Method for grounding electrode line fault ranging of direct current transmission system based on complex frequency injection

Abstract

The application discloses a DC power transmission system grounding electrode line fault distance measurement method based on complex frequency injection. Under injection of two groups of different frequency signals, different fault distance sets under two groups of different transition resistances are obtained. According to line parameters, the coherent distance and coherent resistance of the line under injection of two frequency signals are calculated, and different fault distance sets under different injection signal frequencies are listed. Since the actual fault distance corresponding to the actual transition resistance is contained in both sets, accurate fault distance determination can be realized by comparing the fault distance measurement result sets under different signal injections to find the fault distance with the same or similar fault distance measurement result. The application is suitable for grounding electrode line fault distance measurement under different transition resistances, has high measurement precision, high transition resistance tolerance and can obtain a unique fault distance result.

Description

Technical Field

[0001] This invention relates to the field of transmission line protection in DC transmission systems, and specifically to a fault location method for grounding electrode lines. Background Technology

[0002] Fault location in transmission lines is one of the key technologies for line protection in DC transmission systems, while fault location in grounding electrode lines is a challenging aspect of line protection. Grounding electrode lines provide a path for unbalanced current in bipolar operation of DC transmission systems and act as a temporary current path in unipolar operation. Rapid protection and timely fault elimination of grounding electrode lines are crucial for ensuring the normal operation of DC transmission systems.

[0003] After a grounding electrode line fault occurs, in addition to detecting the line fault, it is also required to pinpoint the specific location of the fault, thereby reducing the difficulty of fault repair for operation and maintenance personnel. Grounding electrode lines can be temporarily used as power transmission channels, and the characteristic electrical quantities generated after a fault are similar to those of conventional lines. Fault location methods mainly include traveling wave method and fault analysis method. These methods have certain limitations in application scenarios, so it is necessary to seek diversified fault location methods for grounding electrode lines.

[0004] By actively injecting a high-frequency current signal at the beginning of the grounding electrode line, a stable current can exist in the line even when the grounding electrode is operating in bipolar balance in a DC system, thereby achieving the purpose of detecting the system status. Because the signal frequency injected by the current source is high, its half-wavelength is much shorter than the length of the grounding electrode line. However, to reduce the impact of grounding current on converter stations and other equipment, the length of common grounding electrode lines can be several times the wavelength of the injected signal. Unlike conventional AC transmission lines, the measured impedance of the grounding electrode line exhibits a spiral curve as it changes with fault distance. The impedance of the grounding electrode line is affected by the transition resistance; under different transition resistances, the measured impedance curves will overlap, severely affecting the fault location method based on high-frequency impedance measurement. To address this problem, it is necessary to improve the fault location method for grounding electrode lines based on high-frequency impedance measurement and design a reliable fault location method applicable to different transition resistances. Summary of the Invention

[0005] For the protection of grounding electrode lines under high-frequency signal injection, especially the grounding electrode line fault location method based on high-frequency measurement impedance, the purpose of this invention is to propose a fault location method for grounding electrode lines in DC transmission systems with complex frequency injection. This method utilizes the characteristic that the line measurement impedance distribution differs under different injection signal frequencies to achieve fault distance measurement of grounding electrode lines.

[0006] To achieve the above-mentioned objectives, the present invention utilizes the following technical solution:

[0007] A method for fault location in a DC grounding electrode line based on complex frequency injection includes the following steps:

[0008] Step 1: After a grounding electrode fault occurs, a complex frequency current source actively injects two signals of different frequencies into the line to determine the frequency values ​​of the two injected signals.

[0009] Step 2: Calculate the conventional impedance of the grounding electrode line under the two injected signal frequency values, as shown in the following formula;

[0010]

[0011] Among them, Z c0 R is the zero-sequence impedance of the line. G The matching resistor installed on the grounding electrode side, γ0 is the zero-sequence propagation coefficient of the line, and l is the length of the grounding line;

[0012] Step 3: Select a distance range where a fault occurs, and create two measurement impedances at different transition resistances under different injected signal frequencies, as shown in the following formula:

[0013]

[0014] Among them, R eq =R 1-1 +2R 1-g R 1-1 R is the transition resistance between the two grounding wires. 1-g Here, x represents the grounding resistance, and x represents the fault distance.

[0015] Step 4: Measure the high-frequency voltage and current under steady-state fault conditions using the voltage and current transformers installed at the beginning of the grounding electrode line, and calculate the high-frequency impedance change Z, as shown in the following formula:

[0016]

[0017] in, Z represents the voltage and current signals measured at the measurement point set at the beginning of the grounding electrode line. nor This is the conventional impedance of the grounding electrode line;

[0018] Calculate the magnitude of the corresponding measured impedance change |Z f | and phase angle Φ f (Z), where f represents the frequency of the injected signal;

[0019] Step 5: Measure the amplitude of the impedance transformation at the two injected signal frequency values ​​|Z f | and phase angle Φ f(Z) Substitute the values ​​of the high-frequency impedance change and phase angle corresponding to different transition resistances into the table for comparison, and judge the result based on the following formula:

[0020]

[0021] Among them, A up To measure the upper limit of the amplitude range of the impedance change, A dn To measure the lower bound of the amplitude range of impedance change, This is the upper bound of the phase angle interval for measuring impedance changes. This is the lower bound of the phase angle interval for measuring impedance changes;

[0022] The distance interval that satisfies the condition of equation (4) shall be taken as the distance interval where the fault occurs;

[0023] Step 6: Calculate the fault distance d based on the high-frequency impedance change measured in Step 4 and the boundary phase angle value of the fault occurrence distance interval described in Step 5, as shown in the following formula:

[0024]

[0025] Where, d up This represents the location of the upper limit of the fault distance interval. To measure the difference between the impedance phase angle and the upper limit of the phase angle interval, L sec To measure the length of the distance interval containing the impedance;

[0026] Step 7: Calculate the co-homing distance under the two injected signals based on the line parameters:

[0027]

[0028] Where f is the injected signal frequency, L0 and C0 are the zero-sequence equivalent series inductance and parallel capacitance of the grounding electrode line, respectively, and k is a positive integer;

[0029] Step 8: Compare all elements in the fault distance set generated by the two injection signal frequencies, and select the average value of the two distance elements with the closest fault distance in the fault distance set as the final ranging result.

[0030] Compared with the prior art, the present invention can achieve the following beneficial technical effects:

[0031] It is suitable for line faults with different transition resistances, with high measurement accuracy and high transition resistance tolerance. Attached Figure Description

[0032] Figure 1 This is a schematic diagram showing the impedance measurement results under different transition resistances;

[0033] Figure 2 A schematic diagram of a grounding electrode line protection device for a DC transmission system;

[0034] Figure 3 This is a flowchart of the DC grounding electrode line fault location method based on complex frequency injection of the present invention;

[0035] Figure 4 Figure 4a shows an embodiment of the DC grounding electrode line fault location method based on complex frequency injection of the present invention. (4b) Select a suitable complex frequency injection signal curve. (4c) The amplitude and phase angle of the fault measurement impedance change. (4d) The relationship curves between fault distance and amplitude, and between fault distance and phase angle. (4e) The relationship curve between fault distance and amplitude of impedance change. Detailed Implementation

[0036] The technical solution will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] like Figure 1 As shown, the measured impedance spiral curves overlap under different transition resistances. Under a double-circuit cross-line fault, the fault measured impedance spiral curves for the same grounding electrode line overlap under different transition resistances. Clearly, using a single measured impedance for fault location has inherent limitations.

[0038] like Figure 2 As shown, in the grounding electrode line protection device of the DC transmission system, a wave trap connected to the neutral bus is installed at the input end, and a complex frequency current source signal is injected at the beginning of the grounding electrode line. Two types of wave traps are connected in series at the neutral point to prevent complex frequency injected current source signals from entering the converter station. A lightning protection wire and a grounding circuit connect the pole and the neutral point. An impedance monitoring and protection device, serving as a measurement point, is installed at the beginning of the grounding electrode line. The voltage and current signals measured at this point are... A matching impedance is provided at the polarity to reduce the reflection of the injected signal at the grounding point.

[0039] The distance measurement method based on the amplitude and phase angle characteristics of the high-frequency measured impedance at the head end of the grounding electrode obtained by the impedance monitoring and protection device has certain limitations. The high-frequency measured impedance generated by a high-resistance fault near the grounding electrode line may be the same as that generated by a low-resistance fault at the far end. This will result in multiple values ​​for the final distance measurement result obtained based on a single measured impedance, which is not conducive to timely fault elimination.

[0040] To address the technical problem that "fault location using a single measuring impedance is obviously flawed," this invention proposes a fault location method for DC grounding electrode lines based on complex frequency injection. The theoretical basis of this invention is described in detail below:

[0041] Injecting a high-frequency signal at the beginning of the grounding electrode line in a DC transmission system and calculating the measured impedance deviation at the beginning of the grounding electrode line can solve line protection problems under conditions such as bipolar balanced operation. This measured impedance is affected by the fault distance and can serve as a basis for fault location measurement on the grounding electrode line. This measured impedance is also affected by the transition resistance, and research shows that the measured impedance spiral curves may intersect or even coincide under different transition resistances; that is, a certain fault measured impedance may correspond to different fault distances under different transition resistances.

[0042] This invention proposes the concept of "coordinated resistance," which refers to the phenomenon where, under different transition resistances, the measured impedance spirals partially overlap. These resistances are then called coordinated resistances, and their corresponding spiral curves are said to be mutually coordinated. The invention also introduces the concept of "coordinated distance," which is the fault distance of the coordinated spiral curve corresponding to the first endpoint of the deeper spiral curve under coordinated resistance. The expression for the measured impedance generated when a double-circuit cross-grounding fault occurs in the grounding electrode line is:

[0043]

[0044] Among them, R eq Z is the equivalent impedance associated with the transition resistance. c0 Let Z be the zero-sequence wave impedance of the line, γ0 be the zero-sequence propagation coefficient of the line, and x be the fault distance. Furthermore, the measured impedance Z... mea Related to line parameters.

[0045] In the event of a double-circuit cross-line fault in a grounding electrode line, the fault impedance spiral curves corresponding to different transition resistances may overlap. The relationship between measured impedance, transition resistance, and fault distance is Z when a double-circuit cross-line fault occurs in a grounding electrode line. mea (R ho (x), as shown in the following formula:

[0046] Z mea (R ho ,x)=Z mea (R l-g ,x+x ho )

[0047] Among them, R l-g R is the transition resistance. ho For the same tuning resistor, x ho The synchronization distance; at the original transition resistance R l-g An additional resistor R1 is set on top of the existing structure;

[0048] Combining the above two equations and considering the purely resistive nature of the transition resistor, we obtain the following equation:

[0049]

[0050] The homology distance x ho Substituting into equation (3), the additional resistance R1 can be calculated. It is worth noting that the co-modulation distance and co-modulation resistance calculated by this method are a series of values, indicating that a single high-frequency measurement impedance of the grounding electrode line can correspond to multiple fault distances.

[0051] Based on the above analysis, the homology distance x ho In conjunction with the additional resistance R1, the line zero-sequence propagation coefficient γ0, and the line zero-sequence wave impedance Z c0 The two parameters mentioned above are only related to the frequency of the injected signal when the parameters of the grounding electrode transmission line remain unchanged. The distribution of the co-modulation distance can be changed by changing the frequency of the injected signal.

[0052] Specific details of this invention:

[0053] By using the ranging method based on impedance amplitude and phase angle characteristics under the injection of two sets of signals with different frequencies, different sets of fault distances under different transition resistances can be obtained. Both sets contain the actual fault distances corresponding to the actual transition resistances. Therefore, by comparing the fault ranging result sets under different signal injections, the fault distances with the same or similar fault ranging results can be found, thus achieving accurate fault distance determination.

[0054] like Figure 3 As shown, the present invention provides a method for fault location of a DC grounding electrode line based on complex frequency injection, comprising the following steps:

[0055] Step 1: After a grounding electrode fault occurs, a complex frequency current source actively injects two frequencies of signals into the line. The two frequency values ​​are determined according to the design method of the injection frequency at the beginning of the grounding electrode line. Among them, the least common multiple of the half wavelength of the injected signal should be as large as possible.

[0056] Step 2: Calculate the conventional impedance of the line under the two frequency values ​​injected, according to the measurement impedance expression (1):

[0057]

[0058] Among them, Z c0 R is the zero-sequence impedance of the line. G The matching resistor installed on the grounding electrode side, γ0 is the zero-sequence propagation coefficient of the line, and l is the length of the grounding line;

[0059] Step 3: Select a suitable distance range for the fault to occur, generally recommended to be 1km; create a table of measured impedance change amplitude and phase angle values ​​for different transition resistances at two frequencies, as shown in the following formula:

[0060]

[0061] Among them, Req =R 1-1 +2R 1-g R 1-1 R is the transition resistance between the two grounding wires. 1-g Here, x represents the grounding resistance, and x represents the fault distance.

[0062] Step 4: Measure the high-frequency voltage and current under steady-state fault conditions using the voltage and current transformers installed at the beginning of the grounding electrode line, and calculate the high-frequency impedance change Z, as shown in the following formula:

[0063]

[0064] in, Z represents the voltage and current signals measured at the measurement point set at the beginning of the grounding electrode line. nor This is the conventional impedance of the grounding electrode line;

[0065] The amplitude and phase angle of the high-frequency current signal at the two injected signal frequencies f1 and f2 are calculated using the FFT algorithm, and the amplitude |Z| of the measured impedance change is obtained. f | and phase angle Φ f (Z), where f represents the frequency values ​​of the two injected signals;

[0066] Step 5: Measure the amplitude of the impedance transformation at the two injected signal frequency values ​​|Z f | and phase angle Φ f (Z) Substitute the values ​​of the high-frequency impedance change and phase angle corresponding to different transition resistances into the table for comparison, and judge the result based on the following formula:

[0067]

[0068] Among them, A up These are the upper limits of the amplitude range for the measured impedance change, A. dn These represent the lower bound of the amplitude range for the measured impedance change. These are the upper bounds of the phase angle interval for measuring impedance changes. These are the lower bounds of the phase angle interval for measuring impedance changes;

[0069] The distance interval that satisfies the condition of equation (4) is taken as the distance interval where the fault occurs, which is the interval when the transition resistance is zero.

[0070] Step 6: Calculate the fault distance d based on the high-frequency impedance change measured in Step 4 and the boundary phase angle value of the fault occurrence distance interval described in Step 5, as shown in the following formula:

[0071]

[0072] Where, d up This represents the location of the upper limit of the fault distance interval. To measure the difference between the impedance phase angle and the upper limit of the phase angle interval, L sec To measure the length of the distance interval containing the impedance;

[0073] Step 7: Calculate the co-modulation distance under the two injected signals based on the line parameters, as shown in the following formula:

[0074]

[0075] Where f is the injected signal frequency, L0 and C0 are the zero-sequence equivalent series inductance and parallel capacitance of the grounding electrode line, respectively, and k is a positive integer; using the fault distance d column calculated in step 6, write out the high-resistance fault distance at different frequencies, obtain different fault distances under different transition resistances, and generate the measurement impedance based on the different fault distances;

[0076] Step 8: Due to the inconsistent grounding electrode line characteristics caused by the inconsistent distribution of co-homogeneous distances under different injection frequencies corresponding to the two frequency values, the average value of the two distance elements with the closest fault distances is selected as the final ranging result by comparing the fault distance sets generated by the two injection signal frequencies. See Table 1 for an example.

[0077] Table 1

[0078]

[0079] In this invention, the selection principle for the two frequencies of the injected signal is as follows: the target frequency should be selected such that the half wavelength λ of the two sets of signals is equal. f The least common multiple of / 2 should be large enough, at least higher than the corresponding transition resistance R. ho_max The corresponding maximum cohomology distance x ho_max Where λ f R ho_max x ho_max The results are obtained by equations (7) to (9) respectively.

[0080]

[0081]

[0082]

[0083] Where, k max This represents the maximum value of k that satisfies the condition (homogeneity distance + initial fault distance) < line length.

[0084] Under normal circumstances, R ho_max Preferably, the resistance is below 100Ω.

[0085] The above description is merely an embodiment of this application and is not intended to limit the scope of protection sought by this invention. For those skilled in the art, any modifications, changes, equivalent substitutions, or variations made without departing from the spirit and principles of this invention fall within the scope of protection defined by the appended claims.

Claims

1. A method for fault location on grounding electrode lines in a DC transmission system based on complex frequency injection, characterized in that, Includes the following steps: Step 1: After a grounding electrode fault occurs, a complex frequency current source actively injects two signals of different frequencies into the line to determine the frequency values ​​of the two injected signals. Step 2: Calculate the conventional impedance of the grounding electrode line under the two injected signal frequency values, as shown in the following formula; Among them, Z c0 R is the zero-sequence impedance of the line. G The matching resistor installed on the grounding electrode side, γ0 is the zero-sequence propagation coefficient of the line, and l is the length of the grounding line; Step 3: Select a distance range where a fault occurs, and create two measurement impedances at different transition resistances under different injected signal frequencies, as shown in the following formula: Among them, R eq =R 1-1 +2R 1-g R 1-1 R is the transition resistance between the two grounding wires. 1-g Here, x represents the grounding resistance, and x represents the fault distance. Step 4: Measure the high-frequency voltage and current under steady-state fault conditions using the voltage and current transformers installed at the beginning of the grounding electrode line, and calculate the high-frequency impedance change Z, as shown in the following formula: in, Z represents the voltage and current signals measured at the measurement point set at the beginning of the grounding electrode line. nor This is the conventional impedance of the grounding electrode line; Calculate the magnitude of the corresponding measured impedance change |Z f | and phase angle Φ f (Z), where f represents the frequency of the injected signal; Step 5: Measure the amplitude of the impedance transformation at the two injected signal frequency values ​​|Z f | and phase angle Φ f (Z) Substitute the values ​​of the high-frequency impedance change and phase angle corresponding to different transition resistances into the table for comparison, and judge the result based on the following formula: Among them, A up To measure the upper limit of the amplitude range of the impedance change, A dn To measure the lower bound of the amplitude range of impedance change, This is the upper bound of the phase angle interval for measuring impedance changes. This is the lower bound of the phase angle interval for measuring impedance changes; The distance interval that satisfies the condition of equation (4) shall be taken as the distance interval where the fault occurs; Step 6: Calculate the fault distance d based on the high-frequency impedance change measured in Step 4 and the boundary phase angle value of the fault occurrence distance interval described in Step 5, as shown in the following formula: Where, d up This represents the location of the upper limit of the fault distance interval. To measure the difference between the impedance phase angle and the upper limit of the phase angle interval, L sec To measure the length of the distance interval containing the impedance; Step 7: Calculate the co-homogeneity distance under the two injected signals based on the line parameters: Where f is the frequency of the injected signal, L0 and C0 are the zero-sequence equivalent series inductance and parallel capacitance of the grounding electrode line, respectively, and k is a positive integer; Step 8: Compare all elements in the fault distance set generated by the two injection signal frequencies, and select the average value of the two distance elements with the closest fault distance in the fault distance set as the final ranging result.

2. The method for fault location of grounding electrode lines in a DC transmission system based on complex frequency injection according to claim 1, characterized in that, The selection of the injection signal frequency should satisfy the condition that the half wavelength λ of the two sets of injection signals is equal. f The least common multiple of / 2 is at least higher than the corresponding transition resistance R. ho_max The corresponding maximum cohomology distance x ho_max ; The wavelengths λ of the two sets of injected signals f Transition resistance R ho_max x ho_max The following equations (7) to (9) are respectively: Where, k max This represents the maximum value of k that satisfies the condition (homogeneity distance + initial fault distance) < line length.

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