Protection method for low-voltage power grid

Abstract

The invention discloses a protection method for a low-voltage power grid, the low-voltage power grid comprises a transformer area intelligent terminal and a plurality of intelligent switches, the transformer area intelligent terminal and the plurality of intelligent switches are connected through power lines, and the method comprises the following steps: establishing a longitudinal communication network between the transformer area intelligent terminal and the plurality of intelligent switches; determining a branch level of the low-voltage power grid according to the voltage, the current, the power, the electric energy and the alternating-current zero crossing point; drawing an electrical topological relation of the plurality of intelligent switches based on the branch hierarchy; establishing a transverse communication network of the plurality of intelligent switches based on the electrical topological relation; and when the power line has a short circuit or a grounding fault, the fault area is cut off through the corresponding intelligent switch, the fault information is broadcasted and the fault area is positioned through the transverse communication network, and the fault information is reported to the station area intelligent terminal through the longitudinal communication network. According to the protection method, the fault area can be accurately positioned, so that the emergency situation of the low-voltage power grid can be efficiently and quickly handled in real time.

Description

Technical Field

[0001] The present invention relates to the technical field of low-voltage power grids, and in particular to a protection method for low-voltage power grids. Background Art

[0002] In traditional low-voltage power grids, the network architecture is widely built based on "cloud-pipe-edge-end". The cloud is the main station, responsible for large-scale data storage and processing. The main station, substation equipment, and users generally rely on vertical communication technology to concentrate the data of the end devices on the substation smart terminal, and then the substation smart terminal sends the edge side data to the main station. The storage and processing of edge side data by the main station side realizes the management, protection and control of the low-voltage power grid.

[0003] The drawback of the vertical communication network based on "cloud-pipe-edge-end" is that when a short circuit or ground fault occurs between the edge and the end, the vertical communication network is easily interrupted by the tripping of the switch, making it difficult to locate the fault area and causing maintenance difficulties. In addition, the amount of data in the low-voltage power grid is growing exponentially. If a centralized processing method is used, the computing power requirements of the platform will become higher and higher, and the transmission delay will become lower and lower. The current method is difficult to adapt to market demand. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the first purpose of the present invention is to propose a protection method for a low-voltage power grid, which integrates vertical and horizontal communications, and can not only interact with the main station through vertical communication, but also interact with the surrounding intelligent terminals through horizontal communication and carry out information exchange and collaborative control, ensuring that the low-voltage power grid can be perceived and controlled in real time, stably, reliably and economically, so as to solve the problem that the branch nodes and terminals of the low-voltage substation cannot communicate when the vertical communication network is interrupted, and can accurately locate the fault area, thereby realizing real-time, efficient and fast response to emergencies in the low-voltage power grid.

[0005] To achieve the above-mentioned purpose, the first aspect of the embodiment of the present invention proposes a protection method for a low-voltage power grid, wherein the low-voltage power grid includes a substation intelligent terminal and multiple intelligent switches, and the substation intelligent terminal and the multiple intelligent switches are connected through a power line. The method includes: establishing a longitudinal communication network between the substation intelligent terminal and the multiple intelligent switches; collecting the voltage, current, power, electric energy and AC zero-crossing point of the power line, and determining the branch hierarchy of the low-voltage power grid according to the voltage, the current, the power, the electric energy and the AC zero-crossing point; drawing the electrical topological relationship of the multiple intelligent switches based on the branch hierarchy; establishing a transverse communication network of the multiple intelligent switches based on the electrical topological relationship; when a short circuit or grounding fault occurs in the power line, the fault area is cut off by the corresponding intelligent switch, and the fault information is broadcast and the fault area is located through the transverse communication network, and the fault information is reported to the substation intelligent terminal through the longitudinal communication network.

[0006] According to the protection method for low-voltage power grid of the embodiment of the present invention, firstly, a longitudinal communication network is established between the intelligent terminal of the substation and multiple intelligent switches, then the voltage, current, power, electric energy and AC zero-crossing point of the power line are collected, and the branch level of the low-voltage power grid is determined according to the voltage, current, power, electric energy and AC zero-crossing point, and then the electrical topological relationship of multiple intelligent switches is drawn based on the branch level, and a horizontal communication network of multiple intelligent switches is established based on the electrical topological relationship, when a short circuit or grounding fault occurs in the power line, the fault area is cut off by the corresponding intelligent switch, and the fault information is broadcast and the fault area is located through the horizontal communication network, and the fault information is reported to the intelligent terminal of the substation through the longitudinal communication network. Thus, the method integrates longitudinal and transverse communications, and can not only exchange data with the main station through longitudinal communication, but also exchange information and coordinate control with the surrounding intelligent terminals through transverse communication, so as to ensure that the low-voltage power grid can be perceived and controlled in real time, stably, reliably and economically, so as to solve the problem that the branch nodes and terminals of the low-voltage substation cannot communicate when the longitudinal communication network is interrupted, and the fault area can be accurately located, so as to achieve real-time, efficient and fast response to the sudden situation of the low-voltage power grid.

[0007] In addition, the protection method for a low-voltage power grid according to the above embodiment of the present invention may also have the following additional technical features:

[0008] According to one embodiment of the present invention, determining the branch level of the low-voltage power grid based on the voltage, the current, the power, the electric energy and the AC zero-crossing point includes: determining a stratification index by weighted summation based on the voltage, the current, the power, the electric energy and the AC zero-crossing point; determining the branch level of the low-voltage power grid based on the stratification index and a preset stratification index threshold.

[0009] According to one embodiment of the present invention, the stratification index is determined in the following manner:

[0010] P=α*(ΔV+ΔA)+β*(ΔPF+ΔP)+γ*ΔT

[0011] Among them, P is the stratification index, α, β and γ are weights, ΔV, ΔA, ΔPF, ΔP, ΔT are respectively the voltage difference, current difference, power factor difference, electric energy difference and AC zero-crossing time difference of the power lines where two adjacent intelligent switches are located.

[0012] According to one embodiment of the present invention, determining the branch level of the low-voltage power grid based on the stratification index and the preset stratification index threshold includes: determining the interval in which the stratification index is located, wherein the interval is obtained based on at least one different preset stratification index threshold, and different intervals correspond to different branch levels; determining the branch level of the low-voltage power grid based on the interval.

[0013] According to one embodiment of the present invention, before collecting the voltage, current, power, electric energy and AC zero-crossing point of the power line, the method also includes: based on the clock of the substation intelligent terminal and the timer of each of the intelligent switches, synchronizing the clocks of the multiple intelligent switches through the longitudinal communication network.

[0014] According to one embodiment of the present invention, the clock of the multiple intelligent switches is synchronized through the longitudinal communication network based on the clock of the substation intelligent terminal and the timer of each of the intelligent switches, including: controlling the substation intelligent terminal to broadcast the time calibration time through the longitudinal communication network, wherein each of the intelligent switches receives the time calibration time, and records the delay time of receiving the time calibration time through the timer, and performs clock synchronization based on the delay time and the time calibration time.

[0015] According to one embodiment of the present invention, the low-voltage power grid also includes distributed renewable energy, and the method further includes: when a short circuit or ground fault occurs in the power line, the distributed renewable energy is controlled to be disconnected to perform anti-islanding protection on the distributed renewable energy.

[0016] According to one embodiment of the present invention, the smart switch includes a collection module for collecting electrical parameters of the power line where the smart switch is located, a switch module and a control module for controlling the on and off of the power line where the smart switch is located, and the method also includes: obtaining the electrical parameters through the control module, determining whether a short circuit or a ground fault occurs in the power line based on the electrical parameters, and when a short circuit or a ground fault occurs in the power line, controlling the switch module so that the smart switch cuts off the fault area.

[0017] According to an embodiment of the present invention, the electrical parameters include voltage and current.

[0018] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of a protection method for a low voltage power grid according to an embodiment of the present invention;

[0020] Figure 2 is a schematic diagram of a low voltage power grid according to an embodiment of the present invention;

[0021] Figure 3 A schematic diagram of a low-voltage power grid containing distributed renewable energy according to an embodiment of the present invention;

[0022] Figure 4 FIG. 4 is a block diagram of an intelligent switch according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0024] The following describes a protection method for a low-voltage power grid according to an embodiment of the present invention with reference to the accompanying drawings.

[0025] Figure 1 The figure is a flow chart of a protection method for a low voltage power grid according to an embodiment of the present invention.

[0026] In one embodiment of the present invention, Figure 2 As shown, the low-voltage power grid includes an area intelligent terminal and multiple intelligent switches, and the area intelligent terminal and the multiple intelligent switches are connected through power lines. Figure 2A black square in the figure refers to a smart switch. The master station and the smart terminal in the substation use 4G / 5G public network or power dedicated network communication. The smart terminal in the substation and each smart switch communicate through HPLC (High-Speed ​​Power Line Carrier) or HPLC dual-mode communication.

[0027] like Figure 1 As shown, the protection method for a low-voltage power grid according to an embodiment of the present invention may include the following steps:

[0028] S1, establish a longitudinal communication network between the substation intelligent terminal and multiple intelligent switches.

[0029] Specifically, if Figure 2 As shown, the low-voltage power grid includes a main station, an intelligent terminal in the substation area, an intelligent switch, an intelligent energy meter, a distribution cabinet, a branch box and a meter box. Based on HPLC or HPLC dual-mode communication, a vertical communication network of "main station-substation intelligent terminal-intelligent switch" is established.

[0030] S2, collects the voltage, current, power, electric energy and AC zero-crossing point of the power line, and determines the branch level of the low-voltage power grid based on the voltage, current, power, electric energy and AC zero-crossing point.

[0031] S3, draws the electrical topology relationship of multiple smart switches based on the branch hierarchy.

[0032] S4, establishing a horizontal communication network of multiple intelligent switches based on electrical topology relationships.

[0033] S5, when a short circuit or ground fault occurs in the power line, the fault area is cut off through the corresponding intelligent switch, and the fault information and location of the fault area are broadcast through the horizontal communication network, and the fault information is reported to the intelligent terminal in the substation through the vertical communication network.

[0034] Specifically, firstly, based on HPLC or HPLC dual-mode communication, a vertical communication network of "master station-substation intelligent terminal-intelligent switch" is established, and the voltage, current, power and electric energy data of residential loads, industrial and commercial loads and distributed power sources and AC zero-crossing points are collected to the master station through the vertical communication network through the substation intelligent terminal. The master station will perform unified management and control, and the master station will determine the branch level of the low-voltage power grid based on the voltage, current, power, electric energy and AC zero-crossing point. Figure 2 Taking the identification of the relationship between the first-level branch and the second-level branch as an example, the first-level branch refers to the branch in the distribution cabinet, and the second-level branch refers to the branch in the branch box. The logical association between the second-level branch and the household meter is determined through business rules such as the meter number and user number, and the location of the smart switch in the branch box, meter box and inlet and outlet lines is determined.

[0035] Furthermore, according to the identified branch level, the electrical topology relationship of each smart switch under the substation is drawn, and then based on the electrical topology relationship of the smart switch, a horizontal communication network between "smart switch-smart switch" is established nearby. The horizontal communication network allows direct communication between smart switches, which enhances the responsiveness and flexibility. When a short circuit or ground fault occurs in the power line, the corresponding smart switch can cut off the fault area, which can prevent the spread of the fault and protect other parts of the power grid from damage; and broadcast the fault information and locate the fault area through the horizontal communication network to notify other switches, and report the fault information to the substation smart terminal through the vertical communication network, and then report it to the main station system by the substation smart terminal, and other switches remain in their original state.

[0036] For example, refer to Figure 2 The main incoming line, No. 1 outgoing line switch, incoming line 1, outgoing line 1, outgoing line 2, outgoing line 3, meter box incoming line 1, meter box incoming line 2, and meter box incoming line 3 form a horizontal communication network. If a short circuit or grounding fault occurs between the secondary branch and the household meter, or between the outgoing line 2 and the meter box incoming line 2, the switches of the outgoing line 2 and the meter box incoming line 2 will both trip for protection. After the tripping protection, the main incoming line, the No. 1 outgoing line switch, the incoming line 1 and the outgoing line 2 can sense the fault current, but the switch of the meter box incoming line 2 cannot sense the current, because the meter box incoming line 2 has no power and cannot work. At this time, other intelligent switches cannot communicate with the meter box incoming line 2. At the same time, although the switch of the outgoing line 2 is also disconnected, the outgoing line 2 still has power to work, so other intelligent switches can still communicate with the outgoing line 2. In this way, based on the switches in the horizontal communication network, the fault is quickly located between the outgoing line 2 and the meter box incoming line 2 switches through horizontal communication, and the outgoing line 2 and the meter box incoming line 2 switches trip for protection. The outgoing line 2 switch broadcasts the fault information to other switches through horizontal communication and reports it to the intelligent terminal in the substation area through vertical communication, and then the intelligent terminal in the substation area reports it to the main station system, and other switches remain in their original state.

[0037] For another example, if a short circuit or grounding fault occurs between the No. 1 outgoing line switch and the incoming line 1 switch between the primary branch and the secondary branch, the main incoming line and No. 1 outgoing line switch sense the fault current, while incoming line 1, outgoing line 1, outgoing line 2, outgoing line 3, meter box incoming line 1, meter box incoming line 2, and meter box incoming line 3 cannot sense the fault current. Based on the switches in the horizontal communication network, the fault is quickly located between the No. 1 outgoing line switch and the incoming line 1 switch through horizontal communication, and the No. 1 outgoing line switch and the incoming line 1 switch trip for protection. The No. 1 outgoing line switch broadcasts the fault information to other switches through horizontal communication and reports it to the substation intelligent terminal through vertical communication, which then reports to the main station system through the substation intelligent terminal, and the other switches remain in their original state.

[0038] According to one embodiment of the present invention, the branch level of the low-voltage power grid is determined according to the voltage, current, power, electric energy and AC zero-crossing point, including: determining the stratification index by weighted summation according to the voltage, current, power, electric energy and AC zero-crossing point; determining the branch level of the low-voltage power grid according to the stratification index and the preset stratification index threshold. The preset stratification index threshold can be set and adjusted according to the historical data of the specific substation area.

[0039] Further, according to an embodiment of the present invention, the stratification index is determined in the following manner:

[0040] P=α*(ΔV+ΔA)+β*(ΔPF+ΔP)+γ*ΔT (1)

[0041] Among them, P is the hierarchical index, α, β and γ are weights, ΔV, ΔA, ΔPF, ΔP and ΔT are the voltage difference, current difference, power factor difference, electric energy difference and AC zero-crossing time difference of the power lines where two adjacent smart switches are located, respectively.

[0042] Specifically, after collecting the voltage, current, power, electric energy and AC zero-crossing point of the power line, the voltage difference ΔV of the power lines where two adjacent intelligent switches are located is calculated according to the collected voltage, the current difference ΔA of the power lines where two adjacent intelligent switches are located is calculated according to the collected current, the power factor difference ΔPF of the power lines where two adjacent intelligent switches are located is calculated according to the collected power, the electric energy difference ΔP of the power lines where two adjacent intelligent switches are located is calculated according to the collected electric energy, and the AC zero-crossing time difference ΔT of the power lines where two adjacent intelligent switches are located is calculated according to the collected AC zero-crossing point. Then, ΔV, ΔA, ΔPF, ΔP, and ΔT are substituted into the above formula (1) and weighted summation is performed to obtain the hierarchical index P. It should be noted that a larger voltage difference and current difference can indicate the existence of a branch point, the obvious difference in power factor is related to the branch structure, the larger electric energy difference indicates the existence of a branch, and the change in time difference is related to the branch position. The weight coefficients α, β, and γ of each part may be different in different substations.

[0043] Further, according to an embodiment of the present invention, the branch level of the low-voltage power grid is determined according to the hierarchical index and the preset hierarchical index threshold, including: determining the interval in which the hierarchical index is located, wherein the interval is obtained based on at least one different preset hierarchical index threshold, and different intervals correspond to different branch levels; determining the branch level of the low-voltage power grid according to the interval.

[0044] Specifically, after obtaining the stratification index P, the threshold segmentation method can be used and the preset stratification index threshold T can be adjusted according to the substation. By comparing the preset stratification index threshold T with the stratification index P, the stratification index P can be divided into different intervals to determine the hierarchical relationship of the substation branches.

[0045] According to one embodiment of the present invention, before collecting the voltage, current, power, electric energy and AC zero-crossing point of the power line, the above method also includes: based on the clock of the substation intelligent terminal and the timer of each intelligent switch, synchronizing the clocks of multiple intelligent switches through a longitudinal communication network.

[0046] That is to say, before collecting the voltage, current, power, electric energy and AC zero-crossing point of the power line, the clock of the intelligent terminal in the substation can be used as a reference to synchronize and calibrate the clocks of multiple intelligent switches through the longitudinal communication network to ensure that all intelligent switches remain in a synchronized state, thereby ensuring the consistency and accuracy of the collected power line data.

[0047] Further, according to one embodiment of the present invention, based on the clock of the intelligent terminal in the substation and the timer of each intelligent switch, the clocks of multiple intelligent switches are synchronized through the longitudinal communication network, including: the intelligent terminal in the substation broadcasts the time calibration time through the longitudinal communication network, wherein each intelligent switch receives the time calibration time, and records the delay time of receiving the time calibration time through the timer, and performs clock synchronization based on the delay time and the time calibration time.

[0048] Specifically, before collecting the voltage, current, power, electric energy and AC zero-crossing point of the power line, the clock of the substation intelligent terminal is used as the benchmark, and the 32-bit timer of the HPLC module on the substation intelligent terminal and the intelligent switch is used. The substation intelligent terminal broadcasts the time calibration and timer calibration to the entire network through the vertical communication network. The timer is mainly used to determine the network transmission delay. The intelligent switch receives the broadcast time calibration time, and records the delay time of receiving the time calibration time through the timer. Then, the clocks of multiple intelligent switches are synchronized according to the delay time and the time calibration time, and the time of the intelligent switch is determined to achieve microsecond clock synchronization.

[0049] According to one embodiment of the present invention, the low-voltage power grid also includes distributed renewable energy, and the above method also includes: when a short circuit or ground fault occurs in the power line, the distributed renewable energy is controlled to be disconnected to perform anti-islanding protection on the distributed renewable energy.

[0050] Specifically, if Figure 3As shown, when the meter box is connected to distributed new energy, the distributed new energy includes distributed photovoltaic, household energy storage, V2G electric vehicles, etc. When the power line is short-circuited or grounded, the protection logic is the same as above, and the distributed new energy is quickly cut off, so as to avoid the island effect when the distributed new energy still supplies power to the grid when the power supply is interrupted due to low-voltage grid failure or power outage maintenance. Therefore, the present invention can achieve anti-islanding protection function and promote the consumption of distributed new energy. It should be noted that distributed new energy refers to distributed photovoltaic, energy storage and electric vehicles that can sell electricity to the grid. These power sources are connected to the grid. When the grid fails or the power is normally shut down for maintenance, if these distributed power sources cannot sense whether the grid is out of power, the photovoltaic, energy storage and electric vehicles connected to the grid will continue to supply power to the grid, forming an island effect. For example, still taking the example of a short circuit or grounding fault between outgoing line 2 and meter box incoming line 2, the switches of outgoing line 2 and meter box incoming line 2 are both disconnected. At this time, there is power in meter box incoming line 2, but there is no power in outgoing line 2. The distributed power source cannot feed power to the grid, thereby providing anti-islanding protection for the distributed new energy.

[0051] According to one embodiment of the present invention, the intelligent switch includes a collection module for collecting electrical parameters of the power line where the intelligent switch is located, a switch module and a control module for controlling the on and off of the power line where the intelligent switch is located. The above method also includes: obtaining the electrical parameters through the control module, determining whether a short circuit or a ground fault occurs in the power line based on the electrical parameters, and when a short circuit or a ground fault occurs in the power line, controlling the switch module to enable the intelligent switch to cut off the fault area.

[0052] Further, according to an embodiment of the present invention, the electrical parameters include voltage and current.

[0053] Specifically, the block diagram of the intelligent switch is as follows: Figure 4As shown, the AC voltage of the incoming line end and the outgoing line segment is transmitted to the voltage transformer in the acquisition module, and the AC current is transmitted to the current transformer in the acquisition module. After the voltage transformer completes the voltage sampling and the current transformer completes the current sampling, they are respectively transmitted to the AC sampling unit in the control module for calculation, and the calculation results are transmitted to the management unit and the communication unit in the control module by communication. The switch state detection unit in the switch module can transmit the switch state to the management and communication part. The control module can determine whether the power line is short-circuited or grounded according to the voltage and current, and when the power line is short-circuited or grounded, the action execution mechanism in the switch module is opened to control the intelligent switch to cut off the fault area. It should be noted that the management unit includes management main control chip, liquid crystal, indicator light, Bluetooth, infrared and other components, which can run embedded real-time multi-task operating system and is responsible for data processing, storage and opening and closing instruction issuance. The AC sampling unit can realize the collection of electric energy metering data and protection data, and transmit the collected data to the management unit. The communication unit supports carrier, micro-power wireless and other communications, and has horizontal and vertical communication capabilities.

[0054] In summary, the protection method for a low-voltage power grid according to an embodiment of the present invention can achieve the following beneficial effects:

[0055] (1) Based on the topological relationship of the low-voltage substation, a horizontal communication network between adjacent low-voltage power grid protection devices is constructed, which can solve the problem of communication failure between branch nodes and terminals of the low-voltage substation when the vertical communication network is interrupted.

[0056] (2) The vertical and horizontal communication networks based on HPLC or HPLC dual-mode communication can realize decentralized island protection, improve the low-voltage power grid's ability to absorb distributed power sources, and promote the large-scale application of distributed new energy.

[0057] (3) Utilizing horizontal communication technology to decentralize the low-voltage power grid, topology identification, load identification, power quality analysis, broadband oscillation analysis and suppression, distributed energy management, load management, and distribution transformer monitoring can be calculated on the edge side, reducing the pressure of data collection, transmission, calculation, storage, and security on the master station and substation sides, and enabling real-time, efficient, and quick response to emergencies in the low-voltage power grid.

[0058] (4) By making full use of the balanced allocation of tasks and taking into account the HPLC and HPLC dual-mode vertical and horizontal communication networks, the utilization rate of the network is greatly improved, and the perception and coordination of the power grid status are enhanced.

[0059] (5) The method proposed in the present invention is not limited to traditional low-voltage power grids, but can also be applied to distributed power supply networks such as distributed photovoltaics, household energy storage and V2G electric vehicles.

[0060] In summary, according to the protection method for low-voltage power grid according to the embodiment of the present invention, a longitudinal communication network is first established between the substation intelligent terminal and multiple intelligent switches, and then the voltage, current, power, electric energy and AC zero-crossing point of the power line are collected, and the branch hierarchy of the low-voltage power grid is determined based on the voltage, current, power, electric energy and AC zero-crossing point. Then, the electrical topology relationship of multiple intelligent switches is drawn based on the branch hierarchy, and a horizontal communication network of multiple intelligent switches is established based on the electrical topology relationship. When a short circuit or ground fault occurs in the power line, the fault area is cut off by the corresponding intelligent switch, and the fault information is broadcast and the fault area is located through the horizontal communication network, and the fault information is reported to the substation intelligent terminal through the longitudinal communication network. Therefore, the method integrates vertical and horizontal communications, and can not only exchange data with the main station through vertical communication, but also exchange information and coordinate control with the surrounding smart terminals through horizontal communication, ensuring that the low-voltage power grid can be perceived and controlled in real time, stably, reliably and economically, thereby solving the problem of the lack of communication between branch nodes and terminals in the low-voltage substation when the vertical communication network is interrupted, and can accurately locate the fault area, thereby realizing real-time, efficient and fast response to emergencies in the low-voltage power grid.

[0061] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection portion with one or more wirings (electronic device), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0062] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0063] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0064] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0065] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0066] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A protection method for a low voltage power grid, characterized in that: The low-voltage power grid includes a station area intelligent terminal and a plurality of intelligent switches, the station area intelligent terminal and the plurality of intelligent switches are connected via a power line, and the method includes: Establishing a longitudinal communication network between the intelligent terminal in the substation area and the plurality of intelligent switches; Collecting the voltage, current, power, electric energy and AC zero-crossing point of the power line, and determining the branch level of the low-voltage power grid according to the voltage, current, power, electric energy and AC zero-crossing point; Drawing an electrical topological relationship of the plurality of intelligent switches based on the branch hierarchy; Establishing a lateral communication network of the plurality of intelligent switches based on the electrical topological relationship; When a short circuit or ground fault occurs in the power line, the fault area is cut off by a corresponding intelligent switch, and the fault information is broadcast and the fault area is located through the horizontal communication network, and the fault information is reported to the substation intelligent terminal through the vertical communication network.

2. The method according to claim 1, characterized in that The step of determining the branch level of the low-voltage power grid according to the voltage, the current, the power, the electric energy and the AC zero-crossing point comprises: Determine the stratification index by weighted summation according to the voltage, the current, the power, the electric energy and the AC zero-crossing point; The branch level of the low-voltage power grid is determined according to the hierarchical index and a preset hierarchical index threshold.

3. The method according to claim 2, characterized in that The stratification index is determined by: P=α*(ΔV+ΔA)+β*(ΔPF+ΔP)+γ*ΔT Among them, P is the stratification index, α, β and γ are weights, ΔV, ΔA, ΔPF, ΔP, ΔT are respectively the voltage difference, current difference, power factor difference, electric energy difference and AC zero-crossing time difference of the power lines where two adjacent intelligent switches are located.

4. The method according to claim 2, characterized in that: The step of determining the branch level of the low-voltage power grid according to the hierarchical index and a preset hierarchical index threshold comprises: Determine the interval in which the stratification index is located, wherein the interval is obtained based on at least one different preset stratification index threshold, and different intervals correspond to different branch levels; A branching level of the low-voltage power grid is determined according to the intervals.

5. The method according to any one of claims 1 to 4, characterized in that: Before collecting the voltage, current, power, electric energy and AC zero-crossing point of the power line, the method further includes: Based on the clock of the area intelligent terminal and the timer of each of the intelligent switches, the clocks of the multiple intelligent switches are synchronized through the longitudinal communication network.

6. The method according to claim 5, characterized in that The clock synchronization of the plurality of intelligent switches is performed through the longitudinal communication network based on the clock of the intelligent terminal in the substation area and the timer of each intelligent switch, including: Control the intelligent terminal in the substation area to broadcast the time calibration time through the longitudinal communication network, wherein each of the intelligent switches receives the time calibration time, and records the delay time of receiving the time calibration time through the timer, and performs clock synchronization based on the delay time and the time calibration time.

7. The method according to any one of claims 1 to 4, characterized in that: The low-voltage power grid also includes distributed new energy, and the method further includes: When a short circuit or ground fault occurs in the power line, the distributed new energy is also controlled to be disconnected to perform anti-islanding protection on the distributed new energy.

8. The method according to claim 1, characterized in that The smart switch includes a collection module for collecting electrical parameters of the power line where the smart switch is located, a switch module and a control module for controlling the on-off of the power line where the smart switch is located, and the method further includes: The electrical parameters are acquired by the control module, and whether a short circuit or a ground fault occurs in the power line is determined based on the electrical parameters. When a short circuit or a ground fault occurs in the power line, the switch module is controlled so that the intelligent switch cuts off the fault area.

9. The method according to claim 8, characterized in that The electrical parameters include voltage and current.

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