the stator winding, I. fd1 =k1I0,I fd2 =k2I0, where k1 and k2 represent the coefficients of the short circuit.

[0021] Optionally, the permeability per unit area of ​​the air gap is specifically manifested as follows:

[0022]

[0023] In the formula, g0 is the average air gap length of the generator, μ0 is the air permeability, and Λ0 is the permeability constant per unit area of ​​the air gap.

[0024] Optionally, the air gap magnetic flux density of the generator is specifically expressed as follows:

[0025]

[0026] Optionally, the unbalanced magnetic pull on the rotor manifests itself in the following form:

[0027]

[0028] In the formula, L is the length of the stator core and R is the radius of the outer surface of the rotor core.

[0029] Optionally, when the generator is in normal operation, the unbalanced magnetic pull on the rotor manifests as follows:

[0030]

[0031] Optionally, when a generator experiences a dynamic inter-turn short-circuit fault in its stator windings, the unbalanced magnetic pull on the rotor manifests as follows:

[0032]

[0033] A generator stator winding dynamic inter-turn short circuit fault detection device includes: a generator, a drive motor, a signal acquisition instrument, a host computer, an acceleration sensor, a short circuit terminal block, a relay, and a pulse generator;

[0034] The pulse generator, relay, short-circuit terminal block, generator, and drive motor are connected in sequence.

[0035] An acceleration sensor is installed on the bearing housing of the generator rotor to measure the vibration signal of the generator rotor. The acceleration sensor is connected to a signal acquisition instrument, which is then connected to a host computer.

[0036] As can be seen from the above technical solution, compared with the prior art, this invention discloses a method for detecting dynamic inter-turn short-circuit faults in generator stator windings, including: real-time measurement of generator rotor vibration signals; transformation of the vibration signals from time-domain signals to frequency-domain signals using fast Fourier transform; comparison of the acquired time-domain signals and transformed frequency-domain signals with the spectral components of vibration signals under normal conditions to determine whether a dynamic inter-turn short-circuit fault has occurred in the generator stator windings. This invention identifies whether a generator has experienced a dynamic inter-turn short-circuit fault in its stator windings by detecting the generator rotor vibration. This invention is simple and easy to implement, overcomes the shortcomings of current methods for detecting dynamic inter-turn short-circuit faults in generator stator windings, has obvious detection characteristics, and good results, providing a reference for the detection and diagnosis of dynamic inter-turn short-circuit faults in generator stator windings. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0038] Figure 1 A vector diagram of the air gap magnetomotive force of the generator under normal conditions provided by the present invention;

[0039] Figure 2 A vector diagram of the air gap magnetomotive force under dynamic inter-turn short circuit of the generator stator winding provided by the present invention;

[0040] Figure 3 This is a schematic diagram of a generator stator winding short-circuit tap provided by the present invention;

[0041] Figure 4 A schematic diagram of the short-circuit terminal block provided by the present invention;

[0042] Figure 5 This is a schematic diagram showing the connection between the short-circuit terminal block and the stator A-phase winding provided by the present invention.

[0043] Figure 6 This is a schematic diagram of the experimental platform connection provided by the present invention;

[0044] Figure 7 The flowchart for detecting dynamic inter-turn short-circuit faults in windings provided by the present invention;

[0045] The labels in the diagram are as follows: 1. Drive motor, 2. Accelerometer, 3. Generator, 4. Relay, 5. Pulse generator, 6. Signal acquisition device, 7. Host computer. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] This invention discloses a method for detecting dynamic inter-turn short-circuit faults in generator stator windings. The method involves measuring the generator rotor vibration signal in real time and using it as a diagnostic parameter. The vibration signal is acquired by an accelerometer and then converted into a spectral signal by a Fast Fourier Transform (FFT). The acquired time-domain signal and the transformed frequency-domain signal are then compared with the spectral components of the vibration signal under normal conditions to determine whether a dynamic inter-turn short-circuit fault has occurred in the generator stator windings.

[0048] like Figure 7 As shown, the specific steps of this method are as follows:

[0049] a. Install an acceleration sensor on the bearing housing of the generator rotor and build an experimental platform;

[0050] b. Use an accelerometer to measure rotor vibration signals;

[0051] c. Use Fast Fourier Transform to transform the vibration signal from a time-domain signal to a frequency-domain signal;

[0052] d. Confirm the generator's operating status by comparing the time domain and frequency domain, and determine whether the generator has a dynamic inter-turn short circuit fault in the stator winding;

[0053] In one specific embodiment, the stress on the generator rotor is calculated by combining the following formulas, thereby determining the characteristic frequency components of rotor vibration when a dynamic inter-turn short-circuit fault occurs in the stator winding of the generator.

[0054] like Figure 6 As shown, acceleration sensors are installed on the bearing housings of the generator rotor. Two sensors are installed in the horizontal and two in the vertical radial directions of the two bearing housings to measure the vibration signal of the generator rotor. The acceleration sensors are connected to a signal acquisition instrument, which is connected to a host computer.

[0055] After the vibration signal of the generator rotor is measured by the accelerometer, the vibration signal is transformed from the time domain signal to the frequency domain signal by the FFT fast Fourier transform in the host computer to obtain the frequency domain signal of the rotor vibration, and the characteristic frequency amplitude from 0Hz to 300Hz is recorded.

[0056] Dynamic inter-turn short faults in generator stator windings are determined by comparing time and frequency domains. The previously acquired time domain signal is transformed by FFT, and the transformed frequency domain signal is compared with the spectral components in the vibration signal data sample under normal conditions.

[0057] When the amplitude of the time-domain waveform of the generator rotor vibration signal and the amplitude of each harmonic component in the spectrum increase, and the frequency corresponding to each harmonic in the spectrum is from the first to the sixth harmonic, then the generator has a dynamic inter-turn short fault in the stator winding. The larger the amplitude of each corresponding frequency, the greater the degree of dynamic inter-turn short fault in the stator winding.

[0058] The characteristic frequencies of rotor vibration before and after a dynamic inter-turn short fault in the stator winding of the generator were obtained by calculation, such as Figure 1 and Figure 2 As shown, E0 is the phase A electromotive force, β1 is the angle between the air gap magnetomotive force and the rotor magnetomotive force under normal conditions, and β2 is the angle between the air gap magnetomotive force and the rotor magnetomotive force under dynamic inter-turn short circuit of the stator winding. Therefore, the expressions for the air gap magnetomotive force of the generator under normal operation and under dynamic inter-turn short circuit fault of the stator winding are as follows:

[0059]

[0060] In the formula, ω is the electrical frequency, t is time, I0 is the excitation current of the generator, and K = 2qw c k wl τfL, q is the number of slots per pole per phase, w c qw represents the number of turns of the coil. c k is the total number of turns in the parallel branches of the stator winding. wl τ is the fundamental winding factor, f is the stator winding pitch, L is the generator frequency, and γ is the stator core length; γ is the harmonic order, γ = 1, 3, 5, 7; η is the coefficient of stator magnetomotive force relative to rotor magnetomotive force; Ψ is the generator's internal power factor angle, determined by load characteristics; α m β1 is the circumferential position angle of the air gap; β2 is the angle between the resultant magnetomotive force of the air gap and the rotor magnetomotive force when the stator winding is in normal operation; I is the angle between the resultant magnetomotive force of the air gap and the rotor magnetomotive force when the stator winding is dynamically short-circuited between turns. fd1 and I fd2 These are the amplitudes of the first and second current harmonics generated in the excitation winding under a dynamic inter-turn short circuit in the stator winding, I. fd1 =k1I0,I fd2 =k2I0, where k1 and k2 represent the coefficients of the short circuit.

[0061] Under dynamic inter-turn short-circuit faults in the stator windings, the radial length of the generator's air gap remains constant, and the permeability per unit area is inversely proportional to the radial length of the air gap. Therefore, the permeability per unit area can be expressed by the following formula:

[0062]

[0063] In the formula, g0 is the average air gap length of the generator, μ0 is the air permeability, and Λ0 is the permeability constant per unit area of ​​the air gap.

[0064] The air gap magnetic flux density of the generator is obtained by multiplying the air gap magnetomotive force and the air gap permeability. The value of the stator winding before and after a dynamic inter-turn short-circuit fault can be expressed as:

[0065]

[0066] Under normal conditions, the air gap magnetic flux density of a generator contains only the fundamental wave and odd-order harmonics. When a dynamic inter-turn short-circuit fault occurs in the stator winding, the amplitude of the fundamental wave of the air gap magnetic flux density decreases, and even-order harmonics appear in the air gap magnetic flux density.

[0067] The excitation force of rotor vibration is the unbalanced magnetic pull on the rotor, which is obtained by integrating the magnetic pull per unit area on the outer surface of the rotor over the entire circumference, as shown in the following expression:

[0068]

[0069] In the formula, L is the length of the stator core and R is the radius of the outer surface of the rotor core.

[0070] When the generator is in normal operation, the unbalanced magnetic pull on the rotor manifests as follows:

[0071]

[0072] The unbalanced magnetic pull on the generator rotor in both the X and Y directions is zero, so theoretically the generator rotor does not produce radial vibration under normal operating conditions.

[0073] When a generator experiences a dynamic inter-turn short-circuit fault in its stator windings, the unbalanced magnetic pull on the rotor manifests as follows:

[0074]

[0075] As shown in the above formula, the unbalanced magnetic pull on the rotor includes a DC component and first, second, third, fourth, fifth, and sixth harmonics. The more severe the short circuit, the greater the amplitude of each harmonic of the unbalanced magnetic pull. Since rotor vibration is a response to the unbalanced magnetic pull on the rotor, when a dynamic inter-turn short circuit fault occurs in the stator winding, the generator rotor will vibrate at frequencies of 1f, 2f, 3f, 4f, 5f, and 6f. Furthermore, as the degree of short circuit increases, the vibration amplitude of different frequency components will increase significantly.

[0076] An acceleration sensor is installed on the generator rotor bearing housing. Once the motor is running smoothly, ten sets of rotor vibration acceleration signal data are collected. Each of these ten sets of data undergoes a Fast Fourier Transform (FFT) to obtain the frequency domain signal of the acceleration signal. The average amplitude corresponding to the characteristic frequency of each of the ten sets of data is calculated to obtain a data sample of the rotor vibration acceleration signal. This sample is compared with the data sample of the rotor vibration acceleration signal under normal conditions to determine whether a dynamic inter-turn short-circuit fault has occurred in the generator stator winding.

[0077] An experimental setup was used to simulate a dynamic inter-turn short-circuit fault in the stator winding. Figure 3 This is a schematic diagram of the three-phase stator winding of a generator. Five sets of short-circuit taps are connected to one branch of each phase of the three-phase stator winding, namely tap A1: 0%, tap A2: 2%, tap A3: 4%, tap A4: 6% and tap A; tap B1: 0%, tap B2: 2%, tap B3: 4%, tap B4: 6% and tap B; tap C1: 0%, tap C2: 2%, tap C3: 4%, tap C4: 6% and tap C.

[0078] Figure 4 This is a schematic diagram of a short-circuit terminal block, which has five short connectors.

[0079] Figure 5 This diagram shows the connection between each short-circuit tap on the stator A-phase winding and the short-circuit terminal block. The relay is connected to the short-circuit terminal block, and by cooperating with each short-circuit tap on the stator winding, the simulation of inter-turn short-circuit faults of different degrees in the three-phase stator winding can be realized.

[0080] In simulating specific inter-turn short circuit faults, taking phase A as an example, the relays connected to interfaces A1 and A2 of the short-circuit terminal block can simulate a 2% inter-turn short circuit in the stator phase A winding; the relays connected to interfaces A1 and A3 of the short-circuit terminal block can simulate a 4% inter-turn short circuit in the stator phase A winding; and the relays connected to interfaces A1 and A4 of the short-circuit terminal block can simulate a 6% inter-turn short circuit in the stator phase A winding.

[0081] The pulse generator is connected to a relay and can generate pulse signals of different periods as needed. When the relay receives a pulse signal, it will open or close according to the period of the pulse signal. Based on the above design, the simulation of dynamic inter-turn short circuit faults in the generator stator winding can be realized at different degrees and with accurate and controllable frequency. The vibration data of the rotor under different operating conditions of the generator is recorded and saved by an accelerometer and a signal acquisition instrument.

[0082] A generator stator winding dynamic inter-turn short circuit fault detection device includes: generator 3, drive motor 1, signal acquisition instrument 6, host computer 7, acceleration sensor 2, short circuit terminal block, relay 4 and pulse generator 5;

[0083] The pulse generator 5, relay 4, short-circuit terminal block, generator 3, and drive motor 1 are connected in sequence;

[0084] Accelerometer 2 is installed on the bearing housing of the rotor of generator 3. Two accelerometers are installed in the horizontal and vertical directions of the two bearing housings to measure the vibration signal of the generator rotor. Accelerometer 2 is connected to signal acquisition instrument 6, and signal acquisition instrument 6 is connected to host computer 7.

[0085] The pulse generator 5 is connected to the relay 4 and can generate pulse signals of different periods as needed. When the relay 4 receives the pulse signal, it will open or close according to the period of the pulse signal. Based on the above design, the simulation of dynamic inter-turn short circuit faults of generator stator windings of different degrees and with accurate and controllable frequency can be realized.

[0086] This invention can effectively detect dynamic inter-turn short-circuit faults in stator windings, and a device is designed to verify the accuracy of the detection method. Using this detection method, the fault can be diagnosed and eliminated in a timely manner, reducing economic losses caused by downtime and other problems.

[0087] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0088] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting dynamic inter-turn short-circuit faults in generator stator windings, characterized in that, include: Real-time measurement of generator rotor vibration signals; The vibration signal is transformed from a time-domain signal to a frequency-domain signal using the Fast Fourier Transform. By comparing the transformed frequency domain signal with the spectrum components of the vibration signal under normal conditions, and considering that the frequencies corresponding to each harmonic in the spectrum graph are from the first to the sixth harmonic, it is determined that the generator has a dynamic inter-turn short circuit fault in the stator winding.

2. The method for detecting dynamic inter-turn short-circuit faults in generator stator windings according to claim 1, characterized in that, The real-time measurement of the generator rotor vibration signal specifically refers to: An acceleration sensor is installed on the bearing housing of the generator rotor to measure the rotor vibration signal.

3. The method for detecting dynamic inter-turn short-circuit faults in generator stator windings according to claim 1, characterized in that, Determining whether a generator has experienced a dynamic inter-turn short-circuit fault in its stator windings specifically includes: When the amplitude of the time-domain waveform of the generator rotor vibration signal and the amplitude of each harmonic component in the spectrum increase, and the frequencies corresponding to each harmonic in the spectrum are from the first to the sixth harmonic, then the generator has a dynamic inter-turn short fault in the stator winding. The larger the amplitude of each corresponding frequency domain, the greater the degree of the dynamic inter-turn short fault in the stator winding.

4. A device for detecting dynamic inter-turn short-circuit faults in generator stator windings, characterized in that, The method for detecting dynamic inter-turn short circuit faults in generator stator windings according to any one of claims 1-3 includes: a generator, a drive motor, a signal acquisition instrument, a host computer, an acceleration sensor, a short circuit terminal block, a relay, and a pulse generator; The pulse generator, relay, short-circuit terminal block, generator, and drive motor are connected in sequence. An acceleration sensor is installed on the bearing housing of the generator rotor to measure the vibration signal of the generator rotor. The acceleration sensor is connected to a signal acquisition instrument, which is then connected to a host computer.

5. The generator stator winding dynamic inter-turn short-circuit fault detection device according to claim 4, characterized in that, The pulse generator is connected to the relay and generates pulse signals of different periods as needed. When the relay receives the pulse signal, it opens or closes according to the period of the pulse signal.

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