Transmitting line distance protection method and system based on transient fault characteristics

Abstract

The invention belongs to the technical field of power system relay protection, and provides a transmission line distance protection method and system based on transient fault characteristics. The method comprises the steps that when the phase voltage difference value of at least three continuous sampling points is larger than a protection starting threshold value, the moment of the first sampling point in the continuous sampling points is determined as the fault occurrence moment, and protection starting is controlled; after protection is started, the fault type is judged according to the instantaneous value of each phase voltage of each sampling point within the delay set time of the fault occurrence moment; when it is judged that the fault type is a single-phase earth fault, protection is controlled not to act; and when the fault type is judged to be a two-phase interphase short circuit or a three-phase grounding fault, according to the oscillation frequency of each voltage instantaneous value of each sampling point within the delay set time of the fault occurrence moment, in combination with the setting value of the protection action, controlling the protection action. And compared with the traditional single-ended power frequency protection, the action speed is higher, and the sensitivity is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection of electric power systems, and in particular relates to a distance protection method and system for transmission lines based on transient fault characteristics. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] As the proportion of new energy continues to increase, the power grid will shift from being dominated by traditional synchronous machines to being dominated by new energy. In order to compensate for the overall decline in system inertia, strength and short-circuit capacity, some scholars have proposed a grid-type inverter. The grid-type inverter plays an important role in power systems with a high proportion of new energy. When a fault occurs in the transmission line of the grid-type inverter, especially when the voltage at the inverter port drops below the minimum voltage specified by the low voltage crossing, a large transient overcurrent will be generated, affecting the equipment safety of the inverter. Therefore, a quick protection action is required to remove the fault.

[0004] At present, the protection for transmission lines can be divided into protection based on double-ended quantities and protection based on single-ended quantities. Double-ended protection has certain requirements for channels and is more expensive than single-ended protection. In single-ended protection, protection using power frequency quantities is difficult to meet the requirements of action speed, and protection using transient quantities, such as traveling wave information, requires a higher sampling rate, which increases the cost of protection accordingly. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a transmission line distance protection method and system based on transient fault characteristics, which has faster action speed and higher sensitivity than traditional single-ended power frequency protection.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a distance protection method for a transmission line based on transient fault characteristics.

[0008] In one or more embodiments, a method for distance protection of a transmission line based on transient fault characteristics is provided, comprising:

[0009] Obtain the instantaneous value of each phase voltage of the sampling point at one end of the inverter power supply in the grid-forming inverter power supply transmission line and the phase voltage sampling value corresponding to the previous cycle, and obtain the phase voltage difference of each sampling point by subtracting the two;

[0010] When the phase voltage difference of at least three consecutive sampling points is greater than the threshold value for protection startup, the time of the first sampling point among the consecutive sampling points is determined as the time of fault occurrence and the protection startup is controlled;

[0011] After the protection is activated, the fault type is judged according to the instantaneous values of the phase voltages at each sampling point within the set time delay from the fault occurrence moment, and whether the protection operates is controlled according to the fault type;

[0012] Among them, when the judged fault type is a single-phase grounding fault, the protection is controlled not to operate; when the judged fault type is a two-phase short circuit or a three-phase grounding fault, according to the oscillation frequency of the instantaneous voltage values at each sampling point within the set time delay from the fault occurrence moment, combined with the setting value of the protection operation, the protection operation is controlled.

[0013] As an implementation manner of the first aspect of the present invention, the process of judging that the fault type is a single-phase grounding fault is as follows:

[0014] The instantaneous values of the phase voltages at the same sampling point within the set time delay from the fault occurrence moment are added to obtain the cumulative sum u of the phase voltages at each sampling point ∑ ;

[0015] By the formula u ∑ <u0, the number N of sampling points less than the judged zero-sequence voltage threshold u0 among all sampling points p within the set time delay from the fault occurrence moment is determined;

[0016] If the ratio of N to p is greater than N0, it is judged that the fault type is not a single-phase grounding fault, otherwise, it is judged that the fault type is a single-phase grounding fault; N0 is the threshold for judging whether it is a single-phase grounding short circuit.

[0017] As an implementation manner of the first aspect of the present invention, the process of judging that the fault type is a two-phase short circuit or a three-phase grounding fault is as follows:

[0018] When it is judged that the fault type is not a single-phase grounding fault, the instantaneous phase voltage values at the same sampling point within the set time delay from the fault occurrence moment are added pairwise to obtain three two-phase sum voltage values;

[0019] Then, the difference is taken for these three two-phase sum voltage values to obtain the corresponding two-phase sum voltage difference values, and the corresponding variances are calculated for these three two-phase sum voltage difference values;

[0020] If one of the variances is less than the preset threshold, it is judged that the fault type is a two-phase short circuit, otherwise it is judged that the fault type is a three-phase symmetric fault.

[0021] As an implementation manner of the first aspect of the present invention, the setting value of the protection operation is determined by the characteristic equation of the fault additional state of the RLC network between the post-fault network-forming inverter power supply and the farthest protection distance of its outgoing line.

[0022] As an implementation of the first aspect of the present invention, when the oscillation frequency of the instantaneous voltage values of each sampling point within the set time delay from the fault occurrence moment is greater than the setting value of the protection action, it is determined as an in-zone fault and a tripping signal is sent to the circuit breaker on the fault section.

[0023] The second aspect of the present invention provides a transmission line distance protection system based on transient fault characteristics.

[0024] In one or more embodiments, a transmission line distance protection system based on transient fault characteristics includes:

[0025] A phase voltage difference calculation module, which is used to obtain the instantaneous phase voltage values of each phase at the sampling point at one end of the inverter power supply in the transmission line of the grid-forming inverter power supply and the corresponding phase voltage sampling values of the previous cycle, and obtain the phase voltage difference of each sampling point by taking the difference between the two;

[0026] A fault occurrence moment determination module, which is used to determine the moment of the first sampling point among the continuous sampling points as the fault occurrence moment and control the protection to start when the phase voltage difference of at least three continuous sampling points is greater than the threshold value for protection startup;

[0027] A protection action control module, which is used to judge the fault type according to the instantaneous voltage values of each sampling point within the set time delay from the fault occurrence moment after the protection starts, and control whether the protection acts according to the fault type;

[0028] Among them, when it is judged that the fault type is a single-phase ground fault, the protection is controlled not to act; when it is judged that the fault type is a two-phase short circuit between phases or a three-phase ground fault, the protection action is controlled according to the oscillation frequency of the instantaneous voltage values of each sampling point within the set time delay from the fault occurrence moment, in combination with the setting value of the protection action.

[0029] As an implementation of the second aspect of the present invention, in the protection action control module, the process of judging the fault type as a single-phase ground fault is as follows:

[0030] The sum of the instantaneous phase voltage values of each phase at the same sampling point within the set time delay from the fault occurrence moment is added to obtain the cumulative sum u of the phase voltage of each sampling point ∑ ;

[0031] Through the formula u Σ <u0, the number N of sampling points less than the judgment zero-sequence voltage threshold u0 among all sampling points p within the set time delay from the fault occurrence moment is determined;

[0032] If the ratio of N to p is greater than N0, it is judged that the fault type is a non-single-phase ground fault, otherwise, it is judged that the fault type is a single-phase ground fault; N0 is the threshold value for judging whether it is a single-phase ground short circuit.

[0033] As an implementation of the second aspect of the present invention, in the protection action control module, the process of determining whether the fault type is a two-phase short circuit or a three-phase grounding fault is:

[0034] When the fault type is determined to be a non-single-phase grounding fault, the instantaneous values ​​of the phase voltages at the same sampling point within the delay setting time at the time of the fault occurrence are added in pairs to obtain three two-phase sum voltage values;

[0035] Then, the differences of the three two-phase added voltage values ​​are obtained to obtain corresponding two-phase added voltage difference values, and the corresponding variances of the three two-phase added voltage difference values ​​are calculated;

[0036] If one of the variances is smaller than a preset threshold, the fault type is determined to be a two-phase short circuit, otherwise the fault type is determined to be a three-phase symmetrical fault.

[0037] A third aspect of the present invention provides a computer-readable storage medium.

[0038] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps in the above-mentioned method for distance protection of a transmission line based on transient fault characteristics.

[0039] A fourth aspect of the present invention provides an electronic device.

[0040] An electronic device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps in the method for distance protection of a transmission line based on transient fault characteristics as described above are implemented.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] In order to improve the action speed of the protection in the grid-type inverter power grid-connected system transmission line, and take into account the cost consideration, the present invention proposes a distance protection method using the transient fault characteristics of the grid-type inverter power transmission line. According to the changes in the control system of the grid-type inverter power supply with a voltage and current dual-loop control structure at the initial moment of the fault, an equivalent model of the inverter power supply access line is established for the grid-type inverter power transmission line. The transient frequency characteristics of the voltage at the inverter end after the transmission line fails are analyzed through the above model, and a distance protection scheme for the grid-type inverter power transmission line for three-phase symmetrical faults and two-phase short circuits is designed based on the characteristics. The protection scheme has a fast action speed and the required transient information frequency band is lower than the frequency band of the traveling wave. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0044] Figure 1 It is a flow chart of a method for distance protection of a transmission line based on transient fault characteristics according to an embodiment of the present invention;

[0045] Figure 2 It is a transmission line distance protection process based on transient fault characteristics in an embodiment of the present invention;

[0046] Figure 3 A flow chart of a method for determining a fault type according to an embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of an additional state of an equivalent RLC network fault after a fault in an embodiment of the present invention;

[0048] Figure 5 A schematic diagram of a grid-type inverter power supply simulation model according to an embodiment of the present invention;

[0049] Figure 6 A schematic diagram of the structure and fault location of a grid-connected inverter power supply transmission line system provided in an embodiment of the present invention;

[0050] Figure 7 It is a schematic diagram of the structure of a transmission line distance protection system based on transient fault characteristics according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0052] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0053] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0054] Figure 1 1 is a flow chart of a method for distance protection of a transmission line based on transient fault characteristics in an embodiment of the present invention. Figure 1 and Figure 2, the transmission line distance protection method based on transient fault characteristics in this embodiment may include:

[0055] S101, obtaining the instantaneous value of each phase voltage of the sampling point at one end of the inverter power supply in the grid-forming inverter power supply transmission line and the phase voltage sampling value corresponding to the previous cycle, and obtaining the phase voltage difference value of each sampling point by subtracting the two.

[0056] The instantaneous value of each phase voltage at the sampling point at one end of the inverter power supply in the grid-forming inverter power supply transmission line here is the instantaneous voltage value data measured at the protection installation.

[0057]

[0058] Where: Indicates voltage difference, represents the voltage change at the kth sampling moment, represents the instantaneous value of the voltage at the kth sampling moment, and N represents the number of sampling points Δu in one cycle of the voltage.

[0059] S102, when the phase voltage difference of at least three consecutive sampling points is greater than the threshold value for protection startup, determining the time of the first sampling point among the consecutive sampling points as the time of fault occurrence and controlling the protection startup.

[0060] When the phase voltage difference of at least three consecutive sampling points is greater than the threshold value of protection startup, that is, Start to judge the fault type. set Indicates the threshold value for protection activation.

[0061] S103, when the protection is started, the fault type is determined according to the instantaneous value of each phase voltage at each sampling point within the delay setting time (such as 2ms, which can be set according to the actual situation) at the time of the fault occurrence, and the protection is controlled to operate according to the fault type, such as Figure 3 As shown;

[0062] Among them, when the fault type is judged to be a single-phase grounding fault, the control protection does not operate; when the fault type is judged to be a two-phase short circuit or a three-phase grounding fault, the protection action is controlled according to the oscillation frequency of the instantaneous value of the voltage at each sampling point within the delay setting time at the time of the fault occurrence, combined with the setting value of the protection action.

[0063] In step S103, the process of determining whether the fault type is a single-phase grounding fault is as follows:

[0064] Step S10311: Add the instantaneous values ​​of the phase voltages at the same sampling point within the delay setting time according to the fault occurrence time to obtain the phase voltage cumulative sum u of each sampling point ∑ ;u ∑ =u a+u b +u c ; u a , u b , u c are the instantaneous values of the phase A, phase B, and phase C voltages;

[0065] Step S10312: Through the formula u ∑ <u0, determine the number N of sampling points p that are less than the judgment zero-sequence voltage threshold u0 among all sampling points p within the delay setting time from the fault occurrence moment; the threshold u0 can be set according to the value that can avoid acquisition errors;

[0066] Step S10313: If the ratio of N to p is greater than N0, then judge that the fault type is a non-single-phase grounding fault; otherwise, judge that the fault type is a single-phase grounding fault; N0 is the threshold for judging whether it is a single-phase grounding short circuit. N0 can be set according to the error determined at the fault starting moment.

[0067] When a two-phase interphase short circuit occurs, since the fault electromotive force (-U f ) at the fault point is equal in magnitude and opposite in direction in the two fault phases, the transient responses in the two-phase RLC network are also equal in magnitude and opposite in direction. The responses of the two phases are superimposed on the sinusoidal quantity at a frequency of 50 Hz. Since the acquisition time required is very short, adding the responses of the two phases should approximately result in a straight line.

[0068] Among them, the process of judging the fault type as a two-phase interphase short circuit or a three-phase grounding fault is as follows:

[0069] Step S10321: When it is judged that the fault type is a non-single-phase grounding fault, add the instantaneous values of the phase voltages at the same sampling point within the delay setting time from the fault occurrence moment in pairs to obtain three two-phase sum voltages, which are u1, u2, and u3 respectively; that is:

[0070] Step S10322: Then take the difference of these three two-phase sum voltages to obtain the corresponding two-phase sum voltage difference values, and calculate the corresponding variances for these three two-phase sum voltage difference values;

[0071] Among them, the three two-phase sum voltage difference values are Δu1, Δu2, and Δu3 respectively; that is:

[0072]

[0073] Step S10323: If one of the variances is less than the preset threshold, then judge that the fault type is a two-phase interphase short circuit; otherwise, judge that the fault type is a three-phase symmetrical fault. Among them, the size of the preset threshold can be set according to the value that can avoid acquisition errors.

[0074] In step S103, the setting value f of the protection actionset It is determined by the characteristic equation of the fault additional state of the RLC network between the grid-forming inverter power supply and the farthest protection distance of its transmission line after the fault, as follows: Figure 4 shown.

[0075] The calculation process of the setting value of the protection action is:

[0076] Obtain the RLC equivalent circuit of the additional state after the fault, and obtain the characteristic equation of the RLC circuit related to the distance l from the fault point to the protection installation. rel Set to 0.8 to 0.85, and l1 = K rel · Substitute l into the characteristic equation and use the numerical method to calculate the frequency corresponding to the dominant pole as the frequency setting value f set .

[0077] Figure 4 Medium o , R o , C o are the inductance, capacitance and resistance of the filter respectively; L T is the transformer inductance; U1 is the transformer high-voltage side voltage; L1 and C1 are the line inductance and capacitance; A is the fault point, R f is the transition resistance; -U f is the fault electromotive force.

[0078] Since the transition resistance R f The role of the RLC system is to provide damping, which has little effect on the frequency characteristic calculation, so the transition resistance R is ignored. f ,get

[0079]

[0080] Where c0=L1+L o +L T ,

[0081] c1=(L1+L o +L T )C o R o ,

[0082] c2=[L1(L T +L o )(C1 / 2)+L o (L1+L T )C o ],

[0083] c3=L1(L o +L T )C o (C1 / 2)R,

[0084] c4=L1L T L o C o (C1 / 2).

[0085] The line parameter L1=L x l, C1=C x l; L x is the line inductance per unit length, C x is the line capacitance per unit length, and l is the maximum protection distance of the transmission line.

[0086] The maximum protection distance l of the transmission line is determined as follows:

[0087] l=K rel l1,

[0088] l1 represents the total length of the transmission line; in order to ensure that only the fault of the transmission line is reflected, it should be reliable and not act when a fault occurs at the outlet of the lower line. The reliability coefficient K rel Set to 0.8 to 0.85.

[0089] Taking the denominator of formula (1) and setting it to 0, we get

[0090] c4s 4 +c3s 3 +c2s 2 +c1s+c0=0(2)

[0091] By solving equation (2) numerically, the main pole of the real part close to the imaginary axis is obtained as

[0092] x 1,2 =A+j2πf set (3)

[0093] When the oscillation frequency of the instantaneous voltage values ​​of each sampling point within the delay setting time at the time of the fault occurrence is greater than the setting value of the protection action, it is judged as an internal fault and a trip signal is sent to the circuit breaker on the fault section.

[0094] A simulation model of a grid-forming inverter power supply connected to a 35kV medium-voltage distribution network was built on the existing simulation software, and a transmission line distance protection method based on transient fault characteristics of the grid-forming inverter power supply proposed in the embodiment was simulated and verified.

[0095] Model building:

[0096] The grid-connected inverter power supply simulation model is as follows: Figure 5 As shown, the rated capacity of the inverter is 5MW, the inverter filter capacitor is 1000μF, the inverter filter capacitor branch resistance is 0.33Ω, and the inverter filter inductor is 0.1mH.

[0097] The simulation model of grid-type inverter power supply connected to 35kV medium voltage distribution network is as follows Figure 6 As shown, E vsg The representative grid-type inverter power supply has a transformer ratio of 0.69kV / 35kV and a leakage inductance of L T1 The equivalent value to the high voltage side is 0.0039H, the transmission line length l1 is 10km, and the transmission line unit length inductance L x The transmission line capacitance per unit length is 0.0003024H / km. x is 2.98*10 -7 F / km, the transformation ratio of transformer T2 is 110kV / 35kV, the system voltage E is 110kV, the transformation ratio of transformer T3 is 35kV / 10kV, and the fault occurs at 0.508s.

[0098] Simulation analysis:

[0099] In order to verify the feasibility of the transmission line distance protection method based on the transient fault characteristics of the grid-type inverter power supply proposed in this embodiment, faults with different conditions are set at points A, B, and C, and the results are recorded in Tables 1 and 2. Table 1 shows the frequency and protection action of the protection installation measured at different fault types, different fault sections, different fault distances, and different transition resistances using a sampling frequency of 100kHz; Table 2 shows the frequency and protection action of the protection installation measured at a sampling rate of 50kHz using a three-phase symmetrical fault as an example.

[0100] Table 1 Verification of the proposed protection scheme under different conditions

[0101]

[0102] Table 2 Operation at a sampling rate of 50kHz

[0103]

[0104]

[0105] As can be seen from Table 1, the transmission line distance protection method based on the transient fault characteristics of the grid-type inverter power supply proposed in this embodiment can protect 80% of the length of the transmission line according to the transient frequency characteristics within 2ms after the fault, which is greatly improved compared with the traditional protection action speed, meeting the rapidity required for protection; for out-of-zone faults, it can be guaranteed to be reliable and non-action, ensuring the selectivity of the designed protection. As can be seen from Table 2, the protection scheme proposed by reducing the sampling rate of the protection device can also correctly reflect the faults within the protection setting range.

[0106] Figure 7It is a schematic structural diagram of a transmission line distance protection system based on transient fault characteristics in an embodiment of the present invention. This embodiment corresponds to the Figure 1 transmission line distance protection method based on transient fault characteristics, as Figure 7 shown. The transmission line distance protection system based on transient fault characteristics in this embodiment may include:

[0107] A phase voltage difference calculation module 701, which is configured to obtain the instantaneous values of the phase voltages at the sampling points at one end of the inverter power supply in the transmission line of the network-forming inverter power supply and the corresponding phase voltage sampling values in the previous cycle, and obtain the phase voltage differences at each sampling point by taking the difference between the two;

[0108] A fault occurrence time determination module 702, which is configured to determine the time of the first sampling point in the continuous sampling points as the fault occurrence time and control the protection to start when the phase voltage differences at at least three consecutive sampling points are greater than the threshold value for protection startup;

[0109] A protection action control module 703, which is configured to, after the protection is started, determine the fault type based on the instantaneous values of the phase voltages at each sampling point within a set time delay from the fault occurrence time, and control whether the protection acts according to the fault type;

[0110] Among them, when it is determined that the fault type is a single-phase ground fault, the protection is controlled not to act; when it is determined that the fault type is a two-phase short circuit or a three-phase ground fault, the protection is controlled to act according to the oscillation frequency of the instantaneous values of the phase voltages at each sampling point within a set time delay from the fault occurrence time, in combination with the setting value of the protection action.

[0111] Specifically, in the protection action control module 703, the process of determining that the fault type is a single-phase ground fault is as follows:

[0112] The sum of the instantaneous values of the phase voltages at the same sampling point within a set time delay from the fault occurrence time is obtained to obtain the cumulative sum u of the phase voltages at each sampling point ∑ ;

[0113] By the formula u ∑ <u0, the number N of sampling points less than the judgment zero-sequence voltage threshold u0 among all sampling points p within a set time delay from the fault occurrence time is determined;

[0114] If the ratio of N to p is greater than N0, it is determined that the fault type is a non-single-phase ground fault; otherwise, it is determined that the fault type is a single-phase ground fault; N0 is the threshold value for judging whether it is a single-phase ground short circuit.

[0115] In the protection action control module 703, the process of determining that the fault type is a two-phase short circuit or a three-phase ground fault is as follows:

[0116] When the fault type is determined to be a non-single-phase grounding fault, the instantaneous values ​​of the phase voltages at the same sampling point within the delay setting time at the time of the fault occurrence are added in pairs to obtain three two-phase sum voltage values;

[0117] Then, the differences of the three two-phase added voltage values ​​are obtained to obtain corresponding two-phase added voltage difference values, and the corresponding variances of the three two-phase added voltage difference values ​​are calculated;

[0118] If one of the variances is smaller than a preset threshold, the fault type is determined to be a two-phase short circuit, otherwise the fault type is determined to be a three-phase symmetrical fault.

[0119] It should be noted here that Figure 7 The modules in the transmission line distance protection system based on transient fault characteristics are Figure 1 The various steps in the transmission line distance protection method based on transient fault characteristics correspond one to one, and the specific implementation process is the same, which will not be repeated here.

[0120] The method and system for transmission line distance protection based on transient fault characteristics of the present invention have the following advantages:

[0121] (1) By utilizing the transient fault characteristics of the grid-connected inverter power transmission line, the protection has a faster action speed and higher sensitivity than traditional single-ended power frequency protection.

[0122] (2) The transient fault characteristics of the grid-type inverter power transmission line are lower than the frequency band where the characteristic frequency of the traveling wave generated after the fault is located. Therefore, the sampling frequency requirements of the protection device are lower, which can reduce the cost of the protection device.

[0123] (3) The protection scheme proposed in the present invention uses single-ended protection, which has the advantages of no channel requirements compared to the existing double-ended protection, and effectively reduces the construction cost of the protection scheme.

[0124] In one or more embodiments, an electronic device is provided including a central processing unit (CPU), which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) or a program loaded from a storage portion into a random access memory (RAM). In the RAM, various programs and data required for system operation are also stored. The central processing unit, ROM, and RAM are connected to each other via a bus. An input / output (I / O) interface is also connected to the bus.

[0125] The following components are connected to the I / O interface: an input section including a keyboard, a mouse, etc.; an output section including a cathode ray tube (CRT), a liquid crystal display (LCD), etc., and a speaker, etc.; a storage section including a hard disk, etc.; and a communication section including a network interface card such as a local area network (LAN) card, a modem, etc. The communication section performs communication processing via a network such as the Internet. A drive is also connected to the I / O interface as needed. Removable media, such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, etc., are installed on the drive as needed so that a computer program read therefrom is installed into the storage section as needed.

[0126] When the central processing unit in the electronic device of this embodiment executes the program, the following is achieved: Figure 1 The steps in the transmission line distance protection method based on transient fault characteristics are shown.

[0127] In particular, according to an embodiment of the present application, the process described above with reference to the flowchart can be implemented as a computer software program. For example, an embodiment of the present application includes a computer program product, which includes a computer program carried on a computer readable medium, the computer program including a computer program for executing Figure 1 In such an embodiment, the computer program can be downloaded and installed from a network through a communication part, and / or installed from a removable medium. When the computer program is executed by a central processing unit, various functions defined in the device of the present application are executed.

[0128] in, Figure 1 The computer program instructions corresponding to the method shown 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 a product including 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.

[0129] A person skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium, and when the program is executed, it can include the processes of the embodiments of the above-mentioned methods. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc.

[0130] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A transmission line distance protection method based on transient fault characteristics, characterized in that: include: Obtain the instantaneous value of each phase voltage of the sampling point at one end of the inverter power supply in the grid-forming inverter power supply transmission line and the phase voltage sampling value corresponding to the previous cycle, and obtain the phase voltage difference of each sampling point by subtracting the two; When the phase voltage difference of at least three consecutive sampling points is greater than the threshold value for protection startup, the time of the first sampling point among the consecutive sampling points is determined as the time of fault occurrence and the protection startup is controlled; When the protection is started, the fault type is determined based on the instantaneous value of each phase voltage at each sampling point within the delay setting time at the time of the fault occurrence, and the protection is controlled to operate according to the fault type; Among them, when the fault type is judged to be a single-phase grounding fault, the control protection does not operate; when the fault type is judged to be a two-phase short circuit or a three-phase grounding fault, the protection action is controlled according to the oscillation frequency of the instantaneous value of the voltage at each sampling point within the delay setting time at the time of the fault occurrence, combined with the setting value of the protection action.

2. The transmission line distance protection method based on transient fault characteristics according to claim 1, characterized in that: The process of determining whether the fault type is a single-phase grounding fault is as follows: The phase voltage accumulation sum u of each sampling point is obtained by adding the instantaneous values ​​of each phase voltage at the same sampling point within the delay setting time at the time of fault occurrence. ∑ ; Pass-through u ∑ <Determine the number N of sampling points p that are less than the judged zero-sequence voltage threshold u0 among all sampling points p within the delay setting time when a fault occurs; If the ratio of N to p is greater than N0, the fault type is judged to be a non-single-phase grounding fault, otherwise, the fault type is judged to be a single-phase grounding fault; N0 is the threshold value for judging whether it is a single-phase grounding short circuit.

3. The transmission line distance protection method based on transient fault characteristics according to claim 1, characterized in that: The process of judging whether the fault type is a two-phase short circuit or a three-phase grounding fault is as follows: When the fault type is determined to be a non-single-phase grounding fault, the instantaneous values ​​of the phase voltages at the same sampling point within the delay setting time at the time of the fault occurrence are added in pairs to obtain three two-phase sum voltage values; Then, the three two-phase added voltage values ​​are differentiated to obtain corresponding two-phase added voltage difference values, and corresponding variances are calculated for the three two-phase added voltage difference values; If one of the variances is smaller than a preset threshold, the fault type is determined to be a two-phase short circuit, otherwise the fault type is determined to be a three-phase symmetrical fault.

4. The transmission line distance protection method based on transient fault characteristics according to claim 1, characterized in that: The setting value of the protection action is determined by the characteristic equation of the fault additional state of the RLC network between the grid-forming inverter and the farthest protection distance of its transmission line after the fault.

5. The transmission line distance protection method based on transient fault characteristics according to claim 1, characterized in that: When the oscillation frequency of the instantaneous voltage values ​​of each sampling point within the delay setting time at the time of the fault occurrence is greater than the setting value of the protection action, it is judged as an internal fault and a trip signal is sent to the circuit breaker on the fault section.

6. A transmission line distance protection system based on transient fault characteristics, characterized in that: include: The phase voltage difference calculation module is used to obtain the instantaneous value of each phase voltage at the sampling point at one end of the inverter power supply in the grid-forming inverter power supply transmission line and the phase voltage sampling value corresponding to the previous cycle, and obtain the phase voltage difference of each sampling point by subtracting the two; A fault occurrence time determination module, which is used to determine the time of the first sampling point among the continuous sampling points as the fault occurrence time and control the protection start when the phase voltage difference of at least three continuous sampling points is greater than the threshold value of the protection start; The protection action control module is used to determine the fault type according to the instantaneous value of each phase voltage at each sampling point within the delay setting time at the time of the fault occurrence after the protection is started, and to control whether the protection is activated according to the fault type; Among them, when the fault type is judged to be a single-phase grounding fault, the control protection does not operate; when the fault type is judged to be a two-phase short circuit or a three-phase grounding fault, the protection action is controlled according to the oscillation frequency of the instantaneous value of the voltage at each sampling point within the delay setting time at the time of the fault occurrence, combined with the setting value of the protection action.

7. The transmission line distance protection system based on transient fault characteristics according to claim 6, characterized in that: In the protection action control module, the process of determining whether the fault type is a single-phase grounding fault is as follows: The phase voltage accumulation sum u of each sampling point is obtained by adding the instantaneous values ​​of each phase voltage at the same sampling point within the delay setting time at the time of fault occurrence. ∑ ; Pass-through u ∑ <Determine the number N of sampling points p that are less than the judged zero-sequence voltage threshold u0 among all sampling points p within the delay setting time when a fault occurs; If the ratio of N to p is greater than N0, the fault type is judged to be a non-single-phase grounding fault, otherwise, the fault type is judged to be a single-phase grounding fault; N0 is the threshold value for judging whether it is a single-phase grounding short circuit.

8. The transmission line distance protection system based on transient fault characteristics according to claim 6, characterized in that: In the protection action control module, the process of determining whether the fault type is a two-phase short circuit or a three-phase grounding fault is as follows: When the fault type is determined to be a non-single-phase grounding fault, the instantaneous values ​​of the phase voltages at the same sampling point within the delay setting time at the time of the fault occurrence are added in pairs to obtain three two-phase sum voltage values; Then, the three two-phase added voltage values ​​are differentiated to obtain corresponding two-phase added voltage difference values, and corresponding variances are calculated for the three two-phase added voltage difference values; If one of the variances is smaller than a preset threshold, the fault type is determined to be a two-phase short circuit, otherwise the fault type is determined to be a three-phase symmetrical fault.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps in the method for distance protection of a transmission line based on transient fault characteristics as described in any one of claims 1 to 5 are implemented.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps in the method for distance protection of a transmission line based on transient fault characteristics as described in any one of claims 1 to 5 are implemented.

Images