Distance protection method for decoupling protection range and system operation mode

Abstract

The invention discloses a distance protection method for decoupling a protection range and a system operation mode. The distance protection method comprises the following steps of S1, performing fault type judgment based on voltage sequence component characteristics; s2, performing additional impedance calculation based on the impedance geometric model; and S3, based on the impedance geometric model, measuring impedance compensation is carried out, and fault distance output is carried out. On the basis of considering implementation feasibility and cost effectiveness, performance progress of a power grid protection system and reliability of power supply can be ensured.

Description

Technical Field

[0001] The invention relates to a distance protection method for decoupling a protection range from a system operation mode in the field of smart grid distance protection. Background Art

[0002] Distance protection is one of the key technologies used in power systems to ensure the safe operation of transmission lines. It works by measuring the impedance change between the fault point and the installation location of the protection device, thereby achieving rapid isolation of the fault. The importance of distance protection is reflected in its ability to provide selectivity, speed, sensitivity and reliability, which are essential for the stable operation of modern ultra-high voltage and large-capacity power grids. It can adapt to power systems with complex structures and variable operating modes, effectively avoid the expansion of faults, and reduce the impact on power equipment and the entire power grid. In practical applications, distance protection can adopt a variety of configuration schemes to adapt to different power grid structures and operating requirements. For example, on lines that require full-line speed, distance protection can be used as the main protection; in other cases, it can also be used as backup protection. In addition, distance protection also has remote monitoring and diagnosis functions, and can achieve real-time monitoring and fault diagnosis of the power system through communication technology connection with the monitoring center.

[0003] However, the access of photovoltaic power generation systems has brought challenges to the distance protection of power systems. Due to the volatility and uncertainty of photovoltaic output, traditional distance protection may be affected, resulting in a decrease in protection performance. Photovoltaic power generation systems are connected to the grid through inverters. The addition of this power electronic interface changes the fault characteristics of the system, which may cause false operation or refusal of distance protection, affecting the stability and safety of the power grid. In addition, the presence of distance transition resistance may affect the correctness of the distance protection action, resulting in false operation or refusal of protection. To solve this problem, researchers have proposed a variety of improvement schemes, including adaptive distance protection and distance protection based on artificial neural networks. These methods improve the performance of distance protection by training and learning power grid data, but their practicality is low and large-scale improvements to protection devices in the power grid are required. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a distance protection method that decouples the protection range from the system operation mode, which can ensure the performance improvement of the power grid protection system and the reliability of power supply while considering the feasibility and cost-effectiveness of implementation.

[0005] A technical solution to achieve the above purpose is: a distance protection method that decouples the protection range from the system operation mode, comprising the following steps:

[0006] S1, fault type identification based on voltage sequence component characteristics;

[0007] S2, additional impedance calculation based on the impedance geometry model;

[0008] S3, performs measurement impedance compensation based on the impedance geometry model and outputs the fault distance.

[0009] Furthermore, the fault types in S1 include three-phase short circuit fault, two-phase short circuit fault, single-phase ground fault and two-phase ground fault.

[0010] Furthermore, we define U A - is the negative sequence voltage amplitude of phase A. When U A - When it is greater than the threshold value of 0.1pu, it is determined that one of a two-phase short circuit fault, a single-phase grounding fault and a two-phase grounding fault occurs; otherwise, it is determined that a three-phase short circuit fault occurs.

[0011] Furthermore, we define δ A + is the angle at which the negative sequence voltage of phase A leads the positive sequence voltage of phase A. A + When δ is greater than 150° and less than 270°, it is determined that a phase A ground fault has occurred; A + When it is greater than -30° and less than 30°, it is determined that a BC two-phase short circuit or BC two-phase grounding fault has occurred.

[0012] Furthermore, we define U 0 is the zero-sequence voltage amplitude, when U 0 When it is greater than the threshold value of 0.1pu, it is determined that a two-phase grounding fault has occurred, otherwise it is determined that a two-phase short-circuit fault has occurred.

[0013] Furthermore, in S2, when there are three short-circuit faults, the measured impedance Z measured by the distance protection at the protection installation is AG As shown in the following formula,

[0014]

[0015] In the formula, the measured impedance includes the additional impedance Z fujia and the actual short-circuit impedance αZ L Impedance, where α is the fault location, Z L is the line impedance, R g is the ground transition resistance, K (0) is the zero-sequence compensation coefficient, I (0) is the zero sequence current, I A and I A-f are the A-phase current at the protection installation and the A-phase current at the fault point, U A To protect the A phase voltage at the installation location;

[0016] The phase of the additional impedance is given by:

[0017]

[0018] is the additional impedance angle;

[0019] The additional impedance amplitude is calculated as follows:

[0020]

[0021] is the line impedance phase angle, To measure the impedance angle, Z celiang To measure impedance.

[0022] Furthermore, in S2, when a two-phase short circuit fault occurs, the measured impedance Z measured by the distance protection at the protection installation is BC As shown in the following formula,

[0023]

[0024] In the formula, R ph is the phase transition resistance, I B and I C They are respectively the B-phase current and the C-phase current at the protection installation, U B To protect the B phase voltage at the installation location, U C To protect the C phase voltage at the installation location, I A-f - is the negative sequence current of phase A at the fault point. By using the phase of the negative sequence current flowing through the protection installation to be equivalent to the phase of the negative sequence current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula:

[0025]

[0026] I A - To protect the negative sequence current of phase A at the installation location;

[0027] The additional impedance amplitude is calculated as follows:

[0028]

[0029] is the line impedance phase angle, To measure the impedance angle, Z celiang To measure impedance.

[0030] Furthermore, in S2, when a single-phase ground fault occurs, the measured impedance Z measured by the distance protection at the protection installation is AG As shown in the following formula,

[0031]

[0032] In the formula, I f (0) is the zero-sequence current at the fault point. By using the phase of the zero-sequence current flowing through the protection installation to be equivalent to the phase of the zero-sequence current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula:

[0033]

[0034] I A To protect the zero-sequence current of phase A at the installation location;

[0035] The additional impedance amplitude is calculated as follows:

[0036]

[0037] is the line impedance phase angle, To measure the impedance angle, Z celiang To measure impedance.

[0038] Furthermore, in S2, when two phases are grounded, Z BCG As a new measurement impedance expression, as shown below,

[0039]

[0040] By using the phase of the zero-sequence current flowing through the protection installation to be equivalent to the phase of the zero-sequence current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula:

[0041]

[0042] The additional impedance amplitude is calculated as follows:

[0043]

[0044] is the line impedance phase angle, To measure the impedance angle, Z celiang To measure impedance.

[0045] Furthermore, S3 is specifically:

[0046] After the additional impedance is calculated based on the impedance geometry model, the measured impedance is equal to the sum of the additional impedance and the actual short-circuit impedance. The measured impedance minus the additional impedance can be obtained to obtain the new measured impedance Z m new The expressions are as follows under four types of faults:

[0047]

[0048] Using Z m new Divide by Z L The fault distance calculation formula can be obtained as shown below:

[0049]

[0050] α is the fault distance.

[0051] The present invention provides a distance protection method with a protection range decoupled from a system operation mode. Under the background that the power grid is widely connected to photovoltaic power stations, resulting in large changes in the system operation mode, compensation and optimization are performed on the measured impedance measured by the distance protection under three-phase short circuit, two-phase short circuit, single-phase grounding and two-phase grounding faults, so that the distance protection can accurately reflect the actual fault impedance, improve the calculation accuracy of the fault distance, ensure that the protection range of the distance protection is not affected when the system operation mode changes, achieve decoupling of the protection range from the system operation mode, and improve the fault removal capability and safe operation capability of the power grid containing the photovoltaic power station.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] 1. The present invention compensates and optimizes the measured impedance measured by the distance protection, eliminating the influence of the additional impedance caused by the transition resistance. This enables the proposed method to have a strong ability to resist transition resistance, especially since the transition resistance of a single-phase grounding fault is usually large. The present invention can significantly enhance the performance of the distance protection under a single-phase grounding fault.

[0054] 2. The present invention takes into account the impact of changes in system operating modes on the additional impedance, and further analyzes the impact of this impact on the protection range of distance protection, and eliminates this impact by compensating for the additional impedance in the measured impedance, thereby ensuring that the protection range of distance protection is not subject to large-scale fluctuations due to changes in system operating modes. The present invention improves the ability of distance protection to cope with changes in system operating modes.

[0055] 3. The present invention takes into account both economy and effectiveness, and only requires modification of the algorithm part, and the existing distance protection device does not need to be redesigned. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a schematic diagram of the impedance geometry model;

[0057] Figure 2 A schematic flow chart of a distance protection method of the present invention in which a protection range is decoupled from a system operation mode;

[0058] Figure 3 It is a comparison between the traditional distance protection and the distance protection method of the present invention (operation mode 1, three-phase short circuit fault);

[0059] Figure 4 It is a comparison between the traditional distance protection and the distance protection method of the present invention (operation mode 1, two-phase short circuit fault);

[0060] Figure 5 It is a comparison between the traditional distance protection and the distance protection method of the present invention (operation mode 1, single-phase grounding fault);

[0061] Figure 6 It is a comparison between the traditional distance protection and the distance protection method of the present invention (operation mode 1, two-phase grounding fault);

[0062] Figure 7 It is a comparison between the traditional distance protection and the distance protection method of the present invention (operation mode 2, three-phase short circuit fault);

[0063] Figure 8 It is a comparison between the traditional distance protection and the distance protection method of the present invention (operation mode 2, two-phase short circuit fault);

[0064] Fig. 9 It is a comparison between the traditional distance protection and the distance protection method of the present invention (operation mode 2, single-phase grounding fault);

[0065] Fig.10 The figure is a comparison between the traditional distance protection and the distance protection method of the present invention (operation mode 2, two-phase grounding fault). DETAILED DESCRIPTION

[0066] In order to better understand the technical solution of the present invention, the following is a detailed description through specific embodiments:

[0067] A distance protection method of the present invention that decouples the protection range from the system operation mode is specifically as follows:

[0068] S1, fault type identification based on voltage sequence component characteristics.

[0069] Since the composition of the measured impedance is different under different fault types, it is necessary to first identify the fault type, and then calculate the additional impedance and compensate the measured impedance for different fault types to improve the distance protection performance.

[0070] Among three-phase short-circuit fault, two-phase short-circuit fault, single-phase grounding fault and two-phase grounding fault, only when three-phase short-circuit fault occurs, there is no negative sequence voltage. Therefore, the negative sequence voltage amplitude is first used to determine whether a three-phase short-circuit fault occurs. Define U A - is the negative sequence voltage amplitude of phase A. When U A -When it is greater than the threshold value of 0.1pu, it is determined that one of a two-phase short circuit fault, a single-phase grounding fault and a two-phase grounding fault occurs; otherwise, it is determined that a three-phase short circuit fault occurs.

[0071] Then, the phase relationship between the negative sequence voltage and the positive sequence voltage is used to distinguish between a single-phase grounding fault and a two-phase short circuit fault and a two-phase grounding fault, as follows. A + The angle at which the negative sequence voltage of phase A leads the positive sequence voltage of phase A. In the case of a single-phase grounding fault (taking the grounding fault of phase A as an example), the positive sequence network of phase A is connected in series with the negative sequence network in reverse order. A + Theoretically, it is 180°; in case of two-phase short circuit fault (taking BC two-phase short circuit fault as an example) and two-phase grounding fault (taking BC two-phase grounding fault as an example), the positive sequence network of the special phase is connected in parallel with the negative sequence network, δ A + Theoretically, it is 0°. A + When δ is greater than 150° and less than 270°, it is determined that a phase A ground fault has occurred; A + When it is greater than -30° and less than 30°, it is determined that a BC two-phase short circuit or BC two-phase grounding fault has occurred.

[0072] Finally, the zero-sequence voltage amplitude is used to distinguish between two-phase short circuit and two-phase grounding fault. In theory, there is no zero-sequence voltage in the case of two-phase short circuit, and there is a zero-sequence voltage in theory in the case of two-phase grounding fault. Therefore, U is defined as 0 is the zero-sequence voltage amplitude, when U 0 When it is greater than the threshold value of 0.1pu, it is determined that a two-phase grounding fault has occurred, otherwise it is determined that a two-phase short-circuit fault has occurred.

[0073] The use of the above fault type identification method can ensure that the fault type can be accurately identified even if the system short-circuit current is low.

[0074] S2, additional impedance calculation based on the impedance geometry model.

[0075] Under three-phase short circuit fault, two-phase short circuit fault, single-phase ground fault and two-phase ground fault, the additional impedance is calculated based on the impedance geometry model as follows.

[0076] (1) Three-phase short circuit fault

[0077] In case of three-phase short circuit fault, the measured impedance Z measured by the distance protection at the protection installation AG As shown in the following formula.

[0078]

[0079] In the formula, the measured impedance includes the additional impedance Zfujia and the actual short-circuit impedance αZ L Impedance (where α is the fault location, Z L is the line impedance), R g is the ground transition resistance, K (0) is the zero-sequence compensation coefficient, I (0) is the zero sequence current, I A and I A-f are the A-phase current at the protection installation and the A-phase current at the fault point, U A To protect the A phase voltage at the installation location. The geometric relationship between the measured impedance, additional impedance, and actual short-circuit impedance constitutes the impedance geometric model, such as Figure 1 As shown in the figure, Z celiang A general term for measuring impedance, φ fujia is the additional impedance angle, φ L is the line impedance phase angle, φ celiang To measure the impedance angle. To obtain the additional impedance, the key is to calculate the phase of the additional impedance. By using the current phase flowing through the protection installation to be equivalent to the phase of the current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula.

[0080]

[0081] Combination Figure 1 The additional impedance amplitude can be calculated as shown below.

[0082]

[0083] From (2) and (3), we can get the expression of additional impedance when three-phase short circuit occurs.

[0084] (2) Two-phase short circuit fault

[0085] In case of two-phase short circuit fault, the measured impedance Z measured by the distance protection at the protection installation BC As shown in the following formula.

[0086]

[0087] In the formula, R ph is the phase transition resistance, I B and I C They are respectively the B-phase current and the C-phase current at the protection installation, U B To protect the B phase voltage at the installation location, U C To protect the C phase voltage at the installation location, I A-f - is the negative sequence current of phase A at the fault point. By using the phase of the negative sequence current flowing through the protection installation to be equivalent to the phase of the negative sequence current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula.

[0088]

[0089] Combination Figure 1 The additional impedance amplitude can be obtained to be the same as (3). From (5) and (3), the expression of the additional impedance in the case of a two-phase short circuit fault can be obtained.

[0090] (3) Single-phase ground fault

[0091] In case of single-phase ground fault, the measured impedance Z measured by the distance protection at the protection installation AG As shown in the following formula.

[0092]

[0093] In the formula, I f (0) is the zero-sequence current at the fault point. By using the phase of the zero-sequence current flowing through the protection installation to be equivalent to the phase of the zero-sequence current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula.

[0094]

[0095] Combination Figure 1 The additional impedance amplitude can be obtained to be the same as (3). From (7) and (3), the expression of the additional impedance in the case of a single-phase grounding fault can be obtained.

[0096] (4) Two-phase grounding fault

[0097] When two-phase ground fault occurs, a new measurement impedance expression is used, with Z BCG It is expressed as shown in the following formula.

[0098]

[0099] By using the phase of the zero-sequence current flowing through the protection installation to be equivalent to the phase of the zero-sequence current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula.

[0100]

[0101] Combination Figure 1 The additional impedance amplitude can be obtained to be the same as (3). From (9) and (3), the expression of the additional impedance in the case of a two-phase grounding fault can be obtained.

[0102] S3, performs measurement impedance compensation based on the impedance geometry model and outputs the fault distance.

[0103] After the additional impedance is calculated based on the impedance geometry model, Figure 1 It can be seen that the measured impedance is equal to the sum of the additional impedance and the actual short-circuit impedance. Therefore, the measured impedance can be subtracted from the additional impedance to obtain the new measured impedance Z. mnew The expressions,under four types of faults are shown as follows.

[0104] (10)

[0106] Using Z m new Divide by Z L The fault distance calculation α can be obtained as shown in the following formula.

[0107]

[0108] The Nanhua 1461 line from Nanshi Substation to Huayuangang Substation within the jurisdiction of State Grid Shanghai Urban Power Supply Company is used as a specific embodiment. The voltage level of the line is 110kV, the positive sequence impedance of the ancestral line is 0.0028+j0.0149Ω, and the zero sequence impedance is 0.01105+j0.01971Ω. The performance of the present invention and the traditional distance protection is tested at the protection installation on the Nanshi side of the Nanhua 1461 line. In order to reflect the adaptability of the present invention to the system operation mode, a photovoltaic power station is connected to the 110kV side of the Nanshi Substation. The distance protection method of the present invention that decouples the protection range from the system operation mode, first, distinguishes symmetrical short circuit and asymmetrical short circuit faults by the negative sequence voltage at the protection installation, and divides asymmetrical faults into two categories according to the angle of the negative sequence voltage of a certain phase leading the positive sequence voltage of the phase, the first category: single-phase grounding fault; the second category: two-phase short circuit fault and two-phase grounding fault, and distinguishes two-phase short circuit fault and two-phase grounding fault by zero sequence voltage. Then, for three-phase short-circuit faults, two-phase short-circuit faults, single-phase grounding faults and two-phase grounding faults, the additional impedance is calculated based on the impedance geometry model using the positive-sequence, negative-sequence and zero-sequence current phases at the protection installation. Finally, the measured impedance is subtracted from the additional impedance to obtain a new measured impedance, and the new measured impedance is used to replace the traditional measured impedance in combination with a circular characteristic impedance relay for fault identification. If the new measured impedance falls within the circle, it is an internal fault and the protection trips; if the new measured impedance does not fall within the circle, it is an external fault and the protection returns. The fault location can also be output by dividing the new measured impedance by the line impedance. The process of the present invention is as follows: Figure 2 shown.

[0109] In order to demonstrate the performance of the distance protection method of the present invention in which the protection scope is decoupled from the system operation mode, two operation modes are set here: operation mode 1: the output power of the photovoltaic power station is 0, and the equivalent impedance of the 110kV side of the Nanshi substation is 0.05+j0.1Ω (equivalent to the Nanshi substation not being connected to the photovoltaic power station), and operation mode 2: the output power of the photovoltaic power station is 1pu, and the equivalent impedance of the 110kV side of the Nanshi substation is 0.5+j1Ω. It should be noted that only the situation of distance protection section I is shown here, and the same is true for distance protection sections II and III.

[0110] (1) Operation mode 1: The output power of the photovoltaic power station is 0, and the equivalent impedance of the 110kV side of the Nanshi substation is 0.05+j0.1Ω

[0111] When a three-phase short circuit fault occurs at the end of the Nanhua 1461 line through a 10Ω transition resistor, the relationship between the impedance measured by the conventional distance protection and the distance protection method of the present invention and the action circle is as follows: Figure 3 shown.

[0112] When a two-phase short circuit fault occurs at the end of the Nanhua 1461 line through a 10Ω transition resistor, the relationship between the impedance measured by the conventional distance protection and the distance protection method of the present invention and the action circle is as follows: Figure 4 shown.

[0113] When a single-phase grounding fault occurs at the end of the Nanhua 1461 line through a 100Ω transition resistor, the relationship between the impedance measured by the traditional distance protection and the distance protection method of the present invention and the action circle is as follows: Figure 5 shown.

[0114] When a two-phase grounding fault occurs at the end of the Nanhua 1461 line through a 10Ω phase-to-phase transition resistor and a 100Ω grounding transition resistor, the relationship between the impedance measured by the conventional distance protection and the distance protection method of the present invention and the action circle is as follows: Figure 6 shown.

[0115] Depend on Figures 3 to 6 It can be seen that due to the influence of the additional impedance caused by the transition resistance, the traditional distance protection measurement impedance cannot fall into the action circle and cannot operate correctly. However, the distance protection of the present invention compensates for the influence of the additional impedance, thereby effectively reducing the influence of the transition resistance. Therefore, the new measurement impedance can fall into the action circle and operate correctly.

[0116] (2) Operation mode 2: The output power of the photovoltaic power station is 1pu, and the equivalent impedance of the 110kV side of the Nanshi substation is 0.5+j1Ω

[0117] When a three-phase short circuit fault occurs at the end of the Nanhua 1461 line through a 10Ω transition resistor, the relationship between the impedance measured by the conventional distance protection and the distance protection method of the present invention and the action circle is as follows: Figure 7 shown.

[0118] When a two-phase short circuit fault occurs at the end of the Nanhua 1461 line through a 10Ω transition resistor, the relationship between the impedance measured by the conventional distance protection and the distance protection method of the present invention and the action circle is as follows: Figure 8 shown.

[0119] When a single-phase grounding fault occurs at the end of the Nanhua 1461 line through a 100Ω transition resistor, the relationship between the impedance measured by the traditional distance protection and the distance protection method of the present invention and the action circle is as follows: Fig. 9 shown.

[0120] When a two-phase grounding fault occurs at the end of the Nanhua 1461 line through a 10Ω phase-to-phase transition resistor and a 100Ω grounding transition resistor, the relationship between the impedance measured by the conventional distance protection and the distance protection method of the present invention and the action circle is as follows: Fig.10 shown.

[0121] Depend on Figure 7-10 It can be seen that the traditional distance protection measurement impedance cannot fall into the action circle and cannot operate correctly, while the new measurement impedance of the distance protection of the present invention can fall into the action circle and operate correctly. Figure 3 and Figure 7 , Figure 4 and Figure 8 , Figure 5 and Fig. 9 , Figure 5 and 10 Analysis shows that the measurement impedance of the traditional distance protection fluctuates dramatically with the change of the operation mode, resulting in an unstable protection range. However, the new measurement impedance of the distance protection of the present invention is almost unaffected by the change of the operation mode, and the protection range is constant.

[0122] The above embodiments prove that the present invention is effective and reasonable.

[0123] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A distance protection method for decoupling the protection range from the system operation mode, characterized in that: The steps include: S1, fault type identification based on voltage sequence component characteristics; S2, additional impedance calculation based on the impedance geometry model; S3, performs measurement impedance compensation based on the impedance geometry model and outputs the fault distance.

2. A distance protection method for decoupling protection range from system operation mode according to claim 1, characterized in that: The fault types in S1 include three-phase short circuit fault, two-phase short circuit fault, single-phase ground fault and two-phase ground fault.

3. A distance protection method for decoupling protection range from system operation mode according to claim 2, characterized in that: Definition U A - is the negative sequence voltage amplitude of phase A. When U A - When it is greater than the threshold value of 0.1pu, it is determined that one of a two-phase short circuit fault, a single-phase grounding fault and a two-phase grounding fault occurs; otherwise, it is determined that a three-phase short circuit fault occurs.

4. A distance protection method for decoupling protection range from system operation mode according to claim 3, characterized in that: Define δ A + is the angle at which the negative sequence voltage of phase A leads the positive sequence voltage of phase A. A + When δ is greater than 150° and less than 270°, it is determined that a phase A ground fault has occurred; A + When it is greater than -30° and less than 30°, it is determined that a BC two-phase short circuit or BC two-phase grounding fault has occurred.

5. A distance protection method for decoupling protection range from system operation mode according to claim 4, characterized in that: So define U 0 is the zero-sequence voltage amplitude, when U 0 When it is greater than the threshold value of 0.1pu, it is determined that a two-phase grounding fault has occurred, otherwise it is determined that a two-phase short-circuit fault has occurred.

6. A distance protection method for decoupling protection range from system operation mode according to claim 2, characterized in that: In S2, when there is a three-term short-circuit fault, the measured impedance Z measured by the distance protection at the protection installation AG As shown in the following formula, In the formula, the measured impedance includes the additional impedance Z fujia and the actual short-circuit impedance αZ L Impedance, where α is the fault location, Z L is the line impedance, R g is the ground transition resistance, K (0) is the zero-sequence compensation coefficient, I (0) is the zero sequence current, I A and I A-f are the A-phase current at the protection installation and the A-phase current at the fault point, U A To protect the A phase voltage at the installation location; The phase of the additional impedance is given by: is the additional impedance angle; The additional impedance amplitude is calculated as follows: is the line impedance phase angle, To measure the impedance angle, Z celiang To measure impedance.

7. A distance protection method for decoupling protection range from system operation mode according to claim 2, characterized in that: In S2, when a two-phase short circuit occurs, the measured impedance Z measured by the distance protection at the protection installation is BC As shown in the following formula, In the formula, R ph is the phase transition resistance, I B and I C They are respectively the B-phase current and the C-phase current at the protection installation, U B To protect the B phase voltage at the installation location, U C To protect the C phase voltage at the installation location, I A-f - is the negative sequence current of phase A at the fault point. By using the phase of the negative sequence current flowing through the protection installation to be equivalent to the phase of the negative sequence current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula: I A - To protect the negative sequence current of phase A at the installation location; The additional impedance amplitude is calculated as follows: is the line impedance phase angle, To measure the impedance angle, Z celiang To measure impedance.

8. A distance protection method for decoupling protection range from system operation mode according to claim 2, characterized in that: In S2, when a single-phase ground fault occurs, the measured impedance Z measured by the distance protection at the protection installation is AG As shown in the following formula, In the formula, I f (0) is the zero-sequence current at the fault point. By using the phase of the zero-sequence current flowing through the protection installation to be equivalent to the phase of the zero-sequence current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula: I A To protect the zero-sequence current of phase A at the installation location; The additional impedance amplitude is calculated as follows: is the line impedance phase angle, To measure the impedance angle, Z celiang To measure impedance.

9. A distance protection method for decoupling protection range from system operation mode according to claim 2, characterized in that: In S2, when two phases are grounded, Z BCG As a new measurement impedance expression, as shown below, By using the phase of the zero-sequence current flowing through the protection installation to be equivalent to the phase of the zero-sequence current at the fault point in the above formula, the phase of the additional impedance can be obtained as shown in the following formula: The additional impedance amplitude is calculated as follows: is the line impedance phase angle, To measure the impedance angle, Z celiang To measure impedance.

10. A distance protection method for decoupling protection range from system operation mode according to claim 2, characterized in that: S3 is specifically: After the additional impedance is calculated based on the impedance geometry model, the measured impedance is equal to the sum of the additional impedance and the actual short-circuit impedance. The measured impedance minus the additional impedance can be obtained to obtain the new measured impedance Z m new The expressions are as follows under four types of faults: Using Z m new Divide by Z L The fault distance calculation formula can be obtained as shown below: α is the fault distance.

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