A single-end protection method and device for offshore wind power transmission line

Abstract

The present invention discloses a single-ended quantity protection method and device for offshore wind power transmission lines, the method comprising: sampling the voltage and current of a flexible direct current power grid line; calculating the voltage gradient based on the line voltage to determine whether the line is faulty; for a faulty line, calculating the voltage change rate based on the sampled line voltage to determine the first extreme point; judging whether the line is an intra-regional fault or intra-regional disturbance based on the first extreme point; for intra-regional fault or intra-regional disturbance lines, judging whether it is an intra-regional fault based on the line current; for intra-regional fault lines, judging the faulty element based on the zero-mode voltage, and executing the corresponding protection export action. The method of the present invention can be applied to the single-ended quantity protection of offshore wind power transmission lines, can quickly detect whether a DC line is faulty, and judge the fault type, which has important practical significance for the rapid isolation of faults and ensuring the safe and stable operation of power systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection of direct current transmission lines, and in particular relates to a single-ended quantity protection method and device for an offshore wind power transmission line. Background Art

[0002] Wind energy is the most mature and widely used renewable energy. Compared with onshore wind farms, offshore wind farms in the eastern coastal areas have great advantages in wind stability, wind speed, and annual power generation hours. Among them, offshore wind power has a large transmission capacity and has broad prospects.

[0003] Offshore wind power full DC collection and transmission is the development trend of large offshore wind farms in the future. There are no practical engineering cases so far, and there are many key technical problems that need to be studied and solved, one of which is relay protection. Among them, the transmission line is responsible for power transmission. Research on the relay protection strategy of the transmission line is of great significance to ensure the system operation performance and safety and promote the development and application of technology.

[0004] The faults of single-end quantity of offshore wind power transmission lines develop and spread quickly and have a wide impact range. In order to reduce the impact range of faults, the system should have the ability to quickly identify and locate faults, and then achieve fault isolation. However, the new system has the characteristics of complex topology, diversified commutation links, and weak boundary characteristics, which puts forward new requirements for the reliability of protection principles. The existing protection principles have shown the problem of insufficient adaptability. Summary of the invention

[0005] The purpose of the present invention is to provide a single-ended quantity protection method and device for an offshore wind power transmission line, which performs single-ended quantity protection for a flexible DC power grid line based on the first extreme point characteristics of a fault voltage. The method and device can be applied to the novel characteristics of offshore wind power transmission lines, and have the advantages of high action reliability, strong ability to tolerate transition resistance, and low requirements on sampling frequency and computing power.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a single-end quantity protection method for an offshore wind power transmission line, comprising:

[0008] Sampling instantaneous voltage and current on the rectifier side of offshore wind power transmission lines;

[0009] Calculate the voltage gradient based on the line voltage to determine whether the line is faulty;

[0010] For the fault line, the voltage change rate is calculated based on the sampled voltage to determine the first extreme point;

[0011] Based on the first extreme point, determine whether the line is an internal fault or an internal disturbance;

[0012] For intra-area faults or intra-area disturbance lines, determine whether it is an intra-area fault based on the line current;

[0013] For faulty lines within the area, the faulty components are judged based on the zero-mode voltage and the corresponding protection output actions are executed.

[0014] Furthermore, the step of calculating the voltage gradient based on the line voltage and determining whether the line is faulty includes:

[0015] The voltage gradient is calculated as follows:

[0016]

[0017] Among them, u(kj) is the voltage sampling value before the jth sampling cycle at the current sampling time k, is the voltage gradient value at the current sampling time k;

[0018] If satisfied It is judged as a line fault;

[0019] Among them, Δ set is the starting threshold value.

[0020] Furthermore, the starting threshold value needs to be selected to be greater than the maximum value of the voltage gradient under normal operating voltage fluctuations.

[0021] Furthermore, the voltage change rate is calculated based on the sampled voltage to determine the first extreme point, including:

[0022] The voltage change rate is calculated as follows:

[0023] Δu(k)=u(k+1)-u(k);

[0024] Wherein, Δu(k) is the voltage change rate at the current sampling time k, and u(k) is the sampled voltage at the current sampling time k;

[0025] When Δu(k)>0 appears for the first time, the first extreme point is obtained, and the time from protection start to reaching the first extreme point is recorded as T, and the amplitude of the voltage first extreme point |u(k)| is H.

[0026] Furthermore, judging whether the line is an intra-area fault or intra-area disturbance based on the first extreme point includes:

[0027] If T < T set And H>H set , or T>T set And U avg >U avg_set , then the line is judged to be an internal fault or internal disturbance;

[0028] Among them, T set is the time window, H set is the first threshold value, U avg It is the inverse of the average value of the line mode voltage fault component of three consecutive sampling points after startup, U avg_set is the second threshold value,

[0029] H set , T set and U avg_set satisfy:

[0030] H set =K rel1 ·H max ;

[0031] T set =K rel2 ·T max ;

[0032] U avg_set =K rel3 ·U avg_max ;

[0033] Among them, H max is the fault voltage peak value of the most serious fault outside the positive direction zone, T max is the maximum time from protection start to the first extreme point under each fault condition, U avg_max K is the maximum value of the opposite number of the average value of the line mode voltage fault component at three consecutive sampling points after the protection is started. rel1 , K rel2 and K rel3 All are reliability coefficients.

[0034] Further, judging whether it is an intra-zone fault based on the line current includes:

[0035] Calculate the fault current in the data window T int The integral value i int ;

[0036] If i int >i int_set , it is judged as an internal fault;

[0037] Among them, i int_set is the third threshold value,

[0038] i int_set satisfy:

[0039]

[0040] Among them, i int_min The data window T of the current fault component after the protection is started under various faults int The minimum value of the integral within Ksen_min For sensitivity.

[0041] Furthermore, the element for judging fault based on zero-mode voltage performs corresponding protection output action, including:

[0042] Calculate the zero mode voltage in the data window T 0_avg The average value U 0_avg ,

[0043] If U is satisfied 0_avg <-Δ, it is judged as a positive pole fault, corresponding to the positive pole protection outlet;

[0044] If U 0_avg >Δ, it is judged as a negative pole fault, corresponding to the negative pole protection outlet;

[0045] If -Δ≤U 0_avg ≤Δ, it is judged as an inter-pole fault, and the corresponding positive pole protection and negative pole protection are simultaneously exported.

[0046] The present invention also provides a single-end protection device for an offshore wind power transmission line, comprising:

[0047] Sampling module, used to sample the instantaneous voltage and current on the rectifier side of the offshore wind power transmission line;

[0048] A first judgment module, used to calculate a voltage gradient based on the line voltage to judge whether the line is faulty;

[0049] The second judgment module is used to calculate the voltage change rate of the fault line based on the sampled voltage and determine the first extreme point;

[0050] A third judgment module is used to judge whether the line is an intra-area fault or an intra-area disturbance based on the first extreme value point;

[0051] A fourth judgment module is used to judge whether the fault in the area or the disturbance line in the area is an internal fault based on the line current;

[0052] The execution module is used to judge the faulty components of the faulty lines in the area based on the zero-mode voltage and execute the corresponding protection output action.

[0053] Furthermore, the first determination module is specifically used for:

[0054] The voltage gradient is calculated as follows:

[0055]

[0056] Among them, u(kj) is the voltage sampling value before the jth sampling cycle at the current sampling time k, is the voltage gradient value at the current sampling time k;

[0057] If satisfied It is judged as a line fault;

[0058] Among them, Δ set is the starting threshold value.

[0059] Furthermore, the second judgment module is specifically used for:

[0060] The voltage change rate is calculated as follows:

[0061] Δu(k)=u(k+1)-u(k);

[0062] Wherein, Δu(k) is the voltage change rate at the current sampling time k, and u(k) is the sampled voltage at the current sampling time k;

[0063] When Δu(k)>0 appears for the first time, the first extreme point is obtained, and the time from protection start to reaching the first extreme point is recorded as T, and the amplitude of the voltage first extreme point |u(k)| is H.

[0064] Furthermore, the third judgment module is specifically used for:

[0065] If T<T set And H>H set , or T>T set AndU avg >U avg_set , then the line is judged to be an internal fault or internal disturbance;

[0066] Among them, T set is the time window, H set is the first threshold value, U avg It is the inverse of the average value of the line mode voltage fault component of three consecutive sampling points after startup, U avg_set is the second threshold value,

[0067] H set , T set and U avg_set satisfy:

[0068] H set =K rel1 ·H max ;

[0069] T set =K rel2 ·T max ;

[0070] U avg_set =K rel3 ·U avg_max ;

[0071] Among them, H maxis the fault voltage peak value of the most serious fault outside the positive direction zone, T max is the maximum time from protection start to the first extreme point under each fault condition, U avg_max K is the maximum value of the opposite number of the average value of the line mode voltage fault component at three consecutive sampling points after the protection is started. rel1 , K rel2 and K rel3 All are reliability coefficients.

[0072] Furthermore, the fourth determination module is specifically used for:

[0073] Calculate the fault current in the data window T int The integral value i int ;

[0074] If i int >i int_set , it is judged as an internal fault;

[0075] Among them, i int_set is the third threshold value,

[0076] i int_set satisfy:

[0077]

[0078] Among them, i int_min The data window T of the current fault component after the protection is started under various faults int The minimum value of the integral within K sen_min For sensitivity.

[0079] Furthermore, the execution module is specifically used for:

[0080] Calculate the zero mode voltage in the data window T 0_avg The average value U 0_avg ,

[0081] If U 0_avg <-Δ, it is judged as a positive pole fault, corresponding to the positive pole protection outlet;

[0082] If U 0_avg >Δ, it is judged as a negative pole fault, corresponding to the negative pole protection outlet;

[0083] If -Δ≤U 0_avg ≤Δ, it is judged as an inter-pole fault, and the corresponding positive pole protection and negative pole protection are simultaneously exported.

[0084] Compared with the prior art, the present invention has the following advantages:

[0085] The present invention performs single-ended quantity protection of flexible DC power grid lines based on the first extreme point feature of the fault voltage. Since the first extreme point feature of the fault voltage has obvious differences under in-zone and out-of-zone faults, the method of the present invention has high action reliability; since the first extreme point feature of the fault voltage is weakly affected by the transition resistance, the method of the present invention has strong tolerance to the transition resistance; since the first extreme point feature of the fault voltage is low in sensitivity to the sampling frequency and the algorithm is simple, the method of the present invention has low requirements for the sampling frequency and computing power. The method of the present invention can be applied to the single-ended quantity protection of offshore wind power transmission lines, can quickly detect whether a DC line has a fault, and judge the type of fault, which has important practical significance for the rapid isolation of faults and ensuring the safe and stable operation of power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 is a topological diagram of an offshore wind power DC collection system in an embodiment of the present invention;

[0087] Figure 2 It is a flow chart of a single-end quantity protection method for an offshore wind power transmission line based on the first extreme point feature of a fault voltage provided by an embodiment of the present invention;

[0088] Figure 3 : is a waveform diagram of line voltage and current after fault F1 in an embodiment of the present invention;

[0089] Figure 4 It is the protection element action signal determined after the fault F1 in the embodiment of the present invention. DETAILED DESCRIPTION

[0090] The present invention is further described below. The following examples are only used to more clearly illustrate the technical solution of the present invention, and are not intended to limit the protection scope of the present invention.

[0091] Example 1

[0092] This embodiment provides a single-end protection method for an offshore wind power transmission line, comprising:

[0093] Sampling instantaneous voltage and current on the rectifier side of offshore wind power transmission lines;

[0094] Calculate the voltage gradient based on the line voltage to determine whether the line is faulty;

[0095] For the fault line, the voltage change rate is calculated based on the sampled line voltage to determine the first extreme point;

[0096] Based on the first extreme point, determine whether the line is an internal fault or an internal disturbance;

[0097] For intra-area faults or intra-area disturbance lines, determine whether it is an intra-area fault based on the line current;

[0098] For faulty lines within the area, the faulty components are judged based on the zero-mode voltage and the corresponding protection output actions are executed.

[0099] It should be noted that the protection of information only at one end of the line is called "single-ended" protection.

[0100] Example 2

[0101] This embodiment provides a single-end protection method for offshore wind power transmission lines based on the first extreme point feature of fault voltage, the process is as follows: Figure 2 As shown, the following steps are included:

[0102] Step 1: Sample the instantaneous voltage and current on the rectifier side of the offshore wind power transmission line;

[0103] Step 2: Calculate the voltage gradient and identify the starting element. If the criteria are met, it is a fault and continue to execute. Otherwise, return to step 1.

[0104] The voltage gradient calculation formula is shown in formula (1):

[0105]

[0106] The discriminant of the start-up element is shown in formula (2).

[0107]

[0108] Where u(kj) is the voltage sampling value before the jth sampling cycle at the current sampling time k, is the voltage gradient value at the current sampling time k. Δ set The threshold value is the starting threshold value, and the threshold value should be selected to be greater than the maximum value of the voltage gradient under normal operating voltage fluctuations, while ensuring accurate and rapid starting of internal faults in the DC grid.

[0109] Step 3: Perform differential processing on the sampled voltage value, calculate its rate of change Δu(k) and find the first extreme point to identify the selected area components. If the judgment criteria are met, it is an in-area fault or in-area disturbance, and continue to execute, otherwise return to step 1;

[0110] The voltage change rate is calculated based on formula (3):

[0111] Δu(k)=u(k+1)-u(k) (3)

[0112] When Δu(k)>0 appears for the first time, the time from protection start to reaching the first extreme value is defined as T, and the amplitude of the voltage first extreme value |u(k)| is H. set , that is, in the time window T set There is a first extreme value H in the memory, and the discriminant of the selected area element is shown in formula (4):

[0113] H>H set (4)

[0114] H set and T set The setting of is shown in equations (5)-(6):

[0115] H set =K rel1 ·H max (5)

[0116] T set =K rel2 ·T max (6)

[0117] In the formula, H max is the fault voltage peak value of the most serious fault outside the positive direction zone, T max K is the maximum time that may be taken for the protection to start to the first extreme point under various fault conditions. rel1 and K rel2 is the reliability coefficient. max and T max Through the theoretical analysis of voltage and current, K rel1 , K rel2 Use experience value.

[0118] For the head-end fault within the area, if T>T set , that is, in the time window T set If the extreme point of the fault voltage cannot be detected, or the first extreme point does not satisfy formula (4), further auxiliary judgment criteria are required, such as formula (7):

[0119] U avg >U avg_set (7)

[0120] Where U avg It is the inverse of the average value of the line mode voltage fault component of three consecutive sampling points after startup, U avg_set is the threshold value, and its setting is shown in formula (8):

[0121] U avg_set =K rel3 ·U avg_max (8)

[0122] Where U avg_max K is the maximum value of the opposite value of the average value of the line mode voltage fault component at three consecutive sampling points after the protection is started. rel3 is the reliability coefficient.

[0123] If the auxiliary criterion is still not met, it is judged as a disturbance or an out-of-zone fault. Return to step 1.

[0124] It should be noted that this step samples the positive and negative voltages of the line, performs differential processing on the two voltages, and performs fault judgments respectively.

[0125] It should be noted that the line mode voltage fault component can be obtained by performing algebraic operations on the sampled voltage.

[0126] It should be noted that step three is to distinguish intra-area faults (including severe intra-area disturbances) from extra-area faults and mild disturbances (including both intra-area and extra-area faults). Therefore, what meets step three should be intra-area faults and severe intra-area disturbances.

[0127] Step 4: Calculate the fault current in the data window T int The integral value i int , perform disturbance element identification, if the criteria are met, it is an in-zone fault, otherwise it is a disturbance or an out-of-zone fault, and return to step 1;

[0128] The criterion of the disturbance discrimination element is shown in formula (9):

[0129] i int >i int_set (9)

[0130] In the formula, i int is the data window T int The integral result of the internal current fault component, i int_set is the corresponding threshold value.

[0131] The calculation of the threshold setting value is shown in formula (10):

[0132]

[0133] In the formula, i int_min The data window T of the current fault component after the protection is started under various fault conditions int The minimum value of the integral within K sen_min For sensitivity.

[0134] It should be noted that the data window T int is the preset value.

[0135] Step 5: Calculate the zero-mode voltage in the data window T 0_avg The average value U 0_avg , perform pole selection component judgment. If any criterion is met, the protection outlet of the corresponding pole is selected, otherwise return to step 1.

[0136] The discriminant of the pole selection element is shown in formula (11):

[0137]

[0138] Where U0_avg The zero mode voltage is in the data window T 0_avg Δ is the average value within the range, and Δ is the threshold value for determining the polarity of zero-mode voltage.

[0139] It should be noted that the zero-mode voltage can be obtained by performing algebraic operations on the sampled voltage.

[0140] It should be noted that the data window T 0_avg It is a preset value.

[0141] Example 3

[0142] This embodiment is based on Figure 1 In the offshore wind power DC collection system shown in the figure, a grounding fault (referred to as fault F1) occurs at the head end of the system's positive transmission line through a 100Ω transition resistance.

[0143] Step 1: When the system fails F1, the voltage and current waveforms on the line rectifier side measured by the sampling element are as follows: Figure 3 shown.

[0144] Step 2: Calculate the voltage gradient according to formula (1) in Example 2

[0145] Δ set Take 0.01pu, and perform the starting element determination according to formula (2) in Example 2. If the determination criterion is met, it is determined to be a fault, and then proceed to step three.

[0146] Step 3: Perform differential processing on the sampled voltage value, calculate its rate of change Δu(k) according to formula (3) in Example 2 and find the first extreme point feature.

[0147] After calculation, it can be obtained that in this fault situation, T≈0, H=217.04V. <T set , that is, there is a first extreme point in the data window, so there is no need for auxiliary judgment.

[0148] According to formula (5) in Example 2, H is set set =182kV, where the reliability factor K rel1 Take 1.1, and select the components according to formula (4). If the criterion is met, it is determined to be an in-zone fault and proceed to step 4.

[0149] Step 4: Calculate the fault current in the data window T int Inner integral value i int .

[0150] Take K sen_min =1.2, and the protection criterion setting value i is calculated according to formula (10) in Example 2 int_set =0.058kA·ms.

[0151] Take T int =0.5ms, calculate the fault condition i int =0.13 kA·ms, disturbance determination is performed according to formula (9) in embodiment 2, the determination criterion is satisfied, it is determined to be a fault, and step five is continued.

[0152] Step 5: Calculate the zero-mode voltage in the data window T 0_avg The average value U 0_avg .

[0153] In the protection criterion, Δ is taken as 0.02pu.

[0154] Take T 0_avg =0.5ms, calculate U under this fault condition 0_avg =-305.98kV, the pole selection element is judged according to formula (11) in embodiment 2, and the positive pole fault judgment criterion is met, and it is judged to be a positive pole fault, corresponding to the positive pole protection outlet.

[0155] Based on the protection element action signal of the judgment process of this embodiment, Figure 4 shown.

[0156] Example 4

[0157] This embodiment provides a single-end protection device for an offshore wind power transmission line, comprising:

[0158] Sampling module, used to sample the voltage and current of offshore wind power transmission lines;

[0159] A first judgment module, used to calculate a voltage gradient based on the line voltage to judge whether the line is faulty;

[0160] The second judgment module is used to calculate the voltage change rate of the fault line based on the sampled line voltage and determine the first extreme point;

[0161] A third judgment module is used to judge whether the line is an intra-area fault or an intra-area disturbance based on the first extreme value point;

[0162] A fourth judgment module is used to judge whether the fault in the area or the disturbance line in the area is an internal fault based on the line current;

[0163] The execution module is used to judge the faulty components of the faulty lines in the area based on the zero-mode voltage and execute the corresponding protection output action.

[0164] In this embodiment, the first judgment module is specifically used for:

[0165] The voltage gradient is calculated as follows:

[0166]

[0167] Among them, u(kj) is the voltage sampling value before the jth sampling cycle at the current sampling time k, is the voltage gradient value at the current sampling time k;

[0168] If satisfied It is judged as a line fault;

[0169] Among them, Δ set is the starting threshold value.

[0170] In this embodiment, the second judgment module is specifically used for:

[0171] The voltage change rate is calculated as follows:

[0172] Δu(k)=u(k+1)-u(k);

[0173] Wherein, Δu(k) is the voltage change rate at the current sampling time k, and u(k) is the sampled voltage at the current sampling time k;

[0174] When Δu(k)>0 appears for the first time, the first extreme point is obtained, and the time from protection start to reaching the first extreme point is recorded as T, and the amplitude of the voltage first extreme point |u(k)| is H.

[0175] In this embodiment, the third judgment module is specifically used for:

[0176] If T<T set And H>H set , or T>T set AndU avg >U avg_set , then the line is judged to be an internal fault or internal disturbance;

[0177] Among them, T set is the time window, H set is the first threshold value, U avg It is the inverse of the average value of the line mode voltage fault component of three consecutive sampling points after startup, U avg_set is the second threshold value,

[0178] H set , T set and U avg_set satisfy:

[0179] H set =K rel1 ·H max ;

[0180] T set =K rel2 ·T max ;

[0181] U avg_set =Krel3 ·U avg_max ;

[0182] Among them, H max is the fault voltage peak value of the most serious fault outside the positive direction zone, T max is the maximum time from protection start to the first extreme point under each fault condition, U avg_max K is the maximum value of the opposite number of the average value of the line mode voltage fault component at three consecutive sampling points after the protection is started. rel1 , K rel2 and K rel3 All are reliability coefficients.

[0183] In this embodiment, the fourth determination module is specifically used for:

[0184] Calculate the fault current in the data window T int The integral value i int ;

[0185] If i int >i int_set , it is judged as an internal fault;

[0186] Among them, i int_set is the third threshold value,

[0187] i int_set satisfy:

[0188]

[0189] Among them, i int_min The current fault component is in the data window T after the protection is started. int The minimum value of the integral within K sen_min For sensitivity.

[0190] In this embodiment, the execution module is specifically used for:

[0191] Calculate the zero mode voltage in the data window T 0_avg The average value U 0_avg ,

[0192] If U 0_avg <-Δ, it is judged as a positive pole fault, and the corresponding positive pole protection output is actuated;

[0193] If U 0_avg >Δ, it is judged as a negative pole fault, and the corresponding negative pole protection output is actuated;

[0194] If -Δ≤U 0_avg ≤Δ, it is judged as an inter-pole fault and the corresponding inter-pole protection outlet is actuated.

[0195] It is worth pointing out that the device embodiment corresponds to the above-mentioned method embodiment, and the implementation methods of the above-mentioned method embodiments are all applicable to the device embodiment and can achieve the same or similar technical effects, so they will not be repeated here.

[0196] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0197] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0198] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0199] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0200] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A single-end protection method for offshore wind power transmission lines, characterized in that: include: Sampling instantaneous voltage and current on the rectifier side of offshore wind power transmission lines; Calculate the voltage gradient based on the sampled voltage to determine whether the line is faulty; For the fault line, the voltage change rate is calculated based on the sampled voltage to determine the first extreme point; Based on the first extreme point, determine whether the line is an internal fault or internal disturbance, including: If T < T set And H>H set , or T>T set AndU avg >U avg_set , then the line is judged to be an internal fault or internal disturbance; Among them, T set is the time window, H set is the first threshold value, U avg It is the inverse of the average value of the line mode voltage fault component of three consecutive sampling points after the protection is started. avg_set is the second threshold value, T is the time from protection start to reaching the first extreme value point, and H is the amplitude of the voltage first extreme value point; H set , T set and U avg_set satisfy: H set =K rel1 ·H max ; T set =K rel2 ·T max ; IN avg_set =K rel3 ·IN avg_max ; Among them, H max is the fault voltage peak value of the most serious fault outside the positive direction zone, T max is the maximum time from protection start to the first extreme point under each fault condition, U avg_max K is the maximum value of the opposite number of the average value of the line mode voltage fault component at three consecutive sampling points after the protection is started. rel1 , K rel2 and K rel3 All are reliability coefficients; For an intra-zone fault or intra-zone disturbed line, determine whether it is an intra-zone fault based on the line current, including: Calculate the fault current in the data window T int The integral value i int ; If i int >i int_set , it is judged as an internal fault; Among them, i int_set is the third threshold value, i int_set satisfy: Among them, i int_min The data window T of the current fault component after the protection is started under various faults int The minimum value of the integral within K sen_min is sensitivity; For faulty lines within the area, the faulty components are judged based on the zero-mode voltage and the corresponding protection output actions are executed.

2. A single-ended protection method for offshore wind power transmission lines according to claim 1, characterized in that: The step of calculating the voltage gradient based on the sampled voltage and determining whether the line is faulty includes: The voltage gradient is calculated as follows: Among them, u(kj) is the voltage sampling value before the jth sampling cycle at the current sampling time k, is the voltage gradient value at the current sampling time k; If satisfied It is judged as a line fault; Among them, Δ set is the starting threshold value.

3. A single-ended protection method for offshore wind power transmission lines according to claim 2, characterized in that: The starting threshold value needs to be selected to be greater than the maximum value of the voltage gradient under normal operating voltage fluctuation.

4. A single-ended protection method for offshore wind power transmission lines according to claim 1, characterized in that: The step of calculating the voltage change rate based on the sampled voltage and determining the first extreme point includes: The voltage change rate is calculated as follows: Δu(k)=u(k+1)-u(k); Wherein, Δu(k) is the voltage change rate at the current sampling time k, and u(k) is the sampled voltage at the current sampling time k; When Δu(k)>0 appears for the first time, the first extreme point is obtained, and the time from protection start to reaching the first extreme point is recorded as T, and the amplitude of the voltage first extreme point |u(k)| is H.

5. A single-ended protection method for offshore wind power transmission lines according to claim 1, characterized in that: The element for judging fault based on zero-mode voltage performs corresponding protection output action, including: Calculate the zero mode voltage in the data window T 0_avg The average value U 0_avg , If U 0_avg <-Δ, it is judged as a positive pole fault, corresponding to the positive pole protection outlet; If U 0_avg >Δ, it is judged as a negative pole fault, corresponding to the negative pole protection outlet; If -Δ≤U 0_avg ≤Δ, it is judged as an inter-pole fault, and the corresponding positive and negative protections are exported at the same time; Wherein, Δ is the threshold value for determining the polarity of zero-mode voltage.

6. A single-end protection device for offshore wind power transmission lines, characterized in that: The device is used to implement the single-end quantity protection method for offshore wind power transmission lines according to any one of claims 1 to 5, and comprises: Sampling module, used to sample the instantaneous voltage and current on the rectifier side of the offshore wind power transmission line; A first judgment module, used to calculate a voltage gradient based on the sampled voltage to judge whether the line is faulty; The second judgment module is used to calculate the voltage change rate of the fault line based on the sampled voltage and determine the first extreme point; The third judgment module is used to judge whether the line is an intra-area fault or intra-area disturbance based on the first extreme point. The specific implementation method is as follows: If T<T set And H>H set , or T>T set AndU avg >U avg_set , then the line is judged to be an internal fault or internal disturbance; Among them, T set is the time window, H set is the first threshold value, U avg It is the inverse of the average value of the line mode voltage fault component of three consecutive sampling points after the protection is started. avg_set is the second threshold value, T is the time from protection start to reaching the first extreme value point, and H is the amplitude of the voltage first extreme value point; H set , T set and U avg_set satisfy: H set =K rel1 ·H max ; T set =K rel2 ·T max ; IN avg_set =K rel3 ·IN avg_max ; Among them, H max is the fault voltage peak value of the most serious fault outside the positive direction zone, T max is the maximum time from protection start to the first extreme point under each fault condition, U avg_max K is the maximum value of the opposite number of the average value of the line mode voltage fault component at three consecutive sampling points after the protection is started. rel1 , K rel2 and K rel3 All are reliability coefficients; A fourth judgment module is used to judge whether the fault in the area or the disturbance line in the area is an internal fault based on the line current; The execution module is used to judge the faulty components of the faulty lines in the area based on the zero-mode voltage and execute the corresponding protection output action.

7. A single-ended protection device for offshore wind power transmission lines according to claim 6, characterized in that: The first judgment module is specifically used for: The voltage gradient is calculated as follows: Among them, u(kj) is the voltage sampling value before the jth sampling cycle at the current sampling time k, is the voltage gradient value at the current sampling time k; If satisfied It is judged as a line fault; Among them, Δ set is the starting threshold value.

8. A single-ended protection device for offshore wind power transmission lines according to claim 6, characterized in that: The second judgment module is specifically used for: The voltage change rate is calculated as follows: Δu(k)=u(k+1)-u(k); Wherein, Δu(k) is the voltage change rate at the current sampling time k, and u(k) is the sampled voltage at the current sampling time k; When Δu(k)>0 appears for the first time, the first extreme point is obtained, and the time from protection start to reaching the first extreme point is recorded as T, and the amplitude of the voltage first extreme point |u(k)| is H.

9. A single-ended protection device for offshore wind power transmission lines according to claim 6, characterized in that: The fourth judgment module is specifically used for: Calculate the fault current in the data window T int The integral value i int ; If i int >i int_set , it is judged as an internal fault; Among them, i int_set is the third threshold value, i int_set satisfy: Among them, i int_min The data window T of the current fault component after the protection is started under various faults int The minimum value of the integral within K sen_min For sensitivity.

10. A single-ended protection device for offshore wind power transmission lines according to claim 6, characterized in that: The execution module is specifically used for: Calculate the zero mode voltage in the data window T 0_avg The average value U 0_avg , If U 0_avg <-Δ, it is judged as a positive pole fault, corresponding to the positive pole protection outlet; If U 0_avg >Δ, it is judged as a negative pole fault, corresponding to the negative pole protection outlet; If -Δ≤U 0_avg ≤Δ, it is judged as an inter-pole fault, and the corresponding positive and negative protections are exported at the same time; Wherein, Δ is the threshold value for determining the polarity of zero-mode voltage.

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