Flexible direct current transmission line protection method and system

Abstract

The invention discloses a flexible direct current transmission line protection method and system, and belongs to the technical field of relay protection. The flexible direct-current transmission line protection method comprises the following steps: after the flexible direct-current transmission line starts protection, detecting and judging the polarity of a first reflected wave of the flexible direct-current transmission line; determining whether a second reflected wave exists within a preset time after protection is started; if the second reflected wave exists, determining the fault type of the flexible DC transmission line according to the polarity of the first reflected wave; and executing a protection action according to the fault type. According to the method, the line fault of the radial multi-terminal flexible direct-current power transmission system can be quickly identified within 1ms, and the method can act sensitively and quickly when an internal fault occurs, and can tolerate 100-ohm transition resistance; the device is reliable and does not act when an external fault occurs.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection, and more specifically, to a flexible direct current transmission line protection method and system based on reflected wave polarity. Background Art

[0002] For flexible DC transmission systems, especially radial multi-terminal flexible DC transmission systems, effective fault current limiting capability at the moment of fault occurrence can limit the development speed of DC faults, thereby reducing the requirements for fault current interruption speed, and reliably protecting the flexible DC system by avoiding or reducing the damage to the DC system from fault impact. After a DC fault occurs, the configuration of a suitable current limiting device can limit the DC fault current with a large amplitude and rise rate and keep it within the acceptable range of the system, thereby reducing the requirements for the current interruption capability such as the breaking capacity and fault removal time of the DC circuit breaker.

[0003] The installation location of the current limiting device has become the focus of discussion. In general, although adding boundary elements is conducive to the design of protection schemes, the cost will increase. The reactors at both ends of the line limit the rate of rise of fault current while also prolonging the time of fault removal, which has a negative impact on the dynamic performance and safety performance of the DC system. Therefore, from the perspective of improving the dynamic performance and economy of the system, the solution of installing the reactor at the outlet of the converter station is more advantageous.

[0004] However, when the reactor is installed at the converter station exit, the DC line loses its clear boundary, which makes fault identification more difficult and significantly reduces the selectivity and reliability of protection based on boundary characteristics. In addition, when the reactor is installed at the converter station exit, there will be almost no obstacles for the line fault to propagate through the converter exits to other fault-free parts of the system, which will accelerate the propagation of the fault and aggravate the consequences. Summary of the invention

[0005] In view of the above problems, the present invention proposes a flexible DC transmission line protection method, comprising:

[0006] After the protection of the flexible DC transmission line is started, detecting and determining the polarity of the first reflected wave of the flexible DC transmission line;

[0007] Determine whether there is a second reflected wave within a preset time after the protection is activated;

[0008] If there is a second reflected wave, determining the fault type of the flexible DC transmission line according to the polarity of the first reflected wave;

[0009] Execute protection actions according to the fault type;

[0010] The first reflected wave is the first reflected wave received at the current moment after the protection of the flexible DC transmission line is started, and the second reflected wave is the second reflected wave received by the flexible DC transmission line at the next moment after the current moment, and the next moment is within the preset time.

[0011] Optionally, a standardized reflected wave detection function for detecting reflected waves of a flexible DC transmission line is as follows:

[0012]

[0013] in:

[0014]

[0015] Among them, D norm (t) is the standardized reflection wave detection function at time t, D norm (t-1) is the standardized reflection wave detection function at time t-1, t s To protect the startup time, is the starting time of the reflected wave;

[0016] If D is calculated based on the standardized reflection wave detection function norm (t) = -1, then the polarity of the first reflected wave is determined to be positive. If D is calculated according to the standardized reflected wave detection function norm (t) = 1, then the polarity of the first reflected wave is determined to be negative.

[0017] Optional, the preset time is 2ms.

[0018] Optionally, if the polarity of the first reflected wave is negative, the numerical relationship between the arrival time of the reflected wave and the fixed value is calculated. If the arrival time is less than the fixed value, the fault type of the flexible DC transmission line is determined to be an intra-area fault, and the protection action is initiated; otherwise, the fault type is determined to be a fuzzy fault.

[0019] Optionally, if it is determined to be a fuzzy fault, the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

[0020] Optional, fixed value setting, including:

[0021] The value of twice the line length divided by the traveling wave speed is set as the constant.

[0022] Optionally, if the polarity of the first reflected wave is negative, it is determined to be a fuzzy fault, and the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

[0023] On the other hand, the present invention also provides a flexible DC transmission line protection system, comprising:

[0024] A detection unit, configured to detect and determine the polarity of a first reflected wave of the flexible DC transmission line after the protection of the flexible DC transmission line is started, and determine whether a second reflected wave exists within a preset time after the protection is started;

[0025] A judging unit, configured to judge the fault type of the flexible DC transmission line according to the polarity of the first reflected wave after the second reflected wave exists;

[0026] A protection unit is used to perform protection actions according to the fault type;

[0027] The first reflected wave is the first reflected wave received at the current moment after the protection of the flexible DC transmission line is started, and the second reflected wave is the second reflected wave received by the flexible DC transmission line at the next moment after the current moment, and the next moment is within the preset time.

[0028] Optionally, a standardized reflected wave detection function for detecting reflected waves of a flexible DC transmission line is as follows:

[0029]

[0030] in:

[0031]

[0032]

[0033] Among them, D norm (t) is the standardized reflection wave detection function at time t, D norm (t-1) is the standardized reflection wave detection function at time t-1, t s To protect the startup time, is the starting time of the reflected wave;

[0034] If D is calculated based on the standardized reflection wave detection function norm (t) = -1, then the polarity of the first reflected wave is determined to be positive. If D is calculated according to the standardized reflected wave detection function norm (t) = 1, then the polarity of the first reflected wave is determined to be negative.

[0035] Optional, the preset time is 2ms.

[0036] Optionally, if the polarity of the first reflected wave is negative, the numerical relationship between the arrival time of the reflected wave and the fixed value is calculated. If the arrival time is less than the fixed value, the fault type of the flexible DC transmission line is determined to be an intra-area fault, and the protection action is initiated; otherwise, the fault type is determined to be a fuzzy fault.

[0037] Optionally, if it is determined to be a fuzzy fault, the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

[0038] Optional, fixed value setting, including:

[0039] The value of twice the line length divided by the traveling wave speed is set as the constant.

[0040] Optionally, if the polarity of the first reflected wave is negative, it is determined to be a fuzzy fault, and the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

[0041] In yet another aspect, the present invention further provides a computing device, comprising: one or more processors;

[0042] a processor for executing one or more programs;

[0043] When the one or more programs are executed by the one or more processors, the above-described method is implemented.

[0044] In yet another aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed, the method described above is implemented.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The present invention provides a flexible direct current transmission line protection method, comprising: after the flexible direct current transmission line starts protection, detecting and judging the polarity of the first reflected wave of the flexible direct current transmission line; determining whether there is a second reflected wave within a preset time after the protection is started; if there is a second reflected wave, determining the fault type of the flexible direct current transmission line according to the polarity of the first reflected wave; and executing a protection action according to the fault type. The present invention can determine the fault type of the flexible direct current transmission line by determining the polarity of the reflected wave and whether there is a second reflected wave, and can effectively execute a protection action according to the fault type, with high efficiency and high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a flow chart of the method of the present invention;

[0048] Figure 2 A protection logic block diagram of an embodiment of the method of the present invention;

[0049] Figure 3 A topological diagram of a radial multi-terminal flexible direct current transmission system according to an embodiment of the method of the present invention;

[0050] Figure 4This is a diagram showing the result of the reflected wave arrival and polarity detection criteria in the scenario of metallic fault at the terminal within the area according to the method embodiment of the present invention;

[0051] Figure 5 This is a result diagram of the auxiliary criterion for judging the current direction in the scenario of metallic fault at the terminal within the zone according to the embodiment of the method of the present invention;

[0052] Figure 6 It is a diagram showing the result of the lower reflected wave arrival and polarity detection criteria determination in the embodiment of the method of the present invention;

[0053] Figure 7 This is a diagram showing the result of the auxiliary criterion for judging the current direction in a high-resistance fault scenario within the area according to an embodiment of the method of the present invention;

[0054] Figure 8 This is a diagram showing the result of the reflected wave arrival and polarity detection criteria determination in an out-of-zone fault scenario of an embodiment of the method of the present invention;

[0055] Fig. 9 This is a diagram showing the result of the auxiliary criterion for judging the current direction in an out-of-zone fault scenario according to an embodiment of the method of the present invention;

[0056] Fig.10 This is a diagram showing the result of the reflected wave arrival and polarity detection criterion determination in a DC bus fault scenario of an embodiment of the method of the present invention;

[0057] Fig.11 This is a diagram showing the result of the auxiliary criterion for current direction determination in a DC bus fault scenario according to an embodiment of the method of the present invention;

[0058] Fig.12 This is a diagram showing the result of the reflected wave arrival and polarity detection criteria in a converter outlet fault scenario according to an embodiment of the method of the present invention;

[0059] Fig.13 This is a diagram showing the result of the auxiliary criterion for judging the current direction in a converter outlet fault scenario according to an embodiment of the method of the present invention;

[0060] Fig.14 This is a diagram showing the result of the reflected wave arrival and polarity detection criterion determination in the current limiting reactance back-side fault scenario of the method embodiment of the present invention;

[0061] Fig.15 This is a diagram showing the result of the auxiliary criterion for judging the current direction in a back-side fault scenario of a current-limiting reactance according to an embodiment of the method of the present invention;

[0062] Fig.16 4 is a system structure diagram of the method of the present invention. DETAILED DESCRIPTION

[0063] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0064] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0065] Embodiment 1:

[0066] The present invention proposes a flexible DC transmission line protection method, such as Figure 1 As shown, including:

[0067] After the protection of the flexible DC transmission line is started, detecting and determining the polarity of the first reflected wave of the flexible DC transmission line;

[0068] Determine whether there is a second reflected wave within a preset time after the protection is activated;

[0069] If there is a second reflected wave, determining the fault type of the flexible DC transmission line according to the polarity of the first reflected wave;

[0070] Execute protection actions according to the fault type;

[0071] The first reflected wave is the first reflected wave received at the current moment after the protection of the flexible DC transmission line is started, and the second reflected wave is the second reflected wave received by the flexible DC transmission line at the next moment after the current moment, and the next moment is within the preset time.

[0072] Among them, the standardized reflected wave detection function for detecting the reflected wave of the flexible DC transmission line is as follows:

[0073]

[0074] in:

[0075]

[0076] Among them, D norm (t) is the standardized reflection wave detection function at time t, D norm (t-1) is the standardized reflection wave detection function at time t-1, ts To protect the startup time, is the starting time of the reflected wave;

[0077] If D is calculated based on the standardized reflection wave detection function norm (t) = -1, then the polarity of the first reflected wave is determined to be positive. If D is calculated according to the standardized reflected wave detection function norm (t) = 1, then the polarity of the first reflected wave is determined to be negative.

[0078] Among them, the preset time is 2ms.

[0079] Among them, if the polarity of the first reflected wave is negative, the numerical relationship between the arrival time of the reflected wave and the fixed value is calculated. If the arrival time is less than the fixed value, the fault type of the flexible DC transmission line is determined to be an intra-area fault, and the protection action is started; otherwise, the fault type is determined to be a fuzzy fault.

[0080] Among them, if it is determined to be a fuzzy fault, the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

[0081] The setting of fixed values ​​includes:

[0082] The value of twice the line length divided by the traveling wave speed is set as the constant.

[0083] Among them, if the polarity of the first reflected wave is negative, it is judged as a fuzzy fault, and the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

[0084] The present invention will be further described below in conjunction with embodiments:

[0085] First, the definition of reflected wave polarity and auxiliary criteria for current direction are explained;

[0086] (1) Reflection wave identification method and polarity definition method;

[0087] Define the instantaneous value of the protection voltage measured on this side as u P (t),u N (t). Calculate the line mode component of the protection measurement on this side according to formula (1):

[0088] u1(t)=[u P (t)-u N (t)] / 2 (1)

[0089] According to formula (2), the differential value of the line mode voltage is obtained:

[0090] du1(t)=u1(t)-u1(t-1) (2)

[0091] According to formula (3), the differential value of the standardized line mode voltage is obtained:

[0092]

[0093] Among them, t s To protect the startup time. According to formula (4), the second-order difference value of the line mode voltage is obtained:

[0094] d 2 u1(t)=du1(t)-du1(t-1) (4)

[0095] The reflection wave detection function is defined according to formula (5):

[0096]

[0097] The standardized reflection wave detection function is defined according to formula (6):

[0098]

[0099] Formula (6) cannot be applied directly, and the standardized reflection wave detection function needs to be modified. For each sampling point, if the following mathematical relationship exists at time t:

[0100]

[0101] Then define the current time as the starting time t1 of the reflected wave aux . If the following mathematical relationship exists at time t:

[0102]

[0103] The previous sampling point of the current moment is defined as the end time of the reflected wave t2 aux For (t1 aux , t2 aux ) The normalized reflection detection function within the time window assumes that there is only one reflection wave.

[0104] The values ​​of the standardized reflected wave detection functions of equations (6) to (8) are used as the basis for judgment to analyze whether the reflected wave arrives and the polarity of the arriving reflected wave. s +1, for each subsequent sampling point, determine whether the function satisfies D norm (t)≠0, the first sampling point that meets this condition is defined as the time when the first reflected wave arrives t f1 ; From sampling point t f1 +1, for each subsequent sampling point, determine whether the function satisfies D norm (t)≠0, the first sampling point that meets this condition is defined as the arrival time of the second reflected wave t f2 .

[0105] For the first reflected wave to arrive at time t f1 , judge D norm (t f1 ) polarity. If D norm (t) = -1, which means that the polarity of the reflected wave at time t is positive; if D norm (t) = 1, indicating that the polarity of the reflected wave at time t is negative.

[0106] (2) Auxiliary criteria for current direction are as follows:

[0107] Define the line mode current on this side as i L , the opposite line mode current is i O For the line mode current, the line mode current transient quantity can be calculated according to formula (9):

[0108] Δi=i(t)-i(t s / 2) (9)

[0109] From the above formula, we can get the transient value of the line mode current Δi on this side: L , and the transient state of the opposite line mode current Δi O According to formula (10), the transient integral value of line mode current is obtained:

[0110]

[0111] Note that the unit of time in equation (10) is milliseconds (ms).

[0112] After the protection is started, the formula (10) is calculated for each sampling point immediately, and the calculation result is transmitted to the opposite line protection device without synchronization. At any sampling point after the protection is started, the Δi at the current sampling point t can be directly calculated. L At the same time, after the line delay, the Δi calculated by the protection device on the opposite side can be received. O .

[0113] (3) The protection principle action process is as follows:

[0114] The protection principle of the present invention uses the polarity of the reflected wave to identify the fault and relies on the auxiliary criterion of the current direction to ensure selectivity. Its design is based on four main ideas:

[0115] 1) In the case of an internal fault, except for the scenario where the fault occurs on the DC bus, the polarity of the first reflected wave is negative, and the arrival time is less than the set value; in the case of an external fault, the polarity of the first reflected wave is positive, and the arrival time is greater than or equal to the set value.

[0116] 2) The reflected wave changes the amplitude and steepness of the waveform, and the characteristics of the reflected wave in the time domain can be abstracted into the direction and acceleration of the fluctuation. When the fluctuation speed of the transient time-domain measured electrical quantity is large and the acceleration is also large, it is judged that a reflected wave has reached the protection installation on this side.

[0117] 3) If the polarity of the first reflected wave is negative and the arrival time is greater than or equal to the fixed value, it cannot be immediately determined whether the fault is inside or outside the zone. Enable the current direction auxiliary criterion.

[0118] 4) Auxiliary current direction judgment criteria can further determine the fault location and open the protection action as appropriate.

[0119] Its protection action process, such as Figure 2 As shown, including the following:

[0120] 1) Protection starts.

[0121] 2) Detect and determine the polarity of the first reflected wave according to equations (1) to (8) to determine whether there is a second reflected wave. If the polarity of the first reflected wave is negative and there is a second reflected wave within 2ms after the protection is started, proceed to step 3); otherwise, proceed to step 4).

[0122] 3) Detect that the polarity of the first reflected wave is negative. Calculate the numerical relationship between the arrival time of the reflected wave and the fixed value. If the arrival time is less than the fixed value, it is determined that an internal fault has occurred and the protection is activated; otherwise, it is determined to be a fuzzy fault and enter step 5). The setting of the fixed value here is set by dividing the length of the line by twice the speed of the traveling wave.

[0123] 4) Detect that the polarity of the first reflected wave is positive. Determine that it is an out-of-zone or fuzzy fault and go to step 5).

[0124] 5) For out-of-zone or fuzzy fault scenarios, the current direction auxiliary judgment criteria of equations (9) to (10) are used to further determine the fault location. If the auxiliary judgment determines that the fault location is an in-zone fault, the exit is allowed; otherwise, the protection is locked.

[0125] For the protection of any side of the line, when f ∑ When (t)>0, the fault is considered to be in the positive direction of the protection on this side; at the same time, the integral value f' of the asynchronous current transient quantity transmitted to the opposite side ∑ (t), when f' ∑ When (t)>0, the fault is considered to be in the positive direction of the opposite protection. ∑ (t)>0, f' ∑ When (t)>0 is established at the same time, the protection action on this side is allowed.

[0126] 6) End.

[0127] PSCAD is used to carry out simulation verification of various fault scenarios in the area. For the convenience of description, the following are given: Figure 3 The five-terminal flexible DC transmission system shown in the figure is used as the analysis model. The M-side protection of the DC line l 1 is taken as the local side protection, and this is used as the best embodiment for analysis. The main parameters of the system are shown in Table 1 below:

[0128] Table 1

[0129]

[0130] (1) In-area terminal metallic fault scenario:

[0131] A positive metallic grounding fault occurred on the simulated line at a distance of 52.3165 km from the M side, i.e., at 95% of the line length.

[0132] The results are as follows Figure 4 and 5 As shown, if the protection start time is 0, the arrival time of the first reflected wave is 0.05ms, and the arrival time of the second reflected wave is 0.25ms; the polarity of the first reflected wave is negative, and the polarity of the second reflected wave is positive. The protection does not need the amplitude information of the N-side current sampling value, and directly trips at 0.25ms.

[0133] (2) In-area high-resistance fault scenario:

[0134] A positive pole grounding fault through a 100 ohm transition resistor occurs on the simulated line at 90% of the line length from the M side.

[0135] The results are as follows Figure 6 and 7 As shown, if the protection start time is 0, the arrival time of the first reflected wave is 0.1ms, and the arrival time of the second reflected wave is 0.3499ms; the polarity of the first reflected wave is negative, and the polarity of the second reflected wave is positive. The protection does not need the amplitude information of the N-side current sampling value, and directly trips at 0.3499ms.

[0136] (2) Out-of-area fault scenario:

[0137] A positive pole grounding fault occurs at the midpoint of simulated line 1 2 through a 17.5 ohm transition resistor.

[0138] The results are as follows Figure 8 and 9 As shown, it can be seen that the arrival time of the first reflected wave is 0.15ms, and the arrival time of the second reflected wave is 0.25ms; the polarity of the first reflected wave is positive, and the polarity of the second reflected wave is negative. The protection will identify the current working condition as an out-of-zone fault and successfully lock it.

[0139] It can be seen from the current direction criterion that the auxiliary criterion can also lock the protection, thereby enhancing the reliability of the present invention.

[0140] (3) DC bus fault scenario:

[0141] A metallic ground fault occurs at the DC busbar on the N side. The fault is located on the back side of the CVT. This fault is an out-of-zone fault.

[0142] The results are as follows Fig.10 and 11 As shown, it can be seen that the arrival time of the first reflected wave is 0.7499ms, and the arrival time of the second reflected wave is 0.7999ms; the polarity of the first reflected wave is positive, and the polarity of the second reflected wave is negative. However, since the arrival time of the first reverse wave is very close to the fixed value of 0.7462ms, the protection will judge the current working condition as a fuzzy fault and call the auxiliary judgment criterion of current direction.

[0143] Since the fault is located on the back side of the N-side protection, the M-side protection device quickly receives the auxiliary criterion calculation value of the N-side, and successfully determines the fault as an out-of-zone fault, thereby correctly locking it.

[0144] (4) Converter outlet failure scenario:

[0145] The current-limiting reactor connected to the simulation station 2 has a positive metallic grounding fault on the line side.

[0146] The results are as follows Fig.12 and 13 As shown, it can be seen that the arrival time of the first reflected wave is 0.05ms, and the arrival time of the second reflected wave is 0.25ms; the polarity of the first reflected wave is positive, and the polarity of the second reflected wave is positive. The protection does not need the N-side current signal, and directly determines the working condition as an out-of-zone fault, and the protection is correctly locked.

[0147] (5) Current-limiting reactance back-side fault scenario:

[0148] The current-limiting reactor connected to the simulation station 2 has a positive metallic grounding fault on the converter side.

[0149] The results are as follows Fig.14 and 15 As shown, it can be seen that the arrival time of the first reflected wave is 0.9998ms, and the arrival time of the second reflected wave is 2.2996ms; the polarity of the first reflected wave is positive, and the polarity of the second reflected wave is positive. The protection does not need the N-side current signal, and directly determines the working condition as an out-of-zone fault, and the protection is correctly locked.

[0150] Embodiment 2:

[0151] The present invention also proposes a flexible DC transmission line protection system 200, such as Fig.16As shown, including:

[0152] The detection unit 201 is used to detect and determine the polarity of the first reflected wave of the flexible DC transmission line after the protection of the flexible DC transmission line is started, and determine whether there is a second reflected wave within a preset time after the protection is started;

[0153] A judging unit 202, configured to judge the fault type of the flexible DC transmission line according to the polarity of the first reflected wave after the second reflected wave exists;

[0154] The protection unit 203 is used to perform protection actions according to the fault type;

[0155] The first reflected wave is the first reflected wave received at the current moment after the protection of the flexible DC transmission line is started, and the second reflected wave is the second reflected wave received by the flexible DC transmission line at the next moment after the current moment, and the next moment is within the preset time.

[0156] Among them, the standardized reflected wave detection function for detecting the reflected wave of the flexible DC transmission line is as follows:

[0157]

[0158] in:

[0159]

[0160] Among them, D norm (t) is the standardized reflection wave detection function at time t, D norm (t-1) is the standardized reflection wave detection function at time t-1, t s To protect the startup time, is the starting time of the reflected wave;

[0161] If D is calculated based on the standardized reflection wave detection function norm (t) = -1, then the polarity of the first reflected wave is determined to be positive. If D is calculated according to the standardized reflected wave detection function norm (t) = 1, then the polarity of the first reflected wave is determined to be negative.

[0162] Among them, the preset time is 2ms.

[0163] Among them, if the polarity of the first reflected wave is negative, the numerical relationship between the arrival time of the reflected wave and the fixed value is calculated. If the arrival time is less than the fixed value, the fault type of the flexible DC transmission line is determined to be an intra-area fault, and the protection action is started; otherwise, the fault type is determined to be a fuzzy fault.

[0164] Among them, if it is determined to be a fuzzy fault, the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

[0165] The setting of fixed values ​​includes:

[0166] The value of twice the line length divided by the traveling wave speed is set as the constant.

[0167] Among them, if the polarity of the first reflected wave is negative, it is judged as a fuzzy fault, and the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

[0168] The present invention can realize rapid identification of radial multi-terminal flexible direct current transmission system line faults within 1ms, can sensitively and quickly act in the event of an in-zone fault, and can tolerate a 100Ω transition resistance; and can reliably not act in the event of an out-of-zone fault.

[0169] Embodiment 3:

[0170] Based on the same inventive concept, the present invention also provides a computer device, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding functions, so as to implement the steps of the method in the above embodiment.

[0171] Embodiment 4:

[0172] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both a built-in storage medium in a computer device and an extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the method in the above embodiment.

[0173] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take 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.) containing computer-usable program codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0174] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks 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 produce 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.

[0175] 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.

[0176] 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 The steps for the functions specified in one or more boxes.

[0177] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0178] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A flexible DC transmission line protection method, characterized in that: include: After the protection of the flexible DC transmission line is started, detecting and determining the polarity of the first reflected wave of the flexible DC transmission line; Determine whether there is a second reflected wave within a preset time after the protection is activated; If there is a second reflected wave, determining the fault type of the flexible DC transmission line according to the polarity of the first reflected wave; Execute protection actions according to the fault type; The first reflected wave is the first reflected wave received at the current moment after the protection of the flexible DC transmission line is started, and the second reflected wave is the second reflected wave received by the flexible DC transmission line at the next moment after the current moment, and the next moment is within the preset time.

2. The flexible DC transmission line protection method according to claim 1, characterized in that: The standardized reflected wave detection function for detecting reflected waves of flexible DC transmission lines is as follows: in: Among them, D norm (t) is the standardized reflection wave detection function at time t, D norm (t-1) is the standardized reflection wave detection function at time t-1, t s To protect the startup time, is the starting time of the reflected wave; If D is calculated based on the standardized reflection wave detection function norm (t) = -1, then the polarity of the first reflected wave is determined to be positive. If D is calculated according to the standardized reflected wave detection function norm (t) = 1, then the polarity of the first reflected wave is determined to be negative.

3. The flexible DC transmission line protection method according to claim 1, characterized in that: The preset time is 2ms.

4. The flexible DC transmission line protection method according to claim 1, characterized in that: If the polarity of the first reflected wave is negative, the numerical relationship between the arrival time of the reflected wave and the fixed value is calculated. If the arrival time is less than the fixed value, the fault type of the flexible DC transmission line is determined to be an intra-area fault, and the protection action is initiated; otherwise, the fault type is determined to be a fuzzy fault.

5. The flexible DC transmission line protection method according to claim 4, characterized in that: If it is determined to be a fuzzy fault, the fault location is determined through the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

6. The flexible DC transmission line protection method according to claim 4, characterized in that: Setting of fixed values ​​includes: The value of twice the line length divided by the traveling wave speed is set as the constant.

7. The flexible DC transmission line protection method according to claim 1, characterized in that: If the polarity of the first reflected wave is negative, it is judged as a fuzzy fault, and the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

8. A flexible DC transmission line protection system, characterized in that: include: A detection unit, configured to detect and determine the polarity of a first reflected wave of the flexible DC transmission line after the protection of the flexible DC transmission line is started, and determine whether a second reflected wave exists within a preset time after the protection is started; A judging unit, configured to judge the fault type of the flexible DC transmission line according to the polarity of the first reflected wave after the second reflected wave exists; A protection unit is used to perform protection actions according to the fault type; The first reflected wave is the first reflected wave received at the current moment after the protection of the flexible DC transmission line is started, and the second reflected wave is the second reflected wave received by the flexible DC transmission line at the next moment after the current moment, and the next moment is within the preset time.

9. The flexible DC transmission line protection system according to claim 8, characterized in that: The standardized reflected wave detection function for detecting reflected waves of flexible DC transmission lines is as follows: in: Among them, D norm (t) is the standardized reflection wave detection function at time t, D norm (t-1) is the standardized reflection wave detection function at time t-1, t s To protect the startup time, is the starting time of the reflected wave; If D is calculated based on the standardized reflection wave detection function norm (t) = -1, then the polarity of the first reflected wave is determined to be positive. If D is calculated according to the standardized reflected wave detection function norm (t) = 1, then the polarity of the first reflected wave is determined to be negative.

10. The flexible DC transmission line protection system according to claim 8, characterized in that: The preset time is 2ms.

11. The flexible DC transmission line protection system according to claim 8, characterized in that: If the polarity of the first reflected wave is negative, the numerical relationship between the arrival time of the reflected wave and the fixed value is calculated. If the arrival time is less than the fixed value, the fault type of the flexible DC transmission line is determined to be an intra-area fault, and the protection action is initiated; otherwise, the fault type is determined to be a fuzzy fault.

12. The flexible DC transmission line protection system according to claim 11, characterized in that: If it is determined to be a fuzzy fault, the fault location is determined through the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

13. The flexible DC transmission line protection system according to claim 11, characterized in that: Setting of fixed values ​​includes: The value of twice the line length divided by the traveling wave speed is set as the constant.

14. The flexible DC transmission line protection system according to claim 8, characterized in that: If the polarity of the first reflected wave is negative, it is judged as a fuzzy fault, and the fault location is determined by the auxiliary criterion of current direction. If the fault location is within the zone, exit is allowed, otherwise the protection is locked.

15. A computer device, characterized in that: include: one or more processors; a processor for executing one or more programs; When the one or more programs are executed by the one or more processors, the method according to any one of claims 1 to 7 is implemented.

16. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed, the method according to any one of claims 1 to 7 is implemented.

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