A single-phase disconnection fault protection method and system for active power distribution network

Abstract

The present invention discloses a single-phase line break fault protection method and system for an active distribution network, comprising the following steps: real-time acquisition of the amplitude of the bus positive-sequence voltage of the active distribution network, the amplitude of the output current of the distributed power source connected to each feeder, and the amplitude of the negative-sequence current at the outlet of each feeder; if there is a real-time change in the amplitude of the output current of the distributed power source of the feeder that meets the conditions; obtain the magnitude of the action threshold value of each feeder action element and the action threshold value of the action element of the corresponding feeder, then the action element is actuated to determine that a single-phase line break fault has occurred in the feeder; the signal element sends a trip command or an alarm signal. Beneficial effects of the present invention: The present invention uses negative-sequence current to monitor single-phase line break faults in an active distribution network; a single-phase line break fault will cause a sudden increase in the negative-sequence current of the faulty feeder, and the present invention has a higher reliability based on the characteristic that the negative-sequence current of the faulty feeder is significantly greater than the negative-sequence current of the non-faulty feeder.

Description

Technical Field

[0001] The present invention relates to the technical field of active distribution network fault protection, and in particular to a negative sequence current-based single-phase line break fault protection method and system for an active distribution network. Background Art

[0002] In recent years, with the rapid development of social economy, energy has played an increasingly important role in human social life, but it has also led to the waste of resources and environmental pollution. In order to reduce the use of fossil energy and environmental pollution, countries around the world have proposed policies and measures to develop and utilize new energy. Sustainable development strategies represented by renewable energy generation such as solar energy and wind energy have become the development strategies of various countries. Connecting to the distribution network in the form of distributed power sources is one of the main forms of renewable energy generation. With the continuous increase in the scale of distributed power sources, the impact on the operation, control, and protection of the distribution network has become increasingly serious. For this reason, the concept of active distribution network has been proposed. Active distribution network is defined as a distribution network that can comprehensively control distributed power sources, flexible loads, and energy storage, and use network technology to achieve effective management of power flow, and can flexibly adjust the network topology. However, the access of distributed power sources has changed the fault characteristics and distribution of electrical quantities, which is quite different from the traditional distribution network, and also brings great difficulties and challenges to protection. Therefore, active distribution network relay protection has become a hot topic in current research. Summary of the invention

[0003] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0004] In view of the above existing problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by the present invention is: to propose a single-phase line break fault protection method for an active distribution network based on negative sequence current, the setting calculation is only related to system parameters, and is independent of the distribution of distributed power sources and the fault location, and has high sensitivity and reliability.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: a single-phase line break fault protection method for an active distribution network based on negative sequence current, comprising the following steps: real-time acquisition of the amplitude of the bus positive sequence voltage of the active distribution network, the amplitude of the output current of the distributed power source connected to each feeder, and the amplitude of the negative sequence current at the outlet of each feeder; if there is a real-time change in the amplitude of the output current of the distributed power source of the feeder that meets the conditions, the starting element is actuated; the magnitude of the action threshold value of the action element of each feeder and the action threshold value of the action element of the corresponding feeder are obtained, and if a feeder meets the conditions, the action element is actuated to determine that a single-phase line break fault occurs in the feeder; it is determined that a single-phase line break fault occurs in the feeder, and the signal element sends a trip command or an alarm signal.

[0007] As a preferred solution of the single-phase disconnection fault protection method of the active distribution network based on negative sequence current described in the present invention, it includes the following steps: real-time acquisition of the amplitude U of the positive sequence voltage of the busbar of the active distribution network M1 , collect the amplitude of the output current of the distributed power source connected to each feeder I DG,ij , collect the amplitude of negative sequence current I at each feeder outlet 2i , where i = 1, 2, ... m, j = 1, 2, ... n i , m is the number of feeders, n i is the number of distributed power sources connected to feeder i; obtain the real-time change in the output current amplitude of each distributed power source of each feeder ΔI DG,ij , according to ΔI DG,ij Determine whether the starting element is actuated. If not, return to re-collect the amplitude until the starting element is actuated; compare the real-time collected negative sequence current amplitude of each feeder I 2i The action threshold value I of the action element of the feeder 2iZD The size of the sensor is used to determine whether the action element is in action. If not, the sensor returns to collect data again until the start element is in action. It is determined that a single-phase disconnection fault occurs on feeder i, and the signal element is started to issue a trip command or alarm signal.

[0008] As a preferred solution of the single-phase line break fault protection method based on negative sequence current of the active distribution network described in the present invention, the real-time change of the output current amplitude of each distributed power source of each feeder ΔI DG,ij As follows:

[0009] ΔI DG,ij =|I DG,ij(t) -I DG,ij(t-T) |

[0010] Among them, I DG,ij(t) is the output current amplitude of the distributed power supply at the current moment, I DG,ij(t-T) It is the output current amplitude of the distributed power supply in the previous cycle.

[0011] As a preferred solution of the single-phase line break fault protection method based on negative sequence current of the active distribution network of the present invention, wherein: the action threshold value I of the action element of the i-th feeder 2iZD As follows:

[0012] I 2iZD =K rel ·{I 2i.min}, i=1,2,…,m

[0013] Where K rel is the reliability coefficient, taking 1.1~1.2, I 2i.min is the minimum negative sequence current when a single-phase disconnection fault occurs on the i-th feeder, where i = 1, 2, …, m, and m is the number of feeders.

[0014] As a preferred solution of the active distribution network single-phase disconnection fault protection method based on negative sequence current described in the present invention, the action criterion of the starting element according to the real-time change amount is:

[0015] ΔI DG,ij >0

[0016] Among them, ΔI DG,ij is the real-time change in the output current amplitude of each distributed power source of each feeder; the action criterion of the action element according to the action threshold value is:

[0017] I 2i >KI 2iZD

[0018] Among them, I 2i is the magnitude of the negative sequence current at the outlet of the ith feeder, I 2iZD is the action threshold value of the action element of the i-th feeder, K is the reliability coefficient, which is 1.1~1.2.

[0019] As a preferred solution of the single-phase disconnection fault protection method for active distribution network based on negative sequence current of the present invention, the minimum negative sequence current I when the single-phase disconnection fault occurs in the i-th feeder is 2i.min As follows:

[0020] I 2i.min =min{I i(1) ,I i(2)}

[0021] In the formula, I i(1) is the minimum negative sequence current of the ith feeder when a single-phase line break occurs upstream of the distributed generation, I i(2) is the minimum negative sequence current of the i-th feeder when a single-phase line break fault occurs downstream of the distributed generation.

[0022] As a preferred solution of the single-phase line break fault protection method based on negative sequence current of the active distribution network described in the present invention, the minimum negative sequence current I of the i-th feeder when the single-phase line break fault occurs upstream of the distributed power source is i(1) As follows:

[0023]

[0024] In the formula, Z S2 is the system equivalent negative sequence impedance, Z iΣ is the total load impedance of feeder i, (Z iN2 ) max is the maximum value of the negative sequence load impedance downstream of the single-phase disconnection fault point of feeder i, (U pcci ) max is the maximum value of the voltage at the grid connection point of the feeder i distributed power source when the single-phase line break fault occurs upstream of the distributed power source; and the minimum value of the negative sequence current I of the i-th feeder when the single-phase line break fault occurs downstream of the distributed power source i(2) As follows:

[0025]

[0026] Where Z0 is the zero-sequence impedance of the system after a single-phase disconnection fault on feeder i.

[0027] As a preferred solution of the single-phase line break fault protection method for active distribution network based on negative sequence current described in the present invention, wherein: when the single-phase line break fault occurs at the upstream of the distributed power source, the maximum value of the grid connection point voltage (U pcci ) max As follows:

[0028]

[0029] Where P refi is the reference power of the distributed generation of the i-th feeder.

[0030] As a preferred solution of the negative sequence current based active distribution network single-phase disconnection fault protection method of the present invention, the zero-sequence impedance Z0 of the system after the single-phase disconnection fault of feeder i is as follows:

[0031]

[0032] In the formula, Z g is the neutral point grounding impedance of the active distribution network; C j is the capacitance of all feeders except feeder i; C i is the capacitance of feeder i, and ω is the system angular frequency.

[0033] The technical problem solved by the present invention is: to propose an active distribution network single-phase disconnection fault protection system based on negative sequence current, and the above method is realized by relying on this system.

[0034] To solve the above technical problems, the present invention provides the following technical solutions: an active distribution network single-phase line break fault protection system based on negative sequence current, comprising a starting element, an action element and a signal element; the starting element starts the action element by comparing the change of the output current of the distributed power source; the action element starts the signal element by comparing the negative sequence current of the feeder with the action threshold value; the signal element is used to issue a tripping command or an alarm signal.

[0035] Beneficial effects of the present invention: The present invention utilizes negative sequence current to monitor single-phase line break faults in active distribution networks; a single-phase line break fault will cause a sudden increase in the negative sequence current of the fault feeder. The present invention has higher reliability based on the characteristic that the negative sequence current of the fault feeder is significantly greater than the negative sequence current of the non-fault feeder. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0037] Figure 1 This is a schematic diagram of the structure of the 10kV active distribution network of the present invention;

[0038] Figure 2 The present invention provides an overall flow chart of the negative sequence current based active distribution network single-phase line break fault protection method. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0040] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0041] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0042] The present invention is described in detail with reference to schematic diagrams. When describing the embodiments of the present invention, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0043] At the same time, in the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper, lower, inner and outer" are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first, second or third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0044] In the present invention, unless otherwise clearly specified and limited, the terms "install, connect, connect" should be understood in a broad sense, for example: it can be a fixed connection, a detachable connection or an integral connection; it can also be a mechanical connection, an electrical connection or a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] Example 1

[0046] Due to the effects of lightning strikes, external forces, electrical and other factors, the frequency of line disconnection faults in distribution networks has increased year by year. Compared with short-circuit faults, line disconnection faults do not cause large currents and high voltages, and the impact is limited. At present, faults are still reflected through voltage anomalies and handled by the "pulling the line method", which is time-consuming and labor-intensive. However, line disconnection faults can cause serious asymmetry in the three-phase voltage and current on the power supply side and the load side, which will not only greatly reduce the benefits and value of distributed power sources, but also cause serious impacts such as damage to electrical equipment, reduced power quality, and power supply interruptions, and may even cause serious personal injury accidents, with disastrous consequences.

[0047] Relay protection of power systems has always been the research focus of technicians in this field. Short-circuit fault protection technology is relatively mature, but there are essential differences in the principles and characteristics of short-circuit faults and line break faults. Short-circuit fault protection methods cannot be used to identify and isolate line break faults. For active distribution networks, there are few studies on line break faults. Most of the existing line break fault protection methods are aimed at traditional distribution networks, and can be roughly divided into three categories: based on voltage characteristics, transient signals, and negative sequence currents. However, the section positioning method based on voltage change characteristics is greatly affected by the neutral point grounding method, the data processing volume is large, and the communication and data synchronization requirements are high. For the line break selection method based on transient signals, the actual noise has a greater impact on the signal. Moreover, most of the above methods are only applicable to the neutral point ungrounded or arc suppression coil grounding method, ignoring the influence of zero-sequence current.

[0048] It is worth noting that the line break protection method based on negative sequence current is currently the most commonly used and simplest method for line break protection in distribution networks. When the system is operating normally, the negative sequence current of the outgoing line is basically 0; when a line break fault occurs, the negative sequence current of the fault line increases suddenly. Negative sequence current protection is based on the principle that the negative sequence current of the fault line is larger than the current of the non-fault line. The setting value of its criterion needs to avoid the maximum negative sequence current of this line when a line break fault occurs in other lines. However, the magnitude of the negative sequence current is greatly affected by the position of the line break and the load distribution. Due to the changeable load conditions of the distribution network, the setting is very difficult. In addition, in the active distribution network, the magnitude of the negative sequence current will also be affected by the distributed power supply. Therefore, the existing negative sequence current protection method has no reference setting calculation method in the active distribution network, so it is difficult to apply.

[0049] In summary, due to the influence of the access of distributed power sources, on the one hand, the existing traditional distribution network disconnection fault protection method is no longer applicable to the active distribution network, and on the other hand, there is a lack of setting calculation and improvement methods for negative sequence current protection of the active distribution network. Therefore, how to achieve accurate line selection for active distribution network disconnection faults and enhance the practicality of protection based on the existing traditional distribution network disconnection protection technology is an urgent problem that technicians in this field need to solve.

[0050] In view of the above problems, this embodiment proposes a negative-sequence current protection criterion for a single-phase line break fault in an active distribution network, which effectively solves technical problems such as the difficulty in setting the negative-sequence current of a single-phase line break fault in an active distribution network in the prior art. The setting calculation is only related to the system parameters and has nothing to do with the distribution of distributed power sources and the fault location, and has high sensitivity and reliability.

[0051] Specifically, this embodiment proposes a single-phase line break fault protection method for an active distribution network based on negative sequence current, comprising the following steps:

[0052] S1: Real-time acquisition of the amplitude of the bus positive sequence voltage of the active distribution network, the amplitude of the output current of the distributed power source connected to each feeder, and the amplitude of the negative sequence current at the outlet of each feeder;

[0053] S2: judging the action of the starting element according to the real-time change of the output current amplitude of the distributed power supply;

[0054] S3: The real-time collected negative sequence current amplitude of each feeder is compared with the action threshold value of the action element of the feeder until it is determined that the starting element is actuated;

[0055] S4: When it is determined that a single-phase disconnection fault occurs in the feeder, the signal element is started and a trip command or alarm signal is issued.

[0056] In layman's terms, first collect the amplitude of the positive-sequence voltage of the active distribution network bus, the amplitude of the output current of the distributed power sources connected to each feeder, and the amplitude of the negative-sequence current at the outlet of each feeder; judge whether the starting element is actuated based on the real-time change in the output current amplitude of each distributed power source of each feeder, and if the starting element action conditions are met, implement the next step, otherwise return to the first step; after the starting element is actuated, calculate the action threshold value of the action element of each feeder based on the system parameters; compare the real-time collected negative-sequence current amplitude of each feeder with the action threshold value of the feeder, and if the action conditions of the action element are met, implement the next step, otherwise return to the first step; after a feeder action element is actuated, it is determined that a single-phase line break fault has occurred in the feeder, and the signal element issues a trip command or an alarm signal.

[0057] Further refinement of the above steps includes the following more specific steps:

[0058] S1: Real-time acquisition of the amplitude of the positive sequence voltage U of the active distribution network busbar M1 , collect the amplitude of the output current of the distributed power source connected to each feeder I DG,ij , collect the amplitude of negative sequence current I at each feeder outlet 2i , where i = 1, 2, ... m, j = 1, 2, ... n i , m is the number of feeders, n i is the number of distributed generation connected to feeder i.

[0059] The minimum negative sequence current I when a single-phase disconnection fault occurs on the i-th feeder 2i.min As follows:

[0060] I 2i.min =min{I i(1) ,I i(2)}

[0061] In the formula, I i(1) is the minimum negative sequence current of the ith feeder when a single-phase line break occurs upstream of the distributed generation, I i(2)is the minimum negative sequence current of the i-th feeder when a single-phase line break fault occurs downstream of the distributed generation.

[0062] S2: Obtain the real-time change ΔI of the output current amplitude of each distributed power source on each feeder DG,ij , according to ΔI DG,ij Determine whether the starting element is actuated. If not, return to re-collect the amplitude until the starting element is actuated.

[0063] Furthermore, the real-time change of the output current amplitude of each distributed power source of each feeder ΔI DG,ij As follows:

[0064] ΔI DG,ij =|I DG,ij(t) -I DG,ij(t-T) |

[0065] Where I DG,ij(t) is the output current amplitude of the distributed power supply at the current moment, I DG,ij(t-T) It is the output current amplitude of the distributed power supply in the previous cycle.

[0066] The action criteria (conditions) of the starting element according to the real-time change are:

[0067] ΔI DG,ij >0

[0068] Among them, ΔI DG,ij The real-time change in the output current amplitude of each distributed power source of each feeder;

[0069] S3: Compare the negative sequence current amplitude I of each feeder collected in real time 2i The action threshold value I of the action element of the feeder 2iZD The size of the action component is used to determine whether it is in action. If not, it returns to collect again until the action of the startup component is started.

[0070] Among them, the action threshold value of the action element of the i-th feeder is I 2iZD As follows:

[0071] I 2iZD =K rel ·{I 2i.min}, i=1,2,…,m

[0072] Where K rel is the reliability coefficient, taking 1.1~1.2, I 2i.min is the minimum negative sequence current when a single-phase disconnection fault occurs on the i-th feeder, where i = 1, 2, …, m, and m is the number of feeders.

[0073] Furthermore, the action criterion (condition) of the action element according to the action threshold value is:

[0074] I 2i >KI 2iZD

[0075] Among them, I 2i is the magnitude of the negative sequence current at the outlet of the ith feeder, I 2iZD is the action threshold value of the action element of the i-th feeder, K is the reliability coefficient, which is 1.1~1.2.

[0076] S4: Determine that a single-phase disconnection fault occurs on feeder i, start the signal element, and issue a trip command or alarm signal.

[0077] It should be noted that the minimum negative sequence current I of the i-th feeder when the single-phase line break fault occurs upstream of the distributed generation is i(1) As follows:

[0078]

[0079] In the formula, Z S2 is the system equivalent negative sequence impedance, Z iΣ is the total load impedance of feeder i, (Z iN2 ) max is the maximum value of the negative sequence load impedance downstream of the single-phase disconnection fault point of feeder i, (U pcci ) max is the maximum value of the voltage at the grid connection point of the distributed power generation of feeder i when a single-phase line break fault occurs upstream of the distributed power generation;

[0080] And the minimum negative sequence current I of the i-th feeder when the single-phase line break fault occurs downstream of the distributed generation i(2) As follows:

[0081]

[0082] Where Z0 is the zero-sequence impedance of the system after a single-phase disconnection fault on feeder i.

[0083] Furthermore, when a single-phase line break occurs upstream of the distributed generation, the maximum value of the grid connection point voltage of the i-th feeder distributed generation (U pcci ) max As follows:

[0084]

[0085] Where P refi is the reference power of the distributed generation of the i-th feeder.

[0086] After a single-phase disconnection fault on feeder i, the system zero-sequence impedance Z0 is as follows:

[0087]

[0088] In the formula, Z g is the neutral point grounding impedance of the active distribution network; C j is the capacitance of all feeders except feeder i; C i is the capacitance of feeder i, and ω is the system angular frequency.

[0089] Example 2

[0090] In this embodiment, an active distribution network single-phase line break fault protection system based on negative sequence current is proposed. The method of the above embodiment is implemented based on this embodiment. The system includes a starting element, an action element and a signal element; wherein the starting element starts the action element by comparing the change of the output current of the distributed power source; the action element starts the signal element by comparing the negative sequence current of the feeder with the action threshold value; the signal element is used to issue a tripping command or an alarm signal.

[0091] The present invention uses negative sequence current to monitor single-phase line break faults in active distribution networks. Single-phase line break faults will cause a sudden increase in the negative sequence current of the fault feeder. The present invention is based on the characteristic that the negative sequence current of the fault feeder is significantly greater than the negative sequence current of the non-fault feeder, and has high reliability. The present invention takes into account the influence of distributed power sources and provides a basis for the setting of negative sequence currents for single-phase line break faults in active distribution networks. Because the negative sequence current of the fault feeder under a single-phase fault in the active distribution network is related to multiple factors such as the system load size, load distribution, fault location, and distributed power supply capacity, the negative sequence current has greater randomness and variability, resulting in difficulty in setting the negative sequence current protection for line break faults. The present invention proposes a detailed calculation method for this purpose. The action elements of each feeder of the present invention have corresponding action threshold values, which are related to the parameters of the feeder and have high sensitivity. The implementation methods of the present invention are clear, including starting elements, action elements and signal elements. The required electrical quantities include the amplitude of the positive-sequence voltage of the active distribution network bus, the amplitude of the output current of the distributed power sources connected to each feeder, and the amplitude of the negative-sequence current at the outlet of each feeder. They are easy to collect and implement in the existing distribution network. Therefore, the present invention has strong practicality and scalability.

[0092] Example 3

[0093] This embodiment is a specific implementation description and verification of the above method.

[0094] Reference Figure 1 The following is a schematic diagram of the 10kV active distribution network structure. T1 is the main transformer, T2 is the grounding transformer, and the neutral point grounding resistor R d is 10Ω, DG is a distributed power source. Distributed power source reference power P ref The system equivalent negative sequence impedance is 1.6MW. S2The positive sequence parameters of the feeder are: R1 = 0.031Ω / km, L1 = 0.096mH / km, C1 = 0.338μF / km, and the zero sequence parameters of the feeder are: R0 = 0.234Ω / km, L0 = 0.355mH / km, C0 = 0.265μF / km. The load size of each feeder and the corresponding access position are shown in Table 1.

[0095] Table 1: Load parameter table.

[0096]

[0097] Based on this embodiment, refer to Figure 2 As shown in FIG. 1 , the single-phase line break fault protection method for active distribution network based on negative sequence current, by substituting the above configuration parameters into the above embodiment method, comprises the following steps:

[0098] S101: Collect the amplitude of the positive sequence voltage U of the active distribution network bus M1 , collect the amplitude of the output current of the distributed power source connected to each feeder I DG,ij , collect the amplitude of negative sequence current I at each feeder outlet 2i , where i = 1, 2, ... m, j = 1, 2, ... n i , m is the number of feeders, n i is the number of distributed generation connected to feeder i.

[0099] S102: Calculate the real-time change ΔI of the output current amplitude of each distributed power source of each feeder DG,ij , according to ΔI DG,ij Determine whether the start-up element is activated. If the start-up element is activated, execute S103; otherwise, return to S101;

[0100] S103: Compare the negative sequence current amplitudes I of each feeder collected in real time 2i The action threshold value I of the action element of the feeder 2iZD The size of the action element is determined to determine whether the action element is in action. If the action element is in action, S104 is implemented; otherwise, the process returns to S101;

[0101] S104: Determine that a single-phase disconnection fault occurs on feeder i, start a signal element, and issue a trip command or an alarm signal.

[0102] It should be noted that when a single-phase disconnection fault occurs in feeder 1, according to S101, the bus positive sequence voltage amplitude U M1 The output current amplitude of the distributed power supply of feeder 1 at the time of fault is I DG,11(t) The output current amplitude of the distributed power supply of feeder 1 in the cycle before the fault is I DG,11(t-T) It is 196.7A.

[0103] According to S101, collect the negative sequence current amplitude I of each feeder 2i Feeder 1 negative sequence current I 21 =328.6A, negative sequence current of feeder 2 I 22 =6.3A, negative sequence current of feeder 3 I 23 =7A, feeder 4 negative sequence current I 24 =10A, feeder 5 negative sequence current I 25 =0.04A.

[0104] According to S102, the real-time change ΔI of the output current amplitude of each distributed power source of each feeder DG,ij Calculate as follows:

[0105] ΔI DG,ij =|I DG,ij(t) -I DG,ij(t-T) |

[0106] Among them, I DG,ij(t) is the output current amplitude of the distributed power supply at the current moment, I DG,ij(t-T) It is the output current amplitude of the distributed power supply in the previous cycle.

[0107] According to S102, the criterion for starting the element action is:

[0108] ΔI DG,ij >0

[0109] Where ΔI DG,ij It is the real-time change of the output current amplitude of each distributed power source of each feeder.

[0110] According to S102, the real-time change ΔI of the output current amplitude of the distributed power supply of feeder 1 is calculated. DG,11 is 94.1A, satisfying ΔI DG,11 >0, the starting element is activated and it is determined that a single-phase disconnection fault occurs in the active distribution network.

[0111] In S103, the criterion for the action of the action element is:

[0112] I 2i >KI 2iZD

[0113] Among them I 2i is the magnitude of the negative sequence current at the outlet of the ith feeder, I 2iZD is the action threshold value of the action element of the i-th feeder, K is the reliability coefficient, which is 1.1~1.2.

[0114] In S103, the action threshold value I of the action element of the i-th feeder 2iZD Calculate as follows:

[0115] I 2iZD =K rel ·{I 2i.min}, i=1,2,…,m

[0116] Where K rel is the reliability coefficient, ranging from 1.1 to 1.2; I 2i.min is the minimum negative sequence current when a single-phase disconnection fault occurs on the i-th feeder, where i = 1, 2, …, m, and m is the number of feeders.

[0117] According to the minimum negative sequence current I when a single-phase disconnection fault occurs on the i-th feeder i2.min Calculated as follows:

[0118] I i2.min =min{I i(1) ,I i(2)}

[0119] In the formula, I i(1) is the minimum negative sequence current of the ith feeder when a single-phase line break occurs upstream of the distributed generation, I i(2) is the minimum negative sequence current of the i-th feeder when a single-phase line break fault occurs downstream of the distributed generation.

[0120] In this specific implementation, when a single-phase line break fault occurs upstream of the distributed power source, the minimum negative sequence current value I of the i-th feeder i(1) Calculated as follows:

[0121]

[0122] In the formula, Z S2 is the system equivalent negative sequence impedance, Z iΣ is the total load impedance of feeder i, (Z iN2 ) max is the maximum value of the negative sequence load impedance downstream of the single-phase disconnection fault point of feeder i, (U pcci ) max It is the maximum value of the voltage at the grid connection point of the distributed generation of feeder i when a single-phase line break fault occurs upstream of the distributed generation.

[0123] In this specific implementation manner, when a single-phase line break fault occurs upstream of the distributed power source, the maximum value of the grid connection point voltage (U pcci ) max Calculated as follows:

[0124]

[0125] Where P refi is the reference power of the distributed generation of the i-th feeder.

[0126] In this specific implementation, when a single-phase line break fault occurs downstream of a distributed power source, the minimum negative sequence current value I of the i-th feeder is i(2) Calculated as follows:

[0127]

[0128] Where Z0 is the zero-sequence impedance of the system after a single-phase disconnection fault on feeder i.

[0129] In this embodiment, the system zero-sequence impedance Z0 after a single-phase disconnection fault of feeder i is calculated according to the following formula:

[0130]

[0131] In the formula, Z g is the neutral point grounding impedance of the active distribution network; C j is the capacitance of all feeders except feeder i; C i is the capacitance of feeder i, and ω is the system angular frequency.

[0132] According to S103, the minimum negative sequence current I of each feeder is calculated when a single-phase line break fault occurs upstream of the distributed power source. i(1) , and the minimum negative sequence current I of each feeder when a single-phase line break occurs downstream of the distributed power source i(2) , thereby determining the minimum negative sequence current I when a single-phase disconnection fault occurs on each feeder 2i.min , where i = 1, 2, ..., 5. Furthermore, the reliability coefficients K and K rel Take 1.1 for all, and calculate the action threshold value I of the action element for the single-phase disconnection fault of each feeder in the active distribution network 2iZD .

[0133] In this embodiment, since feeders 2, 3, 4, and 5 are not connected to distributed power sources, there is no minimum negative sequence current I of each feeder when a single-phase line break occurs upstream of the distributed power source. i(1) , and the minimum negative sequence current I of each feeder when the single-phase line break fault occurs in the downstream of the distributed power supply i(2) The calculation process of I is independent of distributed power generation, so for feeders without distributed power generation, only I i(2) The action threshold calculation process and results are shown in Table 2.

[0134] Table 2: Negative sequence current setting value calculation table.

[0135]

[0136] In this embodiment, according to S103, the negative sequence current protection setting value I of each feeder is compared. i2ZD The negative sequence current amplitude of each feeder I i2As shown in Table 3 below, it is clear that only feeder 1 meets the action condition of the action element, that is, I 21 >1.1I 21ZD The feeder 1 action element is activated.

[0137] Table 3: Feeder negative sequence current comparison table.

[0138]

[0139] According to S104, it is determined that a single-phase disconnection fault occurs in feeder 1, and the signal element issues a trip command or an alarm signal. The present invention determines whether the starting element is actuated based on the real-time change in the output current amplitude of each distributed power source of each feeder. If ΔI DG,ij >0, the starting element will be activated; the action threshold value of each feeder action element is calculated according to the system related parameters. If the negative sequence current of a feeder satisfies I 2i >KI 2iZD , the action element is activated and determines that a single-phase disconnection fault occurs in the feeder; further, the signal element issues a tripping command or an alarm signal.

[0140] It should be appreciated that embodiments of the present invention may be implemented or enforced by computer hardware, a combination of hardware and software, or by computer instructions stored in a non-transitory computer-readable memory. The method may be implemented in a computer program using standard programming techniques - including a non-transitory computer-readable storage medium configured with a computer program, wherein the storage medium so configured causes the computer to operate in a specific and predefined manner - according to the methods and drawings described in the specific embodiments. Each program may be implemented in a high-level procedural or object-oriented programming language to communicate with a computer system. However, if desired, the program may be implemented in an assembly or machine language. In any case, the language may be a compiled or interpreted language. In addition, the program may be run on a programmed ASIC for this purpose.

[0141] Furthermore, the operations of the processes described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The processes described herein (or variations and / or combinations thereof) may be performed under the control of one or more computer systems configured with executable instructions, and may be implemented as code (e.g., executable instructions, one or more computer programs, or one or more applications) that is executed collectively on one or more processors, by hardware, or a combination thereof. The computer program includes a plurality of instructions that may be executed by one or more processors.

[0142] Further, the method can be implemented in any type of computing platform that is operably connected to a suitable computer, including but not limited to a personal computer, a minicomputer, a mainframe, a workstation, a network or distributed computing environment, a separate or integrated computer platform, or in communication with a charged particle tool or other imaging device, etc. Aspects of the present invention can be implemented in machine-readable code stored on a non-transitory storage medium or device, whether removable or integrated into a computing platform, such as a hard disk, an optical read and / or write storage medium, a RAM, a ROM, etc., so that it can be read by a programmable computer, and when the storage medium or device is read by the computer, it can be used to configure and operate the computer to perform the process described herein. In addition, the machine-readable code, or part thereof, can be transmitted via a wired or wireless network. When such media includes instructions or programs that implement the steps described above in conjunction with a microprocessor or other data processor, the invention described herein includes these and other different types of non-transitory computer-readable storage media. When programmed according to the methods and techniques described in the present invention, the present invention also includes the computer itself. The computer program can be applied to input data to perform the functions described herein, thereby converting the input data to generate output data stored in a non-volatile memory. The output information can also be applied to one or more output devices such as a display. In a preferred embodiment of the present invention, the converted data represents a physical and tangible object, including a specific visual depiction of the physical and tangible object produced on a display.

[0143] As used in this application, the terms "component", "module", "system", etc. are intended to refer to a computer-related entity, which can be hardware, firmware, a combination of hardware and software, software, or software in operation. For example, a component can be, but is not limited to: a process running on a processor, a processor, an object, an executable file, a thread in execution, a program, and / or a computer. As an example, an application running on a computing device and the computing device can both be components. One or more components can exist in a process and / or thread in execution, and a component can be located in a computer and / or distributed between two or more computers. In addition, these components can be executed from various computer-readable media having various data structures thereon. These components can communicate in a local and / or remote process manner, such as according to a signal having one or more data packets (e.g., data from a component that interacts with another component in a local system, a distributed system, and / or interacts with other systems in a signal manner through a network such as the Internet).

[0144] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A single-phase line break fault protection method for active distribution network based on negative sequence current, characterized in that: The following steps are included: Real-time collection of the amplitude of the bus positive sequence voltage of the active distribution network, the amplitude of the output current of the distributed power source connected to each feeder, and the amplitude of the negative sequence current at the outlet of each feeder; If there is a real-time change in the output current amplitude of the feeder distributed power supply that meets the conditions, the starting element will act; Obtaining the magnitude of the action threshold value of each feeder action element and the action threshold value of the action element of the corresponding feeder; if a feeder meets the condition, the action element is actuated, and it is determined that a single-phase disconnection fault occurs in the feeder; The action criteria of the action element according to the action threshold value are: I 2i >TO 2iZD Among them, I 2i is the magnitude of the negative sequence current at the outlet of the ith feeder, I 2iZD is the action threshold value of the action element of the i-th feeder, K is the reliability coefficient, which is 1.1~1.2; It is determined that a single-phase disconnection fault occurs in the feeder, and the signal element issues a trip command or an alarm signal.

2. The method for protecting a single-phase line break fault in an active power distribution network based on negative sequence current according to claim 1, characterized in that: The following steps are included: Real-time acquisition of the amplitude of the positive sequence voltage U of the active distribution network bus M1 , collect the amplitude of the output current of the distributed power source connected to each feeder I DG,ij , collect the amplitude of negative sequence current I at each feeder outlet 2i , where i = 1, 2, ... m, j = 1, 2, ... n i , m is the number of feeders, n i is the number of distributed generation connected to feeder i; Obtain the real-time change ΔI of the output current amplitude of each distributed power source on each feeder DG,ij , according to ΔI DG,ij Determine whether the starting element is in action. If not, return to re-collect the amplitude until the starting element is in action. Compare the real-time collected negative sequence current amplitude I of each feeder 2i The action threshold value I of the action element of the feeder 2iZD The size of is used to determine whether the action component is in action. If not, it returns to collect again until the action of the start component is started; It is determined that a single-phase disconnection fault occurs on feeder i, and the signal element is started to issue a trip command or an alarm signal.

3. The method for protecting single-phase line break fault of active power distribution network based on negative sequence current as claimed in claim 2, characterized in that: The real-time change of the output current amplitude of each distributed power source on each feeder ΔI DG,ij As follows: ΔI DG,ij =|I DG,ij(t) -I DG,ij(t-T) | Among them, I DG,ij(t) is the output current amplitude of the distributed power supply at the current moment, I DG,ij(t-T) It is the output current amplitude of the distributed power supply in the previous cycle.

4. The method for protecting a single-phase line break fault in an active power distribution network based on negative sequence current according to claim 2 or 3, characterized in that: The action threshold value I of the action element of the i-th feeder 2iZD As follows: I 2iZD =K rel ·{I 2i.min },i=1,2,…,m Where K rel is the reliability coefficient, taking 1.1~1.2, I 2i.min is the minimum negative sequence current when a single-phase disconnection fault occurs on the i-th feeder, where i = 1, 2, …, m, and m is the number of feeders.

5. The method for protecting single-phase line break fault of active power distribution network based on negative sequence current as claimed in claim 4, characterized in that: The action criteria of the starting element according to the real-time change are: ΔI DG,ij >0 Among them, ΔI DG,ij It is the real-time change of the output current amplitude of each distributed power source of each feeder.

6. The method for protecting single-phase line break fault of active power distribution network based on negative sequence current as claimed in claim 5, characterized in that: The minimum negative sequence current I when a single-phase disconnection fault occurs on the i-th feeder 2i.min As follows: IN 2i.min =min{I i(1) ,IN i(2) } In the formula, I i(1) is the minimum negative sequence current of the ith feeder when a single-phase line break occurs upstream of the distributed generation, I i(2) is the minimum negative sequence current of the i-th feeder when a single-phase line break fault occurs downstream of the distributed generation.

7. The method for protecting single-phase disconnection fault of active power distribution network based on negative sequence current as claimed in claim 6, characterized in that: The minimum negative sequence current I of the i-th feeder when a single-phase line break occurs upstream of the distributed generation i(1) As follows: In the formula, Z S2 is the system equivalent negative sequence impedance, Z iΣ is the total load impedance of feeder i, (Z iN2 ) max is the maximum value of the negative sequence load impedance downstream of the single-phase disconnection fault point of feeder i, (U pcci ) max is the maximum value of the voltage at the grid connection point of the distributed power generation of feeder i when a single-phase line break fault occurs upstream of the distributed power generation; And the minimum negative sequence current I of the i-th feeder when the single-phase line break fault occurs downstream of the distributed generation i(2) As follows: Where Z0 is the zero-sequence impedance of the system after a single-phase disconnection fault on feeder i.

8. The method for protecting single-phase disconnection fault of active power distribution network based on negative sequence current as claimed in claim 7, characterized in that: The maximum value of the grid connection point voltage of the i-th feeder distributed generation when a single-phase line failure occurs upstream of the distributed generation (U pcci ) max As follows: Where P refi is the reference power of the distributed generation of the i-th feeder.

9. The method for protecting a single-phase line break fault in an active power distribution network based on negative sequence current according to claim 7 or 8, characterized in that: After a single-phase disconnection fault on feeder i, the system zero-sequence impedance Z0 is as follows: In the formula, Z g is the neutral point grounding impedance of the active distribution network; C j is the capacitance of all feeders except feeder i; C i is the capacitance of feeder i, and ω is the system angular frequency.

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