New energy station power transmission line protection method based on accumulated difference coefficient and related device

Abstract

The application discloses a new energy station power transmission line protection method based on accumulated difference coefficient and related device. The method comprises the following steps: obtaining discrete current sampling values by sampling the current of the power transmission line; detecting the current extreme values on both sides within a period; calculating the differential current and the braking current at each time; calculating the discriminant factor and its window average value based on the two; counting the proportion of the window average value exceeding the threshold value; dynamically updating the braking current according to the proportion; calculating the action quantity IADI based on the size relationship between the differential current and the updated braking current, and sending a trip signal if the action quantity IADI is greater than the action threshold value. The device comprises a current sampling module, an extreme value detection module, a differential current and braking current calculation module, a discriminant factor calculation module, a proportion counting module, a braking current updating module and a fault judgment module. The application is suitable for the fault characteristics of the new energy station, has strong anti-interference ability, is fast and accurate in action, has low requirements on the sampling frequency, and can significantly improve the reliability of the line protection.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and specifically to an improved cumulative difference coefficient protection method and related device based on time-domain current sequence, applicable to transmission lines connecting new energy power plants. Background Technology

[0002] In recent years, the installed capacity of inverter-interfaced renewable energy sources (IIRESs), represented by direct-drive wind farms and photovoltaic power plants, has grown rapidly. After IIRESs are connected to the grid via converters, their fault current characteristics differ significantly from those of traditional synchronous generators: the fault current amplitude is limited and the phase is controlled, leading to performance degradation and even maloperation of traditional protection schemes (such as distance protection and differential current protection). Existing frequency domain methods (such as transient analysis based on Fourier transform) have strong noise immunity but are easily affected by attenuated DC components; time domain methods (such as protection based on waveform similarity or geometric distance) have low computational burden but are easily affected by non-ideal conditions such as CT saturation and synchronization errors. Therefore, a new protection principle that can adapt to the fault characteristics of IIRESs and has good robustness to non-ideal conditions is urgently needed. Summary of the Invention

[0003] To address the shortcomings of the existing technologies, this invention provides a method and related devices for protecting transmission lines at new energy power stations based on the cumulative difference coefficient, solving the problem of performance degradation after IIRESs are connected. This method, based on the cumulative difference coefficient of the time-domain current sequence, achieves sensitive, reliable, and rapid fault identification by dynamically adjusting the braking current.

[0004] The protection method for transmission lines of new energy power plants based on cumulative difference coefficients includes the following steps:

[0005] Step 1: Sample the current at the installation point of the transmission line protection to obtain discrete current sample values ​​at each moment;

[0006] Step 2: Based on the discrete current sampling values ​​obtained in Step 1, detect the extreme values ​​of the current on both sides within one cycle to obtain the extreme values ​​of the current amplitude on both sides.

[0007] Step 3: Based on the discrete current sampling values ​​from Step 1 and the extreme amplitude values ​​of the currents on both sides detected in Step 2, calculate the differential current i at each moment. op (k) and braking current i res (k);

[0008] Step 4: Based on the dynamic current i calculated in Step 3 op (k) and braking current i res(k), calculate the discriminant factor σ(k) and its window average at each time point. ;

[0009] Step 5: Calculate the window average obtained in Step 4. The proportion σ exceeding the set threshold p ;

[0010] Step Six: Based on the proportion σ calculated in Step Five. p The braking current i obtained in step three res (k) Perform dynamic updates to obtain the updated braking current i res2 (k);

[0011] Step 7: Based on the differential current i from Step 3 op (k) and the updated braking current i after step six res2 (k) The magnitude of the action quantity IADI is calculated. If the action quantity IADI is greater than the preset action threshold value, it is determined to be an internal fault and a trip signal is sent. Otherwise, it is determined to be an external fault and no trip signal is sent.

[0012] Furthermore, the discriminant factor σ(k) value and its window average value mentioned in step four. The calculation formulas are as follows:

[0013] (1);

[0014] (2);

[0015] Where n is the number of sampling points within the window length.

[0016] Furthermore, the updated braking current i in step six res2 (k) The calculation formula is shown in equation (3):

[0017] (3).

[0018] Furthermore, the formula for calculating the motion quantity IADI in step seven is shown in equation (4):

[0019] (4).

[0020] Protection devices for transmission lines at new energy power plants based on cumulative difference coefficients include:

[0021] The current sampling module is used to sample the current at the installation point of the transmission line protection to obtain discrete current sampling values ​​at various times.

[0022] The extreme value detection module is used to detect the extreme values ​​of the current on both sides within a cycle based on the discrete current sampling values ​​obtained by the current sampling module, and to obtain the extreme values ​​of the amplitude of the current on both sides.

[0023] The differential current and braking current calculation module is used to calculate the differential current i at each moment based on the discrete current sampling values ​​and the extreme values ​​of the current amplitudes on both sides. op (k) and braking current i res (k);

[0024] The discriminant factor calculation module is used to calculate the discriminant factor based on the dynamic current i. op (k) and braking current i res (k), calculate the discriminant factor σ(k) and its window average at each time point. ;

[0025] The proportional statistics module is used to calculate the window average obtained in step four. The proportion σ exceeding the set threshold p ;

[0026] The braking current update module is used to update the braking current based on the statistical ratio σ. p For braking current i res (k) Perform dynamic updates to obtain the updated braking current i res2 (k);

[0027] The fault diagnosis module is used to determine the fault based on the differential current i. op (k) and the updated braking current i res2 (k) The magnitude of the action quantity IADI is calculated. If the action quantity IADI is greater than the preset action threshold value, it is determined to be an internal fault and a trip signal is sent. Otherwise, it is determined to be an external fault and no trip signal is sent.

[0028] Furthermore, the discriminant factor σ(k) value and its window average value... The calculation formulas are as follows:

[0029] (1);

[0030] (2);

[0031] Where n is the number of sampling points within the window length.

[0032] Furthermore, the updated braking current i res2 (k) The calculation formula is shown in equation (3):

[0033] (3).

[0034] Furthermore, the formula for calculating the motion quantity IADI is shown in equation (4):

[0035] (4).

[0036] A protection system for transmission lines of new energy power plants based on cumulative difference coefficients, comprising: a computer-readable storage medium and a processor;

[0037] The computer-readable storage medium is used to store executable instructions;

[0038] The processor is used to read executable instructions stored in the computer-readable storage medium and execute the new energy power station transmission line protection method based on the cumulative difference coefficient.

[0039] A non-transitory computer-readable storage medium storing a computer program that, when executed by a processor, implements the aforementioned method for protecting transmission lines of new energy power stations based on cumulative difference coefficients.

[0040] The advantages of this invention over the prior art are:

[0041] It utilizes time-domain current sequence direct calculation, avoiding phasor calculation, and adapts to the complex fault characteristics of IIRESs; through adaptive braking current design, it can effectively cope with the negative impacts of current transformer saturation, synchronization error, measurement error, abnormal data and noise; the action time is only 3-5ms, and it is suitable for various fault types, high transition resistance and different system configurations and sampling frequencies. Attached Figure Description

[0042] Figure 1 This is a flowchart of a new energy power station transmission line protection method based on cumulative difference coefficient, according to an embodiment of the present invention.

[0043] Figure 2 This is a schematic diagram of IIRESs connected to the power grid.

[0044] Figure 3 The diagram shows a comparison of the effects of traditional current differential protection and the proposed protection scheme under the same fault conditions. (a) shows the operation of traditional current differential protection when a phase A ground fault occurs, and (b) shows the operation of the proposed protection scheme when a phase A ground fault occurs. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Please see Figure 1 This invention provides a method for protecting transmission lines of new energy power plants based on cumulative difference coefficients, comprising the following steps:

[0047] Step 1: As Figure 2 Discrete current sample values ​​at both ends of the line (new energy power plant side and grid side) are obtained through current transformers to construct a time-domain current sequence i. c and i g The window length is set to 10 ms (corresponding to half a power frequency cycle); the current sampling sequence i c and i g The formula is as follows:

[0048] (1)

[0049] In the formula, n represents the number of sampling points within a 10ms data window.

[0050] Step Two: As Figure 1 The maximum amplitude of the current on the renewable energy power plant side and the grid side within one cycle is detected based on discrete current sampling values, and denoted as i respectively. cm i gm Let i be the smaller of the two values. min The larger amplitude is denoted as i. max The specific calculation formula is as follows:

[0051] (2)

[0052] (3)

[0053] In the formula, i cmax i cmin i gmax i gmin These are the positive and negative extreme points of the current on the new energy power station side and the positive and negative extreme points of the current on the grid side.

[0054] Step 3: As Figure 1 Calculate the instantaneous differential current i op (k) and braking current i res (k), the specific calculation formula is as follows:

[0055] (4)

[0056] (5)

[0057] Step Four: As Figure 1 Based on instantaneous differential current i op (k) and braking current i res σ(k) is the discriminant factor. The specific calculation formula is as follows:

[0058] (6)

[0059] Let the window average of σ(k) be denoted as The specific calculation formula is as follows:

[0060] (7)

[0061] Step 5: As Figure 1 Statistics within a period The proportion of values ​​exceeding the threshold of 0.25 is denoted as σ. p ;

[0062] Step Six: As Figure 1 For instantaneous braking current i res (k) is updated to obtain i res2 (k), the specific calculation formula is as follows:

[0063] (8)

[0064] Step Seven: As Figure 1 Based on the updated braking current i res2 (k) and differential current i op (k) Calculate the cumulative difference coefficient (IADI). If the IADI exceeds the action threshold of 0.5, it is determined to be an intra-zone fault, and a trip signal is sent; otherwise, no action is taken. The entire process requires no phasor calculations, only time-domain operations. The specific calculation formula is as follows:

[0065] (9)

[0066] (10)

[0067] (11)

[0068] In the formula: H(x) is a step function, when the differential current i op (k) is greater than i res2When (k), the IADI value increases. Taking a phase-A ground fault as an example, the operation of traditional current differential protection and the proposed solution are compared in terms of...

[0069] The simulation results were compared and verified using a PSCAD model integrated with IIRES, with all other parameters being exactly the same. Figure 3 As shown.

[0070] from Figure 3 As can be seen in (a), this describes the operation of a traditional current differential protection system:

[0071] Waveform characteristics: After a phase A ground fault occurs, the differential current and braking current waveforms of traditional current differential protection have significant overlap or fluctuations, the action quantity increases slowly, and it fails to stably exceed the action threshold value for a period of time.

[0072] Action delay: Because the fault current amplitude of inverter-type renewable energy sources (IIRESs) is limited and the phase is controlled, traditional protection methods have difficulty quickly identifying fault characteristics, resulting in a long action time and even the risk of failure to operate or misjudgment.

[0073] Poor robustness: In the early stages of a fault, the traditional method's action fluctuates greatly due to factors such as current transformer saturation and noise, resulting in poor stability.

[0074] from Figure 3 As can be seen in (b), the operation of the protection scheme proposed in this invention is as follows:

[0075] Waveform characteristics: Under the same fault conditions, the differential current waveform of the present invention and the updated braking current waveform are quickly separated, and the action quantity IADI rises rapidly and stabilizes above the action threshold value.

[0076] Rapid response: The IADI exceeds the preset threshold within 3-5ms after a fault occurs, indicating that the present invention can quickly and accurately identify faults within the area.

[0077] Strong robustness: Even in the early stage of the fault, the IADI waveform still rises smoothly and stably, indicating that the method of the present invention has good suppression ability for non-ideal conditions such as CT saturation and noise.

[0078] This invention also provides a protection device for transmission lines of new energy power plants based on cumulative difference coefficients, comprising:

[0079] The current sampling module is used to sample the current at the installation point of the transmission line protection to obtain discrete current sampling values ​​at various times.

[0080] The extreme value detection module is used to detect the extreme values ​​of the current on both sides within a cycle based on the discrete current sampling values ​​obtained by the current sampling module, and to obtain the extreme values ​​of the amplitude of the current on both sides.

[0081] The differential current and braking current calculation module is used to calculate the differential current i at each moment based on the discrete current sampling values ​​and the extreme values ​​of the current amplitudes on both sides. op (k) and braking current i res (k);

[0082] The discriminant factor calculation module is used to calculate the discriminant factor based on the dynamic current i. op (k) and braking current i res (k), calculate the discriminant factor σ(k) and its window average at each time point. ;

[0083] The proportional statistics module is used to calculate the window average obtained in step four. The proportion σ exceeding the set threshold p ;

[0084] The braking current update module is used to update the braking current based on the statistical ratio σ. p For braking current i res (k) Perform dynamic updates to obtain the updated braking current i res2 (k);

[0085] The fault diagnosis module is used to determine the fault based on the differential current i. op (k) and the updated braking current i res2 (k) The magnitude of the action quantity IADI is calculated. If the action quantity IADI is greater than the preset action threshold value, it is determined to be an internal fault and a trip signal is sent. Otherwise, it is determined to be an external fault and no trip signal is sent.

[0086] Compared with the prior art, the present invention has the following advantages:

[0087] (1) Adapting to the fault characteristics of new energy power plants: This invention directly obtains the discrete current value in the time domain through the current sampling module, avoiding the phasor calculation in the traditional frequency domain method. It can effectively cope with the characteristics of limited current amplitude and phase control of inverter-type new energy power supply faults, and solves the problem of failure to operate that may occur due to the weakening of fault characteristics in traditional longitudinal protection.

[0088] (2) Strong anti-interference capability: Through the collaborative work of the extreme value detection module, the discriminant factor calculation module and the proportional statistics module, the present invention dynamically adjusts the protection strategy based on the proportion of the discriminant factor window average value exceeding the threshold. It can effectively overcome the negative impact of non-ideal conditions such as current transformer saturation, synchronization error, measurement error, abnormal data and noise, and has good robustness.

[0089] (3) Adaptive braking characteristics: The present invention uses a braking current update module to dynamically update the instantaneous braking current based on the proportional statistics results, so that the braking current can adaptively track the changes in the system operating status, ensuring the sensitivity of faults within the zone while effectively preventing false tripping due to faults outside the zone.

[0090] (4) Fast and accurate fault identification: The present invention calculates the action quantity IADI based on the relationship between the differential current and the updated braking current through the fault identification module. The action time is only 3-5ms, which can quickly and accurately identify faults inside and outside the zone under various fault types, high transition resistance and different system configurations.

[0091] (5) Strong engineering applicability: The present invention has low requirements for sampling frequency, low computational burden, and is easy to implement in existing protection devices. It can significantly improve the reliability of line protection after the access of new energy power stations and has broad engineering application prospects.

[0092] Another embodiment of the present invention provides a new energy power station transmission line protection system based on cumulative difference coefficient, comprising: a computer-readable storage medium and a processor;

[0093] The computer-readable storage medium is used to store executable instructions;

[0094] The processor is used to read executable instructions stored in the computer-readable storage medium and execute the new energy power station transmission line protection method based on the cumulative difference coefficient.

[0095] Another embodiment of the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the new energy power station transmission line protection method based on cumulative difference coefficient described in the first aspect.

[0096] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0097] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0098] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0099] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A protection method for transmission lines of new energy power plants based on cumulative difference coefficients, characterized in that, Includes the following steps: Step 1: Sample the current at the installation point of the transmission line protection to obtain discrete current sample values ​​at each moment; Step 2: Based on the discrete current sampling values ​​obtained in Step 1, detect the extreme values ​​of the current on both sides within one cycle to obtain the extreme values ​​of the current amplitude on both sides. Step 3: Based on the discrete current sampling values ​​from Step 1 and the extreme amplitude values ​​of the currents on both sides detected in Step 2, calculate the differential current i at each moment. op (k) and braking current i res (k); Step 4: Based on the dynamic current i calculated in Step 3 op (k) and braking current i res (k), calculate the discriminant factor σ(k) and its window average at each time point. ; Step 5: Calculate the window average obtained in Step 4. The proportion σ exceeding the set threshold p ; Step Six: Based on the proportion σ calculated in Step Five. p The braking current i obtained in step three res (k) Perform dynamic updates to obtain the updated braking current i res2 (k); Step 7: Based on the differential current i from Step 3 op (k) and the updated braking current i after step six res2 (k) The magnitude of the action quantity IADI is calculated. If the action quantity IADI is greater than the preset action threshold value, it is determined to be an internal fault and a trip signal is sent. Otherwise, it is determined to be an external fault and no trip signal is sent.

2. The method for protecting transmission lines of new energy power plants based on cumulative difference coefficients according to claim 1, characterized in that: The discriminant factor σ(k) and its window average value mentioned in step four The calculation formulas are as follows: (1)； (2)； Where n is the number of sampling points within the window length.

3. The method for protecting transmission lines of new energy power plants based on cumulative difference coefficients according to claim 1, characterized in that: The updated braking current i in step six res2 (k) The calculation formula is shown in equation (3): (3)。 4. The method for protecting transmission lines of new energy power plants based on cumulative difference coefficients according to claim 1, characterized in that: The formula for calculating the motion quantity IADI in step seven is shown in equation (4): (4)。 5. A protection device for transmission lines of new energy power plants based on cumulative difference coefficients, characterized in that, include: The current sampling module is used to sample the current at the installation point of the transmission line protection to obtain discrete current sampling values ​​at various times. The extreme value detection module is used to detect the extreme values ​​of the current on both sides within a cycle based on the discrete current sampling values ​​obtained by the current sampling module, and to obtain the extreme values ​​of the amplitude of the current on both sides. The differential current and braking current calculation module is used to calculate the differential current i at each moment based on the discrete current sampling values ​​and the extreme values ​​of the current amplitudes on both sides. op (k) and braking current i res (k); The discriminant factor calculation module is used to calculate the discriminant factor based on the dynamic current i. op (k) and braking current i res (k), calculate the discriminant factor σ(k) and its window average at each time point. ; The proportional statistics module is used to calculate the window average obtained in step four. The proportion σ exceeding the set threshold p ; The braking current update module is used to update the braking current based on the statistical ratio σ. p For braking current i res (k) Perform dynamic updates to obtain the updated braking current i res2 (k); The fault diagnosis module is used to determine the fault based on the differential current i. op (k) and the updated braking current i res2 (k) The magnitude of the action quantity IADI is calculated. If the action quantity IADI is greater than the preset action threshold value, it is determined to be an internal fault and a trip signal is sent. Otherwise, it is determined to be an external fault and no trip signal is sent.

6. The new energy power station transmission line protection device based on cumulative difference coefficient according to claim 5, characterized in that: The discriminant factor σ(k) value and its window average value The calculation formulas are as follows: (1)； (2)； Where n is the number of sampling points within the window length.

7. The new energy power station transmission line protection device based on cumulative difference coefficient according to claim 5, characterized in that: The updated braking current i res2 (k) The calculation formula is shown in equation (3): (3)。 8. The new energy power station transmission line protection device based on cumulative difference coefficient according to claim 5, characterized in that: The formula for calculating the IADI (Intensity of Action) is shown in equation (4): (4)。 9. A protection system for transmission lines of new energy power plants based on cumulative difference coefficients, comprising: Computer-readable storage media and processors; The computer-readable storage medium is used to store executable instructions; The processor is used to read executable instructions stored in the computer-readable storage medium and execute the new energy power station transmission line protection method based on the cumulative difference coefficient as described in any one of claims 1-4.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for protecting transmission lines of new energy power stations based on the cumulative difference coefficient as described in any one of claims 1-4.

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