Grid-connected photovoltaic transformer winding high-resistance grounding fault location detection method and device

Abstract

The present disclosure provides a method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding, comprising: measuring the voltage to ground of the starting end and the neutral point of the three-phase winding; calculating the voltage phasor corresponding to the voltage to ground at the inverter switching frequency based on a fast Fourier analysis algorithm; calculating the negative-sequence component and the zero-sequence component of the voltage at the starting end of the three-phase winding at the inverter switching frequency according to the voltage phasor; obtaining the negative-sequence voltage ratio and the zero-sequence voltage ratio at the inverter switching frequency according to the voltage phasor corresponding to the negative-sequence component, the zero-sequence component and the voltage phasor corresponding to the neutral point voltage to ground; judging the phase difference, the distribution position along the winding and the degree of fault development of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio. The present disclosure also provides a device for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding.

Description

Technical Field

[0001] The present disclosure relates to the technical field of transformer fault detection methods, and in particular to a method and device for locating and detecting high-resistance grounding faults of grid-connected photovoltaic transformer windings. Background Art

[0002] By the end of 2021, my country's installed photovoltaic power generation capacity reached 306 million kilowatts, accounting for 12.9% of the total installed power generation capacity. Distributed grid-connected photovoltaic modules are small in scale, large in number, and can be independently controlled, which is conducive to topological transformation and operation mode adjustment. Photovoltaic power generation will become one of the main forms of energy in the future.

[0003] The operating environment of photovoltaic power stations is complex and changeable, and the power transformers in grid-connected photovoltaic systems have the disadvantages of high failure rate and low life cycle. The power of mainstream grid-connected photovoltaic inverters can reach hundreds of kW, and wide bandgap semiconductor power devices such as SiC-MOSFET are gradually being used in grid-connected photovoltaic inverters. The switching frequency of SiC-MOSFET power devices is between tens and hundreds of kHz, and the rising / falling time of each switching action is between tens and hundreds of ns, resulting in a very large change rate of transient voltage (dv / dt). The transient electrical stress and harmonic loss generated by high-frequency and fast switching actions will aggravate the electrical and thermal aging problems of the power transformer connected to the back end, thereby degrading the performance and life of its winding-to-ground insulation components, from a slight ground leakage problem to a high-resistance grounding fault, and finally leading to a serious metallic short circuit fault. In addition, considering that the transient electrical stress mainly acts at the beginning of the transformer winding, the ground insulation components at the beginning of the winding are more seriously aged than the insulation components at other positions. Furthermore, due to the frequent load switching and constantly changing load current of the grid-connected photovoltaic system, the temperature distribution inside the transformer box is uneven, which in turn causes uneven heating of all ground-insulating components distributed along the windings, resulting in local defects with uncertain locations.

[0004] Therefore, combined with the influence of electrical aging and thermal aging, the insulation of the power transformer winding to the ground in the grid-connected photovoltaic system faces the inevitable problem of local degradation. In the long-term operation process, this local insulation defect will gradually develop into a slight low-current grounding fault (equivalent to high-resistance grounding), and finally cause a penetrating high-current grounding fault. Based on this, it is urgent to realize online and sensitive detection and positioning of the high-resistance grounding fault of the power transformer connected to the inverter in the grid-connected photovoltaic system. Summary of the invention

[0005] In view of the above problems, the present disclosure provides a method and device for locating and detecting high-resistance grounding faults in the windings of a grid-connected photovoltaic transformer, aiming to detect and locate high-resistance grounding faults in the kilohm level for each phase winding.

[0006] The first aspect of the present disclosure provides a method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding, comprising: measuring the voltage to ground at the beginning and neutral point of a three-phase winding; calculating the voltage phasor corresponding to the voltage to ground at an inverter switching frequency based on a fast Fourier analysis algorithm; calculating the negative-sequence component and the zero-sequence component of the voltage at the beginning of the three-phase winding at the inverter switching frequency according to the voltage phasor; obtaining the negative-sequence voltage ratio and the zero-sequence voltage ratio at the inverter switching frequency according to the voltage phasor corresponding to the negative-sequence component, the zero-sequence component and the voltage phasor corresponding to the neutral point voltage to ground; judging the phase difference, the distribution position along the winding and the degree of fault development of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio.

[0007] Furthermore, the phase difference, distribution position along the winding and fault development degree of the high-resistance grounding fault of the transformer winding are judged according to the negative-sequence voltage ratio and the zero-sequence voltage ratio, including: judging the phase difference of the high-resistance grounding fault of the transformer winding according to the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio; judging the distribution position along the winding and the fault development degree of the high-resistance grounding fault of the transformer winding according to the negative-sequence voltage ratio and the zero-sequence voltage ratio.

[0008] Furthermore, the phases of the transformer winding high-resistance grounding fault include: the transformer winding high-resistance grounding fault occurs in the A-phase winding, the transformer winding high-resistance grounding fault occurs in the B-phase winding, and the transformer winding high-resistance grounding fault occurs in the C-phase winding.

[0009] Furthermore, according to the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio, the phase difference of the transformer winding high-resistance grounding fault is judged, including: if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within a first phase difference range, the transformer winding high-resistance grounding fault occurs in the A-phase winding; if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within a second phase difference range, the transformer winding high-resistance grounding fault occurs in the B-phase winding; if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within a third phase difference range, the transformer winding high-resistance grounding fault occurs in the C-phase winding.

[0010] Furthermore, based on the negative-sequence voltage ratio and the zero-sequence voltage ratio, the distribution position of the transformer winding high-resistance grounding fault along the winding is determined, including: if the absolute value of the ratio of the difference between the zero-sequence voltage ratio and 1 to the negative-sequence voltage ratio is within a first threshold range, the transformer winding high-resistance grounding fault is close to the starting end of the three-phase winding; if the absolute value of the ratio of the difference between the zero-sequence voltage ratio and 1 to the negative-sequence voltage ratio is within a second threshold range, the transformer winding high-resistance grounding fault is close to the neutral point.

[0011] Furthermore, the fault development degree of the transformer winding high-resistance grounding fault is judged according to the negative-sequence voltage ratio and the zero-sequence voltage ratio, including: if the transformer winding high-resistance grounding fault is close to the starting end of the three-phase winding, the fault development degree of the transformer winding high-resistance grounding fault is judged according to the amplitude of the negative-sequence voltage ratio; if the transformer winding high-resistance grounding fault is close to the neutral point, the fault development degree of the transformer winding high-resistance grounding fault is judged according to the absolute value of the difference between the zero-sequence voltage ratio and 1.

[0012] The second aspect of the present disclosure provides a high-resistance grounding fault positioning and detection device for a grid-connected photovoltaic transformer winding, comprising: a ground voltage measurement module, used to measure the ground voltage at the starting end and the neutral point of the three-phase winding; a voltage phasor calculation module, used to calculate the voltage phasor corresponding to the ground voltage at the inverter switching frequency based on a fast Fourier analysis algorithm; a negative-sequence and zero-sequence component calculation module, used to calculate the negative-sequence component and the zero-sequence component of the voltage at the starting end of the three-phase winding at the inverter switching frequency according to the voltage phasor; a negative-sequence and zero-sequence voltage ratio calculation module, which obtains the negative-sequence voltage ratio and the zero-sequence voltage ratio at the inverter switching frequency according to the voltage phasor corresponding to the negative-sequence component, the zero-sequence component and the neutral point voltage to the ground; a comprehensive fault detection module, used to determine the phase difference, distribution position along the winding and fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio.

[0013] Furthermore, the comprehensive fault detection module is used to determine the phase difference, distribution position along the winding and fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio, including: determining the phase difference of the transformer winding high-resistance grounding fault according to the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio; determining the distribution position along the winding and the fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio.

[0014] Furthermore, the phases of the transformer winding high-resistance grounding fault include: the transformer winding high-resistance grounding fault occurs in the A-phase winding, the transformer winding high-resistance grounding fault occurs in the B-phase winding, and the transformer winding high-resistance grounding fault occurs in the C-phase winding.

[0015] Furthermore, if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the first phase difference range, the transformer winding high-resistance grounding fault occurs in the A-phase winding; if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the second phase difference range, the transformer winding high-resistance grounding fault occurs in the B-phase winding; if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the third phase difference range, the transformer winding high-resistance grounding fault occurs in the C-phase winding.

[0016] The embodiments of the present disclosure provide a method and device for locating and detecting a high-resistance grounding fault in a grid-connected photovoltaic transformer winding. The method clearly distinguishes between the positive and negative components, negative-sequence components and zero-sequence components of electrical quantities at the switching frequency of the inverter, and uses the relationship between the negative-sequence component and the zero-sequence component of the voltage at the switching frequency of the photovoltaic grid-connected inverter to construct a negative-sequence voltage ratio and a zero-sequence voltage ratio. The amplitude and phase relationship between the negative-sequence voltage ratio and the zero-sequence voltage ratio is then used to implement comprehensive detection of a high-resistance grounding fault in a grid-connected transformer winding. The comprehensive detection specifically includes determining the phase, distribution position and development degree of the high-resistance grounding fault in the transformer winding, and the sensitivity can reach the kilo-ohm level. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] For a more complete understanding of the present disclosure and its advantages, reference will now be made to the following description taken in conjunction with the accompanying drawings, in which:

[0018] Figure 1A The schematic diagram of the structure of a typical three-phase grid-connected photovoltaic system is shown;

[0019] Figure 1B The schematic diagram of the three-phase winding of the transformer on the primary side is shown schematically;

[0020] Figure 2 A flowchart of a method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to an embodiment of the present disclosure is schematically shown;

[0021] Figures 3A to 3C A schematic diagram of voltage phasor calculation results according to an embodiment of the present disclosure is schematically shown;

[0022] Figures 4A to 4C The figure schematically shows a voltage ratio calculation result according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0024] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0025] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0026] Traditional methods for detecting insulation faults in power transformers mostly detect additional products of insulation degradation and judge the degree of aging based on signal concentration or intensity. These test items utilize physical signals (temperature, vibration), chemical signals (dissolved gas in oil), partial discharge signals (sound, light, electromagnetic waves) and electrical signals (current, insulation electrical parameters). Among them, the most widely used technical solutions are mainly the following three:

[0027] 1. Dissolved gas method in oil: The detection of dissolved gas in insulating oil has gradually been realized online, becoming the most widely used online means for diagnosing latent insulation defects of transformers. The characteristic gas method, Rogers method and IEC 60599 three-ratio method are the three most basic gas analysis and fault judgment methods. This type of method judges possible faults of the transformer based on the attention value of the content of each gas component or the attention value of the gas growth rate. However, there are many types of gases in the transformer box and the fault types are complex. The current judgment method has a single coding combination and threshold setting rule, and it is difficult to fully consider the complexity of the operating environment of the grid-connected photovoltaic system, including high-frequency switching noise interference and other problems; in addition, for dry-type transformers, this method is invalid.

[0028] 2. Partial discharge method: According to GB / T7354-2018, partial discharge online test items include current pulse detection, ultrasonic method and ultra / ultra-high frequency electromagnetic wave method. The partial discharge positioning technology based on multi-position sensing analyzes the spatial transmission characteristics and attenuation laws of different types of partial discharge signals to identify the detection area on the tank wall that can sensitively reflect the partial discharge position. However, the partial discharge signal verification standards, detection means and calibration methods are not strict and unified, and it is difficult to unify the discharge type. In addition, partial discharge sensors are highly accurate and expensive; they can generally only identify the local range of insulation defects in the box, and cannot determine the exact location of the insulation defect of the winding to the ground.

[0029] 3. Fault analysis method: The fault analysis method of power transformers has been widely discussed, and existing research has proposed several methods based on different principles. The electrical quantities at the transformer port are used to diagnose the type and degree of faults, and are classified according to the characteristics of the electrical quantities, including the use of power frequency amplitude, power frequency phasor and time domain transient waveform. However, a class of methods based on time domain transient waveforms can usually only perform fault diagnosis based on the shape or characteristic quantity of the waveform when the internal fault reaches an observable level, and requires reliance on complex data processing methods. A class of methods based on the power frequency components of voltage and current is difficult to distinguish between the effects of changes in system operating conditions and insulation aging in transformer units, that is, the power frequency electrical quantities are not sensitive enough to reflect insulation aging defects. Some scholars have proposed a protection method based on power frequency negative sequence impedance and power direction, which can realize the detection of transformer hundred-ohm high-resistance grounding faults. However, this method cannot detect more minor early insulation defects to the ground, and often does not have sufficient positioning capabilities.

[0030] Therefore, with regard to the insulation defect problem of transformer windings to the ground in grid-connected photovoltaic systems, it is difficult for existing technologies to sensitively detect and locate high-resistance grounding faults at the kilo-ohm level.

[0031] In view of the problems existing in the prior art, the present invention provides a method for locating and detecting high-resistance grounding faults in the windings of a grid-connected photovoltaic transformer. The method uses a voltage transformer that has been configured in a grid-connected photovoltaic system to measure the voltage at the starting end of the three-phase winding of the transformer and the voltage to the ground of the neutral point of the winding, calculates the negative-sequence component and the zero-sequence component of the voltage at the starting end of the transformer winding at the switching frequency, and the harmonic component of the voltage at the neutral point of the winding to the ground at the switching frequency, constructs a transfer function and corresponding criteria, and realizes the detection and positioning of kilo-ohm-level high-resistance grounding faults in each phase winding.

[0032] The technical solution of the present disclosure will be described in detail below in conjunction with the specific process of the method for locating and detecting the high-resistance grounding fault of the grid-connected photovoltaic transformer winding in the specific embodiment of the present disclosure. It should be understood that the process and calculation structure of the method for locating and detecting the high-resistance grounding fault of the grid-connected photovoltaic transformer winding shown in the accompanying drawings are only exemplary to help those skilled in the art understand the technical solution of the present disclosure, and are not intended to limit the protection scope of the present disclosure.

[0033] Figure 1A The schematic diagram shows the structure of a typical three-phase grid-connected photovoltaic system. Figure 1A As shown in the figure, a typical three-phase grid-connected photovoltaic system includes: photovoltaic power generation unit, photovoltaic grid-connected inverter, filter inductor, transformer and load. The inverter switching frequency is recorded as fs. The transformer winding connection mode is YN / yn, the neutral point of the inverter side winding is suspended, and the neutral point of the grid side winding is grounded through a small resistor Rsn. Voltage transformers are installed at the beginning and neutral point of each winding of the transformer to measure the voltage to ground at the corresponding position.

[0034] like Figure 1B As shown, the voltages at the beginning of the three-phase windings to the ground are denoted as u pa 、u pb and u pc ; The neutral point voltage to ground is denoted as u pn . Take the A-phase winding as an example, there are N coils. Usually, the location and degree of the insulation defect of the winding to the ground are unknown. Assume that a high-resistance grounding fault occurs at coil x, and the grounding resistance is recorded as Rf. x / N represents the location of the fault along the winding. Rf represents the degree of the fault, where the smaller the Rf value, the more serious the fault. x and Rf are unknown quantities to be determined. In addition, high-resistance grounding faults may also occur on the B-phase and C-phase windings, so the fault phase is also a quantity to be determined that needs to be determined.

[0035] Figure 2 The flowchart of a method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to an embodiment of the present disclosure is schematically shown.

[0036] like Figure 2 As shown, the method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding includes steps S201 to S205.

[0037] S201, measure the voltage of the three-phase winding starting point and the neutral point to ground.

[0038] In the embodiment of the present disclosure, the voltage u of the three-phase winding start end to ground is measured respectively. pa 、u pb and u pc , neutral point voltage to ground u pn .

[0039] S202, calculating a voltage phasor corresponding to the voltage to ground at the inverter switching frequency based on a fast Fourier analysis algorithm.

[0040] In the embodiment of the present disclosure, based on the fast Fourier analysis algorithm, the voltage u to ground at the inverter switching frequency fs is calculated. pa 、u pb 、u pc and u pn The corresponding voltage phasor. Among them, the voltage to ground u pa The corresponding voltage phasor is recorded as Voltage to ground u pb The corresponding voltage phasor is recorded as Voltage to ground u pc The corresponding voltage phasor is recorded as Voltage to ground u pn The corresponding voltage phasor is recorded as

[0041] S203, calculating the negative sequence component and the zero sequence component of the voltage at the beginning of the three-phase winding at the inverter switching frequency according to the voltage phasor.

[0042] In the embodiment of the present disclosure, based on the symmetrical component method, according to the voltage phasor and Calculate the negative-sequence component and zero-sequence component of the voltage at the beginning of the three-phase winding at the inverter switching frequency.

[0043] Among them, the negative sequence component of the voltage at the beginning of the three-phase winding is and zero sequence component It is proportional to the voltage phasor and satisfies the following relationship:

[0044]

[0045]

[0046] Where a represents a complex operator, a=e j120° .

[0047] S204, obtaining a negative-sequence voltage ratio and a zero-sequence voltage ratio at an inverter switching frequency according to the voltage phasors corresponding to the negative-sequence component, the zero-sequence component and the neutral point voltage to ground.

[0048] In the embodiment of the present disclosure, according to the negative sequence component The voltage phasor corresponding to the neutral point voltage to ground The ratio of the negative sequence voltage ratio at the inverter switching frequency fs is obtained. According to the zero sequence component The voltage phasor corresponding to the neutral point voltage to ground The ratio of the zero-sequence voltage ratio at the inverter switching frequency fs is obtained. Negative sequence voltage ratio and zero sequence voltage ratio The following relations are satisfied respectively:

[0049]

[0050]

[0051] Among them, the negative sequence voltage ratio The amplitude is recorded as Its phase is recorded as The zero sequence voltage ratio The amplitude is recorded as Its phase is recorded as

[0052] S205, judging the phase difference, distribution position along the winding and fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio.

[0053] In the embodiment of the present disclosure, according to the negative sequence voltage ratio and zero sequence voltage ratio Determine the phase difference, distribution position along the winding and fault development degree of the transformer winding high-resistance grounding fault, including: and zero sequence voltage ratio The phase difference of the transformer winding high-resistance grounding fault can be determined by Zero sequence voltage ratio Determine the distribution location of the transformer winding high-resistance grounding fault along the winding and the degree of fault development.

[0054] Specifically, according to the negative sequence voltage ratio and zero sequence voltage ratio The phase difference of the transformer winding high-resistance grounding fault is determined by: and zero sequence voltage ratio The absolute value of the phase difference (i.e. Determine the phase difference of transformer winding high resistance grounding fault. and zero sequence voltage ratio Phase difference In the first phase difference range, the transformer winding high resistance grounding fault occurs in the A phase winding; if the negative sequence voltage is and zero sequence voltage ratio Phase difference In the second phase difference range, the transformer winding high resistance grounding fault occurs in the B phase winding; if the negative sequence voltage is and zero sequence voltage ratio Phase difference In the third phase difference range, the transformer winding high-resistance grounding fault occurs in the C-phase winding.

[0055] In the embodiment of the present disclosure, the first phase difference range may be, for example, 70° to 110°, which means that the transformer winding high-resistance grounding fault occurs in the A-phase winding. The second phase difference range may be, for example, 190° to 230°, which means that the transformer winding high-resistance grounding fault occurs in the B-phase winding. The third phase difference range may be, for example, 310° to 330°, which means that the transformer winding high-resistance grounding fault occurs in the C-phase winding.

[0056] It should be noted that the above-mentioned first phase difference range, second phase difference range and third phase difference range are only exemplary descriptions, and in some other application scenarios, they can also be other range values, and the embodiments of the present disclosure are not limited to this.

[0057] Specifically, according to the negative sequence voltage ratio and zero sequence voltage ratio Determine the distribution position of transformer winding high-resistance grounding fault along the winding, including: if the zero-sequence voltage ratio The difference between 1 and 1 is related to the negative sequence voltage ratio If the absolute value of the ratio of is within the first threshold range, the transformer winding high-resistance grounding fault is close to the beginning of the three-phase winding; if the zero-sequence voltage ratio The difference between 1 and 1 is related to the negative sequence voltage ratio If the absolute value of the ratio is within the second threshold range, the transformer winding high-resistance grounding fault is close to the neutral point.

[0058] Among them, Then when the value range of SL is within the first threshold range,

[0059] It indicates that the transformer winding high-resistance grounding fault is close to the starting end of the three-phase winding. When the value range of SL is within the second threshold range, it indicates that the transformer winding high-resistance grounding fault is close to the neutral point. For example, when the value of SL is smaller, such as the first threshold range can be less than 1, it indicates that the transformer winding high-resistance grounding fault is close to the starting end of the three-phase winding. When the value of SL is larger, such as the second threshold range can be greater than 1 and much greater than 1, it indicates that the transformer winding high-resistance grounding fault is close to the neutral point. When the value of SL is equal to 1, it indicates that the transformer winding high-resistance grounding fault occurs in the middle of the winding.

[0060] In the embodiment of the present disclosure, for sensitivity considerations, it is necessary to first determine the location of the transformer winding high-resistance grounding fault and then select the negative sequence voltage ratio. The amplitude or zero sequence voltage ratio The absolute value of the difference from 1 To determine the extent of the fault.

[0061] Specifically, according to the negative sequence voltage ratio and zero sequence voltage ratio Determine the fault development degree of the transformer winding high-resistance grounding fault, including: if the transformer winding high-resistance grounding fault is close to the beginning of the three-phase winding, then according to Size, determine the fault development degree of transformer winding high resistance grounding fault; among them, The larger it is, the greater the fault degree is and the smaller Rf is; conversely, The smaller the fault is, the smaller the fault is and the larger the Rf is. If the transformer winding high-resistance grounding fault is close to the neutral point, then according to Size, determine the fault development degree of transformer winding high resistance grounding fault; among them, The larger it is, the greater the fault degree is, and the smaller Rf is; conversely, The smaller it is, the smaller the fault level is and the larger Rf is.

[0062] In the embodiment of the present disclosure, the negative sequence voltage ratio is obtained. and zero sequence voltage ratio Combined with negative sequence voltage ratio and zero sequence voltage ratio Phase difference SL, Amplitude and The evaluation of the transformer insulation defect to ground (taking a slight high-resistance grounding fault as an example) is realized by different phases, distribution positions along the windings and fault severity.

[0063] The following will describe in detail the method for locating and detecting high-resistance grounding faults of grid-connected photovoltaic transformer windings provided by the present disclosure in conjunction with a specific embodiment. It should be noted that the simulation results shown in the following embodiments are only exemplary descriptions and do not constitute limitations on the embodiments of the present disclosure.

[0064] refer to Figure 1A The typical three-phase grid-connected photovoltaic system shown in Figure 1 is simulated in MATLAB / Simulink. Figure 1B In the simulation model, the transformer primary winding is set to have 50 coils, that is, N = 50. On the A-phase winding, x = 1, 11, 21, 31, 41, 51, and these six positions simulate different degrees of high-resistance grounding faults, Rf from 5KΩ to 0.5KΩ (step change 0.1KΩ). Similarly, the above fault conditions can also be numerically simulated on the B-phase and C-phase windings. According to the above method steps, the negative sequence components are calculated respectively Zero sequence component And the voltage phasor corresponding to the neutral point voltage to ground like Figure 3A , 3B As shown in 3C, Real means taking the real part of the phase quantity, and Imag means taking the imaginary part of the phase quantity.

[0065] According to the negative sequence component Zero sequence component And the voltage phasor corresponding to the neutral point voltage to ground The negative sequence voltage ratio and zero sequence voltage ratio Then find the amplitude The relationship between SL and fault severity and fault location is as follows: Figure 4A , 4B and as shown in 4C.

[0066] To more clearly illustrate the embodiments of the present disclosure, a set of specific calculation data of faults in FIG4 is taken, that is, x=31 and Rf=1KΩ. and zero sequence voltage ratio The calculation results are shown in Table 1 below: Table 1

[0067]

[0068] According to Table 1 above, It can be judged from the range that a phase difference of 99.04° belongs to a phase A winding fault, a phase difference of 219.13° belongs to a phase B winding fault, and a phase difference of 339.12° belongs to a phase C winding fault.

[0069] According to SL The slope between and the origin. The data in Table 1 above show that the fault location is in the middle section of the winding. Figures 4A to 4C As shown, when the fault location is closer to the beginning of the winding (such as x=1), the SL is smaller; when the fault location is closer to the neutral point of the winding (such as x=51), the SL is larger.

[0070] According to or Determine the degree of the fault. Figures 4A to 4C As shown in the figure, as the fault level increases, that is, Rf becomes smaller (that is, 1 / Rf becomes larger), the slope between the origin and the and When the fault location is closer to the beginning of the winding, such as when x = 1, Rf = 0.5KΩ and Rf = 0.6KΩ, the fault degree is expressed as To judge, the sensitivity is higher, that is changed by 100%, while The change is almost 0; when the fault location is closer to the winding neutral point, such as when x = 51, Rf = 0.5KΩ and Rf = 0.6KΩ, the fault degree is expressed as To judge, the sensitivity is higher, that is changed by 0.4%, while The change is almost 0.

[0071] An embodiment of the present disclosure provides a method for locating and detecting a high-resistance grounding fault in a grid-connected photovoltaic transformer winding. The method clearly distinguishes between the positive and negative components, negative-sequence components and zero-sequence components of electrical quantities at the switching frequency of the inverter, and uses the relationship between the negative-sequence component and the zero-sequence component of the voltage at the switching frequency of the photovoltaic grid-connected inverter to construct a negative-sequence voltage ratio and a zero-sequence voltage ratio. The amplitude and phase relationship between the negative-sequence voltage ratio and the zero-sequence voltage ratio is then used to implement comprehensive detection of a high-resistance grounding fault in a grid-connected transformer winding. The comprehensive detection specifically includes determining the phase, distribution position and development degree of the high-resistance grounding fault in the transformer winding, and the sensitivity can reach the kilo-ohm level.

[0072] Another aspect of the present disclosure provides a high-resistance grounding fault location detection device for a grid-connected photovoltaic transformer winding, comprising: a ground voltage measurement module, a voltage phasor calculation module, a negative-sequence and zero-sequence component calculation module, a negative-sequence and zero-sequence voltage ratio calculation module, and a comprehensive fault detection module. The device can be used to implement reference Figure 2 The described method for locating and detecting high-resistance grounding faults of grid-connected photovoltaic transformer windings is described.

[0073] The ground voltage measurement module is used to measure the ground voltage of the starting end and neutral point of the three-phase winding.

[0074] The voltage phasor calculation module is used to calculate the voltage phasor corresponding to the ground voltage at the inverter switching frequency based on the fast Fourier analysis algorithm.

[0075] The negative-sequence and zero-sequence component calculation module is used to calculate the negative-sequence component and the zero-sequence component of the voltage at the beginning of the three-phase winding at the inverter switching frequency according to the voltage phasor.

[0076] The negative-sequence and zero-sequence voltage ratio calculation module obtains the negative-sequence voltage ratio and the zero-sequence voltage ratio at the inverter switching frequency according to the voltage phasors corresponding to the negative-sequence component, the zero-sequence component and the neutral point voltage to ground.

[0077] A comprehensive fault detection module is used to determine the phase difference, distribution position along the winding, and fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio. According to an embodiment of the present disclosure, the comprehensive fault detection module is used to determine the phase difference, distribution position along the winding, and fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio, including: determining the phase difference of the transformer winding high-resistance grounding fault according to the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio; determining the distribution position along the winding and fault development degree of the transformer winding high-resistance grounding fault according to the amplitude of the negative-sequence voltage ratio and the zero-sequence voltage ratio. Among them, the phase difference of the transformer winding high-resistance grounding fault includes: the transformer winding high-resistance grounding fault occurs in the A-phase winding, the transformer winding high-resistance grounding fault occurs in the B-phase winding, and the transformer winding high-resistance grounding fault occurs in the C-phase winding.

[0078] Specifically, if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the first phase difference range, the transformer winding high-resistance grounding fault occurs in the A-phase winding; if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the second phase difference range, the transformer winding high-resistance grounding fault occurs in the B-phase winding; if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the third phase difference range, the transformer winding high-resistance grounding fault occurs in the C-phase winding.

[0079] It should be noted that each module in the grid-connected photovoltaic transformer winding high-resistance grounding fault location detection device is used to respectively implement the following Figure 2 The specific implementation of steps S201 to S205 is as shown in the above embodiment and will not be described in detail here.

[0080] While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive.

[0081] It will be appreciated by those skilled in the art that the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of scopes, even if such combinations or combinations are not explicitly described in the present disclosure. In particular, the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of scopes without departing from the spirit and teachings of the present disclosure. All of these combinations and / or combinations fall within the scope of the present disclosure.

[0082] Although the present disclosure has been shown and described with reference to specific exemplary embodiments of the present disclosure, it should be understood by those skilled in the art that various changes in form and details may be made to the present disclosure without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents. Therefore, the scope of the present disclosure should not be limited to the above-mentioned embodiments, but should be determined not only by the appended claims, but also by the equivalents of the appended claims.

Claims

1. A method for locating and detecting high-resistance grounding faults of grid-connected photovoltaic transformer windings, characterized in that: include: Measure the voltage to ground at the beginning and neutral point of the three-phase winding; Calculating a voltage phasor corresponding to the voltage to ground at an inverter switching frequency based on a fast Fourier analysis algorithm; Calculating the negative sequence component and the zero sequence component of the voltage to ground at the starting end of the three-phase winding at the switching frequency of the inverter according to the voltage phasor corresponding to the voltage to ground at the starting end of the three-phase winding; According to the voltage phasors corresponding to the negative-sequence component, the zero-sequence component and the voltage to ground of the neutral point, a negative-sequence voltage ratio and a zero-sequence voltage ratio at the inverter switching frequency are obtained; According to the negative-sequence voltage ratio and the zero-sequence voltage ratio, the phase difference, distribution position along the winding and fault development degree of the transformer winding high-resistance grounding fault are determined.

2. The method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to claim 1 is characterized in that: The method of judging the phase difference, distribution position along the winding and fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio includes: Determining the phase difference of the transformer winding high-resistance grounding fault according to the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio; According to the negative-sequence voltage ratio and the zero-sequence voltage ratio, the distribution position of the transformer winding high-resistance grounding fault along the winding and the fault development degree are determined.

3. The method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to claim 2 is characterized in that: The phases of the transformer winding high-resistance grounding fault include: the transformer winding high-resistance grounding fault occurs in the A-phase winding, the transformer winding high-resistance grounding fault occurs in the B-phase winding, and the transformer winding high-resistance grounding fault occurs in the C-phase winding.

4. The method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to claim 3 is characterized in that: The determining the phase difference of the transformer winding high-resistance grounding fault according to the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio comprises: If the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the first phase difference range, the transformer winding high-resistance grounding fault occurs in the A-phase winding; If the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the second phase difference range, the transformer winding high-resistance grounding fault occurs in the B-phase winding; If the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within a third phase difference range, the transformer winding high-resistance grounding fault occurs in the C-phase winding.

5. The method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to claim 2, characterized in that: The step of determining the distribution position of the transformer winding high-resistance grounding fault along the winding according to the negative-sequence voltage ratio and the zero-sequence voltage ratio comprises: If the absolute value of the ratio of the difference between the zero-sequence voltage ratio and 1 to the negative-sequence voltage ratio is within the first threshold range, the transformer winding high-resistance grounding fault is located close to the starting end of the three-phase winding; If the absolute value of the ratio of the difference between the zero-sequence voltage ratio and 1 to the negative-sequence voltage ratio is within the second threshold range, the transformer winding high-resistance grounding fault is close to the neutral point.

6. The method for locating and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to claim 5, characterized in that: Judging the fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio includes: If the transformer winding high-resistance grounding fault is close to the starting end of the three-phase winding, the fault development degree of the transformer winding high-resistance grounding fault is judged according to the amplitude of the negative sequence voltage ratio; If the transformer winding high-resistance grounding fault is close to the neutral point, the fault development degree of the transformer winding high-resistance grounding fault is determined according to the absolute value of the difference between the zero-sequence voltage ratio and 1.

7. A device for locating and detecting high-resistance grounding faults of grid-connected photovoltaic transformer windings, characterized in that: include: The ground voltage measurement module is used to measure the ground voltage of the starting end and neutral point of the three-phase winding; A voltage phasor calculation module, used for calculating the voltage phasor corresponding to the voltage to ground at the inverter switching frequency based on a fast Fourier analysis algorithm; A negative-sequence and zero-sequence component calculation module, used to calculate the negative-sequence component and the zero-sequence component of the voltage to ground at the starting end of the three-phase winding at the switching frequency of the inverter according to the voltage phasor corresponding to the voltage to ground at the starting end of the three-phase winding; A negative-sequence and zero-sequence voltage ratio calculation module, which obtains a negative-sequence voltage ratio and a zero-sequence voltage ratio at the inverter switching frequency according to the negative-sequence component, the zero-sequence component and the voltage phasor corresponding to the neutral point voltage to ground; The comprehensive fault detection module is used to determine the phase difference, distribution position along the winding and fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio.

8. The device for locating and detecting high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to claim 7, characterized in that: The comprehensive fault detection module is used to determine the phase difference, distribution position along the winding and fault development degree of the transformer winding high-resistance grounding fault according to the negative-sequence voltage ratio and the zero-sequence voltage ratio, including: Determining the phase difference of the transformer winding high-resistance grounding fault according to the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio; According to the negative-sequence voltage ratio and the zero-sequence voltage ratio, the distribution position of the transformer winding high-resistance grounding fault along the winding and the fault development degree are determined.

9. The device for locating and detecting high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to claim 7, characterized in that: The phases of the transformer winding high-resistance grounding fault include: the transformer winding high-resistance grounding fault occurs in the A-phase winding, the transformer winding high-resistance grounding fault occurs in the B-phase winding, and the transformer winding high-resistance grounding fault occurs in the C-phase winding.

10. The device for locating and detecting high-resistance grounding fault of a grid-connected photovoltaic transformer winding according to claim 9, characterized in that: If the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the first phase difference range, the high-resistance grounding fault of the transformer winding occurs in the A-phase winding; if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the second phase difference range, the high-resistance grounding fault of the transformer winding occurs in the B-phase winding; if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is within the third phase difference range, the high-resistance grounding fault of the transformer winding occurs in the C-phase winding.

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