Direct current transmission line protection method and device without inductance boundary element, computer equipment and storage medium

Abstract

The invention relates to a direct current transmission line protection method and device of a non-inductance boundary element, computer equipment and a storage medium. The method comprises the following steps: acquiring voltage data and current data of a current protection unit, and acquiring adjacent current data of an adjacent protection unit connected to the same modular multilevel converter with the current protection unit; under the condition that the voltage data and the current current data meet a preset protection activation condition, according to the current current data and the adjacent current data, determining protection current decay time in a first preset time window; and when the attenuation time of the protection current meets a preset internal fault condition and a tripping signal is received, the current protection unit is controlled to act so as to isolate the fault. Therefore, the protection reliability of the direct-current transmission line of the non-inductive boundary element can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system DC transmission protection, and particularly relates to a DC transmission line protection method and device without inductance boundary element, computer equipment and storage medium. BACKGROUND

[0002] The existing DC line protection mainly relies on inductance boundary elements on both sides of the line to distinguish internal and external faults. The existing technology proposes a protection criterion based on du / dt, which is simple in structure but weak in resistance capacity; uses the strong correlation between inductance voltage and current derivative to enhance the anti-noise performance; and uses the voltage polarity comparison of the reactor in combination with the integral method to suppress the coupled interference.

[0003] However, the above-mentioned solutions all have common defects: insufficient resistance to high resistance faults, and high dependence on inductance boundary elements. Once the boundary element fails, the protection performance will be severely degraded or even completely collapsed.

[0004] In summary, for the transmission line with a direct connection architecture and no inductance boundary element on both sides, at least the fault recognition accuracy is low, resulting in low reliability of the DC transmission line protection without inductance boundary element. SUMMARY

[0005] Therefore, the present application aims to at least solve one of the above technical defects, in particular, the low reliability of the DC transmission line protection in the prior art. The present application provides a DC transmission line protection method and device without inductance boundary element, computer equipment and storage medium.

[0006] In a first aspect, the present application provides a DC transmission line protection method without inductance boundary element. The DC line end of the same modular multilevel converter is provided with two DC transmission lines, and each DC transmission line is provided with a protection unit on the side close to the modular multilevel converter. The method comprises:

[0007] Collecting voltage data and current data of the current protection unit, and collecting adjacent current data of the adjacent protection unit connected to the same modular multilevel converter as the current protection unit;

[0008] In the case that the voltage data and the current data meet the preset protection activation condition, determining the protection current decay time within the first preset time window according to the current data and the adjacent current data;

[0009] In the case that the protection current decay time meets the preset internal fault condition and a trip signal is received, controlling the current protection unit to act to isolate the fault.

[0010] In one of the embodiments, the method further comprises:

[0011] obtain a zero-mode voltage corresponding to the voltage data of the current protection unit;

[0012] determine a fault pole type of the DC transmission line according to the zero-mode voltage and a preset fault pole threshold condition.

[0013] In one of the embodiments, the protection current decay time within the first preset time window is determined according to the current data and the adjacent current data, including:

[0014] sum the current data and the adjacent current data to obtain the protection current;

[0015] obtain the protection current decay time according to a time when a derivative of the protection current decays from a maximum value to a preset value.

[0016] In one of the embodiments, the current protection unit is controlled to act in the case that the protection current decay time satisfies a preset intra-zone fault condition and a trip signal is received, including:

[0017] obtain a first intra-zone fault condition and a second intra-zone fault condition;

[0018] control the current protection unit to act in the case that the protection current decay time satisfies the first intra-zone fault condition and the second intra-zone fault condition and a trip signal is received.

[0019] In one of the embodiments, the method includes:

[0020] determine a corresponding sub-protection current decay time calculated by the current protection unit when a metal fault occurs at a first end of a sub-line of the current protection unit;

[0021] obtain a first decay time threshold according to the sub-protection current decay time and a preset first reliability coefficient;

[0022] if the protection current decay time is less than the first decay time threshold, it represents that the protection current decay time satisfies the first intra-zone fault condition.

[0023] In one of the embodiments, the method includes:

[0024] determine a corresponding end protection current decay time calculated by the current protection unit when a metal fault occurs at an end of the current line of the current protection unit;

[0025] obtain a second decay time threshold according to the end protection current decay time and a preset second reliability coefficient;

[0026] if the protection current decay time is less than the second decay time threshold, it represents that the protection current decay time satisfies the second intra-zone fault condition.

[0027] In one embodiment, the method further comprises:

[0028] Deriving the voltage data and the current data to obtain voltage derivative data and current derivative data, respectively;

[0029] If the absolute value of the voltage derivative data is greater than a preset voltage derivative threshold value, and the absolute value of the current derivative data is greater than a preset current derivative threshold value, it is indicated that the voltage data and the current data satisfy a preset protection activation condition.

[0030] In a second aspect, the application provides a direct current transmission line protection device without inductance boundary element, two direct current transmission lines are arranged at the direct current line end of the same modular multilevel converter, and each direct current transmission line is provided with a protection unit at the side close to the modular multilevel converter; the device comprises:

[0031] A data acquisition module is configured to acquire voltage data and current data of a current protection unit, and acquire adjacent current data of an adjacent protection unit connected to the same modular multilevel converter as the current protection unit;

[0032] A protection current decay module is configured to determine a protection current decay time within a first preset time window according to the current data and the adjacent current data, if the voltage data and the current data satisfy a preset protection activation condition.

[0033] A protection control action module is configured to control the current protection unit to act to isolate a fault, if the protection current decay time satisfies a preset intra-zone fault condition, and a trip signal is received.

[0034] In a third aspect, the application provides a computer device, comprising a memory and a processor, the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0035] In a fourth aspect, the application provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the steps of the above method.

[0036] As can be seen from the above technical solutions, the embodiments of the application have the following advantages:

[0037] The DC power transmission line protection method, device, computer equipment and storage medium provided by the application can realize accurate fault identification under the condition of the inductance-free boundary element, solve the problem of insufficient high-resistance fault identification capability caused by the dependence of the traditional scheme on the inductance boundary, and thus improve the reliability of the DC power transmission line protection of the inductance-free boundary element. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0039] Figure 1 A structure schematic diagram of a four-terminal DC power grid is provided in the present application.

[0040] Figure 2 A flowchart of a DC power transmission line protection method of an inductance-free boundary element is provided in the embodiments of the present application.

[0041] Figure 3 A schematic diagram of a protection current waveform is provided in the embodiments of the present application.

[0042] Figure 4 A schematic diagram of a DTPCS is provided in the embodiments of the present application.

[0043] Figure 5 A schematic diagram of protection current and its derivative waveforms of the same fault position and different fault resistances is provided in the embodiments of the present application.

[0044] Figure 6 A result schematic diagram of a DTPCS under different fault conditions is provided in the embodiments of the present application.

[0045] Figure 7 A trend schematic diagram of a DTPCS with the change of fault distance is provided in the embodiments of the present application.

[0046] Figure 8 A flowchart of specific implementation steps of a DC power transmission line protection method of an inductance-free boundary element is provided in the embodiments of the present application.

[0047] Figure 9 A structure schematic diagram of a DC power transmission line protection device of an inductance-free boundary element is provided in the embodiments of the present application.

[0048] Figure 10 This is a schematic diagram of the internal structure of a computer device provided in an embodiment of this application. Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0050] Existing single-ended protection schemes for DC power grids have the following problems: First, most protection schemes rely on inductive boundary elements. If the inductive boundary elements disappear, the protection scheme will have a dead zone or even fail completely due to the similarity of fault characteristics between the far-end faults in the protection zone and the first-end faults of the downstream lines. Second, the protection schemes lack better protection criteria to withstand fault resistance when facing high-resistance faults.

[0051] Based on this, this application provides a method, apparatus, computer equipment, and storage medium for protecting DC transmission lines without inductive boundary elements, which can improve the reliability of DC transmission line protection without inductive boundary elements.

[0052] In one exemplary embodiment, such as Figure 1 As shown, Figure 1 This application provides a schematic diagram of a four-terminal DC power grid, wherein the protection unit installed on the I-side bus of Line J is marked as P. IJ The corresponding DCCB (DC circuit breaker) is defined as DCCB. IJ Where J takes values ​​of '1', '2', '3', '4', and '5'; I takes values ​​of 'M', 'N', 'P', and 'Q'. For protection unit P... M1 In this context, f1, f2, and f3 represent internal faults, forward external faults, and reverse external faults, respectively. No boundary reactor is installed at the line terminal; the current-limiting inductor (marked as L) is used. limit It is installed at the substation outlet to suppress excessive fault current.

[0053] In one exemplary embodiment, Figure 2 This is a flowchart illustrating a DC transmission line protection method without inductive boundary elements provided in an embodiment of this application, as shown below. Figure 2 As shown, a method for protecting DC transmission lines without inductive boundary elements is provided, which can be applied to... Figure 1With the method taking the terminal as the execution subject as an example, it can be understood that the method can also take the server as the execution subject, and can also be applied to a system including the terminal and the server, and be realized through the interaction of the terminal and the server. The terminal can be, but is not limited to, various personal computers, notebook computers, smart phones, tablet computers. The server can be a stand-alone physical server, can also be a server cluster or a distributed system composed of multiple physical servers, and can also be a cloud server providing cloud computing services. In the embodiment, the method includes the following S201 to S206. The direct current line of the same modular multilevel converter is provided with two direct current transmission lines, and each direct current transmission line is provided with a protection unit on the side close to the modular multilevel converter; wherein:

[0054] S201, collecting voltage data and current data of the current protection unit, and collecting adjacent current data of the adjacent protection unit connected to the same modular multilevel converter as the current protection unit;

[0055] S202, in the case that the voltage data and the current data meet the preset protection activation condition, determining the protection current decay time within the first preset time window according to the current data and the adjacent current data;

[0056] S203, in the case that the protection current decay time meets the preset intra-zone fault condition and the trip signal is received, controlling the current protection unit to act to isolate the fault.

[0057] The protection unit refers to a monitoring and control device arranged on the side of the direct current line close to the converter, which can be specifically realized by an intelligent terminal device integrating a voltage transformer and a current sensor, and is used for real-time acquisition of electrical quantities and execution of protection logic. The protection current decay time refers to the time required for the fault current derivative to decay from the peak value to the preset threshold, which can be specifically realized by differential operation combined with time stamp recording, and the parameter can represent the dynamic decay characteristic of the fault current. The intra-zone fault condition refers to the preset current decay time threshold range, which can be specifically determined by simulating and calculating the typical decay time under different fault positions and combining the reliability coefficient, and is used for distinguishing the fault in the protection area from the fault outside the protection area.

[0058] Exemplarily, when the DC line is faulty, the local protection unit can synchronously collect the bus voltage and the local line current, and simultaneously acquire the current data of the adjacent line protection unit through the communication link. The system performs real-time differential operation on the voltage and current data, and determines that the protection activation condition is met when the voltage derivative exceeds the preset threshold and the current derivative reaches the starting threshold. Subsequently, the local current and the adjacent current are superimposed to obtain the protection current, and the time for the derivative curve of the protection current to decay from the maximum value to a set proportion is taken as the decay time. By comparing the time with the threshold determined based on the metallic fault simulation, whether the fault is located in the protection zone of the protection unit can be accurately determined. If the breaker tripping signal is simultaneously received, the protection action is triggered immediately.

[0059] In actual application, the criterion is constructed by analyzing the dynamic decay characteristics of the multi-terminal current data, which eliminates the dependence on the inductance boundary. The traditional method is prone to misjudgment when the fault resistance is high because the characteristics are not obvious, and the decay time parameter is not sensitive to the change of the fault transition resistance, which significantly improves the resistance capacity. In addition, the cooperative processing mechanism of the adjacent protection unit data effectively avoids the misoperation risk caused by the noise interference of a single data source.

[0060] In the embodiment, by the dynamic decay time criterion and the multi-terminal data fusion, the dependence on the inductance is eliminated while the discrimination between the internal and external faults is enhanced, which ensures the fast and accurate action of the protection system under complex working conditions, thereby the reliability of the DC transmission line protection element without inductance boundary can be improved.

[0061] In an exemplary embodiment, the method further comprises:

[0062] acquiring the zero-mode voltage corresponding to the voltage data of the current protection unit;

[0063] determining the fault pole type of the DC transmission line according to the zero-mode voltage and a preset fault pole threshold condition.

[0064] The zero-mode voltage refers to the sum of the positive and negative voltages, which can be obtained by adding the positive and negative voltage data collected by the voltage sensor, and is used to represent the change of the positive and negative voltages in the line, thereby reflecting the voltage mutation characteristics of the fault pole.

[0065] The fault pole threshold condition refers to the preset voltage threshold range for distinguishing the positive or negative fault, which can be determined by simulation or experiment to determine the zero-mode voltage range under different fault types, and is used to establish the judgment boundary of the positive fault threshold and the negative fault threshold, thereby improving the accuracy of the fault pole type identification.

[0066] Exemplarily, when the zero-mode voltage exceeds the preset negative fault threshold upper limit, it is determined that the negative electrode is faulty; when the zero-mode voltage is lower than the preset positive fault threshold lower limit, it is determined that the positive electrode is faulty. The determination process directly uses the voltage data characteristics to determine the fault electrode by monitoring the amplitude change of the zero-mode voltage in real time, without relying on the voltage or current characteristics of the inductive boundary element. For example, in a bipolar direct current transmission system, if it is detected that the zero-mode voltage suddenly increases to exceed the negative fault threshold, the negative fault protection action logic is triggered, and the positive protection logic is locked to avoid misjudgment.

[0067] Optionally, the determination of the fault electrode depends on the P MN1 The zero-mode voltage is shown in formula (1). Wherein, u M0set is the fault electrode identification threshold, which should be greater than the maximum value of the zero-mode voltage u MN1 of the bipolar fault. M0

[0068] (1) ;

[0069] In actual application, the fault electrode is determined by the voltage polarity or integral value of the inductive boundary element, and the scheme directly determines the fault electrode based on the comparison of the zero-mode voltage and the preset threshold, avoiding the protection logic failure caused by the failure of the inductive element. At the same time, the sudden change characteristics of the zero-mode voltage have higher sensitivity to high resistance faults, which can improve the reliability of fault electrode determination.

[0070] In the embodiment, the fault electrode type of the direct current line can be accurately identified without relying on the inductive boundary element, the problem of reduced protection reliability caused by the failure of the boundary element in the prior art is solved, and the resistance to high resistance faults is enhanced.

[0071] In an exemplary embodiment, according to the current data and the adjacent current data, the protection current decay time in the first preset time window is determined, including:

[0072] The current data and the adjacent current data are summed to obtain the protection current;

[0073] The time from the maximum value of the derivative of the protection current to the preset value is obtained as the protection current decay time.

[0074] ​The current data refers to the real-time current measurement value of the DC transmission line where the protection unit is located, which can be collected by a Hall sensor or a Rogowski coil, and is used to reflect the instantaneous current change of the line. The adjacent current data refers to the current measurement value of the DC transmission line on the other side of the same modular multilevel converter, which can be synchronously obtained through the data communication interface of the adjacent protection unit, and is used to provide the current correlation information between the lines. The protection current refers to the integrated current amount obtained by algebraically summing the current data and the adjacent current data, which can be realized by real-time superposition operation through a digital signal processor, and is used to eliminate the current coupling interference between the lines.

[0075] The protection current decay time refers to the time required for the derivative of the protection current to decrease from the peak value to a preset value, which can be measured by a differential circuit combined with a time counter, and is used to quantify the dynamic characteristics of the current change.

[0076] For example, after detecting that the voltage and current meet the activation condition, the protection unit first collects the current data of the line, and obtains the current data of the adjacent line through the communication link. The two current data are summed to generate the protection current. Then, the derivative of the protection current is obtained by differential processing, and the time window in which the derivative decays from the maximum value to the preset threshold is recorded. The time window reflects the decay speed of the fault current, and in combination with the preset threshold condition, the intra-zone fault and the external disturbance can be effectively distinguished.

[0077] In actual application, the current data of the adjacent line is directly used to generate the integrated protection current, and the fault is judged by the derivative decay time, without the need for additional inductive elements, which avoids the reliability problem caused by the failure of the boundary element, and improves the resistance to high resistance faults.

[0078] In this embodiment, the intra-zone fault of the DC transmission line can be accurately identified, the influence of the current coupling interference between the lines on the protection criterion is eliminated, and the reliability of the protection action and the anti-high resistance fault capability are improved in the scenario without inductive boundary elements.

[0079] In one exemplary embodiment, in the case where the protection current decay time meets the preset intra-zone fault condition and a trip signal is received, the current protection unit is controlled to act, including:

[0080] obtaining a first intra-zone fault condition and a second intra-zone fault condition;

[0081] In the case where the protection current decay time meets the first intra-zone fault condition and the second intra-zone fault condition, and a trip signal is received, the current protection unit is controlled to act.

[0082] The fault condition in the first zone refers to a time threshold calculated by combining the protection current decay time and reliability coefficient corresponding to a metallic fault at the beginning of the downstream line. Specifically, this can be calculated using simulation data of a metallic fault at the beginning of the downstream line combined with preset coefficients, and is used to determine whether a fault has occurred in the zone at the downstream line. The fault condition in the second zone refers to a time threshold calculated by combining the protection current decay time and reliability coefficient corresponding to a metallic fault at the end of the current line. Specifically, this can be calculated using simulation data of a metallic fault at the end of the current line combined with preset coefficients, and is used to determine whether a fault has occurred at the end of the current line.

[0083] For example, when the protection unit detects the current derivative decay result, it needs to simultaneously verify whether the decay time is less than the first-level decay time threshold corresponding to the fault at the beginning of the downstream line, and whether it is less than the second-level decay time threshold corresponding to the fault at the end of the current line. If both conditions are met, it is determined to be an intra-zone fault, and the protection action is triggered in conjunction with the trip signal. This dual-criteria mechanism effectively eliminates interference from external faults by superimposing the verification conditions of two independent fault scenarios.

[0084] By setting two levels of independent verification conditions and constructing composite criterion logic, the identification accuracy of faults inside and outside the zone is significantly improved in scenarios without inductive boundary components.

[0085] In this embodiment, a dual verification mechanism can be constructed based on the metal fault characteristics of different fault locations, enabling accurate differentiation between faults inside and outside the zone in scenarios without inductive boundary components, avoiding false operation caused by a single criterion, and improving the reliability of DC transmission line protection.

[0086] In one exemplary embodiment, the method includes:

[0087] When a metallic fault occurs at the beginning of the downstream line of the current protection unit, the corresponding downstream protection current decay time is calculated through the current protection unit.

[0088] The first-level decay time threshold is obtained based on the decay time of the lower-level protection current and the preset first reliability coefficient.

[0089] If the protection current decay time is less than the first-level decay time threshold, it indicates that the protection current decay time meets the fault conditions in the first zone.

[0090] Among them, the lower-level protection current decay time refers to the time required for the derivative of the protection current to decay from its maximum value to a preset value when a metallic fault occurs at the beginning of the lower-level line. Specifically, it can be obtained through simulation or calibration using actual fault test data, and is used to reflect the dynamic characteristics of current change when a fault occurs at the beginning of the lower-level line.

[0091] The first reliability coefficient refers to the preset coefficient used to adjust the first-level decay time threshold. It can be set using empirical values ​​or based on system stability requirements. For example, it can be a value in the range of 0.7 to 0.9. Its function is to ensure that the threshold is set within the reliable range by introducing redundancy, and to avoid misjudgment due to measurement errors or interference.

[0092] For example, the decay time of the downstream protection current corresponding to a metallic fault at the beginning of the downstream line should be predetermined, for instance, by establishing a time parameter database for typical fault scenarios through offline simulation. The first reliability coefficient is multiplied by the decay time of the downstream protection current to obtain the first-level decay time threshold. In actual operation, if the decay time of the protection current calculated in real time is less than this threshold, it indicates that the decay rate of the current derivative conforms to the typical characteristics of a fault at the beginning of this level of line, thus determining that the fault conditions within the first zone are met, providing a basis for protection action.

[0093] In practical applications, by introducing the typical decay time of faults at the beginning of the lower-level line and combining it with the reliability coefficient to dynamically generate thresholds, it is possible to more accurately distinguish between faults within and outside the zone, and to effectively improve the adaptability of the criterion, especially under conditions without inductance boundaries.

[0094] In this embodiment, high-resistance faults at the end of the line can be accurately identified, avoiding protection failure due to missing boundary elements. At the same time, dynamic threshold setting enhances the tolerance to high-resistance faults, thereby improving the reliability of protection for DC transmission lines without inductance boundaries.

[0095] In one exemplary embodiment, the method includes:

[0096] When a metallic fault occurs at the end of the current line in the current protection unit, the current protection unit calculates the corresponding end protection current decay time.

[0097] The secondary decay time threshold is obtained based on the end protection current decay time and the preset second reliability coefficient;

[0098] If the protection current decay time is less than the secondary decay time threshold, it indicates that the protection current decay time meets the fault conditions in the second zone.

[0099] In this context, the term "end of line" refers to the end region of the DC transmission line where the current protection unit is located. This can be achieved by dividing the line into sections based on the line topology. When a fault occurs in this region, it needs to be quickly identified to narrow down the protection range.

[0100] Metallic faults refer to faults where the line conductors are directly short-circuited, creating extremely low transition resistance. This can be detected through current surge characteristics, and such faults significantly affect the current decay rate. The end-of-line protection current decay time refers to the time required for the derivative of the protection current to decay from its maximum value to a preset value when a metallic fault occurs at the end of the line. This can be achieved through derivative calculation combined with time window statistics. This parameter quantifies the correlation between the fault location and the protection unit. The second reliability coefficient is a safety margin parameter used to adjust the threshold calculation. It can be set based on historical fault data or simulation test results, for example, a range of 1.1 to 1.3, to avoid protection maloperation. The secondary decay time threshold is a reference value obtained by multiplying the end-of-line protection current decay time by the second reliability coefficient. This can be achieved through real-time calculation, and this threshold is used to distinguish between line-end faults and remote faults outside the protection zone.

[0101] For example, when a metallic fault occurs at the end of a line, the derivative of the transient current generated at the fault point decays rapidly within a preset time window. By measuring this decay time in real time and comparing it with a pre-calculated secondary decay time threshold, it can be accurately determined whether the fault is within the jurisdiction of the current protection unit. For instance, when the measured decay time is less than the threshold, it indicates that the fault point is within the protection zone, and the protection action can be triggered by combining this with a trip signal. This method avoids the dependence on inductive boundary elements in traditional solutions by quantifying the logical relationship between the decay time and the preset threshold.

[0102] In practical applications, fault location can be achieved without additional boundary components by directly analyzing the dynamic relationship between the current derivative decay characteristics and a preset threshold. For example, traditional solutions may lead to misjudgment in high-impedance faults due to the weakening of inductor voltage characteristics, while this solution enhances the identification capability under high-impedance conditions by using the current decay time parameter of the end fault.

[0103] In this embodiment, by establishing a correlation mechanism between the attenuation time of the fault current at the end of the circuit and the dynamic threshold, accurate identification of faults within the circuit is achieved, avoiding the decrease in protection reliability caused by the failure of boundary components in traditional solutions. This method is particularly suitable for direct-connection architecture scenarios, and can improve the accuracy of the protection system without adding hardware equipment.

[0104] In some specific embodiments, such as Figure 1 As shown, to protect P M1 For example, Line 1 is P M1 The lines that should be protected are also called the local lines. When Line 1 experiences a fault, P... M1 DCCB as required M1 Take action. When a fault occurs on Line 3, the downstream line, P... M1 It should be identified as an out-of-area fault, and no action should be taken.

[0105] Electromagnetic transient simulation software PSCAD / EMTDC can be used to build systems such as... Figure 1 The four-terminal DC grid shown uses a metal fault set at 900 km to collect data located at P. M1 and P M2 Current data I MNp I MNn I PMp and I PMn The sampling frequency is 500kHz.

[0106] For fault f1 in the positive region, it will be located in P. M1 and P M2 Current decoupling yields a first-mode current I. MN1 and I PM1 The data is summed and named the protection current, with the waveform as follows: Figure 3 As shown. The slope of the protective current reaches P when the traveling wave... M1 It reaches its maximum at one point, then gradually decreases to a steady level until the subsequent traveling wave arrives.

[0107] Differentiate the protection current with respect to the current, and then convert the derivative of the protection current to e, which decays from its maximum value to its maximum value. -m The time required to multiply the current is defined as DTPCS (protective current decay time), such as... Figure 4 As shown.

[0108] Through multiple simulations, the waveforms, derivative waveforms, and DTPCS results of the protection current under different fault conditions were plotted, as shown below. Figure 5 and Figure 6 As shown. Figure 5 This application provides a schematic diagram of the waveforms of the protection current and its derivative at the same fault location with different fault resistors, according to an embodiment of the present application. Figure 6 The results of a DTPCS under different fault conditions are provided in the embodiments of this application.

[0109] according to Figure 4 It can be observed that increasing the fault resistance only changes the amplitude of the protection current traveling wave, while having almost no effect on the decay rate. According to Figure 5 It can be seen that the amplitude of DTPCS is positively correlated with the fault location, and is almost unaffected by the fault resistance. In summary, utilizing the characteristic of DTPCS being almost unaffected by fault resistance to construct protection can greatly improve the protection's ability to withstand fault resistance.

[0110] Using the same method, the DTPCS of a 1000 km line under fault conditions inside and outside the fault zone was calculated through simulation. The trend of DTPCS with fault distance is as follows: Figure 7 As shown, Figure 7The DTPCS provided by the embodiment of the application has a variation trend with the fault distance. The DTPCS monotonously increases with the increase of the fault distance in the case of the in-zone fault and the out-zone fault. However, the DTPCS decreases at the boundary between the in-zone fault and the out-zone fault.

[0111] Optionally, the data window length relied on by the one-stage protection criterion is T1, and the range of T1 is [t act -0.2T1, t act +0.8T1]. The DTPCS is calculated according to the data in T1. If formula (2) is satisfied, the in-zone fault occurs, and the protection immediately takes measures; meanwhile, the trip signal is sent to the opposite end of the line through the optical fiber. Wherein, λ1 represents the corresponding DTPCS when the metal fault occurs at the first end of the lower line, and K1 is a reliability coefficient, and the value of K1 is less than 1.

[0112] (2).

[0113] Optionally, the two-stage protection criterion can include:

[0114] If the DTPCS satisfies formula (3), it is necessary to determine whether to order the trip according to whether the trip signal sent by the opposite end is received. If formula (3) is not satisfied, it means that the out-zone fault occurs, and the protection is deactivated. Wherein, λ2 represents the corresponding DTPCS when the metal fault occurs at the end of the current line, and K2 is a reliability coefficient, and the value of K2 is greater than 1.

[0115] (3).

[0116] If the protection does not receive the trip signal in the case of satisfying formula (3), it means that the out-zone fault occurs, and the protection is deactivated and continues to monitor; if the protection receives the trip signal sent by the opposite end, it means that the in-zone fault occurs, and the protection immediately requires the DCCB to act to isolate the fault.

[0117] In an exemplary embodiment, the method further comprises:

[0118] Derivatives of the voltage data and the current data are obtained respectively to obtain voltage derivative data and current derivative data;

[0119] If the absolute value of the voltage derivative data is greater than a preset voltage derivative threshold value, and the absolute value of the current derivative data is greater than a preset current derivative threshold value, it is indicated that the voltage data and the current data satisfy the preset protection activation condition.

[0120] Wherein, the voltage derivative data refers to the instantaneous change rate obtained by differentiating the voltage signal, which can be realized by a differential circuit or a digital signal processing algorithm, and is used to quickly capture the voltage mutation characteristics. The current derivative data refers to the instantaneous change rate obtained by differentiating the current signal, which can be realized by a Hall sensor cooperating with a differential amplifier, and is used to quantify the current change rate. The voltage derivative threshold refers to the pre-set critical value of the voltage change rate, which can be determined by simulation test or field operation data statistics, and is used to distinguish normal operation fluctuation from fault state. The current derivative threshold refers to the pre-set critical value of the current change rate, which can be calibrated according to the line parameters and fault current characteristics, and is used to exclude non-fault current disturbance.

[0121] Exemplarily, in the protection unit starting stage, the voltage signal and the current signal are synchronously input to the differentiation processing module. The voltage derivative data can quickly identify the line voltage sudden drop or sudden rise phenomenon by calculating the voltage change rate in real time; the current derivative data can effectively capture the mutation characteristics of the fault current by tracking the current change trend. When the absolute value of the voltage derivative data exceeds the pre-set voltage derivative threshold, it indicates that the line voltage appears abnormal fluctuation; at the same time, when the absolute value of the current derivative data exceeds the pre-set current derivative threshold, it indicates that the current change rate reaches the fault level. The joint determination of the two conditions can accurately trigger the protection activation mechanism and avoid the misoperation caused by single criterion.

[0122] In this embodiment, the protection function is reliably activated by the double criteria of voltage and current derivatives, which solves the problem of protection performance degradation caused by the failure of boundary elements in the traditional scheme, and at the same time enhances the protection action accuracy in the high resistance fault scene.

[0123] In some specific embodiments, for the four-terminal DC grid model as shown in Figure 1 , the voltage u and the current i of the positive and negative lines at the installation place of the protection are measured in real time, and the 1-mode and 0-mode voltage and current data are obtained by decoupling. The decoupling calculation formula is as follows:

[0124] (4) ;

[0125] After decoupling, the corresponding voltage and current sampling points are calculated in real time and differentiated. u M1 and i MN1 are the 1-mode voltage and current at P MN1 , respectively. and are the activation thresholds of the voltage and current derivatives, respectively, and the values thereof should be greater than the maximum value of the voltage and current derivatives during normal operation of the line. If formula (2) is met, the protection is activated, and the protection activation time t act is recorded.

[0126] (6);

[0127] In some specific embodiments, the complete protection procedure is as shown in Figure 8 Figure 8 A flowchart of specific implementation steps of a direct current transmission line protection method of a non-inductive boundary element provided by an embodiment of the present application.

[0128] It should be understood that, although each step in the flowchart involved in each embodiment as described above is shown in sequence according to the arrow, these steps are not necessarily executed in sequence according to the arrow. Unless otherwise specified herein, the execution of these steps is not strictly limited in sequence, and these steps can be executed in other sequences. Moreover, at least part of the steps in the flowchart involved in each embodiment as described above can include multiple steps or stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence of these steps or stages is not necessarily sequential, but can be executed alternately or alternately with at least part of other steps or steps or stages in other steps.

[0129] The direct current transmission line protection device of a non-inductive boundary element provided by an embodiment of the present application is described below. The direct current transmission line protection device of a non-inductive boundary element has the same inventive concept as the above-mentioned direct current transmission line protection method of a non-inductive boundary element. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme described in the above-mentioned method. Therefore, the specific limitations in one or more direct current transmission line protection device embodiments of a non-inductive boundary element provided below can refer to the limitations of the direct current transmission line protection method of a non-inductive boundary element described above. The direct current transmission line protection device of a non-inductive boundary element described below can be mutually corresponding to the direct current transmission line protection method of a non-inductive boundary element described above. Here, it is not repeated.

[0130] In one exemplary embodiment, Figure 9 A structural diagram of a direct current transmission line protection device of a non-inductive boundary element provided by an embodiment of the present application is shown in Figure 9 The direct current transmission line protection device 90 of a non-inductive boundary element includes a data acquisition module 910, a protection current attenuation module 920, and a protection control action module 930, wherein:

[0131] The data acquisition module 910 is configured to acquire voltage data and current data of a current protection unit, and acquire adjacent current data of adjacent protection units connected to the same modular multilevel converter as the current protection unit;

[0132] ​The protection current decay module 920 is configured to, when the voltage data and the current data meet the preset protection activation condition, determine a protection current decay time within a first preset time window according to the current data and the adjacent current data.

[0133] The protection control action module 930 is configured to, when the protection current decay time meets the preset in-zone fault condition and a trip signal is received, control the current protection unit to act to isolate the fault.

[0134] In an exemplary embodiment, the apparatus further comprises a fault pole determination module. The fault pole determination module is configured to acquire zero-mode voltage corresponding to the voltage data of the current protection unit; and determine a fault pole type of the DC power transmission line according to the zero-mode voltage and a preset fault pole threshold condition.

[0135] In an exemplary embodiment, the protection current decay module 920 is configured to sum the current data and the adjacent current data to obtain a protection current; and obtain the protection current decay time according to a time for a derivative of the protection current to decay from a maximum value to a preset value.

[0136] In an exemplary embodiment, the protection control action module 930 is configured to acquire a first in-zone fault condition and a second in-zone fault condition; and control the current protection unit to act when the protection current decay time meets the first in-zone fault condition and the second in-zone fault condition and a trip signal is received.

[0137] In an exemplary embodiment, the protection control action module 930 is configured to, when a metal fault occurs at a first end of a lower-level line of the current protection unit, calculate a corresponding lower-level protection current decay time by the current protection unit; obtain a first decay time threshold according to the lower-level protection current decay time and a preset first reliability coefficient; and if the protection current decay time is less than the first decay time threshold, it is indicated that the protection current decay time meets the first in-zone fault condition.

[0138] In an exemplary embodiment, the protection control action module 930 is configured to, when a metal fault occurs at an end of the current line of the current protection unit, calculate a corresponding end protection current decay time by the current protection unit; obtain a second decay time threshold according to the end protection current decay time and a preset second reliability coefficient; and if the protection current decay time is less than the second decay time threshold, it is indicated that the protection current decay time meets the second in-zone fault condition.

[0139] In one example embodiment, the protection current attenuation module 920 is configured to derive the voltage data and the current data respectively to obtain voltage derivative data and current derivative data; if the absolute value of the voltage derivative data is greater than a preset voltage derivative threshold value, and the absolute value of the current derivative data is greater than a preset current derivative threshold value, it is indicated that the voltage data and the current data satisfy the preset protection activation condition.

[0140] In one example embodiment, the present application further provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the steps of the DC power transmission line protection method without inductance boundary element according to any one of the above embodiments.

[0141] In one example embodiment, the present application further provides a computer device, which comprises a memory and a processor, and the memory stores a computer program, and the processor executes the computer program to implement the steps of the DC power transmission line protection method without inductance boundary element according to any one of the above embodiments.

[0142] In one example embodiment, the present application further provides a computer program product, which comprises a computer program, and the computer program is executed by a processor to implement the steps of the DC power transmission line protection method without inductance boundary element according to any one of the above embodiments.

[0143] As shown in Figure 10 , Figure 10 Fig. 1 shows an internal structure of a computer device according to an embodiment of the present application. The computer device 1000 can be provided as a server. As shown in Figure 10 , the computer device 1000 comprises a processing assembly 1002, which further comprises one or more processors, and a memory resource represented by a memory 1001, for storing instructions executable by the processing assembly 1002, such as an application program. The application program stored in the memory 1001 can comprise one or more than one module each corresponding to a set of instructions. In addition, the processing assembly 1002 is configured to execute the instructions to perform the DC power transmission line protection method without inductance boundary element according to any one of the above embodiments.

[0144] The computer device 1000 can further comprise a power supply assembly 1003 configured to perform power supply management of the computer device 1000, a wired or wireless network interface 1004 configured to connect the computer device 1000 to a network, and an input output (I / O) interface 1005. The computer device 1000 can operate based on an operating system stored in the memory 1001, such as Windows Server TM, Mac OS X TM, Unix TM, Linux TM, Free BSD TM or the like.

[0145] Those skilled in the art can understand that Figure 10 The structure shown in the figure is only a block diagram of part of the structure related to the scheme of the present application, and does not constitute a limitation on the computer device to which the scheme of the present application is applied. The specific computer device can include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0146] Finally, it should be noted that in this document, the terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0147] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The various embodiments can be combined as needed, and the same and similar parts refer to each other.

[0148] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for protecting DC transmission lines without inductive boundary elements, characterized in that, Two DC transmission lines are provided at the DC line end of the same modular multilevel converter, and each DC transmission line is equipped with a protection unit on the side closer to the modular multilevel converter; the method includes: Collect the voltage and current data of the current protection unit, and collect the adjacent current data of the adjacent protection units connected to the same modular multilevel converter as the current protection unit; If the voltage data and the current current data meet the preset protection activation conditions, the protection current decay time within the first preset time window is determined based on the current current data and the adjacent current data. When the protection current decay time meets the preset fault conditions within the zone and a trip signal is received, the current protection unit is controlled to operate to isolate the fault.

2. The method according to claim 1, characterized in that, The method further includes: Obtain the zero-mode voltage corresponding to the voltage data of the current protection unit; Based on the zero-mode voltage and the preset fault pole threshold conditions, the fault pole type of the DC transmission line is determined.

3. The method according to claim 1, characterized in that, The step of determining the protection current decay time within a first preset time window based on the current current data and the adjacent current data includes: The protection current is obtained by summing the current data and the adjacent current data. The protection current decay time is obtained by calculating the time it takes for the derivative of the protection current to decay from its maximum value to a preset value.

4. The method according to claim 1, characterized in that, The step of controlling the current protection unit to operate when the protection current decay time meets the preset fault condition within the zone and a trip signal is received includes: Obtain the fault conditions in the first zone and the fault conditions in the second zone; If the protection current decay time meets the fault conditions in the first zone and the fault conditions in the second zone, and a trip signal is received, the current protection unit is controlled to operate.

5. The method according to claim 4, characterized in that, The method includes: When a metallic fault is determined to occur at the beginning of the downstream line of the current protection unit, the corresponding downstream protection current decay time is calculated through the current protection unit. The first-level decay time threshold is obtained based on the decay time of the lower-level protection current and the preset first reliability coefficient. If the protection current decay time is less than the first-level decay time threshold, it indicates that the protection current decay time meets the fault conditions in the first zone.

6. The method according to claim 4, characterized in that, The method includes: When a metallic fault occurs at the end of the current line in the current protection unit, the corresponding end protection current decay time is calculated by the current protection unit. The secondary decay time threshold is obtained based on the end protection current decay time and the preset second reliability coefficient; If the protection current decay time is less than the secondary decay time threshold, it indicates that the protection current decay time meets the fault conditions in the second zone.

7. The method according to any one of claims 1 to 6, characterized in that, The method further includes: Differentiate the voltage data and the current current data respectively to obtain voltage derivative data and current derivative data; If the absolute value of the voltage derivative data is greater than a preset voltage derivative threshold, and the absolute value of the current derivative data is greater than a preset current derivative threshold, then the voltage data and the current current data satisfy the preset protection activation condition.

8. A DC transmission line protection device without inductive boundary elements, characterized in that, Two DC transmission lines are provided at the DC line end of the same modular multilevel converter, and each DC transmission line is equipped with a protection unit on the side closer to the modular multilevel converter; the device includes: The data acquisition module is used to acquire the voltage data and current data of the current protection unit, and to acquire the adjacent current data of adjacent protection units connected to the current protection unit in the same modular multilevel converter. The protection current decay module is used to determine the protection current decay time within a first preset time window based on the current current data and the adjacent current data, when the voltage data and the current current data meet the preset protection activation conditions. The protection control action module is used to control the current protection unit to act in order to isolate the fault when the protection current decay time meets the preset fault conditions in the zone and a trip signal is received.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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