Line reclosing scheme selection method suitable for small hydropower station

Abstract

The invention discloses a circuit reclosing scheme selection method suitable for a small hydropower station. The circuit reclosing scheme selection method comprises the following steps: S1, after a fault occurs, performing circuit reclosing; calling a plurality of groups of active power data of all hydroelectric generating sets and active power data of all loads of the line from the sampling moment closest to the fault moment, and respectively forming a hydroelectric generating set power matrix and a power matrix of all loads of the line; s2, predicting the power at the fault moment, wherein the step a comprises the following sub-steps: a, selecting a set frequency function and fitting parameters to fit a power curve; b, calculating a power value at a fault moment; s3, selecting a reclosing scheme, wherein the reclosing scheme comprises the following sub-steps: c, calculating a power-to-use ratio; and d, selecting a reclosing scheme according to different power-to-use ratios. According to the method, different reclosing strategies are selected by considering the ratio relation between the hydroelectric generating set and the load, and synchronous grid-connected reclosing and small water electrolysis reclosing in the absence of line voltage judgment are realized by optimizing the reclosing action time.

Description

Technical fields:

[0001] This invention patent relates to line reclosing technology for small hydropower stations, belonging to the field of power distribution network relay protection, specifically involving a method for selecting line reclosing schemes suitable for small hydropower stations. Background technology:

[0002] 10kV lines are crucial power supply channels to users. When a line fault causes a substation outgoing switch to trip, it results in 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. Traditional distribution networks often include small hydropower stations, making 10kV line operation more complex. When a line fault causes a trip, the 10kV line may enter islanded operation with the support of the small hydropower station. If reclosing is activated in such a situation, asynchronous closing can occur, impacting the power grid and generator units.

[0003] To avoid asynchronous closing, methods such as reclosing for synchronism checks and voltage de-energization checks can be used. However, according to substation design specifications, voltage transformers are not installed on 10kV lines, only on the 10kV bus side. Since reclosing for synchronism checks and voltage de-energization checks requires monitoring the 10kV line voltage, the current strategy is to extend the 10kV reclosing time, waiting for the small hydropower station to disconnect before reclosing. This solution 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 distributed generation will run for a long time before disconnecting), thus the risk of asynchronous closing still exists.

[0004] When a line fault occurs and the relay protection device trips, it needs to reclose the circuit to obtain the power relationship between the hydroelectric generator units and the total load of the line. However, the protection device cannot collect the real-time power generation of each hydroelectric generator unit. If communication is established with the dispatch automation master station, the power generation data of small hydroelectric power can be obtained periodically. However, the actual fault occurrence time may be between two sampling times. There is no good power reference data when the fault occurs. Therefore, it is necessary to predict the power of the hydroelectric generator units and the load. However, conventional methods can only make a certain prediction of the power value at the next sampling time, and lack further prediction and correction for the fault time. Summary of the Invention:

[0005] To address the problems in existing technologies, this invention provides a method for selecting line reclosing schemes suitable for small hydropower projects. This method selects different reclosing strategies by considering the ratio between hydropower units and loads, and optimizes the reclosing action time to achieve simultaneous grid-connected reclosing and small hydropower unit disconnection reclosing under conditions lacking line voltage judgment.

[0006] To achieve the above objectives, this invention provides a method for selecting line reclosing schemes suitable for small hydropower projects, applied to distributed small hydropower units, comprising the following steps:

[0007] S1. After a fault occurs, retrieve several sets of active power data of all hydroelectric generator sets and active power data of all loads on the line from the sampling time closest to the fault time and form a power matrix of hydroelectric generator sets and a power matrix of all loads on the line respectively.

[0008] S2. Predict the power at the time of the fault, including the following sub-steps:

[0009] a. Fit the power curve P(x) using a predetermined function and fitting parameters:

[0010] P(x) = a0 + a1x + a2x 2 +…+a n x n ;

[0011] Let the independent variable x represent the sampling time, and a n The fitting parameters are represented by the following: The fitting process is as follows: The fitting parameter values ​​are calculated by summing the squares of the differences between the preset function value and the actual power at the sampling time, and the fitting power curve is obtained after setting the sum of squares to 0.

[0012] Based on the fitting process, the fitting function P of the hydroelectric generator set is calculated by using each element value of the power matrix of the hydroelectric generator set as the actual power value. G (x);

[0013] The line load fitting function P is calculated by taking each element of the line load power matrix as the actual power value. L (x);

[0014] b. Calculate the power value at the time of the fault:

[0015] The predicted power value of the hydroelectric generator set at the next sampling time is calculated based on the fitting function of the hydroelectric generator set; assuming the fault time x = t, the predicted power value of the hydroelectric generator set at the fault time is calculated as P. G (t);

[0016] The predicted line load power at the next sampling time is calculated based on the fitted function of the line load; assuming the fault time x = t, the predicted power of the total line load at the fault time is calculated as P. L (t);

[0017] S3. Reclosing scheme selection, including the following sub-steps:

[0018] c. Calculate the usage ratio, based on P predicted in step S2. L (t),P G(t) Calculate the generation-to-consumption ratio λ of distributed generation and load power consumption;

[0019] d. Select the reclosing scheme according to different generation-to-consumption ratios λ.

[0020] In one preferred embodiment, step S1 retrieves 100 sets of active power data from all hydroelectric generator sets and active power data from all line loads, and respectively constructs a power matrix for the hydroelectric generator sets and a power matrix for all line loads; these are respectively represented as:

[0021]

[0022]

[0023] Where: P G Represents the power matrix of a hydroelectric generator set; P represents the active power of all hydropower generator units at the sampling time closest to the time of the fault occurrence; L This represents the power matrix of all loads on the line. This represents the active power of all loads on the line at the sampling time closest to the time the fault occurred.

[0024] In one preferred embodiment, in step a of step S2, a fourth-order function is used to fit the power curve, i.e., the fitted power curve is:

[0025] P(x) = a0 + a1x + a2x 2 +a3x 3 +a4x 4 (1);

[0027] In the formula: the independent variable x represents the sampling time, defined as 0 for the closest sampling time to the fault occurrence time, and -15 for the previous interval; a n These represent the fitting parameters; there are a total of 5 fitting parameters.

[0028] In one preferred embodiment, in step a of step S2, the fitting function P for the line load is calculated. L The specific method for (x) is as follows:

[0029] make When i = 1, x = 0; when i = 2, x = -15, and so on up to i = 100. J(β) represents the sum of squares of the differences between the preset function value and the actual power; P(x) is the preset function value calculated based on the fitting function of the line load. Let J(β) = 0. The fit between the two is the best, which can be represented by a matrix:

[0030] P L =(xa) T(2);

[0031] In the formula: This represents a fourth-order fitted function model; For parameter matrices;

[0032] Through matrix transformation and inversion operations, we can obtain:

[0033] a=(x T x) -1 x T P L T (3);

[0034] After obtaining the fitting parameter matrix a, substitute it back into formula (1) to obtain the fitting function P. L (x).

[0035] In one preferred embodiment, in step a of step S2, the fitting function P of the hydroelectric generator set is calculated. G The specific method for (x) is as follows:

[0036] make When i = 1, x = 0; when i = 2, x = -15, and so on up to i = 100. K(α) represents the sum of squares of the differences between the preset function value and the actual power; P(x) is the preset function value calculated based on the fitting function of the line load. Let J(β) = 0. The fit between the two is the best, which can be represented by a matrix:

[0037] P G =(xa) T (4);

[0038] In the formula: This represents a fourth-order fitted function model; For parameter matrices;

[0039] Through matrix transformation and inversion operations, we can obtain:

[0040] a=(x T x) -1 x T P G T (5);

[0041] After obtaining the fitting parameter matrix a, substitute it back into formula (1) to obtain the fitting function P. G (x).

[0042] In one preferred embodiment, in step b of step S2, the predicted power value P at the time of the line total load fault is calculated. L The specific method for (t) is as follows:

[0043] Calculate the predicted power value P at x=15, i.e., the next sampling time. L (15), believes P L (0),P L (15) The values ​​change linearly, so let the fault time be x = t, then:

[0044]

[0045] Where: P L (t) represents the predicted power value at the moment of line total load failure.

[0046] In one preferred embodiment, in step b of step S2, the predicted power value P at the time of the hydroelectric generator failure is calculated. G The specific method for (t) is as follows:

[0047] Calculate the predicted power value P at x=15, i.e., the next sampling time. G (15), believes P G (0),P G (15) The values ​​change linearly, so let the fault time be x = t, then:

[0048]

[0049] Where: P G (t) represents the predicted power value at the moment of fault load failure of the hydroelectric generator set.

[0050] In one preferred embodiment, in step d of step S3, the reclosing scheme is selected according to different generation-to-utilization ratios λ, specifically as follows:

[0051]

[0052] In the formula: T represents the reclosing waiting time after a fault, in seconds. As can be seen from the formula above,

[0053] When (λ>3), the power supply reclosing scheme is T=2.25λ-6.25. The reclosing time is directly proportional to the generation-to-consumption ratio, with a maximum time of 10s. When the generation-to-consumption ratio λ≥5, the reclosing time is selected as T3=10. This indicates that the power generation of the small hydropower station is much greater than the power load. After the fault, it will operate in an isolated grid. For a short time, the frequency and phase angle will be far away from the main grid. At this time, the small hydropower station should be disconnected and reclosed. That is, wait 10s after the fault occurs to allow sufficient time for the small hydropower station to disconnect from the grid.

[0054] When (0<λ≤3), the inverse time characteristic formula for selecting the reclosing scheme is... The larger λ is, the shorter the reclosing time; (0.3<λ≤3) is fast reclosing. At this time, the power generation of small hydropower and the power load are relatively close. After the fault, the frequency and phase angle of island operation will not be too far apart. After fast reclosing, continuous power supply can be guaranteed. The shortest reclosing time is T2=0.5s; when (λ≤0.3), the power of small hydropower is far from meeting the power load requirements. After the fault, the island network cannot maintain stability. Hydropower will be quickly disconnected. The reclosing time can be appropriately extended, with a maximum of T1=2s.

[0055] The present invention has the following advantages:

[0056] This invention determines the corresponding reclosing strategy based on the ratio of small hydropower generation to electrical load. When the small hydropower generation is relatively small, the isolated grid formed by line tripping cannot maintain stability, and the hydropower will quickly disconnect, allowing for an appropriate extension of the reclosing time. When there is a certain deviation between the small hydropower generation and the electrical load, but still within a reasonable range, the frequency will not change rapidly due to the rotational inertia of the small hydropower units after the isolated grid is formed, and the phase angle difference with the main grid has not yet increased significantly. In this case, rapid reclosing results in a smaller inrush current, enabling uninterrupted power supply to users. When the small hydropower generation is close to the electrical load, the frequency is relatively stable after the isolated grid operation, and the phase angle deviation with the main grid changes slowly. Reclosing is set according to the normal time, and the power supply load will smoothly connect to the main grid after a short period of isolated grid operation, achieving uninterrupted power supply. When the small hydropower generation is much larger than the electrical load, the isolated grid frequency rises rapidly, creating a large phase angle difference with the main grid in a short time. Even with rapid reclosing, a large inrush current will be generated. In this case, the reclosing time should be extended, and the distributed power source should disconnect before reclosing.

[0057] For distribution network lines with small hydropower access, this invention requires consideration of the ratio between hydropower units and loads when reclosing, and selects different reclosing strategies. By optimizing the reclosing action time, it achieves synchronous grid-connected reclosing and small hydropower disconnection reclosing under conditions where line voltage judgment is lacking. Attached Figure Description

[0058] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0059] Figure 1 This is a circuit diagram of a distributed small hydropower unit to which the method of this invention is applied. Detailed Implementation

[0060] 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.

[0061] Taking a sewage system area in a city in Southwest China as an example, the processing procedure of the present invention will be explained.

[0062] This invention provides a method for selecting line reclosing schemes suitable for small hydropower projects, applied to distributed small hydropower units, such as... Figure 1 As shown, the steps are as follows:

[0063] S1. After a fault occurs, retrieve several sets of active power data from all hydroelectric generator units and all line loads, starting from the sampling time closest to the fault time and working backwards, to form a power matrix for the hydroelectric generator units and a power matrix for all line loads, respectively. Retrieve 100 sets of active power data from all hydroelectric generator units and all line loads, and form a power matrix for the hydroelectric generator units and a power matrix for all line loads, respectively, as follows:

[0064]

[0065]

[0066] Where: P G Represents the power matrix of a hydroelectric generator set; P represents the active power of all hydropower generator units at the sampling time closest to the time of the fault occurrence; L This represents the power matrix of all loads on the line. This represents the active power of all loads on the line at the sampling time closest to the time the fault occurred.

[0067] S2. Predict the power at the time of the fault, including the following sub-steps:

[0068] a. A fourth-order function is used to fit the power curve, i.e., the fitted power curve is:

[0069] P(x) = a0 + a1x + a2x 2 +a3x 3 +a4x 4 (1);

[0071] In the formula: the independent variable x represents the sampling time, defined as 0 for the closest sampling time to the fault occurrence time, and -15 for the previous interval; a n These represent the fitting parameters; there are a total of 5 fitting parameters.

[0072] In the formula: the independent variable x represents the sampling time, defined as 0 for the closest sampling time to the fault occurrence time, and -15 for the previous interval; a nThese represent the fitting parameters, a total of 5. Setting J(β) = 0 yields the best fit. This can be represented as a matrix:

[0073] P L =(xa) T (2);

[0074] In the formula: This represents a fourth-order fitted function model; For parameter matrices;

[0075] Through matrix transformation and inversion operations, we can obtain:

[0076] a=(x T x) -1 x T P L T (3);

[0077] After obtaining the fitting parameter matrix a, substitute it back into formula (1) to obtain the fitting function P. L (x).

[0078] 1. Calculate the fitting function P of the hydroelectric generator set. G The specific method for (x) is as follows:

[0079] make When i = 1, x = 0; when i = 2, x = -15, and so on up to i = 100. K(α) represents the sum of squares of the differences between the preset function value and the actual power; P(x) is the preset function value calculated based on the fitting function of the line load. Let J(β) = 0. The fit between the two is the best, which can be represented by a matrix:

[0080] P G =(xa) T (4);

[0081] In the formula: This represents a fourth-order fitted function model; For parameter matrices;

[0082] Through matrix transformation and inversion operations, we can obtain:

[0083] a=(x T x) -1 x T P L T (5);

[0084] After obtaining the fitting parameter matrix a, substitute it back into formula (1) to obtain the fitting function P. G (x).

[0085] b. Calculate the power value at the time of the fault:

[0086] The predicted power value of the hydroelectric generator set at the next sampling time is calculated based on the fitting function of the hydroelectric generator set; assuming the fault time x = t, the predicted power value of the hydroelectric generator set at the fault time is calculated as P. G (t);

[0087] The predicted line load power at the next sampling time is calculated based on the fitted function of the line load; assuming the fault time x = t, the predicted power of the total line load at the fault time is calculated as P. L (t);

[0088] Calculate the predicted power value P at the time of the line total load fault. L The specific method for (t) is as follows:

[0089] Since the fault occurs between two power sampling times, the predicted power value P at the next sampling time, x = 15, is calculated. L (15), believes P L (0),P L (15) The values ​​change linearly, so let the fault time be x = t, then:

[0090]

[0091] Where: P L (t) represents the predicted power value at the moment of line total load failure.

[0092] Calculate the predicted power value P at the moment of failure of the hydroelectric generator unit G The specific method for (t) is as follows:

[0093] Since the fault occurs between two power sampling times, the predicted power value P at the next sampling time, x = 15, is calculated. G (15), believes P G (0),P G (15) The values ​​change linearly, so let the fault time be x = t, then:

[0094]

[0095] Where: P G (t) represents the predicted power value at the moment of fault load failure of the hydroelectric generator set.

[0096] S3. Reclosing scheme selection, including the following sub-steps:

[0097] c. Calculate the usage ratio, based on P predicted in step S2. L (t),P G (t) Calculate the generation-to-consumption ratio λ of distributed generation and load power consumption;

[0098]

[0099] a. Select the reclosing scheme according to different generation-to-consumption ratios, specifically:

[0100]

[0101] In the formula: T represents the reclosing waiting time after a fault, in seconds. As can be seen from the formula above,

[0102] When (λ>3), the power supply reclosing scheme is T=2.25λ-6.25, and the reclosing time is directly proportional to the generation-to-consumption ratio, with a maximum time of 10s. When the generation-to-consumption ratio λ≥5, the reclosing time is selected as T3=10. This indicates that the power generation of the small hydropower station is much greater than the power load, and after the fault, it will operate in an isolated grid. In a short time, the frequency and phase angle will be far away from the main grid. Even if fast reclosing is used, a large inrush current will be generated. At this time, the small hydropower station should be disconnected and reclosed, that is, wait 10s after the fault occurs to allow sufficient time for the small hydropower station to disconnect from the grid.

[0103] When (0<λ≤3), the inverse time characteristic formula for selecting the reclosing scheme is... The larger λ is, the shorter the reclosing time. (0.3 < λ ≤ 3) represents fast reclosing, where the power generation of the small hydropower station and the electrical load are relatively close. After a fault, the frequency and phase angle of the islanded operation will not differ too much, and continuous power supply can be guaranteed after fast reclosing. The shortest reclosing time is T2 = 0.5s. When (λ ≤ 0.3), the power of the small hydropower station is far from meeting the electrical load requirements. After a fault, the islanded grid cannot maintain stability, and the hydropower station will be quickly disconnected. The reclosing time can be appropriately extended, but the maximum reclosing time will not exceed T = 2s.

[0104] 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 method for selecting line reclosing schemes suitable for small hydropower, applied to distributed small hydropower units, characterized in that, Includes the following steps: S1. After a fault occurs, retrieve several sets of active power data of all hydroelectric generator sets and active power data of all loads on the line from the sampling time closest to the fault time and form a power matrix of hydroelectric generator sets and a power matrix of all loads on the line respectively. S2. Predict the power at the time of the fault, including the following sub-steps: a. Fit the power curve P(x) using a predetermined function and fitting parameters: P(x)=a0+a1x+a2x 2 +…+a n x n ; Let the independent variable x represent the sampling time, and a n The fitting parameters are represented by the following: The fitting process is as follows: The fitting parameter values ​​are calculated by summing the squares of the differences between the preset function value and the actual power at the sampling time, and the fitting power curve is obtained after setting the sum of squares to 0. Based on the fitting process, the fitting function P of the hydroelectric generator set is calculated by using each element value of the power matrix of the hydroelectric generator set as the actual power value. G (x); The line load fitting function P is calculated by taking each element of the line load power matrix as the actual power value. L (x); b. Calculate the power value at the time of the fault: The predicted power value of the hydroelectric generator set at the next sampling time is calculated based on the fitting function of the hydroelectric generator set; assuming the fault time x = t, the predicted power value of the hydroelectric generator set at the fault time is calculated as P. G (t); The predicted line load power at the next sampling time is calculated based on the fitted function of the line load; let... If the fault time is x = t, then the predicted power value of the total line load at the fault time is P. L (t); S3. Reclosing scheme selection, including the following sub-steps: c. Calculate the usage ratio, based on P predicted in step S2. L (t),P G (t) Calculate the generation-to-consumption ratio λ of distributed generation and load power consumption; d. Select the reclosing scheme according to different generation-to-consumption ratios λ.

2. The method for selecting a line reclosing scheme applicable to small hydropower stations according to claim 1, characterized in that, Step S1 retrieves 100 sets of active power data for all hydroelectric generator sets and active power data for all line loads, and constructs a power matrix for the hydroelectric generator sets and a power matrix for all line loads, respectively, as follows: Where: P G Represents the power matrix of a hydroelectric generator set; P represents the active power of all hydropower generator units at the sampling time closest to the time of the fault occurrence; L This represents the power matrix of all loads on the line. This represents the active power of all loads on the line at the sampling time closest to the time the fault occurred.

3. The method for selecting a line reclosing scheme applicable to small hydropower stations according to claim 1, characterized in that, In step S2, step a, a fourth-order function is used to fit the power curve, i.e., the fitted power curve is: P(x)=a0+a1x+a2x 2 +a3x 3 +a4x 4 (1); In the formula: the independent variable x represents the sampling time, defined as 0 for the closest sampling time to the fault occurrence time, and -15 for the previous interval; a n These represent the fitting parameters; there are a total of 5 fitting parameters.

4. The method for selecting a line reclosing scheme applicable to small hydropower stations according to claim 1, characterized in that, In step S2, step a, the fitting function P for the line load is calculated. L The specific method for (x) is as follows: make When i = 1, x = 0; when i = 2, x = -15, and so on up to i = 100. J(β) represents the sum of squares of the differences between the preset function value and the actual power; P(x) is the preset function value calculated based on the fitting function of the line load. Let J(β) = 0. The fit between the two is the best, which can be represented by a matrix: P L =(send) T (2); In the formula: This represents a fourth-order fitted function model; For parameter matrices; Through matrix transformation and inversion operations, we can obtain: a=(x T x) -1 x T P L T (3); After obtaining the fitting parameter matrix a, substitute it back into formula (1) to obtain the fitting function P. L (x).

5. The method for selecting a line reclosing scheme applicable to small hydropower stations according to claim 1, characterized in that, In step S2, step a involves calculating the fitting function P of the hydroelectric generator set. G The specific method for (x) is as follows: make When i = 1, x = 0; when i = 2, x = -15, and so on up to i = 100. K(α) represents the sum of squares of the differences between the preset function value and the actual power; P(x) is the preset function value calculated based on the fitting function of the line load. Let J(β) = 0. The fit between the two is the best, which can be represented by a matrix: P G =(send) T (4); In the formula: This represents a fourth-order fitted function model; For parameter matrices; Through matrix transformation and inversion operations, we can obtain: a=(x T x) -1 x T P G T (5); After obtaining the fitting parameter matrix a, substitute it back into formula (1) to obtain the fitting function P. G (x).

6. The method for selecting a line reclosing scheme applicable to small hydropower stations according to claim 1, characterized in that, In step b of step S2, the predicted power value P at the time of the line total load fault is calculated. L The specific method for (t) is as follows: Calculate the predicted power value P at x=15, i.e., the next sampling time. L (15), believes P L (0),P L (15) The values ​​change linearly, so let the fault time be x = t, then: Where: P L (t) represents the predicted power value at the moment of line total load failure.

7. The method for selecting a line reclosing scheme applicable to small hydropower stations according to claim 1, characterized in that, In step b of step S2, the predicted power value P at the moment of failure of the hydroelectric generator set is calculated. G The specific method for (t) is as follows: Calculate the predicted power value P at x=15, i.e., the next sampling time. G (15), believes P G (0),P G (15) The values ​​change linearly, so let the fault time be x = t, then: Where: P G (t) represents the predicted power value at the moment of fault load failure of the hydroelectric generator set.

8. The method for selecting a line reclosing scheme applicable to small hydropower stations according to claim 1, characterized in that, In step S3, step d involves selecting a reclosing scheme based on different generator-to-consumption ratios λ, specifically as follows: In the formula: T represents the reclosing waiting time after a fault, in seconds. As can be seen from the formula above, When (λ>3), the power supply reclosing scheme is T=2.25λ-6.

25. The reclosing time is directly proportional to the generation-to-consumption ratio, with a maximum time of 10s. When the generation-to-consumption ratio λ≥5, the reclosing time is selected as T3=10. This indicates that the power generation of the small hydropower station is much greater than the power load. After the fault, it will operate in an isolated grid. For a short time, the frequency and phase angle will be far away from the main grid. At this time, the small hydropower station should be disconnected and reclosed. That is, wait 10s after the fault occurs to allow sufficient time for the small hydropower station to disconnect from the grid. When (0<λ≤3), the inverse time characteristic formula is selected for the reclosing scheme. The larger λ is, the shorter the reclosing time; (0.3<λ≤3) is fast reclosing. At this time, the power generation of small hydropower and the power load are relatively close. After the fault, the frequency and phase angle of island operation will not be too far apart. After fast reclosing, continuous power supply can be guaranteed. The shortest reclosing time is T2=0.5s; when (λ≤0.3), the power of small hydropower is far from meeting the power load requirements. After the fault, the island network cannot maintain stability. Hydropower will be quickly disconnected. The reclosing time can be appropriately extended, with a maximum of T1=2s.

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