A method and apparatus for inrush blocking based on sampled values ​​with amplified second harmonics.

Abstract

A method and apparatus for inrush current blocking based on sampled values ​​with amplified second harmonics is disclosed. The method includes: determining the faulty phase and the non-faulty phase based on the difference between the differential current changes of the two phases of the transformer; using Fourier decomposition functions to obtain the DC component magnitude, fundamental component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the faulty phase, as well as the fundamental component magnitude of the non-faulty phase; calculating the new fundamental component magnitude of the faulty phase using the fundamental component magnitudes of the faulty phase and the non-faulty phase; calculating the amplified second harmonic magnitude and its average value of the faulty phase using the new fundamental component magnitude, DC component magnitude, second harmonic component magnitude, and third harmonic component magnitude, and setting a set value; if the average value is greater than the set value, it is determined to be inrush current, and the differential protection is blocked. This invention utilizes the amplification of the second harmonic by the DC component and the third harmonic component to more quickly distinguish between inrush current and faults.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, specifically, it relates to an inrush current blocking method and device based on sampling value with amplified second harmonic. Background Technology

[0002] Power transformers are crucial equipment in power systems. In engineering, differential protection is primarily used as their main protection mechanism to ensure timely fault isolation within the transformer's protection zone. However, inrush currents caused by no-load closing of the transformer or voltage recovery after a fault are cleared can easily lead to malfunctions in differential protection, threatening the safe and reliable operation of the transformer. Operational data shows that inrush currents have become one of the main factors contributing to transformer protection malfunctions, resulting in a consistently low accuracy rate of transformer protection operation.

[0003] Current transformer (CT) saturation can affect the harmonic content and discontinuity angle of the differential current to varying degrees, leading to maloperation or failure to operate of transformer differential protection with inrush current braking characteristics. Specifically, CT saturation easily increases the second harmonic content in the fault current, causing misjudgment by the second harmonic braking principle. On the other hand, CT saturation may cause the inrush current discontinuity angle to decrease or even disappear, resulting in misjudgment by the discontinuity angle braking principle and maloperation of the differential protection. Therefore, differential instantaneous overcurrent protection was proposed to prevent CT saturation due to transformer lead short circuits from causing erroneous blocking of the differential protection by inrush current.

[0004] In existing technologies, the mainstream principle of transformer inrush current blocking is second harmonic blocking. The transformer inrush current blocking method (CN102522726B) judges the inrush current based on the differential current harmonics and phase current harmonics on each side of the transformer, identifying the inrush current and internal faults for transformer protection. The rapid identification method for inter-turn faults in transformers (CN109884448B) removes the influence of the load current by differentially analyzing the fault component when the transformer is operating under load. Because the fault component is used, the influence of transformer load and CT characteristics is reduced, lowering the differential action threshold and thus increasing the sensitivity of the transformer protection device, enabling rapid fault clearing. When the transformer is unloaded, the second harmonic and waveform discontinuity angle criteria are combined. If the waveform on the unloaded side of the transformer is uninterrupted and the second harmonic content is within a certain range, it indicates a fault, and the transformer protection device operates. This overcomes the technical defect of conventional methods that wait until the inrush current disappears, allowing the inter-turn fault to continue developing until the differential current meets the operating conditions before initiating protection action. A differential protection method based on second harmonic inrush current of converter transformer (CN104319734B) identifies inrush current by comprehensively judging the second harmonic content in the differential current of the differential protection, the differential current of the Yn / Y converter transformer, and the differential current of the Yn / D converter transformer when a single-phase ground fault occurs in the valve side zone of the converter transformer. This effectively avoids false tripping of the protection caused by the inrush current.

[0005] However, differential current distortion occurs during fault development and changes, disrupting the sinusoidal nature of the waveform and causing it to fail to meet the conditions for expanding into a Fourier series, leading to false blocking. By using sampled values, the main characteristics of the waveform are restored using key points, ensuring it meets the Fourier expansion conditions. The proportion of the second harmonic is increased, making it more prominent at the initial position and thus more sensitive in determining the second harmonic. Since sampled values ​​and Fourier series are completely independent systems—one restores waveform characteristics by extracting data from various points on the wave, while the other decomposes the original waveform into components composed of various harmonic orders—it's crucial to understand that sampled values ​​and Fourier series are entirely separate systems. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a surge current blocking method and apparatus based on sampled values ​​with amplified second harmonics. This method utilizes the non-faulty phase fundamental wave of the sampled values ​​to suppress the faulty phase fundamental wave and DC component, and the third harmonic to amplify the second harmonic. By leveraging the amplification effect of the DC component and the third harmonic component on the second harmonic, surge current and faults can be distinguished more quickly.

[0007] The present invention adopts the following technical solution.

[0008] This invention proposes a surge current blocking method based on sampled values ​​with amplified second harmonics, comprising:

[0009] Step 1: Collect the changes in the differential current sampling values ​​of each phase of the transformer. Based on the difference between the changes in the differential current of two phases, determine the faulty phase and the non-faulty phase. If the difference between the changes in the differential current of two phases is the smallest, then the two phases are determined to be non-faulty phases and the other phase is the faulty phase.

[0010] Step 2: Use the Fourier decomposition function to obtain the DC component magnitude, fundamental component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the faulty phase, as well as the fundamental component magnitude of the non-faulty phase.

[0011] Step 3: Calculate the new fundamental component magnitude of the faulty phase using the fundamental component magnitude of the faulty phase and the fundamental component magnitude of the non-faulty phase.

[0012] Step 4: Using the new fundamental component magnitude, DC component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the faulty phase, calculate the boosted second harmonic magnitude of the faulty phase using the following formula:

[0013]

[0014] In the formula, δI ∑2A_new To increase the second harmonic mode value of the faulty phase, δI ∑0A δI ∑2A δI ∑3A These are the DC component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the fault phase, respectively, δI. ∑1A_new The new fundamental component modulus of the fault phase;

[0015] Step 5: Calculate the average value of the boosted second harmonic mode of the faulty phase and set a set value; if the average value is greater than the set value, it is determined to be inrush current and the differential protection is blocked; otherwise, it is determined that the phase has failed.

[0016] Preferably, in step 1, when collecting the changes in the differential current sampling values ​​of each phase of the transformer, for the recorded waveform, the time of the fault occurrence is taken as the time origin, the waveform corresponding to the time period τ before the time origin is the pre-fault waveform, and the waveform after the time origin is the post-fault waveform; starting from the time origin, the post-fault waveform is recorded once every time period τ; the pre-fault waveform is subtracted from the post-fault waveform recorded each time to obtain the changes in the differential current sampling values ​​of each phase of the transformer.

[0017] Preferably, the time period τ is 20ms.

[0018] Preferably, step 1 includes:

[0019] Step 1.1: Collect the phase current I of each phase of the high-voltage side branch of the transformer. H1A I H1B IH1C The phase current I of the medium-voltage side branch M1A I M1B I M1C The phase current I of the low-voltage side branch L1A I L1B I L1C ;

[0020] Step 1.2, calculate the differential current of each phase using the following formula:

[0021] I CD_A =I H1A +I M1A +I L1A

[0022] I CD_B =I H1B +I M1B +I L1B

[0023] I CD_C =I H1C +I M1C +I L1C

[0024] In the formula, I CD_A I CD_B I CD_C These are the differential currents for phases A, B, and C, respectively.

[0025] Step 1.3: Compare the difference between the differential current changes of the two phases, determine the faulty phase using the following formula, and automatically classify the remaining two phases as non-faulty phases:

[0026]

[0027] In the formula, δI CD_A δI CD_B δI CD_C These represent the changes in differential current for phases A, B, and C, respectively.

[0028] Preferably, in step 1.1, when collecting phase current data of each branch of the transformer, the sampling rate is greater than 1200Hz, ensuring that there are no less than 24 sampling points in one cycle.

[0029] Preferably, in step 3, the new fundamental component modulus δI of the fault phase is calculated using the following formula. ∑1A_new :

[0030] δI ∑1A_new =δI ∑1A -k×δI ∑1BC

[0031] In the formula, δI ∑1AδI represents the fundamental component magnitude of the fault phase. ∑1BC denoted as the fundamental component modulus of the non-faulty phase, k is the modulation coefficient, and k ≤ 0.1.

[0032] Preferably, when calculating the average value, the average value of the current sampling point itself and the 23 points preceding the current sampling point is taken as the value of the current sampling point.

[0033] Preferably, the set value is no greater than 15%.

[0034] In another aspect, the present invention proposes an inrush current blocking device based on sampled value with amplified second harmonics. The device includes: a data acquisition module, a fault phase determination module, a modulus module, and a blocking enable module.

[0035] The acquisition module is used to acquire the changes in the differential current sampling values ​​of each phase of the transformer. For the recorded waveforms, the time origin is the time when the fault occurs. The waveform corresponding to the time period τ before the time origin is the pre-fault waveform, and the waveform after the time origin is the post-fault waveform. Starting from the time origin, the post-fault waveform is recorded once every time period τ. The changes in the differential current sampling values ​​of each phase of the transformer are obtained by subtracting the pre-fault waveform from the post-fault waveform recorded each time.

[0036] The fault phase determination module is used to determine the faulty phase and the non-faulty phase based on the difference between the changes in the differential current of the two phases; if the difference between the changes in the differential current of the two phases is the smallest, then the two phases are determined to be non-faulty phases and the other phase is the faulty phase.

[0037] The modulus module includes: a modulus calculation unit and a modulus increment unit.

[0038] The modulus calculation unit is used to obtain the DC component modulus, fundamental component modulus, second harmonic component modulus and third harmonic component modulus of the faulty phase, as well as the fundamental component modulus of the non-faulty phase, based on the faulty phase and non-faulty phase output by the faulty phase determination module using the Fourier decomposition function.

[0039] The modulus enhancement unit is used to calculate the new fundamental component modulus of the faulty phase using the fundamental component modulus of the faulty phase and the fundamental component modulus of the non-faulty phase; and to calculate the enhanced second harmonic modulus of the faulty phase using the new fundamental component modulus, DC component modulus, second harmonic component modulus and third harmonic component modulus.

[0040] The blocking enable module is used to calculate the average value of the auxiliary second harmonic mode of the faulty phase using the auxiliary second harmonic mode output by the mode value module, and set a set value; if the average value is greater than the set value, it is determined to be an inrush current, and an enable signal is sent to block the differential protection; otherwise, it is determined that the phase has failed.

[0041] The modulus calculation unit includes 5 independent registers.

[0042] The beneficial effects of this invention are that, compared with the prior art, it only uses the differential current on each side of the transformer and the phase selection principle to determine whether inrush current has occurred, without having to calculate the Fourier expansion of the phase current, thus reducing the amount of calculation; after Fourier decomposition, it does not only extract the second harmonic, but also extracts the related DC component, fundamental wave and third harmonic. Since the Fourier decomposition is performed on the same current, the required data can be extracted at once, and the calculation process is not complicated; at the same time, the initial value of the second harmonic after being amplified by these components is larger, which can better show the characteristics of inrush current for a fixed value. Attached Figure Description

[0043] Figure 1 This is a flowchart of an inrush blocking method based on sampled values ​​with amplified second harmonics, proposed in this invention.

[0044] Figure 2 This is a schematic diagram of the principle of amplifying the second harmonic in an embodiment of the present invention;

[0045] Figure 3 This is a graph showing the relationship between the amplified second harmonic and the set value when a surge occurs, as calculated in this embodiment of the invention.

[0046] Figure 4 This is a diagram showing the relationship between the boosted second harmonic and the set value when a fault occurs, as calculated in this embodiment of the invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0048] This invention proposes a surge current blocking method based on sampled values ​​with amplified second harmonics, such as... Figure 1 ,include:

[0049] Step 1: Collect the changes in the differential current sampling values ​​of each phase of the transformer. Based on the difference between the changes in the differential current of two phases, determine the faulty phase and the non-faulty phase. If the difference between the changes in the differential current of two phases is the smallest, then the two phases are determined to be non-faulty phases and the other phase is the faulty phase.

[0050] Specifically, in step 1, when collecting the changes in the differential current sampling values ​​of each phase of the transformer, for the recorded waveform, the time of the fault occurrence is taken as the time origin, the waveform corresponding to the time period τ before the time origin is the pre-fault waveform, and the waveform after the time origin is the post-fault waveform; starting from the time origin, the post-fault waveform is recorded once every time period τ; the pre-fault waveform is subtracted from the post-fault waveform recorded each time to obtain the changes in the differential current sampling values ​​of each phase of the transformer.

[0051] Specifically, the time period τ is 20ms.

[0052] In this embodiment, the time period before the fault is recorded is at least 40ms, or 2 τ, to ensure that there is a large amount of usable data sample before the fault occurs.

[0053] Specifically, step 1 includes:

[0054] Step 1.1: Collect the phase current I of each phase of the high-voltage side branch of the transformer. H1A I H1B I H1C The phase current I of the medium-voltage side branch M1A I M1B I M1C The phase current I of the low-voltage side branch L1A I L1B I L1C .

[0055] Specifically, in step 1.1, when collecting phase current data of each branch of the transformer, the sampling rate is greater than 1200Hz to ensure that there are no less than 24 sampling points in one cycle.

[0056] Step 1.2, calculate the differential current of each phase using the following formula:

[0057] I CD_A =I H1A +I M1A +I L1A

[0058] I CD_B =I H1B +I M1B +I L1B

[0059] I CD_C =I H1C +I M1C +I L1C

[0060] In the formula, I CD_A I CD_B I CD_C These are the differential currents for phases A, B, and C, respectively.

[0061] Step 1.3: Compare the difference between the differential current changes of the two phases, determine the faulty phase using the following formula, and automatically classify the remaining two phases as non-faulty phases:

[0062]

[0063] In the formula, δI CD_A δI CD_B δI CD_C These represent the changes in differential current for phases A, B, and C, respectively.

[0064] Step 2: Use the Fourier decomposition function to obtain the DC component magnitude, fundamental component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the faulty phase, as well as the fundamental component magnitude of the non-faulty phase.

[0065] This invention only uses the differential current on each side of the transformer and the phase selection principle to determine whether inrush current has occurred, without having to calculate the Fourier expansion of the phase current, thus reducing the amount of calculation. After Fourier decomposition, it does not only extract the second harmonic, but also extracts the related DC component, fundamental wave and third harmonic. Since it is the same current that is used for Fourier decomposition, the required data can be extracted at once, and the calculation process is not complicated.

[0066] Step 3: Calculate the new fundamental component magnitude of the faulty phase using the fundamental component magnitude of the faulty phase and the fundamental component magnitude of the non-faulty phase.

[0067] Specifically, in step 3, the new fundamental component modulus δI of the fault phase is calculated using the following formula. ∑1A_new :

[0068] δI ∑1A_new =δI Σ1A -k×δI ∑1BC

[0069] In the formula, δI ∑1A δI represents the fundamental component magnitude of the fault phase. ∑1BC denoted as the fundamental component modulus of the non-faulty phase, k is the modulation coefficient, and k ≤ 0.1.

[0070] The above formula aims to increase the proportion of the second harmonic in step 4. In principle, the fundamental component after being suppressed by the non-faulty phase, when substituted into the formula in step 4, will increase the initial value of the second harmonic proportion, but the rate of change of the second harmonic will slow down. If the modulation coefficient 0.1 is set too high, it can easily lead to the calculated magnitude of the second harmonic of the faulty phase being lower than the set value in step 5, resulting in misjudgment, especially in cases of inrush current.

[0071] Specifically, when calculating the average value, the average value of the current sampling point itself and the 23 points preceding the current sampling point is taken as the value of the current sampling point.

[0072] Step 4: Using the new fundamental component magnitude, DC component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the faulty phase, calculate the boosted second harmonic magnitude of the faulty phase using the following formula:

[0073]

[0074] In the formula, δI ∑2A_new To increase the second harmonic mode value of the faulty phase, δI ∑0A δI ∑2A δI ∑3A These are the DC component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the fault phase, respectively, δI. ∑1A_new The new fundamental component magnitude of the fault phase.

[0075] In this invention, the initial value of the second harmonic after being amplified by these components is larger, and for a fixed value, the characteristics of the inrush flow can be better displayed.

[0076] Figure 2 This is a schematic diagram illustrating the principle of amplifying the second harmonic in this embodiment of the invention. The inequality in step 4 is considered as a linear equation in one variable, and δI is... ∑2A_new As Figure 2 The vertical axis can also be considered as the proportion of the processed second harmonic, and the horizontal axis... This represents the ratio of the second harmonic to the fundamental frequency, and in the new scheme, it represents the inequality in step 4. Part of the original plan indicated It can be seen that the x and y coordinates are the same in the old scheme. Considering that the ratios in the new scheme have also been adjusted, therefore... Figure 2 The middle is reflected in In existing technologies, there is no method to amplify the second harmonic; the determination of whether inrush occurs relies solely on the ratio of the second harmonic to the fundamental frequency. This method is similar to... Figure 2 The solid line passing through the origin has a second harmonic intercept of 0 initially. Over time, for inrush current phenomena, the proportion of the second harmonic will exceed the set value of 0.15. In the rapid identification method for transformer inter-turn faults, if the second harmonic criterion is met, the discontinuity angle criterion must also be applied; protection will only be blocked after the discontinuity angle is determined to be inrush current. The method proposed in this solution will use the amplified second harmonic for identification, such as... Figure 2The dashed line in the diagram shows a significant improvement over the old scheme in terms of intercept. The increased intercept helps the second harmonic reach a value greater than the setpoint of 0.15 more quickly. Furthermore, this scheme increases the proportion of the second harmonic in two ways: first, by reducing the value of the fundamental component of the faulty phase; and second, by using the third harmonic and DC component of the faulty phase as the intercept component in the second harmonic criterion, thus increasing the value of the second harmonic in the initial stage. It no longer relies solely on the second harmonic component, but fully considers the attenuated DC component and the third harmonic in the waveform, while also including the fundamental wave of the non-faulty phase in the calculation. Furthermore, it considers that if the resistance of the non-faulty phase is too strong, it will... Figure 2 The slope of the dashed line in the diagram becomes smaller, which leads to a situation where the proportion of the second harmonic is smaller than that of the old scheme after a period of inrush. After repeated confirmation, the coefficient before the non-faulty phase is determined to be 0.1.

[0077] Step 5: Calculate the average value of the boosted second harmonic mode of the faulty phase and set a set value; if the average value is greater than the set value, it is determined to be inrush current and the differential protection is blocked; otherwise, it is determined that the phase has failed.

[0078] In this implementation, the set value is no greater than 15%.

[0079] Figure 3 In this embodiment of the invention, the relationship between the amplified second harmonic and the set value is calculated when a surge occurs; Figure 4 This is a graph showing the relationship between the boosted second harmonic and the setpoint when a minor fault occurs, as calculated in an embodiment of the present invention. For example... Figure 4 As shown, when a minor fault occurs, only the second harmonic content needs to be considered to determine whether a fault has occurred, without needing to separately confirm the discontinuity angle, which can improve the protection action time.

[0080] In another aspect, the present invention proposes an inrush current blocking device based on sampled value with amplified second harmonics. The device includes: a data acquisition module, a fault phase determination module, a modulus module, and a blocking enable module.

[0081] The acquisition module is used to acquire the changes in the differential current sampling values ​​of each phase of the transformer. For the recorded waveforms, the time origin is the time when the fault occurs. The waveform corresponding to the time period τ before the time origin is the pre-fault waveform, and the waveform after the time origin is the post-fault waveform. Starting from the time origin, the post-fault waveform is recorded once every time period τ. The changes in the differential current sampling values ​​of each phase of the transformer are obtained by subtracting the pre-fault waveform from the post-fault waveform recorded each time.

[0082] The fault phase determination module is used to determine the faulty phase and the non-faulty phase based on the difference between the changes in the differential current of the two phases; if the difference between the changes in the differential current of the two phases is the smallest, then the two phases are determined to be non-faulty phases and the other phase is the faulty phase.

[0083] The modulus module includes: a modulus calculation unit and a modulus increment unit.

[0084] The modulus calculation unit is used to obtain the DC component modulus, fundamental component modulus, second harmonic component modulus and third harmonic component modulus of the faulty phase, as well as the fundamental component modulus of the non-faulty phase, based on the faulty phase and non-faulty phase output by the faulty phase determination module using the Fourier decomposition function.

[0085] The modulus enhancement unit is used to calculate the new fundamental component modulus of the faulty phase using the fundamental component modulus of the faulty phase and the fundamental component modulus of the non-faulty phase; and to calculate the enhanced second harmonic modulus of the faulty phase using the new fundamental component modulus, DC component modulus, second harmonic component modulus and third harmonic component modulus.

[0086] The blocking enable module is used to calculate the average value of the auxiliary second harmonic mode of the faulty phase using the auxiliary second harmonic mode output by the mode value module, and set a set value; if the average value is greater than the set value, it is determined to be an inrush current, and an enable signal is sent to block the differential protection; otherwise, it is determined that the phase has failed.

[0087] The modulus calculation unit includes 5 independent registers.

[0088] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0089] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0090] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0091] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0092] Various aspects of this disclosure are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It should 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-readable program instructions.

[0093] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that, when executed by the processor of the computer or other programmable data processing apparatus, they create means for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium that causes a computer, programmable data processing apparatus, and / or other device to operate in a particular manner; thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing aspects of the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0094] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to perform the functions / actions specified in one or more boxes of a flowchart and / or block diagram.

[0095] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of an instruction containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than those shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0096] 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 protection scope of the claims of the present invention.

Claims

1. A surge current blocking method based on sampled value with amplified second harmonics, characterized in that, The method includes: Step 1: Collect the changes in the differential current sampling values ​​of each phase of the transformer. Based on the difference between the changes in the differential current of two phases, determine the faulty phase and the non-faulty phase. If the difference between the changes in the differential current of two phases is the smallest, then the two phases are determined to be non-faulty phases and the other phase is the faulty phase. Step 2: Use the Fourier decomposition function to obtain the DC component magnitude, fundamental component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the faulty phase, as well as the fundamental component magnitude of the non-faulty phase. Step 3: Calculate the new fundamental component magnitude of the faulty phase using the fundamental component magnitude of the faulty phase and the fundamental component magnitude of the non-faulty phase. Step 4: Using the new fundamental component magnitude, DC component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the faulty phase, calculate the boosted second harmonic magnitude of the faulty phase using the following formula: In the formula, This contributes to increasing the second harmonic mode value of the faulty phase. , , These are the DC component magnitude, second harmonic component magnitude, and third harmonic component magnitude of the faulty phase, respectively. The new fundamental component modulus of the fault phase; Step 5: Calculate the average value of the boosted second harmonic mode of the faulty phase and set a set value; if the average value is greater than the set value, it is determined that the faulty phase has inrush current and the differential protection is blocked; otherwise, it is determined that the faulty phase has a fault.

2. The inrush current blocking method based on sampled value with amplified second harmonic as described in claim 1, characterized in that, In step 1, when collecting the changes in the differential current sampling values ​​of each phase of the transformer, for the recorded waveform, the time origin is taken as the time point before the fault occurrence, and the time period before the time origin is... The corresponding waveform is the waveform before the fault, and the waveform after the time origin is the waveform after the fault; starting from the time origin, each time interval... Record the waveform after each fault; subtract the waveform before the fault from the recorded waveform after each fault to obtain the change in the differential current sampling values ​​of each phase of the transformer.

3. The inrush current blocking method based on sampled value with amplified second harmonic as described in claim 2, characterized in that, Time period The value is 20ms.

4. The inrush current blocking method based on sampled value with amplified second harmonic as described in claim 2, characterized in that, Step 1 includes: Step 1.1: Collect the phase current of each phase of the high-voltage side branch of the transformer. , , The phase currents of each phase in the medium-voltage side branch , , The phase currents of the low-voltage side branch , , ; Step 1.2, calculate the differential current of each phase using the following formula: In the formula, , , These are the differential currents for phases A, B, and C, respectively. Step 1.3: Compare the difference between the differential current changes of the two phases, determine the faulty phase using the following formula, and automatically classify the remaining two phases as non-faulty phases: In the formula, , , These represent the changes in differential current for phases A, B, and C, respectively.

5. The inrush current blocking method based on sampled value with amplified second harmonic as described in claim 4, characterized in that, In step 1.1, when collecting phase current data of each branch of the transformer, the sampling rate is greater than 1200Hz, ensuring that there are no less than 24 sampling points in one cycle.

6. The inrush current blocking method based on sampled value with amplified second harmonic as described in claim 1, characterized in that, In step 3, the new fundamental component magnitude of the fault phase is calculated using the following formula. : In the formula, The fundamental component magnitude of the fault phase. The fundamental component magnitude of the non-faulty phase. Modulation coefficient, and .

7. The inrush current blocking method based on sampled value with amplified second harmonic as described in claim 1, characterized in that, When calculating the average value, the average value of the current sampling point is taken as the average value of the 23 points preceding the current sampling point.

8. The inrush current blocking method based on sampled value with amplified second harmonic as described in claim 1, characterized in that, The fixed value is no greater than 15%.

9. A surge current blocking device based on sampled value with amplified second harmonics, utilizing the method of any one of claims 1-8, the device comprising: The acquisition module, fault phase determination module, modulus module, and interlocking enable module are characterized in that... The acquisition module is used to collect the changes in the differential current sampling values ​​of each phase of the transformer; for the recorded waveforms, the time origin is the time point before the fault occurrence, and the time period before the time origin is... The corresponding waveform is the waveform before the fault, and the waveform after the time origin is the waveform after the fault; starting from the time origin, each time interval... Record the waveform after a fault; subtract the waveform before the fault from each recorded waveform after the fault to obtain the change in the differential current sampling values ​​of each phase of the transformer. The fault phase determination module is used to determine the faulty phase and the non-faulty phase based on the difference between the changes in the differential current of the two phases; if the difference between the changes in the differential current of the two phases is the smallest, then the two phases are determined to be non-faulty phases and the other phase is the faulty phase. The modulus module includes: a modulus calculation unit and a modulus increment unit. The modulus calculation unit is used to obtain the DC component modulus, fundamental component modulus, second harmonic component modulus and third harmonic component modulus of the faulty phase, as well as the fundamental component modulus of the non-faulty phase, based on the faulty phase and non-faulty phase output by the faulty phase determination module using the Fourier decomposition function. The modulus enhancement unit is used to calculate the new fundamental component modulus of the faulty phase using the fundamental component modulus of the faulty phase and the fundamental component modulus of the non-faulty phase; and to calculate the enhanced second harmonic modulus of the faulty phase using the new fundamental component modulus, DC component modulus, second harmonic component modulus and third harmonic component modulus. The blocking enable module is used to calculate the average value of the auxiliary second harmonic mode of the faulty phase using the auxiliary second harmonic mode output by the mode value module, and set a set value. If the average value is greater than the set value, it is determined that the faulty phase has inrush current and an enable signal is sent to block the differential protection; otherwise, it is determined that the faulty phase has a fault.

10. The inrush current blocking device based on sampled value with amplified second harmonic as described in claim 9, characterized in that, The modulus calculation unit includes 5 independent registers.

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