Turbogenerator rotor winding turn-to-turn short circuit fault online diagnosis method

Abstract

The invention discloses a turbonator rotor winding turn-to-turn short circuit fault online diagnosis method, and belongs to the technical field of generators. The device comprises a U-shaped iron core, an insulating shell, a coil, a lead and a data acquisition device. In order to solve the problem that the installation difficulty of a sensor in a casing is large, and based on the phenomenon that a main magnetic field generates an overflow effect due to the ferromagnetism of a generator stator casing, the open iron core tightly attached to the stator casing is used for forcibly draining leakage magnetic flux; data acquisition and frequency domain analysis are carried out on the induced voltage of the coil wound on the U-shaped iron core, k / p (k = 1, 2, 3..., k is not equal to np, and n = 1, 3, 5...) fractional and even harmonic waves are extracted as fault characteristic harmonic waves, and the characteristic harmonic wave content is compared with a normal threshold value to detect the turn-to-turn short circuit fault of the rotor winding. Operation is easy and convenient, and safe operation of the unit is not affected; the anti-interference effect is better, the safety is high, the operation is convenient, and the diagnosis is accurate.

Description

Technical Field

[0001] The invention relates to the technical field of generators, and in particular to an online diagnosis method for inter-turn short-circuit faults of rotor windings of steam turbine generators. Background Art

[0002] With the increasing peak load regulation depth of steam turbine generators, the short-term load change rate of the unit shows a rising trend. The rapid and substantial changes in load and the difference in material properties cause the rotor winding to frequently expand and contract relative to the core, which can easily lead to inter-turn insulation damage and end corner overlap, resulting in a rotor winding inter-turn short-circuit fault. When the inter-turn short-circuit fault of the rotor winding of a steam turbine generator develops to a certain extent, it has a great impact, such as causing the vibration of the unit to intensify, the magnetization of the main shaft, the increase of the excitation current and the relative decrease of the reactive power. Further development may also cause a winding grounding fault, which seriously affects the continuity of the unit operation and limits the basic regulation role of thermal power units in the new power system. Therefore, it is very necessary to carry out real-time monitoring and reliable early warning of the inter-turn short-circuit fault of the rotor winding of the steam turbine generator, which is the basis for implementing targeted technical treatment measures.

[0003] At present, there are many online detection technologies for rotor winding inter-turn short-circuit faults, including excitation current method, stator winding parallel branch circulating current method, virtual power method, expected potential method, differential coil detection method, stator slot coil detection method, shaft voltage method, end leakage flux method and U-shaped detection coil method, etc. These detection methods have their own characteristics, but most of them are difficult to fully take into account technical indicators such as non-intrusiveness, high sensitivity, low cost and low risk.

[0004] In order to improve the convenience of sensor installation, the effectiveness of fault feature extraction and the sensitivity of diagnosis, technical experts continue to conduct in-depth research. Some studies focus on using the generator's inherent components - the through-screw, to diagnose turn-to-turn short-circuit faults by monitoring and analyzing the induced voltage at both ends, avoiding the installation of additional sensors and thus reducing safety risks, but usually requires the support of equipment manufacturers.

[0005] At the same time, the leakage magnetic field in the outer space of the generator can also reflect the short-circuit fault between the turns of the rotor winding. With the help of devices such as weak magnetic sensors, the stray magnetic field on the back of the motor casing can be measured, and the time / frequency domain characteristics of the stray magnetic field can be further analyzed to diagnose and evaluate the short-circuit fault between the turns of the rotor winding. However, the stray magnetic field is usually weak and is easily interfered by the surrounding magnetic field sources during the measurement process, which affects the accuracy of the diagnosis. In order to solve this problem, artificially enhancing the weak magnetic field and improving the anti-interference ability of the detection have become technical approaches that can be tried. Summary of the invention

[0006] The purpose of the present invention is to provide an online diagnosis method for short-circuit faults between turns of a steam turbine generator rotor winding, which can quickly diagnose short-circuit faults between turns of a steam turbine generator rotor winding based on the flux diversion effect, greatly improve the diagnostic sensitivity and reliability, and ensure the stable operation of the power generation equipment.

[0007] To achieve the above object, the present invention provides an online diagnosis method for short-circuit faults between turns of a turbine generator rotor winding, wherein the device comprises a U-shaped iron core, the U-shaped iron core is arranged on one side of the outer surface of a stator housing, a coil is wound around the U-shaped iron core, and the coil is connected to a data acquisition device through a lead wire;

[0008] The method comprises the following steps:

[0009] S1. Fit the magnetic field measurement sensor tightly to the stator housing of the steam turbine generator, and use a data acquisition device to record the induced voltage signal output by the coil in real time;

[0010] S2. performing harmonic analysis on the induced voltage signal to obtain voltage spectrum distribution;

[0011] S3, extracting the fault characteristic harmonics in the induced voltage of the magnetic field measurement coil, and judging whether there is a rotor winding inter-turn short circuit fault according to the amplitude change of the harmonics;

[0012] S4. Calculate the percentage of fault characteristic harmonic content to evaluate the degree of rotor winding inter-turn short-circuit fault.

[0013] Preferably, the U-shaped iron core is made of a high magnetic permeability material; during the operation of the unit, the cross section of the U-shaped iron core is ensured to be in close contact with the stator casing, which can effectively gather and enhance the leakage magnetic field of the casing.

[0014] Preferably, the number of turns of the coil is adjusted according to the specific conditions of the device to optimize the collection and analysis of the induced voltage signal.

[0015] Preferably, the magnetic field measurement unit is placed in the middle of the motor for better detection effect.

[0016] Preferably, in step S2, a voltage spectrum diagram is obtained by performing Fourier transform on the collected induced voltage signal.

[0017] Preferably, in step S3, the fault characteristic harmonic frequency is related to the number of pole pairs of the motor. For a steam turbine generator with p pairs of poles, after a fault, the leakage magnetic field on the back of the casing will have k / p times (k=1, 2, 3...u, k / p≠n, n=1, 3, 5...) characteristic harmonics that are the same as the air gap magnetic field. The characteristic harmonic content is calculated by the following formula:

[0018]

[0019] Among them, Fk / p is the amplitude of the k / pth harmonic, u is the upper limit of k, F i is the amplitude of the i-th harmonic (i=1, 3, 5...m, m is the upper limit of the harmonic order obtained after Fourier decomposition).

[0020] Preferably, in step S4, the fault diagnosis is based on even-order or fractional-order harmonic components contained in the frequency spectrum.

[0021] Preferably, the characteristic harmonic amplitude of the induced voltage of the measuring coil is positively correlated with the degree of the rotor winding inter-turn short-circuit fault, and the fault characteristic harmonic content increases with the deepening of the fault degree.

[0022] Therefore, the present invention adopts a method for online diagnosis of inter-turn short-circuit fault of a steam turbine generator rotor winding using the above structure, which has the following beneficial effects:

[0023] (1) The present invention proposes a detection method for draining the magnetic flux of the casing with the help of a U-shaped iron core, which can identify the inter-turn short-circuit fault of the rotor winding of a steam turbine generator through the change of the harmonic content of the induced voltage. The more serious the fault, the higher the harmonic content, thereby realizing simple and effective fault monitoring.

[0024] (2) The present invention realizes non-intrusive online diagnosis of turbine generator rotor inter-turn short-circuit faults, does not interfere with operation and has high sensitivity. It uses external structures to reflect rotor winding inter-turn short-circuit faults, which is safer and more accurate than traditional methods.

[0025] (3) The present invention utilizes the casing as a sensor carrier, which reduces external interference, highlights fault characteristics, simplifies the detection process, and improves the safety and efficiency of steam turbine generator status monitoring.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the excitation magnetic potential of a turbine generator rotor winding in an online diagnosis method for a turbine generator rotor winding inter-turn short-circuit fault of the present invention;

[0028] Figure 2 A simplified model structure diagram of a steam turbine of an online diagnosis method for a short-circuit fault between turns of a steam turbine generator rotor winding according to the present invention;

[0029] Figure 3 A schematic diagram of a U-shaped iron core placement method and an induced voltage measurement method of an online diagnosis method for a turbine generator rotor winding inter-turn short-circuit fault of the present invention;

[0030] Figure 4A schematic diagram of a normal condition of a generator - voltage and current in an online diagnosis method for a short-circuit fault between turns of a steam turbine generator rotor winding according to the present invention;

[0031] Figure 5 A schematic diagram of the induced voltage waveform of the U-shaped iron core coil of a steam turbine generator rotor winding inter-turn short-circuit fault online diagnosis method of the present invention under the condition of no-load of the generator;

[0032] Figure 6 A schematic diagram of the induced voltage waveform of a U-shaped iron core coil under the condition of a generator load in an online diagnosis method for a short-circuit fault between turns of a steam turbine generator rotor winding according to the present invention;

[0033] Figure 7 A schematic diagram of the frequency domain distribution of the induced voltage of the U-shaped core coil of a steam turbine generator rotor winding inter-turn short-circuit fault online diagnosis method of the present invention under the condition of no-load of the generator;

[0034] Figure 8 A schematic diagram of the frequency domain distribution of the induced voltage of the U-shaped core coil under the generator load condition of an online diagnosis method for inter-turn short-circuit fault of a steam turbine generator rotor winding according to the present invention;

[0035] Fig. 9 A schematic diagram of characteristic harmonic amplitude of induced voltage of a U-shaped core coil of a steam turbine generator rotor winding inter-turn short-circuit fault online diagnosis method of the present invention under no-load condition of the generator;

[0036] Fig.10 A schematic diagram of characteristic harmonic amplitude of induced voltage of a U-shaped core coil of a steam turbine generator rotor winding inter-turn short-circuit fault online diagnosis method of the present invention under a generator load condition;

[0037] Reference numerals

[0038] 1. Stator housing, 2. U-shaped iron core, 3. Insulation shell, 4. Coil, 5. Lead wire, 6. Data acquisition device. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0040] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0041] Example

[0042] The present invention provides an online diagnosis method for a turbine generator rotor winding inter-turn short circuit fault. Figure 3 As shown, the device includes a U-shaped iron core 2, which is arranged on one side of the outer surface of the stator housing 1, and the U-shaped iron core is located inside the insulating shell 3. A coil 4 is wound on the U-shaped iron core 2, and the coil 4 is connected to the data acquisition device 6 through a lead 5.

[0043] The specific steps are as follows:

[0044] S1. Customize the U-shaped iron core 2 to match the size of the stator housing 1, fix it in the plastic insulation shell 3, and wind an appropriate amount of coils 4 to form a magnetic field measurement unit. The number of coil turns is appropriately selected according to the characteristics of the unit to ensure the accuracy of the induced voltage signal and facilitate subsequent analysis.

[0045] S2. When the generator is running, the cross section of the U-shaped iron core 2 is closely fitted to the stator housing 1, and the output voltage of the coil of the U-shaped iron core 2 is collected in real time by the data acquisition device 6.

[0046] S3, perform harmonic analysis on the induced voltage to obtain voltage spectrum distribution. If the spectrum contains fault characteristic harmonics, it is determined that the generator has a rotor winding turn-to-turn short circuit fault, and the process goes to step S4; otherwise, the process goes to step S2.

[0047] S4. Calculate the fault characteristic harmonic content, compare it with the predetermined threshold, and evaluate the rotor winding inter-turn short circuit fault condition.

[0048] In step S3, the fault characteristic harmonic frequency is related to the number of pole pairs of the motor. For a steam turbine generator with p pairs of poles, after a fault, the leakage magnetic field on the back of the casing will have k / p (k=1, 2, 3...u, k / p≠n, n=1, 3, 5...) characteristic harmonics that are the same as the air gap magnetic field.

[0049] The characteristic harmonic content is calculated as follows:

[0050]

[0051] Among them, F k / p is the amplitude of the k / pth harmonic, u is the upper limit of k, F i is the amplitude of the i-th harmonic (i=1, 3, 5...m, m is the upper limit of the harmonic order obtained after Fourier decomposition).

[0052] Furthermore, the fault characteristic harmonic content threshold is set to 3%, and the fault degree is positively correlated with the harmonic content.

[0053] The excitation magnetic potential of the generator before and after the fault is as follows Figure 1 As shown. Under normal circumstances, the rotor winding has the same effective number of winding turns in the slots corresponding to the N and S poles, so the excitation magnetic potential is symmetrical, as shown in Figure 1 Medium F f As shown in the trapezoidal wave, it can be expressed as follows after Fourier decomposition:

[0054]

[0055] Among them, θ r is the rotor space mechanical angle; i is a positive integer; I f is the excitation current; a k is the number of turns of the kth slot winding; γ is the rotor circumference angle of the large tooth area; β is the rotor slot pitch angle; p is the number of pole pairs. It can be seen that under normal circumstances, the excitation magnetic potential only contains odd harmonics.

[0056] When a rotor slot winding is short-circuited, the effective ampere-turns decrease, and the excitation magnetic potential step amplitude of the slot decreases, resulting in an asymmetric rotor magnetic potential distribution. Figure 1 Medium F f As shown in the trapezoidal wave, the excitation magnetic potential becomes:

[0057]

[0058] Among them, Q is the number of turns of the short-circuited winding; m is the rotor slot number starting from the large tooth; j is a positive integer.

[0059] It can be seen from the above formula that for a 2-pole steam turbine generator, even harmonics (2, 4, 6, etc.) appear in the excitation magnetic potential after the inter-turn short circuit; for a 4-pole steam turbine generator, even and fractional harmonics (1 / 2, 3 / 2, 2, 5 / 2, 7 / 2, etc.) will be decomposed in the excitation magnetic potential after the inter-turn short circuit.

[0060] Ignore the core slots, assume that the air gap is uniform, and do not consider magnetic saturation, then the air gap permeability of the steam turbine generator can be regarded as a constant, so the main magnetic field calculation satisfies the superposition theorem, in which the magnetic field generated by the excitation winding is proportional to the excitation magnetic potential. When the rotor winding has a turn-to-turn short circuit, the excitation magnetic field can be expressed as:

[0061] B' gap (θ r )≈Λ·F f '(θ r );

[0062] Where Λ is the air gap permeability per unit area; B' gap is the air gap flux density under fault conditions.

[0063] Therefore, when a turn-to-turn short circuit fault occurs in the rotor winding, a fault harmonic component identical to the excitation magnetic potential will appear in the air gap magnetic flux density, that is: for a 2-pole steam turbine generator, the air gap magnetic flux density produces even harmonics; for a 4-pole steam turbine generator, k / 2 and even harmonics are produced.

[0064] The simplified model of the generator is as follows Figure 2 As shown, the air gap magnetic field is regarded as a source that is transmitted outward to the stator yoke, casing and other media.

[0065] In fact, there will be very small eddy current losses in ferromagnetic materials, so the process of air gap magnetic flux density being transmitted outward will not only cause attenuation in amplitude but also cause phase shift. Ignoring eddy current losses and only considering the attenuation of radial magnetic field amplitude, the attenuation coefficient Ks of the stator core can be expressed as:

[0066]

[0067] Among them, μ r is the magnetic permeability of the stator core; R sin is the inner diameter of the stator; R sout is the stator outer diameter, and all three are constants.

[0068] Therefore, the process of the air gap flux density amplitude attenuating through the stator core to the casing can be approximately considered to be linear.

[0069] Therefore, the relationship between the external leakage magnetic density of the generator and the air gap magnetic flux density is:

[0070] B stray (θ r )≈K s ·B gap (θ r );

[0071] Therefore, when a rotor inter-turn short circuit occurs, characteristic harmonics identical to the air gap flux density will appear in the external leakage magnetic density.

[0072] The casing of steam turbine generators is mostly made of high magnetic permeability materials such as steel plates. By placing the U-shaped core close to the outer wall of the casing, the leakage magnetic flux can be forced to flow to the U-shaped core. If a certain number of turns of wire coils are wound around the U-shaped core, the drainage magnetic field will induce an alternating electromotive force on the coil, generating fault voltage harmonics with the same frequency as the external leakage magnetic density.

[0073] This embodiment is experimentally verified on a three-phase four-pole salient-pole synchronous generator. To simulate the short-circuit fault between the turns of the rotor winding, the excitation winding of a certain magnetic pole of the rotor is selected for physical shearing operation. 10 turns and 20 turns are removed and then reconnected respectively. The simulated short-circuit fault degrees are 6.7% and 13.3% respectively. The number of winding turns of the remaining magnetic poles remains unchanged. The specific parameters of the generator are listed in Table 1.

[0074] Table 1 Basic parameters of three-phase synchronous generator

[0075]

[0076] First, test the rotor in a healthy state, simulate the generator no-load and full-load states, and obtain the stator voltage and stator current, such as Figure 4 When the rotor is in a healthy state, the generator voltage and current are mainly sinusoidal fundamental waves, which are consistent with the rated parameters.

[0077] The drainage magnetic field measurement coil is stably placed in the middle of the top of the generator, and normal and different degrees of short-circuit fault simulations are performed to obtain the coil induced voltage time domain waveforms under no-load and load conditions, such as Figure 5 , Figure 6 As shown in the figure. Under no-load conditions, the waveforms of the coil induced voltage basically overlap under different inter-turn short-circuit fault conditions, and do not show significant differences. The distribution of the coil induced voltage under load conditions is the same as that under no-load conditions. Therefore, based on the time domain characteristics of the induced voltage, it is impossible to effectively distinguish whether an inter-turn short-circuit fault has occurred in the rotor winding.

[0078] Perform Fourier decomposition on the induced voltage in time domain and observe its frequency domain distribution. Figure 7 , Figure 8 Under no-load and load conditions, when a turn-to-turn short circuit occurs, obvious k / p fractional harmonics such as 25Hz, 75Hz, and 125Hz and even harmonics such as 100Hz and 200Hz can be observed in the frequency domain of the induced voltage of the U-core coil, indicating that the rotor turn-to-turn short circuit fault of the steam turbine generator can be judged by this spectrum feature.

[0079] Further extraction of even and fractional harmonics under different fault levels, such as Fig. 9 , Fig.10As shown in the figure, under different working conditions, as the degree of the rotor winding interturn short-circuit fault deepens, the amplitudes of the fractional and even harmonic components gradually increase, and the characteristic harmonic amplitudes are large in the 0-200Hz frequency band. Therefore, this rule can be used to further evaluate the degree of the short-circuit fault.

[0080] It can be seen from Table 2 that under no-load and load conditions, when the motor rotor winding is normal, the characteristic harmonic content of the coil induced voltage is kept below the threshold of 3%. When there is a turn-to-turn short circuit fault, the characteristic harmonic content increases and exceeds the threshold, and the fault degree is positively linearly correlated with the characteristic harmonic content.

[0081] Table 2 Harmonic content of coil induced voltage under different working conditions

[0082]

[0083] The results of the embodiment are consistent with the theoretical analysis, confirming that there is a significant correlation between the magnitude of the fractional harmonics and the degree of inter-turn short circuit of the rotor winding under no-load and load conditions. Therefore, the detection device and method proposed in the present invention can efficiently identify the rotor inter-turn short circuit fault and accurately evaluate the severity of the fault, thereby providing accurate diagnostic information.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. An online diagnosis method for inter-turn short-circuit fault of a turbine generator rotor winding, characterized in that: The device comprises a U-shaped iron core, which is arranged on one side of the outer surface of the stator housing, and a coil is wound around the U-shaped iron core, and the coil is connected to the data acquisition device through a lead wire; The method comprises the following steps: S1. Fit the magnetic field measurement sensor tightly to the stator housing of the steam turbine generator, and use a data acquisition device to record the induced voltage signal output by the coil in real time; S2. performing harmonic analysis on the induced voltage signal to obtain voltage spectrum distribution; S3, extracting the fault characteristic harmonics in the induced voltage of the magnetic field measurement coil, and judging whether there is a rotor winding inter-turn short circuit fault according to the amplitude change of the harmonics; S4. Calculate the percentage of fault characteristic harmonic content to evaluate the degree of rotor winding inter-turn short-circuit fault.

2. The method for online diagnosis of inter-turn short-circuit fault of a turbine generator rotor winding according to claim 1, characterized in that: The U-shaped iron core is made of a high magnetic permeability material and fits tightly with the stator casing when the unit is running, so as to guide and enhance the leakage magnetic field of the casing.

3. The method for online diagnosis of inter-turn short-circuit fault of a turbine generator rotor winding according to claim 1, characterized in that: The number of turns of the coil is adjusted according to the specific conditions of the device to optimize the collection and analysis of the induced voltage signal.

4. The method for online diagnosis of inter-turn short-circuit fault of a turbine generator rotor winding according to claim 1, characterized in that: In step S2, a voltage spectrum diagram is obtained by performing Fourier transform on the collected induced voltage signal.

5. The method for online diagnosis of inter-turn short-circuit fault of a turbine generator rotor winding according to claim 1, characterized in that: In step S3, the fault characteristic harmonic frequency is related to the number of pole pairs of the steam turbine generator. For a steam turbine generator with p pairs of poles, after a fault, k / p-order characteristic harmonics identical to the air gap magnetic field will appear in the leakage magnetic field on the back of the casing, where k=1,2,3..., n=1,3,5..., k / p≠n.

6. The method for online diagnosis of inter-turn short-circuit fault of a turbine generator rotor winding according to claim 1, characterized in that: In step S4, the fault diagnosis is based on the even-order and fractional-order harmonic components contained in the frequency spectrum.

7. The method for online diagnosis of inter-turn short-circuit fault of a turbine generator rotor winding according to claim 1, characterized in that: The characteristic harmonic amplitude of the measuring coil induced voltage is positively correlated with the degree of the rotor winding inter-turn short-circuit fault, and the fault characteristic harmonic content increases with the deepening of the fault severity.

Images