CN115219947A - Grid-connected photovoltaic transformer winding high resistance ground fault location detection method and device - Google Patents

Abstract

The present disclosure provides a method for locating high-resistance grounding faults of grid-connected photovoltaic transformer windings, including: measuring the ground voltage at the beginning and neutral point of three-phase windings; The voltage phasor corresponding to the ground voltage; according to the voltage phasor, calculate the negative-sequence component and zero-sequence component of the voltage at the beginning of the three-phase winding at the switching frequency of the inverter; According to the voltage phasor corresponding to the ground voltage, the negative-sequence voltage ratio and the zero-sequence voltage ratio at the switching frequency of the inverter can be obtained; according to the negative-sequence voltage ratio and the zero-sequence voltage ratio, the phase difference of the high-resistance grounding fault of the transformer winding, along the windings, can be judged. Distribution location and fault development degree. The present disclosure also provides a high-resistance grounding fault location detection device for a grid-connected photovoltaic transformer winding.

Description

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

technical field

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 technique

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

The operating environment of photovoltaic power plants 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-MOSFETs are gradually being applied in grid-connected photovoltaic inverters. The switching frequency of SiC-MOSFET power devices is between tens to hundreds of kHz, and the rising/falling edge time of each switching action is between tens to hundreds of ns, resulting in a very large transient voltage (dv/dt). rate of change. The transient electrical stress and harmonic losses caused by high-frequency and fast switching actions will exacerbate the electrical and thermal aging problems of the power transformers connected at the back end, thereby deteriorating the performance and life of its winding-to-ground insulation components. The leakage problem evolves into a high-resistance ground fault, which eventually leads to a severe metallic short-circuit fault. In addition, considering that the transient electrical stress mainly acts on the beginning of the transformer winding, the insulation components at the beginning of the windings are more seriously aged than the insulating components at other positions. In addition, due to the frequent load switching of grid-connected photovoltaic system and the continuous change of load current, the temperature distribution inside the transformer box is uneven, which in turn causes uneven heating of all ground insulation components distributed along the windings, resulting in uncertain locations. Local defect problem.

Therefore, considering the effects of electrical aging and thermal aging, the insulation of power transformer windings in grid-connected photovoltaic systems faces inevitable local degradation. During long-term operation, this local insulation defect will gradually develop into a slight low-current grounding fault (equivalent to high-resistance grounding), and finally lead to a penetrating high-current grounding fault. Based on this, it is urgent to realize online and sensitive detection and location of high-resistance grounding faults of power transformers connected to inverters in grid-connected photovoltaic systems.

SUMMARY OF THE INVENTION

In view of the above problems, the present disclosure provides a method and device for locating high-resistance grounding faults in grid-connected photovoltaic transformer windings, aiming at detecting and locating thousand-ohm high-resistance grounding faults in each phase winding.

A first aspect of the present disclosure provides a method for locating high-resistance grounding faults in grid-connected photovoltaic transformer windings, including: measuring the voltage to ground at the beginning and neutral point of three-phase windings; The voltage phasor corresponding to the ground voltage at the switching frequency of the inverter; according to the voltage phasor, the negative sequence component and the zero sequence component of the voltage at the beginning of the three-phase winding at the switching frequency of the inverter are calculated; according to the negative sequence component, zero sequence component and The voltage phasor corresponding to the neutral point-to-ground voltage can obtain the negative sequence voltage ratio and zero sequence voltage ratio at the inverter switching frequency; phase difference, distribution location along the winding and fault development degree.

Further, according to the negative-sequence voltage ratio and the zero-sequence voltage ratio, determine the phase difference of the transformer winding high-resistance grounding fault, the distribution position along the winding and the fault development degree, including: according to the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio, Determine the phase difference of the transformer winding high resistance grounding fault; according to the negative sequence voltage ratio and the zero sequence voltage ratio, judge the distribution position of the transformer winding high resistance grounding fault along the winding and the fault development degree.

Further, the phases of the transformer winding high resistance ground fault include: the transformer winding high resistance ground fault occurs in the A phase winding, the transformer winding high resistance ground fault occurs in the B phase winding, and the transformer winding high resistance ground fault occurs in the C phase winding.

Further, according to the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio, judging the phase difference of the high-resistance grounding fault of the transformer winding, including: if the absolute value of the phase difference between the negative-sequence voltage ratio and the zero-sequence voltage ratio is in the first phase 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 A-phase winding. 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 ground fault of the transformer winding occurs in the C-phase winding.

Further, according to the negative-sequence voltage ratio and the zero-sequence voltage ratio, determine the distribution position of the transformer winding high-resistance grounding fault along the winding, including: if the absolute value of the ratio of the difference between the zero-sequence voltage ratio and 1 and the negative-sequence voltage ratio is within Within the first threshold range, the transformer winding high-resistance ground fault is close to the beginning of the three-phase winding; if the absolute value of the ratio of the difference between the zero-sequence voltage ratio and 1 and the negative-sequence voltage ratio is within the second threshold range, then the transformer The location of the winding high resistance ground fault close to the neutral point.

Further, according to the negative sequence voltage ratio and the 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 the negative sequence voltage ratio. The magnitude of the amplitude determines the fault development degree of the high-resistance grounding fault of the transformer winding; if the high-resistance grounding fault of the transformer winding is close to the neutral point, the high-resistance of the transformer winding is judged according to the absolute value of the difference between the zero-sequence voltage ratio and 1. The extent of the fault development of the ground fault.

A second aspect of the present disclosure provides a high-resistance ground fault location detection device for a grid-connected photovoltaic transformer winding, including: a ground voltage measurement module for measuring the ground voltage at the beginning of the three-phase winding and the neutral point; the voltage phase The quantity calculation module is used to calculate the voltage phasor corresponding to the ground voltage at the switching frequency of the inverter based on the fast Fourier analysis algorithm; the negative sequence and zero sequence component calculation module is used to calculate the voltage phasor at the inverter The negative-sequence component and zero-sequence component of the starting voltage of the three-phase winding at the switching frequency of the inverter; the negative-sequence and zero-sequence voltage ratio calculation module, according to the voltage phasor corresponding to the negative-sequence component, the zero-sequence component and the neutral point-to-ground voltage, Obtain the negative-sequence voltage ratio and zero-sequence voltage ratio at the switching frequency of the inverter; the fault comprehensive detection module is used to judge the phase difference and distribution along the winding of the high-resistance grounding fault of the transformer winding according to the negative-sequence voltage ratio and the zero-sequence voltage ratio location and extent of failure development.

Further, the fault comprehensive detection module is used to judge the phase difference of the transformer winding high resistance grounding fault, the distribution position along the winding and the fault development degree according to the negative sequence voltage ratio and the zero sequence voltage ratio, including: according to the negative sequence voltage ratio and the zero sequence voltage ratio. The phase difference of the voltage ratio can judge the phase difference of the high-resistance grounding fault of the transformer winding; according to the negative-sequence voltage ratio and the zero-sequence voltage ratio, the distribution position of the high-resistance grounding fault of the transformer winding along the winding and the development degree of the fault can be judged.

Further, the phases of the transformer winding high resistance ground fault include: the transformer winding high resistance ground fault occurs in the A phase winding, the transformer winding high resistance ground fault occurs in the B phase winding, and the transformer winding high resistance ground fault occurs in the C phase winding.

Further, 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 of the voltage ratio is within the range of the second phase difference, 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 Within the phase difference range, the transformer winding high-resistance ground fault occurs in the C-phase winding.

The embodiments of the present disclosure provide a method and device for locating high-resistance grounding faults in grid-connected photovoltaic transformer windings. The method clearly distinguishes that the electrical quantity at the switching frequency of the inverter has both positive and negative components that are not zero, and negative sequence component and zero-sequence component, and use the relationship between the voltage negative-sequence component and the zero-sequence component at the switching frequency of the photovoltaic grid-connected inverter to construct the negative-sequence voltage ratio and the zero-sequence voltage ratio, and then use the negative-sequence voltage ratio and zero-sequence voltage ratio. The amplitude and phase relationship of the sequence voltage ratio are used to realize the comprehensive detection of the high-resistance grounding fault of the transformer windings connected to the grid. Sensitivity can reach the kiloohm level.

Description of drawings

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:

FIG. 1A schematically shows a schematic structural diagram of a typical three-phase grid-connected photovoltaic system;

FIG. 1B schematically shows a schematic diagram of the three-phase windings of the transformer on the primary side;

FIG. 2 schematically shows a flowchart of a method for locating a high-resistance ground fault in a grid-connected photovoltaic transformer winding according to an embodiment of the present disclosure;

3A-3C schematically show schematic diagrams of voltage phasor calculation results according to an embodiment of the present disclosure;

4A to 4C schematically show schematic diagrams of voltage ratio calculation results according to an embodiment of the present disclosure.

Detailed ways

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood, however, that these descriptions are exemplary only, and are not intended to limit the scope of the present disclosure. In the following detailed description, for convenience of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent, however, that one or more embodiments may be practiced without these specific details. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present disclosure.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure. The terms "comprising", "comprising" and the like used herein indicate the presence of stated features, steps, operations and/or components, but do not preclude the presence or addition of one or more other features, steps, operations or components.

All terms (including technical and scientific terms) used herein have the meaning as commonly understood by one of ordinary skill in the art, unless otherwise defined. It should be noted that terms used herein should be construed to have meanings consistent with the context of the present specification and should not be construed in an idealized or overly rigid manner.

Most of the traditional power transformer insulation fault detection methods are to detect the additional products of insulation degradation, and judge the aging degree according to the 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:

1. Dissolved gas method in oil: The detection of dissolved gas in insulating oil is gradually realized online, and it has become the most widely used online method for diagnosing latent insulation defects of transformers. The characteristic gas method, the Rogers method and the IEC 60599 three-ratio method are the three most basic gas analysis and fault judgment methods. This type of method is based on the attention value of each gas component content or the attention value of the gas growth rate to judge the possibility of a transformer. existing faults. However, there are many types of gases in the transformer box and the types of faults are complex. The current judgment method has problems such as single code combination and threshold setting rules, and it is difficult to fully consider the complexity of the grid-connected photovoltaic system operating environment, including high-frequency switching noise interference. In addition, for For dry-type transformers, this method fails.

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. Based on the partial discharge localization technology of multi-position sensing, by analyzing the spatial transmission characteristics and attenuation laws of different types of partial discharge signals, the detection area on the fuel tank wall that can sensitively reflect the partial discharge position is determined. However, the PD signal verification standards, detection methods and calibration methods are not strict and uniform, and it is difficult to unify the discharge types. In addition, the partial discharge sensor has high precision and high cost; generally, only the local scope of the insulation defect in the box can be determined, and the clear location of the winding-to-ground insulation defect cannot be determined.

3. Fault analysis method: The power transformer fault analysis method is widely discussed, and the existing research proposes several methods based on different principles. Use the electrical quantities at the transformer port to diagnose the type and degree of faults, and classify them by electrical quantity characteristics, 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 only diagnose faults based on the shape or characteristic of the waveform when the internal faults are observable, and need to rely 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 changes of system operating conditions and the influence of insulation aging in transformer units, that is, the sensitivity of power frequency electrical quantities to reflect insulation aging defects is not enough. Some scholars have proposed a protection method based on the power frequency negative sequence impedance and power direction, which can realize the detection of a 100-ohm high-resistance ground fault in a transformer. However, this method is not yet able to detect the more subtle early ground insulation defects, and often does not have sufficient localization capabilities.

Therefore, in view of the insulation defect of the transformer winding of the grid-connected photovoltaic system to the ground, it is difficult for the prior art to sensitively detect and locate the high-resistance ground fault of the kiloohm level.

In view of the problems existing in the prior art, the present disclosure provides a method for locating high-resistance grounding faults in grid-connected photovoltaic transformer windings. The neutral point-to-ground voltage of the winding is calculated to obtain the negative sequence component and zero-sequence component of the voltage at the beginning of the transformer winding at the switching frequency, and the harmonic component of the winding neutral point-to-ground voltage at the switching frequency, and the transfer function is constructed. And the corresponding criterion to realize the detection and location of the high-resistance ground fault of each phase winding thousand-ohm level.

The technical solution of the present disclosure will be described in detail below with reference to the specific flow of the method for locating high-resistance grounding faults of grid-connected photovoltaic transformer windings in specific embodiments of the present disclosure. It should be understood that the process flow and calculation structure of the method for locating high-resistance grounding faults in grid-connected photovoltaic transformer windings shown in the accompanying drawings are only exemplary, to help those skilled in the art understand the technical solutions of the present disclosure, and are not intended to be used for limit the scope of protection of the present disclosure.

FIG. 1A schematically shows a schematic structural diagram of a typical three-phase grid-connected photovoltaic system. As shown in Figure 1A, a typical three-phase grid-connected photovoltaic system includes: photovoltaic power generation units, photovoltaic grid-connected inverters, filter inductors, transformers, and loads. Let the inverter switching frequency be 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. A voltage transformer is installed at the beginning of each winding and at the neutral point of the transformer, which can measure the ground voltage at the corresponding position.

As shown in Figure 1B, the voltages to ground at the beginning of the three-phase windings are respectively denoted as _upa , _upb and _upc ; the voltage to the ground at the neutral point is denoted as _upn . Taking the A-phase winding as an example, there are N coils. Often, the location and extent of winding-to-ground insulation defects are unknown. Assuming that a high-resistance ground fault occurs at coil x, the grounding resistance is denoted as Rf. x/N indicates where the fault occurs along the winding. Rf represents the degree of failure, wherein, the smaller the value of Rf, the more serious the degree of failure. x and Rf are unknown quantities to be solved. In addition, high-resistance ground faults may also occur on the B-phase and C-phase windings, so the fault phase difference also needs to be clearly determined.

FIG. 2 schematically shows a flowchart of a method for locating a high-resistance ground fault in a grid-connected photovoltaic transformer winding according to an embodiment of the present disclosure.

As shown in FIG. 2 , the method for locating a high-resistance grounding fault of a grid-connected photovoltaic transformer winding includes steps S201 to S205 .

S201, measure the voltage to ground at the beginning of the three-phase winding and the neutral point.

In the embodiments of the present disclosure, the ground-to-ground voltages _upa , _upb and _upc at the beginning of the three-phase windings, and the ground-to-ground voltage _upn of the neutral point are measured respectively.

S202, based on a fast Fourier analysis algorithm, calculate a voltage phasor corresponding to the ground voltage at the switching frequency of the inverter.

对地电压u_pb对应的电压相量记为

对地电压u_pc对应的电压相量记为

对地电压u_pn对应的电压相量记为

In the embodiment of the present disclosure, based on the fast Fourier analysis algorithm, the voltage phasors corresponding to the ground voltages _upa , _upb , _upc , and _upn at the inverter switching frequency fs are calculated. Among them, the voltage phasor corresponding to the ground voltage u _pa is recorded as

The voltage phasor corresponding to the ground voltage u _pb is recorded as

The voltage phasor corresponding to the ground voltage u _pc is recorded as

The voltage phasor corresponding to the ground voltage u _pn is recorded as

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

及

计算在逆变器开关频率下三相绕组始端电压的负序分量和零序分量。In the embodiment of the present disclosure, based on the symmetrical component method, according to the voltage phasor

and

Calculate the negative-sequence and zero-sequence components of the voltage at the start of the three-phase windings at the inverter switching frequency.

和零序分量

与电压相量均成正比，具体满足以下关系：Among them, the negative sequence component of the voltage at the beginning of the three-phase winding

and zero sequence components

It is proportional to the voltage phasor, and specifically satisfies the following relationship:

Among them, a represents a complex operator, a=e ^j120° .

S204 , according to the negative sequence component, the zero sequence component and the voltage phasor corresponding to the ground voltage of the neutral point, obtain the negative sequence voltage ratio and the zero sequence voltage ratio at the switching frequency of the inverter.

和中性点的对地电压对应的电压相量

的比值，得到在逆变器开关频率fs下的负序电压比

根据零序分量

和中性点的对地电压对应的电压相量

的比值，得到在逆变器开关频率fs下的零序电压比

即负序电压比

和零序电压比

分别满足以下关系：In the embodiment of the present disclosure, according to the negative sequence component

The voltage phasor corresponding to the neutral-to-ground voltage

The ratio of the negative sequence voltage at the inverter switching frequency fs is obtained

According to the zero sequence component

The voltage phasor corresponding to the neutral-to-ground voltage

The ratio of , to get the zero sequence voltage ratio at the inverter switching frequency fs

the negative sequence voltage ratio

and zero sequence voltage ratio

respectively satisfy the following relations:

的幅值记为

其相位记作

将零序电压比

的的幅值记为

其相位记作

Among them, the negative sequence voltage ratio

The magnitude of is recorded as

Its phase is recorded as

The zero-sequence voltage ratio

The magnitude of is recorded as

Its phase is recorded as

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

和零序电压比

判断变压器绕组高阻接地故障的相别、沿绕组分布位置及故障发展程度，具体包括：根据负序电压比

和零序电压比

的相位差，判断变压器绕组高阻接地故障的相别；根据负序电压比

和述零序电压比

判断变压器绕组高阻接地故障的沿绕组分布位置及故障发展程度。In the embodiment of the present disclosure, according to the negative sequence voltage ratio

and zero sequence voltage ratio

Judging the phase difference, distribution position along the winding and fault development degree of the transformer winding high resistance grounding fault, including: according to the negative sequence voltage ratio

and zero sequence voltage ratio

According to the phase difference of the transformer winding, the phase difference of the high resistance ground fault of the transformer winding is judged; according to the negative sequence voltage ratio

and the zero-sequence voltage ratio

Determine the distribution location of the transformer winding high resistance ground fault along the winding and the fault development degree.

和零序电压比

的相位差，判断变压器绕组高阻接地故障的相别，包括：根据负序电压比

和零序电压比

的相位差的绝对值(即

判断变压器绕组高阻接地故障的相别。其中，若负序电压比

和零序电压比

的相位差

在第一相位差范围内，则变压器绕组高阻接地故障发生在A相绕组；若负序电压比

和零序电压比

的相位差

在第二相位差范围内，则变压器绕组高阻接地故障发生在B相绕组；若负序电压比

和零序电压比

的相位差

在第三相位差范围内，则变压器绕组高阻接地故障发生在C相绕组。Specifically, according to the negative sequence voltage ratio

and zero sequence voltage ratio

The phase difference of the transformer winding is judged to determine the phase difference of the high resistance grounding fault of the transformer winding, including: according to the negative sequence voltage ratio

and zero sequence voltage ratio

The absolute value of the phase difference (ie

Determine the phase of the transformer winding high resistance ground fault. Among them, if the negative sequence voltage ratio is

and zero sequence voltage ratio

phase difference

Within the first phase difference range, the transformer winding high-resistance ground fault occurs in the A-phase winding; if the negative sequence voltage ratio is

and zero sequence voltage ratio

phase difference

Within the second phase difference range, the high-resistance grounding fault of the transformer winding occurs in the B-phase winding; if the negative sequence voltage ratio is

and zero sequence voltage ratio

phase difference

Within the third phase difference range, the high-resistance ground fault of the transformer winding occurs in the C-phase winding.

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

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 may also be values in other ranges. This is not limited.

和零序电压比

判断变压器绕组高阻接地故障的沿绕组分布位置，包括：若零序电压比

和1之间的差值与负序电压比

的比值绝对值在第一阈值范围内，则变压器绕组高阻接地故障的靠近三相绕组始端位置；若零序电压比

和1 之间的差值与负序电压比

的比值绝对值在第二阈值范围内，则变压器绕组高阻接地故障的靠近中性点位置。Specifically, according to the negative sequence voltage ratio

and zero sequence voltage ratio

Determine the distribution position of the transformer winding high resistance ground fault along the winding, including: if the zero-sequence voltage ratio

and the difference between 1 and the negative sequence voltage ratio

If the absolute value of the ratio is within the first threshold range, the transformer winding high-resistance ground fault is close to the beginning of the three-phase winding; if the zero-sequence voltage ratio is

The difference between and 1 to the negative sequence voltage ratio

If the absolute value of the ratio is within the second threshold range, the transformer winding is close to the neutral point of the high-resistance ground fault.

则当SL的数值范围在第一阈值范围内时，Among them, note

Then when the value range of SL is within the first threshold range,

It means that the transformer winding high resistance ground fault is close to the beginning 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 ground fault is close to the neutral point. For example, when the value of SL is smaller, for example, the first threshold value range may be less than 1, it indicates that the transformer winding high resistance ground fault is close to the beginning of the three-phase winding. When the value of SL is larger, for example, when the second threshold value range can be greater than 1 and far greater than 1, it indicates that the transformer winding high-resistance ground fault is close to the neutral point. When the value of SL is equal to 1, it means that the high-resistance ground fault of the transformer winding occurs in the middle of the winding.

的幅值

或零序电压比

与1之间差值的绝对值

来进行故障程度的判断。In the embodiments of the present disclosure, for the sake of sensitivity, it is necessary to first determine the location of the high-resistance grounding fault of the transformer winding, and then select the negative sequence voltage ratio.

The magnitude of

or zero sequence voltage ratio

the absolute value of the difference from 1

to judge the degree of failure.

和零序电压比

判断变压器绕组高阻接地故障的故障发展程度，包括：若变压器绕组高阻接地故障的靠近三相绕组始端位置，则根据

大小，判断变压器绕组高阻接地故障的故障发展程度；其中，

越大，代表故障程度越大，Rf越小；反之，

越小，代表故障程度越小，Rf越大。若变压器绕组高阻接地故障的靠近中性点位置，则根据

大小，判断变压器绕组高阻接地故障的故障发展程度；其中，

越大，代表故障程度越大， Rf越小；反之，

越小，代表故障程度越小，Rf越大。Specifically, according to the negative sequence voltage ratio

and zero sequence voltage ratio

Judging 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, according to

size, to judge the fault development degree of the transformer winding high resistance ground fault; among them,

The larger the value, the greater the degree of failure, and the smaller the Rf; otherwise,

The smaller the value, the smaller the degree of failure and the larger the Rf. If the high-resistance ground fault of the transformer winding is close to the neutral point, according to

size, to judge the fault development degree of the transformer winding high resistance ground fault; among them,

The larger the value, the greater the degree of failure, and the smaller the Rf; otherwise,

The smaller the value, the smaller the degree of failure and the larger the Rf.

和零序电压比

结合负序电压比

和零序电压比

的相位差

SL、幅值

及

实现了变压器对地绝缘缺陷(以轻微的高阻接地故障为例) 的发生相别、沿绕组分布位置和故障程度的评估。In the embodiment of the present disclosure, the obtained negative sequence voltage ratio is used

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 occurrence phase, distribution location along the winding and fault degree of the transformer insulation defect (taking a slight high-resistance ground fault as an example) is realized.

The method for locating high-resistance grounding faults of grid-connected photovoltaic transformer windings provided by the present disclosure will be described in detail below with reference to a specific embodiment. It should be noted that the simulation results shown in the following embodiments are only illustrative, and do not constitute limitations of the embodiments of the present disclosure.

零序分量

及中性点的对地电压对应的电压相量

如图3A、3B 及3C所示。其中，Real表示取相量实部，Imag表示取相量虚部。With reference to the typical three-phase grid-connected photovoltaic system shown in Figure 1A, a simulation model was constructed in MATLAB/Simulink. Referring to FIG. 1B , in the simulation model, the primary winding of the transformer is set to have a total of 50 coils, ie, N=50. On the A-phase winding, x=1, 11, 21, 31, 41, and 51. The six positions simulate different degrees of high-resistance ground faults, and Rf ranges from 5KΩ to 0.5KΩ (step size changes 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 respectively calculated and obtained

zero sequence component

and the voltage phasor corresponding to the ground voltage of the neutral point

As shown in Figures 3A, 3B and 3C. Among them, Real means taking the real part of the phasor, and Imag means taking the imaginary part of the phasor.

零序分量

及中性点的对地电压对应的电压相量

得到的负序电压比

和零序电压比

再求得幅值

和SL与故障程度和故障位置的关系如图4A、4B及4C所示。According to the negative sequence component

zero sequence component

and the voltage phasor corresponding to the ground voltage of the neutral point

The resulting negative sequence voltage ratio

and zero sequence voltage ratio

find the amplitude again

The relationship between and SL and the degree of failure and the location of the failure are shown in Figs. 4A, 4B and 4C.

和零序电压比

计算结果如下表1所示：表1To illustrate the embodiments of the present disclosure more clearly, take the specific calculation data of a group of faults in FIG. 4 , that is, x=31 and Rf=1KΩ. Negative sequence voltage ratio

and zero sequence voltage ratio

The calculation results are shown in Table 1 below: Table 1

范围可以判断，相位差99.04°属于A相绕组故障，相位差219.13°属于B相绕组故障，相位差339.12°属于C相绕组故障。From Table 1 above, according to

The range can be judged that the phase difference of 99.04° belongs to the A-phase winding fault, the phase difference of 219.13° belongs to the B-phase winding fault, and the phase difference of 339.12° belongs to the C-phase winding fault.

与原点之间的斜率。由上表1中数据表明，故障位置处于绕组中间段。如图4A～4C所示，当故障位置越靠近绕组始端(如x＝1)，SL越小；当故障位置越靠近绕组中性点(如 x＝51)，SL越大。According to SL

Slope from the origin. The data in Table 1 above shows that the fault location is in the middle section of the winding. As shown in Figures 4A to 4C, when the fault location is closer to the beginning of the winding (eg x=1), the SL is smaller; when the fault location is closer to the neutral point of the winding (eg x=51), the SL is greater.

或

对故障程度进行判断。如图4A～4C所示，随着故障程度加深，即Rf越小(即1/Rf越大)，与原点之间的斜率，

和

两者均呈现增大趋势。当故障位置越靠近绕组始端，如当x＝1， Rf＝0.5KΩ和Rf＝0.6KΩ时，故障程度用

来判断，灵敏度更高，即

变化了100％，而

变化几乎为0；当故障位置越靠近绕组中性点，如当x＝51，Rf＝0.5KΩ和Rf＝0.6KΩ时，故障程度用

来判断，灵敏度更高，即

变化了0.4％，而

变化几乎为0。Then according to

or

Judge the degree of failure. As shown in Figures 4A to 4C, as the degree of failure deepens, that is, the smaller Rf is (that is, the larger 1/Rf is), the slope between the origin and the origin,

and

Both showed an increasing trend. When the fault position is closer to the beginning of the winding, such as when x=1, Rf=0.5KΩ and Rf=0.6KΩ, the fault degree is calculated by

To judge, the sensitivity is higher, that is

changed 100%, while

The change is almost 0; when the fault position is closer to the neutral point of the winding, such as when x=51, Rf=0.5KΩ and Rf=0.6KΩ, the fault degree is calculated by

To judge, the sensitivity is higher, that is

changed by 0.4%, while

The change is almost 0.

The embodiments of the present disclosure provide a method for detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding, which clearly distinguishes that the electrical quantity at the switching frequency of the inverter has both positive and negative components, negative sequence components and At the same time, the relationship between the voltage negative-sequence component and the zero-sequence component at the switching frequency of the photovoltaic grid-connected inverter is used to construct the negative-sequence voltage ratio and the zero-sequence voltage ratio, and then the negative-sequence voltage ratio and the zero-sequence voltage are used. It can realize the comprehensive detection of high-resistance grounding faults in grid-connected transformer windings. The comprehensive detection includes judging the phase difference, distribution position and development degree of high-resistance grounding faults in transformer windings. up to the kiloohm level.

Another aspect of the present disclosure provides a grid-connected photovoltaic transformer winding high-resistance ground fault location detection device, including: 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 Sequence voltage ratio calculation module and fault comprehensive detection module. The device can be used to implement the method for locating a high-resistance ground fault in a grid-connected photovoltaic transformer winding described with reference to FIG. 2 .

The ground voltage measurement module is used to measure the ground voltage at the beginning and neutral point of the three-phase winding.

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

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

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

The fault comprehensive detection module is used for judging the phase difference of the transformer winding high resistance grounding fault, the distribution position along the winding and the fault development degree according to the negative sequence voltage ratio and the zero sequence voltage ratio. According to the embodiment of the present disclosure, the comprehensive fault detection module is used to judge 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: according to the negative sequence voltage ratio and the zero sequence voltage ratio. The phase difference between the sequence voltage ratio and the zero-sequence voltage ratio is used to judge the phase difference of the high-resistance grounding fault of the transformer winding; according to the amplitude of the negative-sequence voltage ratio and the zero-sequence voltage ratio, the distribution position and the distribution position of the high-resistance grounding fault of the transformer winding along the winding are judged. Degree of failure development. Among them, the phases of the transformer winding high resistance ground fault include: the transformer winding high resistance ground fault occurs in the A phase winding, the transformer winding high resistance ground fault occurs in the B phase winding and the transformer winding high resistance ground fault occurs in the C phase winding.

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 negative-sequence voltage ratio and the zero-sequence voltage ratio are If the absolute value of the phase difference is within the second phase difference range, then the transformer winding high resistance ground fault occurs in the B-phase winding; 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, Then the transformer winding high resistance ground fault occurs in the C-phase winding.

It should be noted that each module in the high-resistance grounding fault location detection device for grid-connected photovoltaic transformer windings is used to respectively implement steps S201 to S205 shown in FIG. Describe in detail.

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

Those skilled in the art will appreciate that various range combinations and/or combinations of features recited in various embodiments and/or claims of the present disclosure are possible, even if such combinations or combinations are not expressly recited in the present disclosure. In particular, various combinations and/or combinations of the features recited in the various embodiments of the present disclosure and/or in the claims may be made without departing from the spirit and teachings of the present disclosure. All such combinations and/or combinations fall within the scope of this disclosure.

Although the present disclosure has been shown and described with reference to specific exemplary embodiments of the present disclosure, those skilled in the art will appreciate that, without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents, Various changes in form and detail have been made in the present disclosure. Therefore, the scope of the present disclosure should not be limited to the above-described embodiments, but should be determined not only by the appended claims, but also by their equivalents.

Claims (10)

1. A method for positioning and detecting a high-resistance grounding fault of a grid-connected photovoltaic transformer winding is characterized by comprising the following steps:

measuring the voltages to earth of the starting end and the neutral point of the three-phase winding;

calculating a voltage phasor corresponding to the voltage to ground at the inverter switching frequency based on a fast Fourier analysis algorithm;

calculating a negative sequence component and a zero sequence component of the voltage of the starting end of the three-phase winding under the switching frequency of the inverter according to the voltage phasor;

obtaining a negative sequence voltage ratio and a zero sequence voltage ratio under the switching frequency of the inverter according to the negative sequence component, the zero sequence component and a voltage phasor corresponding to the voltage to earth of the neutral point;

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

2. The method for positioning and detecting the high-resistance grounding fault of the grid-connected photovoltaic transformer winding according to claim 1, wherein the step of judging the phase, 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 comprises the following steps:

judging the phase 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;

and judging the distribution position of the high-resistance grounding fault of the transformer winding along the winding and the fault development degree according to the negative sequence voltage ratio and the zero sequence voltage ratio.

3. The grid-connected photovoltaic transformer winding high resistance ground fault location detection method according to claim 2, wherein the phases of the transformer winding high resistance ground fault include: the transformer winding high-resistance grounding fault occurs in an A-phase winding, the transformer winding high-resistance grounding fault occurs in a B-phase winding and the transformer winding high-resistance grounding fault occurs in a C-phase winding.

4. The method for positioning and detecting the high-resistance ground fault of the grid-connected photovoltaic transformer winding according to claim 3, wherein the step of judging the phase of the high-resistance ground fault of the transformer winding according to the phase difference between the negative sequence voltage ratio and the zero sequence voltage ratio comprises the following steps:

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 high-resistance grounding fault of the transformer winding occurs in an 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 a phase B winding;

and 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.

5. The method for positioning and detecting the high-resistance ground fault of the grid-connected photovoltaic transformer winding according to claim 2, wherein the step of judging the distribution positions of the high-resistance ground fault of the transformer winding along the winding according to the negative sequence voltage ratio and the zero sequence voltage ratio comprises the following steps:

if the absolute value of the ratio of the difference value of the zero sequence voltage ratio and 1 to the negative sequence voltage ratio is within a first threshold range, the position of the transformer winding high-resistance grounding fault close to the starting end of the three-phase winding is determined;

and if the absolute value of the ratio of the difference value of the zero sequence voltage ratio and 1 to the negative sequence voltage ratio is within a second threshold range, the position of the transformer winding high-resistance grounding fault close to the neutral point is determined.

6. The method for positioning and detecting the high-resistance ground fault of the grid-connected photovoltaic transformer winding according to claim 5, wherein the step of judging the fault development degree of the high-resistance ground fault of the transformer winding according to the negative sequence voltage ratio and the zero sequence voltage ratio comprises the following steps:

if the high-resistance grounding fault of the transformer winding is close to the starting end position of the three-phase winding, judging the fault development degree of the high-resistance grounding fault of the transformer winding according to the amplitude of the negative sequence voltage ratio;

and if the high-resistance grounding fault of the transformer winding is close to the neutral point, judging the fault development degree of the high-resistance grounding fault of the transformer winding according to the absolute value of the difference value between the zero-sequence voltage ratio and 1.

7. The utility model provides a high resistance ground fault location detection device of grid-connected photovoltaic transformer winding which characterized in that includes:

the voltage-to-ground measurement module is used for measuring the voltage-to-ground of the starting end and the neutral point of the three-phase winding;

the voltage phasor calculation module is used for calculating a voltage phasor corresponding to the voltage to ground under the switching frequency of the inverter based on a fast Fourier analysis algorithm;

the negative sequence and zero sequence component calculation module is used for calculating the negative sequence component and the zero sequence component of the voltage at the starting end of the three-phase winding under the switching frequency of the inverter according to the voltage phasor;

the negative sequence and zero sequence voltage ratio calculation module is used for obtaining a negative sequence voltage ratio and a zero sequence voltage ratio under the switching frequency of the inverter according to the negative sequence component, the zero sequence component and a voltage phasor corresponding to the voltage to earth of the neutral point;

and the fault comprehensive detection module is used for judging the phase of the high-resistance grounding fault of the transformer winding, the distribution position along the winding and the fault development degree according to the negative sequence voltage ratio and the zero sequence voltage ratio.

8. The grid-connected photovoltaic transformer winding high resistance ground fault location detection device of claim 7, wherein the fault comprehensive detection module is configured to determine a phase of the transformer winding high resistance ground fault, a distribution position along the winding, and a fault development degree according to the negative sequence voltage ratio and the zero sequence voltage ratio, and includes:

judging the phase 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;

and judging the distribution position of the high-resistance grounding fault of the transformer winding along the winding and the fault development degree according to the negative sequence voltage ratio and the zero sequence voltage ratio.

9. The grid-connected photovoltaic transformer winding high resistance ground fault location detection device of claim 7, characterized in that, the phase of the transformer winding high resistance ground fault includes: the transformer winding high-resistance grounding fault occurs in an A-phase winding, the transformer winding high-resistance grounding fault occurs in a B-phase winding, and the transformer winding high-resistance grounding fault occurs in a C-phase winding.

10. The grid-connected photovoltaic transformer winding high resistance ground fault location detection device of claim 9, characterized in that if the absolute value of the phase difference of the negative sequence voltage ratio and the zero sequence voltage ratio is within a first phase difference range, the transformer winding high resistance ground fault occurs in an 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 high-resistance grounding fault of the transformer winding occurs in a phase B winding; and 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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