Power distribution network protection method and device, electronic equipment and storage medium

Abstract

The invention discloses a power distribution network protection method and device, electronic equipment and a storage medium. The method comprises the steps that the zero-sequence voltage and the zero-sequence current of the position where a protection device is located in the power distribution network are collected, and the protection device is used for protecting the power distribution network during operation; in response to the zero-sequence current meeting a first control condition, the zero-sequence current is adjusted based on the zero-sequence voltage to obtain a target current, and the first control condition at least comprises a first calibration current; and in response to the target current satisfying a second control condition, controlling the protection device to start to protect the power distribution network, the second control condition at least comprising a second calibration current, and the first calibration current being smaller than the second calibration current. According to the invention, the technical problem of poor flexibility of power distribution network protection in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the field of power distribution networks, and in particular to a power distribution network protection method, device, electronic equipment and storage medium. Background Art

[0002] With the acceleration of urbanization and the shortage of urban land, underground cables have gradually replaced overhead lines. The cable has a large capacitance to the ground, which leads to a large capacitance current to the ground when a fault occurs. The traditional arc suppression coil compensation method is inconvenient to install in this case, and its configuration speed cannot keep up with the expansion speed of cable lines in the distribution network. Therefore, the low resistance grounding method has been widely used in urban distribution networks with rapidly expanding cable lines.

[0003] There are also some problems with relay protection for low-resistance grounded distribution networks, among which high-resistance grounding faults are the most significant. In current related technologies, zero-sequence overcurrent protection is often used to handle grounding faults. The protection threshold is often set based on the premise of avoiding the maximum capacitive current of a sound line. Taking the zero-sequence overcurrent protection setting of 60A commonly used in the field as an example, the maximum transition resistance capacity it can withstand is only about 100Ω. At the same time, since the distribution network is deep in the load center and its environment is complex and changeable, faults of grounding through non-ideal conductors such as branches, soil, ponds or cement buildings, that is, single-phase high-resistance grounding faults, often occur. The transition resistance is often thousands of ohms, and the fault current is very weak. Therefore, the existing overcurrent protection will refuse to operate, resulting in poor flexibility in the protection of the distribution network in related technologies.

[0004] To address the above-mentioned problems, no effective solution has been proposed yet. Summary of the invention

[0005] The embodiments of the present invention provide a distribution network protection method, device, electronic device and storage medium to at least solve the technical problem of poor flexibility in distribution network protection in related technologies.

[0006] According to one aspect of an embodiment of the present invention, a distribution network protection method is provided, comprising: collecting a zero-sequence voltage and a zero-sequence current at a location of a protection device in the distribution network, wherein the protection device is used to protect the distribution network during operation; in response to the zero-sequence current satisfying a first control condition, adjusting the zero-sequence current based on the zero-sequence voltage to obtain a target current, wherein the first control condition at least includes a first calibrated current; in response to the target current satisfying a second control condition, controlling the protection device to start to protect the distribution network, wherein the second control condition at least includes a second calibrated current, and the first calibrated current is less than the second calibrated current.

[0007] Optionally, the zero-sequence current is adjusted based on the zero-sequence voltage to obtain a target current, including: obtaining the line length and zero-sequence capacitance of the line where the protection device is located; obtaining the adjusted current based on the product of the zero-sequence voltage, the line length, the zero-sequence capacitance, and a preset coefficient; and obtaining the target current based on the difference between the zero-sequence current and the adjusted current.

[0008] Optionally, the distribution network protection method also includes determining a first calibrated current and a second calibrated current that match the system identifier of the distribution network from a calibrated ammeter, wherein the calibrated ammeter is used to store an association between the first calibrated current, the second calibrated current and the system identifier; in response to the zero-sequence current being greater than the first calibrated current, determining that the zero-sequence current satisfies a first control condition; in response to the target current being greater than the second calibrated current, determining that the target current satisfies a second control condition.

[0009] Optionally, the distribution network protection method also includes obtaining the system voltage of the distribution network, the line structure of the distribution network, the transition resistance of the distribution network, and the protective resistance of the protection device, wherein the transition resistance is used to characterize the resistance between the fault location and the ground when a fault occurs in the distribution network; determining a first calibration current based on the system voltage, the transition resistance and the protective resistance; determining a second calibration current based on the line structure and the system voltage; and constructing a calibration current table based on the system identification of the distribution network, the first calibration current and the second calibration current.

[0010] Optionally, based on the system voltage, transition resistance and protection resistance, a first calibration current is determined, including: obtaining the line voltage based on the quotient of the system voltage and a first coefficient; obtaining the first resistance value based on the sum of the transition resistance and the protection resistance; obtaining the second resistance value based on the product of the first resistance value and the second coefficient; obtaining the initial calibration current based on the quotient of the line voltage and the second resistance value; and adjusting the initial calibration current based on the reliability coefficient of the distribution network to obtain the first calibration current.

[0011] Optionally, based on the line structure and the system voltage, a second calibration current is determined, including: obtaining a maximum unbalanced current that matches the line structure and the system voltage from a balancing current meter, wherein the balancing current meter is used to store the correlation between the line structure, the system voltage and the maximum unbalanced current; and adjusting the maximum unbalanced current based on the reliability coefficient of the distribution network to obtain the second calibration current.

[0012] According to another aspect of an embodiment of the present invention, a distribution network protection device is also provided, including: an acquisition module, used to acquire the zero-sequence voltage and zero-sequence current at the location of the protection device in the distribution network, wherein the protection device is used to protect the distribution network during operation; an adjustment module, used to respond to the zero-sequence current satisfying a first control condition, and to adjust the zero-sequence current based on the zero-sequence voltage to obtain a target current, wherein the first control condition at least includes a first calibrated current; and a control module, used to respond to the target current satisfying a second control condition, and to control the protection device to start to protect the distribution network, wherein the second control condition at least includes a second calibrated current, and the first calibrated current is less than the second calibrated current.

[0013] According to another aspect of an embodiment of the present invention, there is further provided an electronic device, comprising: a memory storing an executable program; and a processor for running the program, wherein the above-mentioned distribution network protection method is executed when the program is running.

[0014] According to another aspect of an embodiment of the present invention, a computer-readable storage medium is further provided. The computer-readable storage medium includes a stored executable program, wherein when the executable program runs, the device where the storage medium is located is controlled to execute the above-mentioned distribution network protection method.

[0015] According to another aspect of an embodiment of the present invention, a computer program product is further provided. When the computer program is executed by a processor, the above-mentioned distribution network protection method is implemented.

[0016] In an embodiment of the present invention, after collecting the zero-sequence voltage and zero-sequence current at the location of the protection device in the distribution network, in response to the zero-sequence current satisfying the first control condition, the zero-sequence current is adjusted based on the zero-sequence voltage to obtain the target current, and in response to the target current satisfying the second control condition, the protection device is controlled to start, thereby achieving the purpose of protecting the distribution network. It is easy to notice that in the present application, based on the zero-sequence voltage and zero-sequence current, it is possible to flexibly determine whether the protection device meets the control conditions when a fault occurs in the distribution network. First, it is determined whether the zero-sequence current meets the first control condition, that is, the zero-sequence current is greater than the first calibration current. If not, the protection device is not started, ensuring that the healthy outlet does not malfunction under a low threshold during a high-resistance fault. If the first control condition is met, the zero-sequence current is adjusted based on the zero-sequence voltage to obtain the target current, and then it is determined whether the target current meets the second control condition, that is, the target current is greater than the second calibration current. If so, the protection device is activated. The above process ensures the correct operation of the faulty outlet during a high-resistance fault, avoids the distribution network safety problem caused by a high-resistance fault, and thus solves the technical problem of poor flexibility in distribution network protection in the related technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] Figure 1 is a flow chart of a distribution network protection method according to an embodiment of the present invention;

[0019] Figure 2 is a flow chart of an optional distribution network protection method according to an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of a typical 10kV low-resistance grounding system single-phase grounding simulation model;

[0021] Figure 4 This is the relationship between the zero-sequence current of the faulty outgoing line and the sound outgoing line without compensation and the commonly used protection threshold (40-60A) when a single-phase grounding fault occurs at point F1;

[0022] Figure 5 It is a relationship diagram between the zero-sequence current of each outgoing line before and after compensation and the low protection threshold set by the present invention;

[0023] Figure 6 is a schematic diagram of a distribution network protection device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0025] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0026] According to an embodiment of the present invention, an embodiment of a distribution network protection method is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0027] Figure 1 is a flow chart of a distribution network protection method according to an embodiment of the present invention. Figure 1 As shown, the method comprises the following steps:

[0028] Step S102, collecting the zero-sequence voltage and zero-sequence current at the location of the protection device in the distribution network, wherein the protection device is used to protect the distribution network during operation.

[0029] The protection device in the above steps is used to describe the device used to detect and isolate faults in the power system. Protecting the power system through the protection device can reduce the impact of the fault on the power grid and users, and improve the protection level and reliability of the distribution network. The protection device may include but is not limited to overcurrent protection devices, zero-sequence current protection devices, distance protection devices, quick-break protection devices, and power factor protection devices. The above protection devices can be used alone or in combination, and need to be determined according to the protection requirements of the power system and related parameters, which are not limited here.

[0030] The zero-sequence voltage in the above steps is used to describe the voltage component in the three-phase power system where the vector sum of the three-phase voltages is zero. Under normal operating conditions, the three-phase voltages are balanced, so theoretically there is no zero-sequence voltage. However, when a ground fault or other asymmetric fault occurs, the vector sum of the three-phase voltages is no longer zero, resulting in a zero-sequence voltage. Therefore, the zero-sequence voltage may include but is not limited to the zero-sequence voltage during a single-phase ground fault, the zero-sequence voltage during a two-phase ground fault, and the zero-sequence voltage during three-phase unbalanced operation. In the power system, the monitoring and analysis of the zero-sequence voltage is crucial to maintaining the normal operation of the power system. By monitoring the zero-sequence voltage, various asymmetric faults can be discovered and handled in a timely manner to ensure the safe and reliable operation of the power system.

[0031] The zero-sequence current in the above steps is used to describe the remaining current component when the vector sum of the three-phase currents is zero in a three-phase AC power system. The zero-sequence current usually appears when there is a ground fault or an asymmetric load in the system. The zero-sequence current may include but is not limited to normal zero-sequence current, ground fault zero-sequence current, zero-sequence current caused by resonance, zero-sequence current caused by asymmetric load, and zero-sequence current caused by external interference.

[0032] In an optional embodiment, in order to ensure the safety of the distribution network and prevent ground faults and other factors from causing damage to the distribution network, a protection device can be set for the distribution network according to the needs of the distribution network. The protection device is usually set in a substation or distribution room. Further, at the installation location of the protection device, the effective value of the zero-sequence voltage and zero-sequence current is collected. These electrical quantity information is crucial for subsequent fault detection and protection actions. Among them, the collection method includes but is not limited to multi-function meter collection, power analyzer collection, Hall effect sensor collection, and capacitive sensor collection.

[0033] Step S104, in response to the zero-sequence current satisfying a first control condition, adjusting the zero-sequence current based on the zero-sequence voltage to obtain a target current, wherein the first control condition at least includes a first calibrated current.

[0034] The first calibrated current in the above steps is used to describe the minimum current threshold for the protection device to start. That is to say, only when the current flowing through the protection device reaches or exceeds this value, the protection device will start working and enter a ready state. This value is usually set to take into account the maximum unbalanced current generated by the power grid during normal operation to ensure that the protection device will not malfunction due to small current fluctuations during normal operation of the power grid. It is usually determined by the system voltage, system resistance and the protection resistance of the protection device. The specific current calculation standard needs to be determined according to the power system and is not limited here.

[0035] The first control condition in the above steps is used to describe the conditions that the distribution network protection system needs to meet first when a fault or abnormality occurs, including but not limited to fault detection conditions, fault type identification conditions, fault location conditions and protection action conditions, etc. In the present invention, it can be a condition constructed based on the first rated current. The specific control conditions need to be determined according to the actual power system conditions and are not limited here.

[0036] The above-mentioned target current is used to describe the specific current value used for judgment and decision-making in the process of fault detection and processing. It is usually based on the zero-sequence current monitored by the protection device and is obtained after certain processing and calculation. It is used to determine whether a fault occurs and the nature of the fault.

[0037] In an optional embodiment, the three-phase current in the power distribution network is usually balanced. When a ground fault occurs, the balance of the three-phase current is broken, generating a zero-sequence current. The protection device in the distribution network will monitor the zero-sequence current and zero-sequence voltage of each outgoing line in real time. When the monitored zero-sequence current exceeds the preset first calibration current, that is, the "first control condition" is met, the protection device will start further fault detection and processing procedures. Among them, the zero-sequence voltage is a manifestation of the imbalance of the three-phase voltage in the power system, which usually changes significantly when a ground fault occurs; the protection device will adjust the zero-sequence current based on the measured zero-sequence voltage. This adjustment process may involve complex algorithms, which can be to first calculate the adjustment current based on the capacitance current, load characteristics, etc. of the line, and then use the zero-sequence current to subtract the adjustment current to obtain the adjusted zero-sequence current, that is, the target current. This current value is the current value that the protection device expects to obtain after considering all relevant factors, and is used to more accurately determine whether a ground fault has occurred.

[0038] Step S106, in response to the target current satisfying the second control condition, controlling the protection device to start to protect the distribution network, wherein the second control condition at least includes a second calibrated current, and the first calibrated current is less than the second calibrated current.

[0039] The second calibrated current in the above step is used to describe the current threshold value of the protection device action, that is, when the current flowing through the protection device reaches or exceeds this value, the protection device will perform its protection action, such as disconnecting the circuit. The setting of the specific current value needs to take into account factors such as the current level of the distribution network when a fault occurs, so as to ensure that the faulty part can be cut off in time when a fault occurs in the distribution network to protect the safety of the distribution network, which is not limited here.

[0040] The second control condition in the above steps is used to describe that on the basis of satisfying the first control condition, the distribution network achieves more precise control and protection of the power system, including but not limited to fault current limiting conditions, fault recovery conditions and protection device startup conditions, etc. In the present invention, it can be a condition constructed based on the second calibrated current, wherein the first calibrated current is less than the second calibrated current. The specific control conditions need to be determined according to the actual situation of the power system and are not limited here.

[0041] In an optional embodiment, Figure 2 It is a flow chart of an optional distribution network protection method, such as Figure 2 As shown in the figure, the protection method for ground fault in distribution network mainly includes the following steps: first, measure the power frequency zero sequence voltage and current at each outgoing line protection installation and calculate the effective values ​​3I0 and 3U0; when 3I0 is greater than the starting current 3I sThe distribution network protection device starts when the protection is on, otherwise the distribution network protection device does not start; then the zero-sequence current measured at the protection installation is compensated and its effective value is calculated. That is, the current after the zero-sequence current is corrected; if The distribution network protection device will start to protect the distribution network, otherwise the distribution network protection device will not operate.

[0042] In an embodiment of the present invention, after collecting the zero-sequence voltage and zero-sequence current at the location of the protection device in the distribution network, in response to the zero-sequence current satisfying the first control condition, the zero-sequence current is adjusted based on the zero-sequence voltage to obtain the target current, and in response to the target current satisfying the second control condition, the protection device is controlled to start, thereby achieving the purpose of protecting the distribution network. It is easy to notice that in the present application, based on the zero-sequence voltage and zero-sequence current, it is possible to flexibly determine whether the protection device meets the control conditions when a fault occurs in the distribution network. First, it is determined whether the zero-sequence current meets the first control condition, that is, the zero-sequence current is greater than the first calibration current. If not, the protection device is not started, ensuring that the healthy outlet does not malfunction under a low threshold during a high-resistance fault. If the first control condition is met, the zero-sequence current is adjusted based on the zero-sequence voltage to obtain the target current, and then it is determined whether the target current meets the second control condition, that is, the target current is greater than the second calibration current. If so, the protection device is activated. The above process ensures the correct operation of the faulty outlet during a high-resistance fault, avoids the distribution network safety problem caused by a high-resistance fault, and thus solves the technical problem of poor flexibility in distribution network protection in the related technology.

[0043] Optionally, the zero-sequence current is adjusted based on the zero-sequence voltage to obtain a target current, including: obtaining the line length and zero-sequence capacitance of the line where the protection device is located; obtaining the adjusted current based on the product of the zero-sequence voltage, the line length, the zero-sequence capacitance, and a preset coefficient; and obtaining the target current based on the difference between the zero-sequence current and the adjusted current.

[0044] The zero-sequence capacitance in the above steps may refer to the capacitance of a winding or conductor on the ground or between them, and its type may be determined based on factors such as the number of conductors and the conductor connection method, and may include but is not limited to self-zero-sequence capacitance, mutual zero-sequence capacitance, parallel zero-sequence capacitance, series zero-sequence capacitance, and zero-sequence capacitance to ground.

[0045] In an optional embodiment, the zero-sequence current adjustment method includes using the line length and zero-sequence capacitance parameters to correct the zero-sequence current. First, the zero-sequence current I0, the zero-sequence voltage U0, the length l of each outgoing line and the zero-sequence capacitance c0 per unit length at the installation location of each outgoing line protection device are collected, wherein the zero-sequence current I0 includes the healthy outgoing line zero-sequence current I 0i The zero-sequence current of the fault line is I 0up Then the current adjustment of each outgoing line under non-fault conditions is calculated, that is,

[0046] I comi =U0jωc0l;

[0047] Among them, w represents the angular frequency and j represents the imaginary unit. Then, the actual measured zero-sequence current value is corrected using the calculated theoretical value, and the target current is obtained after correction, that is,

[0048]

[0049] in, It indicates the corrected result under the condition of healthy outgoing line, that is, the target current under the condition of healthy outgoing line. It indicates the corrected result under faulty outgoing line condition, that is, the target current under faulty outgoing line condition.

[0050] For a healthy line, I comi This is the theoretical value of the zero-sequence capacitance current of the outgoing line to ground, and the actual measured value of the zero-sequence current at the installation location of the protection device I 0i The difference is not big, the corrected result under the condition of sound exit Close to zero. For the faulty outgoing line, I comi This is the theoretical value of the zero-sequence current of a healthy line with the same length and parameters as the outgoing line. Studies have shown that in the case of high-resistance grounding, the zero-sequence current in the faulty outgoing line is always more than ten times that of all healthy outgoing lines. Therefore, the corrected result in the case of a faulty outgoing line is Compared with the original measured value I 0up Not much difference.

[0051] Optionally, the distribution network protection method also includes: determining a first calibrated current and a second calibrated current that match the system identifier of the distribution network from a calibrated ammeter, wherein the calibrated ammeter is used to store an association relationship between the first calibrated current, the second calibrated current and the system identifier; in response to the zero-sequence current being greater than the first calibrated current, determining that the zero-sequence current satisfies a first control condition; in response to the target current being greater than the second calibrated current, determining that the target current satisfies a second control condition.

[0052] The calibrated ammeter in the above steps may refer to a data table for recording current, voltage or other data, including but not limited to storing different data and the corresponding relationship between data, and may be used to store the first calibrated current and the second calibrated current.

[0053] In an optional embodiment, the target current With the second calibration current I set By comparison, as the criterion for the zero-sequence overcurrent protection with improved sensitivity in this application:

[0054]

[0055] For faulty outgoing lines Protection action; for healthy outgoing lines The protection does not operate. This action characteristic is not affected by the transition resistance, which can ensure that the faulty outgoing line operates correctly in the case of a high-resistance fault and that the sound outgoing line does not operate incorrectly under a low threshold in the case of a resistance fault. In a low-resistance grounded distribution network, when the distributed generation (Distributed Generation) DG is connected to the grid in an ungrounded manner, the fault zero-sequence network of the system does not change, and the above derivation process is still applicable.

[0056] Optionally, the distribution network protection method also includes: obtaining the system voltage of the distribution network, the line structure of the distribution network, the transition resistance of the distribution network, and the protective resistance of the protection device, wherein the transition resistance is used to characterize the resistance between the fault location and the ground when a fault occurs in the distribution network; determining a first calibration current based on the system voltage, the transition resistance and the protective resistance; determining a second calibration current based on the line structure and the system voltage; and constructing a calibration current table based on the system identification of the distribution network, the first calibration current and the second calibration current.

[0057] The system voltage in the above steps may refer to the voltage value of each point in the power system, which may be a line voltage (the voltage between two phases) or a phase voltage (the voltage between a phase and the ground), and the like.

[0058] The transition resistance in the above steps may refer to the resistance value of a non-metallic conductor or medium through which the grounding current passes when a single-phase grounding fault occurs in an electrical system. Its functions include but are not limited to limiting the impact of the grounding current on the power grid, improving system stability, and reducing the risk of equipment damage. In actual applications, the size and characteristics of the transition resistance will vary depending on the type of grounding fault, the nature of the grounding medium, and the configuration of the electrical system. Therefore, it is not limited here. When designing and maintaining electrical systems, the impact of the transition resistance needs to be comprehensively considered to ensure the safe, reliable, and economical operation of the system.

[0059] The protection resistor in the above steps can be used to withstand current within a certain range in the circuit. When the current exceeds a predetermined value, it can limit the current by generating heat, changing the resistance value or other mechanisms, thereby protecting other important components in the circuit, which may include but are not limited to fixed protection resistors, variable protection resistors, fuses, and overvoltage protection resistors.

[0060] In an optional embodiment, during the implementation of the protection method of the distribution network, it is first necessary to obtain the key parameters of the distribution network, including the system voltage, line structure, transition resistance and protection resistance of the protection device; then based on the obtained system voltage, transition resistance and protection resistance, the first calibration current is determined by calculation or table lookup, and the first calibration current is the expected action current of the protection device in the face of a specific transition resistance; secondly, according to the line structure and system voltage of the distribution network, the second calibration current is determined, and the second calibration current is related to the carrying capacity of the line, the length of the line or other electrical characteristics; and then the system identification of the distribution network (including the name, location, voltage level and other information of the distribution network), the first calibration current and the second calibration current are used to construct a calibration current meter, which is a reference for the action of the protection device to ensure that the protection device can respond correctly under different conditions. In the whole process, the construction of the calibration current meter is the key, which needs to comprehensively consider the various operating parameters and conditions of the distribution network to ensure that effective protection can be provided in various situations. At the same time, this process also requires the protection device to have a certain degree of intelligence and be able to make quick and accurate judgments based on real-time data.

[0061] Optionally, based on the system voltage, transition resistance and protection resistance, a first calibration current is determined, including: obtaining the line voltage based on the quotient of the system voltage and a first coefficient; obtaining the first resistance value based on the sum of the transition resistance and the protection resistance; obtaining the second resistance value based on the product of the first resistance value and the second coefficient; obtaining the initial calibration current based on the quotient of the line voltage and the second resistance value; and adjusting the initial calibration current based on the reliability coefficient of the distribution network to obtain the first calibration current.

[0062] The first coefficient and the second coefficient in the above steps are used to describe the multiple relationship between numerical values, and are usually determined according to the specific relationship between numerical values ​​in actual applications. Here, the first coefficient can be √3, and the second coefficient can be 3.

[0063] The first resistance value in the above step may refer to the sum of the transition resistance value and the protection resistance value.

[0064] The second resistance value in the above steps refers to the product of the first resistance value and the second coefficient.

[0065] The initial calibration current in the above steps can refer to I 0up .

[0066] The reliability coefficient in the above steps can be a coefficient used to measure the probability that a system or device will operate normally or achieve a predetermined function within a specific time. In the power system, the reliability coefficient can be used to evaluate the ability of the power grid to meet user needs, including the stability and continuity of power supply.

[0067] In an optional embodiment, when a 2000Ω ground fault occurs in a 10kV system, ignoring the line impedance, the zero-sequence current at the fault outlet, i.e., the initial calibration current, is:

[0068]

[0069] Among them, U A Indicates the system voltage, R n With R f They represent transition resistance and protection resistance respectively.

[0070] In order to make the protection method of this application able to cope with a transition resistance of about 2000Ω, the setting value of the protection action should be greater than 0.96A. Considering a certain reliability coefficient (K rel =1.2), the protection action value should be 0.96 / 1.2≈0.8A. The protection device is generally connected to 3 times the zero-sequence current, corresponding to the setting value 3I set It is 2.4A.

[0071] Affected by factors such as three-phase closing at different times, unbalanced three-phase parameters, and non-full-phase power supply, zero-sequence unbalanced current will also be generated during normal operation of the system. Therefore, the setting value of the protection starting current should be greater than the maximum balanced current of the system. According to existing literature, the maximum unbalanced current of overhead lines and cable lines in a 10kV low-resistance grounded distribution network is 0.37A and 0.26A. The setting value of the current in this application is three times the zero-sequence current. Therefore, considering the reliability factor (K rel =1.2), the setting value of the starting current is 3I s It can be 1.33 A. Regardless of cable lines or overhead lines, the zero-sequence unbalanced current will not exceed the protection starting current.

[0072] Optionally, based on the line structure and the system voltage, a second calibration current is determined, including: obtaining a maximum unbalanced current that matches the line structure and the system voltage from a balancing current meter, wherein the balancing current meter is used to store the correlation between the line structure, the system voltage and the maximum unbalanced current; and adjusting the maximum unbalanced current based on the reliability coefficient of the distribution network to obtain the second calibration current.

[0073] The maximum unbalanced current in the above steps is used to describe an unbalanced current generated in the system when there is a difference in the amplitude or phase of the three-phase current, which may include but is not limited to steady-state unbalanced current, transient unbalanced current and random unbalanced current. The existence of the maximum unbalanced current will increase the energy consumption of the line and affect the safety and stability of the power equipment, so it needs to be adjusted to reduce the impact on the system.

[0074] The balancing ammeter in the above steps may refer to a data table used to record current, voltage or other data, including but not limited to storing different data and the correspondence between data, and can be used to store maximum unbalanced current, system voltage, line structure data and the relationship between data.

[0075] In an optional embodiment, Figure 3 This is a typical 10kV low-resistance grounding system single-phase grounding simulation model schematic diagram. Figure 3 The four outgoing lines (outgoing line 1, outgoing line 2, outgoing line 3 and outgoing line 4) are all cable lines, and the neutral point grounding resistance R n =10Ω, the grounding transformer is represented by capital letters 301, and 302 is distributed generation. The fault trigger time is set at 0.1s, the fault initial phase angle is set to 0°, and the sampling frequency is set to 6.4kHz. The fault type is a single-phase grounding fault, and the fault points (F1, F2) are set at phase A at different positions of outgoing line 1 and outgoing line 2. P1, P2, P3, and P4 in the figure are protection devices installed at each outgoing line outlet, and the distributed power source is connected to the grid at the midpoint of outgoing line 3. The line parameters are shown in Table 1:

[0076] Table 1 Line parameters

[0077]

[0078] Assuming that a single-phase grounding fault occurs at phase A F1 of outgoing line 1, and the transition resistance is a linear resistance, simulations are performed when the transition resistance is 0-2200Ω, and the action of the protection proposed by the present invention is shown in Table 2.

[0079] Table 2 Protection action (stable ground fault occurs at F1)

[0080]

[0081] Note: In Table 2, the first column is the transition resistance value, the second column is three times the busbar zero-sequence voltage, the third, fifth, seventh, and ninth columns are three times the actual measured value of the zero-sequence current at each outgoing line protection installation, the fourth, sixth, eighth, and tenth columns are three times the zero-sequence current value after correction at each outgoing line protection installation, and the eleventh and twelfth columns are the protection action conditions when the measured value at the protection installation (before correction) and the zero-sequence current value after correction (after correction) are compared with the protection threshold. ↑↓ indicates that the protection is reset after starting, ↑√ indicates that the protection is actuated after starting, ↑☆ indicates that the protection is actuated after starting but the sensitivity is less than 1.2, × indicates that the protection is not started, and - indicates that the measured value is less than the starting current and does not need to be corrected. The above rules also apply to Table 3, which will not be repeated below.

[0082] According to the data recorded in Table 2, after lowering the protection threshold, the zero-sequence overcurrent protection can operate correctly under the condition of transition resistance below 2000Ω and meet certain sensitivity requirements (K sen =1.2); when the transition resistance reaches 2200Ω, the protection can still work correctly but does not meet the sensitivity requirement; when the transition resistance is higher, the protection will refuse to work. Therefore, the method proposed in the present invention can withstand transition resistance of more than 2000Ω when the transition resistance is linear.

[0083] For low-resistance grounding faults with a transition resistance of less than 100Ω, if the measured value at the protection installation is directly compared with the protection threshold, the healthy outgoing line protection (P1, P3, P4) will be misactivated. After adding current correction, the healthy outgoing line protection in low-resistance grounding conditions can be reliably non-activated.

[0084] When a single-phase grounding fault occurs in the actual system, intermittent arc grounding is more likely and the damage is the most serious. When a single-phase metallic grounding fault occurs in the distribution network, the power grid is allowed to operate with the fault for two hours, while the arc grounding fault needs to be quickly cleared.

[0085] The present invention adopts the classic cybernetics model to model the arc for intermittent arc grounding faults. In the cybernetics model, the fault transition resistance is composed of nonlinear arc resistance and linear resistance in series. Assume that the single-phase grounding fault occurs in phase A (at F2) of the outgoing line 2, which is 7 km away from the busbar, and is an intermittent arc grounding fault. The protection action under different transition resistance conditions is shown in Table 3.

[0086] Table 3 Protection action (intermittent arc grounding fault occurs at F2)

[0087]

[0088] It can be seen from Table 3 that when an intermittent arc grounding fault occurs, the protection method can also withstand transition resistance up to 2000Ω. However, due to the current correction of the fault line, the zero-sequence current is slightly reduced, resulting in the protection action not meeting certain sensitivity requirements (K) in the case of a 2000Ω fault after correction. sen =1.2), sacrificing a part of the transition resistance capability, but the transition resistance capability of this method is still close to 2000Ω.

[0089] In the case of low-resistance grounding, comparing the zero-sequence current measured at the protection installation with the action threshold will still cause false operation of the healthy outgoing line protection; however, using the corrected zero-sequence current to make protection judgments can ensure that the healthy outgoing line will reliably not operate.

[0090] Therefore, the protection method proposed in the present invention can still take into account the sensitivity of protection during high-resistance grounding faults and the selectivity of protection during low-resistance grounding faults in the case of intermittent arc grounding.

[0091] Taking the single-phase grounding fault at F1 of outgoing line 1 as an example, the relationship between the zero-sequence current of the faulty outgoing line and the sound outgoing line without compensation and the commonly used protection threshold (40-60A) is as follows: Figure 4 The relationship between the zero-sequence current of each outgoing line before and after compensation and the low protection threshold set by the present invention is shown in Figure 5 As shown, 501 represents the corrected zero-sequence current of the healthy outgoing line, 502 represents the zero-sequence current of the healthy outgoing line before correction, 503 represents the corrected zero-sequence current of the faulty outgoing line, and 504 represents the zero-sequence current of the faulty outgoing line before correction.

[0092] Depend on Figure 4 It can be seen that the threshold value of the traditional zero-sequence overcurrent protection is 40-60A, and the protection method can withstand a transition resistance of 90-140Ω, which cannot cope with ground faults of thousands of ohms. Figure 5 It can be seen that the zero-sequence current of the healthy outgoing line is close to zero after compensation, while the zero-sequence current of the faulty outgoing line does not change much after compensation. If the protection threshold is lowered blindly without current compensation, the protection will malfunction when the low-resistance grounding fault is satisfied under the premise of the protection action when the high-resistance grounding fault is satisfied. However, by adopting the protection method proposed by the present invention, the protection can not only tolerate a transition resistance of up to 2000Ω, but also the healthy line will not malfunction when the low-resistance grounding fault occurs.

[0093] According to another aspect of an embodiment of the present invention, a distribution network protection device is also provided, which can execute the battery insulation detection method of the above embodiment. The specific implementation method and preferred application scenario are the same as the above embodiment and will not be repeated here.

[0094] Figure 6 is a schematic diagram of a distribution network protection device according to an embodiment of the present application, such as Figure 6 As shown, the device includes the following: a collection module 602 , an adjustment module 604 , and a control module 606 .

[0095] Wherein, the acquisition module 602 is used to acquire the zero-sequence voltage and zero-sequence current at the location of the protection device in the distribution network, wherein the protection device is used to protect the distribution network during operation; the adjustment module 604 is used to respond to the zero-sequence current satisfying the first control condition, adjust the zero-sequence current based on the zero-sequence voltage, and obtain the target current, wherein the first control condition at least includes the first calibration current; the control module 606 is used to respond to the target current satisfying the second control condition, control the protection device to start, so as to protect the distribution network, wherein the second control condition at least includes the second calibration current, and the first calibration current is less than the second calibration current. Optionally, the adjustment module includes: an acquisition unit, used to obtain the line length and zero-sequence capacitance of the line where the protection device is located; a calculation unit, used to obtain the adjustment current based on the zero-sequence voltage, the line length, the zero-sequence capacitance, and the product of the preset coefficient; a determination unit, used to obtain the target current based on the difference between the zero-sequence current and the adjustment current.

[0096] Optionally, the above-mentioned device also includes: a first determination module, used to determine a first calibrated current and a second calibrated current that match the system identifier of the distribution network from a calibrated ammeter, wherein the calibrated ammeter is used to store the association relationship between the first calibrated current, the second calibrated current and the system identifier; a second determination module, used to determine that the zero-sequence current satisfies the first control condition in response to the zero-sequence current being greater than the first calibrated current; and a third determination module, used to determine that the target current satisfies the second control condition in response to the target current being greater than the second calibrated current.

[0097] Optionally, the above-mentioned device also includes: an acquisition module, which is used to acquire the system voltage of the distribution network, the line structure of the distribution network, the transition resistance of the distribution network, and the protective resistance of the protection device, wherein the transition resistance is used to characterize the resistance between the fault location and the ground when a fault occurs in the distribution network; a fourth determination module, which is used to determine the first calibration current based on the system voltage, the transition resistance and the protective resistance; a fifth determination module, which is used to determine the second calibration current based on the line structure and the system voltage; and a sixth determination module, which is used to construct a calibration current meter based on the system identification of the distribution network, the first calibration current and the second calibration current.

[0098] Optionally, the fourth determination module also includes: obtaining the line voltage based on the quotient of the system voltage and the first coefficient; obtaining the first resistance value based on the sum of the transition resistance and the protection resistance; obtaining the second resistance value based on the product of the first resistance value and the second coefficient; obtaining the initial calibration current based on the quotient of the line voltage and the second resistance value; and adjusting the initial calibration current based on the reliability coefficient of the distribution network to obtain the first calibration current.

[0099] Optionally, the fifth determination module includes: obtaining a maximum unbalanced current that matches the line structure and the system voltage from a balancing current meter, wherein the balancing current meter is used to store the correlation relationship between the line structure, the system voltage and the maximum unbalanced current; adjusting the maximum unbalanced current based on the reliability coefficient of the distribution network to obtain a second calibrated current.

[0100] According to another aspect of an embodiment of the present invention, there is also provided an electronic device, comprising: one or more processors; a storage device for storing one or more programs; when the one or more programs are executed by one or more processors, the one or more processors execute the above-mentioned distribution network protection method.

[0101] The storage device in the above steps can be a kind of sequential logic circuit, a memory component used to store data and instructions, etc., mainly used to store programs and data; the processor can be a functional unit that interprets and executes instructions, and it has a unique set of operating commands, which can be called the instruction set of the processor, such as storage, loading, etc. are all operations; the storage device stores computer programs, which can be a set of instructions that can be recognized and executed by a computer, running on an electronic computer, and is an information tool that meets certain needs of people.

[0102] According to another aspect of an embodiment of the present invention, a computer-readable storage medium is further provided. The computer-readable storage medium includes a stored program, wherein when the program is executed, the processor of the device where the program is located is controlled to execute the above-mentioned distribution network protection method.

[0103] The computer storage medium in the above steps can be a medium used to store certain discontinuous physical quantities in a computer memory, and the computer storage medium mainly includes semiconductors, magnetic cores, magnetic drums, magnetic tapes, laser disks, etc. The stored program included in the computer-readable storage medium can be a set of instructions that can be recognized and executed by a computer, running on an electronic computer, and is an information tool that meets certain needs of people.

[0104] According to another aspect of the embodiments of the present invention, a computer program product is provided, including a computer program. When the computer program is executed by a processor, the distribution network protection method in each embodiment of the present invention is implemented.

[0105] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0106] In the above embodiments of the present invention, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0107] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are only schematic. For example, the division of the units can be a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, which can be electrical or other forms.

[0108] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple units. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0109] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0110] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program codes.

[0111] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A distribution network protection method, It is characterized in that include: Collecting zero-sequence voltage and zero-sequence current at a location of a protection device in a distribution network, wherein the protection device is used to protect the distribution network during operation; In response to the zero-sequence current satisfying a first control condition, adjusting the zero-sequence current based on the zero-sequence voltage to obtain a target current, wherein the first control condition at least includes a first calibration current; In response to the target current satisfying a second control condition, the protection device is controlled to start to protect the distribution network, wherein the second control condition at least includes a second rated current, and the first rated current is less than the second rated current.

2. The method according to claim 1, It is characterized in that The zero-sequence current is adjusted based on the zero-sequence voltage to obtain a target current, including: Obtaining the line length and zero-sequence capacitance of the line where the protection device is located; Obtaining an adjustment current based on the product of the zero-sequence voltage, the line length, the zero-sequence capacitance, and a preset coefficient; The target current is obtained based on the difference between the zero-sequence current and the adjustment current.

3. The method according to claim 1, It is characterized in that The method further comprises: Determining the first calibration current and the second calibration current matching the system identifier of the power distribution network from a calibration current meter, wherein the calibration current meter is used to store an association relationship between the first calibration current, the second calibration current and the system identifier; In response to the zero-sequence current being greater than the first calibration current, determining that the zero-sequence current satisfies the first control condition; In response to the target current being greater than the second rated current, it is determined that the target current satisfies the second control condition.

4. The method according to claim 3, It is characterized in that The method further comprises: Acquire the system voltage of the distribution network, the line structure of the distribution network, the transition resistance of the distribution network, and the protection resistance of the protection device, wherein the transition resistance is used to characterize the resistance between the fault location and the ground when a fault occurs in the distribution network; Determining the first calibration current based on the system voltage, the transition resistance and the protection resistance; Determining the second calibration current based on the line structure and the system voltage; The calibrated current table is constructed based on the system identifier of the power distribution network, the first calibrated current, and the second calibrated current.

5. The method according to claim 4, It is characterized in that Determining the first calibration current based on the system voltage, the transition resistance, and the protection resistance includes: Obtaining a line voltage based on a quotient of the system voltage and a first coefficient; Obtaining a first resistance value based on the sum of the transition resistance and the protection resistance; Obtaining a second resistance value based on the product of the first resistance value and a second coefficient; obtaining an initial calibration current based on a quotient of the line voltage and the second resistance value; The initial calibration current is adjusted based on the reliability coefficient of the distribution network to obtain the first calibration current.

6. The method according to claim 4, It is characterized in that Determining the second calibration current based on the line structure and the system voltage includes: Acquire a maximum unbalanced current matching the line structure and the system voltage from a balancing current table, wherein the balancing current table is used to store an association relationship between the line structure, the system voltage, and the maximum unbalanced current; The maximum unbalanced current is adjusted based on the reliability coefficient of the distribution network to obtain the second calibrated current.

7. A distribution network protection device, used to implement the distribution network protection method described in claim 1, It is characterized in that include: A collection module, used for collecting zero-sequence voltage and zero-sequence current at a location of a protection device in a distribution network, wherein the protection device is used for protecting the distribution network during operation; an adjustment module, configured to adjust the zero-sequence current based on the zero-sequence voltage to obtain a target current in response to the zero-sequence current satisfying a first control condition, wherein the first control condition at least includes a first calibration current; A control module is used to control the protection device to start in response to the target current satisfying a second control condition to protect the distribution network, wherein the second control condition at least includes a second calibrated current, and the first calibrated current is less than the second calibrated current.

8. An electronic device, It is characterized in that include: A memory storing an executable program; A processor is used to run the program, wherein the program executes the distribution network protection method described in any one of claims 1 to 7 when running.

9. A computer-readable storage medium, It is characterized in that The computer-readable storage medium includes a stored executable program, wherein when the executable program is executed, the device where the storage medium is located is controlled to execute the distribution network protection method according to any one of claims 1 to 7.

10. A computer program product, It is characterized in that The invention comprises a computer program, which implements the power distribution network protection method according to any one of claims 1 to 7 when being executed by a processor.

Images