Power transformer turn-to-turn short circuit fault monitoring method based on high-frequency magnetic flux leakage characteristics

Abstract

The invention discloses a power transformer turn-to-turn short circuit fault monitoring method based on high-frequency magnetic flux leakage characteristics. The method comprises the following steps: acquiring a high-frequency magnetic flux leakage change signal generated when a power transformer has turn-to-turn short circuit; performing fast Fourier transform on the high-frequency magnetic flux leakage change signal, and performing energy normalization on a component result to obtain a normalized frequency spectrum component; the window of the fast Fourier transform is translated backwards by 1 / 8 period, and the next fast Fourier transform is carried out after the data of the next period is obtained again; and finally, comparing the size change of the frequency component at each moment to realize turn-to-turn short circuit fault monitoring of the power transformer. And sensitive monitoring and relatively accurate positioning of the turn-to-turn short circuit fault of the transformer are realized by using the rule of leakage magnetic flux change when the turn-to-turn short circuit fault of the transformer occurs.

Description

Technical Field

[0001] The invention belongs to the technical field of power transformer detection, and in particular relates to a method for monitoring inter-turn short-circuit faults of power transformers based on high-frequency magnetic leakage characteristics. Background Art

[0002] Power transformers are important equipment in power systems. The most important equipment for power systems to achieve voltage rise and fall is power transformers. Therefore, power transformers are the core equipment for voltage conversion and power transmission in power systems. Therefore, transformer failure will seriously affect the reliability of power supply and the normal operation of the system. According to previous data statistics, about 70% to 80% of transformer failures are inter-turn failures of windings. One of the more important problems is inter-turn short circuit of windings. Inter-turn short circuit is the direct contact of two or more turns of coils that are close to each other due to the destruction of the insulation layer. When the transformer is pressurized and shaped during the production process, excessive force will cause damage to the coil insulation. Long-term operation is prone to insulation aging. The transformer will have an inter-turn short circuit failure when overcurrent or overvoltage occurs. The probability of damage to the transformer after a short circuit increases significantly, and transformer damage accidents caused by transformer short circuits account for 50% of the total accident ratio. In addition, after an internal fault occurs in a power transformer, there is a high probability that an explosion and fire accident will occur, causing serious accidents and property losses. Therefore, it is of great significance to develop an effective method for monitoring and locating inter-turn short circuit faults in power transformers.

[0003] At present, current differential protection and gas protection are mainly used as the main protection of transformers in engineering, but these protection methods have various shortcomings when facing inter-turn short circuit. Differential protection is the main protection of transformers, and the main faults it responds to are inter-phase short circuit of transformer internal windings, single-phase serious inter-turn short circuit and other conditions. When a slight inter-turn short circuit occurs in the transformer, the current in the short-circuited turn is large and destructive, but the characteristic quantity reflected on the differential current between phases has only a slight change, so it is difficult for differential protection to effectively protect the inter-turn short circuit fault of power transformers. In addition, although gas protection is for internal faults of transformers. However, the judgment basis of heavy gas protection is the oil speed in the oil pillow connecting pipe, and the inter-turn fault requires a large electric power to drive the oil flow rate to the set value, and it takes a certain amount of time for the oil flow to accelerate to the set value, and its action time will be affected by factors such as the location of the fault point, gas production and production rate, and the viscosity of the insulating oil. Therefore, although heavy gas protection can protect the inter-turn short circuit fault of power transformers, its sensitivity and rapidity are insufficient. Therefore, it is of great significance to develop a method that can quickly protect against turn-to-turn short-circuit faults. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for monitoring inter-turn short-circuit faults of power transformers based on high-frequency magnetic leakage characteristics in response to the deficiencies in the above-mentioned prior art, so as to realize sensitive monitoring and positioning of inter-turn short-circuit faults of transformers, and to solve the technical problem that the inter-turn short-circuit faults of transformers cannot be monitored quickly and sensitively during transformer fault monitoring.

[0005] The present invention adopts the following technical solutions: A method for monitoring inter-turn short-circuit faults of power transformers based on high-frequency magnetic leakage characteristics. Obtain the high-frequency leakage flux change signal generated when a turn-to-turn short circuit occurs in the power transformer; Perform fast Fourier transform on the high-frequency magnetic flux leakage change signal, perform energy normalization on the component results, and obtain normalized spectrum components; The fast Fourier transform window is shifted backward by 1 / 8 cycle, and the next fast Fourier transform is performed after the next cycle data is obtained again; finally, the size changes of the frequency components at each moment are compared with the pre-set threshold frequency components of the power transformer turn-to-turn short-circuit fault, so as to realize the monitoring of the power transformer turn-to-turn short-circuit fault.

[0006] Preferably, a high-frequency magnetic field sensor is placed on the inner wall of the power transformer to measure radial leakage magnetic intensity.

[0007] Preferably, the high-frequency magnetic field sensors include two, corresponding to the uppermost end and the lowermost end of the internal winding of the power transformer.

[0008] Preferably, the height of the high frequency magnetic field sensor is 0%±5% and 100%±5%.

[0009] Preferably, the sampling rate of the high frequency magnetic field sensor is AHz, and the default A is 51.2kHz.

[0010] Preferably, the high-frequency magnetic field sensor and the box wall of the power transformer are arranged at the same potential.

[0011] Preferably, the component results of 0-450 Hz are taken for energy normalization.

[0012] Preferably, the normalized spectral components Specifically:

[0013] in, is the spectrum energy of each sub-frequency from 0 to 450 Hz, It is the total energy in the range of 0~450Hz.

[0014] Preferably, for:

[0016] Preferably, the power transformer turn-to-turn short-circuit fault threshold is specifically: 0Hz, 50Hz, 100Hz, and 150Hz components are necessary conditions; 250Hz and 350Hz components are sufficient conditions.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: A method for monitoring inter-turn short-circuit faults of power transformers based on high-frequency magnetic leakage characteristics. When an inter-turn short-circuit fault occurs in a power transformer, an arc current will be generated inside the transformer, introducing a nonlinear component. Therefore, there is a significant change in the distribution of the high-frequency component of the magnetic leakage, which provides the possibility for sensitive monitoring of inter-turn short-circuit faults.

[0018] Furthermore, the high-frequency magnetic field sensor is placed on the inner wall of the power transformer. The change characteristics of the radial magnetic field inside the power transformer are most obvious. By collecting the radial leakage magnetic intensity, the accuracy of fault diagnosis can be improved.

[0019] Furthermore, the high-frequency magnetic field sensors are arranged corresponding to the top and bottom ends of the internal windings of the power transformer. The high-frequency variation of the internal magnetic field of the power transformer is most obvious, which is suitable for monitoring at the lowest cost.

[0020] Furthermore, the magnetic leakage sensors with relative winding heights of 0% and 100% are high-frequency magnetic leakage sensors. When a turn-to-turn short circuit fault occurs in the transformer, the high-frequency magnetic leakage sensor can quickly detect the fault signal transmitted by the magnetic field and respond to the fault.

[0021] Furthermore, the equipotential arrangement of the magnetic field sensor and the box wall of the power transformer can reduce the influence of the electric field inside the transformer on the leakage magnetic sensor, ensuring the safe operation of the sensor inside the power transformer.

[0022] Furthermore, the power transformer turn-to-turn short-circuit fault threshold is set to adjust the high-frequency leakage magnetic characteristics of the power transformer when an arc fault occurs, which can determine the fault more accurately and concisely.

[0023] In summary, the present invention utilizes the law of leakage flux change when a turn-to-turn short-circuit fault occurs in the transformer to achieve sensitive monitoring and relatively accurate positioning of the turn-to-turn short-circuit fault of the transformer.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of a power transformer; Figure 2 It is a schematic diagram of the arrangement of the magnetic flux leakage sensor of the present invention; Figure 3 Schematic diagram of magnetic field intensity component test, where (a) is radial magnetic field comparison, and (b) is axial magnetic field comparison; Figure 4 It is a schematic diagram of the arrangement of the magnetic flux leakage sensor of the present invention.

[0026] Among them: 1. Iron core; 2. Low voltage winding; 3. Medium voltage winding; 4. High voltage winding. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "one side", "one end", "one side" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, in the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0029] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0031] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0032] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0033] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0034] There is a close connection between the electric field and the magnetic field, and they are an integral relationship. Therefore, when a short-circuit fault occurs in the power transformer, the spatial distribution of the leakage magnetic field around the power transformer winding is affected by the winding current and the fault location, and shows a certain regularity. When the proportion of short-circuit turns is small, the leakage magnetic field change is still significant and the sensitivity is very high.

[0035] The present invention provides a method for monitoring the inter-turn short-circuit fault of a power transformer based on high-frequency magnetic leakage characteristics. Based on a 500kV real transformer model, simulation is first performed, and a method for quickly diagnosing the inter-turn short-circuit fault of the power transformer by using the transformer magnetic leakage amplitude is proposed. Then, the diagnostic method is verified through experimental examples, thereby providing an effective way to protect the power transformer.

[0036] See also Figure 2 The present invention provides a method for monitoring a power transformer turn-to-turn short-circuit fault based on high-frequency magnetic leakage characteristics, comprising the following steps: S1, obtaining a high-frequency leakage flux change signal generated when a turn-to-turn short circuit occurs in a power transformer; See also Figure 1 The judgment basis of the monitoring method of the present invention is that when a short circuit occurs between turns of a power transformer, an arc will be generated in the oil between the windings. Because the leakage magnetic flux caused by the nonlinear arc contains specific high-order harmonic components, a magnetic field sensor is placed inside the power transformer to obtain the change of the leakage magnetic flux intensity.

[0037] According to experiments, placing the magnetic field sensor near the inner wall of the power transformer and then measuring the radial leakage magnetic intensity can achieve better results. The specific arrangement is as follows: Figure 1 As shown, two high-frequency sensors are respectively arranged at the wall of the power transformer box and are arranged at the same potential as the box wall.

[0038] At the same time, the arrangement height of the magnetic field sensor matches the top and bottom of the winding, and the distribution heights are 0%±5% and 100%±5% respectively.

[0039] The sampling rate of the high-frequency magnetic field sensor is set to AHz, where the default A is 51.2kHz. The high-frequency sensor 1 and the high-frequency sensor 2 are arranged to measure the leakage magnetic change signal generated when the power transformer has a turn-to-turn short circuit, especially the high-order harmonic components caused by the nonlinear arc.

[0040] S2, performing fast Fourier transform on the leakage magnetic flux change signal obtained in step S1, and taking the component results of 0-450 Hz for energy normalization; Determine the FFT time window to be 20ms, i.e. A / 50 data points, perform FFT operations on high-frequency sensor 1 and high-frequency sensor 2, and obtain the spectrum components between DC 0 and A / 2 Hz, with a spectrum interval of 50 Hz.

[0041] For the 20 spectral components from 0 to 450 Hz ~ Perform energy normalization to obtain normalized ~ .

[0042]

[0043]

[0044] in, is the total energy in the range of 0~450Hz, is the energy of each spectral component, is the energy of each spectral component after normalization.

[0045] S3. After step S2 is completed, the FFT window is shifted backward by 1 / 8 cycle, that is, A / 400 data points are shifted backward, and the next FFT is performed after the next cycle data is obtained again; finally, the size changes of the frequency components at each moment are compared to realize the inter-turn short-circuit fault monitoring of the power transformer.

[0046]

[0047] The present invention sets the power transformer turn-to-turn short-circuit fault threshold as: 0Hz, 50Hz, 100Hz, and 150Hz components are necessary conditions; The 250Hz and 350Hz components are sufficient conditions.

[0048] It is necessary to monitor the normalized components of the magnetic field at 0Hz, 50Hz, 100Hz, and 150Hz at each moment, and compare them according to the above turn-to-turn short-circuit fault threshold monitoring. If 0Hz is greater than 0.01; 50Hz is less than 0.8; 100Hz is greater than 0.03; and 150Hz is greater than 0.03, it is determined that a turn-to-turn short-circuit fault exists.

[0049] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0050] Example 1 Measuring intermittent arcing between turns See also Figure 3 When insulation damage occurs between adjacent winding turns of a 500kV power transformer, an intermittent arc is formed between the turns at the initial fault. The typical waveforms of the current and voltage are as follows: Figure 3 shown.

[0051] When an intermittent arc is formed at 25% height in the 500kV power transformer model, within a 20ms period of the fault, the high-frequency sensor 1 measures the change in high-frequency leakage magnetic flux caused by the intermittent arc, and after energy normalization, the following is obtained:

[0052] This proves that a turn-to-turn short circuit fault occurred in the power transformer at this time.

[0053] Example 2 Measuring turn-to-turn short-circuit faults with stable arc formation between turns See also Figure 4 When a 500kV power transformer has a continuous fault between winding turns, the heat generated by the arc will cause further damage to the local insulation, thus forming a stable arc. At this time, the typical waveforms of the current and voltage are as follows: Figure 4 shown.

[0054] When an intermittent arc is formed at 75% height in the 500kV power transformer model, within a 20ms period of the fault, the high-frequency sensor 2 measures the change in high-frequency leakage magnetic flux caused by the intermittent arc, and after energy normalization, the following is obtained:

[0055] This proves that a turn-to-turn short circuit fault occurred in the power transformer at this time.

[0056] In summary, the present invention provides a method for monitoring turn-to-turn short-circuit faults of power transformers based on high-frequency magnetic leakage characteristics, which realizes sensitive monitoring and relatively accurate positioning of turn-to-turn short-circuit faults of transformers.

[0057] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for monitoring inter-turn short-circuit faults of power transformers based on high-frequency magnetic leakage characteristics, characterized in that: The following steps are involved: Obtain high-frequency leakage flux change signal generated when a turn-to-turn short circuit occurs in a power transformer; Perform fast Fourier transform on the high-frequency magnetic flux leakage change signal, perform energy normalization on the component results, and obtain normalized spectrum components; The fast Fourier transform window is shifted backward by 1 / 8 cycle, and the next fast Fourier transform is performed after the next cycle data is obtained again; finally, the size changes of the frequency components at each moment are compared with the pre-set threshold frequency components of the power transformer turn-to-turn short-circuit fault, so as to realize the monitoring of the power transformer turn-to-turn short-circuit fault.

2. The method for monitoring turn-to-turn short-circuit fault of a power transformer based on high-frequency magnetic leakage characteristics according to claim 1 is characterized in that: Place the high-frequency magnetic field sensor on the inner wall of the power transformer to measure the radial leakage magnetic intensity.

3. The method for monitoring turn-to-turn short-circuit fault of a power transformer based on high-frequency magnetic leakage characteristics according to claim 2 is characterized in that: The high frequency magnetic field sensors include two, corresponding to the uppermost end and the lowermost end of the inner winding of the power transformer.

4. The method for monitoring turn-to-turn short-circuit fault of a power transformer based on high-frequency magnetic leakage characteristics according to claim 3 is characterized in that: The heights of the high frequency magnetic field sensor are 0%±5% and 100%±5%.

5. The method for monitoring inter-turn short-circuit fault of power transformer based on high-frequency magnetic leakage characteristics according to claim 2 is characterized in that: The sampling rate of the high-frequency magnetic field sensor is AHz, and the default A is 51.2kHz.

6. The method for monitoring inter-turn short-circuit fault of power transformer based on high-frequency magnetic leakage characteristics according to claim 2 is characterized in that: The high-frequency magnetic field sensor is arranged at the same potential as the box wall of the power transformer.

7. The method for monitoring turn-to-turn short-circuit fault of a power transformer based on high-frequency magnetic leakage characteristics according to claim 1 is characterized in that: The component results from 0 to 450 Hz are taken for energy normalization.

8. The method for monitoring turn-to-turn short-circuit fault of a power transformer based on high-frequency magnetic leakage characteristics according to claim 6 is characterized in that: Normalized spectral components Specifically: in, is the spectrum energy of each sub-frequency from 0 to 450 Hz, It is the total energy in the range of 0~450Hz.

9. The method for monitoring turn-to-turn short-circuit fault of a power transformer based on high-frequency magnetic leakage characteristics according to claim 8, characterized in that: Total energy in the range of 0~450Hz for: 。 10. The method for monitoring turn-to-turn short-circuit fault of a power transformer based on high-frequency magnetic leakage characteristics according to any one of claims 1 to 9, characterized in that: The specific fault threshold of the power transformer turn-to-turn short circuit is: 0Hz, 50Hz, 100Hz, and 150Hz components are necessary conditions; 250Hz and 350Hz components are sufficient conditions.

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