A method for automatically closing a loop of a power distribution network across a 30-degree angle difference

Abstract

The application discloses a kind of methods of power distribution network across 30 degrees angle difference automatic loop closing, belong to power distribution network technical field.The method includes constructing the typical distribution line of power distribution network across 30 degrees angle difference, obtains the real-time operating condition parameter of typical distribution line;According to real-time operating condition parameter, the switch protection setting value of typical distribution line is calculated;According to real-time operating condition parameter, the loop closing current is calculated, constructs safe loop closing condition, executes loop closing operation.Can be realized in the automatic loop closing between the distribution line of power distribution network existing 30 degrees phase difference, reduce the influence of power failure on user.Solved the problem of prior art exists "if ring-opening switch is refused to move due to primary equipment mechanism or secondary communication abnormality etc., causes the simultaneous tripping of two line station switches participating in load transfer".

Description

Technical Field

[0001] This application relates to the field of power distribution network technology, and in particular to a method for automatic loop closing of a power distribution network across a 30-degree angle difference. Background Technology

[0002] The statements in this section merely refer to the background art relevant to this application and do not necessarily constitute prior art.

[0003] In existing power distribution networks, due to differences in the Y / Δ wiring configurations of the main transformers in upstream substations, some interconnecting lines have a 30-degree phase angle difference. According to current dispatching regulations, these lines are not allowed to be closed-loop dispatched; a "break-then-close" power outage method must be used for load transfer, inevitably causing short-term power outages for users. To minimize the impact of power outages on users, operations are generally scheduled at night or in the early morning. However, during severe winters or hot summers, such operations pose a serious challenge to the physical condition of line maintenance personnel. In recent years, some power supply companies in the province have routinely implemented "one-click power transfer" power outage operations using the advanced functions of the new generation of distribution automation systems, controlling outage duration to around 10 seconds, essentially achieving "zero-perception" of power outages for customers. However, this still cannot solve the problem of power outages in areas with low-voltage tripping functions. The closing and opening / closing of loops with phase differences on both sides of the interconnecting switches in distribution lines, especially the 30-degree phase angle difference caused by the wiring configuration of the upstream main transformer, has always been a difficult problem to solve in the power distribution network.

[0004] Currently, 30-degree angle difference loop closing operation has not been officially carried out in China. Only simple loop closing calculation methods can be found in some papers. The steady-state current generated by loop closing is related to the voltage difference, angle difference, loop impedance and load current on both sides of the loop closing point. However, due to factors such as the variety of T-connected equipment, transformer load fluctuations, and uneven low-voltage photovoltaic power generation, it is impossible to accurately calculate the magnitude of the loop closing current. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a method for automatic loop closing in a distribution network across a 30-degree angle difference. First, a typical distribution line with a 30-degree angle difference is proposed. Then, the switch settings under normal operating conditions are theoretically calculated. Finally, based on the allowable current of the line, the switch settings for automatic loop closing under the closed state are set, ultimately achieving the purpose of loop closing operation across a 30-degree angle difference.

[0006] This application provides a method for automatic loop closing in a power distribution network across a 30-degree angle difference; A method for automatic loop closure of a power grid across a 30-degree angle difference includes: Construct a typical power distribution line across a 30-degree angle difference in the power distribution network and obtain the real-time operating parameters of the typical power distribution line; Calculate the switch protection settings for typical power distribution lines based on real-time operating parameters; Based on real-time operating parameters, calculate the current after loop closure, construct safe loop closure conditions, and execute the loop closure operation.

[0007] Furthermore, the typical power distribution line includes a first substation, a second substation, and a third substation. The 35kV busbar side of the third substation is electrically connected to the first transformer of the first substation, and the 110kV busbar side of the third substation is electrically connected to the second transformer of the second substation. A tie switch is installed between the first substation and the second substation, forming a loop between them.

[0008] Furthermore, the first substation also includes a first circuit breaker, a first busbar, and a first outgoing circuit breaker connected in sequence, and the second substation also includes a second circuit breaker, a first busbar, and a second outgoing circuit breaker connected in sequence. A first intermediate circuit breaker is installed between the first outgoing circuit breaker and the tie switch, and a second intermediate circuit breaker is installed between the second outgoing circuit breaker and the tie switch.

[0009] Furthermore, the calculation of the switch protection settings for a typical power distribution line specifically involves: Based on the line fault status, the magnitude of the short-circuit current, the line operating current, and the positive definiteness of the sensitivity, the magnitude of the protection current of each protection device in the line is calculated. Based on the distribution of each protection device in the line, calculate the timing overcurrent protection action time of each protection device in the line.

[0010] Furthermore, the line fault states include time-limited instantaneous overcurrent, overvoltage blocking overcurrent, current instantaneous overcurrent, and timed overcurrent.

[0011] Furthermore, the real-time operating parameters include the maximum allowable current of the line, the line operating current, and the circuit breaking current.

[0012] Furthermore, the specific conditions for constructing a secure loop are as follows: The load current after loop closure is less than 80% of the line operating current; Adjust the timing overcurrent protection action time of the first outgoing circuit breaker of the first substation and the second outgoing circuit breaker of the second substation to create a step difference of 0.2s; Adjust the switch protection settings of each protection device in the line to the calculated values.

[0013] Furthermore, the specific steps of performing the loop closing operation are as follows: Close the interconnection switch between the first and second substations in a typical power distribution line; If the load current after loop closure is greater than 80% of the line operating current, the first intermediate circuit breaker between the first substation and the tie switch in a typical distribution line will automatically trip, and the loop will be successfully disconnected; if the load current after loop closure is less than 80% of the line operating current, the first intermediate circuit breaker will be manually disconnected.

[0014] Furthermore, it also includes: After the loop closing operation is completed, the switch protection settings of each protection device in the line are adjusted back to their original protection settings.

[0015] Furthermore, it also includes: Each time the loop is closed, a portable waveform recorder is used to measure the loop closure current.

[0016] Compared with the prior art, the beneficial effects of this application are: 1. The technical solution provided in this application can realize automatic loop closing between power distribution lines with a 30-degree phase difference in the power distribution network, reducing the impact of power outages and power adjustments on users.

[0017] The technical solution provided in this application adjusts the action time of the timed overcurrent protection of the switch inside the station to form a step difference of 0.2S, so as to prevent the 10kV Diyi Line 011 switch and Ningyi Line 012 switch from tripping simultaneously when the external de-loop switch fails to trip when it should, thereby improving the reliability of power dispatching. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0019] Figure 1 A flowchart illustrating an embodiment of this application; Figure 2 A schematic diagram of the connection of a power distribution line with a 30-degree angle difference provided in an embodiment of this application; Figure 3 This is a schematic diagram of 10 kV line protection setting calculation provided in an embodiment of this application; Figure 4 A schematic diagram for calculating short-circuit current at the installation points of various levels of 10 kV protection provided in this application embodiment; Figure 5 This application provides schematic diagrams of phase-to-phase short-circuit protection settings for various protection levels in its embodiments. Figure 6 This is a schematic diagram of the protection settings during the loop closing operation of each level of switch provided in the embodiments of this application. Detailed Implementation

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0021] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. Furthermore, it should be understood that the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or apparatus.

[0022] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0023] Example 1 This application provides a method for automatic loop closing across a 30-degree angle difference in a distribution network. Next, in conjunction with... Figure 1-2 This embodiment provides a detailed description of a method for automatic loop closing across a 30-degree angle difference in a power distribution network.

[0024] A method for automatic loop closing in a power distribution network across a 30-degree angle difference includes the following steps: S1. Construct a typical power distribution line across a 30-degree angle difference in the power distribution network and obtain the real-time operating parameters of the typical power distribution line. For example, a typical power distribution line includes a first substation, a second substation, and a third substation. The 35kV busbar of the third substation is electrically connected to the first transformer of the first substation, and the 110kV busbar of the third substation is electrically connected to the second transformer of the second substation. A tie switch is installed between the first and second substations, forming a loop between them. The first substation also includes a first circuit breaker, a first busbar, and a first outgoing circuit breaker connected in sequence. The second substation also includes a second circuit breaker, a first busbar, and a second outgoing circuit breaker connected in sequence. A first intermediate circuit breaker is installed between the first outgoing circuit breaker and the tie switch, and a second intermediate circuit breaker is installed between the second outgoing circuit breaker and the tie switch.

[0025] Next, with Figure 2Taking a typical power distribution line as an example, a detailed description is provided. The 35kV busbar side of the 220kV substation is electrically connected to the transformer of the 35kV substation, and the 110kV busbar side of the 220kV substation is electrically connected to the transformer of the 110kV substation. A tie switch 00 is installed between the 35kV and 220kV substations, forming a loop between them. The 35kV substation also includes a first circuit breaker 001, the 10kV busbar, and the 011 switch, which are connected in sequence. The first circuit breaker 001 is electrically connected to the transformer of the 35kV substation. The 110kV substation also includes a second circuit breaker 002, the 10kV busbar, and the 012 switch, which are connected in sequence. The second circuit breaker 002 is electrically connected to the transformer of the 110kV substation. A first intermediate circuit breaker ZJ01 is installed between switch 011 of the power line and switch 00 of the tie line, and a second intermediate circuit breaker ZJ02 is installed between switch 012 of the Ning line and switch 00 of the tie line.

[0026] Under the same 220kV power grid system, there is often a 30-degree phase angle difference between the 10kV lines distributed from the 35kV substation and the 10kV lines distributed from the 110kV substation, and there is also a 30-degree phase angle difference at the 10kV tie switch.

[0027] The known conditions for this typical power distribution line are as follows: The base capacity is 1000MVA, the main transformer capacity is 63MVA, the rated current on the low-voltage side is 3464A, and the impedance of the 10kV bus system is: 4* for large-scale and 6* for small-scale (per-unit values, recommended parameters); the lengths of each conductor section are as follows: Figure 3 As shown, the cable line impedance is 0.1Ω / kM, the overhead line impedance is 0.4Ω / kM, the outgoing circuit breaker's distribution transformer capacity is 12500kVA, the intermediate circuit breaker's distribution transformer capacity is 4000kVA; the sectionalizing circuit breaker FJ's distribution transformer capacity is 2*1250kVA, each transformer's impedance is 40* (per-unit value, recommended parameter); all circuit breaker CT ratios are 600 / 5, and the line allowable current is 600A.

[0028] S2. Calculate the switch protection settings for typical power distribution lines based on real-time operating parameters; Under line fault conditions, the calculation results of the short-circuit current are as follows: Figure 4 As shown, the calculation method for the short-circuit current is the existing method used in substations, and will not be elaborated further here. Based on the short-circuit current magnitude, the calculation process for the protection settings of each level of switch is as follows: S201, Protection setting calculation for the 10kV side circuit breakers of the main transformer (circuit breaker 001, circuit breaker 002) (1) Time-limited rapid interruption a) Under time-limited instantaneous tripping conditions, a metallic short-circuit fault occurs on this side of the 10kV busbar (the short-circuit circuit is...). Figure 4 If K1 (small) has a sensitivity setting of 1.5 times, then I dzj =½√3*Short-circuit current / Sensitivity=0.866*9167 / 1.5=5292A.

[0029] Based on the four basic requirements of relay protection (selectivity, speed, sensitivity, and reliability), in order to ensure safety during loop closing, the protection current is set to 5300A, tripping the sectional circuit breaker (bus tie switch in the station) in 0.6S, blocking the automatic transfer switch of the sectional circuit breaker (bus tie switch in the station) on this side, and tripping the circuit breaker on this side in 0.8S (value selected considering all factors).

[0030] (2) Overcurrent blocking under pressure a) Set according to the rated current of the transformer side.

[0031] I dzl =Calculation coefficient * Low-voltage side current of main transformer = 1.5 * 3464 = 5196A.

[0032] b) When a metallic short-circuit fault (K1 small) occurs on this side of the busbar, the sensitivity is not less than 1.5 times.

[0033] I dzj =½√3 * short-circuit current / sensitivity = 0.866 * 9167 / 1.5 = 5292A The protection current of the 10kV side circuit breaker of the main transformer is 5200A. It trips the sectional (bus tie) circuit breaker in 1.1 seconds, blocks the automatic transfer of the sectional (bus tie) circuit breaker on this side, and trips the circuit breaker on this side in 1.4 seconds.

[0034] S202, Calculation of DL protection settings for outgoing circuit breakers (1) Instantaneous overcurrent a) This is a public line; therefore, the sectionalizing circuit breaker FJ3 should not be within the protection range of this section and must be avoided. Fault at the installation location of the sectionalizing circuit breaker FJ3 (K6 major).

[0035] I dzj =Reliability coefficient * Fault current at K6 = 1.35 * 11000 = 14850A.

[0036] b) The calculated value is greater than the maximum short-circuit current of the 10kV busbar, 13750A (K1 large), meaning the protection will not operate if a fault occurs at the line outlet. Therefore, based on the calculation that the protection has 1.2 times the sensitivity for a fault at the end of this protection range (K6 small), a voltage blocking element is added.

[0037] Protection current of current-carrying elements: I dzj=½√3 * short-circuit circuit / sensitivity coefficient = 0.866 * 7857 / 1.2 = 5670A The protection current of the outgoing circuit breaker DL is 5600A, and the timed overcurrent protection action time is 0S.

[0038] (2) Time-limited rapid interruption a) The coordination requirements of the time-limited instantaneous overcurrent protection of the upstream transformer should be met.

[0039] I dzj =Time-limited instantaneous overcurrent protection setting value of 10kV side circuit breaker of main transformer * reliability coefficient = 5300 / 2 = 2650A b) It is advisable to avoid the inrush current of the distribution transformers it is connected to, and set the current according to twice the rated current of all the distribution transformers it is connected to.

[0040] I dzj =2 * (capacity of distribution transformer connected to outgoing circuit breaker / √3 / voltage) 2 * (12500 / 1.732 / 10) = 1443A c) It is advisable to avoid faults on the low-voltage side of the distribution transformer (K10 is large).

[0041] I dzj =Reliability factor * Fault current at K10 = 1.35 * 1222 = 1650A The protection current of the outgoing circuit breaker DL is 2400A, and the timed overcurrent protection action time is 0.4S.

[0042] (3) Timed overcurrent a) Coordination requirements with the overcurrent protection of the overvoltage lockout of the upper transformer.

[0043] Idzj = Protection current of the 10kV side circuit breaker of the main transformer / coordination coefficient = 5200 / 2 = 2600A (Considering the successive faults of the two lines, the protection setting of the outgoing circuit breaker of the line needs to match the protection setting of the main transformer. Take the higher coordination coefficient, which is 2). b) The current should be avoided from the maximum load current and should be set at 1.5 times the maximum allowable load current.

[0044] I dzj =Setting factor * Line allowable current = 1.5 * 600 = 900A The protection current of the outgoing circuit breaker DL is 960A, and the timed overcurrent protection action time is 0.6S.

[0045] S203, Calculation of protection settings for intermediate circuit breaker ZJ (1) Time-limited rapid interruption a) Coordination with the time-limited instantaneous overcurrent protection of the upstream circuit breaker (outgoing circuit breaker DL) to meet the selectivity requirements of relay protection.

[0046] I dzj =Protection current of outgoing circuit breaker / Coordination factor = 2400 / 1.2 = 2000A b) It is advisable to avoid the inrush current of the distribution transformers it is connected to, and the current can be set at twice the rated current of all the distribution transformers it is connected to.

[0047] Idzj = 2 * (capacity of distribution transformer connected to intermediate circuit breaker / √3 / voltage) = 2 * (4000 / 1.732 / 10) = 462A C) The current should not be less than 600A, which is the allowable current of the line.

[0048] I dzj =Protection setting matching coefficient * Line allowable current = 1.2 * 600 = 720A The protection current of the intermediate circuit breaker ZJ is 780A, and the timed overcurrent protection action time is 0.4S. (2) Timed overcurrent: a) Coordination with the timing overcurrent protection of the upstream circuit breaker (outgoing circuit breaker DL).

[0049] I dzj =Outgoing circuit breaker protection current / Protection setting matching coefficient = 960 / 1.2 = 800A b) The sensitivity should be no less than 1.3 times when a metallic short-circuit fault (K3 small) occurs at the end of this protection range.

[0050] I dzj ==√3 / 2*Short-circuit current at K3 / Sensitivity coefficient=0.866*873 / 1.3=581A c) The current should be kept below the maximum load current and should not be less than the line's allowable current of 600A.

[0051] Idzj = Protection setting matching coefficient * (Capacity of distribution transformer connected to intermediate circuit breaker / √3 / Voltage) = 1.5 * (4000 / 1.732 / 10) = 347A The protection current of the intermediate circuit breaker ZJ is 540A, and the timing overcurrent protection action time is 0.6S. 4. Calculation of protection settings for the interconnecting switch (1) Time-limited rapid interruption a) Coordination with the time-limited instantaneous overcurrent protection of the upstream circuit breaker (outgoing circuit breaker DL) I dzj =Outgoing circuit breaker protection current / coordination factor = 2400 / 1.2 = 2000A b) It is advisable to avoid the inrush current of the distribution transformers it is connected to, and the current can be set at twice the rated current of all the distribution transformers it is connected to.

[0052] Idzj =2*(Capacity of distribution transformer connected to outgoing circuit breaker / / √3 / voltage)=2*(12500 / 1.732 / 10)=1444A C) Coordination with the time-limited instantaneous overcurrent protection of the intermediate circuit breaker.

[0053] I dzj >720A Based on the requirements of a, b, and c, the protection current of the tie switch is set at 1800A, and the timing overcurrent protection operation time is 0S.

[0054] (2) Timed overcurrent: a) Coordination with the timing overcurrent protection of the upstream circuit breaker (outgoing circuit breaker DL) to meet the selectivity of relay protection.

[0055] Idzj = Protection current of outgoing circuit breaker / Coordination factor = 960 / 1.2 = 800A The protection current of the interconnection switch is 840A, and the timing overcurrent protection action time is 0.3S.

[0056] S3. Calculate the loop closing current based on real-time operating parameters, construct safe loop closing conditions, and execute the loop closing operation.

[0057] For example, taking the "closing and switching of the load on the line between the ZJ01 intermediate circuit breaker and the 00 tie switch of the 10kV Dianyi Line to the 10kV Ningyi Line" as an example, the 00 tie switch is the closing switch and the ZJ01 intermediate circuit breaker is the opening switch. The operation steps are explained as follows: S301. The calculated load current after loop closure must be less than the line operating current of 600A*80%=480A to ensure that the connecting line is not overloaded after the load is transferred.

[0058] S302. Adjust the timing overcurrent protection action time of 10kV Diyi Line 011 switch and Ningyi Line 012 switch to form a step difference of 0.2S, so as to prevent 10kV Diyi Line 011 switch and Ningyi Line 012 switch from tripping simultaneously when the external disconnection switch fails to trip as it should.

[0059] S303, Adjust the protection settings of the 10kV Dianyi Line ZJ01 intermediate circuit breaker, Lianhe 00 switch, and 10kV Ningyi Line ZJ02 intermediate circuit breaker.

[0060] (1) The setting value of the 10kV line ZJ01 intermediate circuit breaker should be set to avoid the maximum load current and be set at 1.5 times the maximum allowable load current.

[0061] I dzj =1.5 * Line allowable current = 1.5 * 600 = 900A The protection current of the 10kV ZJ01 intermediate circuit breaker is 900A, and the timed overcurrent protection action time is 0S.

[0062] (2) The protection of the 00 switch and the 10kV Ningyi Line ZJ02 intermediate circuit breaker is deactivated.

[0063] S304. Perform the loop closing operation. Close the tie 00 switch to close the loop. If the load current after loop closing is greater than 900A, the 10kV line ZJ01 intermediate circuit breaker will automatically trip, and the loop will be successfully closed. If the load current after loop closing is less than 900A, the 10kV line ZJ01 intermediate circuit breaker needs to be manually opened to manually close the loop.

[0064] S305. After the loop closing operation is completed, the 10kV Ningyi Line 012 switch, the 10kV Dianying Line ZJ01 intermediate circuit breaker, the Lianhe 00 switch, and the 10kV Ningyi Line ZJ02 intermediate circuit breaker shall be restored to their original protection settings.

[0065] S306. Each time the loop is closed, a portable waveform recorder is used to measure the loop current for data reference during the next loop closure adjustment.

[0066] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for automatic loop closure across a 30-degree angle difference in a power distribution network, characterized in that, include: Construct a typical power distribution line across a 30-degree angle difference in the power distribution network and obtain the real-time operating parameters of the typical power distribution line; Calculate the switch protection settings for typical power distribution lines based on real-time operating parameters; The typical power distribution line includes a first substation, a second substation, and a third substation. The 35kV busbar side of the third substation is electrically connected to the first transformer of the first substation, and the 110kV busbar side of the third substation is electrically connected to the second transformer of the second substation. A connecting switch is installed between the first substation and the second substation, and a loop is formed between the first substation and the second substation through the connecting switch. The first substation also includes a first circuit breaker, a first busbar, and a first outgoing circuit breaker connected in sequence. The second substation also includes a second circuit breaker, a first busbar, and a second outgoing circuit breaker connected in sequence. A first intermediate circuit breaker is provided between the first outgoing circuit breaker and the tie switch, and a second intermediate circuit breaker is provided between the second outgoing circuit breaker and the tie switch. Based on real-time operating parameters, calculate the current after loop closure, construct safe loop closure conditions, and execute the loop closure operation. The specific conditions for constructing a secure loop are as follows: The load current after loop closure is less than 80% of the line operating current; Adjust the timing overcurrent protection action time of the first outgoing circuit breaker of the first substation and the second outgoing circuit breaker of the second substation to create a step difference of 0.2s; Adjust the switch protection settings of each protection device in the line to the calculated values.

2. The method for automatic loop closure across a 30-degree angle difference in a distribution network as described in claim 1, characterized in that, The specific calculation of the switch protection settings for a typical power distribution line is as follows: Based on the line fault status, the magnitude of the short-circuit current, the line operating current, and the positive definiteness of the sensitivity, the magnitude of the protection current of each protection device in the line is calculated. Based on the distribution of each protection device in the line, calculate the timing overcurrent protection action time of each protection device in the line.

3. The method for automatic loop closure across a 30-degree angle difference in a distribution network as described in claim 1, characterized in that, Line fault conditions include time-limited instantaneous overcurrent, overvoltage blocking overcurrent, instantaneous current overcurrent, and timed overcurrent.

4. The method for automatic loop closure across a 30-degree angle difference in a distribution network as described in claim 1, characterized in that, The real-time operating parameters include the maximum allowable current of the line, the line operating current, and the circuit breaking current.

5. The method for automatic loop closure across a 30-degree angle difference in a distribution network as described in claim 1, characterized in that, The specific steps of performing the loop closing operation are as follows: Close the interconnection switch between the first and second substations in a typical power distribution line; If the load current after loop closure is greater than 80% of the line operating current, the first intermediate circuit breaker between the first substation and the tie switch in a typical distribution line will automatically trip, and the loop will be successfully disconnected; if the load current after loop closure is less than 80% of the line operating current, the first intermediate circuit breaker will be manually disconnected.

6. The method for automatic loop closure across a 30-degree angle difference in a distribution network as described in claim 1, characterized in that it further... include: After the loop closing operation is completed, the switch protection settings of each protection device in the line are adjusted back to their original protection settings.

7. The method for automatic loop closure across a 30-degree angle difference in a distribution network as described in claim 1, characterized in that, Also includes: Each time the loop is closed, a portable waveform recorder is used to measure the loop closure current.

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