Method and device for discriminating ferromagnetic saturation and inrush current reflected by concave-convex offset of current waveform

Abstract

The application discloses a ferromagnetic saturation and inrush current discrimination method and device reflecting concave-convex offset of current waveform, and the method comprises the following steps: obtaining three-phase differential current waveform according to three-phase currents of each side of a transformer, and collecting variation sequence of three-phase differential currents of the transformer based on the three-phase differential current waveform; calculating current variation difference, absolute value of the current variation difference, current period integral of the current variation difference, current period integral of the absolute value of the current variation difference, T / 3 period integral, 2T / 3 period integral and maximum number of two points of the absolute value of the current variation difference; when the sum of the T / 3 period integral, the 2T / 3 period integral, the maximum number of two points of the absolute value of the current variation difference, the absolute value of the current period integral of the current variation difference satisfies the ferromagnetic saturation and inrush current criterion reflecting the concave-convex offset of the current waveform, the inrush current or CT saturation is determined, and the differential protection is blocked. The same criterion is used, and effective identification of the inrush current and the saturation is realized.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, specifically relating to a method and device for judging ferromagnetic saturation and inrush current based on the deviation of current waveform. Background Technology

[0002] In recent years, with the gradual maturation of smart substation technology, smart substations have been widely put into operation on the power grid. However, transformer protection maloperation has occurred frequently. The main reasons for this are twofold: (1) The process layer of smart substations widely adopts the cooperation of transformers, data acquisition units, and merging units to realize digital sampling circuits. Complex digital sampling circuits are more likely to cause abnormal sampling data, leading to transformer protection maloperation; (2) The influence of excitation inrush current when the transformer is put into operation and the restorative inrush current when the external fault is cleared can easily cause transformer protection maloperation. In response to the above problems, the existing device adopts dual AD data acquisition and verification. Both AD sampling data are used for logic operations to jointly control the protection output, which improves the reliability of the sampling circuit. In addition, through the analysis of the transformer excitation inrush current type, differential current second harmonic mutual blocking is used. When the transformer is put into operation, differential protection is opened by phase comprehensive harmonics. When restorative inrush current occurs, differential protection is opened by phase differential current second harmonics using a "three-out-of-two" method.

[0003] For transformer differential protection, because it involves two or more current transformers (CTs) at different voltage levels, a situation may still occur where one CT is unsaturated and the other is deeply saturated during an external fault. This will drastically increase the unbalanced current of the differential protection, and the currently widely used ratio braking characteristic alone cannot prevent maloperation of the differential protection. Saturation may 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, causing misjudgment by the discontinuity angle braking principle and maloperation of the differential protection. In traditional differential protection, the ratio braking coefficient is increased to avoid the unbalanced current caused by CT saturation during external faults, but this undoubtedly reduces the sensitivity of the protection operation during internal faults.

[0004] In existing technologies, the mainstream principle of transformer inrush current blocking is second harmonic blocking. Patent CN102522726B proposes a method for transformer excitation inrush current blocking, which judges the excitation inrush current based on the differential current harmonics and phase current harmonics on each side of the transformer, identifying the excitation inrush current and internal faults. Patent CN109884448B proposes a rapid identification method for transformer inter-turn faults. When the transformer is operating normally under load, the influence of the load current is removed through differential detection of the fault component. Because the fault component is used, the influence of transformer load and CT characteristics is reduced, lowering the differential action threshold and thus improving 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, a fault is indicated, 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 action conditions before initiating protection action. The patent with publication number CN104319734B proposes a large differential protection method based on the second harmonic excitation inrush current of a converter transformer. When a single-phase ground fault occurs in the valve side zone of the converter transformer, the method uses the second harmonic content in the differential current of the large differential protection, the differential current of the Yn / Y converter transformer differential protection, and the differential current of the Yn / D converter transformer differential protection to comprehensively identify the excitation inrush current, effectively avoiding the protection maloperation caused by this.

[0005] Patent CN113267698A proposes a method, system, and storage medium for determining transformer CT saturation. It obtains the full-cycle differential current integral based on the second harmonic amplitude of the transformer's high-voltage side, the braking current, and the differential current input at the current sampling point of the transformer using a preset full-cycle differential current integral function. Based on the full-cycle differential current integral and preset discrimination rules, transformer CT saturation is determined. Patent CN115912263A proposes a method and system for identifying CT saturation faults. It sets two parameters: when the ratio of the original differential current to the original braking current is greater than a first set parameter, severe saturation is considered; when it is less than the first set parameter but greater than a second set parameter, slight saturation is considered. However, the CT saturation criteria in these two patents cannot be combined with inrush current criteria to effectively identify both inrush current and saturation using a single criterion. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method and apparatus for identifying ferromagnetic saturation and inrush current that reflects the convexity and convexity of the current waveform. It utilizes a certain linear relationship where the ratio of the sum of the T / 3 cycle integral and the sum of the two maximum values ​​of the differential current absolute value is lower than the ratio of the absolute value of the current cycle integral to the T / 3 cycle integral, which can more quickly confirm whether inrush current and saturation have occurred.

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

[0008] A method for determining ferromagnetic saturation and inrush current based on the deviation of current waveform includes the following steps:

[0009] Step 1: Obtain the three-phase differential current waveform based on the three-phase current on each side of the transformer, and collect the change sequence of the three-phase differential current of the transformer based on the three-phase differential current waveform;

[0010] Step 2: Sum the changes in the three-phase differential currents in the sequence obtained in Step 1 for each phase to obtain the differential current of the three-phase current changes, and then obtain the absolute value of the differential current;

[0011] Step 3: Using the current time point and the previous 23 time points as the current period, calculate the current period integral of the differential flow and the current period integral of the absolute value of the differential flow.

[0012] Step 4: For the absolute value of the differential flow, take the 8 points with the smallest values ​​in the current period, calculate its integral, and obtain the T / 3 period integral. Subtract the T / 3 period integral from the current period integral of the absolute value of the differential flow to obtain the 2T / 3 period integral.

[0013] Step 5: For the absolute value of the differential flow, calculate the sum of the maximum and second maximum values ​​within the current cycle, and use this sum as the maximum number of the absolute value of the differential flow at point 2.

[0014] Step 6: Determine whether the T / 3 cycle integral, 2T / 3 cycle integral, the sum of the two largest values ​​of the differential current absolute value, and the absolute value of the current cycle integral satisfy the ferromagnetic saturation and inrush current criteria that reflect the current waveform convexity and convexity deviation. If they are satisfied, it is determined to be inrush current or CT saturation, and the differential protection is blocked.

[0015] Preferably, step 1 specifically includes:

[0016] Step 1.1: Collect the three-phase current I of the high-voltage side branch of the transformer. H1A I H1B I H1C The three-phase current I of the medium-voltage side branch M1A I M1B I M1C The three-phase current I of the low-voltage side branch L1A I L1B I L1C ;

[0017] Step 1.2: Based on the three-phase current data of each branch collected in Step 1.1, calculate the three-phase differential current and generate the three-phase differential current waveform:

[0018] I CD_A =I H1A +IM1A +I L1A

[0019] I CD_B =I H1B +I M1B +I L1B

[0020] I CD_C =I H1C +I M1C +I L1C

[0021] In the formula, I CD_A I CD_B I CD_C These are the differential currents for phases A, B, and C, respectively.

[0022] Step 1.3: Based on the three-phase differential current waveform, collect the change in the three-phase differential current dI. CD_A dI CD_B and dI CD_B sequence.

[0023] Preferably, in step 1.1, when collecting the three-phase current data of each branch of the transformer, the sampling rate is greater than 1200Hz, and there are no less than 24 sampling points in one sampling period.

[0024] Preferably, when collecting the change sequence of the three-phase differential current of the transformer, for the three-phase differential current 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 waveform before the fault, and the waveform after the time origin is the waveform after the fault.

[0025] Starting from the origin of time, record the waveform after the fault once every time interval τ;

[0026] The sequence of changes in the three-phase differential current of the transformer is obtained by subtracting the waveform before the fault from the waveform recorded after each fault.

[0027] Preferably, the time period τ is 20ms.

[0028] Preferably, in step 3, the formulas for the current period integral of the differential current and the current period integral of the absolute value of the differential current are:

[0029]

[0030]

[0031] In the formula, 24′ k Represents the current period integral of the differential flow;

[0032] twenty four kThe current period integral represents the absolute value of the differential flow;

[0033] The subscript k represents the current time point, and k is greater than 23;

[0034] δi Σi' Indicates the differential flow at point i'. Σi' The change in quantity.

[0035] Preferably, in step 6, the ferromagnetic saturation and inrush current criteria reflecting the current waveform's convexity / convexity shift are:

[0036]

[0037] In the formula, This represents the largest number of points with a differential absolute value of 2.

[0038] min T / 3 Indicates the integral over a period of T / 3;

[0039] max 2T / 3 This represents an integral over 2T / 3 periods;

[0040] c and b represent the slope and intercept of a linear function of the dependent variable, with the ratio of the absolute value of the current period integral to the T / 3 period integral as the value of the integral.

[0041] Preferably, the ferromagnetic saturation and inrush current criteria reflecting the current waveform's convexity / convexity offset have the following usage thresholds:

[0042] min T / 3 ≥0.004I e

[0043] Where, min T / 3 Indicates the integral over a period of T / 3;

[0044] I e Indicates the rated current of the high voltage;

[0045] If the above thresholds are not met, then lockout protection will be applied.

[0046] Preferably, the slope c is 0.016, and the intercept b is a function of time t:

[0047]

[0048] A ferromagnetic saturation and inrush current discrimination device that reflects the convexity and convexity of current waveform includes:

[0049] The acquisition module is used to obtain the three-phase differential current waveform based on the three-phase current on each side of the transformer, and to acquire the change sequence of the three-phase differential current of the transformer based on the three-phase differential current waveform.

[0050] The modulus calculation module is used to calculate the differential current and absolute value of the three-phase current change, the current cycle integral of the differential current and the current cycle integral of the absolute value of the differential current, the T / 3 cycle integral, the 2T / 3 cycle integral, and the maximum number of the absolute value of the differential current at two points.

[0051] The lockout enable module is used to determine whether the differential protection is inrush current or CT saturation when the T / 3 cycle integral, 2T / 3 cycle integral, the sum of the two maximum values ​​of the differential current absolute value, and the absolute value of the current cycle integral of the differential current meet the ferromagnetic saturation and inrush current criteria that reflect the current waveform convexity and convexity deviation.

[0052] Preferably, different calculation processes in the modulus calculation unit are performed using independent registers.

[0053] The beneficial effects of this invention are compared with those of the prior art:

[0054] 1. This invention is applicable to the discrimination of inrush flow and also to the discrimination of CT saturation. Only when the ratio of the sum of the T / 3 cycle integral and the sum of the two largest values ​​of the differential flow absolute value is lower than a certain linear relationship between the absolute value of the current cycle integral and the T / 3 cycle integral, it can reflect the occurrence of inrush flow or CT saturation, thereby locking the protection. It uses the same criterion to achieve effective identification of inrush flow and saturation.

[0055] 2. This invention does not use second harmonics, but directly uses discrete point data collected by the device, thereby avoiding Fourier series operations, so that the instability caused by cross-window calculation can be ignored when the device is running.

[0056] 3. When calculating the T / 3 period integral, this invention does not take the minimum value from 8 consecutive points, but instead selects the 8 smallest points (which may not be consecutive) within the current period. This better reflects the position of the discontinuity within the current period, highlighting the concavity and bulge of the waveform. The proportional relationship between the T / 3 period integral and the 2T / 3 period integral is used to reflect the concavity and bulge of the current waveform. The smaller the T / 3 period integral, the more obvious the concavity of the waveform. It can be used as a benchmark to judge whether the waveform has inrush current and saturation. Attached Figure Description

[0057] Figure 1 This is a flowchart of a method for judging ferromagnetic saturation and inrush current based on the current waveform concavity and convexity deviation of the present invention;

[0058] Figure 2 This is a graph showing the relationship between the ratio of the T / 3 cycle integral to the sum of the 2T / 3 cycle integral and the maximum number of the absolute value of the differential flow at two points when saturation occurs, and the ratio of the absolute value of the current cycle integral to the T / 3 cycle integral in this embodiment of the invention.

[0059] Figure 3 This is a graph showing the relationship between the ratio of the T / 3 cycle integral to the sum of the 2T / 3 cycle integral and the maximum number of the absolute value of the differential flow at two points when a surge occurs, and the ratio of the absolute value of the current cycle integral to the T / 3 cycle integral in this embodiment of the invention.

[0060] Figure 4 This is a graph showing the relationship between the ratio of the T / 3 cycle integral to the sum of the 2T / 3 cycle integral and the maximum sum of the absolute values ​​of the differential current at two points when a fault occurs, and the ratio of the absolute value of the current cycle integral to the T / 3 cycle integral. Detailed Implementation

[0061] 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, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0062] like Figure 1 As shown, Embodiment 1 of the present invention provides a method for determining ferromagnetic saturation and inrush current based on the deviation of the current waveform. In a preferred but non-limiting embodiment of the present invention, the method includes:

[0063] Step 1: Obtain the three-phase differential current waveform based on the three-phase current on each side of the transformer, and collect the change sequence of the three-phase differential current of the transformer based on the three-phase differential current waveform;

[0064] More preferably, this step involves obtaining the change in the three-phase differential current of the transformer using a recursive algorithm based on the three-phase currents on each side of the transformer, specifically including:

[0065] Step 1.1: Collect the three-phase current I of the high-voltage side branch of the transformer. H1A I H1B I H1C The three-phase current I of the medium-voltage side branch M1A I M1B I M1C The three-phase current I of the low-voltage side branch L1A I L1B I L1C ;

[0066] When collecting three-phase current data of each branch of the transformer, the sampling rate is greater than 1200Hz, ensuring no less than 24 sampling points in one cycle.

[0067] Step 1.2: Based on the three-phase current data of each branch collected in Step 1.1, calculate the three-phase differential current and generate the three-phase differential current waveform:

[0068] I CD_A =I H1A +I M1A +I L1A

[0069] I CD_B =I H1B +I M1B +I L1B

[0070] I CD_C =I H1C +I M1C +I L1C

[0071] In the formula, I CD_A I CD_B I CD_C These are the differential currents for phases A, B, and C, respectively.

[0072] Step 1.3: Based on the three-phase differential current waveform, obtain the changes in multiple three-phase differential currents, dI. CD_A dI CD_B dI CD_C ; where dI CD_A dI CD_B dI CD_C These represent the differential current changes for phases A, B, and C, respectively.

[0073] When collecting the changes in the three-phase differential current sampling values ​​of the transformer, for the recorded three-phase differential current waveform, the time origin is taken as the time of the fault occurrence. The waveform corresponding to the time period τ before the time origin is the waveform before the fault, and the waveform after the time origin is the waveform after the fault. Preferably, the time period τ is 20ms.

[0074] Starting from the origin of time, record the waveform after the fault once every time interval τ;

[0075] The changes in the three-phase differential current sampling values ​​of the transformer are obtained by subtracting the pre-fault waveform from the post-fault waveform recorded each time. This is the sequence of changes in the three-phase differential current sampling values ​​of the transformer. The number of samplings depends on the length of the fault waveform. Starting from the time origin and continuing until the end of the waveform, the post-fault waveform is recorded once every time interval.

[0076] 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.

[0077] Step 2: Sum the changes in the three-phase differential currents in the sequence obtained in Step 1 for each phase to obtain the differential current of the three-phase current changes, and then obtain the absolute value of the differential current;

[0078] That is, step 1 yields dI CD_A dI CD_B dI CD_C After sequencing, step 2 will extract all dI values ​​from the sequence. CD_A Summing these values ​​yields the differential current of phase A, and all dI CD_B Summing these values ​​yields the differential current of phase B, and all dI values ​​are calculated. CD_C Summing the values ​​yields the differential current of the C-phase current change. Taking the absolute value of the differential current gives the absolute value of each difference.

[0079] Step 3: Define the time origin when the fault occurs, at which time t is 0. As time t changes, the point corresponding to time t is called the current point. The set of 24 points consisting of the current point and the previous 23 points is used as the current period. Using the differential flow and the absolute value of the differential flow, the current period integral of the differential flow and the current period integral of the absolute value of the differential flow are calculated by recursion.

[0080]

[0081]

[0082] In the formula, 24′ k Represents the current period integral of the differential current, 24 k The current period integral represents the absolute value of the differential flow, with the subscript k indicating the current time point; δi Σi' Indicates the differential flow at point i'. Σi' The change in k is the differential current of the phase current change; as k changes, i' can guarantee that the differential current of the phase current change has been traversed through the current point and the previous 23 points; it can be understood as a time window. As k gradually increases, the length of i' is constant. No matter how k changes, the existence of i' can always keep the length of the time window at 24 points.

[0083] From the formula above, we know that the value of k at the current point needs to be greater than 23. Since the time origin is set to point 0, the points before the time origin can be understood as negative numbers, representing data before the fault. Therefore, when k is less than 23, 24 is calculated. k This involves data from before the fault occurred. Therefore, k needs to be greater than 23, at which point i' has a minimum value of 1, indicating that data from after the fault is retrieved.

[0084] Step 3 calculates 24′ k With 24 kThe process utilizes the concept of the current period, defined as a set of 24 points consisting of the current point and the previous 23 points. The calculation must not exceed this range. Any subsequent mention of the current period refers to this concept.

[0085] Step 4: Simultaneously, using the absolute value of the differential flow, take the 8 points with the smallest values ​​in the current period (which may not be continuous), calculate their integral, and obtain the T / 3 period integral. Subtract the T / 3 period integral from the current period integral of the absolute value of the differential flow to obtain the 2T / 3 period integral.

[0086] max 2T / 3 =24 k -min T / 3

[0087] In the formula, min T / 3 Represents the integral over a period of T / 3, max 2T / 3 This represents an integral over 2T / 3 periods;

[0088] In step 4, when calculating the T / 3 cycle integral, it is necessary to select the 8 points with the smallest absolute value of the differential current in the current cycle. These 8 points do not need to be continuous, so as to ensure that they are not affected by the discontinuity angle after CT saturation, and to highlight the concavity and bulge of the waveform.

[0089] Step 5: Then, using the absolute value of the differential flow, calculate the sum of the maximum and second maximum values ​​within the current cycle, which will be used as the maximum number of the absolute value of the differential flow at point 2.

[0090] Step 6: Determine whether the T / 3 cycle integral, 2T / 3 cycle integral, the sum of the two largest values ​​of the differential current absolute value, and the absolute value of the current cycle integral satisfy the ferromagnetic saturation and inrush current criteria that reflect the current waveform convexity and convexity deviation. If they are satisfied, it is determined to be inrush current or CT saturation, and the differential protection is blocked.

[0091] If the ratio of the sum of the T / 3 cycle integral and the sum of the two maximum values ​​of the differential current absolute value is lower than a certain linear relationship between the ratio of the absolute value of the current cycle integral and the T / 3 cycle integral, then it is determined to be inrush flow or CT saturation, and the differential protection is blocked. The specific criteria are as follows:

[0092]

[0093] In the formula, Let represent the maximum absolute value of the differential flow at 2 points, and c and b represent the slope and intercept of the linear function of the dependent variable, with the ratio of the absolute value of the current period integral of the differential flow to the integral of T / 3 periods as the value.

[0094] Further preferably, to ensure that this criterion applies to both inrush closure and CT saturation discrimination, after verification and function fitting using typical inrush and multiple sets of CT saturation waveforms, the slope c is set to 0.016, and the intercept b is set as a function of time t:

[0095]

[0096] That is, when b = 0.0007t + 0.03, and 0.0007t + 0.03 ≥ 0.135, then b = 0.135.

[0097] Because in step 6, min T / 3 As the denominator, it must be ensured that it cannot be 0, but in the min... T / 3 During the calculation, if the current point is one of the first 8 points after the fault occurred, the result will be 0. Therefore, this criterion needs to have a threshold set, i.e., min. T / 3 ≥0.004I e , where I e This is the rated current for high voltage.

[0098] If the above threshold is not met, the protection is locked. If a fault exists, this threshold will be easily reached. The purpose of the threshold is to prevent the opening criterion from being falsely opened due to excessively low current.

[0099] Figure 2 , Figure 3 , Figure 4 This is a graph illustrating a linear relationship between the ratio of the T / 3 cycle integral to the sum of the maximum sum of the 2T / 3 cycle integral and the absolute value of the differential flow at two points when saturation, inrush, and fault occur, and the ratio of the absolute value of the current cycle integral to the T / 3 cycle integral. Figure 4 As shown, in the event of a minor fault, the left side of the inequality in step 6 quickly becomes greater than the right side of the inequality, thus opening the protection.

[0100] Embodiment 2 of the present invention provides a ferromagnetic saturation and inrush current discrimination device that reflects the convexity and concavity of current waveform. The device includes: a data acquisition module, a calculation module, and a lockout enable module.

[0101] The acquisition module is used to obtain the three-phase differential current waveform based on the three-phase current on each side of the transformer, and to acquire the change sequence of the three-phase differential current of the transformer based on the three-phase differential current waveform.

[0102] The modulus calculation module is used to calculate the differential current and absolute value of the three-phase current change, the current-cycle integral of the differential current and the current-cycle integral of the absolute value of the differential current, the T / 3 cycle integral, the 2T / 3 cycle integral, and the maximum number of the absolute value of the differential current at two points; preferably, the modulus calculation unit includes three independent registers.

[0103] The lockout enable module is used to determine whether the differential protection is inrush current or CT saturation when the T / 3 cycle integral, 2T / 3 cycle integral, the sum of the two maximum values ​​of the differential current absolute value, and the absolute value of the current cycle integral of the differential current meet the ferromagnetic saturation and inrush current criteria that reflect the current waveform convexity and convexity deviation.

[0104] The beneficial effects of this invention are compared with those of the prior art:

[0105] 1. This invention is applicable to the discrimination of inrush flow and also to the discrimination of CT saturation. Only when the ratio of the sum of the T / 3 cycle integral and the sum of the two largest values ​​of the differential flow absolute value is lower than a certain linear relationship between the absolute value of the current cycle integral and the T / 3 cycle integral, it can reflect the occurrence of inrush flow or CT saturation, thereby locking the protection. It uses the same criterion to achieve effective identification of inrush flow and saturation.

[0106] 2. This invention does not use Fourier series, so that the instability caused by cross-window calculation can be ignored when the device is running;

[0107] 3. When calculating the T / 3 cycle integral, this invention abandons the traditional concept of taking the smallest discontinuity from 8 consecutive points. Instead, it selects the 8 smallest points (which may not be consecutive) within the current cycle. This better reflects the position of the discontinuity within the current cycle and highlights the concavity and convexity of the waveform, reflecting the concavity and convexity shift of the current waveform.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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 method for determining ferromagnetic saturation and inrush current based on the deviation of current waveform, characterized in that: The method includes the following steps: Step 1: Obtain the three-phase differential current waveform based on the three-phase current on each side of the transformer, and collect the change sequence of the three-phase differential current of the transformer based on the three-phase differential current waveform; Step 2: Sum the changes in the three-phase differential currents in the sequence obtained in Step 1 for each phase to obtain the differential current of the three-phase current changes, and then obtain the absolute value of the differential current; Step 3: Using the current time point and the previous 23 time points as the current period, calculate the current period integral of the differential flow and the current period integral of the absolute value of the differential flow; the formulas for calculating the current period integral of the differential flow and the current period integral of the absolute value of the differential flow are as follows: In the formula, Represents the current period integral of the differential flow; The current period integral represents the absolute value of the differential flow; the subscript k indicates the current time point, and k is greater than 23; Indicates the first Spread flow The change in; Step 4: For the absolute value of the differential flow, take the 8 points with the smallest values ​​in the current period, calculate its integral, and obtain the T / 3 period integral. Subtract the T / 3 period integral from the current period integral of the absolute value of the differential flow to obtain the 2T / 3 period integral. Step 5: For the absolute value of the differential flow, calculate the sum of the maximum and second maximum values ​​within the current cycle, and use this sum as the maximum number of the absolute value of the differential flow at point 2. Step 6: Determine whether the T / 3 cycle integral, 2T / 3 cycle integral, the maximum number of differential current absolute values ​​at 2 points, and the absolute value of the current cycle integral of the differential current satisfy the ferromagnetic saturation and inrush current criteria that reflect the current waveform convexity and convexity deviation. If they are satisfied, it is determined to be inrush current or CT saturation, and the differential protection is blocked.

2. The method for determining ferromagnetic saturation and inrush current based on the deviation of current waveform according to claim 1, characterized in that: Step 1 specifically includes: Step 1.1: Collect the three-phase current of the high-voltage side branch of the transformer. , , The three-phase current of the medium-voltage side branch , , Three-phase current of the low-voltage side branch , , ; Step 1.2: Based on the three-phase current data of each branch collected in Step 1.1, calculate the three-phase differential current and generate the three-phase differential current waveform: In the formula, , , These are the differential currents for phases A, B, and C, respectively. Step 1.3: Based on the three-phase differential current waveform, collect the change in the three-phase differential current. , and sequence.

3. The method for determining ferromagnetic saturation and inrush current based on the deviation of current waveform according to claim 2, characterized in that: In step 1.1, when collecting the three-phase current data of each branch of the transformer, the sampling rate is greater than 1200Hz, and there are no less than 24 sampling points in one sampling period.

4. The method for determining ferromagnetic saturation and inrush current based on the deviation of current waveform according to claim 1 or 2, characterized in that: When collecting the sequence of changes in the three-phase differential current of a transformer, for the three-phase differential current waveform, the time origin is the moment of 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 origin of time, each time interval Record the waveform after a fault; The sequence of changes in the three-phase differential current of the transformer is obtained by subtracting the waveform before the fault from the waveform recorded after each fault.

5. The method for determining ferromagnetic saturation and inrush current based on the deviation of current waveform according to claim 4, characterized in that: Time period The value is 20ms.

6. The method for determining ferromagnetic saturation and inrush current based on the deviation of current waveform according to claim 1, characterized in that: In step 6, the ferromagnetic saturation and inrush current criteria reflecting the current waveform's convexity / convexity shift are as follows: In the formula, This represents the largest number of the absolute value of the differential flow at 2 points; Indicates the integral over a period of T / 3; This represents an integral over 2T / 3 periods; c and b represent the slope and intercept of a linear function of the dependent variable, with the ratio of the absolute value of the current period integral to the T / 3 period integral as the value of the integral.

7. A method for determining ferromagnetic saturation and inrush current based on the deviation of current waveform according to claim 1 or 6, characterized in that: The ferromagnetic saturation and inrush current criteria, which reflect the convexity and convexity of the current waveform, have the following usage thresholds: in, Indicates the integral over a period of T / 3; Indicates the rated current of the high voltage; If the above thresholds are not met, then the system will lock out.

8. The method for determining ferromagnetic saturation and inrush current based on the deviation of current waveform according to claim 6, characterized in that: The slope c is 0.016, and the intercept b is a function of time t: 。 9. A device for determining ferromagnetic saturation and inrush current based on the deviation of current waveform, utilizing the method described in any one of claims 1-8, characterized in that: The device includes: The acquisition module is used to obtain the three-phase differential current waveform based on the three-phase current on each side of the transformer, and to acquire the change sequence of the three-phase differential current of the transformer based on the three-phase differential current waveform. The modulus calculation module is used to calculate the differential current and absolute value of the three-phase current change, the current cycle integral of the differential current and the current cycle integral of the absolute value of the differential current, the T / 3 cycle integral, the 2T / 3 cycle integral, and the maximum number of the absolute value of the differential current at two points. The lockout enable module is used to determine whether the current surge is inrush or the current transformer (CT) is saturated when the T / 3 cycle integral, 2T / 3 cycle integral, the maximum number of differential current absolute values ​​at 2 points, and the absolute value of the current ...

10. The ferromagnetic saturation and inrush current discrimination device reflecting the convexity and convexity of current waveform according to claim 9, characterized in that: Different calculation processes in the modulus calculation unit are performed using independent registers.

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