A flexible direct current transmission line pilot protection method and device and storage medium

Abstract

The application discloses a kind of flexible direct current transmission line longitudinal protection method, device and storage medium, belong to electric power system direct current transmission field.Therein method includes: setting measuring point in the two ends of line, the polar line voltage of line two sides measuring point, line two sides current-limiting reactance voltage;According to polar line voltage, preliminary judgment is carried out, and when it is judged that it satisfies starting criterion, protection starts;The ratio of current-limiting reactance voltage of line two sides and the voltage of two sides measuring point is calculated;The standard deviation coefficient of the ratio of current-limiting reactance voltage of line two sides and the voltage of two sides measuring point is calculated;According to the standard deviation coefficient obtained, the corresponding fault type is identified, and fault selection pole is carried out, and corresponding protection action is executed.The application uses standard deviation coefficient to measure the waveform change trend of current-limiting reactance and measuring point voltage ratio under positive and negative direction fault, principle is simple, in theory, not affected by transition resistance, there is no protection dead zone.In addition, the calculation of protection is only based on local information, and does not need data synchronization system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system DC transmission, in particular to a flexible DC transmission line pilot protection method, device and storage medium. BACKGROUND

[0002] The flexible DC transmission system based on the modular multilevel converter (MMC) has the advantages of low harmonic content, large-scale renewable energy consumption and no commutation failure, and has been widely used all over the world.

[0003] However, the DC power grid is a low inertia network, and after a short-circuit fault occurs on the DC side, the converter station will feed short-circuit current to the fault point, and the fault current will be discharged rapidly in a short time, which makes the fault current rise rapidly and have a large amplitude. Therefore, the rapid and reliable identification of the flexible DC power grid fault is still a key problem to be solved.

[0004] The traditional DC transmission line mainly uses traveling wave protection, differential under-voltage and voltage jump protection, which has good speed and is usually used as the main protection in DC line protection; the traditional current differential protection uses two-terminal electrical quantities and has strong selectivity and sensitivity.

[0005] The disadvantages of the traveling wave protection and the traditional current differential protection are as follows:

[0006] 1) The traveling wave protection method has problems such as excessive dependence on boundary elements, insufficient resistance to transition resistance, and poor anti-interference ability. In addition, for remote faults, the selectivity may also not meet the requirements.

[0007] 2) The current differential protection is easily affected by distributed capacitance, so a longer delay time needs to be set to avoid the transient discharge process of the distributed capacitance, which affects the speed of the protection.

[0008] Therefore, how to improve the resistance to transition resistance of the traveling wave protection and the speed of the current differential protection has become one of the important directions of the existing DC line fault protection. SUMMARY

[0009] To at least partially solve one of the technical problems in the prior art, the purpose of the present application is to provide a flexible DC transmission line pilot protection method, device and storage medium.

[0010] The technical solution adopted by the present application is:

[0011] A flexible DC transmission line pilot protection method, comprising the following steps:

[0012] Setting measuring points at both ends of the line, measuring the polar line voltage of the measuring points at both sides of the line and the voltage of current limiting reactance at both sides of the line;

[0013] In the starting unit, a preliminary judgment is made according to the polar line voltage, and when it is determined that the starting criterion is met, the starting is protected;

[0014] The ratio of the current limiting reactance voltage at both sides of the line to the voltage of the measuring points at both sides is calculated;

[0015] The standard deviation coefficient of the ratio of the current limiting reactance voltage at both sides of the line to the voltage of the measuring points at both sides is calculated;

[0016] According to the obtained standard deviation coefficient, the corresponding fault type is identified, the fault polar selection is performed, and the corresponding protection action is executed.

[0017] Further, the gradient of the polar line voltage wave is used as the starting criterion of the protection, and the calculation formula of the gradient of the polar line voltage wave is as follows:

[0018]

[0019] (ΔU p >k v U ref )U(ΔU n >k v U ref )=1

[0020] In the formula, ΔU p is the positive DC line voltage variation, ΔU n is the negative DC line voltage variation, j is the voltage gradient calculation point number, i is the current sampling point, U ref is the rated line voltage, and k v is the voltage fluctuation coefficient.

[0021] Further, the calculation formula of the ratio of the current limiting reactance voltage at both sides of the line to the voltage of the measuring points M and N at both sides is as follows:

[0022]

[0023] In the formula, U Ldc1 is the line mode voltage at both ends of the left current limiting reactance L dc1 of the DC line, U Ldc2 is the line mode voltage at both ends of the right current limiting reactance L dc2 of the DC line, U M1 is the line mode voltage at the measuring point M, U N1 is the line mode voltage at the measuring point N, Rat Ldc1_M1 is the ratio of U Ldc1 to U M1 , and Rat Ldc2_N1 is the ratio of U Ldc2With U N1 The ratio.

[0024] Further, the calculation formula of the standard deviation coefficient of the ratio of the current limiting reactance voltage on both sides of the line and the voltage at the measuring point is as follows:

[0025]

[0026] In the formula, S M is the standard deviation coefficient of Rat Ldc2_M1 , S N is the standard deviation coefficient of Rat Ldc2_N1 ; N is the number of sampling points in the time window T; and respectively represent the average value of Rat Ldc2_M1 and Rat Ldc2_N1 .

[0027] Further, the corresponding fault type is identified according to the obtained standard deviation coefficient, comprising:

[0028] When the fault is in the area, Rat Ldc1_M1 , Rat Ldc1_N1 tends to be stable, S M and S N are close to 0; when the forward out-of-area fault occurs, Rat Ldc2_M1 tends to be stable, Rat Ldc2_N1 changes exponentially, S M is close to 0, and S N is large; when the reverse out-of-area fault occurs, Rat Ldc2_M1 changes exponentially, Rat Ldc2_N1 tends to be stable, S M is large, and S N is close to 0; the expressions are as follows:

[0029]

[0030] In the formula, K set is the action threshold.

[0031] Further, the criterion for selecting the fault pole is as follows:

[0032]

[0033] In the formula, U0 is the zero-mode voltage; p set is a preset threshold, which is set according to the sum of the maximum earth mode voltages when the line avoids the inter-pole fault.

[0034] Further, the zero-mode voltage U0 is obtained by calculation in the following manner:

[0035]

[0036] In the formula, U1 represents a line mode voltage; U p represents a positive electrode line voltage; U n represents a negative electrode line voltage.

[0037] Further, the executing of the corresponding protection action comprises:

[0038] If it is a positive electrode line fault, the positive electrode protection action; if it is a negative electrode line fault, the negative electrode protection action; if it is a line inter-electrode fault, the positive electrode and the negative electrode protection actions; otherwise, it is identified as an out-of-area fault, and the protection does not act.

[0039] Another technical solution adopted by the present application is:

[0040] A flexible direct current transmission line pilot protection device comprises:

[0041] at least one processor;

[0042] at least one memory for storing at least one program;

[0043] When the at least one program is executed by the at least one processor, the at least one processor implements the above method.

[0044] Another technical solution adopted by the present application is:

[0045] A computer readable storage medium, wherein a processor executable program is stored, the processor executable program is used for executing the above method when executed by a processor.

[0046] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0047] 1) The ratio of the current limiting reactance to the measurement point voltage is beneficial to amplify the difference between the in-area and out-of-area fault characteristics caused by the direct current line boundary. The standard deviation coefficient is used to measure the waveform trend of the ratio of the current limiting reactance to the measurement point voltage under the positive and negative direction faults. The principle is simple, and theoretically, it is not affected by the transition resistance, and there is no protection dead zone.

[0048] 2) Through simulation test, the effectiveness and reliability of the proposed protection scheme are verified. Under all fault types, the fault type can be accurately identified, has strong resistance to transition resistance, has low requirements for the sampling frequency of the protection device, and can identify the in-area and out-of-area faults at low sampling frequency. In addition, under strong white noise interference, the proposed protection can still act correctly, and the noise has little effect on the scheme.

[0049] 3) The protection calculation is only based on local information, only needs to exchange the fault direction through the optical fiber, and the proposed protection scheme does not need a data synchronization system. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following introduces the drawings of the related technical solutions in the embodiments of the present application or the prior art. It should be understood that the drawings in the following introduction are only for the convenience of clearly describing part of the embodiments of the technical solutions of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the premise of the drawings.

[0051] Figure 1 is a schematic diagram of a flexible HVDC transmission system in an embodiment of the present application;

[0052] Figure 2 is a flow chart of a flexible HVDC transmission line fast pilot protection method in an embodiment of the present application.

[0053] Figure 3 is a result diagram of an internal fault in an embodiment of the present application.

[0054] Figure 4 is a result diagram of an external fault in an embodiment of the present application;

[0055] Figure 5 is a simulation result diagram of internal and external faults in an embodiment of the present application.

[0056] Figure 6 is a schematic diagram of a four-port flexible HVDC transmission system in an embodiment of the present application;

[0057] Figure 7 is a step flow chart of a flexible HVDC transmission line pilot protection based on transient voltage waveform characteristics in an embodiment of the present application. DETAILED DESCRIPTION

[0058] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. For the step numbers in the following embodiments, they are only set for the convenience of description and explanation, and the order between the steps is not limited in any way, and the execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0059] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by the upper, lower, front, rear, left, right and the like, is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as limiting the indicated device or element to have a specific orientation, to be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application.

[0060] In the description of the present application, one or more is understood as one or more, more than two is understood as more than two, greater than, less than, more than and the like are understood as not including the number, above, below, within and the like are understood as including the number. If the first, second is described, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the sequence of indicated technical features.

[0061] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting and the like should be understood in a broad sense, and the person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0062] In view of the existing technical problems, the present application provides a flexible DC transmission line pilot protection scheme based on transient voltage waveform characteristics, which comprises: taking a modular multilevel converter (MMC) flexible DC transmission system as the research object, obtaining the line pole line voltage measured by the line first and last end measuring points; measuring the current limiting reactor voltage at both ends of the line; calculating the gradient of the pole line voltage; calculating the ratio of the current limiting reactor voltage to the measuring point voltage; calculating the standard deviation coefficient of the ratio; calculating the ground mode voltage; judging whether the pole line voltage gradient criterion meets the condition; making a preliminary judgment in the starting unit, and starting the protection when the starting criterion is met. Calculate the ratio of the current limiting reactor voltage to the measuring point voltage, and then calculate the standard deviation coefficient in a certain time window. The standard deviation coefficient information is transmitted to the opposite side of the DC line. If both ends of the DC line meet the criterion condition, it can be identified as an internal fault, and the fault pole is selected. Judge whether the ground mode voltage meets the condition; in the protection unit, according to the processing result of the internal fault identification and fault pole selection unit, the corresponding protection action is performed. The scheme of the present application has good internal and external fault discrimination, high sensitivity, can quickly respond to the line fault of the flexible DC transmission line and is not prone to misjudgment. And overcome the shortcomings of the existing longitudinal protection method, such as low speed and poor reliability.

[0063] As Figure 7 shown, the present embodiment provides a flexible DC transmission line pilot protection method based on transient voltage waveform characteristics, comprising the following steps:

[0064] S1, setting measuring points at both ends of the line, measuring the polar line voltage and the current-limiting reactance voltage at both sides of the line.

[0065] S2, making a preliminary judgment according to the polar line voltage, and starting protection when the starting criterion is met.

[0066] The starting unit uses the gradient of the polar line voltage traveling wave as the starting criterion of protection, which specifically includes:

[0067]

[0068] (ΔU p >k v U ref )U(ΔU n >k v U ref )=1

[0069] Wherein, U ref is the rated line voltage; a represents the fault pole, k v is the voltage fluctuation coefficient. In order to avoid the influence of steady-state and transient voltage fluctuation, the value of k v should be greater than the maximum value of voltage gradient in normal system operation and less than the minimum value that may occur in fault. In some embodiments, k v is 0.02.

[0070] S3, calculating the ratio of the current-limiting reactance voltage at both sides of the line to the voltage at both sides of the measuring point.

[0071] The ratio of the measuring point voltage and the current-limiting reactance voltage measured by the measuring points R12 and R21 is:

[0072]

[0073] S4, calculating the standard deviation coefficient of the ratio of the current-limiting reactance voltage at both sides of the line to the voltage at both sides of the measuring point.

[0074] As an optional implementation, the standard deviation coefficient of the ratio of the current-limiting reactance voltage at both ends of the line to the voltage at the measuring point is calculated by the following formula:

[0075]

[0076] Wherein, N is the number of sampling points in the time window T; and respectively represent the average values of Rat Ldc2_M1 and Rat Ldc2_N1 . When the fault is in the area, Rat Ldc1_M1 , Rat Ldc1_N1 tend to be stable, S M and S N are close to 0; when the forward fault is outside the area, RatLdc2_M1 tends to be stable, Rat Ldc2_N1 changes exponentially, S M close to 0, S N larger; when a reverse area external fault occurs, Rat Ldc2_M1 changes exponentially, Rat Ldc2_N1 tends to be stable, S M larger, S N close to 0.

[0077] S5, identifying the corresponding fault type according to the obtained standard deviation coefficient, and performing fault selection.

[0078] The in-zone fault identification and fault selection unit identifies the in-zone fault by using the standard deviation coefficient of the ratio of the current-limiting reactance voltage at both ends of the line to the voltage at the measuring point, and performs fault selection. The in-zone fault criterion is constructed as follows:

[0079]

[0080] In the formula, K set is the action threshold, the value of which is selected according to the maximum value that may occur at the measuring point at both ends when an in-zone fault occurs. When an in-zone fault occurs, Rat Ldc2_M1 , Rat Ldc2_N1 tends to be stable, and theoretically S M / N_in / ex is close to 0. It is shown by multiple simulation tests that S M / N_in / ex is between 0 and 0.2. In order to avoid measurement errors and noise interference and take into account a certain margin, in some optional embodiments, the action threshold K set = 0.5.

[0081] The fault selection criterion is constructed as follows:

[0082]

[0083] In the formula, p set is set according to the sum of the maximum ground mode voltages when an inter-pole fault occurs on the line, while the reliability of the criterion is taken into account and a certain margin is reserved. In some optional embodiments, p set = 50 kV.

[0084] S6, performing a corresponding protection action according to the fault identification result.

[0085] Specifically, the protection unit performs a corresponding protection action according to the processing result of the in-zone fault identification and fault selection unit: if it is a positive pole fault of the line, the positive pole protection acts; if it is a negative pole fault of the line, the negative pole protection acts; if it is an inter-pole fault of the line, the positive and negative pole protections act together; otherwise, it is identified as an external fault, and the protection does not act.

[0086] The above method is explained in detail below in combination with the drawings and specific embodiments.

[0087] Embodiment 1

[0088] This embodiment takes a true bipolar MMC flexible DC transmission system as an example to analyze the fault voltage traveling wave, and the system topology structure is as shown in Figure 1 The DC transmission line is a bipolar overhead line, L dc is a current limiting reactor for suppressing the fault current rising rate, and M and N are protection installation positions at both ends of the DC line. Figure 1 Typical fault points are given, wherein f1 is an in-zone fault point on Line1, f2 is an out-of-zone fault point on the side of MMC1, and f3 is an out-of-zone fault point on the side of MMC2.

[0089] Referring to Figure 2 , the flexible DC transmission line pilot protection method based on transient voltage waveform characteristics provided in this embodiment includes the following steps:

[0090] S101, measuring points are arranged at the beginning and end of the line to measure the pole-line voltage and the voltage across the current limiting reactor at the beginning and end of the line.

[0091] In one embodiment, the arrangement of the protection measuring points is specifically: measuring points R12 and L dc are arranged at the beginning of the line Line1 to measure the pole-line voltage and the current limiting reactor voltage data at the beginning of the line; and measuring points R21 and L dc are arranged at the end of the line Line1 to measure the pole-line voltage and the current limiting reactor voltage data at the end of the line.

[0092] S102, preliminary judgment is performed in the starting unit, and the protection is started when the starting criterion is met.

[0093] In one embodiment, the gradient of the pole-line voltage traveling wave at both ends of the line Line1 is used as the starting criterion of the protection, specifically:

[0094]

[0095] (ΔU p >k v U ref )U(ΔU n >k v U ref )=1

[0096] Wherein, U ref is the rated line voltage; a indicates the fault pole, k v is the voltage fluctuation coefficient. In order to avoid the influence of steady-state and transient voltage fluctuations, the value should be greater than the maximum value of the voltage gradient during normal operation of the system and less than the minimum value that may occur during a fault.v Take 0.02.

[0097] S103, the ratio of the current limiting reactance voltage measured by the protection measuring point R12, R21 to the measuring point voltage is calculated.

[0098]

[0099] S104, the standard deviation coefficient of the ratio of the current limiting reactance voltage measured by the protection measuring point R12, R21 to the measuring point voltage is calculated.

[0100]

[0101] Take the voltage data 0.5 ms after the fault occurs, and calculate Rat Ldc1 M1 and Rat Ldc2_N1 . When the fault is in the area, Rat Ldc1_M1 , Rat Ldc1_N1 tend to be stable, S M and S N are close to 0; when the forward fault is outside the area, Rat Ldc2_M1 tends to be stable, Rat Ldc2_N1 changes exponentially, S M is close to 0, and S N is large; when the reverse fault is outside the area, Rat Ldc2_M1 changes exponentially, Rat Ldc2_N1 tends to be stable, S M is large, and S N is close to 0, and there are:

[0102]

[0103] In the formula, K set is an action threshold value, which is selected according to the maximum value that may appear at the measuring point on both sides when the fault is in the area. When the fault is in the area, Rat Ldc2_M1 , Rat Ldc2_N1 tend to be stable, and theoretically S M / N_in / ex is close to 0. After multiple simulation tests, it is shown that S M / N_in / ex is between 0 and 0.2. In order to avoid measurement errors and noise interference and considering a certain margin, the action threshold value K set selected in the embodiment is 0.5.

[0104] As can be seen from the above, the protection proposed does not need to transmit the electrical quantity signal on the opposite side to the side, and the protection calculation on each side only needs to independently calculate the electrical quantity information on the side, and only needs to transmit the logical signal obtained on the side to the opposite end to identify the fault type. Therefore, the protection proposed does not need to consider data communication.

[0105] S5, calculating zero-mode voltage U0 according to positive and negative DC line voltages:

[0106]

[0107] As can be seen from the formula, when bipolar fault occurs, the zero-mode voltage will be 0 due to the symmetry between the positive and negative poles; when positive pole fault occurs, the positive pole voltage transiently drops, so the ground-mode voltage is negative; conversely, when negative pole fault occurs, the negative pole voltage transiently drops, so the ground-mode voltage is positive. Therefore, the sum of the ground-mode voltages is selected for pole selection in the patent, that is,

[0108]

[0109] wherein, p set According to the maximum sum of the ground-mode voltages when the line pole-to-pole fault occurs, the reliability of the criterion is considered, and a certain margin is reserved, p set = 50 kV is selected in the embodiment.

[0110] S106, performing corresponding protection actions according to the processing results of the in-zone fault identification and fault pole selection units.

[0111] In one embodiment, if the maximum value of the sum of the positive pole line and the negative DC line is less than -p set , the criterion is met, the fault is identified as a positive pole line fault, and the positive pole protection acts; if the maximum value of the sum of the positive pole line and the negative DC line is greater than p set , the criterion is met, the fault is identified as a negative pole line fault, and the negative pole protection acts; if the maximum value of the sum of the positive pole line and the negative DC line is between [-p set , p set ], the criterion is met, the fault is identified as a line pole-to-pole fault, and the positive and negative pole protections act together; if none of them is met, it is identified as an out-zone fault, and the protection does not act.

[0112] The application is further described below through a specific simulation example.

[0113] In the embodiment, a double-ended flexible DC power transmission system model as shown in Figure 1 is built in PSCAD / EMTDC for simulation test. The converter stations all adopt MMC model, and the specific model parameters are shown in Table 1. The DC power transmission line adopts a frequency-variable parameter model. Considering the requirement of protection quickness, 0.5 ms after the fault occurs is taken as the protection time window. The sampling frequency is selected as 10 kHz.

[0114] Table 1 Model parameters

[0115]

[0116] A protection algorithm was written on the MATLAB platform, and fault simulation data from the constructed PSCAD model was imported to verify the protection's operation. Due to the symmetry of the positive and negative lines, the positive protection of line Line1 was used as an example for explanation.

[0117] Taking a positive ground fault as an example, when a metallic fault is set 180km away from the protection installation location, the voltage gradient and Rat on the M and N sides... Ldc_M1 Rat Ldc_N1 The simulation results of the waveform and the zero-mode component of the voltage are as follows: Figure 3 As shown.

[0118] from Figure 3 As shown in (a) and (b), the positive and negative voltage gradients at measurement points M and N are both greater than the set value of 10kV, and the protection at both M and N starts within 0.5ms. Taking a 0.5ms data window from the start time, the calculation... Figure 3 (c) Rat Ldc1_M1 Rat Ldc1_N1 The standard deviation coefficient is used to obtain S. M =0.0032, S N =0.0031, both are less than the setpoint K set This can be identified as a fault within the area. Figure 3 As can also be seen from (d), the zero-mode voltage is less than -p. set This can be identified as a positive grounding fault.

[0119] Taking a fault on the positive terminal of the inverter-side current-limiting reactor valve as an example, set the fault f2, voltage gradient on the M and N sides, and Rat. Ldc_M1 Rat Ldc_N1 The waveform diagram and simulation results of the zero-mode voltage component are as follows: Figure 4 As shown.

[0120] from Figure 4 As shown in (a) and (b), the positive and negative voltage gradients at measurement points M and N are both greater than the set values, and the protection at both M and N starts within 0.5ms. Taking a 0.5ms data window from the start time, the calculation... Figure 4 (c) Rat Ldc1_M1 Rat Ldc1_N1 The standard deviation coefficient is used to obtain S. M =0.0028, S N =2.9697, S M Less than the set value K set S N Greater than the set value K set This can be identified as an external fault. Figure 4 As can also be seen in (d), the zero-mode voltage is less than -p. set This can be identified as a positive electrode fault.

[0121] Different fault types, locations, and transition resistances were set up for faults inside and outside the zone. The simulation results are shown in Table 2.

[0122] Table 2 Protection Judgment Results

[0123]

[0124] Table 2 shows that for different fault distances and different transition resistances under intra-regional fault conditions, the S values ​​at the measurement points on both sides of the line are... M With S N All values ​​are less than the set value, and the protection can operate reliably; for faults outside the zone at the inverter station outlet, S M Less than the set value, S N Greater than the set value; for faults outside the rectifier station outlet area, S M Greater than the set value, S N The resistance is less than the set value. Therefore, the proposed protection scheme is basically unaffected by the transition resistance and fault distance. Simulations were performed for the entire protection zone along the line length, with a 1000Ω fault within the zone as an example and a metallic grounding fault outside the zone as an example. The simulation results are as follows: Figure 5 As shown.

[0125] from Figure 5 Observations show that S under faults inside and outside the zone M With S N There is a significant difference; even under high-resistance grounding faults within the zone, the proposed protection scheme can still protect the entire length of the line.

[0126] Example 2:

[0127] To further test the adaptability of the proposed scheme to different topology systems, a system was built as follows: Figure 6 The four-port MMC model shown is used as an example for fault simulation verification.

[0128] In such Figure 6 In the four-port network shown, faults within the zone (f1) and outside the zone (f2, f3) are set respectively. The proposed protection scheme is simulated and analyzed, and the simulation results are shown in Table 3.

[0129] Table 3. Discrimination results of protection schemes under the four-port MMC model.

[0130]

[0131] As can be seen from the data in Table 3, the proposed protection scheme is not affected by the topology structure and has a strong ability to withstand transition resistance.

[0132] This embodiment also provides a longitudinal protection device for flexible DC transmission lines, including:

[0133] at least one processor;

[0134] at least one memory for storing at least one program;

[0135] when the at least one program is executed by the at least one processor, the at least one processor implements Figure 5 the method.

[0136] The flexible DC transmission line pilot protection device of the embodiment can execute the flexible DC transmission line pilot protection method provided by the method embodiment, can execute the implementation steps of any combination of the method embodiment, and has the corresponding functions and beneficial effects of the method.

[0137] The embodiment of the application further discloses a computer program product or a computer program, which comprises computer instructions stored in a computer readable storage medium. A processor of a computer device can read the computer instructions from the computer readable storage medium, and the processor executes the computer instructions, so that the computer device executes Figure 7 the method.

[0138] The embodiment further provides a storage medium which stores instructions or programs which can execute the flexible DC transmission line pilot protection method provided by the method embodiment of the application, and when the instructions or programs are executed, implementation steps of any combination of the method embodiment can be executed, and the corresponding functions and beneficial effects of the method are possessed.

[0139] In some alternative embodiments, the functions / operations mentioned in the block diagram can not occur in the order mentioned in the operation diagram. For example, depending on the functions / operations involved, two blocks shown in succession can actually be executed substantially simultaneously or the blocks can sometimes be executed in reverse order. In addition, the embodiments presented and described in the flowcharts of the application are provided by way of example, with the purpose of providing a more comprehensive understanding of the technology. The disclosed method is not limited to the operations and logical flows presented herein. Alternative embodiments are contemplated in which the order of various operations is changed and in which sub-operations described as part of larger operations are independently executed.

[0140] Furthermore, although the present application is described in the context of functional modules, it is to be understood that one or more of the described functions and / or features can be integrated in a single physical device and / or software module, or one or more functions and / or features can be implemented in separate physical devices or software modules. It will also be appreciated that detailed discussion of the actual implementation of each module is not necessary to an understanding of the application. Rather, the actual implementation of the modules, in combination with their attributes, functions, and internal relationships, are to be understood within the context of the devices disclosed herein. Thus, those skilled in the art with access to patents, scientific journals, and other public sources known by those skilled in the art will be able to practice the application as set forth in the claims without undue experimentation, using ordinary skill in the art along with the present disclosure. It is also to be understood that the specific concepts disclosed are merely illustrative and that the scope of the present application is to be determined by the entire scope of the claims, along with all equivalents of the claims and their equivalents.

[0141] If the functions are implemented in software, the functions can be stored in or implemented as one or more computer program products, which can be incorporated into a computer-readable medium for use by or in connection with an apparatus, method or system as described herein. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, or a computer-readable signal. The computer-readable medium can be, for example, but is not limited to, volatile or non-volatile memory, a floppy diskette, a compact disk, a tape, a hard disk drive, a solid state memory drive, a memory stick, or any other such medium that can be used to store or transfer software in the form of computer-readable instructions or data structures and that can be accessed by a computer. The computer-readable medium can also be, for example, but is not limited to, a data transmission or data signal in which the software is embodied as carrier wave, such as an electromagnetic wave, a radio frequency wave, a microwave frequency wave, or other transmission. The computer-readable medium can also be a computer program product that can be distributed over a network, for example, the Internet, a local area network, a wide area network, a point-to-point dial-up network, or any other such network and can be carried on a computer-readable medium as described above. The computer-readable medium can be accessible as a file on the network, e.g., as a file on a web server, a file downloadable from an Internet file server, a file downloadable from a web site, a file downloadable via a file transfer protocol, or a file downloadable via a peer-to-peer network.

[0142] The logic and / or steps represented in the flow diagrams, or otherwise described herein, for example, can be considered as a sequence of instructions executed in an order to achieve a logic function, and can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch instructions from a instruction execution system, apparatus, or device and execute the instructions, or in conjunction with which the instructions can be executed. For purposes of this specification, a "computer-readable medium" can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium.

[0143] More specific examples (a non-exhaustive list) of the computer-readable medium include the following: an electrical connection (electronic) having one or more wires, a portable computer diskette (magnetic), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can also be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, for example, via optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory.

[0144] It should be understood that aspects of the application can be implemented in hardware, software, firmware or combinations thereof. In the above embodiments, various steps or methods can be implemented in software or firmware which are stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any of the following technologies, known in the art, or their combinations can be used: discrete logic circuitry having logic gates for implementing logic functions upon an application of data signals, application specific integrated circuits having appropriate combinational logic gates, programmable gate arrays (PGA), field programmable gate arrays (FPGA), and the like.

[0145] In the above description of the present specification, the description referring to the terms "one embodiment", "another embodiment", or "certain embodiments" or the like means that a specific feature, structure, material or characteristic described in connection with the embodiments or examples is included in at least one embodiment or example of the present application. The illustrative expressions of the above terms do not necessarily refer to the same embodiment or example in the present specification. Also, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0146] Although the embodiments of the present application have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, alternatives and variations to these embodiments can be made without departing from the principles and spirit of the application, the scope of which is defined by the claims and their equivalents.

[0147] The above is a specific description of the preferred embodiments of the present application, but the present application is not limited to the above-described embodiments, and those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present application, and these equivalent modifications or substitutions are included in the scope defined by the claims of the present application.

Claims

1. A longitudinal protection method for flexible DC transmission lines, characterized in that, Includes the following steps: Measuring points are set at both ends of the DC line to measure the pole line voltage and the current-limiting reactance voltage on both sides of the line. A preliminary judgment is made based on the pole line voltage, and the protection is activated when the start-up criterion is met. Calculate the ratio of the current-limiting reactor voltage on both sides of the line to the voltage at the measuring points on both sides; Calculate the standard deviation coefficient of the ratio of the current-limiting reactor voltage on both sides of the line to the voltage at the measuring points on both sides; Based on the obtained standard deviation coefficient, the corresponding fault type is identified, fault polarity is selected, and corresponding protection actions are executed. The criteria for fault selection are as follows: In the formula, Zero-mode voltage; p set The preset threshold is set according to the sum of the maximum ground mode voltages when the line experiences an inter-pole fault.

2. The longitudinal protection method for flexible DC transmission lines according to claim 1, characterized in that, The gradient of the pole voltage traveling wave is used as the protection activation criterion. The formula for calculating the gradient of the pole voltage traveling wave is as follows: In the formula, This represents the voltage change of the positive DC line. This represents the voltage change of the negative DC line. Calculate the number of points for the voltage gradient. The sampling point at the current moment, Rated line voltage, This is the voltage fluctuation coefficient.

3. The longitudinal protection method for flexible DC transmission lines according to claim 1, characterized in that, The formula for calculating the ratio of the current-limiting reactor voltage on both sides of the line to the voltage at measuring points M and N on both sides is as follows: In the formula, Current-limiting reactor on the left side of the DC line L dc1 Line-mode voltage at both ends Current-limiting reactor on the right side of the DC line L dc2 Line-mode voltage at both ends; The line-mode voltage at measurement point M on the left side of the line. The line-mode voltage at measurement point N on the right side of the line; for and The ratio, for and The ratio.

4. The longitudinal protection method for flexible DC transmission lines according to claim 3, characterized in that, The formula for calculating the standard deviation coefficient of the ratio of the current-limiting reactor voltage on both sides of the line to the measuring point voltage is as follows: In the formula, for The standard deviation coefficient for The standard deviation coefficient; N For time windows T Number of sampling points within; and They represent and The average value.

5. The longitudinal protection method for flexible DC transmission lines according to claim 4, characterized in that, The step of identifying the corresponding fault type based on the obtained standard deviation coefficient includes: When a fault occurs within the area, , The situation is stabilizing. S M and S N Approaching 0; during a fault outside the positive zone, tending to stabilize It changes exponentially. S M Close to 0 S N Larger; when there is a fault outside the reverse region, Exponential change The situation is stabilizing. S M Larger S N Approaching 0; the expression is as follows: In the formula, K set This is the action threshold.

6. The longitudinal protection method for flexible DC transmission lines according to claim 1, characterized in that, The zero-mode voltage It is obtained through the following calculation method: In the formula, U 1 represents line-mode voltage; U p Indicates the voltage of the positive terminal line; U n This indicates the voltage of the negative terminal line.

7. The longitudinal protection method for flexible DC transmission lines according to claim 1, characterized in that, The execution of the corresponding protection actions includes: If the fault is on the positive pole of the line, the positive pole protection will activate; if the fault is on the negative pole of the line, the negative pole protection will activate; if the fault is between poles of the line, both the positive and negative pole protections will activate together; otherwise, it will be identified as an external fault and the protection will not activate.

8. A longitudinal protection device for flexible DC transmission lines, characterized in that, include: At least one processor; At least one memory for storing at least one program; When the at least one program is executed by the at least one processor, the at least one processor implements the longitudinal protection method for flexible DC transmission lines as described in any one of claims 1-7.

9. A computer-readable storage medium storing a processor-executable program, characterized in that, The program executable by the processor is used, when executed by the processor, to perform a longitudinal protection method for flexible DC transmission lines as described in any one of claims 1-7.

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