A hybrid DC circuit breaker graded reclosing method and device

Abstract

The present invention relates to a hybrid DC circuit breaker hierarchical reclosing method and device. The hierarchical reclosing of the circuit breaker is used to realize a strategy for judging whether a fault has disappeared. According to the characteristics of the voltage and current of the system after reclosing, a judgment criterion for identifying whether a fault exists and whether the fault has disappeared is set to control the hierarchical reclosing of the DC circuit breaker, and a clear calculation method is proposed for the time interval of the hierarchical reclosing. By identifying whether the fault has disappeared, the impact of the reclosing on the system caused by permanent faults can be avoided. After some modules of the reclosing are tripped, the circuit breaker still has the ability to reclose again. For instantaneous faults with a long recovery time, the probability of successful reclosing is improved.

Description

Technical Field

[0001] The present invention relates to the technical field related to direct current transmission systems, and in particular to a hybrid direct current circuit breaker hierarchical reclosing method and device. Background Art

[0002] With the rapid development and increasing maturity of DC transmission technology, multi-terminal DC transmission with multiple sending ends and multiple landing points has become the main development trend at present. The multi-corridor circuit has great advantages in improving the power supply capacity and the power mutual assistance of each end of the power grid.

[0003] With the increase of power supply circuits, the probability of transmission line failure also increases accordingly. Since the DC line has low line damping and fast fault propagation speed, it is particularly important to quickly remove the fault line. Hybrid DC circuit breakers for high-voltage DC transmission are gradually put into use. They can interrupt the fault current within a few millimeters, isolate the fault point, and maintain the safe operation of the power grid. However, the tripping of the circuit breaker causes the reduction of the transmission circuit and the limited transmission power of the system. Research data shows that more than 80% of DC line faults are transient faults. After the circuit breaker trips, the fault point disappears. If the circuit breaker is reclosed in time, the system transmission power can be quickly restored. At present, the development of DC circuit breaker technology is still immature, and the reclosing circuit breaker is a great test for the safety of the equipment. Therefore, a reliable and safe reclosing strategy is needed to avoid reclosing on permanent faults to avoid damage to the circuit breaker and the converter equipment.

[0004] The hybrid DC circuit breaker in the prior art has been put into use, which can realize the rapid reclosing after the DC line fault. The existing circuit breaker reclosing scheme mainly adopts the delayed reclosing strategy. The specific action process is:

[0005] 1. When a fault occurs in the DC line, the line protection device identifies the fault information and sends a trip signal to the circuit breaker, which disconnects the circuit breaker;

[0006] 2. The line current disappears, and after the de-ionization time, the circuit breaker enters the normal closing process;

[0007] 3. If the fault point does not disappear, the current surges after closing the circuit breaker, the line DC voltage cannot be established, the protection device operates again, and the circuit breaker trips again;

[0008] 4. If the fault point disappears, after closing the circuit breaker, the transmission channel is restored, the line DC voltage returns to normal, power transmission gradually recovers, and the circuit breaker is closed and restarted successfully.

[0009] In the prior art described above, when the DC circuit breaker is reclosed, an indifferent reclosing method is adopted, and the reclosing success rate is low, and there are great safety risks to the equipment:

[0010] 1. When reclosing, it is impossible to reliably identify whether the fault has disappeared. When reclosing on a fault, the fault current surges, causing a secondary impact on the equipment;

[0011] 2. After the circuit breaker trips, the module capacitor voltage deviates from the rated value and directly recloses, which is a great test for the equipment safety of the circuit breaker and damages the service life of the equipment;

[0012] 3. Due to the type of fault and the influence of the external environment, the line insulation recovery speed is different after the fault is isolated, and the time-delay reclosing is set. If the reclosing occurs before the insulation strength is restored, the only chance for the circuit breaker to reclose will be wasted. Summary of the invention

[0013] Based on the above situation of the prior art, the purpose of the present invention is to propose a hybrid DC circuit breaker graded reclosing method and device, which utilizes the circuit breaker graded reclosing to implement a strategy for determining whether the fault has disappeared, thereby solving the problem of low reclosing success rate caused by the indiscriminate reclosing method in the prior art and greater safety risks to the equipment.

[0014] To achieve the above object, according to one aspect of the present invention, a hybrid DC circuit breaker hierarchical reclosing method is provided, comprising the steps of:

[0015] S1. When a line fault occurs, the circuit breaker trips and waits for the de-ionization time;

[0016] S2, calculate the minimum number of reclosing IGBT modules for the circuit breaker transfer branch and put the minimum reclosing IGBT module into use;

[0017] S3, determine whether the fault still exists, if yes, jump to step S6; if no, go to step S4;

[0018] S4, determine whether the fault disappears, if the fault disappears, go to step S5; if the fault does not disappear, jump to step S7;

[0019] S5, gradually put the remaining IGBT modules into operation, the circuit breaker is reclosed successfully, and the process ends;

[0020] S6: Determine whether the number of determinations m in step S3 is greater than the preset number of determinations m set , if it is greater than, jump to step S8; if it is not greater than, m=m+1, and jump to step S1;

[0021] S7, after the first preset time T1, the IGBT module of the next-level transfer branch reclosing is put into operation, and the process jumps to step S3;

[0022] S8. Line shutdown for maintenance, ended.

[0023] Further, the calculation of the minimum number of reclosing IGBT modules for the transfer branch of the circuit breaker includes using the following formula for calculation:

[0024]

[0025] Among them, N min is the minimum number of reclosing IGBT modules, U DC is the voltage on the DC bus side of the circuit breaker, U L is the line side voltage of the circuit breaker, U C is the average voltage of the IGBT module in the transfer branch; according to the number of lightning arresters in series of the DC circuit breaker, the transfer branch of the circuit breaker is divided into 1-N levels according to the priority of the modules put into use, N is the total number of IGBT modules in the transfer branch, and round() is the integer function.

[0026] The conditions for determining whether the fault still exists in step S3 include:

[0027]

[0028] Among them, i l is the branch current, k1 is the first reliability coefficient, i SET1 is the first current setting threshold, Δt1 is the delay time for the branch current to meet the above conditions, t set1 The first delay time.

[0029] Furthermore, the conditions for determining whether the fault disappears in step S4 include:

[0030]

[0031] Among them, k2 is the reliability coefficient of current criterion, i SET2 is the second current setting threshold, k3 is the voltage criterion reliability coefficient, n is the number of modules put into operation, Δt2 is the delay time for the branch current and line voltage to meet the above conditions, t set2 The second delay time.

[0032] Furthermore, after the first preset time T1, the S5 puts the IGBT module of the next-level transfer branch into operation, including calculating the first preset time T1 by the following formula:

[0033]

[0034] Among them, L is the total length of the line, v is the speed of light, and k4 is the second reliability coefficient.

[0035] Furthermore, the step S7 gradually puts the remaining IGBT modules into operation, and the circuit breaker is successfully reclosed, including:

[0036] After each second preset time T2, the number of IGBT modules to be switched on is increased until all the IGBT modules of the transfer branch are switched on;

[0037] After all the transfer branches are reclosed, the main branch is reclosed and the circuit breaker is reclosed successfully.

[0038] Furthermore, the second preset time T2 is calculated using the following formula:

[0039]

[0040] Wherein, k is the third reliability coefficient.

[0041] According to another aspect of the present invention, there is provided a hybrid DC circuit breaker hierarchical reclosing device, comprising a tripping module, a minimum reclosing IGBT module quantity calculation module, a fault existence judgment module, a fault disappearance judgment module, a re-entry module, a judgment times counting module, a reclosing module, and a shutdown maintenance module;

[0042] The tripping module trips the circuit breaker when a line fault occurs and waits for a de-ionization time;

[0043] The minimum reclosing IGBT module quantity calculation module calculates the minimum reclosing IGBT module quantity of the circuit breaker transfer branch and puts the minimum reclosing IGBT module into use;

[0044] The fault existence judgment module judges whether the fault still exists. If so, it goes to the judgment times counting module; if not, it goes to the fault disappearance judgment module;

[0045] The fault disappearance judgment module judges whether the fault disappears. If the fault disappears, it goes to the reclosing module; if the fault does not disappear, it goes to the re-entry module;

[0046] The re-entry module, after a first preset time T1, enters the IGBT module of the next-level transfer branch reclosing, and sends it to the fault existence judgment module;

[0047] The judgment times counting module determines whether the judgment times m of the fault existence judgment module is greater than the preset times m set , if it is greater than, then go to the shutdown maintenance module; if it is not greater than, then m=m+1, and go to the trip module;

[0048] The reclosing module gradually puts the remaining IGBT modules into operation, and the circuit breaker is reclosed successfully;

[0049] The shutdown and maintenance module controls the line to be shut down for maintenance.

[0050] Furthermore, in the fault existence judgment module, the conditions for judging whether the fault still exists include:

[0051]

[0052] Among them, i l is the branch current, k1 is the first reliability coefficient, i SET1 is the first current setting threshold, Δt1 is the delay time for the branch current to meet the above conditions, t set1 The first delay time.

[0053] Furthermore, in the fault disappearance judgment module, the conditions for judging whether the fault disappears include:

[0054]

[0055] Among them, k2 is the reliability coefficient of current criterion, i SET2 is the second current setting threshold, k3 is the voltage criterion reliability coefficient, n is the number of modules put into operation, Δt2 is the delay time for the branch current and line voltage to meet the above conditions, t set2 The second delay time.

[0056] In summary, the present invention provides a hybrid DC circuit breaker graded reclosing method and device, which adopts the circuit breaker graded reclosing to implement a strategy for judging whether the fault has disappeared. According to the characteristics of the system voltage and current after reclosing, a judgment criterion for identifying whether the fault exists and whether the fault has disappeared is set to control the DC circuit breaker graded reclosing, and a clear calculation method is proposed for the time interval of the graded reclosing. By identifying whether the fault has disappeared, the impact of the reclosing on the system caused by permanent faults can be avoided; after some modules of the reclosing trip, the circuit breaker still has the ability to reclose again, which improves the probability of successful reclosing for transient faults with a long recovery time. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is the topological diagram of the hybrid DC circuit breaker;

[0058] Figure 2 It is a flow chart of the hybrid DC circuit breaker hierarchical reclosing method of the present invention;

[0059] Figure 3 It is a schematic diagram of the electrical path of the circuit breaker after the overlapping part of the transfer branch is turned on;

[0060] Figure 4 It is a structural block diagram of the hybrid DC circuit breaker graded reclosing device of the present invention. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0062] The technical solution of the present invention is described in detail below with reference to the accompanying drawings. According to one embodiment of the present invention, a hybrid DC circuit breaker hierarchical reclosing method is provided, which is used for the hierarchical reclosing of the hybrid DC circuit breaker. The topology diagram of the hybrid DC circuit breaker is shown in FIG. Figure 1 As shown: the circuit breaker structure is divided into a main branch, a transfer branch and an energy-consuming branch. The transfer branch can be closed in stages to form different electrical paths. This method uses a circuit breaker hierarchical reclosing strategy to determine whether the fault has disappeared. According to the characteristics of the system voltage and current after reclosing, a criterion for identifying whether a fault exists and whether the fault has disappeared is set to control the hierarchical reclosing of the DC circuit breaker. According to the judgment requirements of the reclosing identification strategy, the voltages at both ends of the circuit breaker, the voltages of each module of the circuit breaker, and the currents of each branch are sampled, which may include the voltage U on the DC bus side of the circuit breaker. DC , circuit breaker line side voltage U L , transfer branch IGBT module average voltage U C The flow chart of this method is as follows: Figure 2 As shown, the steps include:

[0063] S1. When a line fault occurs, the circuit breaker trips and waits for the de-ionization time.

[0064] S2. Calculate the minimum number of reclosing IGBT modules for the transfer branch of the circuit breaker and put the minimum reclosing IGBT module into operation.

[0065] After a fault occurs, the circuit breaker trips. After the de-ionization time, the residual voltage of the module is detected. When the line is turned on, the number of IGBT modules that the circuit breaker transfers to reclose the branch is calculated. The calculation formula is:

[0066]

[0067] Using the rounding function, the minimum number of coincidences is:

[0068]

[0069] Among them, N min is the minimum number of reclosing IGBT modules, U DC is the voltage on the DC bus side of the circuit breaker, U L is the line side voltage of the circuit breaker, U Cis the average voltage of the transfer branch IGBT module; according to the number of lightning arresters in series of the DC circuit breaker, the circuit breaker transfer branch is divided into N levels, 1 to N respectively. The number determines the priority of the module input, and N is the total number of transfer branch IGBT modules.

[0070] At this time, the schematic diagram of the electrical path of the circuit breaker is as follows: Figure 3 As shown: the circuit breaker current forms an electrical path through the parallel energy-consuming branch of the reclosed transfer branch and the unreclosed branch.

[0071] S3. Determine whether the fault still exists. If it does, jump to step S6; if not, jump to step S4. After reclosing the n-level module, if the following conditions are met, it is considered that the fault still exists and the closed module is disconnected again:

[0072] 1) The branch current is greater than the first current setting threshold i for a certain period of time set1 ;

[0073] The expression of condition 1) is:

[0074]

[0075] In the formula, i l is the branch current, k1 is the first reliability coefficient, which can be 1.1, i set1 is the first current setting threshold, Δt1 is the delay time for the branch current to meet the above conditions, t set1 It is the first delay time and is set according to the line transmission time.

[0076] S4, determine whether the fault disappears. If the fault disappears, jump to step S5; if the fault does not disappear, go to step S7. That is, if the conditions in the above step S3 are not met, the fault disappearance judgment is performed, and the judgment conditions are as follows:

[0077] 1) The branch current is small, which is the current that the DC power supply charges the line through the lightning arrester and is smaller than the second current setting threshold iset2;

[0078] 2) The line side voltage rises steadily, is greater than the preset voltage threshold and meets a certain delay;

[0079] The expressions of condition 1) and condition 2) are:

[0080]

[0081] Among them, k2 is the reliability coefficient of current criterion, which can be taken as 0.9, i set2 is the second current setting threshold, k3 is the voltage criterion reliability coefficient, for example, it can be 0.8-1; U lis the line side voltage, n is the number of modules put into operation, Δt2 is the delay time for the branch current and line voltage to meet the above conditions, t set2 is the second delay time, which can usually be 10 sampling cycles.

[0082] S5, gradually put the remaining IGBT modules into operation, the circuit breaker is reclosed successfully, and the process ends. When the conditions in the above step S4 are met, it is determined that the fault has disappeared, and the number of IGBT modules to be closed is increased every T2 delay until all the IGBT modules of the transfer branch are put into operation. The second preset time T2 can be calculated using the following formula:

[0083]

[0084] Among them, k is the third reliability coefficient, which can be 1.1. After all the transfer branches are reclosed, the main branch is reclosed, and the line is reclosed successfully.

[0085] S6: Determine whether the number of determinations m in step S3 is greater than the preset number of determinations m set , m set It can be set according to the restart times required by the engineering design, generally not more than 3 times; if more than, jump to step S8; if not more than, m=m+1, and jump to step S1.

[0086] S7, after the first preset time T1, the IGBT module of the next-level transfer branch reclosing is put into operation, and the process jumps to step S3. The first preset time T1 can be calculated using the following formula:

[0087]

[0088] Among them, L is the total length of the line, v is the speed of light, and k4 is the second reliability coefficient, which can be 1.2-2.

[0089] S8. Line shutdown for maintenance, ended.

[0090] According to another embodiment of the present invention, a hybrid DC circuit breaker hierarchical reclosing device is provided. The structure block diagram of the device is as follows: Figure 4 As shown, it includes a tripping module, a minimum reclosing IGBT module quantity calculation module, a fault existence judgment module, a fault disappearance judgment module, a re-entry module, a judgment times counting module, a reclosing module, and a shutdown maintenance module.

[0091] The trip module trips the circuit breaker when a line fault occurs and waits for the de-ionization time.

[0092] The minimum reclosing IGBT module quantity calculation module calculates the minimum reclosing IGBT module quantity of the circuit breaker transfer branch and puts the minimum reclosing IGBT module into use.

[0093] The fault existence judgment module judges whether the fault still exists. If it does, it goes to the judgment times counting module; if it does not, it goes to the fault disappearance judgment module. The conditions for judging whether the fault still exists include:

[0094]

[0095] Among them, i l is the branch current, k1 is the first reliability coefficient, i set1 is the first current setting threshold, Δt1 is the delay time for the branch current to meet the above conditions, t set1 The first delay time.

[0096] The fault disappearance judgment module judges whether the fault disappears. If the fault disappears, it goes to the reclosing module; if the fault does not disappear, it goes to the re-entry module. The conditions for judging whether the fault disappears include:

[0097]

[0098] Among them, k2 is the reliability coefficient of current criterion, i set2 is the second current setting threshold, k3 is the voltage criterion reliability coefficient, U l is the line side voltage, n is the number of modules put into operation, Δt2 is the delay time for the branch current and line voltage to meet the above conditions, t set2 The second delay time.

[0099] The re-activation module, after the first preset time T1, activates the IGBT module of the next-level transfer branch reclosing, and goes to the fault existence judgment module.

[0100] A judgment count module is used to judge whether the judgment times m of the fault existence judgment module is greater than a preset times m set , if it is greater than, then go to the shutdown maintenance module; if it is not greater than, then m=m+1, and go to the tripping module.

[0101] The reclosing module gradually puts the remaining IGBT modules into operation and the circuit breaker is reclosed successfully.

[0102] Shutdown and maintenance module, controls the line shutdown and maintenance.

[0103] In each of the above modules, the calculation of relevant parameters is the same as that involved in the method provided in the first embodiment of the present invention, and will not be repeated here.

[0104] In summary, the present invention relates to a hybrid DC circuit breaker graded reclosing method and device, which adopts the circuit breaker graded reclosing to realize the strategy of judging whether the fault disappears, and according to the characteristics of the system voltage and current after reclosing, sets the judgment criteria of whether the fault exists and whether the fault disappears to control the graded reclosing of the DC circuit breaker, and proposes a clear calculation method for the time interval of the graded reclosing, and can avoid the impact of the reclosing on the system caused by permanent faults by identifying whether the fault disappears; after some modules of the reclosing trip, the circuit breaker still has the ability to reclose again, and for instantaneous faults with a long recovery time, the probability of successful reclosing is improved.

[0105] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A hybrid DC circuit breaker hierarchical reclosing method, characterized in that: Includes steps: S1. When a line fault occurs, the circuit breaker trips and waits for the de-ionization time; S2, calculate the minimum number of reclosing IGBT modules for the circuit breaker transfer branch and put the minimum reclosing IGBT module into use; S3. Determine whether the fault still exists based on the following conditions: If it exists, jump to step S6; if it does not exist, go to step S4; where i l is the branch current, k1 is the first reliability coefficient, i set1 is the first current setting threshold, Δt1 is the delay time for the branch current to meet the above conditions, t set1 is the first delay time; S4. Determine whether the fault disappears according to the following conditions: If the fault disappears, go to step S5; if the fault does not disappear, jump to step S7; where k2 is the reliability coefficient of the current criterion, i set2 is the second current setting threshold, k3 is the voltage criterion reliability coefficient, n is the number of modules put into operation, Δt2 is the delay time for the branch current and line voltage to meet the above conditions, t set2 is the second delay time; U DC is the voltage on the DC bus side of the circuit breaker, U L is the line side voltage of the circuit breaker, U C is the average voltage of the transfer branch IGBT module; S5, gradually put the remaining IGBT modules into operation, the circuit breaker is reclosed successfully, and the process ends; S6, judging whether the number of times m in step S3 is greater than the preset number mset, if so, jumping to step S8; if not, m=m+1, and jumping to step S1; S7, after the first preset time T1, the IGBT module of the next-level transfer branch reclosing is put into operation, and the process jumps to step S3; S8. Line shutdown for maintenance, ended.

2. The method according to claim 1, characterized in that The calculation of the minimum number of reclosing IGBT modules for the circuit breaker transfer branch includes using the following formula: Among them, N min is the minimum number of reclosing IGBT modules, U DC is the voltage on the DC bus side of the circuit breaker, U L is the line side voltage of the circuit breaker, U C is the average voltage of the IGBT module in the transfer branch; according to the number of lightning arresters in series of the DC circuit breaker, the transfer branch of the circuit breaker is divided into 1-N levels according to the priority of the modules put into use, N is the total number of IGBT modules in the transfer branch, and round() is the integer function.

3. The method according to claim 2, characterized in that After the first preset time T1, S5 puts the IGBT module of the next-level transfer branch into operation, including calculating the first preset time T1 by the following formula: Among them, L is the total length of the line, v is the speed of light, and k4 is the second reliability coefficient.

4. The method according to claim 3, characterized in that The step S7 of gradually putting the remaining IGBT modules into operation and successfully reclosing the circuit breaker includes: After each second preset time T2, the number of IGBT modules to be switched on is increased until all the IGBT modules of the transfer branch are switched on; After all the transfer branches are reclosed, the main branch is reclosed and the circuit breaker is reclosed successfully.

5. The method according to claim 4, characterized in that The second preset time T2 is calculated using the following formula: Wherein, k is the third reliability coefficient.

6. A hybrid DC circuit breaker hierarchical reclosing device, characterized in that: It includes a tripping module, a minimum reclosing IGBT module quantity calculation module, a fault existence judgment module, a fault disappearance judgment module, a re-entry module, a judgment times counting module, a reclosing module, and a shutdown maintenance module; The tripping module trips the circuit breaker when a line fault occurs and waits for a de-ionization time; The minimum reclosing IGBT module quantity calculation module calculates the minimum reclosing IGBT module quantity of the circuit breaker transfer branch and puts the minimum reclosing IGBT module into use; The fault existence judgment module judges whether the fault still exists, and if so, it goes to the judgment number counting module; If it does not exist, go to the fault disappearance judgment module; The conditions for determining whether the fault still exists include: Among them, i l is the branch current, k1 is the first reliability coefficient, i set1 is the first current setting threshold, Δt1 is the delay time for the branch current to meet the above conditions, t set1 is the first delay time; The fault disappearance judgment module judges whether the fault disappears. If the fault disappears, it goes to the reclosing module; if the fault does not disappear, it goes to the re-entry module. The conditions for judging whether the fault disappears include: Among them, k2 is the reliability coefficient of current criterion, i set2 is the second current setting threshold, k3 is the voltage criterion reliability coefficient, n is the number of modules put into operation, Δt2 is the delay time for the branch current and line voltage to meet the above conditions, t set2 is the second delay time, U DC is the voltage on the DC bus side of the circuit breaker, U L is the line side voltage of the circuit breaker, U C is the average voltage of the transfer branch IGBT module; The re-entry module, after a first preset time T1, enters the IGBT module of the next-level transfer branch reclosing, and sends it to the fault existence judgment module; The judgment times counting module judges whether the judgment times m of the fault existence judgment module is greater than the preset times mset, if so, it goes to the shutdown maintenance module; if not, m=m+1, and goes to the tripping module; The reclosing module gradually puts the remaining IGBT modules into operation, and the circuit breaker is reclosed successfully; The shutdown and maintenance module controls the line to be shut down for maintenance.

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