High-voltage direct-current power grid power transmission line protection method and system

Abstract

The invention discloses a high-voltage DC power grid power transmission line protection method and system, and relates to the field of power system relay protection, and the method comprises the steps: processing a current fault waveform signal through employing a T-type correlation degree algorithm, analyzing the correlation characteristics between fault transient currents, and obtaining a current fault waveform signal; the overall T-shaped correlation degree of fault current increments at the two ends of each pole in the same time period is obtained and compared to construct a protection criterion, when the high-voltage direct-current power grid breaks down, a protection system of a fault line can act quickly, a protection system of a non-fault line does not act mistakenly, and meanwhile the action time of the protection scheme is relatively short; meanwhile, good reliability and selectivity are shown in the aspect of tolerance to transition resistance, and rapidity and adaptive capacity are improved; the sampling frequency required by the protection is low, and the requirement for a sampling channel is not too high. According to the method, internal and external fault identification and fault pole selection are carried out on the direct current transmission line, and compared with traditional pilot protection, the robustness is better, and the reliability is higher.

Description

Technical Field

[0001] The present invention relates to the field of relay protection of power systems, and specifically to a protection method and system for a high-voltage DC power grid transmission line. Background Art

[0002] Multi-terminal flexible DC power grids will play a more important role in the power system. It can not only meet the growing power demand, but also promote the large-scale application and development of clean energy, contributing to the construction of a clean, low-carbon, and efficient energy system. However, as an emerging power transmission technology, the flexible DC power transmission system still faces many challenges in market promotion and practical application. Among them, the selective and rapid isolation technology for DC line faults has not been perfected, which has become a key factor restricting the further promotion of the flexible DC power transmission system. In a flexible DC power grid, the rapid handling of DC line faults is crucial. Once a fault occurs, the rapid response ability of the DC circuit breaker is crucial for ensuring the normal operation of non-fault lines. However, the fault characteristics of the DC power grid are significantly different from those of the AC power grid, posing a severe challenge to the stability of the system. Therefore, the research and development of a more mature and reliable rapid DC line fault handling technology has become the key to the development of the flexible DC power transmission system. Against this background, it is particularly urgent and important to study a reliable, rapid, sensitive, and selective multi-terminal flexible DC power transmission line protection scheme. The present invention will deeply analyze the fault characteristics of the DC power grid, explore the line protection principle, and strive to propose a DC line protection scheme that is both practical and meets various requirements to ensure the stable and reliable operation of the power system. Summary of the Invention

[0003] In view of the above existing problems, the present invention is proposed.

[0004] Therefore, the technical problem solved by the present invention is: how to use the T-type correlation algorithm to process the current fault waveform signal, analyze the correlation characteristics between its fault transient currents, obtain and compare the overall T-type correlation of the fault current increments at both ends of each pole within the same time period to construct a protection criterion.

[0005] To solve the above technical problem, the present invention provides the following technical solution: a protection method for a high-voltage DC power grid transmission line, which includes the following steps,

[0006] Collect grid data information through a line protection device to determine whether to activate line protection;

[0007] After the protection is activated, use the current transient electrical quantities collected at each measurement point of the converter station to extract the current increment sequence;

[0008] Calculate the positive and negative pole fault current T-type correlations between two converter stations using the current increment sequence;

[0009] By comparing the T-type correlation degree of the positive and negative pole fault current increments between two converter stations with the protection setting value, internal and external faults are identified, and the faulty pole is identified.

[0010] As a preferred solution of a high-voltage DC power grid transmission line protection method described in the present invention, wherein: determining whether to activate the line protection by collecting grid data information through the line protection device is to determine whether to activate the line protection by comparing the current fault component collected by the line protection device with the starting threshold;

[0011] The protection device continuously monitors the fault current values at several different monitoring points, calculates the current fault component for each monitoring point, and when the current fault components are calculated continuously for a corresponding number of times at several monitoring points and are greater than the preset threshold, the line protection device activates the line protection.

[0012] As a preferred solution of a high-voltage DC power grid transmission line protection method described in the present invention, wherein: after the protection is activated, the current transient electrical quantities collected by each measuring point of the converter station are used to extract the current increment sequence by using the current electrical quantities, including

[0013] When a fault occurs in the DC transmission line, a suitable sampling frequency and sampling time window are selected, and the expression is:

[0014] t∈[A, B]

[0015] B>A≥0

[0016] Δt x =t x -t x-1 , x=2, 3…, n

[0017] wherein, t is the time period, A and B refer to the sampling time window, t x , t x-1 are the sampling time points, and Δt x is the time interval between two sampling time points.

[0018] For the values of each point in the [A, B] interval of the time series of the fault current at the beginning and end of the DC positive or negative pole line are respectively:

[0019]

[0020] wherein, I1 and I2 are the fault current sequences at the beginning and end of the line, I1(t1), I1(t2), …I1(t n ) are the sampling values at the beginning of the line within the sampling time window, and I2(t1), I2(t2), …I2(t n ) are the sampling values at the end of the line within the sampling time window.

[0021] Normalize two fault current sequences and obtain the two fault current increment sequences. The expression is as follows:

[0022]

[0023] Among them, ΔI1 and ΔI2 are the fault current sequences at the head and end of the line after normalization.

[0024] As a preferred solution of a high-voltage DC grid transmission line protection method described in the present invention, wherein: calculating the positive and negative pole fault current T-type correlation degrees between two converter stations by using the current increment sequences is to calculate the correlation coefficients of the two fault current increment sequences at each time period within the same sampling time window. The expression is as follows:

[0025]

[0026] Among them, ξ(t x ) is the correlation coefficient at each time period within the sampling time window, x = 2, 3,... n;

[0027] Calculate the correlation degree of the two currents within the total sampling time window. Denote the correlation coefficient of the original time current sequences I1 and I2 as r(I1, I2). The corresponding T-type correlation degree expression is as follows:

[0028]

[0029] Among them, r y = r(I1, I2) is the T-type correlation degree of the original time current sequences I1 and I2;

[0030] When -1 ≤ r(I1, I2) < 0, I1 and I2 are negatively correlated within the time window [A, B], and the strength of the negative correlation increases with the increase of |r(I1, I2)|;

[0031] When 0 < r(I1, I2) ≤ 1, I1 and I2 are positively correlated within the time window [A, B], and the strength of the positive correlation increases with the increase of r(I1, I2).

[0032] As a preferred solution of a high-voltage DC grid transmission line protection method described in the present invention, wherein: identifying internal and external faults and identifying the faulty pole by comparing the positive and negative pole fault current increment T-type correlation degrees between two converter stations with the protection setting value includes,

[0033] When r p > k set or r n > k set it indicates that an internal fault has occurred in the DC transmission line, and the T-type correlation degree of the current increment at the protection installation locations at both ends of the positive or negative pole of the transmission line is a positive correlation;

[0034] When r p < -k set and r n < -k set it indicates that an external fault has occurred in the DC transmission line or the system is operating normally; the T - type correlation degree of the current increments at the protection installation points at both ends of the positive and negative poles of the transmission line is negatively correlated;

[0035] The fault recognition criterion constructed by the T - type correlation degree has the expression:

[0036]

[0037] where r p represents the T - type correlation degree of the fault current increment at both ends of the positive - pole DC transmission line, r n represents the T - type correlation degree of the fault current increment at the head and end of the negative - pole line, and k set is the setting threshold value.

[0038] As a preferred scheme of a high - voltage DC grid transmission line protection method described in the present invention, among them: the method of identifying internal and external faults and the faulty pole by comparing the T - type correlation degrees of the positive and negative pole fault current increments between two converter stations further includes,

[0039] When a positive - pole in - zone grounding fault occurs in the DC transmission line, the T - type correlation degree r p calculated from the fault current increment at the protection installation points at both ends of the positive - pole line is positively correlated, while the negative - pole line is a sound pole, and the calculated T - type correlation degree r n of the current increments at both ends is negatively correlated;

[0040] When a negative - pole in - zone grounding fault occurs in the DC transmission line, the T - type correlation degree r n calculated from the two fault current increments at the protection installation points at both ends of the negative - pole line is positively correlated, while the positive - pole line is a sound pole, and the calculated T - type correlation degree r p of the current increments at both ends is negatively correlated;

[0041] When a bipolar in - zone fault occurs in the DC transmission line, the T - type correlation degrees r p 、r n calculated from the fault current increments at the protection installation points at both positive and negative poles are both positively correlated;

[0042] Construct the faulty - pole selection criterion, and the expression is:

[0043]

[0044] When the P - pole type correlation degree r p ≥r set and when the T - type correlation degree r n of the N - pole ≥rset When it is, it is judged as a bipolar fault in the zone;

[0045] When the P-pole type correlation degree r p ≥r set And when the T-type correlation degree r of the N-pole n <r set When it is, it is judged as a positive-pole fault in the zone;

[0046] When the P-pole type correlation degree r p <r set And when the T-type correlation degree r of the N-pole n <r set When it is, it is judged as a negative-pole fault in the zone.

[0047] Another object of the present invention is to provide a transmission line protection system for a high-voltage DC power grid, which can analyze the correlation between the current fault increments at both ends of the converter station in real time through the T-type correlation degree algorithm, calculate the T-type correlation degree of the positive and negative pole fault currents, and combine the setting threshold to judge the internal and external faults and the fault polarities, realizing high-precision and high-response transmission line protection, and solving the problems of insufficient extraction of transient signal characteristics, low accuracy of fault recognition and pole selection, and especially high misoperation rate under complex working conditions in the existing DC transmission line protection methods.

[0048] To solve the above technical problems, the present invention provides the following technical solutions: A transmission line protection system for a high-voltage DC power grid, including: a signal acquisition module, a fault recognition module, and a fault pole selection module;

[0049] The signal acquisition module acquires and stores the current at the data protection installation location, and acquires the current at each measurement point in real time. If the protection startup criterion is met, the protection starts and enters the fault recognition module; otherwise, it does not start.

[0050] The fault recognition module is used to identify internal and external faults when the protection starts. If it is judged as an external fault, the protection does not act; if it is an internal fault, it enters the fault pole selection module.

[0051] The fault pole selection module judges whether the system has a positive-pole, negative-pole or bipolar fault through a fault pole selection function;

[0052] The signal acquisition module includes a data acquisition unit that acquires the analog signals output from the secondary side of the current transformers at each protection installation location in real time; an analog-to-digital conversion unit that converts the current analog signals at each measurement point into digital signals; and a protection startup unit that judges whether the current digital signal is greater than the set startup threshold. If so, it reads the startup time and stores the data;

[0053] The fault recognition module includes a parameter setting unit that sets the setting protection threshold value k set 、protection threshold rset ; A numerical calculation unit that calculates the T-type correlation degree of the p-pole and n-pole; compares the T-type correlation degree with a set protection threshold value to distinguish between internal and external faults;

[0054] The fault pole selection module includes a data sorting unit that outputs and sorts the data that needs to be polarity judged when it is determined as an internal fault; a polarity judgment unit that calculates the T-type correlation degree of the fault current increments of the positive and negative pole currents and compares it with the protection setting value;

[0055] Identify the fault pole. If r p ≥r set and r n <r set , it is an internal positive pole fault; if r p <r set and r n ≥r set , it is an internal negative pole fault; if r p ≥r set and r n ≥r set , it is an internal bipolar fault.

[0056] A computer device includes a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements the steps of the above-mentioned high-voltage DC power grid transmission line protection method.

[0057] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it implements the steps of the above-mentioned high-voltage DC power grid transmission line protection method.

[0058] Advantages of the present invention: When a fault occurs in the present invention, the protection system of the faulty line can act quickly, while the protection systems of non-faulty lines will not malfunction. After a fault occurs, the calculation of the T-type correlation degree of the fault current increments at both ends of the protection installation can be completed in about 0.5 ms. Considering a certain margin, when an internal fault occurs, the action time of the protection scheme proposed in this paper is not long. It has high reliability, is not easily affected by noise interference, and at the same time, compared with traditional protection in the presence of a certain transition resistance, this protection scheme shows good reliability and selectivity, improving the rapidity and adaptability. The sampling frequency is low, there is no high requirement for the sampling channel, and it has good robustness. Compared with traditional pilot protection, the implementation principle of this protection scheme is clear and simple, without the need for cumbersome processing of current characteristic quantities, the calculation amount is relatively small, the response is rapid, and the requirement for the sampling rate is not high. Description of the Drawings

[0059] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0060] Figure 1 It is the overall flowchart of a protection method for a high-voltage DC grid transmission line provided by the first embodiment of the present invention.

[0061] Figure 2 It is the simulation topology diagram in a protection method for a high-voltage DC grid transmission line provided by the first embodiment of the present invention.

[0062] Figure 3 It is the marked diagram of various types of internal and external faults occurring in the Line1 section of the transmission line in a protection method for a high-voltage DC grid transmission line provided by the first embodiment of the present invention.

[0063] Figure 4 It is the waveform diagram of the fault current increment in the case of a positive pole grounding fault in the Line1 section of a transmission line in a protection method for a high-voltage DC grid transmission line provided by the first embodiment of the present invention.

[0064] Figure 5 It is the diagram of a positive pole grounding fault on the valve side of the smoothing reactor at the m side of the line protection installation in a protection method for a high-voltage DC grid transmission line provided by the first embodiment of the present invention.

[0065] Figure 6 It is the structural diagram of a protection system for a high-voltage DC grid transmission line provided by the second embodiment of the present invention. Specific Embodiments

[0066] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will make a detailed description of the specific embodiments of the present invention in conjunction with the drawings of the specification. Obviously, the described embodiments are some, rather than all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0067] Embodiment 1, referring to Figures 1 to 5 As an embodiment of the present invention, a protection method for a high-voltage DC grid transmission line is provided, including:

[0068] The four-terminal double-mesh flexible DC grid model is as shown in the appendix Figure 2As shown, the DC voltage is 380 kV. Taking Line1 as the research object, the transmission line is 100 km long. The sampling frequency is set to 10 kHz and the data sampling time window length is 5 ms. In the simulation model, a positive pole metal grounding fault (f1) occurs at the midpoint within the DC line Line1, as Figure 3 shown.

[0069] The specific implementation steps are as follows:

[0070] Step1: The current fault component ΔI collected by the line protection device t is compared with the starting threshold I op_set to determine the protection startup. When ΔI t is greater than I op_set for 3 consecutive times, the line protection device starts to operate.

[0071] Step2: After the protection starts, the current transient electrical quantities collected by each measuring point of the converter station are used to extract the current increment sequence from the current electrical quantities. As Figure 4 , 5 shown, IP1 and IP2 are the fault current increment sequences at both ends of the P-pole line after processing, and IN1 and IN2 are the fault current increment sequences at both ends of the N-pole line after processing.

[0072] It can be seen from Figure 4 that the change directions of the IP1 and IN1 fault current increment sequences are opposite, showing negative correlation, and the calculated T-type correlation degree is negative; the change directions of the IP2 and IN2 fault current increment sequences are opposite, showing negative correlation, and the calculated T-type correlation degree is also negative.

[0073] It can be seen from Figure 5 that the change directions of the IP1 and IN1 fault current increment sequences are the same, showing positive correlation, and the calculated T-type correlation degree is positive; the change directions of the IP2 and IN2 fault current increment sequences are the same, showing positive correlation, and the calculated T-type correlation degree is also positive.

[0074] Step2.1: When a fault occurs in the DC transmission line, the specific calculation of the T-type correlation degree of the fault current at both ends of a certain pole transmission line is as follows. After the DC line fails, a suitable sampling frequency and sampling time window t∈[A, B] are selected, where B > A ≥ 0, and Δt x = t x - t x-1 , x = 2, 3…, n, Δt x ∩Δt x-1 = φ, For the DC positive or negative pole line, the values of the time series of the fault current at both ends at each point in the [A, B] interval are:

[0075]

[0076] Step2.2: Standardization processing.

[0077] First step, obtain D1 and D2:

[0078]

[0079] Second step, standardize the two current data to obtain their standardized sequences.

[0080]

[0081] Step2.3: After standardizing the fault current data at both ends, obtain the two fault current increment sequences.

[0082]

[0083] Step3: Calculate the positive and negative pole fault current T-type correlation degrees r p and r n .

[0084] Step3.1: Calculate the correlation coefficients of the two fault current increment sequences at each time period within the same sampling time window.

[0085]

[0086] Step3.2: Calculate the correlation degree of the two currents within the total sampling time window. Denote the correlation coefficient of the original time current sequences I1 and I2 as r(I1, I2), and there is

[0087]

[0088] When -1 ≤ r(I1, I2) < 0, I1 and I2 are negatively correlated (negatively related) within the time window [A, B], and the strength of the negative correlation increases with the increase of |r(I1, I2)|. r y = -1 indicates that the change laws of the two time sequences I1 and I2 are completely opposite, and the correlation degree is the strongest negative; when 0 < r(I1, I2) ≤ 1, I1 and I2 are positively correlated (positively related) within the time window [A, B], and the strength of the positive correlation increases with the increase of r(I1, I2). r y = 1 indicates that the change laws of the two time sequences I1 and I2 are completely the same, and the degree of correlation is the strongest.

[0089] Step4: By comparing the positive and negative pole fault current T-type correlation degrees r p and r n between the two converter stations with the protection setting value r setSize, faults inside and outside the recognition area: When r does not satisfy p ≥r set or r n ≥r set , it is determined that the system is normal or an external fault has occurred, and the protection is reset; when r satisfies p ≥r set or r n ≥r set , and the calculated value of the T-type correlation degree is continuously judged 3 times, it is determined as an internal fault.

[0090] Step4.1: (1) When r p >k set or r n >k set , it indicates that an internal fault has occurred in the DC transmission line, and the T-type correlation degree of the current increment at the protection installation points at both ends of the positive or negative pole of the transmission line is positively correlated;

[0091] Step4.2: (2) When r p <-k set and r n <-k set , it indicates that an external fault has occurred in the DC transmission line or the system is operating normally; the T-type correlation degree of the current increment at the protection installation points at both ends of the positive and negative poles of the transmission line is negatively correlated;

[0092] Step4.3: The fault recognition criterion constructed by the T-type correlation degree is as follows:

[0093]

[0094] In the above, r p represents the T-type correlation degree of the fault current increment at both ends of the positive DC transmission line, and r n represents the T-type correlation degree of the fault current increment at the head and end of the negative line. In order to ensure the reliability of the internal and external fault protection criterion, a suitable setting threshold value needs to be selected. According to a large number of simulation experiments and considering a certain margin, this paper sets the setting threshold value k set =0.5.

[0095] Step5: Compare the T-type correlation degrees r p , r n calculated from the positive and negative fault current increments with the protection setting value r set to identify the faulty pole: If r p ≥r set and r n <r set , it is an internal positive pole fault; if r p <r set and r n ≥rset , it is a negative pole fault within the zone; if r p ≥r set and r n ≥r set , it is a bipolar fault within the zone.

[0096] Step5.1: When a positive pole grounding fault occurs within the DC transmission line, the T-type correlation degree r calculated from the increment of the fault current at both ends of the protection installation on the positive pole line is positively correlated, while the negative pole line is a sound pole, and the T-type correlation degree r calculated from the increment of the current at both ends is negatively correlated; p When a negative pole grounding fault occurs within the DC transmission line, the T-type correlation degree r calculated from the increment of the fault current at both ends of the protection installation on the negative pole line is positively correlated, while the positive pole line is a sound pole, and the T-type correlation degree r calculated from the increment of the current at both ends is negatively correlated; n ;

[0097] Step5.2: When a negative pole grounding fault occurs within the DC transmission line, the T-type correlation degree r calculated from the increment of the two fault currents at both ends of the protection installation on the negative pole line is positively correlated, while the positive pole line is a sound pole, and the T-type correlation degree r calculated from the increment of the current at both ends is negatively correlated; n When a negative pole grounding fault occurs within the DC transmission line, the T-type correlation degree r calculated from the increment of the fault current at both ends of the protection installation on the negative pole line is positively correlated, while the positive pole line is a sound pole, and the T-type correlation degree r calculated from the increment of the current at both ends is negatively correlated; p ;

[0098] Step5.3: When a bipolar fault occurs within the DC transmission line, the T-type correlation degrees r p , r n calculated from the increment of the fault current at both ends of the positive and negative poles' protection installations are both positively correlated;

[0099] Step5.4: Construct a fault pole selection criterion as follows:

[0100]

[0101] In this embodiment, considering the influence of noise, communication error, and transformer measurement error on the protection criterion, based on a large number of simulation experiments, and then considering a certain margin and combining with the set threshold r set = 0.5.

[0102] Example 2, referring to Figure 6 This is an embodiment of the present invention, providing a system for a protection method of a high-voltage DC grid transmission line, including: a signal acquisition module, used for collecting and storing the current at the protection installation, collecting the current at each measuring point in real time, if the protection start criterion is met, the protection starts and enters the fault identification module; otherwise, it does not start.

[0103] The fault identification module, when the protection starts, is used to identify faults inside and outside the zone. If it is determined to be an external fault, the protection does not act; if it is an internal fault, it enters the fault pole selection module.

[0104] The fault pole selection module determines whether the system has a positive pole, negative pole, or bipolar fault through a fault pole selection function.

[0105] The described high-voltage DC power grid transmission line protection system is characterized in that the signal acquisition module specifically includes:

[0106] A data acquisition unit for real-time acquisition of analog signals output from the secondary side of current transformers at each protection installation location;

[0107] An analog-to-digital conversion unit for converting the current analog signals at each measurement point into digital signals;

[0108] A protection startup unit for determining whether the current digital signal is greater than a set startup threshold. If so, it reads the startup time and stores the data.

[0109] The described high-voltage DC power grid transmission line protection system is characterized in that the fault identification module specifically includes:

[0110] A parameter setting unit for setting the setting protection threshold value k set , protection threshold value r set ; In this embodiment, both the protection threshold value and the protection threshold value are set to 0.5;

[0111] A numerical calculation unit for calculating the T-type correlation degrees of the p-pole and n-pole; comparing the T-type correlation degrees with the set protection threshold value to distinguish internal and external faults: identifying internal and external faults: when r p ≥r set or r n ≥r set , it is determined that the system is normal or an external fault has occurred, and the protection is reset; when r p ≥r set or r n ≥r set , and the calculated value of the T-type correlation degree is continuously judged 3 times, it is determined that an internal fault has occurred; in this embodiment, r p =-0.96, r n =-1, it is determined that f5 is an external fault.

[0112] The described high-voltage DC power grid transmission line protection system is characterized in that the fault pole selection module specifically includes:

[0113] A data sorting unit for sorting and outputting the data that needs to be polarity judged when it is determined to be an internal fault;

[0114] A polarity judgment unit for comparing the T-type correlation degrees r p , r n calculated from the positive and negative pole current fault current increments with the protection setting value r set to identify the fault pole: if r p ≥r set and r n<r set If so, it is a positive pole fault within the zone; if r p <r set and r n ≥r set If so, it is a negative pole fault within the zone; if r p ≥r set and r n ≥r set If so, it is a bipolar fault within the zone. In this embodiment, it is determined that an external fault occurs at f5, so Line1 no longer discriminates the faulty pole.

[0115] Verification shows that the high-voltage DC grid transmission line protection method and system described in the present invention are highly reliable and logical.

[0116] If the above functions are implemented in the form of software function units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0117] Logic and / or steps represented in the flowchart or described in other ways herein, for example, can be considered as a definite sequence list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device), or in combination with these instruction execution systems, apparatuses, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transmit a program for use by or in combination with an instruction execution system, apparatus, or device.

[0118] More specific examples (a non-exhaustive list) of computer-readable media include the following: an electrical connection (electronic device) having one or more wirings, a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable media can even be paper or other suitable media on which the program can be printed, as the program can be obtained electronically, for example, by optically scanning the paper or other media, then editing, interpreting, or otherwise processing it as appropriate, and then storing it in a computer memory.

[0119] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

[0120] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A protection method for a transmission line in a high-voltage DC power grid, characterized in that, Including: Collecting power grid data information through a line protection device to determine whether to activate line protection; After protection is activated, the current transient electrical quantities collected by each measuring point of the converter station are used to extract the current increment sequence from the current electrical quantities; Calculating the T-type correlation degree of the positive and negative pole fault currents between two converter stations using the current increment sequence; Identifying internal and external faults and the faulty pole by comparing the T-type correlation degrees of the positive and negative pole fault current increments between two converter stations with the protection setting value.

2. The method for protecting a transmission line of a high-voltage DC power grid according to claim 1, characterized in that: The determination of whether to activate line protection by collecting power grid data information through a line protection device is to determine whether to activate line protection by comparing the current fault component collected by the line protection device with the starting threshold; The protection device continuously monitors the fault current values at several different monitoring points, calculates the current fault component for each monitoring point, and when the current fault components are continuously calculated a corresponding number of times greater than the preset threshold at several monitoring points, the line protection device activates line protection.

3. The method for protecting a transmission line of a high-voltage DC power grid according to claim 2, wherein: The extraction of the current increment sequence from the current transient electrical quantities collected by each measuring point of the converter station after protection is activated includes When a DC transmission line fails, select an appropriate sampling frequency and sampling time window, and the expression is: t ∈ [A, B] B > A ≥ 0 Δt x = t x - t x-1 where x = 2, 3…, n Among them, t is the time period, A and B refer to the sampling time window, t x and t x-1 are the time points of sampling, and Δt x is the time interval between two sampling time points; For the values of the time series of the fault currents at the beginning and end of the DC positive or negative pole line at each point in the interval [A, B] are: Among them, I1 and I2 are the fault current sequences at the beginning and end of the line. I1(t1), I1(t2), …, I1(t n ) are the sampled values at the beginning of the line within the sampling time window, and I2(t1), I2(t2), …, I2(t n ) are the sampled values at the end of the line within the sampling time window; Normalize the two fault current sequences and obtain the two fault current increment sequences, and the expression is: Where, ΔI1 and ΔI2 are the fault current sequences at the beginning and end of the line after normalization.

4. The method for protecting a transmission line of a high-voltage DC power grid according to claim 3, wherein: Calculating the T-type correlation degree of the positive and negative pole fault currents between two converter stations using the current increment sequence is to calculate the correlation coefficients of the two fault current increment sequences at each time period within the same sampling time window, and the expression is: Among them, ξ(t x ) is the correlation coefficient of each period within the sampling time window, x = 2, 3, … n; Calculate the correlation degree of the two currents within the total sampling time window. Denote the correlation coefficient of the original time current sequences I1 and I2 as r(I1, I2), and the corresponding T-type correlation degree expression is: where r y = r(I1, I2) is the T-type correlation degree of the original time-current sequences I1 and I2; When -1 ≤ r(I1, I2) < 0, I1 and I2 are negatively correlated within the time window [A, B], and the strength of the negative correlation increases with the increase of |r(I1, I2)|; When 0 < r(I1, I2) ≤ 1, I1 and I2 are positively correlated within the time window [A, B], and the strength of the positive correlation increases with the increase of r(I1, I2).

5. The method for protecting a transmission line of a high-voltage DC power grid according to claim 4, characterized in that: The identification of internal and external faults and the faulty pole by comparing the T-type correlation degrees of the positive and negative pole fault current increments between two converter stations with the protection setting value includes When r p > k set or r n > k set it indicates that a line fault occurs within the HVDC transmission line, and the T-type correlation degree of the current increment at the protection installation points at both ends of the positive or negative pole of the transmission line is positively correlated; When r p < -k set and r n < -k set it indicates that an external fault has occurred in the DC transmission line or the system is operating normally; the T-type correlation degree of the current increment at the protection installation points at both the positive and negative poles of the transmission line is negatively correlated; The fault identification criterion constructed by the T-type correlation degree, and the expression is: Among them, r p represents the T-type correlation degree of the fault current increment at both ends of the positive DC transmission line, and r n represents the T-type correlation degree of the fault current increment at the beginning and end of the negative line. k set is the setting threshold value.

6. The method for protecting a transmission line of a high-voltage DC power grid according to claim 5, characterized in that: The identification of internal and external faults and the faulty pole by comparing the T-type correlation degrees of the positive and negative pole fault current increments between two converter stations with the protection setting value also includes When a positive pole ground fault occurs in the DC transmission line area, the T-type correlation degree r calculated from the increment of the fault current at the protection installation locations at both ends of the positive pole line p is positively correlated, while the negative pole line is a sound pole, and the T-type correlation degree r of the current increment calculated at both ends n is negatively correlated; When a negative pole grounding fault occurs within the DC transmission line, the T-type correlation degree r calculated from the increments of the two fault currents at the protection installation locations at both ends of the negative pole line n is positively correlated, while the positive pole line is a healthy pole, and the T-type correlation degree r of the current increments at both ends calculated p is negatively correlated; When a bipolar fault occurs in the DC transmission line, the T-type correlation degrees r p and r n calculated from the fault current increments at the protection installation locations at both the positive and negative poles are both positively correlated; Constructing a fault pole selection criterion, and the expression is: When the P - pole type correlation degree r p ≥r set and when the T - type correlation degree r of the N - pole n ≥r set it is judged as a bipolar fault in the area; When the P-pole type correlation degree r p ≥r set and when the T-type correlation degree r of the N-pole n <r set it is judged as a positive pole fault in the zone; When the P-pole type correlation degree r p < r set and when the T-pole type correlation degree r of the N-pole n < r set it is judged as a negative pole fault in the area.

7. A system adopting a high-voltage DC power grid transmission line protection method as described in any one of claims 1 to 6, characterized in that: Including a signal acquisition module, a fault identification module, and a fault pole selection module; The signal acquisition module collects and stores the current at the data protection installation location, and continuously collects the current at each measuring point. If the protection start criterion is met, the protection is activated and enters the fault identification module; otherwise, it does not start. The fault identification module is used to identify internal and external faults when the protection is activated. If it is judged as an external fault, the protection does not operate; if it is an internal fault, it enters the fault pole selection module. The fault pole selection module judges whether the system has a positive pole, negative pole or bipolar fault through a fault pole selection function; The signal acquisition module includes a data acquisition unit that continuously acquires the analog signals output from the secondary side of the current transformers at each protection installation location; an analog-to-digital conversion unit that converts the current analog signals at each measurement point into digital signals; a protection activation unit that judges whether the current digital signal is greater than a set activation threshold value. If so, it reads the activation time and stores the data; The fault identification module includes a parameter setting unit for setting the setting protection threshold value k set , the protection threshold value r set ; a numerical calculation unit that calculates the T-type correlation degree of the p-pole and n-pole; compares the T-type correlation degree with a set protection threshold value to distinguish internal and external faults; The fault pole selection module includes a data arrangement unit that outputs and arranges the data that needs to be polarity judged when it is judged as an internal fault; a polarity judgment unit that compares the calculated T-type correlation degree of the positive and negative pole fault current increments with the protection setting value; Identify the faulty pole. If r p ≥ r set and r n < r set , it is a positive pole fault within the zone. If r p < r set and r n ≥ r set , it is a negative pole fault within the zone. If r p ≥ r set and r n ≥ r set , it is a bipolar fault within the zone.

8. A computer device, comprising a memory and a processor, the memory storing a computer program, characterized in that, When the processor executes the computer program, it implements the steps of a high-voltage DC grid transmission line protection method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of a high-voltage DC grid transmission line protection method according to any one of claims 1 to 6.

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