A method and system for dividing small hydropower island microgrid after fault

Abstract

The present invention provides a method and system for dividing a small hydropower island microgrid after a fault, and the method includes the following steps: S1, after a fault occurs, the feeder automation terminal FTU of each line of the small hydropower island microgrid determines whether the line is located upstream or downstream of the fault point according to the fault characteristic information; S2, if the feeder automation terminal FTU of each line of the small hydropower island microgrid determines that the line is located downstream of the fault point, the line enters an island state and starts island division; S3, after the island division is started, each disconnector downstream of the fault is disconnected according to the positive time limit characteristics according to the flow size on both sides before the fault; S4, each feeder automation terminal FTU in the line is disconnected successively according to the positive time limit characteristics, until the feeder automation terminal FTU stops operating after detecting all the fault characteristic quantities, and forms a plurality of stable island microgrids. The present invention forms a stable island quickly, reduces the fault recovery time, and reduces unnecessary load losses.

Description

Technical Field

[0001] The present invention relates to the technical field of power system fault recovery, and in particular to a method and system for dividing a small hydropower island microgrid after a fault. Background Art

[0002] As energy crisis and environmental problems become increasingly prominent, small hydropower, as a distributed power source with decentralization, simplicity and flexibility, has been widely used in distribution networks in mountainous areas and rural areas. The access of a large number of small hydropower to the distribution network has not only reduced environmental degradation and solved various problems of traditional power grids, but also changed the operating characteristics of the power grid, bringing challenges to the safe and stable operation of the power grid. Since the lines of small hydropower microgrids are often distributed in a radial manner, when a short circuit occurs at a point in the branch, the line downstream of the fault point will enter an island state. Mountainous and rural areas where small hydropower is more distributed have abundant hydropower resources but less load consumption. Therefore, small hydropower microgrids are typical power transmission systems. If the small hydropower microgrid enters the island mode and cannot transmit excess power to the large power grid, it will lead to instability of frequency and voltage in the island, and may even cause the island to be decoupled. Therefore, it is of great significance to design a reliable island division strategy after a small hydropower microgrid fault.

[0003] There are two main existing methods for dividing small hydropower microgrids. The first method is that when the feeder automation terminal (FTU) of each line of the small hydropower microgrid detects a fault, the disconnectors in the small hydropower microgrid are disconnected in sequence from the end of the line until the feeder automation terminal FTU can no longer detect the fault. The second method is that when the feeder automation terminal FTU detects a fault, all the disconnectors in the small hydropower microgrid are disconnected first, and then reclosed in sequence from the head end of the line. If the fault section is reclosed, the switch of the fault section is disconnected again, and the reclosing is stopped. Since both of the above methods use action delay to ensure selectivity, they consume a relatively long time and are prone to cutting off too many unnecessary loads. In summary, it is necessary to develop a method for dividing small hydropower microgrid fault islands that is fast and can minimize the number of loads cut off. Summary of the invention

[0004] In order to solve the technical problems existing in the prior art, the present invention provides a method and system for dividing a small hydropower island microgrid after a fault. By judging whether the line is located upstream and downstream of the fault point, when the line fault point is located downstream, the island division is started, and the disconnectors downstream of the fault are disconnected according to the positive time limit characteristics according to the flow size on both sides before the fault, thereby forming a stably operating island microgrid, greatly reducing the fault recovery time, and achieving a reduction in unnecessary load losses.

[0005] The method of the present invention is implemented by the following technical scheme: A method for dividing a small hydropower island microgrid after a fault, comprising the following steps:

[0006] S1. After the fault occurs, the feeder automation terminal FTU of each line of the small hydropower island microgrid determines whether the line is located upstream or downstream of the fault point based on the fault characteristic information;

[0007] S2. If the feeder automation terminal FTU of each line of the small hydropower island microgrid determines that the line is located upstream of the fault point, the line will not enter the island state and the island division will not be started; if the line is located downstream of the fault point, the line will enter the island state, the island division will be started, and the process goes to step S3;

[0008] S3. After the island division is started, the disconnectors downstream of the fault are disconnected according to the positive time limit characteristics based on the magnitude of the current on both sides before the fault;

[0009] S4. Each feeder automation terminal FTU in the line is disconnected successively according to the positive time limit characteristics until the feeder automation terminal FTU stops operating after detecting all fault characteristic quantities, forming several stably operating isolated island microgrids.

[0010] The system of the present invention adopts the following technical solutions to achieve: A system for dividing a small hydropower island microgrid after a fault, comprising:

[0011] Upstream and downstream judgment module: The feeder automation terminal FTU of each line of the small hydropower island microgrid determines whether the line is upstream or downstream of the fault point according to the fault characteristic information;

[0012] Island division module: through the upstream and downstream judgment module, when the judgment result is that the line is located downstream of the fault point, the line enters the island state and the island division is started;

[0013] Disconnector disconnection module: After starting the island division module, the disconnectors downstream of the fault are disconnected according to the positive time limit characteristics based on the flow size on both sides before the fault;

[0014] Island microgrid formation module: The feeder automation terminals FTU in the line are disconnected successively according to the positive time limit characteristics until the feeder automation terminal FTU detects all fault characteristic quantities and stops operating, thus forming several stable island microgrids.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0016] 1. The present invention determines whether the line is located upstream or downstream of the fault point. When the line fault point is located downstream, the island division is started, and the disconnectors downstream of the fault are disconnected according to the positive time limit characteristics based on the flow size on both sides before the fault, thereby forming a stably operating island microgrid, greatly reducing the fault recovery time and achieving a reduction in unnecessary load losses.

[0017] 2. The present invention uses the pre-fault power flow recorded by the feeder automation terminal FTU as an important basis for division, avoiding complex post-fault power flow calculation, improving the calculation speed and saving calculation resources.

[0018] 3. The island division of the present invention can be completed by only using the local fault information measured by the feeder automation terminal FTU, without the need to establish a specific communication channel, which greatly saves construction costs and is suitable for the relatively backward infrastructure conditions in mountainous areas and rural areas where small hydropower microgrids are distributed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of the method of the present invention;

[0020] Figure 2 This is a schematic diagram of island division based on the positive time-limit characteristic of the pre-fault power flow of the present invention;

[0021] Figure 3 It is a topological structure diagram of a small hydropower island microgrid system of the present invention;

[0022] Figure 4 It is the per unit value of the voltage of each node recorded by the feeder automation terminal FTU of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0024] Example

[0025] like Figure 1 As shown, the present embodiment provides a method for dividing a small hydropower island microgrid after a fault, comprising the following steps:

[0026] S1. After the fault occurs, the feeder automation terminal FTU of each line of the small hydropower island microgrid determines whether the line is located upstream or downstream of the fault point based on the fault characteristic information;

[0027] S2. If the feeder automation terminal FTU of each line of the small hydropower island microgrid determines that the line is located upstream of the fault point, the line will not enter the island state and the island division will not be started; if the line is located downstream of the fault point, the line will enter the island state, the island division will be started, and the process goes to step S3;

[0028] S3. After the island division is started, the disconnectors downstream of the fault are disconnected according to the positive time limit characteristics based on the magnitude of the current on both sides before the fault;

[0029] S4. Each feeder automation terminal FTU in the line is disconnected successively according to the positive time limit characteristics until the feeder automation terminal FTU stops operating after detecting all fault characteristic quantities, forming several stably operating isolated island microgrids.

[0030] In this embodiment, the process of judging whether the line is located upstream or downstream of the fault point in step S1 is as follows: according to the small hydropower island microgrid line being a radial line and operating in an open loop under normal operation, the feeder automation terminal FTU of each line of the small hydropower island microgrid can judge whether the line is located upstream or downstream of the fault point according to the direction of the fault current in the line; if the direction of the fault current is from the busbar to the load, it is judged that the line is located upstream of the fault point; if the direction of the fault current is from the load to the busbar, it is judged that the line is located downstream of the fault point.

[0031] In this embodiment, the specific process after the island division in step S3 is started is as follows: after the island division is started, each feeder automation terminal FTU located downstream of the fault point is based on the flow size on both sides of each line disconnector recorded before the fault, as follows: Figure 2 The positive time limit characteristic shown controls the disconnection of each disconnector, and the positive time limit characteristic expression is:

[0032]

[0033] in, t 0 is the minimum action delay, and its value is set to 50ms; K is the positive time limit characteristic coefficient; i and j represent any two adjacent nodes in the small hydropower microgrid; is the effective value of the power flow between node i and node j; t is the action delay of the feeder automation terminal FTU.

[0034] Specifically, in this embodiment, the smaller the current on both sides of each line disconnector recorded before the fault, the shorter the action delay of the disconnector; the larger the current on both sides of each line disconnector recorded before the fault, the longer the action delay of the disconnector.

[0035] This embodiment uses Figure 3 The small hydropower island microgrid system shown in the figure is taken as an example; the node voltage per unit value recorded by the feeder automation terminal FTU of the small hydropower island microgrid before the fault is as follows Figure 4 shown.

[0036] When a short circuit fault occurs at point f1 in the system, the feeder automation terminal FTU located at nodes 1 to 8 and nodes 21 to 37 detects a forward fault current, and the feeder automation terminal FTU determines that the line is located upstream of the fault point; the feeder automation terminal FTU located at nodes 9 to 19 and nodes 39 to 51 detects a reverse fault current, and the feeder automation terminal FTU determines that the line is located downstream of the fault point. Therefore, the feeder automation terminal FTU at nodes 1 to 8 and nodes 21 to 37 upstream of the fault point does not enter the island division mode, and the feeder automation terminal FTU at nodes 9 to 19 and nodes 39 to 51 downstream of the fault point enters the island division mode.

[0037] according to Figure 4 As shown in the figure, the flow value recorded by the feeder automation terminal FTU before the fault is the smallest between nodes 13 and 14. The disconnector is actuated first according to the positive time limit characteristic, and nodes 14 to 19 are divided into island 1. After island 1 is formed, the feeder automation terminal FTU in the island cannot detect the fault characteristic quantity and exits the island division mode. After excluding the flow data of the nodes included in island 1, the flow between node 10 and node 41 is the smallest. Therefore, the line between the two nodes is disconnected according to the positive time limit characteristic, and nodes 41 to 51 are divided into island 2. After island 2 is formed, the feeder automation terminal FTU in each node in island 2 cannot detect the fault characteristic quantity and exits the island division mode. Similarly, nodes 11 to 13 and nodes 38 to 40 can be divided into island 3 and island 4 respectively according to the same principle. Finally, the line downstream of the fault point of the small hydropower island microgrid is divided into 4 island microgrids that can operate stably. The division results are shown as follows. Figure 4 shown.

[0038] Based on the same inventive concept, the present invention also proposes a post-fault small hydropower island microgrid partitioning system, which comprises:

[0039] Upstream and downstream judgment module: The feeder automation terminal FTU of each line of the small hydropower island microgrid determines whether the line is upstream or downstream of the fault point according to the fault characteristic information;

[0040] Island division module: through the upstream and downstream judgment module, when the judgment result is that the line is located downstream of the fault point, the line enters the island state and the island division is started;

[0041] Disconnector disconnection module: After starting the island division module, the disconnectors downstream of the fault are disconnected according to the positive time limit characteristics based on the flow size on both sides before the fault;

[0042] Island microgrid formation module: The feeder automation terminals FTU in the line are disconnected successively according to the positive time limit characteristics until the feeder automation terminal FTU detects all fault characteristic quantities and stops operating, thus forming several stable island microgrids.

[0043] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for dividing a small hydropower island microgrid after a fault, characterized in that: The following steps are involved: S1. After the fault occurs, the feeder automation terminal FTU of each line of the small hydropower island microgrid determines whether the line is located upstream or downstream of the fault point based on the fault characteristic information; S2. If the feeder automation terminal FTU of each line of the small hydropower island microgrid determines that the line is located upstream of the fault point, the line will not enter the island state and the island division will not be started; If the line is located downstream of the fault point, the line will enter an island state, and island division will be started, and step S3 will be entered; S3. After the island division is started, the disconnectors downstream of the fault are disconnected according to the positive time limit characteristics based on the magnitude of the current on both sides before the fault; S4. Each feeder automation terminal FTU in the line is disconnected successively according to the positive time limit characteristics until the feeder automation terminal FTU stops operating after detecting all fault characteristic quantities, forming several isolated island microgrids with stable operation; The process of determining whether the line is located upstream or downstream of the fault point in step S1 is as follows: since the small hydropower island microgrid line is a radial line and operates in an open loop under normal operation, the feeder automation terminal FTU of each line of the small hydropower island microgrid determines whether the line is located upstream or downstream of the fault point according to the direction of the fault current in the line; If the direction of the fault current is from the busbar to the load, it is determined that the line is located upstream of the fault point; If the direction of the fault current is from the load to the busbar, it is determined that the line is located downstream of the fault point; The specific process after the island division is started in step S3 is as follows: after the island division is started, each feeder automation terminal FTU located downstream of the fault point controls the disconnection of each disconnector by using the positive time limit characteristic according to the flow size on both sides of each line disconnector recorded before the fault. The positive time limit characteristic expression is: Among them, t0 is the minimum action delay; K is the positive time limit characteristic coefficient; i and j represent any two adjacent nodes in the small hydropower microgrid; is the effective value of the power flow between node i and node j; t is the action delay of the feeder automation terminal FTU.

2. The partitioning system of the method for partitioning a small hydropower island microgrid after a fault according to claim 1 is characterized in that: include: Upstream and downstream judgment module: The feeder automation terminal FTU of each line of the small hydropower island microgrid determines whether the line is upstream or downstream of the fault point according to the fault characteristic information; Island division module: through the upstream and downstream judgment module, when the judgment result is that the line is located downstream of the fault point, the line enters the island state and the island division is started; Disconnector disconnection module: After starting the island division module, the disconnectors downstream of the fault are disconnected according to the positive time limit characteristics based on the flow size on both sides before the fault; Island microgrid formation module: The feeder automation terminals FTU in the line are disconnected successively according to the positive time limit characteristics until the feeder automation terminal FTU detects all fault characteristic quantities and stops operating, thus forming several stable island microgrids.

Images