Self-adaptive composite arc extinction method based on zero-sequence voltage threshold value of power distribution network

Abstract

The invention is suitable for the technical field of arc extinction of a power distribution network, and provides a self-adaptive composite arc extinction method based on a zero-sequence voltage threshold value of the power distribution network, which comprises the following steps: monitoring the neutral point voltage of the power distribution network, and judging whether the power distribution network has a single-phase earth fault or not; when the single-phase earth fault does not occur in the power distribution network, injecting a first current into the neutral point of the power distribution network, and calculating an earth parameter of the power distribution network and an earth capacitance current when the voltage of the neutral point of the power distribution network is zero; when a single-phase earth fault occurs in the power distribution network, injecting a second current into the neutral point of the power distribution network, and calculating a fault point offset voltage of the power distribution network; and calculating a voltage threshold value and a corrected current arc extinction reference value based on the ground parameter, the ground capacitance current and the fault point offset voltage, if the neutral point voltage of the power distribution network is smaller than the voltage threshold value when the single-phase ground fault occurs, adopting voltage arc extinction, otherwise, adopting the corrected current arc extinction reference value to implement current arc extinction. According to the invention, the reliability of single-phase earth fault arc extinction can be improved.

Description

Technical Field

[0001] This application belongs to the technical field of arc suppression in distribution networks, and particularly relates to an adaptive composite arc suppression method based on the zero-sequence voltage threshold of a distribution network. Background Art

[0002] The distribution network has a complex structure and is prone to various faults, most of which are single-phase grounding faults. To ensure power supply reliability, the neutral point of the distribution network adopts a small-current grounding method. After a fault, the line voltage remains unchanged and does not affect the normal power supply on the user side. According to relevant operating regulations, when the grounding current is less than 10A, it can continue to operate with the fault for a period of time, but the existing step voltage may cause personal electric shock and casualties; the arc cannot be extinguished easily induces wildfires, and even causes overvoltage, resulting in the breakdown of weak links in the system and damage to power grid equipment.

[0003] The main influencing factors for the extinction of the single-phase grounding fault arc are the magnitude of the grounding fault current and the recovery voltage of the fault phase. The corresponding arc suppression methods are the current arc suppression method and the voltage arc suppression method respectively. In the existing arc suppression methods, the current arc suppression method needs to measure the parameters to the ground to achieve full compensation of the grounding fault current and cannot adapt to the change of the distribution network structure parameters; the voltage arc suppression method indirectly limits the fault voltage to zero by regulating the neutral point voltage, but the arc suppression effect is limited by the line voltage drop. Therefore, at present, the reliability of single-phase grounding fault arc suppression is poor and it is difficult to meet the actual needs. Summary of the Invention

[0004] The embodiment of this application provides an adaptive composite arc suppression method based on the zero-sequence voltage threshold of a distribution network, which can solve the problem of poor reliability of single-phase grounding fault arc suppression.

[0005] The embodiment of this application provides an adaptive composite arc suppression method based on the zero-sequence voltage threshold of a distribution network, including:

[0006] Monitoring the neutral point voltage of the distribution network, and judging whether the distribution network has a single-phase grounding fault based on the monitored neutral point voltage;

[0007] When the distribution network does not have a single-phase grounding fault, injecting a first current into the neutral point of the distribution network, and obtaining the neutral point voltage of the distribution network after injecting the first current. According to the first current and the neutral point voltage of the distribution network after injecting the first current, calculating the parameters to the ground of the distribution network and the capacitive current to the ground of the distribution network when the neutral point voltage of the distribution network is zero;

[0008] When the distribution network has a single-phase grounding fault, injecting a second current into the neutral point of the distribution network, and obtaining the neutral point voltage of the distribution network after injecting the second current. According to the second current and the neutral point voltage of the distribution network after injecting the second current, calculating the offset voltage of the fault point of the distribution network;

[0009] Calculate the voltage threshold and the corrected arc suppression reference value of the current based on the earth parameters, the earth capacitance current, and the offset voltage at the fault point. If the neutral point voltage of the distribution network is less than the voltage threshold when a single-phase grounding fault occurs, use voltage arc suppression to eliminate the arc in the distribution network. If the neutral point voltage of the distribution network is greater than or equal to the voltage threshold when a single-phase grounding fault occurs, use current arc suppression to eliminate the arc in the distribution network; the value of the injected current for current arc suppression is the corrected arc suppression reference value of the current.

[0010] Optionally, calculate the earth parameters of the distribution network and the earth capacitance current of the distribution network when the neutral point voltage of the distribution network is zero based on the first current and the neutral point voltage of the distribution network after injecting the first current, including:

[0011] Construct the current relationship formula of the equivalent circuit model of the single-phase grounding fault of the distribution network based on Kirchhoff's current law; the current relationship formula is: is the current injected into the neutral point of the distribution network, is the single-phase grounding fault current, is the neutral point voltage of the distribution network, Y d is the earth parameter of the distribution network, is the earth capacitance current of the distribution network when the neutral point voltage of the distribution network is zero;

[0012] Set the single-phase grounding fault current to zero, and substitute the first current and the neutral point voltage of the distribution network after injecting the first current into the current relationship formula to obtain the first equation;

[0013] Set the single-phase grounding fault current and the current injected into the neutral point of the distribution network to zero, and substitute the neutral point voltage of the distribution network before injecting the first current into the current relationship formula to obtain the second equation;

[0014] Solve the earth parameter Y d and the earth capacitance current

[0015] Optionally, calculate the offset voltage at the fault point of the distribution network based on the second current and the neutral point voltage of the distribution network after injecting the second current, including:

[0016] Based on the equivalent circuit model of the single-phase grounding fault of the distribution network, construct the neutral point voltage expression of the distribution network;

[0017] Based on the neutral point voltage expression and the current relationship formula, obtain the offset voltage relationship formula;

[0018] Based on the second current, the neutral point voltage of the distribution network after injecting the second current, and the offset voltage relationship formula, calculate the offset voltage at the fault point of the distribution network.

[0019] Optionally, the neutral point voltage expression of the distribution network is:

[0020]

[0021] Wherein, is the neutral point voltage of the distribution network, G f is the grounding fault resistance, Y L is the line impedance between the fault point and the bus, Y ca is the coupling impedance after star-delta transformation between the faulty phase A and the non-faulty phase C, Y ab is the coupling impedance after star-delta transformation between the faulty phase A and the non-faulty phase B, is the fault point offset voltage.

[0022] Optionally, the offset voltage relation is:

[0023]

[0024] Optionally, based on the second current, the neutral point voltage of the distribution network after injecting the second current, and the offset voltage relation, the fault point offset voltage of the distribution network is calculated, including:

[0025] Substitute the second current and the neutral point voltage of the distribution network after injecting the second current into the offset voltage relation to obtain the third equation;

[0026] Let the current injected into the neutral point of the distribution network be zero, and substitute the neutral point voltage of the distribution network before injecting the second current into the current relation to obtain the fourth equation;

[0027] Solve based on the third equation and the fourth equation to obtain the fault point offset voltage

[0028] Optionally, based on the ground parameters, the ground capacitance current, and the fault point offset voltage, the voltage threshold and the corrected arc suppression reference current value are calculated, including:

[0029] Calculate the voltage threshold U 0set :

[0030]

[0031] Calculate the corrected arc suppression reference current value through the following formula

[0032]

[0033] Wherein, is the electromotive force of the faulty phase.

[0034] Optionally, based on the monitored neutral point voltage, it is judged whether a single-phase grounding fault occurs in the distribution network, including:

[0035] If the monitored neutral point voltage is greater than 15% of the phase voltage, it is determined that a single-phase grounding fault has occurred in the distribution network; if the monitored neutral point voltage is less than or equal to 15% of the phase voltage, it is determined that no single-phase grounding fault has occurred in the distribution network.

[0036] Optionally, after arc suppression is performed on the distribution network, the adaptive composite arc suppression method further includes:

[0037] After a preset time interval, reduce the output voltage or current of the arc suppression device, and determine whether the zero-sequence current or voltage of the distribution network changes proportionally after reducing the output of the arc suppression device;

[0038] If so, remove the arc suppression device;

[0039] Otherwise, isolate the grounded fault phase feeder of the distribution network and remove the arc suppression device.

[0040] Optionally, the preset time is 2 seconds.

[0041] The above solution of the present application has the following beneficial effects:

[0042] In the embodiment of the present application, by judging whether to adopt voltage arc suppression or current arc suppression according to the voltage threshold, the voltage threshold can determine the effective use range of the voltage arc suppression method. Therefore, it is possible to use voltage arc suppression to extinguish the arc when the voltage method is effective, and adopt the corrected current arc suppression reference value to implement current arc suppression when the voltage arc suppression method fails, thereby improving the reliability of single-phase grounding fault arc suppression. At the same time, since the voltage threshold changes with the fault location, grounding fault resistance, and line parameters, it can adapt to different grounding fault conditions and further improve the reliability of single-phase grounding fault arc suppression.

[0043] Other beneficial effects of the present application will be described in detail in the subsequent specific implementation part. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0045] Figure 1 It is a flowchart of an adaptive composite arc suppression method based on the zero-sequence voltage threshold of a distribution network provided by an embodiment of the present application;

[0046] Figure 2 It is a simplified model diagram of a single-phase grounding fault of phase A in a distribution network in the related art;

[0047] Figure 3 It is the equivalent circuit model diagram of the single-phase grounding fault of phase A in the distribution network in the related technology;

[0048] Figure 4 It is the topological structure diagram of the IEEE13-node 10kV distribution network in an experiment;

[0049] Figure 5a It is the waveform diagram of using the traditional voltage arc suppression method at the K3 fault point in an experiment;

[0050] Figure 5b It is the waveform diagram of using the traditional voltage arc suppression method at the K5 fault point in an experiment;

[0051] Figure 6a It is the waveform diagram of using the improved current arc suppression method at the K3 fault point in an experiment;

[0052] Figure 6b It is the waveform diagram of using the improved current arc suppression method at the K5 fault point in an experiment;

[0053] Figure 7a It is the waveform diagram of using the traditional voltage arc suppression method at the K1 fault point in an experiment;

[0054] Figure 7b It is the waveform diagram of using the improved current arc suppression method at the K1 fault point in an experiment;

[0055] Figure 8a It is the waveform comparison diagram of the single-phase grounding fault of 20Ω in phase A at K5 in an experiment;

[0056] Figure 8b It is the waveform comparison diagram of the single-phase grounding fault of 20Ω in phase B at K5 in an experiment;

[0057] Figure 8c It is the waveform comparison diagram of the single-phase grounding fault of 20Ω in phase C at K5 in an experiment;

[0058] Figure 9 It is the schematic diagram of the physical experiment platform of the 80V distribution network in an experiment;

[0059] Figure 10a It is the waveform diagram of the fault voltage and current after arc suppression using the traditional voltage and current in an experiment;

[0060] Figure 10b It is the waveform diagram of the fault voltage and current after arc suppression using the composite arc suppression of the present application in an experiment. Specific implementation manner

[0061] In the following description, specific details such as specific system architectures, technologies, etc. are presented for purposes of illustration and not limitation, so as to provide a thorough understanding of the embodiments of the present application. However, those skilled in the art should clearly understand that the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from obscuring the description of the present application.

[0062] It should be understood that when used in the specification of the present application and the appended claims, the term "comprising" indicates the presence of the described features, wholes, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0063] It should also be understood that the term "and / or" as used in the specification of the present application and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0064] As used in the specification of the present application and the appended claims, the term "if" can be interpreted as "when" or "once" or "in response to determining" or "in response to detecting" depending on the context. Similarly, the phrase "if determined" or "if [the described condition or event] is detected" can be interpreted as meaning "once determined" or "in response to determining" or "once [the described condition or event] is detected" or "in response to detecting [the described condition or event]" depending on the context.

[0065] In addition, in the description of the specification of the present application and the appended claims, the terms "first", "second", "third", etc. are only used for differentiating descriptions and cannot be understood as indicating or implying relative importance.

[0066] The reference to "one embodiment" or "some embodiments" etc. described in the specification of the present application means that a specific feature, structure, or characteristic described in connection with that embodiment is included in one or more embodiments of the present application. Thus, statements such as "in one embodiment", "in some embodiments", "in other some embodiments", "in still other embodiments", etc. that appear in different places in this specification do not necessarily all refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in another way. The terms "comprising", "including", "having", and their variants all mean "including but not limited to", unless otherwise specifically emphasized in another way.

[0067] Aiming at the problem of poor reliability of arc suppression for single-phase grounding faults at present, the embodiment of the present application provides an adaptive composite arc suppression method based on the zero-sequence voltage threshold of the distribution network. This method determines whether to adopt voltage arc suppression or current arc suppression according to the voltage threshold. This voltage threshold can determine the effective use range of the voltage arc suppression method. Therefore, it can achieve voltage arc suppression and extinction when the voltage method is effective, and adopt a corrected current arc suppression reference value to implement current arc suppression when the voltage arc suppression method fails, thereby improving the reliability of arc suppression for single-phase grounding faults. At the same time, since this voltage threshold changes with the fault location, grounding fault resistance, and line parameters, it can adapt to different grounding fault conditions and further improve the reliability of arc suppression for single-phase grounding faults.

[0068] The following is an exemplary description of the adaptive composite arc suppression method based on the zero-sequence voltage threshold of the distribution network provided by the present application in combination with specific embodiments.

[0069] As Figure 1 shown, the adaptive composite arc suppression method based on the zero-sequence voltage threshold of the distribution network provided by the embodiment of the present application includes the following steps:

[0070] Step 11, monitor the neutral point voltage of the distribution network, and determine whether a single-phase grounding fault occurs in the distribution network based on the monitored neutral point voltage. When no single-phase grounding fault occurs in the distribution network, execute Step 12. When a single-phase grounding fault occurs in the distribution network, execute Step 13.

[0071] Step 12, inject a first current into the neutral point of the distribution network, and obtain the neutral point voltage of the distribution network after injecting the first current. According to the first current and the neutral point voltage of the distribution network after injecting the first current, calculate the ground parameters of the distribution network and the capacitive current to the ground of the distribution network when the neutral point voltage is zero.

[0072] Step 13, inject a second current into the neutral point of the distribution network, and obtain the neutral point voltage of the distribution network after injecting the second current. According to the second current and the neutral point voltage of the distribution network after injecting the second current, calculate the offset voltage of the fault point of the distribution network.

[0073] Step 14, calculate the voltage threshold and the corrected current arc suppression reference value based on the ground parameters, the capacitive current to the ground, and the offset voltage of the fault point. If the neutral point voltage of the distribution network is less than the voltage threshold when a single-phase grounding fault occurs, adopt voltage arc suppression to suppress the arc of the distribution network. If the neutral point voltage of the distribution network is greater than or equal to the voltage threshold when a single-phase grounding fault occurs, adopt current arc suppression to suppress the arc of the distribution network; the value of the injected current for current arc suppression is the corrected current arc suppression reference value.

[0074] It should be noted that during the execution of the above adaptive composite arc suppression method, the neutral point voltage of the distribution network can be periodically monitored to determine whether a single-phase grounding fault occurs. When no single-phase grounding fault occurs, step 12 is executed. After step 12 is executed, when the next cycle arrives, step 11 is continued. When a single-phase grounding fault occurs, steps 13 and 14 are executed to complete arc suppression.

[0075] It should be further noted that the adaptive composite arc suppression method of the embodiment of the present application records the neutral point voltage during the normal operation of the distribution network, injects the first current into the neutral point of the distribution network during normal operation, and records the neutral point voltage after injecting the first current, so as to solve the ground parameters of the distribution network and the ground capacitance current of the distribution network when the neutral point voltage is zero based on the recorded values during normal operation; then when a single-phase grounding fault occurs in the distribution network, injects the second current into the neutral point of the distribution network, and records the neutral point voltage before and after injecting the second current, so as to calculate the fault point offset voltage of the distribution network based on the data before and after injecting the second current, and further calculate the voltage threshold and the corrected current arc suppression reference value.

[0076] After calculating the voltage threshold and the corrected current arc suppression reference value, it is possible to judge whether to adopt voltage arc suppression or current arc suppression by comparing the voltage threshold with the neutral point voltage of the distribution network when a single-phase grounding fault occurs. The voltage threshold can determine the effective use range of the voltage arc suppression method, so that voltage arc suppression can be adopted when the voltage method is effective, and the corrected current arc suppression reference value can be adopted to implement current arc suppression when the voltage arc suppression method fails, thereby improving the reliability of single-phase grounding fault arc suppression. At the same time, since the voltage threshold will change with the fault location, grounding fault resistance, and line parameters, it can adapt to different grounding fault conditions and further improve the reliability of single-phase grounding fault arc suppression.

[0077] In some embodiments of the present application, after arc suppression is performed on the distribution network, the adaptive composite arc suppression method further includes: reducing the output voltage or current of the arc suppression device after a preset time interval (the preset time can be set according to actual conditions, for example, set to 2 seconds) (it can be understood that if the arc suppression device outputs current, the output current of the arc suppression device is reduced, and if the arc suppression device outputs voltage, the output voltage of the arc suppression device is reduced), and judging whether the zero-sequence current or zero-sequence voltage of the distribution network (the zero-sequence current can be understood as the sum of the currents of phases A, B, and C; the zero-sequence voltage can be understood as the sum of the voltages of phases A, B, and C) changes proportionally after reducing the output of the arc suppression device. If so, it indicates that the arc has been extinguished and the arc suppression device can be removed; otherwise, it indicates that the arc has not been extinguished, and the grounded fault phase feeder of the distribution network needs to be isolated and the arc suppression device needs to be removed for further detection by relevant personnel.

[0078] The following is an exemplary description of the specific implementation methods of the above steps in combination with specific embodiments.

[0079] In some embodiments of the present application, the neutral point voltage of the distribution network can be monitored through a voltmeter to collect the neutral point voltage. The specific implementation method for determining whether a single-phase ground fault occurs in the distribution network based on the monitored neutral point voltage in step 11 above is as follows: If the monitored neutral point voltage is greater than 15% of the phase voltage, it is determined that a single-phase ground fault has occurred in the distribution network; if the monitored neutral point voltage is less than or equal to 15% of the phase voltage, it is determined that no single-phase ground fault has occurred in the distribution network. Among them, in the residential power consumption system, the phase voltage is 220V, and in the 10kV system, the phase voltage is 8165V.

[0080] It can be understood that the single-phase ground fault in the distribution network can occur in any one of phases A, B, and C. For ease of description, in the following description of the specific implementation methods of other steps, phase A is taken as the fault phase as an example. It can be understood that when phase B or C fails, the same processing process as when phase A fails. Or rather, phase A in the following text can be regarded as a general concept, and its essence can be any one of phases A, B, and C. Phases B and C in the following text generally refer to the other two non-fault phases.

[0081] In some embodiments of the present application, when no single-phase ground fault occurs in the distribution network, a first current injected into the neutral point of the distribution network is an inductive current, which only needs to ensure that the fault current does not increase during a fault, and this inductive current cannot be too small so that the zero-sequence voltage (i.e., the neutral point voltage) does not change significantly after the injection current. The specific implementation method for calculating the earth parameters of the distribution network and the capacitive current of the distribution network to the ground when the neutral point voltage of the distribution network is zero according to the first current and the neutral point voltage of the distribution network after injecting the first current in step 12 above includes the following steps:

[0082] Step 12.1, construct a current relationship formula for the equivalent circuit model of a single-phase ground fault in the distribution network based on Kirchhoff's current law.

[0083] In the related art, the simplified model of a single-phase ground fault in phase A of the distribution network is as Figure 2 shown, Figure 2 where, is the injected current (i.e., the output current of the arc suppression device), Y x represents the ground conductance of phase x (Y a is the ground conductance of phase A (i.e., the earth parameter), Y b is the ground conductance of phase B, Y c is the ground conductance of phase C), which also includes the line and load impedances of the non-faulty lines. λ is obtained by dividing the distance of the fault location from the bus by the total line length. Z Lx is the line impedance of the faulty feeder (ZLa is the line impedance of the faulty phase A, Z Lb is the line impedance of the non-faulty phase B, Z Lc is the line impedance of the non-faulty phase C), Z LDx is the load impedance (converted to Y - connection, Z LDa is the load impedance of the faulty phase A, Z LDb is the load impedance of the non-faulty phase B, Z LDc is the load impedance of the non-faulty phase C), is the neutral point voltage of the distribution network, represents the potential of the faulty phase (i.e., the potential of phase A), is the potential of phase B, is the potential of phase C, G f is the grounding fault resistance.

[0084] According to Figure 2 the circuit topology diagram shown, by performing the star - delta transformation (i.e., Y - △ transformation) on nodes 1, 2, and 4, we can obtain Figure 3 the circuit diagram (i.e., the equivalent circuit model of single - phase - to - ground fault in the A - phase of the distribution network), where the physical quantities after transformation are as shown in Equation (1). represents the potential of the faulty phase, are the potentials of the non - faulty phases respectively. G f is the grounding fault resistance. Y a is the parameter to the ground of the faulty phase, Y b , Y c is the parameter to the ground of the non - faulty phase, Y L is the line impedance between the fault point and the bus, Y ab is the coupling impedance after star - delta transformation between the faulty phase A and the non - faulty phase B. Y ca is the coupling impedance after star - delta transformation between the faulty phase A and the non - faulty phase C, Y bc is the coupling impedance after star - delta transformation between the non - faulty phase B and the non - faulty phase C. is the neutral point voltage during the fault (i.e., the zero - sequence voltage), is the voltage at the fault point, is the single - phase - to - ground fault current, is the capacitive current from the faulty phase A to the ground, is the capacitive current from the non - faulty phase B to the ground, is the capacitive current from the non - faulty phase C to the ground.

[0085]

[0086] After obtaining the equivalent circuit model of single - phase - to - ground fault in the distribution network (in this example, it is the equivalent circuit model of single - phase - to - ground fault in the A - phase of the distribution network), the following current relationship can be obtained according to Kirchhoff's current law: is the current injected into the neutral point of the distribution network, is the single-phase grounding fault current, is the neutral point voltage of the distribution network, Y d are the parameters of the distribution network to the ground, is the capacitive current to the ground of the distribution network when the neutral point voltage of the distribution network is zero.

[0087] Step 12.2, set the single-phase grounding fault current to zero, and substitute the first current and the neutral point voltage of the distribution network after injecting the first current into the current relationship formula to obtain the first equation. That is, the first equation is is 0, is the first current, is the current relationship formula when the neutral point voltage of the distribution network after injecting the first current.

[0088] Step 12.3, set both the single-phase grounding fault current and the current injected into the neutral point of the distribution network to zero, and substitute the neutral point voltage of the distribution network before injecting the first current into the current relationship formula to obtain the second equation. That is, the second equation is is 0, is 0, is the current relationship formula when the neutral point voltage of the distribution network before injecting the first current.

[0089] Step 12.4, solve for the parameter Y to the ground d and the capacitive current to the ground Specifically, by relating the first equation and the second equation, the parameter Y to the ground can be solved d and the capacitive current to the ground

[0090] In some embodiments of the present application, when a single-phase grounding fault occurs in the distribution network and a second current is injected into the neutral point, the specific implementation manner of calculating the fault point offset voltage of the distribution network according to the second current and the neutral point voltage of the distribution network after injecting the second current in the above step 13 includes the following steps:

[0091] Step 13.1, based on the single-phase grounding fault equivalent circuit model of the distribution network, construct the neutral point voltage expression of the distribution network.

[0092] Specifically, based on the single-phase grounding fault equivalent circuit model of the distribution network, the neutral point voltage expression of the distribution network can be calculated as:

[0093]

[0094] Among them, is the neutral point voltage of the distribution network, G f is the grounding fault resistance, YL is the line impedance between the fault point and the bus, Y ca is the coupling impedance after star-delta transformation between the fault phase A and the non-fault phase C, Y ab is the coupling impedance after star-delta transformation between the fault phase A and the non-fault phase B, is the offset voltage of the fault point.

[0095] Step 13.2: Based on the neutral point voltage expression and the current relationship, obtain the offset voltage relationship.

[0096] Specifically, the offset voltage relationship can be derived through the neutral point voltage expression and the current relationship, and this offset voltage relationship is:

[0097]

[0098] where the parameter Y to the ground d and the capacitive current to the ground can be substituted according to the solution result of Step 12.4.

[0099] Step 13.3: Based on the second current, the neutral point voltage of the distribution network after injecting the second current, and the offset voltage relationship, calculate the offset voltage of the fault point of the distribution network.

[0100] In some embodiments of the present application, the specific implementation manner of Step 13.3 includes the following steps:

[0101] Step 13.31: Substitute the second current and the neutral point voltage of the distribution network after injecting the second current into the offset voltage relationship to obtain a third equation. That is, this third equation is is the second current, is the offset voltage relationship when the neutral point voltage of the distribution network after injecting the second current.

[0102] Step 13.32: Let the current injected into the neutral point of the distribution network be zero, and substitute the neutral point voltage of the distribution network before injecting the second current into the current relationship to obtain a fourth equation. That is, this fourth equation is is 0, is the offset voltage relationship when the neutral point voltage of the distribution network before injecting the second current.

[0103] Step 13.33: Solve the fault point offset voltage based on the third equation and the fourth equation

[0104] It should be noted that although G in the offset voltage relationship f , Y L +Y ca +Y abis also an unknown quantity, but the two do not need to be solved, so by combining the third and fourth equations, these two unknown quantities can be eliminated, and the fault point offset voltage can be solved.

[0105] In some embodiments of the present application, the specific implementation method of calculating the voltage threshold and the corrected current arc extinguishing reference value based on the ground parameters, the ground capacitance current and the fault point offset voltage in the above step 14 is:

[0106] The voltage threshold U is calculated by the following formula 0set :

[0107]

[0108] The corrected arc extinguishing current reference value is calculated by the following formula:

[0109]

[0110] in, is the fault phase potential.

[0111] In some embodiments of the present application, when the voltage arc extinguishing method is used to extinguish the arc by comparing the neutral point voltage and the voltage threshold during the fault, the neutral point voltage expression can be made The injection current command value of voltage arc extinguishing can be obtained Substituting the current command value into the current relationship, the residual current I after voltage arc extinguishing can be obtained. r (At this time That is I r ) and the zero-sequence voltage (i.e., neutral point voltage) when no measures are taken after the fault. According to the national standard GB / T 50064-2014, when the fault current is less than 10A, the fault arc can be guaranteed to be self-extinguished. According to the voltage threshold expression, when the neutral point voltage after the fault is less than the voltage threshold, the fault current limit can be below 10A by using voltage arc extinguishing; when the neutral point voltage after the fault is greater than or equal to the voltage threshold, the improved current method is used to limit the fault current, that is, the modified current arc extinguishing reference value is used to implement current arc extinguishing.

[0112] It is worth mentioning that the voltage threshold and the corrected current arc extinguishing reference value obtained by this method can be obtained by injecting power frequency current twice through active devices in normal and fault conditions and monitoring the neutral point voltage. Both of them will change with the fault location, ground fault resistance, and line parameters, so they can adapt to different ground fault conditions and further improve the reliability of single-phase ground fault arc extinguishing.

[0113] The adaptive composite arc extinguishing method based on the zero-sequence voltage threshold of the distribution network of the present application is exemplarily described below in combination with specific experimental data.

[0114] To verify the correctness and effectiveness of the above adaptive composite arc suppression method, an IEEE 13-node 10 kV distribution network as shown in Figure 4 is built in Matlab / Simulink, and the influence of multi-terminal power supply is considered. The following Experiment 1 is the analysis of a single-phase grounding fault with a 30 Ω resistor; Experiment 2 is the analysis of a long-distance low-resistance (1 Ω) grounding fault. Figure 4 where S a is the complex power of the load in phase A, S b is the complex power of the load in phase B, and S c is the complex power of the load in phase C.

[0115] Experiment 1

[0116] The allowable value after arc suppression selected for the simulation is 10 A. The fault occurs at t = 0.01 s, and arc suppression is carried out at t = 0.05 s. As Figures 5a to 5b shown, for the fault points K3 and K5, the residual fault current is still above 10 A after traditional voltage arc suppression. At this time, the improved current arc suppression (i.e., implementing current arc suppression using the corrected current arc suppression reference value) can achieve the effect of limiting the residual fault current below 10 A, as Figures 6a to 6b shown. Other fault conditions are shown in Table 1, and Table 1 is the residual fault current corresponding to the arc suppression method.

[0117]

[0118]

[0119] Table 1

[0120] Experiment 2

[0121] In the case of a long-distance low-resistance grounding fault, as can be seen from Figure 7a , when using the traditional voltage arc suppression method at this time, not only can the arc suppression effect not be achieved, but the fault current will also increase. At this time, the improved current arc suppression proposed in this application can achieve the arc suppression effect, as Figure 7b shown. Other fault conditions are shown in Table 2, and Table 2 is the residual fault current corresponding to the arc suppression method.

[0122]

[0123] Table 2

[0124] Experiment 3

[0125] A comparison of different arc suppression methods was carried out for a 20 Ω single-phase grounding fault occurring in different phases at K5. As Figures 8a to 8cThe arc extinguishing waveforms of the three phases A, B, and C at K5 with a 20Ω single-phase grounding fault are shown. From Table 3 (Table 3 shows the arc extinguishing residual current under the 20Ω single-phase grounding fault at different phases at K5), it can be seen that the traditional voltage method is not within the effective area of successful arc extinguishing at this time, and the simulation waveform also confirms this. From the simulation results, compared with the traditional voltage and traditional current arc extinguishing methods, the composite method of the present application has the best arc extinguishing effect.

[0126]

[0127] Table 3

[0128] In order to verify the correctness and effectiveness of the control strategy proposed in this application, a Figure 9 The 80V distribution network topology shown in the figure. The permissible value after arc extinction selected in the experiment is 1A. Figures 10a to 10b As shown in the figure, for a single-phase grounding fault close to the load side, the fault current itself is very small, only 1.5A, but after traditional voltage and current arc extinguishing, the fault current increases instead, reaching 8.3A and 7.6A respectively, making the situation worse. At this time, the use of composite arc extinguishing can achieve the effect of limiting the fault residual current to below 1A.

[0129] In summary, the present application determines whether to adopt voltage arc extinguishing or current arc extinguishing according to the voltage threshold. The voltage threshold can determine the effective use range of the voltage arc extinguishing method, so that the voltage arc extinguishing method can be used to extinguish the arc when the voltage method is effective, and the corrected current arc extinguishing reference value can be used to implement current arc extinguishing when the voltage arc extinguishing method fails, thereby improving the reliability of single-phase ground fault arc extinguishing. At the same time, because the voltage threshold will change with the fault location, ground fault resistance, and line parameters, it can adapt to different ground fault conditions, further improving the reliability of single-phase ground fault arc extinguishing.

[0130] The above is a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles described in the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. An adaptive composite arc suppression method based on the zero-sequence voltage threshold of a distribution network, characterized in that Including: Monitoring the neutral point voltage of the distribution network and determining whether a single-phase grounding fault occurs in the distribution network based on the monitored neutral point voltage; When no single-phase grounding fault occurs in the distribution network, injecting a first current into the neutral point of the distribution network, obtaining the neutral point voltage of the distribution network after injecting the first current, and calculating the ground parameters of the distribution network and the capacitive current to the ground of the distribution network when the neutral point voltage of the distribution network is zero according to the first current and the neutral point voltage of the distribution network after injecting the first current; When a single-phase grounding fault occurs in the distribution network, injecting a second current into the neutral point of the distribution network, obtaining the neutral point voltage of the distribution network after injecting the second current, and calculating the fault point offset voltage of the distribution network according to the second current and the neutral point voltage of the distribution network after injecting the second current; Calculating a voltage threshold and a corrected arc suppression reference current value based on the ground parameters, the capacitive current to the ground, and the fault point offset voltage, and if the neutral point voltage of the distribution network is less than the voltage threshold when a single-phase grounding fault occurs, performing arc suppression on the distribution network using voltage arc suppression, and if the neutral point voltage of the distribution network is greater than or equal to the voltage threshold when a single-phase grounding fault occurs, performing arc suppression on the distribution network using current arc suppression; The value of the injected current for the current arc suppression is the corrected arc suppression reference current value.

2. The adaptive composite arc suppression method according to claim 1, wherein The calculating the ground parameters of the distribution network and the capacitive current to the ground of the distribution network when the neutral point voltage of the distribution network is zero according to the first current and the neutral point voltage of the distribution network after injecting the first current includes: Construct the current relationship of the equivalent circuit model of the single-phase grounding fault in the distribution network based on Kirchhoff's current law; the current relationship is as follows: is the current injected into the neutral point of the distribution network, is the single-phase grounding fault current, is the neutral point voltage of the distribution network, Y d is the parameter of the distribution network to the ground, is the capacitive current to the ground of the distribution network when the neutral point voltage of the distribution network is zero; Setting the single-phase grounding fault current to zero and substituting the first current and the neutral point voltage of the distribution network after injecting the first current into the current relationship formula to obtain a first equation; Setting the single-phase grounding fault current and the current injected into the neutral point of the distribution network to zero and substituting the neutral point voltage of the distribution network before injecting the first current into the current relationship formula to obtain a second equation; Solve for the ground parameter Y based on the first equation and the second equation d and the ground capacitance current 3. The adaptive composite arc suppression method according to claim 2, characterized in that The calculating the fault point offset voltage of the distribution network according to the second current and the neutral point voltage of the distribution network after injecting the second current includes: Based on the single-phase grounding fault equivalent circuit model of the distribution network, constructing an expression for the neutral point voltage of the distribution network; Based on the neutral point voltage expression and the current relationship formula, obtaining an offset voltage relationship formula; Based on the second current, the neutral point voltage of the distribution network after injecting the second current, and the offset voltage relationship formula, calculating the fault point offset voltage of the distribution network.

4. The adaptive composite arc suppression method according to claim 3, wherein The expression for the neutral point voltage of the distribution network is: Wherein, is the neutral point voltage of the distribution network, G f is the grounding fault resistance, Y L is the line impedance between the fault point and the bus, Y ca is the coupling impedance after star-delta transformation between the faulty phase A and the unfaulty phase C, Y ab is the coupling impedance after star-delta transformation between the faulty phase A and the unfaulty phase B, is the fault point offset voltage.

5. The adaptive composite arc suppression method according to claim 4, characterized in that The offset voltage relationship formula is:

6. The adaptive composite arc suppression method according to claim 5, wherein The calculating the fault point offset voltage of the distribution network based on the second current, the neutral point voltage of the distribution network after injecting the second current, and the offset voltage relationship formula includes: Substituting the second current and the neutral point voltage of the distribution network after injecting the second current into the offset voltage relationship formula to obtain a third equation; Let the current injected into the neutral point of the distribution network be zero, and substitute the neutral point voltage of the distribution network before injecting the second current into the current relationship formula to obtain a fourth equation; Solve for the fault point offset voltage based on the third equation and the fourth equation 7. The adaptive composite arc suppression method according to claim 6, characterized in that, The calculating of the voltage threshold and the corrected arc suppression reference current based on the ground parameters, the capacitive current to ground and the fault point offset voltage includes: The voltage threshold U is calculated by the following formula 0set :[[]]END]] Calculate the corrected current arc suppression reference value using the following formula Among them, is the potential of the faulty phase.

8. The adaptive composite arc suppression method according to claim 1, wherein The judging whether a single-phase grounding fault occurs in the distribution network based on the monitored neutral point voltage includes: If the monitored neutral point voltage is greater than 15% of the phase voltage, it is determined that a single-phase grounding fault occurs in the distribution network; if the monitored neutral point voltage is less than or equal to 15% of the phase voltage, it is determined that no single-phase grounding fault occurs in the distribution network.

9. The adaptive composite arc suppression method according to claim 1, characterized in that, After arc suppression is performed on the distribution network, the adaptive composite arc suppression method further includes: Reducing the output voltage or current of the arc suppression device after a preset time interval, and judging whether the zero-sequence current or voltage of the distribution network changes proportionally after reducing the output of the arc suppression device; If so, remove the arc suppression device; Otherwise, isolate the grounded fault phase feeder of the distribution network and remove the arc suppression device.

10. The adaptive composite arc suppression method according to claim 9, characterized in that, The preset time is 2 seconds.

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