Petals active distribution network inverse time overcurrent protection method based on improved voltage acceleration factor

Abstract

The present application relates to a kind of petal active distribution network inverse time overcurrent protection methods based on improved voltage acceleration factor, comprising 1) the starting current of each protection, time coefficient and voltage parameter are set;2) the above setting value is entered into each protection device, while entering action characteristic equation;3) when fault occurs, the direction of the fault current flowing through protection device and the positive direction of protection preset are judged and the start and lock of protection are decided;4) the fault voltage and current information collected are substituted into action characteristic equation, and the action time of each protection is calculated, each protection action time delay action, and the line fault is removed.The present application is scientifically and reasonably designed, significantly improves the speed of overcurrent protection under the premise of improving protection coordination, and only needs to use the local current and voltage information at the protection installation place, without the aid of communication, avoids expensive communication cost, and is easy to implement in engineering;The protection method of the present application is not affected by fault type.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power system distribution network relay protection, and is specifically a petal-shaped active distribution network inverse-time overcurrent protection method based on an improved voltage acceleration factor, based on the unique fault characteristics of the petal-shaped active distribution network. BACKGROUND

[0002] To build a new power system with low carbon, safety and high efficiency, and to realize the low-carbon transformation of electric power energy, the form structure of the power system is undergoing profound changes.

[0003] On the one hand, in order to meet the requirements of high-tech regional power users for power supply reliability and power quality, petal-shaped distribution networks in closed-loop operation are constructed in regions with high load density and high power supply reliability requirements in Guangzhou, Taizhou, Xiong'an and other regions in China, by referring to the connection mode of the Singapore distribution network whose power supply reliability level is at the international leading position. Compared with the traditional radial distribution network, the petal-shaped distribution network has flexible and variable operation mode, often has shorter power outage time, higher equipment utilization rate and better power quality. On the other hand, with the development of new energy generation technology and the support of national policy, more and more distributed power sources are connected to the distribution network, which changes the power supply mode of the distribution network and makes the distribution of the power flow of the distribution network more complex.

[0004] When the distributed power source is connected to the petal-shaped distribution network, the new distribution network grid structure cooperates with the distributed power source, improves the voltage distribution of the power system node, improves the power supply efficiency and reliability of the power grid, and at the same time makes the petal-shaped active distribution network present more complex fault characteristics, thereby bringing great challenges to the protection of the distribution network.

[0005] When the traditional inverse-time overcurrent protection is applied to the petal-shaped active distribution network, the upstream protection of the fault point has a selectivity disorder problem, and the downstream protection of the fault point has a coordination mismatch problem. In addition, due to the great difference between the fault voltage characteristics of the petal-shaped distribution network and the radial distribution network, the change law of the fault voltage with the movement of the fault position is no longer a simple monotonic relationship, but presents a trend of first increasing and then decreasing with the increase of the fault distance, and has a certain symmetry. This characteristic makes it difficult to realize the acceleration principle of the conventional voltage acceleration factor, which leads to the difficulty of applying the voltage acceleration inverse-time overcurrent protection based on the fault voltage characteristics of the radial active distribution network to the petal-shaped active distribution network.

[0006] Therefore, it is necessary to study a new voltage acceleration inverse-time overcurrent protection method suitable for the petal-shaped active distribution network, so as to adapt to its unique fault characteristics, ensure the coordination of protection, and improve the protection speed. SUMMARY

[0007] The purpose of the present application is to overcome the deficiencies of the prior art, based on the unique fault voltage characteristics of the petal type distribution network, an improved inverse time action characteristic equation is constructed, and a petal type active distribution network inverse time overcurrent protection method based on an improved voltage acceleration factor is proposed, which significantly improves the speed of overcurrent protection under the premise of improving protection coordination.

[0008] The present application solves its technical problems by the following technical solutions:

[0009] A petal type active distribution network inverse time overcurrent protection method based on an improved voltage acceleration factor, characterized in that the method comprises the following steps:

[0010] S1, the starting current Ip, time coefficient TDS and voltage parameter k of each protection are set, and the setting values of the starting current Ip, time coefficient TDS and voltage parameter k that meet the action time coordination relationship of each protection are obtained;

[0011] S2, the starting current Ip and time coefficient TDS setting values obtained by setting are input into each protection device, and the inverse time overcurrent protection action characteristic equation based on the improved voltage acceleration factor is also input;

[0012] S3, when a fault occurs on the main line of the petal type active distribution network, if the direction of the fault current flowing through the protection device is opposite to the preset positive direction of the protection, the protection is immediately locked; if the direction of the fault current flowing through the protection device is the same as the preset positive direction of the protection, and the protection device detects that the fault current flowing through is greater than the starting current setting value, the protection is immediately started and enters the fault identification mode;

[0013] S4, after the protection is started and enters the fault identification mode, the collected fault voltage and current information are substituted into the inverse time overcurrent protection action characteristic equation based on the improved voltage acceleration factor, and the action time of each protection is calculated, and each protection is delayed according to the calculated action time to remove the line fault.

[0014] Moreover, the inverse time overcurrent protection action characteristic equation based on the improved voltage acceleration factor in steps S2 and S4 is based on fully considering the change rule of the voltage of each bus of the petal type distribution network moving with the fault position, and the improved voltage acceleration factor is used to segmentally optimize the inverse time action characteristic equation, and the expression of the action characteristic equation is:

[0015]

[0016] Wherein:

[0017] I thiFor each protection current threshold, since the fault voltage presents the trend of increasing first and then decreasing with the change of fault location, there must be a fault location to make the fault voltage get the maximum value, and the fault current flowing through the protection when the fault occurs at this location is defined as the current threshold;

[0018] k i For each protection voltage parameter, the value thereof is related to the maximum value of the fault voltage at the protection when the petal type distribution network fails.

[0019] Moreover, the setting of the starting current Ip in the step S1 is specifically operated as:

[0020] Since the maximum load currents of each line in the petal type distribution network have symmetry, if the starting current is determined according to the inverse time overcurrent protection starting current setting calculation formula of the radial distribution network as shown in the formula (2), there will be a contradictory relationship between the starting current size of the protection and the protection action time cooperation, thereby leading to the intersection of the protection action curve,

[0021]

[0022] In the 10kV petal type active distribution network topology, the starting current of the protection 9 is determined according to the formula (2) to set the value, the starting currents of the protections 1, 3, 5 and 7 are determined according to the formula (3) to set the value,

[0023]

[0024] ΔI set The starting current setting difference of the upper and lower protections is referenced to the difference between the starting current setting values of each protection when the conventional setting method is adopted, and is taken as 0.1kA here, so that the starting currents of the protections 1, 3, 5, 7 and 9 meet I p1 >I p3 >I p5 >I p7 >I p9 Similarly, the starting current setting values of the protections 2, 4, 6, 8 and 10 are determined according to the same idea.

[0025] Moreover, the setting of the time coefficient TDS and the voltage parameter k in the step S1 is specifically operated as:

[0026] Considering that the inverse time overcurrent protection is the main protection when the fault occurs in the line and is the backup protection when the fault occurs in the lower line, the sum of the main and backup protection action times when the fault occurs in each line is taken as the optimization target to establish the following optimization objective function:

[0027]

[0028] Wherein, T is the sum of the main and backup protection action times under all fault conditions.

[0029] M is the total number of all fault points;

[0030] N is the number of all main protections;

[0031] L is the number of all backup protections;

[0032] t pij and t bik are the action times of the main protection j and the backup protection k respectively when a fault occurs at point i;

[0033] In order to ensure the selectivity of the protection, the following constraint condition is set to ensure the cooperation between the main and backup protections,

[0034] t pij -t bik ≥ Δt (5)

[0035] Wherein: Δt is the action time level difference of the main and backup protections, which is related to the type of the protection device, and herein is taken as 0.3s,

[0036] In addition, the value range of the parameters TDS and k needs to be specified, as shown in the following formula:

[0037] TDS min ≤ TDS i ≤ TDS max (6)

[0038] k min ≤ k i ≤ k max (7)

[0039] Wherein: TDS max and TDS min are the upper limit and the lower limit of the value of the time coefficient TDS respectively, and herein are taken as 1 and 0.001 respectively;

[0040] k max and k min are the upper limit and the lower limit of the value of the voltage parameter k respectively, and herein are taken as 50 and 0 respectively;

[0041] The inverse time overcurrent protection parameter optimization setting model is built with the formula (4) as the objective function and the formulas (5)-(7) as the constraints, the mathematical model is solved based on the MATLAB simulation software, and the optimized protection time coefficient and the voltage parameter setting value are obtained.

[0042] The advantages and beneficial effects of the present application are:

[0043] This invention employs inverse time overcurrent protection based on an improved voltage acceleration factor in a petal-type active power distribution network, significantly enhancing the speed of overcurrent protection while improving protection coordination. Compared with existing technologies, the positive effects of this invention include the following:

[0044] 1. The present invention only needs to use the local current and voltage information of the protection installation location without the need for communication, thus avoiding expensive communication costs and being easy to implement in engineering.

[0045] 2. The present invention is based on the characteristic that the fault voltage first increases and then decreases with the increase of the fault distance. Since the petal-type active distribution network has this voltage fault characteristic when various types of short-circuit faults occur, the inverse time overcurrent protection method proposed in the present invention is not affected by the fault type.

[0046] 3. The protection method proposed in the present invention can not only greatly improve the protection action speed, but also maintain a relatively stable main and backup protection action time difference. Under the premise of ensuring protection selectivity, it will not cause the problem of backup protection action time being too long, thereby ensuring the coordination and cooperation relationship between the upper and lower protection levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the topological structure diagram of the 10kV petal-type active distribution network;

[0048] Figure 2 for Figure 1 The graph of the fault voltage of each bus in the distribution network moving with the fault location is shown;

[0049] Figure 3 This is a schematic diagram of the inverse time action characteristic curve of the petal-type distribution network when the starting current is set using the conventional method;

[0050] Figure 4 Flowchart of the present invention. DETAILED DESCRIPTION

[0051] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0052] The fault voltage characteristics of the petal-shaped distribution network are very different from those of the radial distribution network. The change pattern of the fault voltage with the movement of the fault location is no longer a simple monotonic relationship, but shows a trend of first increasing and then decreasing with the increase of the fault distance, and has a certain symmetry.

[0053] The acceleration principle of the inverse time overcurrent protection based on the conventional voltage acceleration factor: when a line fault occurs, the size of the voltage acceleration factor is directly proportional to the distance between the fault point and the protection, that is, the closer the protection is to the fault point, the smaller the voltage acceleration factor and the shorter the protection action time.

[0054] The unique fault voltage characteristics of the petal-type distribution network make it difficult to establish the acceleration principle of the inverse time overcurrent protection based on the conventional voltage acceleration factor, resulting in the voltage-accelerated inverse time overcurrent protection proposed based on the fault voltage characteristics of the radial active distribution network being difficult to apply to the petal-type active distribution network. It is necessary to propose a new voltage-accelerated inverse time overcurrent protection method based on the unique fault voltage characteristics of the petal-type active distribution network.

[0055] like Figure 4 As shown, the present invention provides a petal-type active distribution network inverse time overcurrent protection method based on an improved voltage acceleration factor, the innovation of which is that the method comprises the following steps:

[0056] S1. Adjust the starting current Ip, time coefficient TDS and voltage parameter k of each protection to obtain the setting values ​​of the starting current Ip, time coefficient TDS and voltage parameter k that meet the coordination relationship of the action time of each protection;

[0057] S2. Enter the starting current Ip and time coefficient TDS setting values ​​obtained by setting into each protection device, and at the same time enter the inverse time overcurrent protection action characteristic equation based on the improved voltage acceleration factor;

[0058] S3. When a fault occurs on the main line of the petal-type active distribution network, if the direction of the fault current flowing through the protection device is opposite to the preset positive direction of the protection, the protection will be immediately locked; if the direction of the fault current flowing through the protection device is the same as the preset positive direction of the protection, and the protection device detects that the fault current flowing is greater than the starting current setting value, the protection will be immediately started and enter the fault identification mode;

[0059] S4. When the protection starts and enters the fault identification mode, the collected fault voltage and current information are substituted into the inverse time overcurrent protection action characteristic equation based on the improved voltage acceleration factor to calculate the action time of each protection. Each protection will delay action according to the calculated action time to clear the line fault.

[0060] The inverse time overcurrent protection action characteristic equation based on the improved voltage acceleration factor in steps S2 and S4 is based on fully considering the variation of the voltage of each busbar of the petal-type distribution network as the fault position moves during a fault, and constructing an improved voltage acceleration factor to perform segmented optimization on the inverse time action characteristic equation. The expression of the action characteristic equation is:

[0061]

[0062] wherein:

[0063] I thi is the current threshold of each protection, since the fault voltage presents the trend of increasing first and then decreasing with the change of fault location, there must be a certain fault location to make the fault voltage obtain the maximum value, when the fault occurs at this position, the fault current flowing through the protection is defined as the current threshold;

[0064] k i is the voltage parameter of each protection, which is related to the maximum value of the fault voltage at the protection of the petal type distribution network when a fault occurs.

[0065] The voltage correction principle of the petal type active distribution network inverse time overcurrent protection based on the improved voltage acceleration factor is clearly defined. Figure 1 The voltage correction principle of the voltage acceleration inverse time overcurrent protection method proposed in the present application is illustrated by taking protection 1 as an example.

[0066] In the Figure 1 , the main trunk line contains 5 lines, which are numbered as L1-L5 in clockwise direction; protection devices are configured at both ends of each line, which are numbered as protection 1-10, for a line of a certain number of protections, the line where the protection device with smaller number is located is defined as the upstream line, and vice versa. In addition, the system contains 5 busbars, which are numbered as A-E in clockwise direction, busbar A is the 10kV busbar at the outlet of the petal network substation, busbars B-E are all switch station busbars, each switch station contains multiple feeder lines. The distributed power supply is connected at busbar E, its control strategy and fault equivalent model remain unchanged with those in document [1] Chen Xiaolong, Yuan Shu, Li Yongli, etc. Single-phase ground fault characteristics analysis of petal type distribution network containing inverter type distributed power supply [J]. Power automation equipment, 2022, 42(04): 129-13. T1 is the main transformer, whose transformation ratio is 110kV / 10kV; T2 is the system grounding transformer; R S is the neutral point grounding resistance of T2, which is taken as 6Ω.

[0067] The fault voltage at protection 1 is U A . According to the improved voltage acceleration inverse time overcurrent protection action characteristic equation shown in equation (1), when the fault current is greater than the current threshold, the form of the voltage acceleration factor is U A , when the fault current is less than the current threshold, the form of the voltage acceleration factor is k1-U A . The fault voltage curve after k1-U A transformation is as shown in the Figure 2The improved voltage acceleration factor can monotonously increase with the increase of fault distance, meets the acceleration principle that the closer to the fault point the protection is, the smaller the acceleration factor is, and effectively solves the problem that the fault voltage characteristics of the petal-type distribution network are contrary to the voltage acceleration principle. Moreover, the value of the voltage parameter is related to the maximum fault voltage at the protection, and the voltage parameter k1 of the protection 1 needs to be not less than 2 times of the maximum fault voltage U 1max .

[0068] The setting of the starting current Ip in step S1 is specifically as follows:

[0069] Since the maximum load currents of the lines in the petal-type distribution network have symmetry, if the starting current is determined according to the inverse time overcurrent protection starting current setting calculation formula of the radial distribution network as shown in formula (2), there will be a contradictory relationship between the starting current size and the protection action time cooperation of the protection, thereby causing the protection action curves to have intersection points. For example, the protection action characteristic curves of the protections 1, 3, 5, 7 and 9 are as shown in the accompanying drawings. Figure 3

[0070]

[0071] In the 10kV petal-type active distribution network topology, the starting current of the protection 9 is determined according to formula (2), and the starting currents of the protections 1, 3, 5 and 7 are determined according to formula (3),

[0072]

[0073] ΔI set is the starting current setting difference between the upper and lower protections, which is determined by reference to the difference between the starting current setting values of the protections when the conventional setting method is adopted, and is taken as 0.1kA in this case, so that the starting currents of the protections 1, 3, 5, 7 and 9 meet I p1 >I p3 >I p5 >I p7 >I p9 By analogy, the starting current setting values of the protections 2, 4, 6, 8 and 10 are determined according to the same idea.

[0074] The setting of the time coefficient TDS and the voltage parameter k in step S1 is specifically as follows:

[0075] Considering that the inverse time overcurrent protection is the main protection when the fault occurs in the line and is the backup protection when the fault occurs in the lower line, the sum of the main and backup protection action times when the fault occurs in each line is taken as the optimization target, and the following optimization objective function is established:

[0076]

[0077] ​Wherein: T is the sum of the action time of the main backup protection under all fault conditions;

[0078] M is the total number of all fault points;

[0079] N is the number of all main protections;

[0080] L is the number of all backup protections;

[0081] t pij and t bik are the action time of the main protection j and the backup protection k respectively when a fault occurs at point i;

[0082] In order to ensure the selectivity of the protection, the following constraint condition is set to ensure the cooperation between the main backup protection,

[0083] t pij -t bik ≥ Δt (5)

[0084] Wherein: Δt is the action time difference of the main backup protection, which is related to the type of protection device, and is taken as 0.3s here,

[0085] In addition, the value range of parameters TDS and k needs to be specified, as shown in the following formula:

[0086] TDS min ≤ TDS i ≤ TDS max (6)

[0087] k min ≤ k i ≤ k max (7)

[0088] Wherein: TDS max and TDS min are the upper and lower limits of the value of the time coefficient TDS respectively, which are taken as 1 and 0.001 respectively here;

[0089] k max and k min are the upper and lower limits of the value of the voltage parameter k respectively, which are taken as 50 and 0 respectively here;

[0090] The inverse time overcurrent protection parameter optimization setting model is built with formula (4) as the objective function and formula (5)-(7) as the constraints, and the mathematical model is solved based on MATLAB simulation software to obtain the optimized protection time coefficient and voltage parameter setting value.

[0091] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A petal type active distribution network inverse time overcurrent protection method based on improved voltage acceleration factor, characterized in that: The method comprises the following steps: S1, setting the starting current Ip, the time coefficient TDS and the voltage parameter k of each protection to obtain the setting values of the starting current Ip, the time coefficient TDS and the voltage parameter k meeting the action time coordination relationship of each protection; S2, recording the setting values of the starting current Ip and the time coefficient TDS obtained in each protection device, and recording the inverse-time overcurrent protection action characteristic equation based on the improved voltage acceleration factor at the same time; S3, when a fault occurs on the main line of the petal-shaped active power distribution network, if the direction of the fault current flowing through the protection device is opposite to the preset positive direction of the protection, the protection is immediately locked; If the direction of the fault current flowing through the protection device is the same as the preset positive direction of the protection, and the protection device detects that the fault current flowing through is greater than the setting value of the starting current, the protection is immediately started and enters the fault identification mode; S4, after the protection is started and enters the fault identification mode, the collected fault voltage and current information are substituted into the inverse-time overcurrent protection action characteristic equation based on the improved voltage acceleration factor to calculate the action time of each protection, and each protection is delayed according to the calculated action time to remove the line fault; The inverse-time overcurrent protection action characteristic equation based on the improved voltage acceleration factor in steps S2 and S4 is based on fully considering the change rule of the voltage of each bus of the petal-shaped distribution network moving with the fault position, and the improved voltage acceleration factor is used to segmentally optimize the inverse-time action characteristic equation, and the expression of the action characteristic equation is as follows: (1) Wherein: I thi For each protected current threshold, since the fault voltage presents a trend of first increasing and then decreasing with the change of fault location, there must be a certain fault location that makes the fault voltage reach the maximum value. When a fault occurs at this location, the fault current flowing through the protection is defined as the current threshold. k For each protected voltage parameter, its value is related to the maximum fault voltage at the protection when the petal-type distribution network fails. The setting of the starting current Ip in step S1 is specifically as follows: Since the maximum load current of each line in the petal-shaped distribution network has symmetry, if the inverse-time overcurrent protection starting current setting calculation formula of the radial distribution network as shown in formula (2) is used to determine, there will be a contradictory relationship between the starting current size of the protection and the protection action time coordination, thereby causing the intersection of the protection action curves, (2) In the 10kV petal-shaped active power distribution network topology, the starting current of protection 9 is determined according to formula (2), and the starting currents of protections 1, 3, 5 and 7 are determined according to formula (3), (3) Delta I set The difference between the starting current settings of the upper and lower levels is set to 0.1 kA, which is the difference between the starting current settings of each protection when the traditional setting method is used, so that the starting currents of protections 1, 3, 5, 7, and 9 meet I p1 I p3 I p5 I p7 I p9 Similarly, the starting current settings of protections 2, 4, 6, 8, and 10 are determined according to the same idea.​​​​ 2. The petal type active distribution network inverse time overcurrent protection method based on improved voltage acceleration factor according to claim 1, characterized in that: The setting of the time coefficient TDS and the voltage parameter k in step S1 is specifically as follows: Considering that the inverse-time overcurrent protection is the main protection when the fault occurs in each line and the backup protection when the fault occurs in the lower line, the sum of the main and backup protection action times when the fault occurs in each line is taken as the optimization target, and the following optimization target function is established: (4) wherein: T is the sum of the action times of the main and backup protection for all fault conditions; M Total number of all fault points; N is the number of primary protection; and L is the number of all backup protection numbers; t pij and t bik are the action times of the main protection i and the back-up protection j when the fault occurs at point k ; In order to ensure the selectivity of the protection, the following constraint condition is set to ensure the coordination between the main and backup protections, (5) Where: Δ t is the main backup protection action time difference, which is related to the type of protection device, and is taken as 0.3 s here, Furthermore, the value range of the parameter TDS and k is specified as follows: (6) (7) Wherein: TDS max And TDS min The upper and lower limits of the value of the time coefficient TDS are 1 and 0.001, respectively. k max and k min are the upper and lower limits of the value of the voltage parameter k respectively, taken as 50, 0, respectively, here. The inverse-time overcurrent protection parameter optimization setting model with formula (4) as the target function and formulas (5)-(7) as the constraints is built, the setting model is solved based on the MATLAB simulation software, and the optimized time coefficient and voltage parameter setting values of each protection are obtained.

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