A single-phase grounding fault positioning method for a wind farm based on zero sequence power balance

Abstract

The application discloses a kind of single-phase grounding fault positioning methods of wind farm based on zero sequence power balance, comprising: before and after wind farm grounding fault, the power of net is measured respectively in the low voltage side of main transformer;According to the principle of zero sequence power balance, single-phase grounding fault transition resistance is obtained;According to the transition resistance of grounding fault, zero sequence voltage and zero sequence current, the distance of single-phase grounding fault point and bus of collection line is obtained.The single-phase grounding fault transition resistance of single-phase grounding fault of collection line is calculated using the change of zero sequence power before and after fault, and then the distance of single-phase grounding fault point and bus of collection line is obtained, the positioning of single-phase grounding fault is realized, the problem that single-phase grounding fault of overhead line of wind farm collection line occurs frequently, fault point positioning is difficult, and power supply recovery time is long is solved, and the utilization rate of wind power is improved.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, specifically relating to a method for locating single-phase grounding faults in wind farms based on zero-sequence power balance. Background Technology

[0002] Wind farm collector lines are mostly overhead lines, and the harsh environment leads to frequent short-circuit faults, with single-phase grounding faults accounting for about 80% and having the highest probability of occurrence. The neutral point of the wind farm collector system generally uses low-resistance grounding. When a single-phase grounding short-circuit fault occurs in the collector line, the short-circuit current is small. In this case, the zero-sequence current protection installed at the beginning of the collector line will trip and disconnect the grounding fault after a short delay. At this point, it is necessary to locate the fault location on the collector line to restore power supply promptly and improve wind power utilization.

[0003] Fault location methods can be classified into impedance method and traveling wave method according to the location principle, and into single-end measurement method and two-end measurement method according to the information source required for location.

[0004] The traveling wave method primarily utilizes the detection of the traveling wave front and the calculation of the wave velocity to determine the time of fault occurrence and the location of the fault point. While the traveling wave method and its improved versions have shown good results in fault location for transmission lines and distribution networks, wind farm lines are typically 10–20 km long. Due to the difficulty in capturing transient fault signals, especially in multi-branch mixed networks with joints where reflection and refraction are severe, the traveling wave method often results in significant location errors. Furthermore, because wind farm collector lines have numerous branches with intervals of only about 100 meters, the reflection and refraction of transient traveling waves generated after a fault at each branch point are complex, making the use of the traveling wave method for fault location in wind farm collector lines quite challenging.

[0005] The impedance method calculates the total impedance of the fault circuit using voltage and current data obtained at measurement points after a fault occurs, and then determines the fault distance. The impedance method utilizes the property that the line impedance at the observation point is proportional to the distance to the fault point; by calculating the line impedance, the distance from the observation point to the fault point is obtained, thus achieving distance measurement. The impedance method has advantages such as fewer measurement points, low equipment requirements, and good economy. However, the traditional impedance method is greatly affected by transition resistance, and the presence of many branches on the collector line leads to larger errors. Summary of the Invention

[0006] The purpose of this invention is to address the problems of high frequency of single-phase grounding faults in current wind farm collector lines, difficulty in fault location, and long power restoration time, and to propose a single-phase grounding fault location method for wind farms based on zero-sequence power balance.

[0007] This invention is achieved using the following technical solution:

[0008] A method for locating single-phase grounding faults in wind farms based on zero-sequence power balance includes:

[0009] Before and after a grounding fault in a wind farm, the on-grid power of the low-voltage side of the main transformer is measured. Based on the zero-sequence power balance principle, the transition resistance of a single-phase grounding fault is calculated. Based on the grounding fault transition resistance, zero-sequence voltage, and zero-sequence current, the distance between the single-phase grounding fault point on the collector line and the busbar is calculated.

[0010] A further improvement of the present invention is that the method specifically includes the following steps:

[0011] 1) Before the fault, the on-grid power on the low-voltage side of the main transformer was measured to be P0;

[0012] 2) When a single-phase ground fault occurs in the collector line of the wind farm through the transition resistor Rg, the on-grid power on the low-voltage side of the main transformer is measured as P1.

[0013] 3) The neutral point grounding resistance of the wind farm's collector system is Rn, and the zero-sequence impedance of the grounding transformer is Xn. When a single-phase ground fault occurs in the collector line, the measured current flowing through the neutral point grounding resistance is... Its modulus is I0, and the zero-sequence current flowing through the fault collector is measured as follows: Its modulus is I l0 ;

[0014] 4) Solve for the single-phase ground fault transition resistance R. g ;

[0015] 5) After a single-phase ground fault occurs in the collector wire, the distance l between the location of the single-phase ground fault in the collector wire and the busbar is... K .

[0016] A further improvement of this invention is that, in step 4), the single-phase ground fault transition resistance R is calculated based on the zero-sequence power balance principle. g .

[0017] A further improvement of this invention is that, in step 4), the zero-sequence power balance principle is as follows:

[0018] A further improvement of the present invention is that, in step 4), the single-phase ground fault transition resistor...

[0019] A further improvement of the present invention is that, in step 5),

[0020] A further improvement of the present invention is that, The measured zero-sequence voltage of the bus is denoted as .

[0021] A further improvement of the present invention is that, This is the zero-sequence impedance per unit length of the collector wire.

[0022] The present invention has at least the following beneficial technical effects:

[0023] 1. The present invention proposes a method for locating single-phase grounding faults in wind farms based on zero-sequence power balance. This method is applicable to the location of single-phase grounding faults in wind farm collection systems grounded through transition resistors. By calculating the power difference between the active power on the low-voltage side of the step-up transformer before and after the fault, the zero-sequence power after the fault is obtained, and then the grounding fault transition resistor is obtained. This eliminates the influence of the transition resistor on fault location and improves the accuracy of fault location.

[0024] 2. The method proposed in this invention is a single-phase grounding fault location method for wind farms based on zero-sequence power balance. It is not affected by the branch current in the collector system because the wind turbine connected to the collector branch does not provide zero-sequence current, and the zero-sequence current does not flow through the circuit of the wind turbine during normal operation. Therefore, the zero-sequence current measured at the measurement point at the bus is equal to the zero-sequence current of the entire collector line, thereby eliminating the influence of the collector branch on fault location.

[0025] Compared with existing technologies, the present invention has the following significant advantages:

[0026] 1. This invention proposes a method for locating single-phase grounding faults in wind farms based on zero-sequence power balance. It cleverly utilizes the characteristic of zero-sequence power balancing before and after a fault to calculate the transition resistance of the single-phase grounding fault, thereby improving the accuracy of fault location. According to "A Method for Locating Single-Phase Grounding Faults in Wind Farm Collector Lines Based on Segmented Impedance Matching" (Zhai Yujia), at the initial moment of a collector line fault, since the wind turbine itself is not faulty and the wind speed and other operating conditions have not changed, the wind turbine's speed control system cannot change in time, so the active power remains constant. According to "Energy Metering Scheme Based on Positive-Sequence Active Power under Negative-Sequence Conditions" (Xu Xin), active power is the sum of the active power of each phase, and is equal to the sum of the positive-sequence, negative-sequence, and zero-sequence active power. Because the low-voltage side of the step-up transformer is connected in a delta configuration, no zero-sequence power passes through; that is, only positive-sequence and negative-sequence power are present. Therefore, by calculating the power difference of the active power on the low-voltage side of the step-up transformer before and after the fault, the zero-sequence power after the fault is obtained.

[0027] 2. The wind farm single-phase grounding fault location method proposed in this invention based on zero-sequence power balance requires fewer measurement points, has low equipment requirements, is economical, and is easy to apply in the field. The method requires fewer parameters to be measured, and the fault quantity required for single-phase grounding fault location can be obtained by using the fault recorder equipped in the wind farm. Attached Figure Description

[0028] Figure 1 This is a flowchart of the steps of the method of the present invention. Detailed Implementation

[0029] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] like Figure 1 As shown, the present invention provides a method for locating single-phase grounding faults in wind farms based on zero-sequence power balance, which specifically includes the following steps:

[0031] 1) Before the fault, the on-grid power on the low-voltage side of the main transformer was measured to be P0;

[0032] 2) When a single-phase ground fault occurs in the collector line of the wind farm through the transition resistor Rg, the on-grid power on the low-voltage side of the main transformer is measured as P1.

[0033] 3) The neutral point grounding resistance of the wind farm's collector system is Rn, and the zero-sequence impedance of the grounding transformer is Xn. When a single-phase ground fault occurs in the collector line, the measured current flowing through the neutral point grounding resistance is... Its modulus is I0, and the zero-sequence current flowing through the fault collector is measured as follows: Its modulus is I l0 ;

[0034] 4) Based on the zero-sequence power balance principle The solution yields the single-phase ground fault transition resistance as follows:

[0035]

[0036] 5) After a single-phase ground fault occurs in the collector line, the zero-sequence voltage of the busbar is measured as follows: The zero-sequence impedance per unit length of the collector wire is The distance between the location of a single-phase ground fault in the collector wire and the busbar is:

[0037]

[0038] Example:

[0039] Step S11: At a certain wind farm, before the fault, the on-grid power of the low-voltage side of the main transformer was measured to be P0, 68.42MW.

[0040] When a single-phase ground fault occurs in the collector line of the wind farm, which is grounded through the transition resistor Rg, the on-grid power on the low-voltage side of the main transformer is measured to be P1, 63.85MW.

[0041] The neutral point grounding resistor in the wind farm's collector system has a resistance value of Rn, which is 71.3Ω. The zero-sequence impedance of the grounding transformer is 72.83Ω. When a single-phase ground fault occurs in the collector line, the measured current flowing through the neutral point grounding resistor is... Its modulus I0 is 239A, and the measured zero-sequence current flowing through the fault collector is... Its modulus I l0 It is 230A;

[0042] Step S12, based on the zero-sequence power balance principle The transition resistance of a single-phase ground fault can be calculated as follows:

[0043] Step S13: After a single-phase ground fault occurs in the collector line, the zero-sequence voltage of the bus is measured as follows: The zero-sequence current flowing through the faulty collector is measured as follows: The zero-sequence impedance per unit length of the collector wire is The distance from the busbar to the location of a single-phase ground fault in the collector wire is:

[0044]

[0045] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for locating single-phase grounding faults in wind farms based on zero-sequence power balance, characterized in that, include: Before and after a grounding fault at a wind farm, the grid-connected power on the low-voltage side of the main transformer is measured. Based on the zero-sequence power balance principle, the transition resistance of a single-phase grounding fault is calculated. The distance between the single-phase ground fault point on the collector line and the busbar can be calculated based on the ground fault transition resistance, zero-sequence voltage, and zero-sequence current. This method specifically includes the following steps: 1) Before the fault, the on-grid power on the low-voltage side of the main transformer was measured to be P0; 2) When a single-phase ground fault occurs in the collector line of the wind farm through the transition resistor Rg, the on-grid power on the low-voltage side of the main transformer is measured as P1. 3) The neutral point grounding resistance of the wind farm's collector system is Rn, and the zero-sequence impedance of the grounding transformer is Xn. When a single-phase ground fault occurs in the collector line, the measured current flowing through the neutral point grounding resistance is: Its modulus is The zero-sequence current flowing through the fault collector is measured as follows: Its modulus is ; 4) Solve for the single-phase ground fault transition resistance. Based on the zero-sequence power balance principle, the transition resistance of a single-phase ground fault is calculated. The zero-sequence power balance principle is ; 5) After a single-phase ground fault occurs in the collector line, the distance between the location of the single-phase ground fault in the collector line and the busbar is... .

2. The method for locating single-phase grounding faults in wind farms based on zero-sequence power balance according to claim 1, characterized in that, In step 4), the single-phase ground fault transition resistor .

3. The method for locating single-phase grounding faults in wind farms based on zero-sequence power balance according to claim 1, characterized in that, In step 5), .

4. The method for locating single-phase grounding faults in wind farms based on zero-sequence power balance according to claim 3, characterized in that, The measured zero-sequence voltage of the bus is denoted as .

5. The method for locating single-phase grounding faults in wind farms based on zero-sequence power balance according to claim 3, characterized in that, This is the zero-sequence impedance per unit length of the collector wire.

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