A distribution line adaptive reclosing method

Abstract

A distribution line adaptive reclosing method belongs to the field of distribution automation technology. It is characterized by comprising the following steps: step a, judging whether a distribution line fails; step b, obtaining the bus voltage before tripping; step c, judging whether the bus voltage before tripping meets the first judgment range; step d, judging whether the bus voltage before tripping meets the second judgment range; steps e to f, respectively determining the off-grid time of DER in each judgment range; step g, respectively determining the reclosing waiting time of DER in each judgment range; step h, reclosing after the reclosing waiting time is reached. In this distribution line adaptive reclosing method, the bus voltage is supported by the main grid and is higher than the voltage of the distributed power source grid connection point. The monitored bus voltage is used to consider the supporting role of the distributed power source low voltage crossing on the main grid to infer the off-grid time of the distributed power source island protection action, so as to achieve the effect of fast adaptive reclosing.

Description

Technical Field

[0001] The invention discloses an adaptive reclosing method for a power distribution line, belonging to the technical field of power distribution automation. Background Art

[0002] In the existing technology, for distribution networks with a high penetration rate of distributed power sources, the fault current output by the inverter-type distributed power source (IIDG) is limited, and the current protection cannot be reliably operated. The distributed power source can only be cut off by anti-islanding protection. The existing anti-islanding protection mainly adopts the passive protection principle of detecting voltage / frequency, and the action time is generally less than 2s. When the frequency and voltage disturbances occur in the power system, it is easy to cause large-scale disconnection of distributed power sources from the grid, posing a threat to the stable operation of the power system.

[0003] The current standard "GB / T 29319-2012 Technical Regulations for Photovoltaic Power Generation System Access to Distribution Network" stipulates that when the voltage at the grid connection point of the photovoltaic power generation system exceeds the specified voltage range, power supply to the grid line should be stopped within the corresponding time. This requirement applies to any phase in a multi-phase system. However, the current measures to solve the above problems are to extend the anti-islanding protection action time limit and improve the system disturbance ride-through capability of distributed power sources. In the IEEE 1547 DER grid connection technical standard promulgated in 2018, the longest action time limit of anti-islanding protection has exceeded 300s. The extension of the anti-islanding protection action time limit will bring intolerable delays to the reclosing of distribution line faults, seriously affecting the reliability of power supply. If the anti-islanding protection is given priority and the anti-islanding protection action time is set to 2s, the problem of IIDG low voltage ride-through will be faced when the system is disturbed.

[0004] For distribution lines with high penetration of distributed power generation, if the distributed power generation has not exited when the reclosing is performed after the protection action trips, it is easy to cause secondary impact on distribution lines, distributed power generation and other equipment. Reclosing by checking no voltage requires the installation of line voltage transformers. However, since many substations are not equipped with line voltage transformers in practice, it is difficult to reclose by checking no voltage. If no voltage cannot be checked, considering that the inverter-type distributed power generation needs to ride through low voltage when the system is disturbed, the waiting time for reclosing may take several minutes, which seriously affects the reliability of power supply. Summary of the invention

[0005] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art and provide a distribution line adaptive reclosing method which utilizes the characteristics that the bus voltage is supported by the main grid and is higher than the voltage of the distributed power supply grid connection point, utilizes the monitored bus voltage, and considers the supporting effect of the low voltage crossing of the distributed power supply on the main grid to infer the grid-off time of the distributed power supply island protection action, so as to realize fast adaptive reclosing.

[0006] The technical solution adopted by the present invention to solve the technical problem is: the adaptive reclosing method for distribution lines is characterized by comprising the following steps:

[0007] Step a, determining whether a fault occurs in the power distribution line. If a fault occurs, executing step b. If no fault occurs, continuing to determine the fault in the line;

[0008] Step b: After a fault occurs in the distribution line, the main grid side and the distributed power supply inject current into the fault point at the same time. The line outlet protection trips after detecting the fault, and obtains the bus voltage before tripping. U l ;

[0009] Step c: Determine the bus voltage before tripping U l Whether it meets the first judgment range, if it is judged that the bus voltage before tripping U l Meet the first judgment range, execute step f, if it is judged that the bus voltage before tripping U l If the first determination range is not met, execute step d;

[0010] Step d: Determine the bus voltage before tripping U l Whether it meets the second judgment range, if it is judged that the bus voltage before tripping U l Meet the second judgment range, execute step f, if it is judged that the bus voltage before tripping U l If the second determination range is not met, execute step e;

[0011] Step e, when the bus voltage before tripping U l If the first judgment range and the second judgment range are not met, the bus voltage before tripping U l If the third determination range is met, step f is executed; the voltage values ​​of the first determination range, the second determination range, and the third determination range are decreased in sequence;

[0012] Step f, respectively determining the off-grid time of the DER under the satisfied determination range;

[0013] Step g, respectively determining the reclosing waiting time of the DER under the satisfied determination range;

[0014] Step h: After the reclosing waiting time is reached and all DERs are ensured to be off-grid, the reclosing operation is performed.

[0015] Preferably, between step g and step h, the method further includes determining a reclosing time, and the reclosing time is delayed based on the reclosing waiting time.

[0016] Preferably, the reclosing time is extended by 1-2s based on the reclosing waiting time.

[0017] Preferably, the first determination range is: bus voltage before tripping U l Satisfied: 0.5 pu ≤ U l <0.88 pu ; The second judgment range is: bus voltage before tripping U l Satisfied: 0.45 pu ≤ U l <0.5 pu ; The third judgment range is: bus voltage before tripping U l satisfy: U l <0.45 pu .

[0018] Preferably, in the step f, the bus voltage before tripping U l When the first judgment range is met, the low voltage ride-through time of Class I DER is 2s, the low voltage ride-through time of Class II DER is 10s, and the low voltage ride-through time of Class III DER is 21s; the bus voltage before tripping U l When the second judgment range is met, the low voltage ride-through time of Class I DER is 2s, the low voltage ride-through time of Class II DER is 10s, and the low voltage ride-through time of Class III DER is 2s; the bus voltage before tripping U l When the third determination range is met, the low voltage ride-through time of Category I DER is 0.16s, the low voltage ride-through time of Category II DER is 0.160s, and the low voltage ride-through time of Category III DER is 2s.

[0019] Preferably, in step g, the bus voltage before tripping U l When the first judgment range is met, the DER reclosing waiting time is 21s; the bus voltage before tripping U l When the second judgment range is met, the DER reclosing waiting time is 10s; the bus voltage before tripping U l When the third judgment range is met, the DER reclosing waiting time is 2s.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] In this distribution line adaptive reclosing method, the bus voltage is supported by the main grid and is higher than the voltage of the distributed power source grid connection point. The monitored bus voltage is used to consider the supporting role of the distributed power source low voltage ride-through on the main grid to infer the grid-trip time of the distributed power source island protection action, so as to achieve the effect of fast adaptive reclosing.

[0022] In this distribution line adaptive reclosing method, DER can provide reliable voltage support when disturbances occur in the power system, and can quickly reclose in the event of a fault, ensuring the stability of the operation of the new power system and the reliability of power supply.

[0023] In the adaptive reclosing method for distribution lines, it is not necessary to install a line voltage transformer, and coordination between the reclosing and the low voltage ride-through time of the anti-islanding protection can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The figure is a flow chart of the adaptive reclosing method for distribution lines.

[0025] Figure 2 Schematic diagram of the distribution line connected to distributed power sources. DETAILED DESCRIPTION

[0026] Figure 1~2 The best embodiment of the present invention is shown below in conjunction with the attached Figure 1~2 The present invention is further described.

[0027] like Figure 1 As shown, a distribution line adaptive reclosing method comprises the following steps:

[0028] Step 1001, start;

[0029] The adaptive reclosing method for the distribution line is started, and whether a fault occurs in the distribution line is detected.

[0030] Step 1002, determining whether a power distribution line fails;

[0031] Determine whether a fault occurs in the power distribution line. If a fault occurs, execute step 1003; if no fault occurs, return to step 1001.

[0032] Step 1003, obtaining the bus voltage before tripping U l ;

[0033] After a fault occurs on the distribution line, the main grid and distributed power sources inject current into the fault point at the same time. The line outlet protection detects the fault and the protection trips. The DER connected to the distribution line performs low voltage ride-through according to the low voltage ride-through requirements. After the protection trips, the reclosing is started, and the reclosing controller obtains the bus voltage before tripping. U l , the low voltage ride-through requirements of the DER connected to the line are known.

[0034] The idea of ​​the adaptive reclosing method for distribution lines is that the anti-islanding protection action time is related to the voltage. The lower the voltage at the grid connection point, the faster the anti-islanding protection action time.

[0035] Distributed power supply anti-islanding protection includes low voltage protection, which is generally used to trip when the line fails. The low voltage protection setting is known according to the regulations. The action time of the anti-islanding protection can be inferred based on the bus voltage before the fault, and the reclosing time can be coordinated with this time. Since the bus voltage is definitely higher than the voltage on the line, the time inferred by the bus voltage can only be slower than the actual low voltage protection action time of the distributed power supply on the line, not faster, so there will be no coordination problem.

[0036] By detecting the voltage before tripping (it is difficult to detect the voltage on the line side, the existing transformer can be used to detect the voltage on the bus side. The bus voltage is detected by the bus voltage transformer), the reclosing action time is set according to the pre-set anti-islanding protection action time considering low voltage crossing, so as to achieve the coordination of reclosing and anti-islanding protection and realize adaptive reclosing.

[0037] Step 1004, U l Whether the first determination range is satisfied;

[0038] Determine the bus voltage before tripping U l Whether it meets the first judgment range, the first judgment range is that the bus voltage meets: 0.5 pu ≤ U l <0.88 pu If the bus voltage before tripping is U l Satisfies the first determination range, execute step 1006. If it is determined that the bus voltage before tripping U l If the first determination range is not met, step 1005 is executed.

[0039] Step 1005, U l whether the second determination range is satisfied;

[0040] Determine the bus voltage before tripping U l Whether it meets the second judgment range, the second judgment range is that the bus voltage meets: 0.45 pu ≤ U l <0.5 pu If the bus voltage before tripping is U l Meet the second determination range, execute step 1006, if it is determined that the bus voltage before tripping U l If the second determination range is not satisfied, step 1006 is executed simultaneously.

[0041] Step 1006, determining the offline time of the DER under the satisfied determination range;

[0042] When the bus voltage U l If the above, first determination range and second determination range are not met, the bus voltage at this time can be determined U l satisfy: U l <0.45 pu (recorded as the third determination range).

[0043] Bus voltage before tripping (hereinafter referred to as bus voltage) U l When the first judgment range mentioned above is met, the bus voltage is greater than the DER grid connection point voltage. At this time, the Class I DER will be disconnected from the grid at most 2 seconds after the low voltage ride-through, the Class II DER will be disconnected from the grid at most 10 seconds after the low voltage ride-through, and the Class III DER will be disconnected from the grid at most 21 seconds after the low voltage ride-through.

[0044] When the bus voltage U l When the above second judgment range is met, the bus voltage is greater than the DER grid connection point voltage. At this time, the Class I DER will be disconnected from the grid at most 2 seconds after the low voltage ride-through, the Class II DER will be disconnected from the grid at most 10 seconds after the low voltage ride-through, and the Class III DER will be disconnected from the grid at most 2 seconds after the low voltage ride-through.

[0045] When the bus voltage U l When the third judgment range mentioned above is met, the bus voltage is greater than the DER grid connection point voltage at this time, and the Class I DER will be disconnected from the grid at most 0.16s after the low voltage ride-through, the Class II DER will be disconnected from the grid at most 0.16s after the low voltage ride-through, and the Class III DER will be disconnected from the grid at most 2s after the low voltage ride-through.

[0046] Step 1007, determining the reclosing waiting time of the DER under the satisfied determination range;

[0047] When the bus voltage U l When the first determination range is met, it can be seen from the above that the Class III DER requires the longest time for low voltage ride-through support and is disconnected from the grid the latest. In order to ensure that all DERs are disconnected from the grid when reclosing, the reclosing waiting time is the time required for low voltage ride-through by Class III DER: 21s.

[0048] When the bus voltage U l When the second judgment range is met, it can be seen from the above that the Class II DER requires the longest time for low voltage ride-through support and is disconnected from the grid the latest. In order to ensure that all DERs are disconnected from the grid when reclosing, the reclosing waiting time is the time required for low voltage ride-through by Class II DER: 10s.

[0049] When the bus voltage U l When the third determination range is met, it can be seen from the above that the Class III DER requires the longest time for low voltage ride-through support and is disconnected from the grid the latest. In order to ensure that all DERs are disconnected from the grid when reclosing, the reclosing waiting time is the time required for low voltage ride-through by Class III DER: 2s.

[0050] Step 1008, all DERs are disconnected from the network;

[0051] Reserve low voltage ride-through time for DERs according to the bus voltage, and ensure that all DERs are disconnected from the grid when the reclosing waiting time expires.

[0052] Step 1009, executing reclosing delay;

[0053] Combination Figure 2 In the actual distribution line, when a fault occurs at point F1, the voltage at the circuit breaker QF2 decreases, and the voltage at the distributed generation grid connection point PCC decreases. The bus voltage detected at QF2 must be higher than the voltage at the PCC point. The voltage at the PCC point is inferred based on the bus voltage detected before the circuit breaker QF2 trips, and the time of low voltage ride-through is determined. The reclosing time is extended by 1~2s based on the reclosing waiting time.

[0054] Step 1001, end;

[0055] When the preset delay time is reached, the reclosing switch is activated to control the circuit breaker to reclose.

[0056] If the distribution line that has tripped protection is connected to multiple distributed power sources, such as Class I and Class III at the same time, then the reclosing circuit breaker needs to be coordinated with the requirement for a relatively long low voltage ride-through time to avoid the situation where the line is still reclosed while there are still distributed power sources that have not been disconnected from the grid.

[0057] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A distribution line adaptive reclosing method, characterized in that: The steps include: Step a, determining whether a fault occurs in the power distribution line. If a fault occurs, executing step b. If no fault occurs, continuing to determine the fault in the line; Step b: After a fault occurs in the distribution line, the main grid side and the distributed power supply inject current into the fault point at the same time. The line outlet protection trips after detecting the fault, and obtains the bus voltage before tripping. U l ; Step c: Determine the bus voltage before tripping U l Whether it meets the first judgment range, if it is judged that the bus voltage before tripping U l Meet the first judgment range, execute step f, if it is judged that the bus voltage before tripping U l If the first determination range is not met, execute step d; Step d: Determine the bus voltage before tripping U l Whether it meets the second judgment range, if it is judged that the bus voltage before tripping U l Meet the second judgment range, execute step f, if it is judged that the bus voltage before tripping U l If the second determination range is not met, execute step e; Step e, when the bus voltage before tripping U l If the first judgment range and the second judgment range are not met, the bus voltage before tripping U l If the third determination range is met, step f is executed; the voltage values ​​of the first determination range, the second determination range, and the third determination range are decreased in sequence; Step f, respectively determining the off-grid time of the DER under the satisfied determination range; Step g, respectively determining the reclosing waiting time of the DER under the satisfied determination range; Step h: After the reclosing waiting time is reached and all DERs are ensured to be off-grid, the reclosing operation is performed.

2. The adaptive reclosing method for distribution lines according to claim 1, characterized in that: Between step g and step h, the method further includes determining a reclosing time, where the reclosing time is delayed based on the reclosing waiting time.

3. The adaptive reclosing method for distribution lines according to claim 2, characterized in that: The reclosing time is extended by 1 to 2 seconds based on the reclosing waiting time.

4. The adaptive reclosing method for distribution lines according to claim 1, characterized in that: The first determination range is: bus voltage before tripping U l Satisfied: 0.5 pu ≤ U l <0.88 pu ; The second judgment range is: bus voltage before tripping U l Satisfied: 0.45 pu ≤ U l <0.5 pu ; The third judgment range is: bus voltage before tripping U l satisfy: U l <0.45 pu .

5. The adaptive reclosing method for distribution lines according to claim 1, characterized in that: In step f, the bus voltage before tripping U l When the first judgment range is met, the low voltage ride-through time of Class I DER is 2s, the low voltage ride-through time of Class II DER is 10s, and the low voltage ride-through time of Class III DER is 21s; the bus voltage before tripping U l When the second judgment range is met, the low voltage ride-through time of Class I DER is 2s, the low voltage ride-through time of Class II DER is 10s, and the low voltage ride-through time of Class III DER is 2s; the bus voltage before tripping U l When the third determination range is met, the low voltage ride-through disconnection time of Category I DER is 0.16s, the low voltage ride-through disconnection time of Category II DER is 0.160s, and the low voltage ride-through disconnection time of Category III DER is 2s.

6. The adaptive reclosing method for distribution lines according to claim 1, characterized in that: In step g, the bus voltage before tripping U l When the first judgment range is met, the DER reclosing waiting time is 21s; the bus voltage before tripping U l When the second judgment range is met, the DER reclosing waiting time is 10s; the bus voltage before tripping U l When the third judgment range is met, the DER reclosing waiting time is 2s.

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