An active power distribution network current pilot protection method and system

Abstract

The present disclosure belongs to the technical field of active power distribution network relay protection, and particularly relates to an active power distribution network current pilot differential protection method and system, which comprises the following steps: acquiring phase current information of a protected section line system side and a distributed power supply side, and judging whether to start protection; after starting protection, collecting cycle currents before and after a fault mutation point, calculating the amplitude and phase of a fault current and a positive sequence current fault component, and calculating an adaptive braking compensation coefficient; based on the calculated adaptive braking compensation coefficient, constructing a current pilot differential protection criterion; and realizing current pilot differential protection of the active power distribution network according to the constructed current pilot differential protection criterion.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of active power distribution network relay protection, and particularly relates to an active power distribution network current pilot differential protection method and system. BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

[0003] With the shortage of fossil fuels, the increasing deterioration of the environment and the development of power electronic technology, distributed generators (DG) using clean energy such as solar energy and wind energy begin to be massively connected to the power distribution network, so that the power distribution network is transformed from a simple single-source radial power supply network into a complex multi-source power supply network. Therefore, the operation mode, power flow direction and fault characteristics of the active power distribution network containing distributed generators are complex and changeable, which leads to the fact that the traditional three-section current protection is no longer applicable.

[0004] According to the different grid connection interfaces, the DGs can be divided into rotating electric machine type distributed generators (MTDG) directly connected to the grid and inverter type distributed generators (IIDG) connected to the grid through an inverter. The fault response of the IIDG is quite different from that of the traditional synchronous generator. The fault characteristics of the IIDG are affected by factors such as control strategy, low voltage ride-through characteristic, current limiting link and fault condition. The uncertainty of the output current of the IIDG poses great challenges to the setting and coordination of the traditional protection. SUMMARY

[0005] In order to solve the above problems, the present disclosure provides an active power distribution network current pilot differential protection method and system, which introduces an adaptive braking compensation coefficient, can meet the protection requirements of the active power distribution network under various fault scenarios, and realizes sensitive action in case of intra-zone fault and reliable braking in case of out-of-zone fault.

[0006] According to some embodiments, the first aspect of the present disclosure provides an active power distribution network current pilot differential protection method, which adopts the following technical scheme:

[0007] An active power distribution network current pilot differential protection method, comprising:

[0008] Obtaining phase current information of a line system side and a distributed generator side of a protected section, and determining whether to start protection;

[0009] After starting the protection, collecting cycle currents before and after a fault point, calculating the amplitude and phase of the fault current and the positive sequence current fault component, and calculating an adaptive braking compensation coefficient;

[0010] Based on the calculated adaptive braking compensation coefficient, a current pilot differential protection criterion is constructed;

[0011] Based on the constructed current longitudinal differential protection criteria, current longitudinal differential protection of active distribution networks is realized.

[0012] As a further technical limitation, in the process of calculating the adaptive braking compensation coefficient, the fault current is calculated based on the two-cycle current data before and after the fault abrupt change point. The amplitude and phase of the positive-sequence current fault component are calculated using a fast Fourier transform. Fault information is then sent to the other end, and information from the other end is requested. If no information from the other end is received, the phase current information is reacquired to determine whether to activate the protection. When information from the other end is received, the deformed sigmoid function f(|θ) is calculated. mn |) and the exponential function g(ε), according to Calculate the adaptive braking compensation coefficient K DG .

[0013] As a further technical limitation, the current longitudinal differential protection criterion is as follows: Where K is the braking coefficient; and These represent the positive-sequence current fault components on the line system side and the distributed power source side, respectively, K. DG This is the adaptive braking compensation coefficient.

[0014] As a further technical limitation, in the process of realizing the current longitudinal differential protection of the active distribution network based on the constructed current longitudinal differential protection criterion, it is necessary to determine whether the constructed current longitudinal differential protection criterion is valid. If it is valid, it is necessary to determine whether there is an unmeasurable load branch in the protected section; otherwise, it is determined to be an external fault.

[0015] Furthermore, when the protected section contains branches of unmeasurable loads, it is necessary to determine whether the auxiliary criteria are valid. If they are valid, the fault is determined to be within the protected area; otherwise, it is determined to be outside the protected area.

[0016] Furthermore, the auxiliary criterion is Among them, Z act Z is the operating impedance. act >0 indicates that the fault occurred within the range of the end protection; Z mea The measured impedance for end protection; Z L K represents the impedance value from the end protection to the protected feeder system side. rel The reliability coefficient is determined by factors such as transformer error, relay error, and parameter measurement error; Z set The set impedance corresponds to the total length of the line from the end protection to the protected feeder system.

[0017] Furthermore, when the protected section does not contain any unmeasurable load branches, it is determined to be an external fault.

[0018] According to some embodiments, the second solution of this disclosure provides an active distribution network current longitudinal differential protection system, which adopts the following technical solution:

[0019] An active distribution network current longitudinal differential protection system includes:

[0020] The acquisition module is configured to acquire phase current information from the line system side and the distributed power source side of the protected section, and determine whether to activate the protection.

[0021] The calculation module is configured to collect the cycle current before and after the fault abrupt point after the protection is activated, calculate the magnitude and phase of the fault current and the positive sequence current fault component, and calculate the adaptive braking compensation coefficient.

[0022] The module is configured to construct the current longitudinal differential protection criterion based on the calculated adaptive braking compensation coefficient;

[0023] The differential protection module is configured to realize current longitudinal differential protection of the active distribution network based on the constructed current longitudinal differential protection criterion.

[0024] According to some embodiments, a third aspect of this disclosure provides a computer-readable storage medium, employing the following technical solution:

[0025] A computer-readable storage medium having a program stored thereon that, when executed by a processor, implements the steps of the active distribution network current longitudinal differential protection method as described in the first aspect of this disclosure.

[0026] According to some embodiments, the fourth solution of this disclosure provides an electronic device that adopts the following technical solution:

[0027] An electronic device includes a memory, a processor, and a program stored in the memory and executable on the processor, wherein the processor, when executing the program, implements the steps of the active distribution network current longitudinal differential protection method as described in the first aspect of this disclosure.

[0028] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0029] This disclosure uses positive sequence current fault components to construct a current longitudinal differential protection, which can effectively eliminate the influence of load current, reflect all fault types, greatly reduce the amount of communication data transmission, and has strong tolerance to transition resistance. By introducing an adaptive braking compensation coefficient, the protection has higher sensitivity when operating during faults within the zone and higher reliability when braking during faults outside the zone, which can meet the protection needs of active distribution networks under any fault scenario.

[0030] This disclosure utilizes the polarity information of the operating impedance of the end protection to construct an auxiliary criterion, effectively solving the problem that unmeasurable load branches may cause protection maloperation. This invention can adaptively compensate for the braking current based on the amplitude ratio of the positive sequence current fault components on both sides of the line, resulting in strong protection resistance to time synchronization errors. Attached Figure Description

[0031] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure.

[0032] Figure 1 This is a flowchart of the active distribution network current longitudinal differential protection method in Embodiment 1 of this disclosure;

[0033] Figure 2 The function f(|θ) in Embodiment 1 of this disclosure mn |) Curve graph;

[0034] Figure 3 This is a graph of the function g(ε) in Embodiment 1 of this disclosure;

[0035] Figure 4 The braking coefficient K in Embodiment 1 of this disclosure DG *K surface plot;

[0036] Figure 5 This is the protection zone of the DG-containing distribution network in Embodiment 1 of this disclosure;

[0037] Figure 6 This is a schematic diagram of a 10kV active distribution network simulation model in Embodiment 1 of this disclosure;

[0038] Figure 7 This is a structural block diagram of the active distribution network current longitudinal differential protection system in Embodiment 2 of this disclosure. Detailed Implementation

[0039] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0040] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0041] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this disclosure. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0042] In this disclosure, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements in this disclosure, and do not specifically refer to any component or element in this disclosure, nor should they be construed as limiting this disclosure.

[0043] In this disclosure, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this disclosure based on the specific circumstances, and they should not be construed as limitations on this disclosure.

[0044] Where there is no conflict, the embodiments and features described herein can be combined with each other.

[0045] Example 1

[0046] Embodiment 1 of this disclosure introduces a method for longitudinal differential protection of active distribution network current.

[0047] like Figure 1 The active distribution network current longitudinal differential protection method shown includes the following steps:

[0048] Step S01: Acquire phase current information on the system side and DG side of the protected line in real time;

[0049] Step S02: After the protection is started, collect two cycles of current data before and after the fault change point, calculate the fault current, and then use fast Fourier transform to calculate the amplitude and phase of the positive sequence current fault component, send the fault information to the other end and request the other end's information.

[0050] Step S03: If information is received from the other end, calculate the deformed sigmoid function f(|θ) mn |) and the exponential function g(ε), and calculate the adaptive braking compensation coefficient K. DG ;

[0051] Step S04: Determine whether the current longitudinal differential protection criterion based on the adaptive braking compensation coefficient is valid. If it is not valid, it is determined to be an external fault. If it is valid, it is necessary to further determine whether there are unmeasurable load branches inside the protected section.

[0052] Step S05: If the protected section contains unmeasurable load branches, determine whether the auxiliary criterion is valid. If it is valid, it is determined to be an internal fault; if it is not valid, it is determined to be an external fault.

[0053] As one or more implementation methods, in step S01, a phase current sudden change fault detection algorithm is used to detect whether a fault has occurred, thereby determining whether the protection should be activated. The phase current sudden change fault detection algorithm is ||i(k)-i(kN)|-|i(kN)-i(k-2N)||≥K S I N Where i(k) is the sampled value of the phase current at time k; N is the number of sampling points per cycle; K s The starting coefficient, with a value ranging from 0.1 to 0.3; I N The rated current of the protected feeder is given. If the above formula is satisfied, the protection will be activated.

[0054] As one or more implementation methods, in step S03, specifically... K DG The adaptive braking compensation coefficients are determined using the deformed e-exponential function, which determines g(ε) and f(|θ). mn |), that is

[0055]

[0056] Where, |θ mn | and ε are the absolute value and amplitude ratio of the phase difference between the positive sequence current fault components on the protected line system side and the DG side, respectively; the function f(|θ mn |) is the transformed sigmoid function with (b, 0.5) as the symmetric point, and the larger the value of a, the steeper the function is; the function g(ε) is the exponential function of e, which passes through the point (d, 1), and the larger the value of c, the faster the function decreases.

[0057] For faults outside the protection zone, whether it is a distribution network containing MTDG or IIDG, under ideal conditions, the amplitude ratio of the positive sequence current fault components on both sides of the protected section is 1, and the phase difference is 180°. However, in actual engineering, the measurement error of the current transformer and the blocking angle of the current longitudinal differential protection need to be considered. The maximum measurement error of the current transformer is usually taken as ±10%, so the range of the amplitude ratio of the positive sequence current fault components on both sides is [0.82, 1.22]. Assuming that the blocking angle of the current longitudinal differential protection is 45°, the phase difference of the positive sequence current fault components on both sides during faults outside the protection zone is [135°, 225°].

[0058] Amplitude and phase characteristics of positive sequence current fault components in distribution networks containing MTDG:

[0059] The MTDG is analyzed as an equivalent voltage source and internal impedance in series. The analysis shows that when there is a fault in the zone, the amplitude ratio of the positive sequence current fault components on both sides of the protected line is relatively large, with the upper limit being greater than 1 and the lower limit being less than 1; the phase difference of the positive sequence current fault components on both sides is between 0 and 18°.

[0060] Amplitude and phase characteristics of positive-sequence current fault components in distribution networks containing IIDG:

[0061] Analyzing the IIDG as an equivalent voltage-controlled current source, it can be found that during faults within the zone, the ratio of the magnitudes of the positive-sequence current fault components on both sides of the protected line is much greater than 1. Considering extreme cases, current transformer measurement errors, and certain margins, the minimum value of the ratio of the magnitudes of the positive-sequence current fault components on both sides can be considered to be approximately 1.6. The phase difference of the positive-sequence current fault components on both sides is affected by factors such as voltage drop at the grid connection point and fault conditions, and its value ranges from 0° to 180°.

[0062] Based on the boundary conditions for faults outside the aforementioned area, and taking into account a certain margin, K can be determined. DG The values ​​of b and d are 3π / 4 and 1.25, respectively. Based on the fault boundary conditions within the above area, the values ​​of a, c, and K can be determined to be 5, 6, and 0.3, respectively, and f(|θ mn |) The graph of the function is as follows Figure 2 As shown, the graph of the g(ε) function is as follows: Figure 3 As shown, the braking coefficient K DG *K surface diagram as shown Figure 4 As shown; where, Figure 2 , Figure 3 The shaded area represents the region corresponding to the fault outside the designated area. According to... Figure 4 It can be seen that after adaptive compensation, the braking coefficient is larger when there is a fault outside the zone and smaller when there is a fault inside the zone. The braking coefficient is adaptively adjusted according to the amplitude ratio and phase difference of the positive sequence current fault components on both sides of the line.

[0063] As one or more implementation methods, in step S04, the traditional current longitudinal differential protection criterion is:

[0064]

[0065] Wherein, K is the braking coefficient, which is usually set to avoid the saturation current of the TA during a fault outside the zone, and its value is less than 1; These are the positive sequence current fault components on the line system side and the DG side, respectively.

[0066] Introducing an adaptive braking compensation coefficient K DG Subsequently, a novel current longitudinal differential protection criterion based on adaptive braking compensation coefficient is established.

[0067]

[0068] The operating characteristics of the novel current longitudinal differential protection based on adaptive braking compensation coefficient are as follows:

[0069] (1) For non-faulty sections, under ideal conditions, the amplitude ratio of the positive sequence current fault components on both sides of the section is 1, and the phase difference is 180°, K DG =+∞, the protection is reliable and does not operate. Considering the measurement error of the current transformer, the blocking angle, and a certain margin, it can be assumed that the amplitude ratio of the positive sequence current fault components on both sides ε∈[0.8,1.25], and the phase difference |θ mn |∈[135°,180°]. When taking the limiting case ε=1.25, |θ mn When |=135°, K DG The minimum value is 2. Even after compensation, the braking current is still greater than the differential current, so the protection is reliable and does not operate.

[0070] (2) For a fault section downstream of the fault point connected to an MTDG, the phase angle difference |θ| between the positive sequence current fault components on both sides mn |smaller,|θ mn |∈[0°,18°], at this time K DG The braking current is approximately 0 after compensation, ensuring reliable protection operation and high sensitivity.

[0071] (3) For a fault section downstream of the fault point connected to an IIDG, when the phase difference |θ mn When |<π / 2, f(|θ) mn |)≈0,K DG ≈0, the braking current after compensation is approximately 0, and the protection is sensitive and reliable; when the phase difference π / 2 ≤ |θ mn When |≤π and ε>>1, then g(ε)≈0, K DG ≈0, the braking current is approximately 0, ensuring sensitive and reliable protection; when taking the limiting case |θ mnWhen |=π and ε=1.6, this is the fault scenario with the lowest protection sensitivity. At this time, K*K DG =0.22, the differential current is still greater than the braking current after compensation, and the protection operates reliably.

[0072] As one or more implementation methods, in step S05, it is assumed that there are unmeasurable load branches inside the protected section. The fault points are located outside the zone and upstream of the unmeasurable load branch, outside the zone and downstream of the unmeasurable load branch, inside the zone and upstream of the unmeasurable load branch, and inside the zone and downstream of the unmeasurable load branch, respectively. Corresponding positive sequence fault component composite sequence networks are generated and analyzed. The analysis shows that when an external fault occurs, the unmeasurable load branch located downstream of the fault point will cause the protection device of the section to malfunction. In the other three fault cases, the influence of the unmeasurable load branch on the protection can be ignored. Therefore, it is necessary to establish corresponding auxiliary criteria to prevent the protection from malfunctioning.

[0073] The protection zone is divided with the DG grid connection point as the boundary, such as Figure 5 As shown, the system is broadly divided into upstream protection zones and downstream protection zones. Zones 1, 2, and 4 are upstream protection zones, while zones 3 and 5 are downstream protection zones. The feeders in the upstream protection zones are equipped with the protection proposed in this invention. The protection device furthest from the system power supply within the upstream protection zone is called the end protection for that zone, such as protection 7 in zone 1, protection 9 in zone 2, and protection 13 in zone 4. Introducing the voltage at the grid connection point, an auxiliary criterion is constructed using the operating impedance polarity information of the end protection. Referring to the operating characteristics of the amplitude-modulation directional impedance relay, the auxiliary criterion is...

[0074]

[0075] Among them, Z act Z is the operating impedance. act >0 indicates that the fault occurred within the range of the end protection; Z mea The measured impedance for end protection; Z L K represents the impedance value from the end protection to the protected feeder system side. rel The reliability coefficient is determined by factors such as transformer error, relay error, and parameter measurement error; Z set The set impedance corresponds to the total length of the line from the end protection to the protected feeder system.

[0076] A 10kV active distribution network model was built using PSCAD / EMTDC simulation software. The model structure is as follows: Figure 6As shown. Transformer T has a capacity of 50MVA and a transformer ratio of 35kV / 10.5kV. Lines B2B4, B4B5, and B5B6 are 6km, 6km, and 5km long, respectively, while the remaining line sections are all 4km long. The line parameters are (0.13+i0.402)Ω / km. Distributed power sources DG1, DG2, and DG3 are all IIDGs with rated capacities of 2.5MW, 2.5MW, and 2MW, respectively. DG4 is an MTDG with a rated capacity of 4MW. The load capacity is 2MW for all lines, and the load power factor is 0.9.

[0077] Define the sensitivity coefficient K sen for

[0078]

[0079] Where K′=K, K sen The sensitivity corresponding to traditional current longitudinal differential protection; K′=K*K DG At that time, K sen The sensitivity of the novel current longitudinal differential protection proposed in this invention. When K sen Greater than 1, protective action, and K sen The higher the value, the more sensitive the protection action; when K sen If the value is less than 1, the protection will not activate, and K sen The smaller the value, the higher the reliability of the protection against failure to activate.

[0080] The differential protection described in this embodiment is then tested for short-circuit faults, resistance to transition resistance, and adaptability to unmeasurable load branches.

[0081] Short circuit fault test

[0082] For feeders containing IIDG, with line B4B5 as the protected section, different types (two-phase, two-phase grounding, and three-phase) metallic short-circuit faults were simulated at different locations (start, middle, and end) within this section. The simulation results are shown in Table 1. Similarly, for feeders containing MTDG, with line B7B8 as the protected section, the corresponding simulation results are shown in Table 2. In the tables, A-CDP and T-CDP represent the new type of current longitudinal differential protection and the traditional current differential protection, respectively. As can be seen from Tables 1 and 2, both A-CDP and T-CDP can operate correctly when a metallic short-circuit fault occurs, but the sensitivity of A-CDP is significantly higher than that of T-CDP.

[0083] Table 1 Simulation results of short-circuit fault in feeder B4B5

[0084]

[0085] Table 2 Simulation results of short-circuit faults in feeders B7 and B8.

[0086]

[0087] Transition resistance test

[0088] Two-phase ground faults were set at different locations on line B5B6 to test the ability to withstand transition resistance. The transition resistances were 25Ω, 50Ω, 100Ω, and 150Ω, respectively. The simulation results are shown in Table 3. Table 3 shows that when a high-resistance ground fault occurs in the area, the A-CDP operates correctly with high sensitivity. As the transition resistance at the fault point increases, the sensitivity of the T-CDP gradually decreases. When the transition resistance is greater than 50Ω, the T-CDP may fail to operate. For example, when the fault occurs at the end of the line with a transition resistance of 100Ω, or when the fault occurs in the middle of the line with a transition resistance of 150Ω, the T-CDP will fail to operate. Since the sensitivity value of the T-CDP under high resistance conditions is mainly concentrated around 1, and the uncertainty of external factors such as transformer transmission error, protection measurement error, and data processing error may cause traditional current longitudinal differential protection to fail to operate correctly under high-resistance ground fault conditions, the novel protection method proposed in this invention has superior operating performance compared to traditional protection.

[0089] Table 3 Simulation results of high-resistance short-circuit fault in feeder B5B6

[0090]

[0091] Protection against unmeasurable load branch adaptability test

[0092] Using feeder B4B5 as the protected section, an unmeasurable load branch was added inside it. The operating performance of the new protection system under faults inside and outside the protected section was tested. The simulation results are shown in Table 4. The simulation results show that when the fault point f1 is located inside the protected section, the protection operates correctly and has high sensitivity; when the fault point f3 is located outside the protected section and upstream of the unmeasurable load branch, the ratio of the positive sequence current fault component amplitudes on both sides of the protected section is greater than 1. At this time, K sen The value increased slightly, but K sen If the value is still less than 1, the operating impedance polarity is negative, and the protection is reliable and does not operate; when the fault point f2 is located outside the protected section and downstream of an unmeasurable load branch, K sen When the value equals 0, the operating impedance polarity is negative, and the protection reliably does not operate. This demonstrates that the novel protection method proposed in this invention can effectively adapt to feeders containing branches with unmeasurable loads.

[0093] Table 4 Simulation Results of Faults in Branch Lines with Unmeasurable Loads

[0094]

[0095] This embodiment employs positive-sequence current fault components to construct a longitudinal differential protection system, effectively eliminating the influence of load current, reflecting all fault types, significantly reducing the amount of data transmitted during communication, and exhibiting strong tolerance to transition resistance. By introducing an adaptive braking compensation coefficient, the protection achieves higher sensitivity during faults within the protection zone and higher reliability during faults outside the zone, meeting the protection requirements of active distribution networks under any fault scenario. The auxiliary criterion is constructed using the polarity information of the operating impedance of the end-point protection, effectively solving the problem of potential maloperation of the protection due to unmeasurable load branches. This invention can adaptively compensate the braking current based on the amplitude ratio of the positive-sequence current fault components on both sides of the line, resulting in strong protection resistance to time synchronization errors.

[0096] Example 2

[0097] Embodiment 2 of this disclosure introduces an active power distribution network current longitudinal differential protection system.

[0098] like Figure 7 The active distribution network current longitudinal differential protection system shown includes:

[0099] The acquisition module is configured to acquire phase current information from the line system side and the distributed power source side of the protected section, and determine whether to activate the protection.

[0100] The calculation module is configured to collect the cycle current before and after the fault abrupt point after the protection is activated, calculate the magnitude and phase of the fault current and the positive sequence current fault component, and calculate the adaptive braking compensation coefficient.

[0101] The module is configured to construct the current longitudinal differential protection criterion based on the calculated adaptive braking compensation coefficient;

[0102] The differential protection module is configured to realize current longitudinal differential protection of the active distribution network based on the constructed current longitudinal differential protection criterion.

[0103] The detailed steps are the same as those of the active distribution network current longitudinal differential protection method provided in Example 1, and will not be repeated here.

[0104] Example 3

[0105] Embodiment 3 of this disclosure provides a computer-readable storage medium.

[0106] A computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps of the active distribution network current longitudinal differential protection method as described in Embodiment 1 of this disclosure.

[0107] The detailed steps are the same as those of the active distribution network current longitudinal differential protection method provided in Example 1, and will not be repeated here.

[0108] Example 4

[0109] Embodiment 4 of this disclosure provides an electronic device.

[0110] An electronic device includes a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the active distribution network current longitudinal differential protection method as described in Embodiment 1 of this disclosure.

[0111] The detailed steps are the same as those of the active distribution network current longitudinal differential protection method provided in Example 1, and will not be repeated here.

[0112] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

[0113] While the specific embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this disclosure. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this disclosure are still within the scope of protection of this disclosure.

Claims

1. A method for longitudinal differential protection of active distribution network current, characterized in that, include: Obtain phase current information from the line system side and distributed power source side of the protected section to determine whether to activate protection; After the protection is activated, the cycle current before and after the fault abrupt change point is collected, the magnitude and phase of the fault current and the positive sequence current fault component are calculated, and the adaptive braking compensation coefficient is calculated. Based on the calculated adaptive braking compensation coefficient, a current longitudinal differential protection criterion is constructed. Based on the constructed current longitudinal differential protection criteria, current longitudinal differential protection of active distribution networks is realized; In the process of calculating the adaptive braking compensation coefficient, the fault current is calculated based on the two-cycle current data before and after the fault abrupt change point. The amplitude and phase of the positive sequence current fault component are calculated by combining the fast Fourier transform. Fault information is sent to the other end and information from the other end is requested. If no information is received from the other end, the phase current information is reacquired to determine whether to activate the protection; when information is received from the other end, the modified phase current information is calculated. sigmoid function and e Exponential function g ( ε ),according to Calculate the adaptive braking compensation coefficient K DG The modified sigmoid function and e Exponential function g ( ε )for: ， in, , ε These are the absolute value and amplitude ratio of the phase difference between the positive sequence current fault components on the protected line system side and the DG side, respectively; function by( b (0.5) is a symmetrical point, and a The larger the value, the steeper the function; the function g ( ε )go through( d ,1) point, and c The larger the value of , the faster the function decreases; The current longitudinal differential protection criterion is as follows: ;in, K This is the braking coefficient; and These are the positive-sequence current fault components on the line system side and the distributed power source side, respectively. K DG This is the adaptive braking compensation coefficient.

2. The active distribution network current longitudinal differential protection method as described in claim 1, characterized in that, In the process of realizing the current longitudinal differential protection of the active distribution network based on the constructed current longitudinal differential protection criterion, it is necessary to determine whether the constructed current longitudinal differential protection criterion is valid. If it is valid, it is necessary to determine whether there are unmeasurable load branches in the protected section. Otherwise, it is determined to be an out-of-area fault.

3. The active distribution network current longitudinal differential protection method as described in claim 2, characterized in that, When the protected section contains branches of unmeasurable loads, it is necessary to determine whether the auxiliary criteria are valid. If they are valid, the fault is determined to be within the protected area; otherwise, it is determined to be outside the protected area.

4. The active distribution network current longitudinal differential protection method as described in claim 3, characterized in that, The auxiliary criterion is ;in, Z act For the action impedance, Z act >0 indicates that the fault occurred within the range of the end protection; Z mea The measured impedance for end protection; Z L The impedance value from the end protection to the protected feeder system side; K rel The reliability coefficient is determined by factors such as transformer error, relay error, and parameter measurement error. Z set The set impedance corresponds to the total length of the line from the end protection to the protected feeder system.

5. The active distribution network current longitudinal differential protection method as described in claim 2, characterized in that, When the protected section does not contain any unmeasurable load branches, it is determined to be an external fault.

6. An active distribution network current longitudinal differential protection system, characterized in that, include: The acquisition module is configured to acquire phase current information from the line system side and the distributed power source side of the protected section, and determine whether to activate the protection. The calculation module is configured to collect the cycle current before and after the fault abrupt point after the protection is activated, calculate the magnitude and phase of the fault current and the positive sequence current fault component, and calculate the adaptive braking compensation coefficient. The module is configured to construct the current longitudinal differential protection criterion based on the calculated adaptive braking compensation coefficient; The differential protection module is configured to realize current longitudinal differential protection of the active distribution network based on the constructed current longitudinal differential protection criterion. In the process of calculating the adaptive braking compensation coefficient, the fault current is calculated based on the two-cycle current data before and after the fault abrupt change point. The amplitude and phase of the positive sequence current fault component are calculated by combining the fast Fourier transform. Fault information is sent to the other end and information from the other end is requested. If no information is received from the other end, the phase current information is reacquired to determine whether to activate the protection; when information is received from the other end, the modified phase current information is calculated. sigmoid function and e Exponential function g ( ε ),according to Calculate the adaptive braking compensation coefficient K DG After deformation sigmoid function and e Exponential function g ( ε )for: ， in, , ε These are the absolute value and amplitude ratio of the phase difference between the positive sequence current fault components on the protected line system side and the DG side, respectively; function by( b (0.5) is a symmetrical point, and a The larger the value, the steeper the function; the function g ( ε )go through( d ,1) point, and c The larger the value of , the faster the function decreases; The current longitudinal differential protection criterion is as follows: ;in, K This is the braking coefficient; and These are the positive-sequence current fault components on the line system side and the distributed power source side, respectively. K DG This is the adaptive braking compensation coefficient.

7. A computer-readable storage medium having a program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the active distribution network current longitudinal differential protection method as described in any one of claims 1-5.

8. An electronic device comprising a memory, a processor, and a program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the active distribution network current longitudinal differential protection method as described in any one of claims 1-5.

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