Quadrant-based current transformer saturation identification method, system, device, and medium

Abstract

The application relates to the technical field of current transformer saturation identification, and discloses a current transformer saturation identification method, system, equipment and medium based on a quadrant, which comprises the following steps: sampling a differential current to obtain a differential current sample value, dividing a sampling time period to obtain a cycle time window; obtaining a differential current change amount of the sampling time period and the cycle time window according to the differential current sample value; calculating a differential current change coefficient according to the differential current change amount of the cycle time window, and calculating a differential current continuous coefficient according to the differential current change coefficient and the differential current change amount of the sampling time period; summing and calculating the differential current sample values of the cycle time window, performing extreme value screening on the differential current sample sum, performing axial analysis, and obtaining an off-axis coefficient; constructing a coordinate value according to the differential current continuous coefficient and the off-axis coefficient, and determining the saturation type of the current transformer according to the quadrant to which the coordinate value belongs. The application can accurately identify the saturation state of the current transformer and improve the reliability of the saturation locking protection of the current transformer.

Description

Technical Field

[0001] This invention relates to the field of current transformer saturation identification technology, and in particular to a quadrant-based current transformer saturation identification method, system, device and medium. Background Technology

[0002] Transformers are core equipment in power grids, playing a vital role in the entire power system. In engineering, transformer main protection typically employs a ratio-controlled current differential protection scheme to ensure timely fault isolation within the transformer's protection zone. However, due to the different voltage levels on each side of the transformer, the corresponding current transformers (CTs) differ in parameters such as capacity, turns ratio, rated current, and rated secondary load. Therefore, the same model of CT cannot be used on each side. Under external fault conditions, if transient saturation occurs on each side of the transformer's CTs, the degree of saturation may vary, leading to a significant increase in unbalanced current. Especially when a CT on one side of the transformer is severely saturated while others are not, a large-amplitude false differential current may be generated, exhibiting characteristics similar to an internal fault, thus causing maloperation of the transformer differential protection.

[0003] Existing CT saturation blocking criteria mostly employ harmonic content, time-difference method, and differential current change rate, but these methods all have certain limitations. For example, the time-difference method requires precise location of the fault occurrence and differential current occurrence. When the difference between these two times is very small, the location may be inaccurate, leading to significant deviations in the detection results and causing maloperation of the differential protection. Harmonic content and differential current change rate criteria are easily affected by external factors, impacting the accuracy of identification. Furthermore, current transformers can also experience a saturation state where the CT operates completely above the saturation inflection point, with very low harmonic content. The electrical characteristics of this saturation state are completely different from other saturation states, and existing technologies cannot effectively identify this special saturation state, thus failing to ensure the reliability of transformer differential protection. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a quadrant-based method, system, device, and medium for identifying current transformer saturation. By analyzing the continuity and axiality of the differential current, it can accurately identify current transformer saturation under differential protection conditions, thereby improving the reliability of current transformer saturation blocking protection.

[0005] In a first aspect, the present invention provides a quadrant-based method for identifying saturation in current transformers, the method comprising: In response to the detection of differential current in the transformer, the differential current is sampled according to a preset sampling time period to obtain differential current sample value, and the sampling time period is divided into time windows to obtain multiple cyclic time windows; Based on the differential current sampling values, the differential current changes during the sampling time period and each cycle time window are obtained respectively; Based on the differential current change in each cycle time window, calculate the differential current change coefficient for each cycle time window, and based on the differential current change coefficient and the differential current change in the sampling time period, calculate the differential current continuity coefficient for the sampling time period. The differential current sampling values ​​of each cycle time window are summed, and the extreme values ​​of the differential current sampling values ​​of each cycle time window are screened. Based on the screened extreme values, axial analysis is performed to obtain the off-axis coefficient. Based on the differential current continuity coefficient and the off-axis coefficient, coordinate values ​​are constructed, and the saturation type of the current transformer is determined according to the quadrant to which the coordinate values ​​belong in the coordinate system.

[0006] Furthermore, the step of calculating the differential current variation coefficient for each cycle time window based on the differential current variation for each cycle time window includes: Calculate the difference component of the differential flow change based on the differential flow change in each cycle time window; The differential flow change and the differential component are summed to obtain the differential flow change coefficient for each cycle time window.

[0007] Further, the step of calculating the differential current continuity coefficient for the sampling time period based on the differential current variation coefficient and the differential current variation during the sampling time period includes: The minimum value among the differential current variation coefficients of all cyclic time windows is taken as the differential current variation coefficient of the sampling time period, and the differential current variation of the sampling time period is added together to obtain the differential current variation and value of the sampling time period. The ratio of the differential flow variation coefficient during the sampling period to the sum of the differential flow changes during the sampling period is used as the initial differential flow continuity coefficient. The initial differential flow continuity coefficients are subjected to interval transformation and normalization to obtain the differential flow continuity coefficients for the sampling time period.

[0008] Further, the step of performing interval transformation and normalization on the initial differential flow continuity coefficients to obtain the differential flow continuity coefficients for the sampling time period includes: The coefficient range of the initial differential current continuity coefficient is determined based on the saturation type of the current transformer; Based on the end values ​​of the coefficient interval, a translation coefficient is determined, and the coefficient interval of the initial differential flow continuity coefficient is translated according to the translation coefficient. Based on the duration of the sampling time period and the duration of the cyclic time window, the initial differential flow continuity coefficient after translation is normalized to obtain the differential flow continuity coefficient of the sampling time period.

[0009] Furthermore, the step of performing extreme value screening on the differential current sampling and values ​​of each calculated cycle time window, and performing axial analysis based on the screened extreme values ​​to obtain the off-axis coefficient includes: The maximum and minimum values ​​are selected from the differential sampling values ​​obtained from each cycle time window; Multiply the maximum value and the minimum value, and normalize the product to obtain the off-axis coefficient.

[0010] Further, the step of constructing coordinate values ​​based on the differential current continuity coefficient and the off-axis coefficient, and determining the saturation type of the current transformer based on the quadrant to which the coordinate values ​​belong in the coordinate system, includes: Using the differential continuity coefficient as the abscissa and the off-axis coefficient as the ordinate, construct coordinate values ​​and determine the quadrant to which the coordinate values ​​belong in the coordinate system; If the current transformer is determined to be in the first quadrant, it is considered to be in concealed saturation. If the current transformer is determined to be in transient saturation when its quadrant is the second quadrant; If the current transformer is determined to be in steady-state saturation because its quadrant is the third quadrant; If the quadrant is the fourth quadrant, the current transformer is determined to be in the zone fault.

[0011] Furthermore, the step of determining the quadrant to which the coordinate value belongs in the coordinate system includes: Determine whether the coordinate value is within the preset inner ring area; if so, scale the coordinate value proportionally using dual-axis coordinates. Determine the quadrant based on the magnified coordinate values.

[0012] Secondly, the present invention provides a quadrant-based current transformer saturation identification system, the system comprising: The differential current sampling module is used to sample the differential current according to a preset sampling time period in response to the detection of the differential current of the transformer, obtain the differential current sampling value, and divide the sampling time period into time windows to obtain multiple cyclic time windows. The continuous analysis module is used to obtain the differential flow change during the sampling time period and each cycle time window based on the differential flow sampling value. Based on the differential current change in each cycle time window, calculate the differential current change coefficient for each cycle time window, and based on the differential current change coefficient and the differential current change in the sampling time period, calculate the differential current continuity coefficient for the sampling time period. The axial analysis module is used to sum the differential current sampling values ​​of each cycle time window, perform extreme value screening on the calculated differential current sampling values ​​of each cycle time window, and perform axial analysis based on the screened extreme values ​​to obtain the off-axis coefficient. The saturation identification module is used to construct coordinate values ​​based on the differential current continuity coefficient and the off-axis coefficient, and to determine the saturation type of the current transformer based on the quadrant to which the coordinate values ​​belong in the coordinate system.

[0013] Thirdly, embodiments of the present invention also provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described method.

[0014] Fourthly, embodiments of the present invention also provide a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the above-described method.

[0015] This invention provides a quadrant-based method, system, device, and storage medium for identifying the saturation state of current transformers. Compared to traditional methods that require accurate location of the fault occurrence and differential current occurrence, detection of the current transformer's current transmission zone, and susceptibility to interference from various external parameters, this invention accurately identifies the saturation state of current transformers by analyzing the differential current continuity and axiality differences over a short time period. The algorithm is simple, fast, and reliable, significantly improving the reliability of current transformer saturation blocking protection. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the quadrant-based current transformer saturation identification method in an embodiment of the present invention. Figure 2 This is a schematic diagram of the differential current under transient saturation state in an embodiment of the present invention; Figure 3 This is a schematic diagram of the differential current under the concealed saturation state in an embodiment of the present invention; Figure 4 This is a schematic diagram of the differential current under steady-state saturation in an embodiment of the present invention; Figure 5 This is a schematic diagram of the differential current under fault conditions within the zone in an embodiment of the present invention; Figure 6 This is a schematic diagram of the fault type quadrant criterion in an embodiment of the present invention; Figure 7 This is a schematic diagram of the differential current in the concealed saturation experiment in this embodiment of the invention; Figure 8 This is a quadrant position diagram of the identification results of the concealed saturation experiment in an embodiment of the present invention; Figure 9 This is a schematic diagram of the differential current in the transient saturation experiment in this embodiment of the invention; Figure 10This is a quadrant position diagram of the identification results of the transient saturation experiment in this embodiment of the invention; Figure 11 This is a schematic diagram of the differential current in the steady-state saturation experiment in this embodiment of the invention; Figure 12 This is a quadrant position diagram of the identification results of the steady-state saturation experiment in this embodiment of the invention; Figure 13 This is a schematic diagram of the differential current in the fault experiment within the zone in this embodiment of the invention; Figure 14 This is a quadrant position diagram of the identification results of the fault test within the region in this embodiment of the invention; Figure 15 This is a schematic diagram of the quadrant-based current transformer saturation identification system in an embodiment of the present invention; Figure 16 This is an internal structural diagram of the computer device in an embodiment of the present invention.

[0017] Figure label: 10. Differential sampling module; 20. Continuity analysis module; 30. Axial analysis module; 40. Saturation identification module. Detailed Implementation

[0018] 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.

[0019] Please see Figure 1 The first embodiment of the present invention proposes a quadrant-based current transformer saturation identification method, including steps S10 to S50: Step S10: In response to the detection of differential current of transformer, the differential current is sampled according to a preset sampling time period to obtain differential current sampling value, and the sampling time period is divided into time windows to obtain multiple cyclic time windows. Step S20: Based on the differential current sampling values, obtain the differential current change during the sampling time period and each cycle time window, respectively; Step S30: Calculate the differential current change coefficient for each cycle time window based on the differential current change amount for each cycle time window, and calculate the differential current continuity coefficient for the sampling time period based on the differential current change coefficient and the differential current change amount for the sampling time period. Step S40: Sum the differential current sampling values ​​for each cycle time window, perform extreme value screening on the calculated differential current sampling values ​​for each cycle time window, and perform axial analysis based on the screened extreme values ​​to obtain the off-axis coefficient. Step S50: Construct coordinate values ​​based on the differential current continuity coefficient and the off-axis coefficient, and determine the saturation type of the current transformer based on the quadrant to which the coordinate values ​​belong in the coordinate system.

[0020] Before detailing the saturation identification method for current transformers provided in this embodiment, a brief explanation of transformer differential protection and current transformer saturation is given first. Transformer differential protection is the main protection of the transformer, installed based on the circulating current principle. It is primarily used to protect against various phase-to-phase short-circuit faults occurring within the windings and leads of double-winding or triple-winding transformers, and can also protect against single-phase turn-to-turn short-circuit faults. Current transformers are installed on both sides of the winding transformer, with their secondary sides connected according to the circulating current method. That is, if the same polarity terminals of the current transformers on both sides face the busbar side, the same polarity terminals are connected, and a current relay is connected in series between the two connections. The current flowing through the relay coil is the difference in secondary currents of the two current transformers; in other words, the differential relay is connected in the differential circuit. Theoretically, the differential circuit current is zero during normal operation and external faults. In reality, due to reasons such as the characteristics of the two current transformers not being completely identical, an unbalanced current still flows through the differential circuit during normal operation and external short circuits. Therefore, the unbalanced current should be as small as possible to ensure that the relay does not malfunction.

[0021] A current transformer (CT) is a crucial component of transformer differential protection, used to measure current and detect transformer faults. Under normal conditions, the magnetic flux in the core of a current transformer is in an unsaturated state. At this time, the load impedance and excitation current are relatively small, while the excitation impedance is relatively large, and the magnetomotive forces of the primary and secondary windings are in equilibrium. If the magnetic flux density in the core of the current transformer increases and reaches saturation, the excitation impedance will decrease rapidly with increasing saturation. This disrupts the linear proportional relationship between different excitation currents, leading to distortion of the secondary current and affecting the reliability of the transformer differential protection.

[0022] External faults are a common cause of current transformer saturation. Currently, current transformer saturation is mainly classified into two types: steady-state saturation and transient saturation. Steady-state saturation is caused by a large-capacity, steady-state symmetrical short-circuit current, while transient saturation is caused by the presence of non-periodic components in the short-circuit current and residual magnetism in the core. These two types of saturation have significantly different characteristics. Furthermore, when a current transformer (CT) saturates and, with the accumulation of magnetic flux, operates almost entirely above the core saturation inflection point, the permeability and equivalent excitation reactance remain essentially constant, with no alternation between saturation and desaturation. The second harmonic content of the CT's secondary current is very small. The electrical characteristics at this point are completely different from those of conventional transient saturation. This embodiment defines this saturation state as CT hidden saturation. Hidden saturation is a saturation state under special operating conditions and is not necessarily present. However, conventional saturation identification methods cannot accurately determine this saturation state. Therefore, this embodiment provides a method for accurately identifying the saturation type of a current transformer to prevent maloperation of differential protection.

[0023] The differential current of a transformer refers to the vector difference between the currents on the high-voltage side and the low-voltage side. The current characteristics of the differential current differ under different conditions, such as different saturation states caused by external faults and internal faults. For example, the differential current under transient saturation conditions... Figure 2 As shown, when the CT experiences transient saturation, the differential current is either constantly positive or constantly negative, and there is a period within one cycle during which the differential current is close to zero; the differential current under the hidden saturation state is as follows: Figure 3 As shown, when the CT experiences hidden saturation, the differential current is either constantly positive or constantly negative, and there is essentially no situation where the differential current is zero within one cycle; the differential current under steady-state saturation is as follows: Figure 4 As shown, when the CT reaches steady-state saturation, although the differential current can be positive or negative, there is a period of time within each cycle when the differential current is zero; the differential current under fault conditions within the zone is as follows: Figure 5 As shown, when a fault occurs in the transformer area, the differential current corresponds to the fault current. In a normal power system, various fault types can be approximately equivalent to a first-order RL circuit. The corresponding fault current is a decaying DC component superimposed with a power frequency component. Furthermore, the initial value of the DC component will not be greater than the amplitude of the power frequency component. Therefore, the differential current within one cycle must be both positive and negative, and there is basically no situation where the differential current is zero within one cycle.

[0024] Based on the above differential current characteristics, this embodiment starts differential current sampling when differential current is detected in the transformer, collects the differential current within a preset time period, and extracts multi-dimensional differential current characteristics from the collected values. In order to ensure that the relevant differential current characteristics can be accurately extracted in the future, the sampling time period should not be less than 20ms. This embodiment uses 20ms as the sampling time period and takes 4K sampling rate as an example to sample the differential current, and obtains a total of 80 sampling points, that is, 80 differential current sampling values.

[0025] Then, based on the sampling points within the sampling time period, time windows are divided. Taking 3ms as a loop time window as an example, a certain sampling point and the 11 sampling points after it are defined as a loop time window, which consists of 12 sampling points (3ms). For 80 sampling points, each sampling point and the multiple sampling points after it form a loop time window, so there are a total of 80 loop time windows. For the last loop time window, for the 11 sampling points that exceed the time period, the method of appending the data from the beginning to the end is used to cyclically supplement them.

[0026] Based on the collected differential current sampling values, the differential current change within each cycle time window and the differential current change throughout the entire sampling period are calculated. The differential current change refers to the difference in differential current between two adjacent sampling points. Then, based on the differential current change in each cycle time window, the differential current change within the cycle time window is analyzed. The specific steps include: Calculate the difference component of the differential flow change based on the differential flow change in each cycle time window; The differential flow change and the differential component are summed to obtain the differential flow change coefficient for each cycle time window.

[0027] In this embodiment, based on the differential current change within each cyclic time window, the difference component of the differential current change within that time window is calculated, that is, the difference between two adjacent differential current changes. Then, the differential current change and the difference component within the cyclic time window are summed to obtain the differential current change coefficient for the cyclic time window. In the formula, This represents the differential current variation coefficient for the k-th cycle time window. This represents the m-th differential current change within the k-th cycle time window. This represents the m-th difference component within the k-th cyclic time window.

[0028] The differential flow variation coefficient characterizes the variability of the differential flow; it is obtained when the differential flow continuously changes. A relatively large value corresponds to continuous differential current; when the differential current value remains essentially unchanged over a period of time, the obtained value is... The value is relatively small, corresponding to intermittent differential flow.

[0029] For each sampling point, a corresponding value can be calculated. Based on the calculated differential current variation coefficients and combined with the differential current variation over the sampling period, the differential current variation coefficient for the sampling period can be calculated. The specific steps include: The minimum value among the differential current variation coefficients of all cyclic time windows is taken as the differential current variation coefficient of the sampling time period; The ratio of the differential current variation coefficient during the sampling period to the differential current variation during the sampling period is used as the initial differential current continuity coefficient. The initial differential flow continuity coefficients are subjected to interval transformation and normalization to obtain the differential flow continuity coefficients for the sampling time period.

[0030] In this embodiment, the minimum value is selected from the calculated differential flow variation coefficients for each cycle time window. As the differential current variation coefficient for the sampling time period, taking 80 sampling points within a 20ms time period as an example, then... It is the minimum value among the differential flow variation coefficients of 80 cyclic time windows. This represents the part of the differential flow that is smoothest during the sampling period.

[0031] Then, the differential current changes over the sampling period are summed to obtain the sum of the differential current changes over the sampling period: In the formula, S represents the differential flow change and value during the sampling period. This represents the nth differential flow change during the sampling period.

[0032] The ratio of the differential current variation coefficient during the sampling period to the sum of the differential current variations during the sampling period (C) MIN The initial differential current continuity coefficient ( / S) is used to determine the differential current continuity of the cycle. Taking the above 20ms sampling time period, 3ms cycle time window, and 4K sampling rate as an example, during steady-state saturation and transient saturation, the CT has a linear transmission region, and the differential current has a period of time where the differential current value is basically constant. Therefore, the value of the initial differential current continuity coefficient is close to zero. During hidden saturation and in-range faults, the differential current is basically a standard sine wave after differential, so the value of the initial differential current continuity coefficient is about 0.3. In order to distinguish the above two cases by positive and negative relationships, it is also necessary to perform interval transformation and normalization on the initial differential current continuity coefficient. The specific steps include: The coefficient range of the initial differential current continuity coefficient is determined based on the saturation type of the current transformer; Based on the end values ​​of the coefficient interval, a translation coefficient is determined, and the coefficient interval of the initial differential flow continuity coefficient is translated according to the translation coefficient. Based on the duration of the sampling time period and the duration of the cyclic time window, the initial differential flow continuity coefficient after translation is normalized to obtain the differential flow continuity coefficient of the sampling time period.

[0033] In this embodiment, the initial differential current continuity coefficients under steady-state and transient saturation states and the initial differential current continuity coefficients under concealed saturation and intra-regional fault states are used as coefficient intervals. Taking the coefficient interval [0, 0.3] as an example, it can be understood that the two extreme values ​​of this coefficient interval correspond to two different states. The mean of the two extreme values ​​is used as the shift coefficient to shift the interval. Subtracting the shift coefficient from the initial differential current continuity coefficient, the coefficient interval is shifted to [-0.15, 0.15]. At this point, the extreme values ​​corresponding to different states can be distinguished by positive and negative values. That is, the initial differential current continuity coefficients under steady-state and transient saturation states are negative, and the initial differential current continuity coefficients under concealed saturation and intra-regional fault states are positive. Finally, the ratio of the sampling time period duration to the cyclic time window duration is used as the normalization coefficient. The normalization coefficient is multiplied by the shifted initial differential current continuity coefficient to achieve normalization processing, resulting in the final differential current continuity coefficient for the sampling time period, the expression of which is: In the formula, The differential continuity coefficient represents the sampling time period, α represents the normalization coefficient, and β represents the shift coefficient. Taking a 20ms sampling time period, a 3ms loop time window, and a 4K sampling rate as an example, then α = 20ms / 3ms = 6.667, and β = 0.15.

[0034] Based on the above calculation process of the differential current continuity coefficient during the sampling time period, it can be seen that the differential current continuity coefficient is negative under steady-state saturation and transient saturation conditions, and positive under hidden saturation and intra-regional fault conditions. However, the differential current continuity coefficient based on the sampling time period still cannot distinguish between steady-state saturation and transient saturation, nor can it distinguish between hidden saturation and intra-regional faults. Therefore, this embodiment performs axial analysis based on the sum of the differential current sampling values ​​of each cycle time window to further distinguish different types of saturation states. The specific steps include: The maximum and minimum values ​​are selected from the differential sampling values ​​obtained from each cycle time window; Multiply the maximum value and the minimum value, and normalize the product to obtain the off-axis coefficient.

[0035] In this embodiment, the differential current sampled values ​​within each cyclic time window are first summed to obtain the differential current sampled sum value for each cyclic time window, which is expressed as follows: In the formula, This represents the differential sampling sum value of the k-th cycle time window. This represents the m-th differential current sample value of the k-th cyclic time window.

[0036] The maximum value is selected from the sequence of differential sampling values ​​for all calculated cycle time windows. and minimum value This can be understood as, and These represent the sum of the sampled values ​​of the differential flow peak and the differential flow trough within the sampling time period, respectively.

[0037] Then calculate and The product of these factors and normalized results in the off-axis coefficient for a single half-axis: In the formula, Indicates the off-axis coefficient. This represents the maximum differential sampling value. This represents the maximum differential sampling value. This represents the normalized reference value, which is the square of the largest absolute value in the sequence of absolute values ​​of the differential sampling sums.

[0038] This embodiment determines the axiality of the differential flow through the off-axis coefficient. Based on the differential flow characteristics under different saturation states, it can be seen that in the hidden saturation and transient saturation states, the differential flow is biased towards one half-axis (i.e., constantly positive or constantly negative). Therefore... and The same sign corresponds to It is a positive value; under steady-state saturation and fault conditions within the region, the differential current can be both positive and negative, therefore, and For different signs, the corresponding It is a negative value.

[0039] As can be seen from the above embodiments, the sign of the differential current continuity coefficient during the sampling time period can distinguish between steady-state saturation and transient saturation, and between hidden saturation and fault conditions within the region. Similarly, the sign of the off-axis coefficient can distinguish between hidden saturation and transient saturation, and between steady-state saturation and fault conditions within the region. Therefore, by combining the differential current continuity coefficient and off-axis coefficient during the sampling time period, accurate differentiation of steady-state saturation, transient saturation, hidden saturation, and fault conditions within the region can be achieved. The specific steps include: Using the differential continuity coefficient as the abscissa and the off-axis coefficient as the ordinate, construct coordinate values ​​and determine the quadrant to which the coordinate values ​​belong in the coordinate system; If the current transformer is determined to be in the first quadrant, it is considered to be in concealed saturation. If the current transformer is determined to be in transient saturation when its quadrant is the second quadrant; If the current transformer is determined to be in steady-state saturation because its quadrant is the third quadrant; If the quadrant is the fourth quadrant, the current transformer is determined to be in the zone fault.

[0040] In this embodiment, the differential continuity coefficient is used. x-axis, off-axis coefficient Construct a coordinate system with the y-axis as the axis. Use the calculated differential flow continuity coefficient and off-axis coefficient to form coordinate values, and determine the quadrant position of these coordinate values ​​within the coordinate system. Different quadrant positions characterize the positive or negative signs of the differential flow continuity coefficient and off-axis coefficient. Different saturation states can be accurately identified through the positive and negative combinations of these coefficients. Therefore, the fault type can be comprehensively determined by the quadrant position of the coordinate values. The quadrant criteria are as follows: Figure 6 As shown, when the coordinate value is in the first quadrant, the differential current continuity coefficient is positive, indicating that the fault type is either concealed saturation or an intra-zone fault. The positive off-axis coefficient further confirms the fault type as concealed saturation. Similarly, when the coordinate value is in the second quadrant, the differential current continuity coefficient is negative, and the off-axis coefficient is positive, indicating the fault type as transient saturation. When the coordinate value is in the third quadrant, both the differential current continuity coefficient and the off-axis coefficient are negative, indicating the fault type as steady-state saturation. When the coordinate value is in the fourth quadrant, the differential current continuity coefficient is positive, and the off-axis coefficient is negative, indicating the fault type as an intra-zone fault.

[0041] Furthermore, such as Figure 6 As shown, since the differential continuity coefficient and the off-axis coefficient are normalized during the calculation process, the values ​​of the two coefficients will not exceed 1. Preferably, the outer ring radius of the quadrant criterion diagram is 1.5 and the inner ring radius is 0.5. In order to avoid misjudgment near the origin, for the case where the coordinate value is in the inner circle, the method of proportionally enlarging the dual-axis coordinate is adopted so that the final coordinate value falls in the ring, thereby ensuring the accuracy of the criterion judgment.

[0042] The identification effect of this embodiment is verified through experiments below. In this experiment, the method provided in this embodiment is used to identify different fault types. The fault types to be identified include current transformer hidden saturation, transient saturation, steady-state saturation caused by external faults, and internal faults. When an external fault is accompanied by CT hidden saturation, its differential current is as follows: Figure 7 As shown, after an external short-circuit fault occurs on the low-voltage side of the transformer, a large through-fault current flows through the transformer, causing the low-voltage side CT to become hidden saturated, resulting in a loss of transmission current and the appearance of differential current. Protection is activated when the absolute value of the differential current exceeds 2A. Figure 7 As shown in the starting point, the differential current continuity coefficient is calculated with a time interval of 20ms. and off-axis coefficient The quadrant positions are obtained by calculating coefficients over multiple time periods, as shown below. Figure 8 As shown, the coordinate values ​​calculated over multiple time periods are all located in the first quadrant. Therefore, it can be determined that the fault type is concealed saturation, and the transformer differential protection is blocked at this time.

[0043] Similarly, when an external fault is accompanied by transient saturation of the CT, its differential current is as follows: Figure 9 As shown, the calculated differential continuity coefficient and off-axis coefficient Quadrant position such as Figure 10 As shown, the coordinate values ​​calculated over multiple time periods are all located in the second quadrant, thus confirming that the fault type is transient saturation, at which point the transformer differential protection is blocked.

[0044] When an external fault is accompanied by steady-state saturation of the CT, its differential current is as follows: Figure 11 As shown, the calculated differential continuity coefficient and off-axis coefficient Quadrant position such as Figure 12 As shown, the coordinate values ​​calculated during this time period are in the third quadrant, so it can be determined that the fault type is steady-state saturation, and at this time the transformer differential protection is blocked.

[0045] When the faulty CT in the zone does not saturate, its differential current is as follows: Figure 13 As shown, its calculated differential continuity coefficient and off-axis coefficient Quadrant position such as Figure 14 As shown, the coordinate values ​​calculated over multiple time periods are all located in the fourth quadrant, confirming the fault type as an intra-zone fault. In this case, the differential protection is activated. The experimental results demonstrate that the method provided in this embodiment can accurately identify current transformer saturation, ensuring the correct operation of the transformer protection and thus improving its reliability.

[0046] This embodiment provides a quadrant-based current transformer saturation identification method. Compared with traditional methods, which require accurate location of the fault occurrence time and differential current occurrence time, need to detect the current transformer's current transmission zone, and are easily affected by various external parameters, this embodiment can accurately identify the saturation state of the current transformer by performing differential current continuity and axial difference analysis on the differential current within a short time period. The algorithm is simple, fast, and reliable, significantly improving the reliability of current transformer saturation blocking protection.

[0047] Please see Figure 15 Based on the same inventive concept, the second embodiment of this invention proposes a quadrant-based current transformer saturation identification system, comprising: The differential current sampling module 10 is used to sample the differential current according to a preset sampling time period in response to the detection of the differential current of the transformer, obtain the differential current sampling value, and divide the sampling time period into time windows to obtain multiple cyclic time windows. The continuous analysis module 20 is used to obtain the differential flow change during the sampling time period and each cycle time window based on the differential flow sampling value. Based on the differential current change in each cycle time window, calculate the differential current change coefficient for each cycle time window, and based on the differential current change coefficient and the differential current change in the sampling time period, calculate the differential current continuity coefficient for the sampling time period. The axial analysis module 30 is used to sum the differential current sampling values ​​of each cycle time window, perform extreme value screening on the calculated differential current sampling values ​​of each cycle time window, and perform axial analysis based on the screened extreme values ​​to obtain the off-axis coefficient. The saturation identification module 40 is used to construct coordinate values ​​based on the differential current continuity coefficient and the off-axis coefficient, and to determine the saturation type of the current transformer based on the quadrant to which the coordinate values ​​belong in the coordinate system.

[0048] The technical features and effects of the quadrant-based current transformer saturation identification system proposed in this invention are the same as those of the method proposed in this invention, and will not be repeated here. Each module in the quadrant-based current transformer saturation identification system can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0049] Furthermore, embodiments of the present invention also propose a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described method.

[0050] Please see Figure 16 The diagram illustrates the internal structure of a computer device in one embodiment. This computer device can specifically be a terminal or a server. The computer device includes a processor, memory, network interface, display, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The network interface of the computer device is used to communicate with external terminals via a network connection. When the computer program is executed by the processor, it implements a quadrant-based current transformer saturation identification method. The display screen of the computer device can be a liquid crystal display (LCD) or an e-ink display. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad mounted on the computer device's casing, or an external keyboard, touchpad, or mouse.

[0051] Those skilled in the art will understand that Figure 16 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computing devices may include more or fewer components than those shown in the figure, or combine certain components, or have the same component arrangement.

[0052] Furthermore, embodiments of the present invention also propose a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the above-described method.

[0053] In summary, the embodiments of this invention propose a quadrant-based current transformer saturation identification method, system, device, and medium. The method, in response to the detection of differential current in the transformer, samples the differential current according to a preset sampling time period to obtain differential current sample values. The sampling time period is divided into multiple cyclic time windows. Based on the differential current sample values, the differential current change amount for each sampling time period and each cyclic time window is obtained. Based on the differential current change amount for each cyclic time window, a differential current change coefficient for each cyclic time window is calculated. Based on the differential current change coefficient and the differential current change amount for the sampling time period, a differential current continuity coefficient for the sampling time period is calculated. The differential current sample values ​​for each cyclic time window are summed. Extreme value screening is performed on the calculated differential current sample sum values ​​for each cyclic time window, and axial analysis is performed based on the screened extreme values ​​to obtain an off-axis coefficient. Based on the differential current continuity coefficient and the off-axis coefficient, coordinate values ​​are constructed, and the saturation type of the current transformer is determined according to the quadrant to which the coordinate values ​​belong in the coordinate system. This invention analyzes the difference in differential current continuity and axiality over a short time period, which can accurately identify the saturation state of the current transformer, thereby significantly improving the reliability of the current transformer saturation blocking protection.

[0054] The various embodiments in this specification are described in a progressive manner. For directly identical or similar parts of the embodiments, refer to each other. Each embodiment focuses on its differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. It should be noted that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0055] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the technical principles of this invention, and these improvements and substitutions should also be considered within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the scope of the claims.

Claims

1. A quadrant-based current transformer saturation identification method, characterized by, include: In response to the detection of differential current in the transformer, the differential current is sampled according to a preset sampling time period to obtain differential current sample value, and the sampling time period is divided into time windows to obtain multiple cyclic time windows; Based on the differential current sampling values, the differential current changes during the sampling time period and each cycle time window are obtained respectively; Based on the differential current change in each cycle time window, calculate the differential current change coefficient for each cycle time window, and based on the differential current change coefficient and the differential current change in the sampling time period, calculate the differential current continuity coefficient for the sampling time period, including: The minimum value among the differential current variation coefficients of all cyclic time windows is taken as the differential current variation coefficient of the sampling time period, and the differential current variation of the sampling time period is added together to obtain the differential current variation and value of the sampling time period. The ratio of the differential flow variation coefficient during the sampling period to the sum of the differential flow changes during the sampling period is used as the initial differential flow continuity coefficient. The initial differential flow continuity coefficients are subjected to interval transformation and normalization to obtain the differential flow continuity coefficients for the sampling time period; The differential current sampled values ​​for each cycle time window are summed. Extreme value filtering is performed on the calculated differential current sampled values ​​for each cycle time window. Axial analysis is then conducted based on the filtered extreme values ​​to obtain the off-axis coefficients, including: The maximum and minimum values ​​are selected from the differential sampling values ​​obtained from each cycle time window; Multiply the maximum value and the minimum value, and normalize the product to obtain the off-axis coefficient; Based on the differential current continuity coefficient and the off-axis coefficient, coordinate values ​​are constructed, and the saturation type of the current transformer is determined according to the quadrant to which the coordinate values ​​belong in the coordinate system.

2. The quadrant-based current transformer saturation identification method according to claim 1, characterized in that, The step of calculating the differential current variation coefficient for each cycle time window based on the differential current variation for each cycle time window includes: Calculate the difference component of the differential flow change based on the differential flow change in each cycle time window; The differential flow change and the differential component are summed to obtain the differential flow change coefficient for each cycle time window.

3. The quadrant-based current transformer saturation identification method according to claim 1, characterized in that, The step of performing interval transformation and normalization on the initial differential current continuity coefficients to obtain the differential current continuity coefficients for the sampling time period includes: The coefficient range of the initial differential current continuity coefficient is determined based on the saturation type of the current transformer; Based on the end values ​​of the coefficient interval, a translation coefficient is determined, and the coefficient interval of the initial differential flow continuity coefficient is translated according to the translation coefficient. Based on the duration of the sampling time period and the duration of the cyclic time window, the initial differential flow continuity coefficient after translation is normalized to obtain the differential flow continuity coefficient of the sampling time period.

4. The quadrant-based current transformer saturation identification method according to claim 1, characterized in that, The step of constructing coordinate values ​​based on the differential current continuity coefficient and the off-axis coefficient, and determining the saturation type of the current transformer based on the quadrant to which the coordinate values ​​belong in the coordinate system, includes: Using the differential continuity coefficient as the abscissa and the off-axis coefficient as the ordinate, construct coordinate values ​​and determine the quadrant to which the coordinate values ​​belong in the coordinate system; If the current transformer is determined to be in the first quadrant, it is considered to be in concealed saturation. If the current transformer is determined to be in transient saturation when its quadrant is the second quadrant; If the current transformer is determined to be in steady-state saturation because its quadrant is the third quadrant; If the quadrant is the fourth quadrant, the current transformer is determined to be in the zone fault.

5. The quadrant-based current transformer saturation identification method according to claim 4, characterized in that, The step of determining the quadrant to which the coordinate value belongs in the coordinate system includes: Determine whether the coordinate value is within the preset inner ring area; if so, scale the coordinate value proportionally using dual-axis coordinates. Determine the quadrant based on the magnified coordinate values.

6. A quadrant-based current transformer saturation identification system, characterized in that, The system is applied to the method as described in any one of claims 1 to 5, comprising: The differential current sampling module is used to sample the differential current according to a preset sampling time period in response to the detection of the differential current of the transformer, obtain the differential current sampling value, and divide the sampling time period into time windows to obtain multiple cyclic time windows. The continuous analysis module is used to obtain the differential flow change during the sampling time period and each cycle time window based on the differential flow sampling value. Based on the differential current change in each cycle time window, calculate the differential current change coefficient for each cycle time window, and based on the differential current change coefficient and the differential current change in the sampling time period, calculate the differential current continuity coefficient for the sampling time period. The axial analysis module is used to sum the differential current sampling values ​​of each cycle time window, perform extreme value screening on the calculated differential current sampling values ​​of each cycle time window, and perform axial analysis based on the screened extreme values ​​to obtain the off-axis coefficient. The saturation identification module is used to construct coordinate values ​​based on the differential current continuity coefficient and the off-axis coefficient, and to determine the saturation type of the current transformer based on the quadrant to which the coordinate values ​​belong in the coordinate system.

7. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 5.

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