Active power distribution network differential protection method based on fault current positive sequence component amplitude ratio

Abstract

The application provides an active power distribution network differential protection method based on a fault current positive sequence component amplitude ratio. First, an active power distribution network fault current positive sequence component network is established, characteristics of fault current positive sequence component amplitudes at both ends of a protection section are analyzed, and an adaptive current differential protection scheme based on the fault current positive sequence component amplitude ratio is provided. The scheme uses the fault current positive sequence component amplitude ratio at both sides of the protection section to construct a braking coefficient setting function, dynamically adjusts the protection braking coefficient under different fault scenarios, and ensures the selectivity and sensitivity of the differential protection when a fault occurs in the line. The PSCAD / EMTDC software is used for verification, and simulation results show that the principle can meet the requirements of the relay protection of the active power distribution network, has the characteristics of high sensitivity, strong anti-transition resistance capacity and the like, and has high practical value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power distribution network protection, and particularly relates to an active power distribution network differential protection method based on a fault current positive sequence component amplitude ratio. BACKGROUND

[0002] The topology structure and fault characteristics of a power distribution network are changed after an inverter type distributed power source is connected, and the line conventional current protection is affected. SUMMARY

[0003] In view of the defects and deficiencies in the prior art, the application first establishes a fault current positive sequence component network of an active power distribution network, analyzes the fault current positive sequence component amplitude characteristics at both ends of a protection section, and proposes an adaptive current differential protection scheme based on a fault current positive sequence component amplitude ratio. The scheme constructs a braking coefficient setting function with the fault current positive sequence component amplitude ratio at both sides of the protection section, dynamically adjusts the protection braking coefficient under different fault scenarios, and ensures the selectivity and sensitivity of the differential protection when a fault occurs in the line. The PSCAD / EMTDC software is used for verification, and the simulation results show that the principle can meet the relay protection requirements of the active power distribution network, has high sensitivity, strong anti-transition resistance capability and other characteristics, and has high practical value.

[0004] The application solves the technical problems by adopting the technical scheme of:

[0005] An active power distribution network differential protection method based on a fault current positive sequence component amplitude ratio, characterized by: collecting current information at both sides of a protection section during normal operation, when a fault is judged to occur, first obtaining a fault additional current through a full-cycle subtraction method, and calculating the positive sequence component amplitudes of the fault additional currents at both sides by using a fast Fourier transform (FFT); constructing a dynamic braking coefficient setting function by using the obtained current amplitude ratio information, and finally judging whether the protection needs to act according to a protection action criterion;

[0006] The basic form of the dynamic braking coefficient setting function is represented as:

[0007]

[0008] In the formula, K r represents a braking coefficient, is a differential current, is a braking current, and the braking coefficient K r is adaptively and dynamically changed with the fault current positive sequence component amplitude ratio λ at both sides, in an extreme case, that is, when λ = 0,

[0009] K r = 0, and the differential current only needs to be greater than a fixed threshold value to act; when λ = 1, K r = +∞, the braking coefficient tends to infinity, and the protection does not act reliably;

[0010] Let the protection sensitivity coefficient be K s The value is defined as the ratio of the differential term to the braking term in the protection action criterion formula (11), that is

[0011]

[0012] From formula (12), the sensitivity coefficient K s The braking coefficient K r is inversely proportional to the value of λ, and the sensitivity coefficient K s is larger, that is, the difference between the positive sequence component amplitudes of the fault currents on both sides of the line is larger.

[0013] Further, after obtaining the additional positive sequence component amplitudes of the fault currents on both sides, the ratio λ of the positive sequence component amplitudes of the fault currents on both sides is calculated, and the braking coefficient K r is calculated, and it is judged whether When it is satisfied, it is judged as an in-zone fault, and the protection action is performed; if it is not satisfied, it is judged as an out-of-zone fault, and the protection action is not performed.

[0014] Further, when the fault occurs, the fault component current values flowing through the protection on both sides are obtained through the current transformers arranged on both sides of the protection zone.

[0015] In order to eliminate the influence of the inverter type distributed power supply on the relay protection after being connected to the power grid, the present application and the preferred scheme thereof propose an adaptive differential protection scheme based on the ratio of the positive sequence component amplitudes of the fault currents on both sides of the line on the basis of the conventional ratio braking type differential protection. The scheme constructs an adaptive setting function of the differential protection braking coefficient with the ratio of the positive sequence component amplitudes of the fault currents on both sides of the protection zone as the independent variable, and controls the action characteristics of the protection device by dynamically adjusting the protection braking coefficient. Through theoretical analysis and simulation analysis, the following conclusions can be obtained:

[0016] (1) The protection scheme proposed in the present application does not need to obtain the voltage information on both sides of the line at the time of fault, reduces the communication amount of data exchange between relays and the dependence on sampling synchronization.

[0017] (2) The protection scheme proposed in the present application has excellent action characteristics, is not affected by the factors such as the access capacity of IIDG, the type of short-circuit fault and the position of short-circuit fault, and is suitable for active distribution networks.

[0018] (3) The protection scheme proposed in the present application can still accurately act when the fault transition resistance is 30Ω, that is, in the case of slight fault, and has higher sensitivity and stronger transition resistance resistance than the conventional ratio braking type differential protection. BRIEF DESCRIPTION OF DRAWINGS

[0019] The present application will be further described in detail below in combination with the drawings and specific embodiments:

[0020] Figure 1 Simplified diagram of IIDG-containing power distribution network;

[0021] Figure 2 Fault component network diagram when fault is outside the area;

[0022] Figure 3 Fault component network diagram when fault is inside the area;

[0023] Figure 4 Braking coefficient K of the embodiment of the application r Schematic diagram of variation with λ;

[0024] Figure 5 Principle diagram of protection action of the embodiment of the application;

[0025] Figure 6 Overall flowchart of protection scheme of the embodiment of the application. DETAILED DESCRIPTION

[0026] In order to make the features and advantages of the patent more obvious and easy to understand, the following embodiments are specifically described, and the detailed description is as follows:

[0027] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise indicated, all technical and scientific terms used in the specification have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0028] It should be noted that the terms used herein are only for the purpose of describing the specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form, and in addition, it should be understood that when the terms "comprise" and / or "include" are used in the specification, they indicate the presence of a feature, step, operation, device, component and / or combination thereof.

[0029] The embodiment of the present application will be further described in detail below in combination with the drawings: 1. Fault current positive sequence component amplitude characteristics of IIDG-containing power distribution network

[0030] Figure 1 Simplified diagram of active power distribution network, in which E s represents system power supply; Z s represents system equivalent impedance; Z AD , Z AB , Z BC represent equivalent impedances of lines AD, AB and BC respectively; CB1 and CB2 represent protections on both sides of line AB.

[0031] During normal grid operation, in order to maximize the utilization of clean energy, the reactive power reference value of the IIDG output is usually set to 0, that is, Q is set to 0. ref =0

[13] However, in the event of a grid fault, according to the "Regulations on the Connection of Photovoltaic Power Stations to the Power System," IIDGs must prioritize outputting reactive current to support the system voltage during low-voltage ride-through, and the voltage at the IIDG grid connection point should not exceed 1.1 times the nominal voltage. In this case, the reactive current output by the IIDG should meet the following requirements:

[0032]

[0033] In the formula, K represents the low voltage ride-through factor, which is usually greater than 1.5; This represents the voltage sag factor, which is the ratio of the voltage at the grid connection point before the fault to the voltage amplitude at the grid connection point after the fault; I N This indicates the rated output current of the IIDG.

[0034] When the fault location is far from the IIDG side and the fault transition resistance is large, the short-circuit current supplied by the system side will continue to supply current downstream of the fault point, causing the short-circuit current on the IIDG side to be dominated by the through load current component. This results in an increase in the phase difference of the short-circuit current on both sides of the protected section, which is close to 180°. The fault current component only appears after the fault occurs and is not affected by the through load current.

[0035] 1.1 Extraction of positive sequence component of fault current

[0036] The transient process of the IIDG inverter is extremely short. The system can be equivalent to a linear system in a short time. According to the principle of circuit superposition, the distribution network model when a fault occurs can be decomposed into a normal operation network and a fault component network. For fast-acting protection, the normal operation component of voltage and current can be considered equal to its pre-fault component.

[0037] When a fault occurs near the IIDG grid connection point, the fault current waveform may be significantly distorted due to the IIDG output characteristics. Therefore, a sampler can be used to store the current before the fault. When the fault occurs, the full-cycle subtraction method can be used to filter out the DC component and all integer harmonics to obtain the corresponding fault component current. Finally, the positive sequence component of the fault current can be obtained by using Fast Fourier Decomposition (FFT).

[0038] 1.2 Amplitude characteristics of positive sequence components of fault current on both sides during external faults

[0039] As can be seen from the analysis in Section 1, the output current of IIDG during line faults is related to the degree of voltage drop at the grid connection point. Therefore, in the fault component network analysis, IIDG is equivalent to a voltage-controlled current source and an impedance in parallel structure.

[0040] by Figure 1Take line AB in the simplified diagram of the active distribution network as an example for analysis. When a short-circuit fault occurs at point f2 outside the protection section, the positive sequence fault component network of the distribution network is as shown in Figure 2 .

[0041] In the figure respectively represent the positive sequence components of the fault currents flowing through the protection CB1 and the protection CB2; Z Bf , Z Cf respectively represent the line impedances from the bus B and the bus C to the fault point f2; R represents the fault transition resistance; represents the current mutation variable of the IIDG after the fault occurs; fault Z IIDG represents the equivalent impedance of the IIDG; represents an additional voltage source at the fault point, which has a value equal to the amplitude of the voltage at the fault point before the fault and a phase difference of 180°.

[0042] The positive sequence components of the fault currents flowing through the protection CB1 and the protection CB2 when a short-circuit fault occurs at point f2 outside the protection section can be calculated by Figure 2 and are and the amplitude ratio λ thereof is:

[0043]

[0044]

[0045]

[0046] It can be known in combination with equations (2)-(4) that when a short-circuit fault occurs on a line outside the protection section, the amplitudes of the positive sequence components of the fault currents of the protections on both sides of the line are equal, and the ratio thereof is always 1 without considering communication errors.

[0047] 1.3 Amplitude characteristics of the positive sequence components of the fault currents on both sides when a fault occurs in the protection section

[0048] When a fault occurs at point f1 in the protection section, the positive sequence fault component network of the active distribution network is as shown in Figure 3 , in which Z Af , Z Bf respectively represent the line impedances from the bus A and the bus B to the fault point f1.

[0049] The positive sequence components of the fault currents flowing through the protection CB1 and the protection CB2 when a short-circuit fault occurs at point f1 in the protection section can be calculated by Figure 3 and are respectively:

[0050]

[0051]

[0052] Since the internal impedance Z IIDG The external performance is infinite, and formula (5) and formula (6) can be simplified as,

[0053]

[0054]

[0055] The amplitude ratio λ of the positive sequence component of the fault current on both sides of the protection section is,

[0056]

[0057] As can be seen from formula (9), when the fault occurs in the protection zone, the amplitude ratio of the positive sequence component of the fault current on both sides of the protection section is related to the fault transition resistance, the fault location, the output limit of the IIDG during the fault, and other factors, and the fault characteristics are very complex.

[0058] Since the output of the IIDG is limited by the inverter, the fault current output by the IIDG is much smaller than the fault current provided by the system side, so it can be initially considered that the amplitude ratio λ of the positive sequence component of the fault current flowing through both sides of the protection section is located in the interval (0, 1], and when λ = 1, the fault occurs outside the protection zone; when λ < 1, the fault occurs in the zone.

[0059] However, in actual situations, due to the influence of the core structure and material properties of the current transformer, there is always a magnetizing current in the winding, and the magnetizing current cannot be transmitted to the secondary side, resulting in a ratio error of the current transformer, and the maximum error can reach ±10%. Therefore, in extreme cases, the maximum relative error of the measured value of the positive sequence component of the fault current flowing through both sides of the protection section will reach 0.9 / 1.1≈0.818, so when 0.818≤λ≤1, the fault may also occur outside the fault zone, and when 0<λ<0.818, it can be initially considered that the fault occurs in the protection zone.

[0060] 1.2 Current differential protection based on the amplitude ratio of the positive sequence component of the fault current

[0061] 2.1 Limitations of conventional differential protection

[0062] Current differential protection currently mainly uses ratio restraint differential protection with through-braking characteristics, in order to Figure 1 Taking the line AB as an example, the basic criterion for protection action is

[0063]

[0064] In the formula, is the differential current, is the braking current, and K represents the ratio restraint coefficient, which is set to avoid the maximum unbalanced current of external faults, and is usually taken as 0.8-1.8.

[0065] Conventional ratio differential braking differential protection uses the total current on both sides of the line to form the differential term and braking term as the action criterion. However, when the fault transition resistance in the zone is too large, the fault component in the total current is too small, and the load current is close to the through current, which seriously affects the magnitude and phase of the total current on both sides, resulting in a decrease in the sensitivity of the differential protection and possible protection failure. At the same time, since the ratio braking coefficient in equation (10) is set according to the maximum unbalanced current, its value is relatively large. However, the load fluctuation of the active distribution network is large, and the output of distributed power sources is affected by many factors. Using a fixed high braking coefficient will lead to insufficient sensitivity of the differential protection in some minor fault scenarios.

[0066] 2.2 Current Differential Protection Principle Based on the Amplitude Ratio of Positive Sequence Component of Fault Current

[0067] The patterns derived from the analysis in Section 1 can be used to make a preliminary determination of the location of line faults, but... Figure 1 For example, when bus A is far from the system side and the fault location is close to the IIDG side, the positive sequence component amplitude ratio λ of the fault current at both ends of the line may be greater than 0.818, causing the protection to fail to operate. In order to adapt to the requirements of active distribution network relay protection, this invention constructs a new adaptive differential protection action criterion based on the positive sequence component amplitude ratio of the fault current, dynamically adjusts the differential protection braking coefficient, further improves the sensitivity and reliability of differential protection action, and eliminates the influence of load current, solving the problems of poor tolerance to transition resistance and insufficient sensitivity in some minor fault scenarios of conventional ratio braking differential protection.

[0068] The basic form of the adaptive current differential protection scheme proposed in this invention is expressed as follows:

[0069]

[0070] In the formula, K r This represents the braking coefficient; other symbols have the same meaning as described above. Under this determination method, the braking coefficient K... r The ratio λ of the positive sequence component amplitude of the fault current on both sides changes adaptively and dynamically, and its variation law is as follows: Figure 4 As shown. In the extreme case, when λ = 0, K r =0, the differential current only needs to be greater than the fixed threshold value to operate; when λ=1, K r =+∞, the braking coefficient approaches infinity, and the protection is reliable and does not operate.

[0071] The protection action criterion proposed in this invention has the following advantages compared with conventional ratio braking current differential protection:

[0072] 1) The fault current component only appears after the fault occurs, which can eliminate the influence of the load current and improve the sensitivity of the protection action in minor fault scenarios.

[0073] 2) The positive sequence component can reflect all types of faults, and compared with the conventional ratio differential protection based on full current, the use of the positive sequence component can effectively reduce the communication volume of data exchange between relays.

[0074] 3) The braking coefficient dynamically changes with the value of λ, which can break through the value range of the braking coefficient of the conventional ratio differential protection, make up for the deficiency of insufficient sensitivity of the differential protection of the distribution network after the IIDG is accessed, and effectively improve the sensitivity and reliability of the protection action.

[0075] 2.3 Sensitivity analysis of the current differential protection based on the amplitude ratio of the positive sequence component of the fault current

[0076] The relay protection that acts on tripping generally needs to meet the requirements of reliability, selectivity, speed and sensitivity on the technical level. Among them, the reliability and speed mainly depend on the manufacturing quality of the protection device itself, the connection of the protection circuit and the level of operation and maintenance, so the selectivity and sensitivity of the protection scheme are analyzed.

[0077] The criterion of formula (11) can effectively distinguish between internal and external faults, and ensure the selectivity of the protection action. Let the protection sensitivity coefficient be K s , which is defined as the ratio of the differential term to the braking term in the protection action criterion formula (11), that is,

[0078]

[0079] As can be seen from formula (12), the sensitivity coefficient K s is inversely proportional to the braking coefficient K r , and combined with Figure 4 Analysis can show that as the value of λ decreases, the sensitivity coefficient K s becomes larger, that is, the difference between the positive sequence component amplitudes of the fault currents on both sides of the line becomes larger, and the action characteristics of the protection scheme are more sensitive.

[0080] 3 Protection action mechanism

[0081] The action principle of the active distribution network differential protection method based on the amplitude ratio of the positive sequence component of the fault current is shown in Figure 5 , in which TA represents a current transformer. When a fault occurs, the fault component current values flowing through the two sides of the protection are first obtained through the two TAs, and the positive sequence component amplitudes are obtained by using fast Fourier decomposition (FFT). The braking coefficient dynamic setting function is constructed by using the obtained current amplitude ratio information, and finally it is judged whether the protection needs to act according to the protection action criterion proposed in the embodiment of the application. In summary, the overall process of the protection scheme proposed in the application is shown in Figure 6 .

[0082] 4 Simulation verification

[0083] The simulation platform of PSCAD / EMTDC is adopted to simulate and verify the scheme. Figure 1 The model is built based on the 10.5kV IIDG active power distribution network topology diagram shown in the figure, the protection action characteristics are analyzed under different IIDG capacities, different fault types, different fault positions and different fault transition resistances, and the effectiveness and reliability of the protection scheme are verified. Among them, the system voltage E s is set to 10.5kV, the system impedance Z s is set to j0.1Ω, the transformer capacity is set to 50MVA, the lines AB, BC and AD are overhead lines, the type is LJ-16, the unit length resistance is 1.96Ω / km, the unit length inductance is 0.404Ω / km, the line lengths are 3km, 4km and 5km respectively, the load L1 rated power is set to 25MVA, the load L2 rated power is set to 15MVA, the power factors are both 0.8, the IIDG is a photovoltaic power source, the PQ control strategy is adopted in normal system operation, and the low voltage ride-through control strategy is adopted in fault.

[0084] 4.1 Different IIDG capacities

[0085] The line AB is taken as the protected line, the fault type is set to three-phase ground short circuit, the transition resistance R is taken as 0.01Ω, the IIDG is an inverter photovoltaic power source, the capacities are taken as 5MW, 10MW and 15MW respectively, the fault point f1 is set to the midpoint of the line AB, and the fault point f2 is set to the midpoint of the line BC, and the protection action simulation results are shown in Table 1.

[0086] Table 1 Protection action under different IIDG capacities

[0087]

[0088] It can be seen from the protection action in Table 1 that when the short circuit fault occurs in the protection zone, the protection scheme proposed in the application can accurately act under the condition of different capacity IIDG access, and has high sensitivity; when the short circuit fault occurs outside the protection zone, the braking coefficient tends to infinity, and the protection scheme proposed in the application can also reliably not act under the condition of different capacity IIDG access.

[0089] 4.2 Different fault types

[0090] In order to further verify the feasibility of the scheme, the line AB is taken as the protected line, the transition resistance R is taken as 0.01Ω, and the IIDG is taken as a 10MW photovoltaic power supply. Since the domestic mainstream 10.5kV distribution network is a neutral point not directly grounded (not grounded, grounded through resonance) system, when a single-phase grounding fault occurs in the line, the fault current is not obvious, and the system can still operate stably for a short time

[19] Therefore, this simulation only analyzes the protection action characteristics of two-phase fault and three-phase fault of the line, the fault point f1 is set at the midpoint of the line AB, the fault point f2 is set at the midpoint of the line BC, and the protection action simulation results are shown in Table 2.

[0091] Table 2 Protection action under different fault types

[0092]

[0093] As can be seen from the protection action in Table 2, when a short-circuit fault occurs in the protection zone, the protection scheme can accurately act in the case of different types of faults of the line, and has high sensitivity. When a short-circuit fault occurs outside the protection zone, the braking coefficient tends to infinity, and the protection scheme can also reliably not act in the case of different types of short-circuit faults.

[0094] 4.3 Different fault locations

[0095] The size of the short-circuit current output by the IIDG increases as the distance between the fault location and the grid connection point decreases, so when the short-circuit fault occurs at different locations, the positive sequence components of the fault currents on both sides of the line will have different amplitude characteristics. On this basis, taking the line AB as the protected line, when a short-circuit fault occurs at the f1 point, the distance from the bus A to the fault point f1 is set as αl AB When a short-circuit fault occurs at the f2 point, the distance from the bus B to the fault point f2 is set as αl BC ,l AB 、l BC respectively represent the length of the line AB and the length of the line BC, α is taken as 0.05, 0.1, 0.5, 0.9, 0.95, the transition resistance R is taken as 0.01Ω, the IIDG is taken as a 10MW photovoltaic power supply, and the protection action analysis results of the short-circuit fault at the f1 point in the zone and the short-circuit fault at the f2 point outside the zone are shown in Table 3.

[0096] Table 3 Protection action under different fault locations

[0097]

[0098]

[0099] From the protection action situation of Table 3, it can be seen that the protection scheme proposed in the application can accurately act in the case of faults occurring at different positions of the line, has high sensitivity, and the sensitivity decreases with the decrease of the distance between the fault point and the IIDG access point. When an out-of-area fault occurs, the protection proposed in the application can also reliably not act.

[0100] 4.4 Different transition resistances

[0101] Taking the line AB as the protected line, the fault type is set to three-phase ground short circuit, the IIDG is a 10MW photovoltaic power supply, and the transition resistance of the medium-voltage distribution network in China is generally not more than 30Ω

[11] Therefore, the fault transition resistance R is respectively 0.01Ω, 15Ω and 30Ω. The fault point f1 is set at the midpoint of the line AB, and the fault point f2 is set at the midpoint of the line BC. The protection action simulation results are shown in Table 4.

[0102] Table 4 Protection action situation under different transition resistances

[0103]

[0104] From the protection action situation of Table 4, it can be seen that when an in-area fault occurs, the protection scheme proposed in the application can accurately act under different fault transition resistances, and still has high sensitivity in the case of a transition resistance of 30Ω, that is, the protection still has high sensitivity under slight fault conditions, and has strong transition resistance resistance compared with the conventional ratio braking differential protection. When an out-of-area short circuit fault occurs, it can reliably not act.

[0105] In summary, the adaptive differential protection scheme based on the amplitude of the positive sequence component of the fault current on both sides of the line proposed in the application can reliably act and has high sensitivity under different IIDG capacities, different fault types, different fault positions and different transition resistances, and can meet the requirements of active distribution network relay protection.

[0106] The above description is only a preferred embodiment of the application, and is not intended to limit other forms of the application. Any person skilled in the art can use the disclosed technical content to make changes or modifications to equivalent embodiments. However, any simple modification, equivalent change and modification made to the above embodiments without departing from the technical solution of the application, and in accordance with the technical essence of the application, still falls within the protection scope of the technical solution of the application.

[0107] The present patent is not limited to the above best embodiment, and anyone can derive other various forms of active distribution network differential protection methods based on the amplitude ratio of the positive sequence component of the fault current under the inspiration of the present patent. Any equivalent change and modification made within the scope of the application should be covered by the present patent.

Claims

1. A method for active power distribution network differential protection based on fault current positive sequence component amplitude ratio, characterized in that: The current information of both sides of the protection zone in normal operation is collected. When it is judged that a fault occurs, the fault additional current is obtained by full-cycle subtraction method, and the amplitude of the positive sequence component of the fault additional current of both sides is calculated by using fast Fourier transform (FFT). The braking coefficient dynamic setting function is constructed by using the obtained current amplitude ratio information, and finally it is judged whether the protection needs to act according to the protection action criterion. The basic form of the braking coefficient dynamic setting function is represented as: where K r represents the braking coefficient, is the differential current, is the braking current, the braking coefficient K r is self-adaptively changed with the ratio λ of the fault current positive sequence component amplitudes on both sides. In the extreme case, when λ = 0, K r = 0, the differential current only needs to be greater than a fixed threshold value to act; when λ = 1, K r = +∞, the braking coefficient tends to infinity, and the protection is reliable and does not act. Let the protection sensitivity coefficient be K s The value of which is defined as the ratio of the differential term to the braking term in the protection action criterion (11), i.e. From formula (12), the sensitivity coefficient K s Braking coefficient K r Inversely proportional, with the decrease of λ value, the sensitivity coefficient K s The greater, that is, the greater the difference between the amplitude of the positive sequence component of the fault current on both sides of the line.

2. The method of active power distribution network differential protection based on fault current positive sequence component amplitude ratio according to claim 1, characterized in that: After the amplitude of the additional positive sequence component of the fault current on both sides is obtained, the amplitude ratio of the positive sequence component of the fault current on both sides is calculated, and the braking coefficient K is calculated r , to determine whether When the condition is met, the fault is determined to be within the protection zone, and the protection action is performed; otherwise, the fault is determined to be outside the protection zone, and the protection action is not performed.

3. The method of active power distribution network differential protection based on fault current positive sequence component amplitude ratio according to claim 1, characterized in that: When the fault occurs, the fault component current values flowing through the protection on both sides are obtained by the current transformers arranged on both sides of the protection zone.

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