Power distribution network rapid automatic reclosing method based on load balance coefficient

Abstract

The invention discloses a power distribution network rapid automatic reclosing method based on a load balance coefficient, and the method comprises the following steps: S1, calling the power flow data of a line protection device after a fault occurs, and collecting the line power flow data once in real time at time intervals by a collection device, totally d power data; s2, calling the electrical load power of all loads of the line at d moments corresponding to the active power matrix at the line outlet; S3, solving the power generation power of the distributed power supply; s4, solving a weighted load balance coefficient; and S5, selecting different reclosing schemes according to the obtained weighted load balance coefficient. According to the invention, rapid reclosing can be ensured when the proportion of the distributed power supply and the load is in a feasible interval, and splitting reclosing can be ensured to be selected when the power generation power of the distributed power supply is too large, so that safe and reliable operation of the power distribution network is ensured to the greatest extent.

Description

Technical Field

[0001] This invention patent relates to line reclosing technology for small hydropower stations, belonging to the field of distribution network relay protection, specifically involving a fast automatic reclosing method for distribution networks based on load balance coefficient. Background Technology

[0002] 10kV lines are crucial power supply channels to users. When a line fault causes a substation outgoing switch to trip, it can lead to a widespread power outage. Since most power line faults are transient, the switch can be automatically reclosed (with a 1-second delay) after tripping, restoring power to users. However, in the context of new power systems, a large number of new power sources (photovoltaics, small wind power) will be connected to 10kV lines. Combined with traditional distributed power sources such as small hydropower, this makes 10kV line operation more complex. When a line fault causes a trip, the 10kV line may enter an islanded operation state with the support of distributed power sources. If reclosing is activated in such a situation, asynchronous closing can easily occur, impacting the power grid and generator units.

[0003] To avoid asynchronous closing, methods such as reclosing with synchronization checks and voltage checks can be used. However, according to substation design specifications, 10kV lines are not equipped with voltage transformers; voltage transformers are only installed on the 10kV bus side. Since reclosing with synchronization checks and voltage checks requires detecting the 10kV line voltage, 10kV lines do not meet the conditions for synchronizing or checking voltage reclosing. For 10kV lines with distributed generation connections, the current strategy is to extend the 10kV reclosing time (delay by 10 seconds) until the distributed generation disconnects. This approach results in longer power outages for users, and even after a long delay, it cannot be guaranteed that the distributed generation has disconnected (when the distributed generation and load are relatively balanced, the isolated grid operates stably, and the disconnection time of the distributed generation will far exceed 10 seconds), thus the risk of asynchronous closing still exists.

[0004] To solve the above problems, a fast reclosing method can be adopted. When the line trips and forms an islanded operation, in the initial stage of island formation, since the synchronous generator and rotating load have a certain inertia, the island frequency will not change significantly, and the phase angle difference between the line fault and the main grid is not large. At this time, fast reclosing (delay 0.5-0.8 seconds) is performed, the inrush current is small, and uninterrupted power supply to users can be achieved. To implement fast reclosing, it is necessary to assess the proportion of power supply of the islanded line and determine the different reclosing strategies and action times. (1) When the proportion of distributed power supply is very small, the line is unlikely to be islanded. The reclosing delay can be set to the normal time of 1 second. The power supply load will be restored after a short power outage. (2) When the power of distributed power supply and the power load are relatively close, the phase angle deviation speed between the line and the main grid after islanded operation will be very slow. The reclosing time can be set to the normal time of 1 second. The power supply load will be smoothly integrated into the main grid after a short islanded operation, achieving uninterrupted power supply. (3) When the power difference between distributed power supply and power load is large, but islanded operation still occurs, fast reclosing should be adopted. The fast reclosing method shortens the reclosing action time and connects to the grid before the phase angle difference between the island and the main grid is widened, thereby reducing the inrush current and ensuring uninterrupted power supply to the load; (4) When the distributed power source is much larger than the power load, the island frequency rises rapidly and the phase angle difference with the main grid is widened in a short time. Even if the fast reclosing method (0.5-0.8 seconds) is used, a large inrush current will be generated. At this time, the reclosing time should be extended. After the distributed power source is disconnected and reclosing, the power supply load will be restored after about 10 seconds of power outage. In summary, different reclosing strategies need to be adopted as the proportion of distributed power sources changes. However, the relay protection device can only collect the power flow of the line and cannot determine the proportion of distributed power sources. Summary of the Invention

[0005] To address the issues of long reclosing times and asynchronous closing in distribution network lines caused by distributed generation access in existing technologies, this invention provides a fast automatic reclosing method for distribution networks based on a load balance coefficient. This invention ensures fast reclosing when the ratio of distributed generation to load is within a feasible range, while also allowing for disconnection reclosing when the distributed generation capacity is excessive, thereby maximizing the safe and reliable operation of the distribution network.

[0006] To achieve the above objectives, the present invention provides a method for fast automatic reclosing of distribution networks based on load balance coefficient, comprising the following steps:

[0007] S1. After a fault occurs, retrieve the power flow data from the line protection device. The data acquisition device collects line power flow data in real time at time intervals, for a total of d power data points:

[0008]

[0009] Where: Ps This represents the active power matrix at the line exit. This represents the active power at the moment the fault occurs; the value flowing into the grid is negative, and the value flowing out of the grid is positive. This represents the active power one time interval before the fault occurred; Δt is the time interval.

[0010] S2. Calling P s The power consumption of all loads on the line at the corresponding d time points:

[0011]

[0012] Where: P L This represents the power matrix of all loads on the line, with m rows, indicating that there are m loads on the line; and d columns, representing d time points. This represents the load power at time t-Δt for the m-th load.

[0013] S3. Find the power generation capacity of the distributed power source, P. D for

[0014] P D =P L -P S (1);

[0016] S4. Calculate the weighted load balance coefficient:

[0017] a. Accumulate the total load power at different times:

[0018]

[0019] b. Calculate the load balance coefficient at different times:

[0020]

[0021] In the formula: A t-kΔt This represents the load balance coefficient at time t-kΔt;

[0022] c. Calculate the weighted load balance coefficient:

[0023]

[0024]

[0025] In the formula: α k This represents the weighting coefficient of the load factor at time t-kΔt. The larger k is, the longer the time distance from the fault time, and the smaller the weighting coefficient is; k=0 indicates the time when the fault occurs, and the weighting coefficient is 0.55.

[0026] S5. Select different reclosing schemes based on the obtained weighted load balance coefficient A.

[0027] In one preferred embodiment, in step S1, the time interval is 15 minutes, and a total of d = 10 power data points are retrieved from 2 hours before the fault occurred to the time of the fault.

[0028] In one preferred embodiment, step S5 involves selecting different reclosing schemes based on the obtained weighted load balance coefficient A, specifically as follows:

[0029]

[0030] In the formula: T represents the reclosing time after the fault, in seconds;

[0031] When (3≤A), the power supply reclosing scheme selects the disconnection reclosing T=10. At this time, the reclosing time is extended, and the distributed power source is disconnected before reclosing. That is, wait 10s after the fault occurs to allow sufficient time for the distributed power source to disconnect from the grid.

[0032] When (1.5 < A < 3), the power supply reclosing scheme selects fast reclosing T = 1 - 0.16A. At this time, the power difference between the distributed power source and the power load is large. After the fault, islanding operation will occur, shortening the reclosing action time. The grid is connected before the phase angle difference between the island and the main grid is widened, and the power supply load can achieve uninterrupted power supply.

[0033] When (0.7≤A≤1.5), the power supply reclosing scheme is selected as T=1. At this time, the power of the distributed power source and the power load are close. After the line is isolated, the phase angle deviation speed with the main network will be very slow. The reclosing time is set to 1 second as normal. After the power supply load is isolated for a short time, it will be smoothly connected to the main network to achieve uninterrupted power supply.

[0034] When (0≤A<0.7), the power supply reclosing scheme is selected as T=1, the reclosing delay is set to 1 second as the normal time, and the power supply load is restored after a short power outage.

[0035] The present invention has the following advantages:

[0036] Since there are no voltage transformers installed at the distribution network outlet, the reclosing verification method cannot be determined by comparing voltage waveforms. Using fast reclosing can achieve synchronous grid connection of the isolated network even in the absence of line voltage, but the ratio of distributed generation to electrical load needs to be determined before implementation. This invention utilizes real-time power flow data collected by the 10kV line protection device and real-time electrical load power of all distribution transformers on the line collected by the power grid dispatch automation master station. The distributed generation power is obtained by subtracting the two data points, thereby analyzing the proportion of distributed generation to load power on the line. Different weighting coefficients are used to obtain the load balance coefficient for a period from before the fault to the fault occurrence. Using the obtained load balance coefficient to select the reclosing action time ensures fast reclosing when the ratio of distributed generation to load is within a feasible range, while also ensuring that disconnection reclosing is used when the distributed generation power is too high, thus maximizing the safe and reliable operation of the distribution network. Detailed Implementation

[0037] The features of the present invention will be further illustrated below through examples. These embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0038] An embodiment of the present invention provides a fast automatic reclosing method for distribution networks based on load balance coefficient, comprising the following steps:

[0039] S1. After the fault occurs, the power flow data of the line protection device is retrieved from the 10KV line outlet. The acquisition device collects the line power flow data in real time every 15 minutes, and a total of 10 power data points from 2 hours before the fault occurred are retrieved:

[0040]

[0041] Where: P s This represents the active power matrix at the line exit. This represents the active power at the moment the fault occurs; the value flowing into the grid is negative, and the value flowing out of the grid is positive. This represents the active power one time interval before the fault occurred; Δt is the interval time of 15 minutes.

[0042] S2. Calling P s The power consumption of all loads on the line at the corresponding 10 time points:

[0043]

[0044] Where: P L This represents the power matrix of all loads on the line, with m rows, indicating that there are m loads on the line; and 10 columns, representing 10 time points; for example... This represents the load power at time t-Δt for the m-th load.

[0045] S3. Calculate the distributed generation power. When the power flow direction is towards the grid, it indicates that the distributed generation power is greater than the power consumption of the line load. Conversely, it indicates that the distributed generation power is insufficient to meet the power consumption of all loads, and the grid needs to bear a portion of the load. Distributed generation power P D for

[0046] P D =P L -P S (1);

[0048] S4. Calculate the weighted load balance coefficient:

[0049] a. Accumulate the total load power at different times:

[0050]

[0051] b. Calculate the load balance coefficient at different times:

[0052]

[0053] In the formula: A t-kΔt Represents the load balance coefficient at time t-kΔt.

[0054] c. Calculate the weighted load balance coefficient:

[0055]

[0056]

[0057] In the formula: α k This represents the weighting coefficient of the load factor at time t-kΔt. The larger k is, the longer the time distance from the fault time, and the smaller the weighting coefficient is; k=0 indicates the time when the fault occurs, and the weighting coefficient is 0.55.

[0058] S5. Select different reclosing schemes based on the obtained weighted load balance coefficient A:

[0059]

[0060] In the formula: T represents the reclosing time after the fault, in seconds.

[0061] When (3≤A), the power supply reclosing scheme selects the disconnection reclosing T=10. At this time, the distributed power source is much larger than the power load. After the fault, the frequency of the islanded grid rises rapidly, and the phase angle difference with the main grid is widened in a short time. Even if fast reclosing is used, a large inrush current will be generated. At this time, the reclosing time should be extended, and the distributed power source should be disconnected before reclosing. That is, wait 10 seconds after the fault occurs to allow sufficient time for the distributed power source to disconnect from the grid.

[0062] When (1.5 < A < 3), the power supply reclosing scheme selects fast reclosing T = 1 - 0.16A. At this time, the power difference between the distributed power source and the power load is large, and islanding will occur after the fault. Shorten the reclosing action time, and connect to the grid before the phase angle difference between the island and the main grid is widened, so as to reduce the inrush current and the power supply load can achieve uninterrupted power supply.

[0063] When (0.7≤A≤1.5), the power supply reclosing scheme is selected as T=1. At this time, the power of the distributed power source and the power load are close. After the line is isolated, the phase angle deviation speed with the main network will be very slow. The reclosing time is set to 1 second as normal. After the power supply load is isolated for a short time, it will be smoothly connected to the main network to achieve uninterrupted power supply.

[0064] When (0≤A<0.7), the power supply reclosing scheme is selected as T=1. At this time, the proportion of distributed power sources is very small, and the line cannot be in islanded operation. The reclosing delay can be set to the normal time of 1 second. The power supply load is restored after a short power outage.

[0065] This invention is not limited to the above-described embodiments. It should be noted that those skilled in the art can make several improvements and modifications without departing from the technical principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention.

Claims

1. A power distribution network fast automatic reclosing method based on load balance coefficient, characterized in that, The method comprises the following steps: S1. After the fault occurs, the power flow data of the line protection device is called, and the device collects the line power flow data every time interval, a total of d power data: where: P s represents the active power matrix at the line exit, represents the active power at the time of fault occurrence, negative for flow into the grid and positive for flow out of the grid; represents the active power one interval time before the fault occurrence; Δt is the interval time; S2. Call the P s The line all load power of the corresponding d time moment: Wherein: P L represents the load power matrix of all lines, m rows, representing m loads of all lines; d columns, representing d time points; represents the load power of the mth load at t-Δt time point; S3. Calculate the distributed power generation power, the distributed power generation power P D For P D = P L - P S (1); S4. The weighted load balance coefficient is calculated: a. The total power of the load at different times is accumulated: b. The load balance coefficient at different times is calculated: In the formula, A t-kΔt represents the load balance coefficient at the t-kΔt moment; c. The weighted load balance coefficient A is calculated: In the formula, α k represents the weighting coefficient of the load factor at t-kΔt, k represents the longer the time distance from the fault time, the smaller the weighting coefficient; k=0 represents the fault time, and the weighting coefficient is 0.55; S5. Different reclosing schemes are selected according to the calculated weighted load balance coefficient A.

2. The method of claim 1, wherein the method further comprises: In step S1, the time interval is 15 minutes, and d=10 power data from 2 hours before the fault occurs to the time of the fault is called.

3. The method of claim 1, wherein the method further comprises: Specifically: In the formula, T represents the reclosing time after the fault, and the unit is second; When (3≤A), the power supply reclosing scheme selects split reclosing T=10, at this time, the reclosing time is extended, and the distributed power is split and reclosed after the distributed power is split and off the grid, that is, after the fault occurs, 10s is waited for the distributed power to reserve enough time to split and off the grid; When (1.5<A<3), the power supply reclosing scheme selects fast reclosing T=1-0.16A, at this time, the power difference between the distributed power and the power load is large, and island operation will occur after the fault, the reclosing action time is shortened, and the island and the main network are connected in parallel before the phase angle difference is opened, and the power supply load can realize uninterrupted power supply; When (0.7≤A≤1.5), the power supply reclosing scheme selects T=1, at this time, the power of the distributed power and the power load is close, and the phase angle deviation speed of the line island operation and the main network will be very slow, the reclosing is set to the normal time 1 second, the power supply load will be smoothly connected to the main network after short-time island operation, and uninterrupted power supply is realized; When (0≤A<0.7), the power supply reclosing scheme selects T=1, and the reclosing delay is set to the normal time 1 second, and the power supply load recovers after a short power failure.

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