Method and system for evaluating multi-voltage-level loop closing operation of urban power grid

Abstract

The invention discloses a method and a system for evaluating multi-voltage-level loop closing operation of an urban power grid, and belongs to the technical field of online safety and stability calculation and analysis of a power system. The method provided by the invention comprises the following steps: calculating equivalent impedance of a power transmitting end and a power receiving end at two sides of a loop point to be closed in a plurality of voltage levels of an urban power grid, and carrying out ride-through load flow calculation to obtain a bus voltage difference; selecting a minimum range interval of a bus voltage difference to determine an online or future state plan load value at the current moment, and determining an alarm threshold value of a to-be-closed loop point in a plurality of voltage levels of the urban power grid; and comparing the loop closing current calculation value with the alarm threshold value of the to-be-closed loop point, and evaluating the loop closing operation of the to-be-closed loop point in the plurality of voltage levels of the urban power grid based on the comparison result. According to the implementation of the method, the loop closing operation is evaluated, and then the loop closing operation is carried out according to the evaluation result, so that protection action tripping and urban power grid equipment damage caused by overlarge loop closing current are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of online safety and stability calculation and analysis of power systems, and more specifically, to a method and system for evaluating multi-voltage level closed-loop operation of urban power grids. Background Art

[0002] When adjusting the operation mode and transferring the load, the urban power grid line usually adopts the closing and opening mode to avoid short-term power outages. When closing the ring, the closing current is too large, which will cause the protection action to trip, resulting in the loss of pressure in the urban power grid line and damage to the equipment. With the rapid expansion of urban scale, the scale of urban power grids is also showing a trend of rapid growth. At the same time, with the adjustment of my country's urban development plan, the original urban peripheral areas will become new load centers, and the power demand and power quality requirements will also increase explosively, which is a huge challenge for the power grid development planning and power grid operation mode arrangement carried out according to the normal urban power grid load growth model. Its prominent manifestation is that during the adjustment period of urban power grid planning and construction, the closing current of multi-voltage levels from 110kV to 10kV will have problems of excessive current and closing operation failure, which requires online analysis and calculation.

[0003] The closed-loop current of urban power grids at different voltage levels from 110kV to 10kV is related to the load flow and equivalent impedance of the loop to be closed. According to different calculation methods, the calculation of closed-loop current can usually be divided into online and offline analysis and calculation. Offline calculation is generally used for planning and design. The online calculation method can select the real-time cross-section load of the power grid, and the calculation results are more meaningful for the current safety and stability analysis and fault abnormality handling of the power grid. However, whether it is online or offline, the existing calculation methods require large-scale and fine simulation modeling of the closed-loop loop. The higher the voltage level of the closed-loop current, the higher the simulation analysis model and the amount of original line data required to be constructed. For urban power grids, some overhead and cable lines have various line types, mixed line diameters, and different lengths. The line parameters are also difficult to obtain through theoretical calculations. In addition, the line changes and modifications are frequent, and the real-time update of model parameters has a high work pressure and work frequency on the power grid control personnel. Manual operation cannot meet the minute-level online calculation requirements. Therefore, the use of traditional closed-loop current calculation methods for online calculation and analysis of the rapidly changing closed-loop current of urban power grids will result in large deviations. Summary of the invention

[0004] In view of the above problems, the present invention proposes a method for evaluating multi-voltage level closed loop operation of an urban power grid, comprising:

[0005] Acquire multiple types of data related to the points to be closed in multiple voltage levels of the urban power grid, calculate the equivalent impedances of the power transmission end and the power receiving end on both sides of the points to be closed in multiple voltage levels of the urban power grid based on the multiple types of data, perform through-flow calculation based on the equivalent impedance and the power flow data of the power transmission end and the power receiving end, and obtain the bus voltage difference;

[0006] Selecting a minimum range of bus voltage difference to determine the current online or future planned load value, and determining the alarm threshold of the to-be-closed point in multiple voltage levels of the urban power grid based on the current online or future planned load value;

[0007] Based on the bus voltage difference, the calculated value of the closing current of the point to be closed is determined, and the calculated value of the closing current is compared with the alarm threshold of the point to be closed. Based on the comparison result, the closing operation of the point to be closed in multiple voltage levels of the urban power grid is evaluated.

[0008] Optionally, multiple types of data, including at least one of the following:

[0009] The planned data, historical data, online operation data of the closing points in multiple voltage levels of the urban power grid, and the local voltage and current phasor measurement data of the closing points.

[0010] Optional, equivalent impedance, including:

[0011] The busbar equivalent impedance from the closing point to the power transmission end, the busbar equivalent impedance from the closing point to the power receiving end, and the equivalent impedance of the entire closing line.

[0012] Optionally, the function expression for calculating the busbar equivalent impedance from the closing point to the transmission end is as follows:

[0013]

[0014] Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, ΔU1' is the change in bus voltage at the transmission end when the loop is closed, Q1 and Q1' are the reactive power at the transmission end before and at the minimum phase difference moment, I1 and I1' are the bus currents at the transmission end before and at the minimum phase difference moment, and Z1 is the bus equivalent impedance from the closing point to the transmission end.

[0015] Optionally, the function expression for calculating the busbar equivalent impedance from the closing point to the receiving end is as follows:

[0016]

[0017] Among them, U2 and U2' are the bus phase voltages at the receiving end before and at the minimum phase difference moment, ΔU2' is the change in bus voltage at the receiving end when the loop is closed, Q2 and Q2' are the reactive power at the receiving end before and at the minimum phase difference moment, I2 and I2' are the bus currents at the receiving end before and at the minimum phase difference moment, and Z2 is the bus equivalent impedance from the closing point to the receiving end.

[0018] Optionally, the function expression for calculating the equivalent impedance of the entire closed-loop line is as follows:

[0019]

[0020] Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, respectively; ΔU1' is the bus voltage change at the transmission end when the loop is closed; U2' is the bus phase voltage at the receiving end at the minimum phase difference moment; ΔU2' is the bus voltage change at the receiving end when the loop is closed; Z is the equivalent impedance of the entire closed-loop line; Q1 is the reactive power at the transmission end before the minimum phase difference moment; Q2' is the reactive power at the receiving end at the minimum phase difference moment; and P2' is the active power at the receiving end at the minimum phase difference moment.

[0021] Optionally, after performing the through flow calculation, the method further includes:

[0022] Whether the closing condition is met is determined based on the through flow to determine the closing operation time of the tie switches at both the power transmission end and the power receiving end. The judgment function is expressed as one of the following:

[0023] |S1-S T |≤η×S LLmax

[0024] Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, S LLmax It is the allowable load of the tie switch closing line.

[0025] Optionally, after performing the through flow calculation, the method further includes:

[0026] Whether the closing condition is met is determined according to the through flow to determine the closing operation time of the tie switch at the closing point. The judgment function is expressed as one of the following:

[0027]

[0028] Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, I LLmaxFor the allowable current, U1 is the bus phase voltage at the power transmission end before the minimum phase difference, and U2 is the bus phase voltage at the power receiving end before the minimum phase difference.

[0029] Optionally, after performing the through flow calculation, the method further includes:

[0030] The loop closing operation on the receiving end allows flow judgment, and the judgment function expression is as follows:

[0031] |S2+S T |≤η×S 2LLmax

[0032] Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through-flow current, η is the reliability coefficient, S 2LLmax It is the allowable load of the closed-loop line at the receiving end.

[0033] Optionally, after performing the through flow calculation, the method further includes:

[0034] According to the through flow, it is judged whether the closing condition is met to decide whether to control the receiving end on the closing line to perform the closing operation. The judgment function expression is as follows:

[0035]

[0036] Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through flow, η is the reliability coefficient, U2 is the bus phase voltage at the receiving end before the minimum phase angle difference, I N is the maximum allowable current.

[0037] Optionally, the function expression for the through flow calculation is as follows:

[0038]

[0039] Among them, ΔU is the bus voltage difference between the power transmission end and the power receiving end, S1 is the load flow of the closed-loop line at the power transmission end, S2 is the load flow of the closed-loop line at the power receiving end, S T For the through flow, U1 is the bus phase voltage at the transmission end before the minimum phase difference, U2 is the bus phase voltage at the receiving end before the minimum phase difference, Z1 is the bus equivalent impedance from the closing point to the transmission end, Z2 is the bus equivalent impedance from the closing point to the receiving end, and Z is the equivalent impedance of the entire closed line.

[0040] In another aspect, the present invention further provides a system for evaluating multi-voltage level closed-loop operation of an urban power grid, comprising:

[0041] The first calculation unit is used to obtain multiple types of data related to the loop points to be closed in multiple voltage levels of the urban power grid, calculate the equivalent impedance of the power transmission end and the power receiving end on both sides of the loop points to be closed in multiple voltage levels of the urban power grid based on the multiple types of data, and perform a through flow calculation based on the equivalent impedance and the power flow data of the power transmission end and the power receiving end to obtain the bus voltage difference;

[0042] The second calculation unit is used to select the minimum range interval of the bus voltage difference to determine the current online or future planned load value, and determine the alarm threshold of the to-be-closed point in multiple voltage levels of the urban power grid based on the current online or future planned load value;

[0043] An evaluation unit is used to determine the calculated value of the closing current of the point to be closed based on the bus voltage difference, compare the calculated value of the closing current with the alarm threshold of the point to be closed, and evaluate the closing operation of the point to be closed in multiple voltage levels of the urban power grid based on the comparison result.

[0044] Optionally, multiple types of data, including at least one of the following:

[0045] The planned data, historical data, online operation data of the closing points in multiple voltage levels of the urban power grid, and the local voltage and current phasor measurement data of the closing points.

[0046] Optional, equivalent impedance, including:

[0047] The busbar equivalent impedance from the closing point to the power transmission end, the busbar equivalent impedance from the closing point to the power receiving end, and the equivalent impedance of the entire closing line.

[0048] Optionally, the function expression for calculating the busbar equivalent impedance from the closing point to the transmission end is as follows:

[0049]

[0050] Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, ΔU1' is the change in bus voltage at the transmission end when the loop is closed, Q1 and Q1' are the reactive power at the transmission end before and at the minimum phase difference moment, I1 and I1' are the bus currents at the transmission end before and at the minimum phase difference moment, and Z1 is the bus equivalent impedance from the closing point to the transmission end.

[0051] Optionally, the function expression for calculating the busbar equivalent impedance from the closing point to the receiving end is as follows:

[0052]

[0053] Among them, U2 and U2' are the bus phase voltages at the receiving end before and at the minimum phase difference moment, ΔU2' is the change in bus voltage at the receiving end when the loop is closed, Q2 and Q2' are the reactive power at the receiving end before and at the minimum phase difference moment, I2 and I2' are the bus currents at the receiving end before and at the minimum phase difference moment, and Z2 is the bus equivalent impedance from the closing point to the receiving end.

[0054] Optionally, the function expression for calculating the equivalent impedance of the entire closed-loop line is as follows:

[0055]

[0056] Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, respectively; ΔU1' is the bus voltage change at the transmission end when the loop is closed; U2' is the bus phase voltage at the receiving end at the minimum phase difference moment; ΔU2' is the bus voltage change at the receiving end when the loop is closed; Z is the equivalent impedance of the entire closed-loop line; Q1 is the reactive power at the transmission end before the minimum phase difference moment; Q2' is the reactive power at the receiving end at the minimum phase difference moment; and P2' is the active power at the receiving end at the minimum phase difference moment.

[0057] Optionally, the first calculation unit is further used to: after performing the through-flow calculation, determine whether the closing condition is met according to the through-flow to determine the closing operation time of the tie switches at both ends of the power transmission end and the power receiving end, and the judgment function is expressed as one of the following:

[0058] |S1-S T |≤η×S LLmax

[0059] Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, S LLmax It is the allowable load of the tie switch closing line.

[0060] Optionally, the first calculation unit is further used to: after calculating the through-flow, determine whether the closing condition is met according to the through-flow, so as to determine the closing operation time of the tie switch at the closing point, and the judgment function is expressed as one of the following:

[0061]

[0062] Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, I LLmax For the allowable current, U1 is the bus phase voltage at the power transmission end before the minimum phase difference, and U2 is the bus phase voltage at the power receiving end before the minimum phase difference.

[0063] Optionally, the first calculation unit is further used to: after performing the through-flow calculation, perform a loop closing operation on the power receiving end to allow flow judgment, and the judgment function expression is as follows:

[0064] |S2+S T |≤η×S 2LLmax

[0065] Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through-flow current, η is the reliability coefficient, S 2LLmax It is the allowable load of the closed-loop line at the receiving end.

[0066] Optionally, the first calculation unit is further used to: after performing the through flow calculation, determine whether the closing condition is met according to the through flow, so as to determine whether to control the receiving end on the closing line to perform the closing operation, and the judgment function expression is as follows:

[0067]

[0068] Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through flow, η is the reliability coefficient, U2 is the bus phase voltage at the receiving end before the minimum phase angle difference, I N is the maximum allowable current.

[0069] Optionally, the function expression for the through flow calculation is as follows:

[0070]

[0071] Among them, ΔU is the bus voltage difference between the power transmission end and the power receiving end, S1 is the load flow of the closed-loop line at the power transmission end, S2 is the load flow of the closed-loop line at the power receiving end, S T For the through flow, U1 is the bus phase voltage at the transmission end before the minimum phase difference, U2 is the bus phase voltage at the receiving end before the minimum phase difference, Z1 is the bus equivalent impedance from the closing point to the transmission end, Z2 is the bus equivalent impedance from the closing point to the receiving end, and Z is the equivalent impedance of the entire closed line.

[0072] In yet another aspect, the present invention further provides a computing device, comprising: one or more processors;

[0073] a processor for executing one or more programs;

[0074] When the one or more programs are executed by the one or more processors, the above-described method is implemented.

[0075] In yet another aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed, the method described above is implemented.

[0076] Compared with the prior art, the present invention has the following beneficial effects:

[0077] The present invention provides a method for evaluating the closing operation of multiple voltage levels of an urban power grid, comprising: obtaining multiple types of data related to the points to be closed in multiple voltage levels of the urban power grid, calculating the equivalent impedance of the power transmission end and the power receiving end on both sides of the points to be closed in multiple voltage levels of the urban power grid based on the multiple types of data, performing a through flow calculation based on the equivalent impedance and the power flow data of the power transmission end and the power receiving end to obtain a bus voltage difference; selecting the minimum range interval of the bus voltage difference to determine the current online or future state planned load value, and determining the alarm threshold of the points to be closed in multiple voltage levels of the urban power grid based on the current online or future state planned load value; determining the closing current calculated value of the points to be closed based on the bus voltage difference, comparing the closing current calculated value with the alarm threshold of the points to be closed, and evaluating the closing operation of the points to be closed in multiple voltage levels of the urban power grid based on the comparison result. The implementation of the present invention, by evaluating the closing operation, and then performing the closing operation according to the evaluation result, avoids the tripping of the protection action and the damage of the urban power grid equipment caused by excessive closing current. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 is a flow chart of the method of the present invention;

[0079] Figure 2 A schematic diagram of a basic flow chart of a method according to an embodiment of the present invention;

[0080] Figure 3 Schematic diagram of the closed loop circuit in the embodiment of the present invention (end A) and when the ring is closed (end B);

[0081] Figure 4 Schematic diagram of the voltage phasor (phase angle) measurement principle in an embodiment of the present invention;

[0082] Figure 5 It is a structural diagram of the system of the present invention. DETAILED DESCRIPTION

[0083] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0084] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0085] Embodiment 1:

[0086] The present invention proposes a method for evaluating multi-voltage level closed loop operation of urban power grids, such as Figure 1 As shown, including:

[0087] Step 1, obtaining multiple types of data related to the points to be closed in multiple voltage levels of the urban power grid, calculating the equivalent impedances of the power transmission end and the power receiving end on both sides of the points to be closed in multiple voltage levels of the urban power grid based on the multiple types of data, and performing a through flow calculation based on the equivalent impedance and the power flow data of the power transmission end and the power receiving end to obtain the bus voltage difference;

[0088] Step 2: Select the minimum range of the bus voltage difference to determine the current online or future planned load value, and determine the alarm threshold of the to-be-closed point in multiple voltage levels of the urban power grid based on the current online or future planned load value;

[0089] Step 3: Based on the bus voltage difference, determine the calculated value of the closing current of the point to be closed, compare the calculated value of the closing current with the alarm threshold of the point to be closed, and based on the comparison result, evaluate the closing operation of the point to be closed in multiple voltage levels of the urban power grid.

[0090] Among them, the multiple types of data include at least one type of data from the following:

[0091] The planned data, historical data, online operation data of the closing points in multiple voltage levels of the urban power grid, and the local voltage and current phasor measurement data of the closing points.

[0092] Among them, the equivalent impedance includes:

[0093] The busbar equivalent impedance from the closing point to the power transmission end, the busbar equivalent impedance from the closing point to the power receiving end, and the equivalent impedance of the entire closing line.

[0094] Among them, the function expression for calculating the busbar equivalent impedance from the closing point to the power transmission end is as follows:

[0095]

[0096] Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, ΔU1' is the change in bus voltage at the transmission end when the loop is closed, Q1 and Q1' are the reactive power at the transmission end before and at the minimum phase difference moment, I1 and I1' are the bus currents at the transmission end before and at the minimum phase difference moment, and Z1 is the bus equivalent impedance from the closing point to the transmission end.

[0097] Among them, the function expression for calculating the busbar equivalent impedance from the closing point to the receiving end is as follows:

[0098]

[0099] Among them, U2 and U2' are the bus phase voltages at the receiving end before and at the minimum phase difference moment, ΔU2' is the change in bus voltage at the receiving end when the loop is closed, Q2 and Q2' are the reactive power at the receiving end before and at the minimum phase difference moment, I2 and I2' are the bus currents at the receiving end before and at the minimum phase difference moment, and Z2 is the bus equivalent impedance from the closing point to the receiving end.

[0100] Among them, the function expression for calculating the equivalent impedance of the entire closed-loop line is as follows:

[0101]

[0102] Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, respectively; ΔU1' is the bus voltage change at the transmission end when the loop is closed; U2' is the bus phase voltage at the receiving end at the minimum phase difference moment; ΔU2' is the bus voltage change at the receiving end when the loop is closed; Z is the equivalent impedance of the entire closed-loop line; Q1 is the reactive power at the transmission end before the minimum phase difference moment; Q2' is the reactive power at the receiving end at the minimum phase difference moment; and P2' is the active power at the receiving end at the minimum phase difference moment.

[0103] After the through-flow calculation is performed, the method further comprises:

[0104] Whether the closing condition is met is determined based on the through flow to determine the closing operation time of the tie switches at both the power transmission end and the power receiving end. The judgment function is expressed as one of the following:

[0105] |S1-S T |≤η×S LLmax

[0106] Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, S LLmax It is the allowable load of the tie switch closing line.

[0107] After the through-flow calculation is performed, the method further comprises:

[0108] Whether the closing condition is met is determined according to the through flow to determine the closing operation time of the tie switch at the closing point. The judgment function is expressed as one of the following:

[0109]

[0110] Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, I LLmax For the allowable current, U1 is the bus phase voltage at the power transmission end before the minimum phase difference, and U2 is the bus phase voltage at the power receiving end before the minimum phase difference.

[0111] After the through-flow calculation is performed, the method further comprises:

[0112] The loop closing operation on the receiving end allows flow judgment, and the judgment function expression is as follows:

[0113] |S2+S T |≤η×S 2LLmax

[0114] Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through-flow current, η is the reliability coefficient, S 2LLmax It is the allowable load of the closed-loop line at the receiving end.

[0115] After the through-flow calculation is performed, the method further comprises:

[0116] According to the through flow, it is judged whether the closing condition is met to decide whether to control the receiving end on the closing line to perform the closing operation. The judgment function expression is as follows:

[0117]

[0118] Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through flow, η is the reliability coefficient, U2 is the bus phase voltage at the receiving end before the minimum phase angle difference, I N is the maximum allowable current.

[0119] Among them, the function expression for through-flow calculation is as follows:

[0120]

[0121] Among them, ΔU is the bus voltage difference between the power transmission end and the power receiving end, S1 is the load flow of the closed-loop line at the power transmission end, S2 is the load flow of the closed-loop line at the power receiving end, S TFor the through flow, U1 is the bus phase voltage at the transmission end before the minimum phase difference, U2 is the bus phase voltage at the receiving end before the minimum phase difference, Z1 is the bus equivalent impedance from the closing point to the transmission end, Z2 is the bus equivalent impedance from the closing point to the receiving end, and Z is the equivalent impedance of the entire closed line.

[0122] The present invention is described below in conjunction with specific implementation cases:

[0123] Example process such as Figure 2 As shown, including:

[0124] S1, for the interconnecting switches of multiple voltage levels from 110kV to 10kV in the urban power grid, the equivalent impedance of the closing point is calculated online and continuously for the A end (transmission end) and B end (receiving end) on both sides of the closing point.

[0125] The equivalent impedance calculation needs to calculate the following contents: the equivalent impedance of the busbar from the system central closing point to the A end, the equivalent impedance of the busbar from the system central closing point to the B end, and the equivalent impedance of the entire closing line;

[0126] S2, for the calculation of the closed-loop current of the specific closed-loop operation expected by the regulation, first collect the bus phase voltage and closed-loop line load flow data at the A and B ends. The data sources include the local voltage and current phase measurement equipment and the power grid SCADA data and other historical and online time series data and future state planning data, and calculate the bus voltage difference between the A and B ends at different time points on the day. The through flow is calculated according to the following formula:

[0127]

[0128] In the above formula, ΔU is the bus voltage difference between end A and end B, S1 and S2 are the load values ​​of end A and end B respectively, U1 and U2 are the bus phase voltages of end A and end B respectively, Z1 and Z2 are the bus equivalent impedances from the system hub to end A and end B respectively, Z is the equivalent impedance of the entire closed-loop line, S T To cross the trend.

[0129] S3, for the interconnecting switches of multiple voltage levels from 110kV to 10kV in the urban power grid, the data required for the equivalent impedance calculation of the A end (transmission end) and the B end (receiving end) on both sides of the closing point needs to comprehensively consider the planned data, historical data, online operation data of the closing points of multiple voltage levels in the urban power grid, as well as the local voltage and current phasor measurement data of the closing points.

[0130] S4, calculates the bus voltage difference, which needs to take into account the time sequence changes, selects the minimum range of the bus voltage difference, and is based on the online or future planned load value at that moment.

[0131] S5, calculates the closing current value of the point to be closed through the through flow obtained in S2, compares the calculated closing current value with the alarm threshold of the closing point, and outputs the closing operation evaluation result.

[0132] Optionally, the function expression for determining the busbar equivalent impedance from the system central closing point to the A end in step S1 is:

[0133]

[0134] The function expression for determining the busbar equivalent impedance from the system central closing point to the B end in step S1 is:

[0135]

[0136] Among them, U1 and U1' are the bus phase voltages at end A before and at the minimum phase difference moment and the minimum phase difference moment selected in step S2, respectively, and correspondingly, I1 and I1' are the bus currents at end A, Z1 is the bus equivalent impedance from the system central closing point to end A, P1 and P1' are the corresponding reactive power at end A, Q1 and Q1' are the active power at end A, and j is an imaginary unit; correspondingly, U2 and U2' are the bus phase voltages at end B at the corresponding moment of end A, I2 and I2' are the bus currents at end B, Z2 is the bus equivalent impedance from the system central closing point to end B, P2 and P2' are the active power at end B, and Q2 and Q2' are the reactive power at end B.

[0137] Optionally, the function expression for determining the equivalent impedance of the entire closed-loop line in step S1 is:

[0138]

[0139] Among them, U1' and U2' are the bus phase voltages at terminals A and B respectively when the loop is closed, ΔU1' is the bus voltage change between terminals A and B when the loop is closed, ΔU1' and ΔU2' are the bus voltage changes at terminals A and B respectively when the loop is closed, and Q1' and Q2' are the reactive power at terminals A and B respectively when the loop is closed.

[0140] Optionally, after the through-flow is calculated in step S2, the process further includes determining whether the closing condition is met according to the through-flow to determine the closing operation time of the tie switches at both ends A and B. The allowable load of the tie switch closing line is S LLmax , the allowable current is I LLmax , the function expression of the closing condition is:

[0141] |S1-S T |≤η×S LLmax

[0142] In the above formula, S1 is the load flow of the closed-loop line at end A, S T is the through-current and η is the reliability coefficient.

[0143] Optionally, after the through-flow is calculated in step S2, the process further includes determining whether the closing condition is met according to the through-flow to determine the closing operation time of the closing point tie switch, and the allowable load of the closing line is S LLmax , the allowable current is I LLmax , the function expression of the closing condition is:

[0144]

[0145] In the above formula, S1 is the load flow of the closed-loop line at end A, P1 is the active power of the closed-loop line load flow at end A, Q1 is the reactive power of the closed-loop line load flow at end A, j is an imaginary unit, S T For through-flow, U1 and U2 are the bus phase voltages at terminals A and B respectively.

[0146] Optionally, after the through flow is calculated in step S2, it is also necessary to determine the allowable flow of the closed loop operation at the B end. The allowable load of the closed loop line at the B end is S 2LLmax , the allowable current is I N , the function expression of the closing condition is:

[0147] |S2+S T |≤η×S 2LLmax

[0148] In the above formula, S2 is the load flow of the closed-loop line at end B, P2 is the active power of the closed-loop line load flow at end B, Q2 is the reactive power of the closed-loop line load flow at end B, j is an imaginary unit, S T To cross the trend.

[0149] Optionally, after the through-flow is calculated in step S2, it is also included to determine whether the closing condition is met according to the through-flow to determine whether to control the B end of the closing line to perform the closing operation. The allowable load of the closing line at the B end is SN, and the allowable current is IN. The function expression of the closing condition is:

[0150]

[0151] In the above formula, is the load flow of the closed-loop line at end B, P2 is the active power of the closed-loop line load flow at end B, Q2 is the reactive power of the closed-loop line load flow at end B, j is an imaginary unit, S T For through-flow, U2 is the bus phase voltage at end B.

[0152] Optionally, collecting the bus voltage and current data of end A and end B in step S2 includes: using two different bus voltage and current phasor measurement devices to respectively collect the bus phase voltage and phase current of the two ends, and the two different bus voltage phasor measurement devices are synchronized in advance using a GPS satellite clock source, so that the two different bus voltage phasor measurement devices collect the bus voltage of end A and end B in a synchronized manner.

[0153] The above steps are specifically as follows:

[0154] S1, for the interconnection switches of multiple voltage levels from 110kV to 10kV in the urban power grid, for the A end (transmission end) and the B end (receiving end) on both sides of the closing point, combined with the online and historical data of the voltage and current phasors obtained by the local voltage and current phasor measurement equipment, the equivalent impedance of the closing point is calculated online and continuously. The equivalent impedance calculation needs to calculate: the equivalent impedance of the busbar from the system central closing point to the A end, the equivalent impedance of the busbar from the system central closing point to the B end, and the equivalent impedance of the entire closing line;

[0155] S2, for the calculation of the closing current of the specific closing operation expected by the regulation, first collect the bus phase voltage and closing line load flow data at the A and B ends. The data sources include the local voltage and current phase measurement equipment and the power grid SCADA data and other historical and online time series data and future state plan data, and calculate the bus voltage difference between the A and B ends at different time points of the day. Before calculating the voltage difference, first select the moment when the voltage and voltage historical measurement values ​​on both sides of the closing point are low and the voltage phase angle difference is small, and based on the online or future state plan load value at that moment, calculate the through flow according to the following formula:

[0156]

[0157] In the above formula, ΔU is the bus voltage difference between end A and end B, S1 and S2 are the load values ​​of end A and end B respectively, U1 and U2 are the bus phase voltages of end A and end B respectively, Z1 and Z2 are the bus equivalent impedances from the system hub to end A and end B respectively, Z is the equivalent impedance of the entire closed-loop line, S T To cross the trend.

[0158] Figure 3 Schematic diagram of the loop circuit before and during loop closing in the embodiment of the present invention. Figure 3In the embodiment shown, the A terminal station has a voltage level of 110kV, the A terminal bus phase voltage is U1, the closed-loop line load flow is P1+jQ1, and the 110kV bus phase voltage of the A terminal station when the ring is closed is U1', and the closed-loop line load flow is P1'+jQ1'; the 110kV bus phase voltage of the B terminal station is U2, and the closed-loop line load flow is P2+jQ2. When the ring is closed, the 110kV bus phase voltage of the B terminal station is U2', and the closed-loop line load flow is P2'+jQ2'; the equivalent impedance of the 110kV bus from the system hub to the A terminal station is the equivalent impedance of the 110kV bus from the system hub to the B terminal station is, and the impedance parameters in the system are approximately linear parameters and remain unchanged.

[0159] Assuming that the voltage of the central node of the system remains unchanged when the loop is closed, we have:

[0160] U-U1=I1Z1

[0161] UU′1=I′1Z1

[0162] In the above formula, are the equivalent current of 10kV busbar from the central point of the system to the A terminal when the ring is closed. Subtract (2) from (1), and we have:

[0163]

[0164] According to formula (4), the busbar equivalent impedance from the system hub to the A end can be obtained. Therefore, the function expression for determining the busbar equivalent impedance from the system hub to the A end in step S1 of this embodiment is shown in formula (4).

[0165] Similarly, the function expression for determining the busbar equivalent impedance from the system hub to the B end in step S1 is:

[0166]

[0167] Among them, and are the bus phase voltages at end A when the and are closed loop, and are the bus currents at end A when the and are closed loop, is the bus equivalent impedance from the system central point to end A, P1 and P1′ are the reactive power at end A when the and are closed loop, Q1 and Q1′ are the active power at end A when the and are closed loop, and j is an imaginary unit; and are the bus phase voltages at end B when the and are closed loop, and are the bus currents at end B when the and are closed loop, is the bus equivalent impedance from the system central point to end B, P2 and P2′ are the active power at end B when the and are closed loop, Q2 and Q2′ are the reactive power at end B when the and are closed loop.

[0168] Figure 4 is the equivalent diagram of the closed-loop power flow in this embodiment. Figure 4 As shown, without considering the influence of the subsequent voltage change on the load current, according to the superposition theorem, the current when the loop is closed can be equivalent to the superposition of the load current and the through current.

[0169] Similarly, without considering the power loss of the closed-loop line itself, Figure 2 The line flow during loop closing can be considered as two parts: load flow P1'+P2'+j(Q1'+Q2')≈P1+P2+j(Q1+Q2) and through flow -(P2'+jQ2').

[0170] The following ideal assumptions are made for the closed-loop line: 1) the line load is evenly distributed; 2) the line impedance is equal everywhere.

[0171] Assuming the equivalent impedance of the entire closed-loop line is Z, the voltage drop ΔU caused by the load flow is:

[0172]

[0173] Therefore, the functional expression for determining the equivalent impedance of the entire closed-loop line in step S1 of this embodiment is as shown in the formula. The equivalent impedance of the entire closed-loop line can be calculated through the closed-loop line flow and the collected bus phase voltage during the closed-loop. The parameters used for the subsequent steady-state closed-loop current online calculation are only the line flow and the bus voltage, and the line current phasor is not used. This can avoid the error in the calculation result caused by the asynchronous sampling of the voltage and current phasor data. The system equivalent impedance calculated by the previous closed-loop data can be used for the next closed-loop flow calculation to determine whether the next closed-loop flow is within the allowable range and whether the closed-loop conditions are met.

[0174] By collecting the data of the previous time and the closing time, the equivalent impedance of the system can be calculated. Without considering the power loss of the closing line itself, the load flow is Without considering the power loss of the closing line itself, the line flow during the closing time can be regarded as two parts: load flow P1′+P2′+j(Q1′+Q2′)≈P1+P2+j(Q1+Q2) and through flow -(P2′+jQ2′).

[0175] Assume that the flow in other parts of the system does not change compared to the closed loop. Assume that the through flow is, the bus voltage difference can be regarded as a voltage drop balance of four parts when the loop is closed: the voltage drop caused by the through flow on the equivalent impedance from the system hub to the bus, the voltage drop caused by the through flow on the equivalent impedance of the closed loop line, and the voltage drop caused by the load flow on the equivalent impedance of the closed loop line.

[0176] Assuming that the bus voltage phase angle at end A (sending station) is ahead, the sending end closing line power will increase when closing the loop, and the closing line power at end B (referred to as the receiving station) will decrease, or even reverse. Even if the closing line power at the receiving end is reversed, the closing line power amplitude will not exceed the closing line at end A. Therefore, the closing and unclosing conditions can be determined by calculating the closing line power at the station with the leading phase angle (if the closing line power at the two stations is the online power, the conclusion is the opposite, that is, the closing and unclosing conditions can be determined by calculating the closing line power at the station with the lagging phase angle).

[0177] As an optional implementation, in this embodiment, after the through-flow is calculated in step S2, it is also included to determine whether the closing condition is met according to the through-flow to determine whether to control the two A ends and B ends on the closed-loop line to perform the closing operation. In this embodiment, after the through-flow is calculated in step S2, it is also included to determine whether the closing condition is met according to the through-flow to determine whether to control the A end on the closed-loop line to perform the closing operation. The allowable load of the closed-loop line at the A end is SN, and the allowable current is IN. The function expression of the closing condition is:

[0178]

[0179] In the above formula, is the load flow of the closed-loop line at end A, P1 is the active power of the load flow of the closed-loop line at end A, Q1 is the reactive power of the load flow of the closed-loop line at end A, and j is an imaginary unit.

[0180] In this embodiment, after the through-flow is calculated in step S2, it is also included to determine whether the closing condition is met according to the through-flow to determine whether to control the B end of the closing line to perform the closing operation. The allowable load of the closing line at the B end is SN, and the allowable current is IN. The function expression of the closing condition is:

[0181]

[0182] In the above formula, S2 is the load flow of the closed-loop line at end B, P2 is the active power of the closed-loop line load flow at end B, Q2 is the reactive power of the closed-loop line load flow at end B, j is an imaginary unit, S T is the through flow, and are the bus phase voltages at end B. It should be noted that the above derivation process and formula have nothing to do with the magnitude and true direction of the closed-loop line flow at end A and end B, that is, the subscripts "1" and "2" in the formula are interchangeable.

[0183] In step S2 of this embodiment, the bus voltages at the A and B terminals are collected by using two different bus voltage and current phasor measurement devices ( Figure 4The two devices (respectively denoted as A and B) collect the bus phase voltage and phase current at the A end and the B end respectively, and the two different bus voltage and current phasor measurement devices are pre-synchronized using the GPS satellite clock source to synchronize the time so that the two different bus voltage phasor measurement devices collect the bus voltage at the A end and the B end respectively. When realizing the closed-loop calculation of the connecting line between the two seats, Machine A and Machine B are responsible for collecting the bus phase voltage and phase current, and communicating with the GPS satellite. The GPS synchronization provides a voltage phase angle reference value, and then the collected data is uploaded to the closed-loop current calculation module through wired data. The real-time flow of the closed-loop line required by the closed-loop current calculation module is forwarded by the dispatching master station system. The closed-loop current calculation module is denoted as the execution body of the online estimation method of the closed-loop current of the urban power grid based on the local phasor measurement data of voltage and current in this embodiment, which can generally be implemented by computer equipment. The bus voltage phasor measurement device is installed on the secondary side of the bus to realize the measurement and upload of the bus voltage and current phasors. Under the condition of meeting a certain sampling accuracy, the synchronous measurement and upload of the bus voltage phasor are realized. Voltage phase angle measurement requires comparison of the rear bus voltage phase with the reference voltage phase. The phase angle measurement error shall not exceed ±0.25°, and the bus voltage and current amplitude measurement errors shall meet the requirements of relevant specifications. The voltage and current phasor measurement device uses wired communication to upload voltage and current phasors.

[0184] Embodiment 2:

[0185] The present invention also proposes a system 200 for evaluating multi-voltage level closed loop operation of a city power grid, such as Figure 5 As shown, including:

[0186] The first calculation unit 201 is used to obtain multiple types of data related to the loop points to be closed in multiple voltage levels of the urban power grid, calculate the equivalent impedance of the power transmission end and the power receiving end on both sides of the loop points to be closed in multiple voltage levels of the urban power grid based on the multiple types of data, and perform a through flow calculation based on the equivalent impedance and the power flow data of the power transmission end and the power receiving end to obtain the bus voltage difference;

[0187] The second calculation unit 202 is used to select the minimum range interval of the bus voltage difference to determine the current online or future planned load value, and determine the alarm threshold of the to-be-closed point in multiple voltage levels of the urban power grid based on the current online or future planned load value;

[0188] The evaluation unit 203 is used to determine the calculated value of the closing current of the point to be closed based on the bus voltage difference, compare the calculated value of the closing current with the alarm threshold of the point to be closed, and evaluate the closing operation of the point to be closed in multiple voltage levels of the urban power grid based on the comparison result.

[0189] Among them, the multiple types of data include at least one type of data from the following:

[0190] The planned data, historical data, online operation data of the closing points in multiple voltage levels of the urban power grid, and the local voltage and current phasor measurement data of the closing points.

[0191] Among them, the equivalent impedance includes:

[0192] The busbar equivalent impedance from the closing point to the power transmission end, the busbar equivalent impedance from the closing point to the power receiving end, and the equivalent impedance of the entire closing line.

[0193] Among them, the function expression for calculating the busbar equivalent impedance from the closing point to the power transmission end is as follows:

[0194]

[0195] Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, ΔU1' is the change in bus voltage at the transmission end when the loop is closed, Q1 and Q1' are the reactive power at the transmission end before and at the minimum phase difference moment, I1 and I1' are the bus currents at the transmission end before and at the minimum phase difference moment, and Z1 is the bus equivalent impedance from the closing point to the transmission end.

[0196] Among them, the function expression for calculating the busbar equivalent impedance from the closing point to the receiving end is as follows:

[0197]

[0198] Among them, U2 and U2' are the bus phase voltages at the receiving end before and at the minimum phase difference moment, ΔU2' is the change in bus voltage at the receiving end when the loop is closed, Q2 and Q2' are the reactive power at the receiving end before and at the minimum phase difference moment, I2 and I2' are the bus currents at the receiving end before and at the minimum phase difference moment, and Z2 is the bus equivalent impedance from the closing point to the receiving end.

[0199] Among them, the function expression for calculating the equivalent impedance of the entire closed-loop line is as follows:

[0200]

[0201] Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, respectively; ΔU1' is the bus voltage change at the transmission end when the loop is closed; U2' is the bus phase voltage at the receiving end at the minimum phase difference moment; ΔU2' is the bus voltage change at the receiving end when the loop is closed; Z is the equivalent impedance of the entire closed-loop line; Q1 is the reactive power at the transmission end before the minimum phase difference moment; Q2' is the reactive power at the receiving end at the minimum phase difference moment; and P2' is the active power at the receiving end at the minimum phase difference moment.

[0202] The first calculation unit 201 is further used to: after calculating the through-flow, determine whether the closing condition is met according to the through-flow, so as to determine the closing operation time of the tie switches at both ends of the power transmission end and the power receiving end, and the judgment function is expressed as one of the following:

[0203] |S1-S T |≤η×S LLmax

[0204] Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, S LLmax It is the allowable load of the tie switch closing line.

[0205] The first calculation unit 201 is further used to: after calculating the through-flow, determine whether the closing condition is met according to the through-flow, so as to determine the closing operation time of the tie switch at the closing point, and the judgment function is expressed as one of the following:

[0206]

[0207] Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, I LLmax For the allowable current, U1 is the bus phase voltage at the power transmission end before the minimum phase difference, and U2 is the bus phase voltage at the power receiving end before the minimum phase difference.

[0208] The first calculation unit 201 is further used to: after performing the through-flow calculation, perform a loop closing operation on the receiving end to allow flow judgment, and the judgment function expression is as follows:

[0209] |S2+S T |≤η×S 2LLmax

[0210] Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through-flow current, η is the reliability coefficient, S 2LLmax It is the allowable load of the closed-loop line at the receiving end.

[0211] The first calculation unit 201 is further used to: after performing the through flow calculation, determine whether the closing condition is met according to the through flow, so as to determine whether to control the receiving end on the closing line to perform the closing operation, and the judgment function expression is as follows:

[0212]

[0213] Among them, S2 is the load flow of the closed-loop line at the receiving end, S Tis the through flow, η is the reliability coefficient, U2 is the bus phase voltage at the receiving end before the minimum phase angle difference, I N is the maximum allowable current.

[0214] Among them, the function expression for through-flow calculation is as follows:

[0215]

[0216] Among them, ΔU is the bus voltage difference between the power transmission end and the power receiving end, S1 is the load flow of the closed-loop line at the power transmission end, S2 is the load flow of the closed-loop line at the power receiving end, S T For the through flow, U1 is the bus phase voltage at the transmission end before the minimum phase difference, U2 is the bus phase voltage at the receiving end before the minimum phase difference, Z1 is the bus equivalent impedance from the closing point to the transmission end, Z2 is the bus equivalent impedance from the closing point to the receiving end, and Z is the equivalent impedance of the entire closed line.

[0217] The present invention calculates equivalent impedance for the detection data of the previous closed-loop operation of the two A and B ends on the closed-loop line, and respectively determines the busbar equivalent impedance from the system central point to the A end, the busbar equivalent impedance from the system central point to the B end, and the equivalent impedance of the entire closed-loop line; for this closed-loop, the busbar voltage of the A end and the B end and the closed-loop line load flow are respectively collected, the busbar voltage difference between the A end and the B end is calculated, and the crossing flow is calculated according to the preset function model. In view of the current practical problems of the difficulty in modeling and maintenance of urban power grid lines and the difficulty in estimating closed-loop flow, the present invention can comprehensively consider the voltage and current phasor data of the contact switch at the closed-loop point, and can reduce the dependence on the correctness of the equivalent model and model parameters of the closed-loop switch to be closed, and can realize the approximate and accurate calculation of the closed-loop current by online calculation. According to the calculation results, it is judged whether the closed-loop operation of the urban power grid can be performed, so as to avoid the tripping of the protection action and the damage of the urban power grid equipment due to the excessive closed-loop current, or the unnecessary adjustment of the main network mode and the power outage and power adjustment of the urban power grid due to the difficulty in estimating the closed-loop current. The present invention can easily realize online analysis of the closed-loop current of the urban power grid by collecting and uploading the bus voltage phasor (phase angle). The approximate calculation result can fully meet the needs of closed-loop judgment, avoiding the tripping of protection action and damage to urban power grid equipment due to excessive closed-loop current. It avoids many problems existing in traditional methods: difficulty in urban power grid modeling, inconvenience in model maintenance, difficulty in obtaining model parameters, and excessive errors in calculation results and loss of reference significance caused by inadequate model maintenance.

[0218] Embodiment 3:

[0219] Based on the same inventive concept, the present invention also provides a computer device, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding functions, so as to implement the steps of the method in the above embodiment.

[0220] Embodiment 4:

[0221] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both a built-in storage medium in a computer device and an extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the method in the above embodiment.

[0222] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0223] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0224] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0225] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0226] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0227] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for evaluating multi-voltage level closed loop operation in an urban power grid, characterized in that: include: Acquire multiple types of data related to the points to be closed in multiple voltage levels of the urban power grid, calculate the equivalent impedances of the power transmission end and the power receiving end on both sides of the points to be closed in multiple voltage levels of the urban power grid based on the multiple types of data, perform through-flow calculation based on the equivalent impedance and the power flow data of the power transmission end and the power receiving end, and obtain the bus voltage difference; Selecting a minimum range of bus voltage difference to determine the current online or future planned load value, and determining the alarm threshold of the to-be-closed point in multiple voltage levels of the urban power grid based on the current online or future planned load value; Based on the bus voltage difference, the calculated value of the closing current of the point to be closed is determined, and the calculated value of the closing current is compared with the alarm threshold of the point to be closed. Based on the comparison result, the closing operation of the point to be closed in multiple voltage levels of the urban power grid is evaluated.

2. The method according to claim 1, characterized in that The multiple types of data include at least one type of data from the following: The planned data, historical data, online operation data of the closing points in multiple voltage levels of the urban power grid, and the local voltage and current phasor measurement data of the closing points.

3. The method according to claim 1, characterized in that The equivalent impedance includes: The busbar equivalent impedance from the closing point to the power transmission end, the busbar equivalent impedance from the closing point to the power receiving end, and the equivalent impedance of the entire closing line.

4. The method according to claim 3, characterized in that The function expression for calculating the busbar equivalent impedance from the closing point to the transmission end is as follows: Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, ΔU1' is the change in bus voltage at the transmission end when the loop is closed, Q1 and Q1' are the reactive power at the transmission end before and at the minimum phase difference moment, I1 and I1' are the bus currents at the transmission end before and at the minimum phase difference moment, and Z1 is the bus equivalent impedance from the closing point to the transmission end.

5. The method according to claim 3, characterized in that: The function expression for calculating the busbar equivalent impedance from the closing point to the receiving end is as follows: Among them, U2 and U2' are the bus phase voltages at the receiving end before and at the minimum phase difference moment, ΔU2' is the change in bus voltage at the receiving end when the loop is closed, Q2 and Q2' are the reactive power at the receiving end before and at the minimum phase difference moment, I2 and I2' are the bus currents at the receiving end before and at the minimum phase difference moment, and Z2 is the bus equivalent impedance from the closing point to the receiving end.

6. The method according to claim 3, characterized in that The function expression for calculating the equivalent impedance of the entire closed-loop line is as follows: Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, respectively; ΔU1' is the bus voltage change at the transmission end when the loop is closed; U2' is the bus phase voltage at the receiving end at the minimum phase difference moment; ΔU2' is the bus voltage change at the receiving end when the loop is closed; Z is the equivalent impedance of the entire closed-loop line; Q1 is the reactive power at the transmission end before the minimum phase difference moment; Q2' is the reactive power at the receiving end at the minimum phase difference moment; and P2' is the active power at the receiving end at the minimum phase difference moment.

7. The method according to claim 1, characterized in that After performing the through flow calculation, the method further includes: Whether the closing condition is met is determined according to the through flow to determine the closing operation time of the tie switches at both the power transmission end and the power receiving end. The judgment function is expressed as one of the following: S1-S T ≤η×S LLmax Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, S LLmax It is the allowable load of the tie switch closing line.

8. The method according to claim 1, characterized in that After performing the through flow calculation, the method further includes: Whether the closing condition is met is determined according to the through flow to determine the closing operation time of the tie switch at the closing point. The judgment function is expressed as one of the following: Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, I LLmax For the allowable current, U1 is the bus phase voltage at the power transmission end before the minimum phase difference, and U2 is the bus phase voltage at the power receiving end before the minimum phase difference.

9. The method according to claim 1, characterized in that: After performing the through flow calculation, the method further includes: The loop closing operation on the receiving end allows flow judgment, and the judgment function expression is as follows: S2+S T ≤η×S 2LLmax Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through-flow current, η is the reliability coefficient, S 2LLmax It is the allowable load of the closed-loop line at the receiving end.

10. The method according to claim 1, characterized in that After performing the through flow calculation, the method further includes: According to the through flow, it is judged whether the closing condition is met to decide whether to control the receiving end on the closing line to perform the closing operation. The judgment function expression is as follows: Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through flow, η is the reliability coefficient, U2 is the bus phase voltage at the receiving end before the minimum phase angle difference, I N is the maximum allowable current.

11. The method according to claim 1, characterized in that: The functional expression for the through flow calculation is as follows: Among them, ΔU is the bus voltage difference between the power transmission end and the power receiving end, S1 is the load flow of the closed-loop line at the power transmission end, S2 is the load flow of the closed-loop line at the power receiving end, S T For the through flow, U1 is the bus phase voltage at the transmission end before the minimum phase difference, U2 is the bus phase voltage at the receiving end before the minimum phase difference, Z1 is the bus equivalent impedance from the closing point to the transmission end, Z2 is the bus equivalent impedance from the closing point to the receiving end, and Z is the equivalent impedance of the entire closed line.

12. A system for evaluating multi-voltage level closed loop operation of urban power grid, characterized in that: include: The first calculation unit is used to obtain multiple types of data related to the loop points to be closed in multiple voltage levels of the urban power grid, calculate the equivalent impedance of the power transmission end and the power receiving end on both sides of the loop points to be closed in multiple voltage levels of the urban power grid based on the multiple types of data, and perform a through flow calculation based on the equivalent impedance and the power flow data of the power transmission end and the power receiving end to obtain the bus voltage difference; The second calculation unit is used to select the minimum range interval of the bus voltage difference to determine the current online or future planned load value, and determine the alarm threshold of the to-be-closed point in multiple voltage levels of the urban power grid based on the current online or future planned load value; An evaluation unit is used to determine the calculated value of the closing current of the point to be closed based on the bus voltage difference, compare the calculated value of the closing current with the alarm threshold of the point to be closed, and evaluate the closing operation of the point to be closed in multiple voltage levels of the urban power grid based on the comparison result.

13. The system according to claim 12, characterized in that The multiple types of data include at least one type of data from the following: The planned data, historical data, online operation data of the closing points in multiple voltage levels of the urban power grid, and the local voltage and current phasor measurement data of the closing points.

14. The system according to claim 12, characterized in that The equivalent impedance includes: The busbar equivalent impedance from the closing point to the power transmission end, the busbar equivalent impedance from the closing point to the power receiving end, and the equivalent impedance of the entire closing line.

15. The system according to claim 14, characterized in that The function expression for calculating the busbar equivalent impedance from the closing point to the transmission end is as follows: Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, ΔU1' is the change in bus voltage at the transmission end when the loop is closed, Q1 and Q1' are the reactive power at the transmission end before and at the minimum phase difference moment, I1 and I1' are the bus currents at the transmission end before and at the minimum phase difference moment, and Z1 is the bus equivalent impedance from the closing point to the transmission end.

16. The system according to claim 14, characterized in that The function expression for calculating the busbar equivalent impedance from the closing point to the receiving end is as follows: Among them, U2 and U2' are the bus phase voltages at the receiving end before and at the minimum phase difference moment, ΔU2' is the change in bus voltage at the receiving end when the loop is closed, Q2 and Q2' are the reactive power at the receiving end before and at the minimum phase difference moment, I2 and I2' are the bus currents at the receiving end before and at the minimum phase difference moment, and Z2 is the bus equivalent impedance from the closing point to the receiving end.

17. The system according to claim 14, characterized in that The function expression for calculating the equivalent impedance of the entire closed-loop line is as follows: Among them, U1 and U1' are the bus phase voltages at the transmission end before and at the minimum phase difference moment, respectively; ΔU1' is the bus voltage change at the transmission end when the loop is closed; U2' is the bus phase voltage at the receiving end at the minimum phase difference moment; ΔU2' is the bus voltage change at the receiving end when the loop is closed; Z is the equivalent impedance of the entire closed-loop line; Q1 is the reactive power at the transmission end before the minimum phase difference moment; Q2' is the reactive power at the receiving end at the minimum phase difference moment; and P2' is the active power at the receiving end at the minimum phase difference moment.

18. The system according to claim 12, characterized in that The first calculation unit is further used to: after calculating the through-flow, determine whether the closing condition is met according to the through-flow, so as to determine the closing operation time of the tie switches at both ends of the power transmission end and the power receiving end, and the judgment function is expressed as one of the following: S1-S T ≤η×S LLmax Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, S LLmax It is the allowable load of the tie switch closing line.

19. The system according to claim 12, characterized in that The first calculation unit is further used to: after calculating the through-flow, determine whether the closing condition is met according to the through-flow, so as to determine the closing operation time of the tie switch at the closing point, and the judgment function is expressed as one of the following: Among them, S1 is the load flow of the closed-loop line at the transmission end, S T is the through-flow current, η is the reliability coefficient, I LLmax For the allowable current, U1 is the bus phase voltage at the power transmission end before the minimum phase difference, and U2 is the bus phase voltage at the power receiving end before the minimum phase difference.

20. The system according to claim 12, characterized in that The first calculation unit is also used to: after performing the through-flow calculation, perform a loop closing operation on the receiving end to allow flow judgment, and the judgment function expression is as follows: S2+S T ≤η×S 2LLmax Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through-flow current, η is the reliability coefficient, S 2LLmax It is the allowable load of the closed-loop line at the receiving end.

21. The system according to claim 12, characterized in that The first calculation unit is further used to: after calculating the through flow, determine whether the closing condition is met according to the through flow, so as to determine whether to control the receiving end on the closing line to perform the closing operation, and the judgment function expression is as follows: Among them, S2 is the load flow of the closed-loop line at the receiving end, S T is the through flow, η is the reliability coefficient, U2 is the bus phase voltage at the receiving end before the minimum phase angle difference, I N is the maximum allowable current.

22. The system according to claim 12, characterized in that The functional expression for the through flow calculation is as follows: Among them, ΔU is the bus voltage difference between the power transmission end and the power receiving end, S1 is the load flow of the closed-loop line at the power transmission end, S2 is the load flow of the closed-loop line at the power receiving end, S T For the through flow, U1 is the bus phase voltage at the transmission end before the minimum phase difference, U2 is the bus phase voltage at the receiving end before the minimum phase difference, Z1 is the bus equivalent impedance from the closing point to the transmission end, Z2 is the bus equivalent impedance from the closing point to the receiving end, and Z is the equivalent impedance of the entire closed line.

23. A computer device, characterized in that: include: one or more processors; a processor for executing one or more programs; When the one or more programs are executed by the one or more processors, the method according to any one of claims 1 to 11 is implemented.

24. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed, the method according to any one of claims 1 to 11 is implemented.

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