Distribution line protection setting and decision-making decentralization method based on primary-secondary integration

Abstract

The invention provides a distribution line protection setting and decision decentralization method based on primary and secondary integration, which belongs to the technical field of distribution. A differential power method is adopted on a transmission line, and a differential current method is adopted on a busbar, so that full coverage of distribution line protection can be achieved, and a system-oriented power method boundary condition is given. In the face of an instantaneous fault, a reclosing switch is equipped, and a method of independently setting a reclosing switch circuit breaker criterion after post-acceleration is adopted in the reclosing switch to quickly restore power supply, thereby improving the selectivity of the initial tripping and avoiding too many loads from being mistakenly disconnected during the initial tripping. In the process of the reclosing switch, synchronization check is adopted to reduce the fluctuation of the system after the closing switch, reduce the impact caused by the closing switch, and cause a secondary fault of the false tripping. The invention adopts an independently set reclosing switch circuit breaker criterion, which can quickly restore power supply to a non-fault area and improve the continuity of power supply. This power grid fault diagnosis and processing method based on full-line protection has a certain theoretical basis and practical engineering significance.

Description

Technical Field

[0001] The present invention relates to the field of power distribution technology, and in particular to a distribution line protection setting and decision decentralization method based on primary and secondary fusion. Background Art

[0002] With the large-scale access of distributed power sources to the distribution network, the original single-power radial network structure of the distribution network no longer exists. The distribution network topology has the characteristics of variable topology and multi-power supply. Traditional fault detection and protection actions cannot adapt to the new distribution network topology. Therefore, the study of fast and reliable fault diagnosis and processing methods is of great significance to ensure the safety and economy of the power system.

[0003] The power grid is located at the end of power transmission and directly faces end users. It is an important public infrastructure serving the people's livelihood. It not only needs to be safe, reliable, and self-healing, but also faces the development needs of energy Internet such as large-scale consumption of new energy, high-proportion access of power electronic devices, and bidirectional power flow. Relay protection is an important basis for maintaining the safe and stable operation of the power system. When a system fails, if the relay protection cannot operate correctly and reliably, it will seriously threaten the safety and reliability of the system operation. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a distribution line protection setting and decision decentralization method based on primary and secondary fusion, comprising:

[0005] Step 1: Collect the operating data of each phase of the busbar in the distribution network, and decompose, reduce noise and display fault information characteristics of the voltage and current data collected in real time;

[0006] Step 2: Determine whether a fault occurs at the bus node based on the differential current method, and determine whether a fault occurs in the distribution line based on the power consumption value of the line;

[0007] Step 3: When a fault is detected, the distribution line is protected by isolating the faulty area by switching on and off the upstream and downstream lines and restoring power to the non-faulty areas.

[0008] The step 1 comprises:

[0009] Step 1.1: Decompose and reduce noise of the collected voltage and current data respectively;

[0010] Step 1.2: Perform fault information feature visualization processing on the decomposed signal.

[0011] The step 1.1 comprises:

[0012] Step 1.1.1: Use the improved RNN algorithm to extend the length of the voltage / current data in the time dimension;

[0013] The objective function based on the RNN algorithm is established as follows:

[0014]

[0015] In the formula, d j is the expected output value, y j is the actual output value, and J is the algorithm accuracy evaluation index;

[0016] The constraint conditions are:

[0017]

[0018] In the formula, represents the connection weight value of the i-th data to the j-th data in the (k - 1)-th iteration process, is the actual output value in the (k - 1)-th iteration process, represents the weighted sum value of the k-th input data, and f(·) represents the output function;

[0019] The weight correction amount is:

[0020]

[0021] In the formula, ε represents the weight correction coefficient;

[0022] Step 1.1.2: For the operating data of each phase of the busbar of the distribution network at a certain time period at the line end point, the function expression y(t) of the operating data is fitted. Using the cubic spline interpolation method for a series of maximum points of y(t), the maximum value function y max (t) is fitted. Using the cubic spline interpolation method for a series of minimum points of y(t), the minimum value function y min (t) is determined;

[0023] Step 1.1.3: Adopt the curve interpolation algorithm to perform upper and lower edge line fitting calculations on the data to obtain the average edge line function m1(t):

[0024]

[0025] Step 1.1.4: Perform low-frequency signal removal processing on m1(t):

[0026] d1(t) = y(t) - m1(t) (6)

[0027] In the formula, d1(t) represents the remaining signal;

[0028] Step 1.1.5: Perform conditional judgment on the remaining signal obtained in formula (6) to ensure that there are no other superimposed signals in the decomposed signal; specifically expressed as:

[0029] 1) The mean value of the function formed by the maximum and minimum points of the signal is zero;

[0030] 2) The maximum difference between the number of extreme points and zero points of the signal is 1;

[0031] When the above conditions 1) and 2) are satisfied simultaneously, it indicates that there is no existence of other superimposed signals in the decomposed signal; otherwise, use the remaining signal as the input signal and repeat steps 1.1.2 to 1.1.4;

[0032] Step 1.1.6: When it is determined that there is no existence of other superimposed signals in the decomposed signal, determine the first-order mode component residual r1(t) according to the sifting threshold; use r1(t) as the input for the next iteration and repeat steps 1.1.2 to 1.1.5 to decompose the signal.

[0033] The specific description of step 1.1.6 is as follows:

[0034] Step 1-1: Set the iteration termination condition as the sifting threshold SD:

[0035]

[0036] In the formula, d g (t) represents the remaining signal of the g-th iteration;

[0037] Step 1-2: Calculate the first-iteration mode component residual r1(t):

[0038] r1(t) = y(t) - c1(t) (8)

[0039] In the formula, c1(t) represents the first-iteration mode component;

[0040] Step 1-3: Use r1(t) as the input for the next iteration and repeat steps 1.1.2 to 1.1.5. When the g-th iteration mode component residual r g (t) is a constant or a monotonic function, the iteration process ends;

[0041] Step 1-4: After the iteration ends, the original data y(t) is decomposed into several component and residual components:

[0042]

[0043] In the formula, r n (t) is the residual component after n iterations.

[0044] The said step 1.2 includes:

[0045] Step 1.2.1: Establish an objective function based on entropy reduction:

[0046]

[0047] In the formula, B is a linear transformation composed of the eigenvector of the data and the eigenvalue of the covariance matrix; M is an unknown full-rank matrix; z represents the whitened principal component signal; H is a non-quadratic function; d is zero mean and unit variance; E represents the mathematical expectation; J represents the objective function; L is the separation matrix to be determined;

[0048] Step 1.2.2: Establish the constraint condition E[(L T z) 2 = ||L|| 2 = 1, and solve for the optimal value of the separation matrix E[zh(L T z)] to be determined;

[0049]

[0050] In the formula, h(·) is the derivative of H(·), L0 is the value of L after optimization, and x represents the observation matrix;

[0051] Step 1.2.3: Establish the iterative formula for the separation matrix L:

[0052]

[0053] Step 1.2.4: Standardize the separation matrix L after the (k + 1)-th iteration: k+1 Perform standardization:

[0054] L' k+1 = L k+1 / ||L k+1 || (13)

[0055] In the formula, L' k+1 is the separation matrix after standardization;

[0056] Step 1.2.5: Use the separation matrix obtained by iteration to linearly combine the whitened principal component z to reveal the fault information characteristics:

[0057] V = L T z (14)

[0058] In the formula, V represents the voltage / current vector.

[0059] The above-mentioned Step 2 determines whether a fault occurs at the bus node according to the differential current method, including:

[0060] Step 2-1.1: When a single-line ground fault occurs on the bus, establish the main criterion action equation for bus protection:

[0061]

[0062] Wherein, No. 1, No. 2, and No. 3 are three outlet numbers optionally selected for the downstream bus, and i l1A (t) represents the value of the phase A current at the No. 1 outlet downstream of the bus node; i l2A (t) represents the value of the phase A current at the No. 2 outlet downstream of the bus node; i l3A (t) represents the value of the phase A current at the No. 3 outlet downstream of the bus node; i sA (t) represents the value of the phase A current at the upstream inlet of the bus node; Δi A represents the phase A leakage current at the bus node; i l1B (t) represents the value of the phase B current at the No. 1 outlet downstream of the bus node; i l2B (t) represents the value of the phase B current at the No. 2 outlet downstream of the bus node; i l3B (t) represents the value of the phase B current at the No. 3 outlet downstream of the bus node; i sB (t) represents the value of the phase B current at the upstream inlet of the bus node; Δi B represents the phase B leakage current at the bus node; i l1C (t) represents the value of the phase C current at the No. 1 outlet downstream of the bus node; i l2C (t) represents the value of the phase C current at the No. 2 outlet downstream of the bus node; i l3C (t) represents the value of the phase C current at the No. 3 outlet downstream of the bus node; i sC (t) represents the value of the phase C current at the upstream inlet of the bus node; Δi C represents the phase C leakage current at the bus node; Max{Δi A , Δi B , Δi C} represents the maximum value among Δi A , Δi B , and Δi C ;

[0063] Step 2-1.2: Take the maximum value among Δi A , Δi B , and Δi C as the differential current. When it is detected that the differential current is greater than or equal to the preset circuit setting value Ki set , it indicates that there is a fault at the bus node, otherwise it indicates that the bus node is normal.

[0064] The said Step 2 determines whether a fault occurs at the bus node according to the differential current method, including:

[0065] Step 2-2.1: Solve the fault power value P d when a single-phase grounding fault occurs in the line:

[0066]

[0067] Wherein, is the voltage vector at the grounding resistance; is the voltage vector at a certain upstream node M; is the current vector flowing through a certain upstream node M; Z M is the line impedance value from the fault point to the upstream end segment; is the voltage vector at a certain downstream node N; is the current vector flowing through a certain downstream node N; Z N is the line impedance value from the fault point to the downstream end segment; R f is the grounding resistance, S is the apparent power, is the conjugate complex number of is the conjugate complex number of

[0068] Step 2 - 2.2: Establish the setting value P set constraint conditions;

[0069]

[0070] In the formula, P set is the setting value, is the conjugate complex number of the current flowing through the faulty line during downstream faults, is the conjugate complex number of the current flowing through the faulty line during upstream faults, Re(·) represents taking the real part of the complex number, P set·R is the absolute value of the active power consumed by the downstream line of the faulty line, P set·L is the absolute value of the active power consumed by the upstream line of the faulty line;

[0071] When P d ≥P set it is judged that the distribution line has a fault, otherwise the line is normal.

[0072] The specific description of the said Step 3 is as follows:

[0073] When reclosing the upstream circuit breaker of the faulty line, the downstream circuit breaker on the faulty section remains in the open state, the local power flow of the line is unidirectional, and the faulty section and the downstream are in the open state. The current detection method is adopted upstream of the faulty line, and the reclosing open - circuit criterion is set:

[0074]

[0075] In the formula, K is the braking coefficient;

[0076] When the reclosing time arrives, the upstream circuit breaker will be closed first during reclosing. When the current value satisfies Equation (18), that is, when there is still a fault on the line, the upstream line will be disconnected for the second time to isolate the faulty line, and the circuit breakers at both ends of the faulty line will be controlled to be self-locked to prevent the circuit breakers from being affected by the disturbance current and misclosing. At the same time, the synchro-check control is started. The tie switch is in the normally open state, and the phase angle difference between the voltages on both sides of the tie switch is detected. When the phase angle difference is less than the set threshold, the tie switch is closed, and the load is transferred to the adjacent large power grid to restore power supply;

[0077] When Equation (18) is not satisfied, the synchro-check at the downstream of the line is started. When the phase angle difference between the voltages at both ends of the circuit breaker at the downstream is within the set range, the downstream circuit breaker is closed, and the load restores power supply.

[0078] The beneficial effects of the present invention are as follows:

[0079] In the present invention, the differential power method is adopted for the transmission line, and the differential current method is adopted for the bus, which can achieve full coverage of the distribution line protection, gives the boundary conditions of the power method for the system, and is equipped with reclosing in the face of instantaneous faults. In the reclosing, the method of independently setting the reclosing circuit breaker criterion with post-acceleration is adopted to quickly restore power supply, improve the selectivity of the first trip to avoid excessive loads being mis-powered off during the first trip, and adopt synchro-check during the reclosing process to reduce the system fluctuation after closing and reduce the impact caused by closing, resulting in mis-tripping secondary faults. The present invention adopts an independently set reclosing circuit breaker criterion, which can quickly restore power supply to the non-faulty area and improve the continuity of power supply; this power grid fault diagnosis and processing method based on full-line protection has certain theoretical basis and engineering practical significance. Brief Description of the Drawings

[0080] Figure 1 It is the flowchart of the method for setting and decision-making decentralization of the distribution line protection based on the integration of primary and secondary in the present invention;

[0081] Figure 2 It is the model of a single distribution line in the present invention;

[0082] Figure 3 It is the schematic diagram of the single-phase grounding fault of the distribution line in the present invention;

[0083] Figure 4 It is the topological diagram of the distribution network in the present invention;

[0084] Figure 5 It is the overall structure diagram of the intelligent switch in the present invention. Detailed Embodiments

[0085] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0086] In this embodiment, the intelligent switch is composed of a circuit breaker and an intelligent acquisition terminal, and the aviation plugs at both ends of the communication cable are connected to the corresponding interfaces of the intelligent acquisition terminal and the circuit breaker respectively. Figure 5 As shown, the intelligent data collection terminal is fixed on the tower, and the circuit breaker is connected in series to the distribution line. The contact switch is installed at the connection of two radial power grids and is in a normally open state.

[0087] like Figure 1 As shown, a distribution line protection setting and decision decentralization method based on primary and secondary integration includes:

[0088] Step 1: Collect the operating data of each phase of the busbar in the distribution network, and decompose, reduce noise and display fault information characteristics of the real-time collected voltage and current data; including:

[0089] Step 1.1: Decompose and reduce noise of the collected voltage and current data respectively; including:

[0090] Step 1.1.1: Use the improved RNN algorithm to extend the length of the voltage / current data in the time dimension; use the recurrent neural network RNN ​​(Recurrent Neural Networks, RNN) to fuse with the original signal decomposition and analysis method. Since the traditional signal processing method has edge effects, the present invention uses the RNN fusion algorithm to suppress the edge effects of decomposition signal analysis. By extending the length of the signal in the time dimension, it effectively solves the problem of large errors in high-frequency components and edge data distortion caused by unreasonable upper and lower data edge lines, and effectively suppresses the edge distorted signal from gradually "polluting" to the center as the signal decomposition is iterated.

[0091] The objective function based on the RNN algorithm is established as:

[0092]

[0093] Where, d j is the expected output value, y j is the actual output value, and J is the algorithm accuracy evaluation index;

[0094] The constraints are:

[0095]

[0096] In the formula, represents the connection weight of the i-th data to the j-th data in the k-1-th iteration process, is the actual output value during the k-1th iteration, represents the weighted sum of the k-th input data, and f(·) represents the output function;

[0097] Weight correction Namely:

[0098]

[0099] In the formula, ε represents the weight correction coefficient;

[0100] Step 1.1.2: For the operating data of each phase of the busbar of the distribution network at a certain time period at the line end point, fit the function expression y(t) of the operating data, find all the extreme points of the function, and set its minimum value as y min , and the maximum value as y max . Using cubic spline interpolation method to fit the maximum value function y max (t) from a series of maximum value points of y(t), and using cubic spline interpolation method to determine the minimum value function y min (t) from a series of minimum value points of y(t);

[0101] Step 1.1.3: Adopt the curve interpolation algorithm to perform upper and lower edge line fitting calculation on the data, and obtain the average edge line function m1(t):

[0102]

[0103] Step 1.1.4: Perform low-frequency signal removal processing on m1(t):

[0104] d1(t) = y(t) - m1(t) (6)

[0105] In the formula, d1(t) represents the remaining signal;

[0106] Step 1.1.5: Perform conditional judgment on the remaining signal obtained from formula (6) to ensure that there is no other superimposed signal in the decomposed signal; The specific description is:

[0107] 1) The mean value of the function formed by the maximum and minimum points of the signal is zero;

[0108] 2) The difference between the number of extreme points and zero points of the signal is at most 1;

[0109] To ensure that there is no other superimposed signal in the decomposed signal;

[0110] When both the above conditions 1) and 2) are satisfied, it indicates that there is no other superimposed signal in the decomposed signal; Otherwise, take the remaining signal as the input signal and repeat steps 1.1.2 - 1.1.4;

[0111] Step 1.1.6: When it is judged that there is no other superimposed signal in the decomposed signal, determine the first-order modal component residual r1(t) according to the sifting threshold; Take r1(t) as the input for the next iteration and repeat steps 1.1.2 - 1.1.5 for signal decomposition; The specific description is:

[0112] Step 1-1: Set the iteration termination condition as the screening threshold value SD:

[0113]

[0114] where d g (t) represents the residual signal of the g-th iteration;

[0115] To avoid falling into an iterative dead loop, when the iteration termination condition is that the screening threshold value SD ∈ [0.2, 0.3], the iteration ends;

[0116] Step 1-2: Calculate the residual r1(t) of the first iteration modal component:

[0117] r1(t) = y(t) - c1(t) (8)

[0118] where c1(t) represents the modal component of the first iteration;

[0119] Step 1-3: Take r1(t) as the input of the next iteration and repeat Steps 1.1.2 to 1.1.5. When the residual r g (t) of the g-th modal component is a constant or a monotonic function, the iteration process ends;

[0120] Step 1-4: After the iteration ends, the original data y(t) is decomposed into several component and residual components:

[0121]

[0122] where r n (t) is the residual component after n iterations;

[0123] Step 1.2: Perform fault information feature visualization processing on the decomposed signal; including:

[0124] Step 1.2.1: The entropy reduction fixed-point iteration is fast. By cross-combining the entropy reduction calculation feature and the fixed-point iteration algorithm feature, establish an objective function based on entropy reduction:

[0125]

[0126] where B is a linear transformation composed of the eigenvector of the data and the eigenvalue of the covariance matrix; M is an unknown full-rank matrix; z represents the whitened principal component signal; H is a non-quadratic function; d is a zero-mean unit variance; E represents the mathematical expectation; J represents the objective function; L is the separation matrix to be determined; x represents the observation matrix; signal vector L T The maximum value of the approximate entropy reduction of z and E{H(L TThe extreme points of z)} are equal. Under the boundary condition E[(L T z) 2 = ||L|| 2 = 1 constraint, at the point where the gradient of E[zh(L T z)] + αL = 0 is zero, E{H(L T z)} reaches an extreme value.

[0127] Step 1.2.2: Establish the constraint condition E[(L T z) 2 = ||L|| 2 = 1, and solve for the optimal value of the separation matrix E[zh(L T z)] to be determined;

[0128]

[0129] where h(·) is the derivative of H(·), L0 is the value of L after optimization, and x represents the observation matrix;

[0130] Step 1.2.3: Establish the iterative formula for the separation matrix L:

[0131]

[0132] Step 1.2.4: Standardize the separation matrix L after the (k + 1)-th iteration: k+1 Perform standardization:

[0133] L' k+1 = L k+1 / ||L k+1 || (13)

[0134] where L' k+1 is the separation matrix after standardization;

[0135] Step 1.2.5: Use the iteratively obtained separation matrix to linearly combine the whitened principal component z to manifest the fault information characteristics:

[0136] V = L T z (14)

[0137] where L is the iteratively obtained separation matrix and V represents the voltage / current vector;

[0138] Step 2: Judge whether a fault occurs at the bus node according to the differential current method, and judge whether a fault occurs in the distribution line according to the power consumption value of the line;

[0139] The judgment of whether a fault occurs at the bus node according to the differential current method includes:

[0140] The principle of the current method is based on Kirchhoff's current law. Assume that there is an incoming line port and three outgoing line ports at a certain busbar. The incoming line port is named s, and the three busbar outgoing line ports are named l1, l2, and l3 respectively. When there is no fault on the busbar, the line currents should satisfy the relationship: i l1 (t)+i l2 (t)+i l3 (t)=i s (t).

[0141] Step 2-1.1: When a single-line-to-ground fault occurs at busbar M, establish the action equation of the main criterion for busbar protection:

[0142]

[0143] In the formula, No. 1, No. 2, and No. 3 are three outlet numbers randomly selected from the downstream busbars. i l1A (t) represents the value of the phase-A current at the No. 1 outlet downstream of the busbar node; i l2A (t) represents the value of the phase-A current at the No. 2 outlet downstream of the busbar node; i l3A (t) represents the value of the phase-A current at the No. 3 outlet downstream of the busbar node; i sA (t) represents the value of the phase-A current at the upstream inlet of the busbar node; Δi A represents the phase-A leakage current at the busbar node; i l1B (t) represents the value of the phase-B current at the No. 1 outlet downstream of the busbar node; i l2B (t) represents the value of the phase-B current at the No. 2 outlet downstream of the busbar node; i l3B (t) represents the value of the phase-B current at the No. 3 outlet downstream of the busbar node; i sB (t) represents the value of the phase-B current at the upstream inlet of the busbar node; Δi B represents the phase-B leakage current at the busbar node; i l1C (t) represents the value of the phase-C current at the No. 1 outlet downstream of the busbar node; i l2C (t) represents the value of the phase-C current at the No. 2 outlet downstream of the busbar node; i l3C (t) represents the value of the phase-C current at the No. 3 outlet downstream of the busbar node; i sC (t) represents the value of the phase-C current at the upstream inlet of the busbar node; Δi C represents the phase-C leakage current at the busbar node; Max{Δi A ,Δi B ,Δi C} represents the maximum value among Δi A ,Δi B ,Δi C ; K is the braking coefficient; i set is the braking quantity;

[0144] Under normal operation of the busbar, considering the errors caused by line capacitance current, load current, signal long-distance transmission delay, as well as various errors such as measurement and calculation, there will be a certain deviation in the sum of currents. Δi is a very small number, and the setting value must be set to avoid the maximum unbalance of Δi. The braking current i set is set at 1‰ of the sum of the currents of the lines connected to the busbar.

[0145] Step 2-1.2: Take Δi A 、Δi B 、Δi C The maximum value among the three is taken as the differential current. When the detected differential current is greater than or equal to the preset circuit setting value Ki set , it indicates that there is a fault at the busbar node; otherwise, it indicates that the busbar node is normal.

[0146] Judging whether the distribution line has a fault according to the power consumption value of the line; the key lies in the setting of the threshold value. The set threshold value should not only ensure that the system can reliably and quickly identify the fault when it occurs, but also pay attention to selectivity, and the adjacent line circuit breakers will not malfunction; including:

[0147] The power method is used for the fault diagnosis of the distribution line, and the setting value can accurately and quickly act as long as it meets the boundary conditions. P set·R and P set·L are the power values of the MN section when there are short-circuit faults in the adjacent lines on the right and left sides of the MN section respectively. When a single-phase ground fault occurs in the MN section, the measured fault power value P d can be calculated by the following formula:

[0148]

[0149] S represents the apparent power;

[0150]

[0151] In the formula, P d represents the absolute value of the active power consumed by the line during the fault;

[0152] When a fault occurs in the adjacent line, the short-circuit current will also flow through this section of the transmission line, causing the line power of the unfaulted section of the transmission line to increase. Therefore, when setting the setting value, it is necessary to consider avoiding short-circuit faults in the adjacent lines to ensure the selectivity of the relay protection and prevent the tripping range from expanding.

[0153] Step 2-2.1: Schematic diagram of a single-phase ground fault of the distribution line, as shown in Figure 3 , solve the fault power value P d when a single-phase ground fault occurs in the line:

[0154]

[0155] In the formula, is the voltage vector at the grounding resistance; is the voltage vector at a certain upstream node M; is the current vector flowing through a certain upstream node M; Z M is the line impedance value from the fault point to the upstream end segment; is the voltage vector at a certain downstream node N; is the current vector flowing through a certain downstream node N; Z N is the line impedance value from the fault point to the downstream end segment; R f is the grounding resistance, S is the apparent power, is the conjugate complex number of is the conjugate complex number of

[0156] Step 2-2.2: The present invention gives a setting scheme for the boundary conditions of the power method setting value. For a single distribution line model, as Figure 2 shown, taking a single multi-segment line as an example, the line includes four bus nodes and three transmission lines. Taking the setting value of the power method in the middle segment as an example, the constraint condition of the setting value P set is established;

[0157]

[0158] In the formula, P set is the setting value, is the conjugate complex number of the current flowing through the faulty line during downstream faults, is the conjugate complex number of the current flowing through the faulty line during upstream faults, Re(·) represents taking the real part of the complex number, P set·R is the absolute value of the active power consumed by the downstream line of the faulty line, P set·L is the absolute value of the active power consumed by the upstream line of the faulty line;

[0159] When P d ≥P set , it is judged that the distribution line has a fault, otherwise the line is normal;

[0160] Step 3: When a fault is detected, the faulty area is isolated by turning on and off the upstream and downstream lines, and the non-faulty area is restored to power supply to protect the distribution line; specifically expressed as:

[0161] To reduce the secondary damage caused by reclosing to a permanent fault to the system, the present invention adopts the post-acceleration method.

[0162] When reclosing the upstream circuit breaker of the faulty line, the downstream circuit breaker on the faulty section remains open. The local power flow of the line is unidirectional, and the faulty section and the downstream are in an open state. When using the current detection method upstream of the faulty line, set the reclosing open circuit criterion:

[0163]

[0164] In the formula, K is the braking coefficient;

[0165] When the reclosing time arrives, the upstream circuit breaker will be closed first during reclosing. When the current value satisfies Equation (18), that is, when there is still a fault on the line, the upstream line will be disconnected for the second time to isolate the faulty line, and the circuit breakers at both ends of the faulty line will be controlled to self-lock to prevent the circuit breakers from being affected by the disturbance current and misclosing. At the same time, the synchro-check control is started. The tie switch is in the normally open state, and the phase angle difference between the voltages on both sides of the tie switch is detected. When the phase angle difference is less than the set threshold, the tie switch is closed, and the load is transferred to the adjacent large power grid to restore power supply;

[0166] When the fault has been eliminated before the upstream circuit breaker of the faulty line recloses, when the upstream circuit breaker recloses and the current value does not satisfy Equation (18), the synchro-check at the downstream intelligent switch is started. Since the downstream of the circuit breaker is in an island operation state, directly closing the circuit breaker may cause overcurrent, impact on the system, misoperation of the line circuit breaker, and further risk of system paralysis. When the phase angle difference between the two ends is within an appropriate range, the downstream circuit breaker can be closed to restore power supply to the load.

[0167] Establish a power grid simulation model. The distribution network topology diagram is as Figure 4 shown. The topology structure contains three unidirectional independent distribution networks, which are connected by normally open tie switches as backup power supplies for each other. In the simulation model, the voltage level of the power grid is 10 kV, the system frequency is 50 Hz, the positive sequence and zero sequence resistances of each kilometer of the transmission line are 0.64 Ω and 2 Ω, and the positive sequence and zero sequence reactance values of each kilometer are 0.12 Ω and 0.4 Ω. This system contains 3 substations (E A 、E B and E C ), 34 normally closed switches (B1~B 34 ), 2 normally open tie switches (M1~M2), 4 distributed power sources DG (Distributed Generation) (DG1~DG4). There are 3 independent distribution networks during normal operation separated by 2 tie switches, and the load is represented by line segments with arrows. Simulation analysis is carried out on this power grid model under different fault positions, different transition resistances and source-load fluctuation conditions. The effectiveness of the present invention is verified through faults at different lines, different positions of the same line and different transition resistances, and the rejection of misoperation of the present invention is verified under source-load fluctuations.

[0168] The fault detection experiment was conducted on the whole network topology respectively, and the present invention can work reliably. Taking the ground fault of the line between BUS8 and BUS9 as an example, the fault test of 0.1Ω, 1Ω, 5Ω, 10Ω, 50Ω and 100Ω fault resistance was conducted at 0%, 25%, 50%, 75% and 100% of the line respectively. The system collected the line data information, processed the data, compared it with the set threshold, and judged whether the tripping action was needed. The fault experiment was conducted on the line from BUS8 to BUS9, and the data information of the adjacent lines was collected at the same time. After the information was processed, it was judged whether the adjacent lines would malfunction. The experimental structure is shown in Tables 1 and 2.

[0169] Table 1 BUS8 to BUS9 fault data analysis

[0170]

[0171]

[0172] Table 2 Adjacent line information when BUS8 to BUS9 fails

[0173]

[0174]

[0175] The present invention proposes a reclosing circuit breaker criterion, and sets a circuit breaker criterion separately during reclosing, which can effectively reduce the secondary impact of permanent fault reclosing on the power grid compared with the method of sharing the setting value. The experimental results are shown in Table 3.

[0176] Table 3 Reclosing of permanent faults on the BUS1 to BUS2 line

[0177]

[0178] The method proposed in the present invention for releasing island operation after frequency detection can effectively reduce the fluctuation influence of instantaneous fault reclosing on the system compared with the original method. As shown in Table 4, taking the instantaneous fault reclosing of the BUS2 to BUS3 line as an example, and conducting a source-load fluctuation experiment on the load controlled by DG3 and B21, the method of the present invention did not cause malfunction. Compared with the previous experiments only conducted in steady state and fault state, the power grid in normal operation state is in a state of real-time fluctuation. This experiment can more effectively prove the engineering practicality and reliability of the present invention.

[0179] Table 4 BUS1 to BUS2 line reclosing check synchronization current meter

[0180]

[0181] The present invention realizes the relay protection for the entire line of the node line, i.e., the distribution network. Based on the principle of active power and differential current in the fault additional network, the present invention proposes a hybrid relay protection scheme, and proposes a scheme for the reclosing breaker criterion in the reclosing part, and conducts system simulation verification. The verification results show that:

[0182] 1) The hybrid relay protection scheme can effectively cope with various resistance grounding faults, and can detect any grounding at any position on the line, reflecting the reliability of the present invention.

[0183] 2) The present invention also innovatively conducts verification tests in the distribution network with fluctuating load power supplies respectively. The method of the present invention does not have misoperation, reflecting good robustness.

[0184] 3) When a fault occurs on a certain line, the adjacent lines will not be affected and trip, reflecting the selectivity of the method of the present invention.

[0185] 4) In the face of permanent faults, the scheme of the reclosing breaker criterion of the present invention can quickly disconnect during reclosing, reducing the secondary impact of reclosing on the system, reflecting the sensitivity and quick action of the scheme of the present invention.

[0186] To ensure the reliability of power supply, the distribution network often adopts the power supply mode of hand-in-hand ring network or double-end large power grid power supply. However, in actual protection operation, the double-end large power grid power supply ring network generally operates in an open-loop manner, and the other large power grid power supply is only used to transfer and restore the load when a fault occurs on this line. The simulation of the present invention is built based on the actual operation mode of the distribution network, and the experimental results are more authentic.

Claims

1. A method for relay setting and decision decentralization of distribution lines based on primary-secondary integration, characterized in that, Including: Step 1: Collect the operating data of each phase of the bus in the distribution network, and perform decomposition, noise reduction, and fault information feature visualization processing on the real-time collected voltage and current data; Step 1.1: Perform decomposition and noise reduction processing on the collected voltage and current data respectively; Step 1.2: Perform fault information feature visualization processing on the decomposed signal; Step 1.2.1: Establish an objective function based on entropy reduction: In the formula, B is a linear transformation composed of the eigenvector of the data and the eigenvalue of the covariance matrix; M is an unknown full-rank matrix; z represents the whitened principal component signal; H is a non-quadratic function; d is a zero-mean unit variance; E represents the mathematical expectation; J represents the objective function; L is the separation matrix to be determined; Step 1.2.2: Establish the constraint condition E[(L T z) 2 = ||L|| 2 = 1, and solve for the optimal value of the separation matrix E[zh(L T z)] to be determined; In the formula, h(·) is the derivative of H(·), L0 is the value of L after optimization, and x represents the observation matrix; Step 1.2.3: Establish an iterative formula for the separation matrix L; Step 1.2.4: Normalize the separation matrix L after the (k + 1)-th iteration k+1 as follows: L' k+1 = L k+1 / ||L k+1 || (13) where L' k+1 is the separated matrix after standardization processing; Step 1.2.5: Use the iteratively obtained separation matrix to linearly combine the whitened principal component z to visualize the fault information features: V = L T z (14) In the formula, V represents the voltage / current vector; Step 2: Judge whether a fault occurs at the bus node according to the differential current method, and judge whether a fault occurs in the distribution line according to the power consumption value of the line; The judging whether a fault occurs in the distribution line according to the power consumption value of the line includes: Step 2-2.1: Solve for the fault power value P when a single-phase grounding fault occurs in the line d : Wherein, is the voltage vector at the grounding resistance; is the voltage vector at a certain upstream node M; is the current vector flowing through a certain upstream node M; Z M is the line impedance value from the fault point to the upstream end segment; is the voltage vector at a certain downstream node N; is the current vector flowing through a certain downstream node N; Z N is the line impedance value from the fault point to the downstream end segment; R f is the grounding resistance, S is the apparent power, is 's conjugate complex number, is 's conjugate complex number; Step 2-2.2: Establish the setting value P set 's constraint conditions; Wherein, P set is the setting value, is the conjugate complex of the current flowing through the faulty line during downstream faults, is the conjugate complex of the current flowing through the faulty line during upstream faults, Re(·) represents taking the real part of a complex number, P set·R is the absolute value of the active power consumed by the downstream line of the faulty line, P set·L is the absolute value of the active power consumed by the upstream line of the faulty line; When P d ≥ P set it is determined that there is a fault in the distribution line, otherwise the line is normal; Step 3: When a fault is detected, isolate the fault area by opening and closing the upstream and downstream lines and restore power supply to the non-fault area to protect the distribution line.

2. A method for setting and decision decentralization of distribution line protection based on primary and secondary integration according to claim 1, characterized in that The said Step 1.1 includes: Step 1.1.1: Use the improved RNN algorithm to extend the length of the voltage / current data in the time dimension; The established objective function based on the RNN algorithm is: where d j is the expected output value, y j is the actual output value, and J is the algorithm accuracy evaluation metric; The constraint condition is: In the formula, represents the connection weight of the i-th data to the j-th data in the (k - 1)-th iteration process, is the actual output value in the (k - 1)-th iteration process, represents the weighted sum value of the k-th input data, and f(·) represents the output function; Weight correction amount is as follows: In the formula, ε represents the weight correction coefficient; Step 1.1.2: For the operating data of each phase of the busbar of the distribution network at a certain time period at the line end point, the function expression y(t) of the operating data is fitted. Using the cubic spline interpolation method for a series of maximum points of y(t), the maximum value function y max (t) is fitted. Using the cubic spline interpolation method for a series of minimum points of y(t), the minimum value function y min (t) is determined; Step 1.1.3: Use the curve interpolation algorithm to fit the upper and lower edge lines of the data and obtain the average edge line function m1(t); Step 1.1.4: Perform low-frequency signal removal processing on m1(t); d1(t) = y(t) - m1(t) (6) In the formula, d1(t) represents the remaining signal; Step 1.1.5: Make a conditional judgment on the remaining signal obtained in formula (6) to ensure that there is no other superimposed signal in the decomposed signal; the specific description is: 1) The mean value of the function formed by the maximum and minimum points of the signal is zero; 2) The difference between the number of extreme points and zero points of the signal is at most 1; When the above conditions 1) and 2) are satisfied simultaneously, it means that there is no other superimposed signal in the decomposed signal; otherwise, use the remaining signal as the input signal and repeat Steps 1.1.2 to 1.1.4; Step 1.1.6: When it is judged that there is no other superimposed signal in the decomposed signal, determine the first-order mode component residual r1(t) according to the sifting threshold value; use r1(t) as the input for the next iteration and repeat Steps 1.1.2 to 1.1.5 to perform signal decomposition.

3. A distribution line protection setting and decision decentralization method based on primary and secondary fusion according to claim 2, characterized in that: The said Step 1.1.6 is specifically described as: Step 1-1: Set the iteration termination condition as the sifting threshold value SD; where d g (t) represents the residual signal of the g-th iteration; Step 1-2: Calculate the first iteration mode component residual r1(t): r1(t) = y(t) - c1(t) (8) Wherein, c1(t) represents the first iteration modal component; Steps 1-3: Repeat Steps 1.1.2 to 1.1.5 with r1(t) as the input for the next iteration. The iteration process ends when the g-th modal component residual r g (t) is a constant or a monotonic function. Step 1-4: After the iteration ends, the original data y(t) is decomposed into several components and a residual component: where r n (t) is the residual component after n iterations.

4. A method for relay setting and decision decentralization of a distribution line based on primary and secondary integration according to claim 3, characterized in that, The said Step 2 determines whether a fault occurs at the bus node according to the differential current method, including: Step 2-1.1: When a single-line-to-ground fault occurs on the bus, establish the operating equation of the main criterion of the bus protection: Wherein, No. 1, No. 2, and No. 3 are three optional outlet numbers of the downstream busbar, and i l1A (t) represents the value of the phase A current at the No. 1 outlet downstream of the busbar node; i l2A (t) represents the value of the phase A current at the No. 2 outlet downstream of the busbar node; i l3A (t) represents the value of the phase A current at the No. 3 outlet downstream of the busbar node; i sA (t) represents the value of the phase A current at the upstream inlet of the busbar node; Δi A represents the phase A leakage current at the busbar node; i l1B (t) represents the value of the phase B current at the No. 1 outlet downstream of the busbar node; i l2B (t) represents the value of the phase B current at the No. 2 outlet downstream of the busbar node; i l3B (t) represents the value of the phase B current at the No. 3 outlet downstream of the busbar node; i sB (t) represents the value of the phase B current at the upstream inlet of the busbar node; Δi B represents the phase B leakage current at the busbar node; i l1C (t) represents the value of the phase C current at the No. 1 outlet downstream of the busbar node; i l2C (t) represents the value of the phase C current at the No. 2 outlet downstream of the busbar node; i l3C (t) represents the value of the phase C current at the No. 3 outlet downstream of the busbar node; i sC (t) represents the value of the phase C current at the upstream inlet of the busbar node; Δi C represents the phase C leakage current at the busbar node; Max{Δi A , Δi B , Δi C} represents the maximum value among Δi A , Δi B , and Δi C ; K is the braking coefficient; i set is the braking amount; Step 2-1.2: Obtain Δi A , Δi B , Δi C Take the maximum value among the three as the differential current. When it is detected that the differential current is greater than or equal to the preset circuit setting value Ki set , it indicates that there is a fault at the bus node; otherwise, it indicates that the bus node is normal.

5. A distribution line protection setting and decision decentralization method based on primary and secondary fusion according to claim 4, characterized in that: The said Step 3 is specifically described as: When reclosing the upstream circuit breaker of the faulty line, the downstream circuit breaker on the faulty section remains open, the local power flow of the line is unidirectional, and the faulty section and the downstream are in an open state. At the upstream of the faulty line, the current detection method is adopted to set the reclosing open circuit criterion: Wherein, K is the braking coefficient; When the reclosing time arrives, the upstream circuit breaker will be closed first during reclosing. When the current value satisfies Equation (18), that is, the line still has a fault, the upstream line will be disconnected for the second time to isolate the faulty line, and the circuit breakers at both ends of the faulty line will be locked to prevent the circuit breakers from being misclosed due to the influence of the disturbance current. At the same time, the synchronization detection control is started, the tie switch is in the open state, the voltage phase angle difference between both sides of the tie switch is detected, and when the phase angle difference is less than the set threshold, the tie switch is closed, and the load is transferred to the adjacent large power grid to restore power supply; When Equation (18) is not satisfied, the synchronization detection at the downstream of the line is started, and when the voltage phase angle difference between both ends of the circuit breaker at the downstream is within the set range, the downstream circuit breaker is closed to restore power supply to the load.

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