Power distribution network real-time health state assessment method considering network node and line importance

Abstract

The method comprises the following steps: regarding each node in the power distribution network as a power distribution transformer node, and taking the real-time health index of the power distribution transformer at each node as the health index of the node; regarding a conductor as a power distribution device, and taking the health index of the conductor between nodes as the health index of the power distribution line between nodes; evaluating the node importance in the power distribution network according to an improved electrical LeaderRank algorithm; evaluating the importance of each line in the power distribution network according to an improved line load moment algorithm; and calculating the health index of the power distribution network according to the health index and the importance of each node in the power distribution network and the health index and the importance of each line. The method effectively avoids the selection and quantification of evaluation indexes, and effectively solves the real-time health state evaluation problem of the complex and variable power distribution network by using a small amount of measured data and a simple algorithm.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system risk assessment, in particular to a power distribution network real-time health state assessment method considering network node and line importance. BACKGROUND

[0002] The power distribution network is a key link connecting the end users and the power transmission network, and its healthy and stable operation directly affects the production and life of the general public. Comprehensive mastery of the health state of the power distribution network is not only conducive to timely arrangement of maintenance plans, but also can maximize the protection of people's power quality and power safety. However, the power distribution network is a dynamic system, and its health state is jointly influenced by the network topology structure change and the operation state of the power distribution equipment. In addition, with the access of a large number of distributed photovoltaics, the operation state of the power distribution network becomes more complex. Therefore, how to perform real-time health state assessment on the complex and variable power distribution system is a new problem faced by the development of modern power distribution network.

[0003] Domestic and foreign scholars have done a lot of research on the health state assessment of the power distribution network. The existing research can be divided into two categories: the first category starts from the power distribution equipment or the power distribution network, establishes evaluation indexes and evaluation models to evaluate the health state of a single power distribution equipment or power distribution network, but fails to combine the two; the other category extends the health state assessment of the power distribution network from the power distribution equipment level to the network structure level, respectively selects power distribution equipment monitoring quantities to perform health assessment on the power distribution equipment level, constructs an index system to assess the network structure level, and combines the assessment results of the two to obtain the health state of the power distribution network.

[0004] The above two methods are both through selecting the operation indexes of the equipment or network in the power distribution network, establishing a power distribution network health state assessment index system, and using fuzzy set theory, analytic hierarchy process and the like to assess the health state of the power distribution network. However, this index-based evaluation method ignores the influence of the network topology structure on the operation state, and the operation state of the power distribution network is variable, and the network topology structure is also changing in real time, so it is difficult to assess the real-time health state of the power distribution network by using the index-based evaluation method. SUMMARY

[0005] To solve the above technical problems, the present application provides a power distribution network real-time health state assessment method considering network node and line importance, which can quickly sort the nodes and lines in the network according to their importance by using a simple and effective algorithm, calculate the health degree of the nodes and lines using a small amount of measurement data, and finally calculate the real-time health index of the power distribution network by using the health degree and importance of the nodes and lines in the power distribution network, to assess the real-time health state of the rural power grid. This method effectively avoids the selection and quantification of evaluation indexes, and effectively solves the problem of real-time health state assessment of the complex and variable power distribution network by using a small amount of measurement data and a simple algorithm.

[0006] The technical scheme adopted by the present application is:

[0007] The real-time health state evaluation method of the power distribution network considering the importance of network nodes and lines comprises the following steps:

[0008] Step 1: regarding each node in the power distribution network as a power distribution transformer node, taking the real-time health index of the power distribution transformer at each node as the health index of the node; regarding the conductor as a power distribution device, and taking the health index of the conductor between nodes as the health index of the power distribution line between nodes;

[0009] Step 2: evaluating the importance of nodes in the power distribution network according to the improved electrical LeaderRank algorithm;

[0010] Step 3: evaluating the importance of each line in the power distribution network according to the improved line load moment algorithm;

[0011] Step 4: calculating the health index of the power distribution network according to the health degree and importance of each node in the power distribution network and the health degree and importance of each line.

[0012] In step 1, the health index calculation method of each node power distribution transformer and each line conductor includes the following steps:

[0013] Step 1.1: obtaining the real-time operation parameters of the power distribution transformer and the conductor through a monitoring device, wherein the selected power distribution transformer operation parameters include the dielectric loss factor, the winding temperature, the box temperature, the top oil temperature, the C2H6 content, the CH4 content, the C2H4 content, the H2 content and the C2H2 content; and the selected conductor operation parameter is the conductor temperature.

[0014] Step 1.2: comparing the upper and lower limit values corresponding to each defect state of the power distribution transformer and the conductor with the actual operation parameters to obtain the health index corresponding to each parameter of the power distribution transformer and the conductor, and the health index calculation method is as follows:

[0015]

[0016] In the formula, are the upper limit values of the power distribution transformer and the conductor corresponding to no defect, slight defect, general defect, serious defect and fatal defect, respectively; are the lower limit values of the power distribution transformer and the conductor corresponding to no defect, slight defect, general defect, serious defect and fatal defect, respectively; k is the total number of selected device operation parameters, n is the nth selected device operation parameter, and x n is the actual operation parameter of the device.

[0017] According to the calculation result of step 1.2, when H n is [0, 1), the parameter is at the fatal defect level, and Hn When [1, 2), the parameter is at a serious defect level, H n When [2, 3), the parameter is at a general defect level, H n When [3, 4), the parameter is at a slight defect level, H n When [4, 5], the parameter is defect-free.

[0018] Step 1.3: Calculate the health index of the node and the line, i.e., the health index of the distribution transformer and the conductor, and take the health index corresponding to the parameter with the worst health status as the health index of the node, as follows:

[0019] H = max{H1, H2,..., Hk} n ,...,H k}

[0020] In the formula, H n (n = 1, 2,..., k) respectively represent the health index corresponding to the nth operating parameter of the distribution transformer and the conductor.

[0021] The step 2 includes the following steps:

[0022] Step 2.1: Optimal power flow solving of the distribution network considering photovoltaic output uncertainty;

[0023] Step 2.2: Obtain the power flow direction between nodes of the distribution network according to the optimal power flow of the distribution network calculated in step 2.1, and establish a directed and weightless topology graph M of the distribution network according to the power flow direction;

[0024] Step 2.3: Select a background node, and calculate the directed adjacency matrix G of the distribution network according to the topology graph M, wherein the elements g ij are defined as follows:

[0025]

[0026] Step 2.4: Considering the influence of factors such as distribution network line flow distribution, load importance, and fault shutdown of a node of the distribution network on the node importance evaluation process of the distribution network, improve the LeaderRank algorithm to obtain an electrical LeaderRank algorithm;

[0027] Step 2.5: Assign the initial value of the electrical network node LR to 1, and the initial value of the background node LR to 0, and set the iteration threshold value of the electrical LeaderRank algorithm, and perform iteration calculation;

[0028] Step 2.6: According to the above steps 2.1-2.5, calculate the LR value of each node and sort the importance of each node of the distribution network, and the larger the LR value is, the earlier the node is sorted, and the higher the importance of the node is;

[0029] Step 2.7: Based on the sorting results, assign corresponding weights ω1, ω2, ..., ω to each node. n , where ω1+ω2+...+ω n =1, ω1,ω2,...,ω n These are the weight values ​​corresponding to each node in the distribution network, and n is the sum of the number of all nodes in the distribution network.

[0030] In step 2.1, considering the uncertainty of photovoltaic output, the interval output power model of the photovoltaic system is established as follows:

[0031]

[0032] In the formula, H ING For interval incident irradiance, These are the upper and lower limits of the incident irradiance, respectively; T C For the range of photovoltaic temperatures, These are the upper and lower limits of the photovoltaic temperature, respectively. P P P represents the interval output power of the photovoltaic system. PV H represents the rated capacity of the photovoltaic system. STC ε is the standard value of incident irradiance. T T0 is the power temperature coefficient, and T0 is the rated reference temperature.

[0033] Combining photovoltaic output interval modeling and optimal power flow theory, with the total active power generation cost as the objective function, the optimal interval power flow is solved as follows:

[0034]

[0035]

[0036] In the formula, This represents the lower limit of the power generation cost; min This represents the minimum lower limit for the cost of electricity generation. These represent the lower limit of the power generation cost for each photovoltaic generator; These represent the lower limit values ​​of active power generated by each photovoltaic power generation node;

[0037] F i Let a be the cost of photovoltaic power generation at node i; 2i a 1i a0 and a0 are the coefficients of the photovoltaic generator consumption characteristic curve, respectively, and i is node i; P i Q i Inject active and reactive power into node i, respectively; R ij X ij These are the real and imaginary parts of the transmission line admittance, respectively; U i Let U be the voltage magnitude at node i.j Vj is the voltage amplitude of node j; θij ij is the phase angle difference between the voltage amplitude of node i and node j; Sij G , Sij R , Sij B are active node, reactive node and normal node, respectively;

[0038] P Gi , Q Gi are the active and reactive power output of the photovoltaic at node i.

[0039] is the upper limit value of the generation cost; min is the minimum upper limit value of the generation cost; are the upper limit values of the generation cost corresponding to each photovoltaic generator;

[0040] are the upper limit values of the active power output of each photovoltaic generation node;

[0041] Considering the uncertainty of photovoltaic output, the transmission power between grid nodes also has uncertainty, which can also be calculated by the above interval optimal power flow model to obtain an interval number, which is expressed as follows:

[0042]

[0043] P ij is the expected value of the transmission power between grid nodes; are the upper and lower limit values of the transmission power between grid nodes.

[0044] Take the expected value of the interval number as the transmission power between two nodes, and the expected value is calculated as follows:

[0045]

[0046] If E(P ij )≥0, it indicates that the power flows from node i to node j; if E(P ij )<0, it indicates that the power flows from node j to node i.

[0047] In step 2.4, according to the characteristics of the distribution network and the influence of each factor on the node importance evaluation, the iteration formula of the electrical LeaderRank algorithm is improved as follows:

[0048]

[0049] In the formula, LR i is the calculation result of the electrical LeaderRank algorithm of the i-th node, α (j→i) is the proportion of the LR value of node j allocated to node i; β(g→i) The proportion of the LR value assigned to node i for background node g; LR j Let LR be the LR value of node j. g The initial LR value is set to 1 for each node in the power grid and 0 for the background node during the iteration process.

[0050] Considering the impact of power transmission between grid nodes and the importance of node loads on node importance assessment, the following applies to α. (j→i) The value is corrected, and the corrected α (j→i) The value is calculated as follows:

[0051]

[0052] In the formula, l i-in and l i-out Let A be the in-degree and out-degree of node i, respectively; let A be the set of outgoing nodes of node j; let x be an element in set A; l x-in With l x-out These are the in-degree and out-degree of node x, respectively; S ji S represents the power transmitted from node j to node i. j This represents the total power transmitted from node j to other nodes.

[0053] The definition is as follows:

[0054]

[0055] In the formula, Ω1 refers to the node set that has at least one external link node in addition to the background node; Ω2 refers to the node set that has only the background node as the only external link node; and n is the total number of nodes.

[0056] Considering the importance of node loads and the potential power loss after a node is attacked, for β (g→i) The value is corrected, and the corrected β (g→i) The value is calculated as follows:

[0057]

[0058] In the formula, B is the set of all nodes in the distribution network except for the background node, y is an element in the set B, and Q is... y Q represents the potential load loss that may occur if node y is attacked. i Q represents the potential power loss that node i might suffer after being attacked. i The calculation formula is as follows:

[0059]

[0060] In the formula, The sum of the number of outgoing links of node i, Q ij The sum of the power transmitted to all outgoing links of node i when it is in normal operation, t is the downtime of node i.

[0061] The importance LR of the jth line in the distribution network in step 3 j The calculation formula is as follows:

[0062]

[0063] In the formula, The load moment normalized value of the jth line in the distribution network, The power loss normalized value after the jth line fails, The LR value normalized value of the downstream node of the line; λ M , λ Q , λ L The weights corresponding to the load moment, power loss, and LR value, respectively.

[0064] The load moment M of the jth line in the distribution network j The calculation method is as follows:

[0065] M j = M cj × M dj

[0066] In the formula, M cj is the power transmission amount when the jth line is in normal operation, M dj is the length of the jth line.

[0067] The power loss Q after the jth line fails j The calculation method is as follows:

[0068] Q j = M cj × t j

[0069] In the formula, t j is the downtime of the jth line.

[0070] According to the sorting result, the corresponding weights ω1, ω2,..., ω m are assigned to each line, such that ω1+ω2+...+ω m =1, and m is the sum of the number of all lines in the distribution network.

[0071] The above physical quantity normalization methods all use the Min-Max normalization method, and the normalization formula is as follows:

[0072]

[0073] In the formula, Xnorm is the normalized parameter value, X max , X min are the maximum and minimum values of the original parameter, respectively. X is the parameter that needs to be normalized.

[0074] In step 4, the power distribution network health index HI calculation method is as follows:

[0075]

[0076] In the formula, HI i is the health index of the i th node, HI j is the health index of the j th line, LR i is the importance of the i th node, LR j is the importance of the j th line, ω n , ω m are the comprehensive weights of the nodes and lines in the power distribution network, n is the total number of nodes, and m is the total number of lines, wherein i ∈ (1 ~ n), j ∈ (1 ~ m).

[0077] The power distribution network real-time health state evaluation method considering the importance of network nodes and lines has the following beneficial effects:

[0078] Each node in the power distribution network is regarded as a power distribution transformer node, and the real-time health index of the power distribution transformer at each node is taken as the health index of the node. The conductor is regarded as a power distribution device, and the health index of the conductor between nodes is taken as the health index of the power distribution line between nodes. The importance of the nodes in the power distribution network is evaluated according to the improved electrical LeaderRank algorithm. The importance of each line in the power distribution network is evaluated according to the improved line load moment algorithm. The health index of the power distribution network is calculated according to the health degree and importance of each node in the power distribution network and the health degree and importance of each line. This method effectively avoids the selection and quantification of evaluation indexes, and effectively solves the problem of real-time health state evaluation of complex and variable power distribution networks by using a small amount of measurement data and a simple algorithm. BRIEF DESCRIPTION OF DRAWINGS

[0079] Figure 1 is the flowchart of the evaluation method of the application.

[0080] Figure 2 is the flowchart of the evaluation of the importance of the nodes in the power distribution network by the improved electrical LeaderRank algorithm.

[0081] Figure 3 is the flowchart of the evaluation of the importance of the lines in the power distribution network by the improved line load moment algorithm.

[0082] Figure 4 is the network topology diagram of a certain 10kV power distribution network.

[0083] Figure 5 This is a schematic diagram showing the calculation results of the LR values ​​and health index of each node in a 10kV power distribution system in a certain area.

[0084] Figure 6 This is a schematic diagram showing the calculation results of the LR values ​​and health index of various lines in a 10kV power distribution system in a certain area.

[0085] Figure 7 This is a graph showing the results of the power distribution system health index calculation. Detailed Implementation

[0086] A real-time health status assessment method for distribution networks considering the importance of network nodes and lines is proposed. This method not only takes into account the electrical characteristics of grid nodes but also the topology of the distribution network, thus improving the accuracy of distribution network health status assessment. Figure 1 As shown, the method includes the following steps:

[0087] Step 101. Treat each node in the distribution network as a distribution transformer node, and use the real-time health index of the distribution transformer at each node as the health index of that node.

[0088] Step 102. Treat the conductors as power distribution equipment, and use the health index of the conductors between nodes as the health index of the power distribution lines between nodes;

[0089] Step 103. Evaluate the importance of nodes in the distribution network according to the improved Electrical LeaderRank algorithm;

[0090] Step 104. Evaluate the importance of each line in the distribution network based on the improved line load moment algorithm;

[0091] Step 105. Calculate the health index of the distribution network based on the health and importance of each node and each line in the distribution network.

[0092] Specifically, step 101 includes:

[0093] Step a: Obtain the electrical and non-electrical parameters of the distribution transformer during real-time operation using a detection device;

[0094] Step b: Compare the upper and lower limits corresponding to each defect state of the distribution transformer with the actual operating parameters to obtain the health index corresponding to each parameter of the distribution transformer. The calculation method of the health index is as follows:

[0095]

[0096] In the formula, These represent the upper and lower limits for no defects, minor defects, general defects, serious defects, and fatal defects, respectively, for distribution transformers and conductors.n The actual operation parameter of the device.

[0097] Step c: According to the calculation result of step b, H n is [0, 1), the parameter is at a fatal defect level, H n is [1, 2), the parameter is at a serious defect level, H n is [2, 3), the parameter is at a general defect level, H n is [3, 4), the parameter is at a slight defect level, H n is [4, 5], the parameter is defect-free.

[0098] Step d: Calculate the health index of the node, that is, the health index of the distribution transformer, and take the health index corresponding to the parameter with the worst health status as the health index of the node, as follows:

[0099] H = max{H1, H2,..., H n ,...,H k}

[0100] In the formula, H n (n = 1, 2,..., k) represents the health index corresponding to the nth operation parameter of the distribution transformer.

[0101] Further, the step 102, the wire health index calculation method is the same as the calculation method of the distribution transformer health index.

[0102] Specifically, the step 103 comprises:

[0103] Step a: Optimal power flow solution of the distribution network considering photovoltaic output uncertainty;

[0104] Step b: According to the optimal power flow of the distribution network calculated in step a, the power flow between the nodes of the distribution network is obtained, and a directed and weightless topology graph M of the distribution network is established according to the power flow;

[0105] Step c: Select a background node, and calculate the directed adjacency matrix G of the distribution network according to the topology graph M. The elements g ij In the matrix G are defined as follows:

[0106]

[0107] Step d: Considering the influence of distribution network line flow distribution, load importance, and fault shutdown of a node of the distribution network on the evaluation process of the importance of the distribution network node, the LeaderRank algorithm is improved to obtain an electrical LeaderRank algorithm;

[0108] Step e: set the initial value of the electrical grid node LR as 1, the initial value of the background node LR as 0, and set the iteration threshold of the electrical LeaderRank algorithm, and perform iteration calculation;

[0109] Step f: according to the above steps, the LR value of each node is calculated, and the importance of each node of the power distribution network is sorted, the larger the LR value is, the higher the node ranking is, and the higher the node importance is;

[0110] Step g: according to the sorting result, the corresponding weight ω1, ω2,..., ω n is given to each node, ω1+ ω2+...+ ω n =1, n is the sum of all node numbers in the power distribution network.

[0111] Further, the step a comprises:

[0112] Considering the uncertainty of photovoltaic output, the interval output power model of the photovoltaic system is established as follows:

[0113]

[0114] In the formula, P P is the interval output power of the photovoltaic system, P PV is the rated capacity of the photovoltaic system, H ING is the interval incident irradiance, H STC is the standard value of incident irradiance, ε T is the power temperature coefficient, T0 is the rated reference temperature, T C is the interval photovoltaic temperature, X + , X - are the upper and lower limit values of each parameter respectively.

[0115] Combined with the interval modeling of photovoltaic output and the optimal power flow theory, the total active power generation cost is taken as the objective function, and the optimal interval power flow is solved as follows:

[0116]

[0117]

[0118] In the formula, F i is the photovoltaic power generation cost at node i, P i , Q i are the active and reactive power injected into node i respectively, R ij , X ij are the real part and imaginary part of the admittance of the power transmission line respectively, U i is the voltage amplitude of node i, θ ij is the voltage amplitude phase angle difference between node i and node j, S G , S R , SB P and Q are active and reactive power of the photovoltaic output at node i, respectively. Gi P and Q are active and reactive power of the photovoltaic output at node i, respectively. Gi P and Q are active and reactive power of the photovoltaic output at node i, respectively.

[0119] Considering the uncertainty of photovoltaic output, the transmission power between grid nodes also has uncertainty, which can also be calculated by the above interval optimal power flow model to obtain an interval number, as shown in the following formula:

[0120]

[0121] Taking the expectation value of the interval number as the transmission power between two nodes, the expectation value is calculated as follows:

[0122]

[0123] If E(P ij )≥0, it indicates that the power flows from node i to node j; if E(P ij )<0, it indicates that the power flows from node j to node i.

[0124] Further, the step d comprises:

[0125] According to the characteristics of the distribution network and the influence of various factors on the node importance evaluation, the iteration formula of the electrical LeaderRank algorithm is improved as follows:

[0126]

[0127] In the formula, LR i is the calculation result of the electrical LeaderRank algorithm of the i-th node, α (j→i) is the proportion of the LR value of node j allocated to node i, and β (g→i) is the proportion of the LR value of the background node g allocated to node i; LR j is the LR value of node j, and LR g is the LR value of the background node; in the iteration process, the initial LR value of each node in the grid is set to 1, and the background node is set to 0.

[0128] Considering the influence of power transmission between grid nodes and the importance of node load on node importance evaluation, the value of α (j→i) is modified, and the calculation method of the modified α (j→i) is as follows:

[0129]

[0130] In the formula, l i-in and l i-outrespectively, A is the set of out-link nodes of node j, x is an element in set A, l x-in respectively, A is the set of out-link nodes of node j, x is an element in set A, l x-out respectively, A is the set of out-link nodes of node j, x is an element in set A, l ji is the power transmitted from node j to node i, S j is the total power transmitted from node j to other nodes. is defined as follows:

[0131]

[0132] where Ω1 is the set of nodes with at least one out-link node except the background node, Ω2 is the set of nodes with the background node as the only out-link node, and n is the total number of nodes.

[0133] The node load importance and the power loss caused by the attack on a certain node are considered to modify β (g→i) The modified β (g→i) is calculated as follows:

[0134]

[0135] where B is the set of all nodes in the distribution network except the background node, y is an element in set B, Q i is the power loss caused by the attack on node i, Q i is calculated as follows:

[0136]

[0137] where is the sum of the out-link nodes of node i, Q ij is the sum of the power transmitted to all out-link lines when node i is normally running, and t is the downtime of node i.

[0138] Specifically, the step 104 comprises:

[0139] The importance LR j of the jth line in the distribution network is calculated as follows:

[0140]

[0141] where is the load moment normalized value of the jth line in the distribution network, is the power loss normalized value of the jth line after failure, is the normalized value of the LR value of the downstream node of the line; λ M , λ Q , λ LThe weight corresponding to the load moment, the power loss amount, and the LR value, respectively.

[0142] Load moment M of the jth line in the distribution network j The calculation method is as follows:

[0143] M j = M cj * M dj

[0144] In the formula, M cj is the power transmission amount when the jth line is normally operated, and M dj is the length of the jth line.

[0145] Power loss Q of the jth line after the fault j The calculation method is as follows:

[0146] Q j = M cj * t j

[0147] In the formula, t j is the outage time of the jth line.

[0148] According to the sorting result, the corresponding weights ω1, ω2,..., ω m are given to each line, and ω1+ω2+...+ω m = 1, and m is the sum of the number of all lines in the distribution network.

[0149] The above physical quantity normalization methods all adopt the Min-Max normalization method, and the normalization formula is as follows:

[0150]

[0151] In the formula, X norm is the normalized parameter value, X max , and X min are the maximum value and the minimum value of the original parameter, respectively.

[0152] Specifically, the step 105 comprises:

[0153] The calculation method of the distribution network health index HI is as follows:

[0154]

[0155] In the formula, HI i is the health index of the ith node, HI j is the health index of the jth line, LR i is the importance of the ith node, LR j is the importance of the jth line, ω n , and ωm are the comprehensive weights of nodes and lines in the power distribution network respectively, n is the total number of nodes, m is the total number of lines, wherein, i∈(1~n), j∈(1~m).

[0156] In the specific embodiments of the present application, a 10kV power distribution system in a certain place is taken as an example for verification, the network topology diagram of the power distribution system is as shown in Figure 4 The region mainly uses electricity for residents, agriculture and industry and commerce, the importance of the load of each node is as shown in Figure 4 The system has 33 conventional nodes, 32 branches, the total load is 9.9MW, contains 33 distribution transformers, and the network is connected with distributed photovoltaic power generation at 5 nodes of nodes 12, 16, 22, 24 and 31, wherein, the distributed photovoltaic power generation penetration rate is 8%.

[0157] In the health index calculation process, the electrical parameters and non-electrical parameters of the distribution transformer are obtained through the monitoring device, and the health index thereof is calculated through the distribution transformer health index calculation method, so as to replace the node health index; similarly, the health index of the conductor between nodes is calculated by the same method, which is used as the health index of each branch. Further, the node importance in the power distribution network is evaluated by using the improved electrical LeaderRank algorithm, and the line importance LR value is obtained by using the improved line load matrix algorithm, and the line importance is evaluated. The LR value and health index calculation results of each node of the system are as shown in Figure 5 The LR value and health index calculation results of each line segment of the system are as shown in Figure 6 The health index of each part of the power distribution system is as shown in Figure 7 .

[0158] From the calculation results, it can be seen that:

[0159] As shown in the node LR value curve Figure 5 , combined with the network topology diagram, it can be seen that in the network, the greater the load transmission of the node, the more branches connected to the node, the greater the node LR value; on each branch, the closer to the branch head, the greater the node LR value, along the branch to the branch end, the node LR value presents a decreasing trend, and the branch end node has the smallest LR value on the branch; the addition of distributed photovoltaic at a certain node changes the line flow, and under the decreasing trend of the LR value of the whole branch, the LR value of the node with distributed photovoltaic decreases to a smaller extent. In addition, node 1, node 2 and node 3 are the top three nodes, and these three nodes are also the three starting nodes of the power distribution system, and once they are out of operation due to failure, the influence on the whole power distribution system is great. Therefore, the improved electrical LeaderRank algorithm has high reliability in the evaluation of node importance, and conforms to the actual power production.

[0160] AsFigure 6 The line load moment (LR) curves shown, combined with the network topology diagram, indicate that the larger the load transmission volume and the closer the line is to the power source, the larger the LR value. When a distributed power source is added to a node, the LR value is also affected by the change in line power flow. Lines 1 and 2 have the largest LR values; these two lines are also the two starting lines of the distribution network, and their stable operation ensures the power supply of the entire system. Therefore, the improved line load moment algorithm has high reliability in assessing line importance and is consistent with actual power production practices.

[0161] Depend on Figure 7 It can be seen that the health index of distribution nodes in this distribution network is 2.8873, and the health index of distribution lines is 2.6143. However, the distribution network health index calculated by the method in this paper is 2.2663, which is lower than the average health index of nodes and lines. This shows that the importance of nodes and lines in the distribution network has a significant impact on the evaluation of the distribution network's health status. In this distribution network, there are certain defects in the network topology, and the health status of some important nodes and lines is poor, requiring strengthened inspection and maintenance of important nodes and lines in this distribution network.

[0162] The penetration rate of distributed photovoltaic power generation was increased by 13.3%. Following the above process, the health index of the distribution system was calculated, resulting in a health index of 2.4612. This indicates that the distribution network is still in a state of general defects, but the health index has increased, suggesting an improvement in its health status. In other words, appropriately increasing the penetration rate of distributed power sources will improve the health status of the distribution network. This conclusion is consistent with relevant literature and further verifies the effectiveness of the method of this invention.

Claims

1. A method for real-time health status assessment of distribution networks taking into account the importance of network nodes and lines, characterized in that... Includes the following steps: Step 1: Treat each node in the distribution network as a distribution transformer node, and use the real-time health index of the distribution transformer at each node as the health index of that node. Treating conductors as power distribution equipment, the health index of conductors between nodes is used as the health index of power distribution lines between nodes; Step 2: Evaluate the importance of nodes in the distribution network based on the improved Electrical LeaderRank algorithm; Step 3: Evaluate the importance of each line in the distribution network based on the improved line load moment algorithm; Step 4: Calculate the health index of the distribution network based on the health index and importance of each node and each line in the distribution network; In step 2, based on the characteristics of the distribution network and the impact of various factors on node importance assessment, the iterative formula of the electrical LeaderRank algorithm is improved as follows: ； In the formula, The result of the Electric LeaderRank algorithm is given for the i-th node. The proportion of the LR value assigned to node i for node j; The proportion of the LR value assigned to node i for background node g; Let LR be the value of node j. The LR value for the background node; During the iteration process, the initial LR value of each node in the power grid is set to 1, and the background node is set to 0; Considering the impact of power transmission between grid nodes and the importance of node loads on node importance assessment, The value is corrected, and the corrected value is... The value is calculated as follows: ； In the formula, and Let i be the in-degree and out-degree of node i, respectively. A Let x be the set of outgoing nodes of node j; let x be... A An element in a set; and Let x be the in-degree and out-degree of node x, respectively. The power transmitted from node j to node i; This represents the total power transmitted by node j to other nodes. The definition is as follows: ； In the formula, A node set that has at least one external link node in addition to the background node; This refers to a set of nodes where only background nodes are used as unique external links, where n is the total number of nodes. Considering the importance of node loads and the potential power loss after a node is attacked, for The value is corrected, and the corrected value is... The value is calculated as follows: ； In the formula, B Let y be the set of all nodes in the distribution network excluding the background nodes. B An element in a set The potential load loss that may occur after node y is attacked; This represents the potential power loss that node i might experience after being attacked. The calculation formula is as follows: ； In the formula, Let be the sum of the number of outgoing nodes of node i. Let t be the sum of the power transmitted by node i to all outgoing links when node i is running normally, and t be the downtime of node i. In step 3, the importance LR of the j-th line in the distribution network is... j The calculation formula is as follows: ； In the formula, Let j be the normalized value of the load moment of the j-th line in the distribution network. Let be the normalized value of the power loss after a fault on the j-th line. This is the normalized LR value of the downstream node of the line; , , These are the weights corresponding to load moment, power loss, and LR value, respectively. The load moment of the j-th line in the distribution network The calculation method is as follows: ； In the formula, Let j be the power transmission amount when the j-th line is operating normally. Let j be the length of the j-th line; Power loss after a fault in line j The calculation method is as follows: ； In the formula, The shutdown time for the j-th line; Each line is assigned a corresponding weight based on the ranking results. ,make , where m is the sum of the number of all lines in the distribution network.

2. The method for real-time health status assessment of distribution networks considering the importance of network nodes and lines according to claim 1, characterized in that: In step 1, the calculation method for the health index of each node distribution transformer and the health index of each line conductor includes the following steps: Step 1.1: Obtain real-time operating parameters of the distribution transformer and conductors through monitoring devices. The operating parameters selected for the distribution transformer include dielectric loss factor, winding temperature, tank temperature, top oil temperature, C2H6 content, CH4 content, C2H4 content, H2 content, and C2H2 content. The operating parameter selected for the conductors is conductor temperature. Step 1.2: Compare the upper and lower limits corresponding to each defect state of the distribution transformer and conductors with the actual operating parameters to obtain the health index corresponding to each parameter of the distribution transformer and conductors. The calculation method of the health index is as follows: ， ； In the formula, These are the upper limits for defects of no defects, minor defects, general defects, serious defects, and fatal defects, respectively, for distribution transformers and conductors. These are the lower limits for no defects, minor defects, general defects, serious defects, and fatal defects corresponding to distribution transformers and conductors, respectively. The total number of selected equipment operating parameters. For the nth operating parameter of the selected device, These are the actual operating parameters of the equipment; The calculation results from step 1.2 show that, When the parameter is [0,1), it is at a critical defect level. When the parameter is [1,2), it is at a severe defect level. When the parameter is [2,3), it is at a general defect level. When the parameter is [3,4), the parameter is at a slight defect level. The parameters are defect-free when the range is [4,5]. Step 1.3: Calculate the health index of the distribution transformer and conductors. The health index corresponding to the parameter with the worst health status is taken as the health index of that node, as shown in the following formula: ； In the formula, These represent the health indices corresponding to the nth operating parameter of the distribution transformer and the conductor, respectively.

3. The method for real-time health status assessment of distribution networks considering the importance of network nodes and lines according to claim 1, characterized in that: Step 2 includes the following steps: Step 2.1: Solving for the optimal power flow of the distribution network considering the uncertainty of photovoltaic output; Step 2.2: Based on the optimal power flow of the distribution network calculated in Step 2.1, obtain the power flow direction between nodes of the distribution network, and establish the directed unweighted topology M of the distribution network accordingly; Step 2.3: Select the background node and calculate the directed adjacency matrix of the power distribution network based on the topology graph M. G , where the matrix G elements in g ij The definition is as follows: ； Step 2.4: Considering the impact of factors such as power flow distribution of distribution network lines, load importance, and outage due to faults at a certain node in the distribution network on the evaluation process of the importance of distribution network nodes, the LeaderRank algorithm is improved to obtain the Electrical LeaderRank algorithm; Step 2.5: Assign an initial LR value of 1 to the power grid node and an initial LR value of 0 to the background node. At the same time, set the iteration threshold for the Electric LeaderRank algorithm and perform iterative calculations. Step 2.6: Calculate the LR value of each node based on Steps 2.1-2.5 above and sort the importance of each node in the distribution network. The larger the LR value, the higher the node is ranked and the higher its importance. Step 2.7: Assign corresponding weights to each node based on the sorting results. ,in , These are the weight values ​​corresponding to each node in the distribution network, and n is the sum of the number of all nodes in the distribution network.

4. The method for real-time health status assessment of distribution networks considering the importance of network nodes and lines according to claim 3, characterized in that: In step 2.1, considering the uncertainty of photovoltaic output, the interval output power model of the photovoltaic system is established as follows: ； In the formula, For interval incident irradiance, These are the upper and lower limits of the incident irradiance, respectively; For the range of photovoltaic temperatures, These are the upper and lower limits of photovoltaic temperature, respectively. The interval output power of the photovoltaic system, The rated capacity of the photovoltaic system, The standard value of incident irradiance, For power temperature coefficient, This is the rated reference temperature; Combining photovoltaic output interval modeling and optimal power flow theory, with the total active power generation cost as the objective function, the optimal interval power flow is solved as follows: ； In the formula, This represents the lower limit of the power generation cost. This represents the minimum lower limit for the cost of electricity generation. , These represent the lower limit of the power generation cost for each photovoltaic generator; , These represent the lower limit values ​​of active power generated by each photovoltaic power generation node; Let be the cost of photovoltaic power generation at node i; , , These are the coefficients of the photovoltaic generator consumption characteristic curve. Let i be the node; , Inject active and reactive power into node i respectively; These are the real and imaginary parts of the transmission line admittance, respectively. Let be the voltage magnitude at node i. Let be the voltage amplitude at node j; Let be the phase angle difference between the voltage magnitudes of node i and node j; These are active nodes, reactive nodes, and ordinary nodes, respectively. These represent the active and reactive power outputs of the photovoltaic system at node i, respectively. This represents the upper limit of the cost of electricity generation. This represents the minimum upper limit for the cost of electricity generation. , , These represent the upper limit of the power generation cost for each photovoltaic generator; , , These represent the upper limit of active power generated by each photovoltaic power generation node; Considering the uncertainty of photovoltaic output, the power transmission between grid nodes is also uncertain. This uncertainty can also be calculated using the aforementioned interval optimal power flow model, yielding an interval number, as follows: ； This represents the expected power transmission between grid nodes; , These are the upper and lower limits of the transmission power between power grid nodes; The expected value of this interval number is taken as the transmission power between the two nodes, and its expected value is calculated as follows: ； like If , it means that power flows from node i to node j; if If , it means that power flows from node j to node i.

5. The method for real-time health status assessment of distribution networks considering the importance of network nodes and lines according to claim 1, characterized in that: In step 3, the physical quantity normalization method adopts the Min-Max normalization method, and the normalization formula is as follows: ； In the formula, These are the normalized parameter values. These are the maximum and minimum values ​​of the original parameters, respectively. These are the parameters that need to be normalized.

6. The method for real-time health status assessment of distribution networks considering the importance of network nodes and lines according to claim 1, characterized in that: In step 4, the distribution network health index HI is calculated as follows: ； In the formula, Let i be the health index of the i-th node. The health index of the j-th line. Let i be the importance of the i-th node. Let the importance of the j-th route be... These represent the combined weights of nodes and lines in the distribution network. n The total number of nodes. m The total number of lines, of which, .

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