Line protection phase selection method and relay protection equipment

Abstract

The invention relates to a line protection phase selection method and relay protection equipment, and belongs to the field of power system relay protection, and the method comprises the steps: respectively extracting a high-frequency current component in a three-phase current signal, and calculating a zero-sequence current integral value, and a current modulus maximum value and a current integral value of each phase based on the three-phase high-frequency current component; when only the maximum value of the first target phase current modulus in the three phases is smaller than a preset current constant value used for determining the single-phase fault or the inter-phase fault of the line, determining the fault of the line as the single-phase fault or the inter-phase fault and the fault phase thereof according to the first target phase current modulus; otherwise, judging whether the zero-sequence current integral value is smaller than a preset zero-sequence current constant value used for determining the three-phase fault of the line or not; if yes, determining that the fault of the line is a three-phase fault; and if not, determining that the fault of the line is an interphase grounding fault, and determining the second target phase with the minimum integral value in the three-phase current integral values as a non-fault phase and the other two phases as fault phases, thereby improving the rapidity and accuracy of phase selection.

Description

Technical Field

[0001] The invention relates to a line protection phase selection method and relay protection equipment, belonging to the field of power system relay protection. Background Art

[0002] After a high-voltage transmission line fails, rapid and accurate phase selection has positive significance for ensuring the safety of the transmission line and the stability of the power system.

[0003] In my country, due to system safety and stability requirements, high-voltage or ultra-high-voltage transmission lines of 220 kV and above generally require phase-by-phase tripping when faults occur. Therefore, high-voltage line protection devices must be able to correctly select the fault phase. Furthermore, correct operation of certain protection elements, such as distance elements and directional elements based on different principles, also requires accurate determination of the fault phase. Therefore, phase selection elements have become a crucial component of high-voltage line protection. Accurate and rapid determination of the fault phase after a high-voltage transmission line fault directly impacts the economic and social benefits of power system operation and plays a significant role in ensuring transmission line safety and power system stability.

[0004] In the existing technology, the phase selection principle based on power frequency is widely used. Although the phase selection performance is stable, when a fault occurs, the voltage and current contain a large amount of harmonics, which makes filtering more difficult and reduces the phase selection accuracy. Summary of the Invention

[0005] The purpose of the present invention is to provide a line protection phase selection method and a relay protection device to solve the problem of low fault detection accuracy.

[0006] To achieve the above object, the present invention proposes a phase selection method for line protection, comprising the following steps:

[0007] 1) In response to a line fault, extract high-frequency current components from the three-phase current signals respectively, and calculate the zero-sequence current integral value, as well as the current modulus maximum value and current integral value of each phase based on the three-phase high-frequency current components;

[0008] 2) When only the maximum value of the current modulus of the first target phase among the three phases is less than the preset current constant value for determining a single-phase fault or an interphase fault in the line, the line fault is determined to be a single-phase fault or an interphase fault and its faulty phase based on the current modulus of the first target phase; otherwise,

[0009] 3) Determine whether the zero-sequence current integral value is less than a preset zero-sequence current constant value for determining a three-phase line fault; if so, determine that the line fault is a three-phase fault; if not, determine that the line fault is a phase-to-ground fault, and determine the second target phase with the smallest integral value among the three-phase current integral values ​​as the non-fault phase, and the remaining two phases as the fault phases.

[0010] Furthermore, the current modulus includes an α-mode current and a β-mode current; wherein, based on the first target phase current modulus, the line fault is determined to be a single-phase fault or an interphase fault and its fault phase by the following method:

[0011] When the α modulus current of the first target phase current modulus is less than the current set value, it is determined that the line fault is an interphase fault, the first target phase is a non-fault phase, and the other two phases are fault phases;

[0012] When the β-mode current of the first target phase current modulus is less than the current set value, it is determined that the line fault is a single-phase fault and the first target phase is the fault phase.

[0013] Furthermore, the high-frequency current component in the three-phase current signal is extracted by the following formula:

[0014]

[0015] Where x is the sampled current data; k is the sampling number; y is the high-frequency component output by the sampled current data after passing through the high-pass filter; b j is the filter coefficient.

[0016] Further, the filter coefficients are 0.0043, 0.0058, 0.0069, 0.0047, -0.0029, -0.0172, -0.0380, -0.0635, -0.0904, -0.1142, -0.1307, 0.8635, -0.1307, -0.1142, -0.0904, -0.0635, -0.0380, -0.0172, -0.0029, 0.0047, 0.0069, 0.0058, and 0.0043.

[0017] Furthermore, the zero-sequence current integral and the current integral value are calculated by the following formula:

[0018]

[0019] Among them, when calculating the zero-sequence current integral, is the zero-sequence current; when calculating the phase current integral, is the phase current; k is the sampling number; N is the number of sampling points in each power frequency cycle.

[0020] Furthermore, the maximum value of the current modulus is calculated by the following method:

[0021] Perform phase modulus transformation on the three-phase high-frequency current components to obtain the three-phase current modulus; determine the maximum value of the current modulus of each phase in the first time period at the beginning of the fault as the current modulus maximum value of the corresponding phase.

[0022] Furthermore, the current constant used to determine whether a line has a single-phase fault or an interphase fault is 1.5 times the absolute value of the instantaneous current value in the power frequency cycle before the line fault occurs.

[0023] Furthermore, the zero-sequence current constant is the minimum integral value among the three-phase current integral values ​​of the power frequency cycle before the line fault occurs.

[0024] On the other hand, the present invention further proposes a relay protection device, comprising a processor, wherein the processor is configured to execute the above-mentioned line protection phase selection method.

[0025] The beneficial effects of the present invention are as follows: in response to a line fault, high-frequency current components in the three-phase current signals are extracted respectively, and based on the three-phase high-frequency current components, the zero-sequence current integral value, as well as the current modulus maximum value and the current integral value of each phase are calculated; when only the current modulus maximum value of the first target phase in the three phases is less than the preset current constant value for determining a single-phase fault or a phase-to-phase fault of the line, the line fault is determined to be a single-phase fault or a phase-to-phase fault and its fault phase according to the first target phase current modulus; otherwise, it is judged whether the zero-sequence current integral value is less than the preset zero-sequence current constant value for determining a three-phase fault of the line; if so, the line fault is determined to be a three-phase fault; if not, the line fault is determined to be a phase-to-ground fault, and the second target phase with the smallest integral value in the three-phase current integral value is determined as the non-fault phase, and the remaining two phases are fault phases, so as to realize rapid determination of the fault phase of a single-phase fault or a phase-to-phase fault, or rapid determination of the fault phase of a three-phase fault and a phase-to-ground fault, while taking into account both the rapidity and accuracy of phase selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of a line protection phase selection method proposed by the present invention in practical application;

[0027] Figure 2 This is a schematic diagram of current fluctuations of the three-phase current modulus when a BN fault occurs in a line in an actual application scenario of a line protection phase selection method proposed by the present invention;

[0028] Figure 3 This is a schematic diagram of current fluctuations of the three-phase current modulus when a CA fault occurs in a line in an actual application scenario of a line protection phase selection method proposed by the invention;

[0029] Figure 4 This is a schematic diagram of fluctuations in the three-phase current modulus, each phase current integral, and zero-sequence current integral calculated by a line protection phase selection method proposed in the present invention when an ABCN fault occurs in a line in an actual application scenario;

[0030] Figure 5This is a schematic diagram of fluctuations in calculating the three-phase current modulus, each phase current integral, and zero-sequence current integral when an ABCN fault occurs in a line protection phase selection method proposed in the present invention in an actual application scenario;

[0031] Figure 6 This is a schematic diagram of the amplitude response of a high-pass filter in an actual application scenario of a line protection phase selection method proposed in the present invention. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and implementation methods.

[0033] The inventive concept of the present invention is: in order to circumvent the problem in the prior art that when a fault occurs, the phase selection accuracy is reduced due to the large amount of harmonic content in the current and voltage, the present invention introduces high-order harmonics to perform phase selection discrimination, and after the fault, the fault phase difference in the case of single-phase and inter-phase faults is quickly distinguished by calculation, and the fault phase difference of three-phase and inter-phase ground faults is calculated by zero-sequence integral current and phase integral current, taking into account both the rapidity and accuracy of phase selection.

[0034] Method Specific Implementation 1:

[0035] On the one hand, the present invention proposes a phase selection method for line protection, which includes steps S11, S12 and S13. Specifically:

[0036] Step S11 , in response to a line fault, extract high-frequency current components from the three-phase current signals respectively, and calculate the zero-sequence current integral value, as well as the current modulus maximum value and current integral value of each phase based on the three-phase high-frequency current components.

[0037] Here, in actual application scenarios, after a fault occurs, the current is passed through a high-pass filter to obtain the high-frequency component in the current signal. The high-pass filter can be expressed by the following formula:

[0038]

[0039] Where x is the sampled current data; k is the sampling number; y is the high-frequency component output by the sampled current data after passing through the high-pass filter; b jAre the filter coefficients, and the filter coefficients are 0.0043, 0.0058, 0.0069, 0.0047, -0.0029, -0.0172, -0.0380, -0.0635, -0.0904, -0.1142, -0.1307, 0.8635, -0.1307, -0.1142, -0.0904, -0.0635, -0.0380, -0.0172, -0.0029, 0.0047, 0.0069, 0.0058, and 0.0043.

[0040] Based on the three-phase high-frequency current components, the zero-sequence current integral value and the current integral value of each phase are calculated using the following formula:

[0041]

[0042] in, is the phase current or zero-sequence current (when calculating the zero-sequence current integral, is the zero-sequence current; when calculating the phase current integral, = (phase current); k is the sampling number; and N is the number of sampling points per power frequency cycle. Furthermore, before calculating the zero-sequence current integral, the three-phase high-frequency current components are summed to form the zero-sequence current, which is then calculated using the above formula.

[0043] The current modulus is obtained by performing phase modulus transformation on the current. In the present invention, it is preferred to perform phase modulus transformation by Clarke transformation to obtain the α modulus and β modulus of phase A, phase B, and phase C. Taking phase A as an example, the transformation matrix is:

[0044]

[0045] Among them, I A α R is the α modulus of phase A current; I A β R is the β modulus of phase A current; I A0 is the A phase current 0 modulus; I A is the A phase current; I B is the B phase current; I C is the C-phase current. Simultaneously, when calculating the maximum three-phase current modulus, phase modulus transformation is performed on the three-phase high-frequency current components to obtain the three-phase current modulus. The maximum value of the current modulus of each phase within the first initial time period of the fault is determined as the current modulus maximum value of the corresponding phase. In the present invention, the maximum current modulus is obtained by taking the maximum absolute value of the instantaneous current of each phase within the first initial time period. Preferably, the first initial time period is 2 ms.

[0046] Step S12: When only the maximum value of the current modulus of the first target phase among the three phases is smaller than the preset current constant for determining a single-phase fault or a phase-to-phase fault of the line, the line fault is determined to be a single-phase fault or a phase-to-phase fault and its faulty phase based on the current modulus of the first target phase; herein, in the present invention, the current constant preferably used to determine a single-phase fault or a phase-to-phase fault of the line is 1.5 times the absolute value of the instantaneous current value of the previous power frequency cycle before the fault occurs in the line.

[0047] Otherwise (i.e., the current modulus maximum value of not only one phase among the three phases is less than the preset current constant for determining a single-phase fault or a phase-to-phase fault of the line), execute step S13 to determine whether the zero-sequence current integral value is less than the preset zero-sequence current constant for determining a three-phase fault of the line; if so, determine that the line fault is a three-phase fault; if not, determine that the line fault is a phase-to-ground fault, and determine the second target phase with the smallest integral value among the three-phase current integral values ​​as the non-fault phase, and the remaining two phases as the fault phases; it should be noted that the zero-sequence current constant is preferably the minimum integral value among the three-phase current integral values ​​of the previous power frequency cycle when the line fault occurs.

[0048] Through the above steps S11 to S13, line protection phase selection is realized based on high-frequency current components, and while the phase selection accuracy is improved, the short window of the first time period at the beginning of the fault is used to quickly distinguish single-phase and inter-phase faults; the zero-sequence current integral and the three-phase current integral are used to quickly distinguish three-phase and inter-phase ground faults, thereby achieving the speed and accuracy of phase selection and improving the protection of relays and lines.

[0049] Method Specific Implementation Method 2:

[0050] Following the above implementation of the present invention, the current modulus includes the α-mode current and the β-mode current. In step S12, based on the first target phase current modulus, the following method is used to determine whether the line fault is a single-phase fault or an interphase fault and the fault phase thereof:

[0051] When the α modulus current of the first target phase current modulus is less than the current constant, it is determined that the line fault is an interphase fault, the first target phase is a non-fault phase, and the other two phases are fault phases.

[0052] When the β-mode current of the first target phase current modulus is less than the current set value, it is determined that the line fault is a single-phase fault and the first target phase is the fault phase.

[0053] like Figure 1 FIG. 1 is a flow chart of a line protection phase selection method proposed by the present invention in practical application, wherein 1) after a fault occurs, the current is passed through a high-pass filter to obtain the high-frequency component in the current signal. The high-pass filter is in the form of: Where x is the sampled data, k is the sampled sequence number, and y is the output data after the sampled data passes through the high-pass filter. 22 They are 0.0043, 0.0058, 0.0069, 0.0047, -0.0029, -0.0172, -0.0380, -0.0635, -0.0904, -0.1142, -0.1307, 0.8635, -0.1307, -0.1142, -0.0904, -0.0635, -0.0380, -0.0172, -0.0029, 0.0047, 0.0069, 0.0058, and 0.0043 respectively.

[0054] 2) Perform phase modulus transformation on the three-phase current after high-pass filtering to obtain the three-phase current modulus and calculate the maximum value of the current modulus in the first time period of the initial fault. Phase modulus transformation is Clarke transformation, and the α modulus and β modulus of the A, B, and C phase currents are calculated respectively, that is, I Aα , I Aβ , I Bα , I Bβ , I Cα , I Cβ The maximum value of the current modulus is calculated by performing phase modulus transformation on the maximum absolute value of the instantaneous value of the current sampling point 2ms after the fault.

[0055] 3) Integrate the absolute values ​​of the instantaneous phase currents after high-pass filtering to obtain the integral value of the phase current. Add the instantaneous values ​​of the three-phase currents after high-pass filtering to obtain the zero-sequence current, and calculate the zero-sequence current according to the formula to obtain the zero-sequence current integral value.

[0056] 4) Determine whether it is a single-phase fault or an interphase fault based on the extreme value of the current modulus. Specifically, compare the maximum current modulus value with the current constant value (i.e., the current constant value preset for determining a single-phase fault or an interphase fault in a line) to determine whether there is one and only one phase whose current modulus maximum value is less than the current constant value. Specifically, the α modulus and β modulus of the currents of phases A, B, and C (i.e., I Aα , I Aβ , I Bα , I Bβ , I Cα , I Cβ ) has only one maximum current modulus value less than the set current value. If the modulus is smaller than the set current value, it indicates a single-phase fault, and the phase with the β modulus is the faulty phase. If the modulus is smaller than the set current value, it indicates an interphase fault, and the phase with the α modulus is the non-faulty phase. The remaining two phases are faulty phases. The set current value is 1.5 times the absolute value of the instantaneous current during the power frequency cycle preceding the fault.

[0057] 5) If the single-phase fault and inter-phase fault conditions are not met (that is, the current modulus maximum value of only one phase is less than the current fixed value, that is to say: the current modulus maximum value of two phases / three phases in the three phases is less than the current fixed value, or the current modulus maximum value of no phase is less than the current fixed value), determine whether it is a three-phase fault based on the zero-sequence current integral value, and compare the zero-sequence current integral value with the zero-sequence current fixed value (the zero-sequence current fixed value is the smallest integral value among the three-phase current integral values ​​in the power frequency cycle before the fault). When the zero-sequence current integral value is less than the zero-sequence current fixed value, the line fault is a three-phase fault.

[0058] 6) If the conditions do not hold that the maximum value of the α- and β-moduli of the currents in phases A, B, and C is less than the set current value, and the zero-sequence current integral is greater than or equal to the set zero-sequence current value, then the line fault is a phase-to-phase ground fault. Calculate the maximum instantaneous values ​​of the three-phase current integrals within one power frequency cycle after the fault. Compare these maximum instantaneous values. The phase with the smallest instantaneous maximum value (i.e., the phase with the smallest instantaneous maximum value of the three-phase current integrals) is the unfaulted phase, and the other two phases are faulty phases.

[0059] As can be seen, to address the difficulty in extracting the power frequency signal after a line fault, the present invention passes the current through a high-pass filter and uses the high-frequency components in the current signal for phase selection calculations. Phase modulus transformation is performed on the three-phase current to obtain the current modulus. The maximum value of the current modulus within a period of time after the fault is initially detected to determine whether it is a single-phase fault or an interphase fault, and to determine the fault phase. If the conditions for single-phase fault and interphase fault are not met, the zero-sequence current integral value is used to determine whether it is a three-phase fault. If none of the above conditions are met, it is a phase-to-phase ground fault, and the fault phase is determined based on the current integral.

[0060] Method Specific Implementation 3:

[0061] For ease of understanding, a line protection phase selection method proposed in the present invention is described below with reference to actual application data.

[0062] like Figure 2 As shown in the figure, it is a schematic diagram of the current fluctuation of the three-phase current modulus when a BN fault occurs in the line in an actual application scenario of a line protection phase selection method proposed by the present invention. Among them, the calculation of the α modulus and β modulus of the current modulus of phases A, B, and C shows that the maximum value of the β modulus of phase B is smaller than the current constant value, and the phase difference of the β modulus is the fault phase, that is, the fault phase is phase B, which is consistent with the actual fault phase difference.

[0063] like Figure 3Figure 2 shows the current fluctuations of the three-phase current modulus during a CA fault in a practical application scenario of the proposed line protection phase selection method. The calculation of the α and β moduli of the current moduli for phases A, B, and C shows that the maximum α modulus of phase B is less than the set current value, indicating an interphase fault. Phase B is the non-fault phase, while the remaining two phases, A and C, are faulty. The phase selection result is consistent with the actual fault phase.

[0064] like Figure 4 Figure 2 shows the fluctuations in the three-phase current moduli, phase current integrals, and zero-sequence current integrals calculated using the proposed line protection phase selection method in an actual application scenario when an ABCN fault occurs. The calculation of the α and β moduli for phases A, B, and C shows that the condition that only one modulus is less than the set current value is not met, indicating a three-phase or interphase ground fault. The zero-sequence current is much less than the set zero-sequence current value, meeting the three-phase fault condition. The phase selection result shows that phases ABC are identical to the actual fault phase.

[0065] like Figure 5 The figure shows a fluctuation diagram of the three-phase current modulus, the current integral of each phase, and the zero-sequence current integral when an ABCN fault occurs in the line in an actual application scenario using a line protection phase selection method proposed by the present invention. The calculation of the α modulus and β modulus of the A, B, and C phase currents shows that the condition that only one modulus is less than the current constant is not met, indicating a three-phase or phase-to-phase ground fault. The zero-sequence current is greater than the zero-sequence current constant, which does not meet the three-phase fault condition and indicates a phase-to-phase ground fault. The current integral of phase B in the three-phase current integral is much smaller than that of phases A and C, indicating a CAN fault. The phase selection result is the same as the actual fault phase.

[0066] At the same time, if Figure 6The figure shows a schematic diagram of the amplitude response of a high-pass filter in an actual application scenario of a line protection phase selection method proposed by the present invention. The figure corresponds to passing the current through a high-pass filter to obtain the high-frequency component in the current signal (using the 23 filter coefficients of the high-frequency filter to filter out the low-frequency component in the current signal). The horizontal axis of the figure is the frequency unit in Hz, and the vertical axis is the amplitude response (the ratio of output to input. Since the output and output units are the same, the units are also canceled after taking the ratio, so the unit is 1). According to the curve in the figure, assuming that the amplitude response corresponding to the horizontal axis of 50Hz is 0.01, it means: if the input frequency is a signal of 50Hz and the amplitude is 1, the output signal frequency is 50Hz and the amplitude is 0.01. According to the curve in the figure, assuming that the amplitude response corresponding to the horizontal axis of 2000Hz is 1, it means: if the input frequency is a signal of 2000Hz and the amplitude is 1, the output signal frequency is 2000Hz and the amplitude is 1. In other words, the given filter can filter out low-frequency signals in the input signal and retain only high-frequency signals in the output, thereby extracting the high-frequency components in the current signal.

[0067] Method Specific Implementation Method 4:

[0068] For example, after a fault occurs, the current is first passed through a high-pass filter to obtain the high-frequency current component in the current signal. Based on the three-phase high-frequency current components, a phase modulus transformation is performed on each phase current to obtain the current modulus. The maximum current modulus is calculated for the initial period of time after the fault. Next, the absolute value of the instantaneous phase current after the high-pass filter is integrated to obtain the phase current integral value. The instantaneous values ​​of the three-phase current are added together to obtain the zero-sequence current, and the zero-sequence current integral value is calculated.

[0069] Secondly, the extreme value of the current modulus is used to determine whether it is a single-phase fault or an interphase fault, and the fault phase is determined. Specifically, assuming that the maximum value of the α modulus and β modulus of the currents of phases A, B, and C is less than the current constant, if the β modulus is less than the current constant, it is a single-phase fault, and the phase of the β modulus is the fault phase. If the α modulus is less than the current constant, it is an interphase fault, and the phase of the α modulus is the non-fault phase, while the remaining two phases are fault phases. The current constant is 1.5 times the absolute value of the instantaneous value of the power frequency cycle before the fault.

[0070] Next, if the single-phase fault and interphase fault conditions are not met, the zero-sequence current integral value is used to determine whether it is a three-phase fault. Specifically, the zero-sequence current integral value is compared with the zero-sequence current fixed value. If the zero-sequence current integral value is less than the fixed value, it is considered a three-phase fault, where the zero-sequence current fixed value is the smallest value among the three-phase current integral values ​​in the power frequency cycle before the fault.

[0071] Finally, if none of the above conditions are met, a phase-to-phase ground fault occurs. The fault phase is determined based on the phase current integral. Specifically, if the zero-sequence current integral value is greater than the zero-sequence current constant, a phase-to-phase ground fault occurs. Calculate the maximum instantaneous value of the three-phase current integral value within one power frequency cycle after the fault occurs. Compare the three phase maximum values. The phase with the smallest value is considered the unfaulted phase, and the other two phases are considered the faulty phases.

[0072] It can be seen that this method uses high-order harmonics for phase selection discrimination, avoiding the problem of difficulty in extracting power frequency quantities due to high harmonic content in fault conditions. After the fault, the fault phase difference in single-phase and inter-phase fault conditions is quickly distinguished through short window calculation, and the fault phase difference in three-phase and inter-phase ground faults is calculated through zero-sequence integral current and phase integral current, taking into account both the speed and accuracy of line protection phase selection.

[0073] Specific implementation of relay protection equipment:

[0074] On the other hand, the present invention also proposes a relay protection device, including a processor, which is used to execute the above-mentioned line protection phase selection method. Here, the specific implementation of the relay protection device can be found in the method specific implementation 1-4, which will not be repeated here.

[0075] In summary, the present invention addresses the difficulty in extracting power frequency signals after a fault, and provides a line protection phase selection method and relay protection equipment, wherein the current is passed through a high-pass filter, and the high-frequency components in the current signal are collected for phase selection calculation. Phase modulus transformation is performed on the three-phase current to obtain the current modulus. Whether it is a single-phase fault or an interphase fault is determined by the maximum value of the modulus within a period of time at the beginning of the fault. If the conditions for single-phase fault and interphase fault are not met, whether it is a three-phase fault is determined based on the zero-sequence current integral value. If none of the above conditions are met, the fault is a phase-to-phase ground fault, and the fault phase is determined based on the current integral.

Claims

1. A phase selection method for line protection, characterized in that: The steps include: 1) In response to a line fault, extract high-frequency current components from the three-phase current signals respectively, and calculate the zero-sequence current integral value, as well as the current modulus maximum value and current integral value of each phase based on the three-phase high-frequency current components; 2) When only the maximum value of the current modulus of the first target phase among the three phases is less than the preset current constant value for determining a single-phase fault or an interphase fault in the line, the line fault is determined to be a single-phase fault or an interphase fault and its faulty phase based on the current modulus of the first target phase; otherwise, 3) Determine whether the zero-sequence current integral value is less than a preset zero-sequence current constant value for determining a three-phase line fault; if so, determine that the line fault is a three-phase fault; if not, determine that the line fault is a phase-to-ground fault, and determine the second target phase with the smallest integral value among the three-phase current integral values ​​as the non-fault phase, and the remaining two phases as the fault phases.

2. The line protection phase selection method according to claim 1, characterized in that: The current modulus includes α-mode current and β-mode current. According to the first target phase current modulus, the line fault is determined to be a single-phase fault or an interphase fault and its fault phase by the following method: When the α modulus current of the first target phase current modulus is less than the current set value, it is determined that the line fault is an interphase fault, the first target phase is a non-fault phase, and the other two phases are fault phases; When the β-mode current of the first target phase current modulus is less than the current set value, it is determined that the line fault is a single-phase fault and the first target phase is the fault phase.

3. The line protection phase selection method according to claim 1, characterized in that: The high-frequency current component in the three-phase current signal is extracted using the following formula: Where x is the sampled current data; k is the sampling number; y is the high-frequency component output by the sampled current data after passing through the high-pass filter; b j is the filter coefficient.

4. The line protection phase selection method according to claim 3, characterized in that: The filter coefficients are 0.0043, 0.0058, 0.0069, 0.0047, -0.0029, -0.0172, -0.0380, -0.0635, -0.0904, -0.1142, -0.1307, 0.8635, -0.1307, -0.1142, -0.0904, -0.0635, -0.0380, -0.0172, -0.0029, 0.0047, 0.0069, 0.0058, and 0.0043.

5. The line protection phase selection method according to claim 1, characterized in that: The zero-sequence current integral and current integral values ​​are calculated using the following formulas: Among them, when calculating the zero-sequence current integral, is the zero-sequence current; when calculating the phase current integral, is the phase current; k is the sampling number; N is the number of sampling points in each power frequency cycle.

6. The line protection phase selection method according to claim 1, characterized in that: The maximum value of the current modulus is calculated by the following method: Perform phase modulus transformation on the three-phase high-frequency current components to obtain the three-phase current modulus; determine the maximum value of the current modulus of each phase in the first time period at the beginning of the fault as the current modulus maximum value of the corresponding phase.

7. The line protection phase selection method according to claim 1, characterized in that: The current constant used to determine a single-phase fault or an interphase fault in a line is 1.5 times the absolute value of the instantaneous current value in the power frequency cycle before the fault occurs in the line.

8. The line protection phase selection method according to claim 1, characterized in that: The zero-sequence current constant is the minimum integral value among the three-phase current integral values ​​in the power frequency cycle before the line fault occurs.

9. A relay protection device, characterized in that: The method comprises a processor, wherein the processor is used to execute the line protection phase selection method according to any one of claims 1 to 8.

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