Unplanned island fault studying and judging locking method and system for new energy access power distribution network

Abstract

The invention provides an unplanned island fault research and judgment locking method and system for a new energy access power distribution network, and belongs to the technical field of power system control. Comprising the steps that after a fault section in a power distribution network is isolated, a section where distributed new energy in the fault area is located enters an unplanned island operation state under the condition that the distributed energy is matched with a load; an upstream section switch and a downstream section switch which are located on the two sides of the section where the distributed new energy is located detect the voltage of the grid-connected point and then are switched on in a delayed mode; after delay closing is finished, anti-islanding protection is started in the section where the distributed new energy is located due to power mismatching, and according to the positive sequence current flowing through the section switches in the voltage loss opening period within the Y time limit after the upstream section switch is closed and the residual voltage detected by the downstream section switch, the anti-islanding protection is started. And determining whether the two section switches start and execute the forward closing and locking function and the reverse closing and locking function or not.

Description

Technical Field

[0001] The present invention relates to the technical field of power system control, and in particular to a method and system for analyzing and locking an unplanned island fault in which a new energy source is connected to a power distribution network. Background Art

[0002] The voltage-time feeder automatic fault analysis method is completed through the mutual coordination of the transformer low-voltage side outgoing circuit breaker or recloser with the sectionalizer in time and voltage. When a fault occurs, the recloser or outgoing circuit breaker trips, and cooperates with the working characteristics of the sectionalizer "no-voltage opening, delayed closing on incoming power", and delays power supply step by step to achieve the positioning and isolation of the faulty section. At the same time, the forward closing lock function and the reverse closing lock function are set to realize automatic positioning and isolation of the faulty section. The forward closing lock function is for the switch connected upstream of the faulty section, and the reverse closing lock function is for the switch connected downstream of the faulty section.

[0003] like Figure 2 As shown in the figure, in the process of voltage-time feeder automation fault analysis, the end of the sectionalizer close to the power supply is generally set as the power supply side, and the other end is set as the load side. After the CB is reclosed twice, the fault section has been isolated, and the load needs to be transferred by closing the tie switch. The voltage is detected on the original load side of the sectionalizer, and the power supply side and the load side of the sectionalizer are interchanged.

[0004] When the CB trips, if the distributed energy in a certain section is exactly matched with the load, a short-term island operation will be formed. At this time, the voltage at the distributed energy grid connection point will increase to near the rated voltage. The two section switches adjacent to the grid connection point will detect that there is pressure on one side and delay closing. If the power does not match after closing, the island will be destroyed. According to the standard requirements, the anti-island protection will be activated within 2s after closing to make the distributed energy exit operation. The section switch detects the loss of pressure within the Y time limit and opens again and starts the forward closing lock function. The switch adjacent to the switch may also detect the instantaneous residual pressure and start the reverse closing lock function, resulting in the judgment of the fault section error or expansion.

[0005] Figure 2 A specific analysis is conducted by taking the case that a permanent fault occurs in the L4 section of the main branch line and the distributed energy and load on the line section between FSW2 and FSW3 form an island. When a permanent fault occurs in the L4 section of the main branch line and the CB trips, all section switches meet the double-side voltage loss tripping conditions and trip, and the timing starts from this time. (1) After the section switches lose voltage and trip, the distributed energy and load on the line section between FSW2 and FSW3 match each other, forming an island. At this time, the voltage at the grid connection point of the distributed new energy will increase to near the rated voltage. Voltage is detected on both the load side of FSW2 and the power side of FSW3, and the delay closing begins. The delay time is X, which is set to 7s. Figure 3 (2) After 7 seconds, the two switches are closed. If the distributed energy in the area does not match the load power after closing, the island is destroyed and the voltage will decrease. The anti-island protection will be activated within 2 seconds after closing to make the distributed energy stop running. Figure 4 (3) FSW2 and FSW3 immediately open the circuit breaker after detecting the loss of pressure on both sides within the Y time limit (set to 5s) after closing the circuit breaker, and start the positive closing lock function, that is, Figure 5 The load side of FSW2 is closed and locked, and the power side of FSW3 is closed and locked. If FSW1 detects instantaneous residual pressure, it will start the reverse closing lock function, that is, the power side of FSW1 is closed and locked. This process occurs within 7-9 seconds after the voltage loss trip; (4) 1.5 seconds after the voltage loss trip, the outgoing line circuit breaker CB is closed for the first time. FSW1 detects that there is voltage on the power side and delays for X time limit. It should close after 8.5 seconds, but during this process, the power side of FSW1 may have started the power side closing lock, so it will not delay closing. If there is a section switch upstream of FSW1, it will definitely close and lock before detecting voltage. At this time, the fault section judgment result is considered to be L2 section, and the fault section judgment is wrong; (5) If FSW1 does not have the function of detecting the instantaneous residual pressure reverse closing lockout, FSW1 will close smoothly at 8.5s; FSW2 detects voltage on the power supply side, and the FSW2 power supply side is not locked. After the delay X time limit, it will close smoothly at 15.5s; FSW3 detects voltage on the power supply side, but FSW3 will not close again even if there is voltage on the power supply side because the power supply side closing lockout function is activated. At this time, an error in the judgment logic occurs, and the fault section judgment will be wrong. Summary of the invention

[0006] In view of this, the present invention provides a method for analyzing and locking unplanned island faults when new energy is connected to a distribution network, so as to solve the problem that after a large-scale new energy is connected to a distribution network, due to the formation of short-term unplanned islands, the forward closing and locking functions of the section switch are logically disordered, resulting in erroneous closing and locking, causing the failure to correctly isolate the faulty section and the failure to smoothly transfer the load.

[0007] The technical solution adopted by the embodiment of the present invention to solve the technical problem is:

[0008] A method for analyzing and blocking unplanned island faults when a new energy source is connected to a distribution network, comprising:

[0009] Step S1, after isolating the fault section in the distribution network, the section where the distributed renewable energy in the fault area is located enters an unplanned island operation state when the distributed energy and load are matched;

[0010] Step S2, the upstream section switch and the downstream section switch located on both sides of the section where the distributed renewable energy source is located perform delayed closing after detecting the grid connection point voltage;

[0011] Step S3, after the delayed closing is completed, the anti-islanding protection is started in the section where the distributed new energy is located due to power mismatch. According to the positive sequence current flowing through the section switch during the period from the closing of the upstream section switch to the voltage loss opening within the Y time limit, and the residual pressure detected by the downstream section switch, it is determined whether the upstream section switch and the downstream section switch start the forward closing lock function and the reverse closing lock function and execute them.

[0012] Preferably, the step S3 comprises:

[0013] Step S31, obtaining the positive sequence current amplitude I flowing through the upstream sectionalizing switch during the period from closing the upstream sectionalizing switch to opening the sectionalizing switch due to voltage loss within a time limit Y FSW ;

[0014] Step S32, calculate the current setting value I of the positive closing lock function set , I set The setting principle is:

[0015]

[0016] In the formula, Ω Li For all sections of the distribution network L i (i=1,2,3....) The set of connected distributed energy resource labels;

[0017]

[0018]

[0019] In the formula, I N.DGi is the rated phase current of distributed renewable energy, P N.DGi Installed capacity for distributed renewable energy;

[0020] Therefore, I set The calculation expression is:

[0021]

[0022] Step S33, according to I set and I FSW Determine whether the upstream section switch has activated the forward closing lockout function:

[0023]

[0024] Step S34, for satisfying I FSW ≥I set The upstream section switch of the condition starts positive blocking;

[0025] Step S35, determining whether to start the reverse closing lock function according to whether the residual pressure detected by the downstream section switch meets the constraint conditions, wherein the constraint conditions include:

[0026] U FSWi.ab ≥U 残压.set &U FSWi.cb ≥U 残压.set &U FSWi.ac ≥U 残压.set

[0027] U 残压.set =30%U N

[0028] Where: U FSWi.ab FSW is the segment switch i The voltage amplitude between phases A and B on the power supply side, U FSWi.cb FSW is the segment switch i The cb phase voltage amplitude on the power supply side, U FSWi.ac FSW is the segment switch i The AC phase-to-phase voltage amplitude on the power supply side; U 残压.set It is the residual pressure detected by the section switch after the reverse closing lock function is activated due to island destruction; U N is the rated voltage;

[0029] Step S36: After confirming that the constraint condition is met, the downstream section switch starts the reverse closing locking function.

[0030] The present invention provides an unplanned island fault analysis and locking system for connecting new energy to a power distribution network, which is used to implement the above-mentioned method.

[0031] It can be seen from the above technical scheme that the unplanned island fault analysis and locking method and system for connecting new energy to the distribution network provided by the embodiment of the present invention first isolates the fault section in the distribution network, and the section where the distributed new energy is located in the fault area enters the unplanned island operation state when the distributed energy and the load are matched; the upstream segment switches and downstream segment switches located on both sides of the section where the distributed new energy is located detect the grid connection point voltage and perform delayed closing; after the delayed closing is completed, the section where the distributed new energy is located starts the anti-island protection due to power mismatch, and according to the positive sequence current flowing through the segment switch during the period from the closing of the upstream segment switch to the voltage loss and opening within the Y time limit, and the residual pressure detected by the downstream segment switch, it is determined whether the two segment switches start the forward closing locking function and the reverse closing locking function and execute them. The present invention is used to solve the problem that the forward and reverse closing locking functions of the segment switch are confused due to the formation of unplanned islands, resulting in erroneous closing locking, which causes the problem that the faulty section cannot be correctly isolated and the load cannot be smoothly transferred. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of the unplanned island fault analysis and blocking method for connecting new energy to a distribution network according to the present invention.

[0033] Figure 2 Schematic diagram of a typical distribution network overhead line fault situation.

[0034] Figure 3 This is a schematic diagram of the main branch section switch opening due to voltage loss in a typical distribution network overhead line.

[0035] Figure 4 This is a schematic diagram of the closing of the section switch of the main branch of a typical distribution network overhead line after 7s.

[0036] Figure 5 This is a schematic diagram of the locking status of the main branch section switches of a typical distribution network overhead line. DETAILED DESCRIPTION

[0037] The technical scheme and technical effects of the present invention are further elaborated in detail below in conjunction with the accompanying drawings of the present invention.

[0038] In the voltage-time feeder automation fault analysis method widely used in distribution networks, the forward closing lock function and the reverse closing lock function are set to automatically locate and isolate the faulty section. That is, when a permanent fault occurs, the section switch connected upstream of the faulty section starts the forward closing lock function to ensure that the switch is no longer closed after the outgoing circuit breaker is closed for the second time; the section switch connected downstream of the faulty section will detect the instantaneous residual pressure after the upstream switch is closed, and start the reverse closing lock function to ensure that it is no longer closed.

[0039] The present invention provides an unplanned island fault analysis and locking method for connecting new energy to a distribution network, comprising the optimization of a forward closing lock function and a reverse closing lock logic, calculating the installed capacity and rated phase current of distributed new energy, calculating the current setting value of the forward locking function according to the new energy capacity, introducing a criterion formula (1) for the current flowing through, and ensuring that the forward locking logic is effectively locked under short-term unplanned islanding; for the reverse locking function, introducing a residual voltage criterion formula (6) to eliminate the influence of short-term unplanned islanding on the reverse locking logic during a fault, and ensuring automatic positioning and isolation of distribution network faults under new energy connection.

[0040] The specific implementation steps of the present invention include:

[0041] Step S1, after isolating the fault section in the distribution network, the section where the distributed renewable energy in the fault area is located enters an unplanned island operation state when the distributed energy and load are matched;

[0042] Step S2, the upstream section switch and the downstream section switch located on both sides of the section where the distributed renewable energy source is located perform delayed closing after detecting the grid connection point voltage;

[0043] Step S3, the delayed closing ends, and the anti-islanding protection is started in the section where the distributed renewable energy is located due to power mismatch. According to the positive sequence current flowing through the section switch from the closing of the upstream section switch to the voltage loss and opening within the Y time limit, and the residual pressure detected by the downstream section switch, it is determined whether the upstream section switch and the downstream section switch start the forward closing lock function and the reverse closing lock function and execute them.

[0044] The specific implementation of step S3 includes:

[0045] Step S31, obtaining the positive sequence current amplitude I flowing through the sectionalizer during the period from the upstream sectionalizer closing to the voltage loss opening within the Y time limit FSW ;

[0046] Step S32, calculate the current setting value I of the positive closing lock function set , I set The setting principle is:

[0047]

[0048] In the formula, Ω Li For all sections of the distribution network L i (i=1,2,3....) The set of connected distributed energy resource labels;

[0049] Considering that the fault current amplitude of distributed renewable energy is generally 1.2 times of the rated current, and ignoring the line impedance, the voltage at the distributed energy grid connection point is almost the same, the voltage drop degree is the same, and the phase of the fault current supplied by the distributed energy is almost the same, it can be concluded that:

[0050]

[0051]

[0052] In the formula, I N.DGi is the rated phase current of distributed renewable energy, P N.DGi Installed capacity for distributed renewable energy;

[0053] Therefore, I set The calculation expression is:

[0054]

[0055] Step S33, according to I set and I FSW Determine whether the upstream section switch has activated the forward closing lockout function:

[0056]

[0057] Step S34, for satisfying I FSW ≥Iset The upstream section switch of the condition starts positive blocking;

[0058] Step S35: For the reverse closing lock function, the residual pressure criterion is introduced as formula (6), and whether to start the reverse closing lock function is determined according to whether the residual pressure detected by the downstream section switch meets the constraint conditions. The constraint conditions include:

[0059]

[0060] Where: U FSWi.ab FSW is the segment switch i The voltage amplitude between phases A and B on the power supply side, U FSWi.cb FSW is the segment switch i The cb phase voltage amplitude on the power supply side, U FSWi.ac FSW is the segment switch i The AC phase-to-phase voltage amplitude on the power supply side; U 残压.set It is the residual pressure detected by the section switch after the reverse closing lock function is activated due to island destruction; U N is the rated voltage;

[0061] Step S36: After confirming that the constraint conditions are met, the downstream section switch starts the reverse closing locking function.

[0062] The present invention further provides a non-planned island fault analysis and blocking system for connecting new energy to a distribution network, which is used to implement Figure 1 The method shown in the figure can solve the problem that after a large-scale new energy access distribution network failure, due to the formation of a short-term unplanned island, the logic of the forward closing and reverse closing lock functions of the section switch is disordered, resulting in an erroneous closing and locking function, which causes the inability to correctly isolate the fault section and the inability to smoothly transfer the load. This method optimizes the fault analysis and locking logic of the traditional distribution network voltage-time feeder automation, effectively avoids the problem of the expansion of the distribution network accident scope caused by short-term unplanned islands after the large-scale new energy access distribution network failure, and ensures the reliable operation of the distribution network after the new energy access.

[0063] The solution of the present invention is mainly used for the voltage-time feeder automation fault analysis logic of the distribution network with large-scale distributed renewable energy access. It solves the problem that after the distributed renewable energy is connected to the distribution network, short-term unplanned islanding will cause one side of the section switch to detect the voltage and delay the closing of the switch for Y time, resulting in a closing lock error, causing the inability to correctly isolate the faulty section and the inability to smoothly transfer the load, thereby ensuring that the distribution network fault can be reliably located and isolated.

[0064] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for analyzing and locking unplanned island faults when new energy is connected to a distribution network, characterized in that: include: Step S1, after isolating the fault section in the distribution network, the section where the distributed renewable energy in the fault area is located enters an unplanned island operation state when the distributed energy and load are matched; Step S2, the upstream section switch and the downstream section switch located on both sides of the section where the distributed renewable energy source is located perform delayed closing after detecting the grid connection point voltage; Step S3, after the delayed closing is completed, the anti-islanding protection is started in the section where the distributed new energy is located due to power mismatch. According to the positive sequence current flowing through the section switch during the period from the closing of the upstream section switch to the voltage loss opening within the Y time limit, and the residual pressure detected by the downstream section switch, it is determined whether the upstream section switch and the downstream section switch start the forward closing lock function and the reverse closing lock function and execute them.

2. The unplanned island fault analysis and blocking method for connecting new energy to the distribution network as claimed in claim 1 is characterized in that: The step S3 comprises: Step S31, obtaining the positive sequence current amplitude I flowing through the upstream sectionalizing switch during the period from closing the upstream sectionalizing switch to opening the sectionalizing switch due to voltage loss within a time limit Y FSW ; Step S32, calculate the current setting value I of the positive closing lock function set , I set The setting principle is: In the formula, Ω Li For all sections of the distribution network L i (i=1,2,3....) The set of connected distributed energy resource labels; In the formula, I N.DGi is the rated phase current of distributed renewable energy, P N.DGi is the installed capacity of distributed renewable energy; therefore, I set The calculation expression is: Step S33, according to I set and I FSW Determine whether the upstream section switch has activated the forward closing lockout function: Step S34, for satisfying I FSW ≥I set The upstream section switch of the condition starts positive blocking; Step S35, determining whether to start the reverse closing lock function according to whether the residual pressure detected by the downstream section switch meets the constraint conditions, wherein the constraint conditions include: IN FSWi.ab ≥U 残压.set &IN FSWi.cb ≥U 残压.set &IN FSWi.ac ≥U 残压.set IN 残压.set =30%U N Where: U FSWi.ab FSW is the segment switch i The voltage amplitude between phases A and B on the power supply side, U FSWi.cb FSW is the segment switch i The cb phase voltage amplitude on the power supply side, U FSWi.ac FSW is the segment switch i The AC phase-to-phase voltage amplitude on the power supply side; U 残压.set It is the residual pressure detected by the section switch after the reverse closing lock function is activated due to island destruction; U N is the rated voltage; Step S36: After confirming that the constraint condition is met, the downstream section switch starts the reverse closing locking function.

3. A non-planned island fault analysis and locking system for new energy access to the distribution network, characterized in that: Used to: After isolating the fault section in the distribution network, the section where the distributed renewable energy in the fault area is located enters the unplanned island operation state when the distributed energy and load are matched; The upstream section switches and downstream section switches on both sides of the distributed renewable energy section will delay closing after detecting the grid connection point voltage; After the delayed closing is completed, the anti-islanding protection is started due to power mismatch in the section where the distributed new energy is located. According to the positive sequence current flowing through the section switch from the closing of the upstream section switch to the voltage loss and opening within the Y time limit, and the residual pressure detected by the downstream section switch, it is determined whether the upstream section switch and the downstream section switch start the forward closing lock function and the reverse closing lock function and execute them.

4. The unplanned island fault analysis and blocking system for connecting new energy to the distribution network as claimed in claim 3 is characterized in that: Also used for: Obtain the positive sequence current amplitude I flowing through the sectionalizer after the upstream sectionalizer is closed and during the period from the voltage loss to the sectionalizer opening within the Y time limit FSW ; Calculate the current setting value I of the positive closing blocking function set , I set The setting principle is: In the formula, Ω Li For all sections of the distribution network L i (i=1,2,3....) The set of connected distributed energy resource labels; In the formula, I N.DGi is the rated phase current of distributed renewable energy, P N.DGi is the installed capacity of distributed renewable energy; therefore, I set The calculation expression is: According to I set and I FSW Determine whether the upstream section switch has activated the forward closing lockout function: To meet I FSW ≥I set The upstream section switch of the condition starts positive blocking; Whether to start the reverse closing lock function is determined according to whether the residual pressure detected by the downstream section switch meets the constraint conditions, and the constraint conditions include: IN FSWi.ab ≥U 残压.set &IN FSWi.cb ≥U 残压.set &IN FSWi.ac ≥U 残压.set IN 残压.set =30%U N Where: U FSWi.ab FSW is the segment switch i The voltage amplitude between phases A and B on the power supply side, U FSWi.cb FSW is the segment switch i The cb phase voltage amplitude on the power supply side, U FSWi.ac FSW is the segment switch i The AC phase-to-phase voltage amplitude on the power supply side; U 残压.set It is the residual pressure detected by the section switch after the reverse closing lock function is activated due to island destruction; U N is the rated voltage; After confirming that the constraint condition is met, the downstream section switch starts the reverse closing locking function.

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