Transformer protection method and system based on excitation inductance parameter identification

Abstract

The invention discloses a transformer protection method and system based on excitation inductance parameter identification, and relates to the technical field of power system relay protection, and the method comprises the steps: judging whether protection is started or not based on a transformer differential current fault component criterion; constructing a transformer excitation branch voltage equation set for each sampling point at the protection starting moment and within 8-12 ms after protection starting based on a transformer T-type equivalent loop; and solving the transformer excitation branch voltage equation set based on a singular value decomposition method to obtain a transformer excitation inductance calculation value at the protection starting moment and within 8-12ms after protection starting. According to the method, the protection criterion is constructed based on excitation inductance parameter identification, and the essential characteristics of the transformer fault can be reflected; a branch equation is constructed through voltage and current instantaneous values, the excitation inductance is solved, the method does not depend on the power frequency quantity, and compared with transformer differential protection based on the power frequency electric quantity, the method is not affected by power source characteristics and is high in sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection in power systems, and particularly to a transformer protection method and system based on excitation inductance parameter identification. Background Art

[0002] A transformer is a key component for energy conversion and transmission in a power system. Reliable transformer protection is of great significance for the safe and stable operation of the power system. Since the pilot current differential protection has the characteristics of simple principle and high sensitivity, it is usually used as the main protection for transformers. In addition, in order to avoid misoperation of the current differential protection caused by inrush current, an inrush current identification criterion based on the second harmonic braking principle is widely used in the industry at present. The second harmonic braking principle is based on the characteristic that a large amount of second harmonic components are contained in the inrush current. When the second harmonic component in the differential current is detected to be greater than the setting value, the differential protection is blocked to prevent misoperation of the protection caused by inrush current.

[0003] Compared with traditional generators, the fault current provided by power electronic power supplies depends on their control strategies during faults and has typical characteristics of limited amplitude and controlled phase. Its "weak feed" characteristic will have a greater impact on relay protection. The access of power electronic devices in each link affects the amplitude, phase angle and frequency of the power frequency fault current. There are also significant differences in the harmonic characteristics of new energy power supplies compared with traditional synchronous generators. The above factors pose new challenges to traditional transformer protection. For example, for the transformer connected to a doubly-fed wind power generation unit, after an external fault occurs in the doubly-fed wind turbine generator set, since the motor rotor is connected to the Crowbar circuit to protect the converter, the frequency of the fault current output at the machine terminal is related to the rotor speed and the frequency shifts. At this time, the Fourier power frequency algorithm cannot accurately extract the second harmonic in the differential current, and the second harmonic component will be amplified by the Fourier power frequency algorithm, which may cause the differential protection to be wrongly blocked. For the power transmission transformer of a photovoltaic power station, since the short-circuit current provided by the photovoltaic power supply is very small, usually only 1.1 times the rated current, the differential calculation result is more biased towards the non-action area during the fault stage, the slope of the ratio restraint is small, and the sensitivity of the differential protection is insufficient. To sum up, the characteristics of new energy power supplies lead to a decline in the performance of traditional transformer differential protection and may even cause misoperation. Therefore, it is of great significance to propose a transformer protection method that is not affected by the power supply characteristics and avoids the influence of inrush current for the reliable operation of a new power system. Summary of the Invention

[0004] In view of the above existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a transformer protection method and system based on excitation inductance parameter identification, which can solve the problems mentioned in the background art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: A transformer protection method based on excitation inductance parameter identification, including: judging whether the protection is started based on the differential current fault component of the transformer;

[0007] Constructing a transformer excitation branch voltage equation set for each sampling point within 8 - 12 ms after the protection start time and at the protection start time based on the T-equivalent circuit of the transformer;

[0008] Solving the transformer excitation branch voltage equation set based on the singular value decomposition method to obtain the calculated value of the transformer excitation inductance within 8 - 12 ms after the protection start time and at the protection start time;

[0009] According to the protection action criterion reflecting the excitation inductance characteristics, judging whether there is a fault within the protection area of the transformer. If there is an internal fault, the protection acts; otherwise, the protection does not act.

[0010] As a preferred scheme of the transformer protection method based on excitation inductance parameter identification of the present invention, wherein: the criterion for protection start is as follows:

[0011] |i d (k) - i d (k - N sample )| > I dset

[0012] In the formula, i d is the differential current, k represents the kth sampling point, N sample is the number of sampling points in one cycle of the measuring device, and I dset is the setting value of the protection start criterion;

[0013] When the protection start criterion is satisfied, the protection starts.

[0014] As a preferred scheme of the transformer protection method based on excitation inductance parameter identification of the present invention, wherein:

[0015] The calculation method of the setting value of the protection start criterion is as follows:

[0016]

[0017] In the formula, K q is the reliability coefficient, which can take values from 1.0 to 2.0; I0 is the effective value of the no-load current of the transformer, which can be measured through the no-load test of the transformer. For transformers with no-load test parameters included in the nameplate, it can be directly calculated according to the corresponding nameplate parameters.

[0018] As a preferred embodiment of the transformer protection method based on excitation inductance parameter identification according to the present invention, wherein: the construction of the transformer excitation branch voltage equation set is specifically to construct a matrix of the transformer excitation branch voltage equation set with the excitation inductance parameters to be obtained, and the specific form is as follows:

[0019]

[0020] In the formula:

[0021]

[0022] In the formula, i1, i2, u1, and u2 are the phase currents and terminal voltages at both ends of the transformer, R m , L m are the resistance and inductance of the transformer excitation branch respectively, k represents the kth sampling point, and ΔT is the time interval between sampling points. For each sampling point at the protection startup moment and within 8 - 12 ms after the protection startup, the excitation branch voltage equation set is formed according to the above formula.

[0023] As a preferred embodiment of the transformer protection method based on excitation inductance parameter identification according to the present invention, wherein: the solution of the transformer excitation branch voltage equation set based on the singular value decomposition method includes:

[0024] For the coefficient matrix A of the excitation branch voltage equation set A k X k = B k at each sampling moment, perform singular value decomposition on the coefficient matrix A k as follows:

[0025] A k = U k Σ k V k T

[0026] In the formula, Σ k is the singular value matrix, the diagonal elements of which are the singular values of the coefficient matrix A k , and the non - diagonal elements are 0. U k , V k are the left singular vector matrix and the right singular vector matrix corresponding to the singular value matrix respectively;

[0027] Calculate the pseudo - inverse matrix of Σ k as follows: as follows:

[0028]

[0029] In the formula, i, j are matrix subscripts, and ε is the precision threshold for judging non - zero matrix elements, which is used to avoid the influence of calculation numerical errors; where ε is selected as ε = 1×10-8 ;;

[0030] The solutions of the voltage equations of the exciting branch at each sampling moment are calculated as follows:

[0031]

[0032] As a preferred solution of the transformer protection method based on exciting inductance parameter identification according to the present invention, wherein: the protection action criterion is specifically:

[0033]

[0034] In the formula, L m (0) is the calculated value of the exciting inductance at the protection starting moment, and L m (k) is the calculated values of all exciting inductances from 8 to 12 ms after the protection starts; when the protection criterion is satisfied, it is judged that there is an internal fault, otherwise there is no internal fault;

[0035] The calculation method of the setting value of the protection action criterion is as follows:

[0036]

[0037] In the formula, K d is the reliability coefficient, which can take 0.8 to 1.0; L m0 is the value of the exciting inductance during the normal operation of the transformer, which can be measured through the no-load test of the transformer. For a transformer with no-load test parameters included in the nameplate, it can be directly calculated according to the corresponding nameplate parameters; K b-min is the minimum value of the ratio of the magnetic permeability in the non-saturated state to the magnetic permeability in the saturated state of the magnetization characteristic curve of the transformer, and can be calculated by querying the corresponding magnetic permeability according to the type of silicon steel sheet of the transformer core.

[0038] To further solve the above technical problems, the present invention provides the following technical solution: a system for transformer protection based on exciting inductance parameter identification, including: a data processing module, which calculates the differential current, exciting inductance, etc. in the above steps according to the collected voltage and current data of each phase of the transformer;

[0039] A protection start module, which determines whether the subsequent protection action module starts according to the calculated differential current and the protection start criterion.

[0040] A protection action module, which determines whether the protection acts according to the protection action criterion of the calculated exciting inductance.

[0041] A computer device includes a memory and a processor. The memory stores a computer program. The processor, when executing the computer program, implements the steps of the transformer protection method based on exciting inductance parameter identification as described above.

[0042] A computer-readable storage medium stores a computer program thereon, wherein the computer program, when executed by a processor, implements the steps of the transformer protection method based on exciting inductance parameter identification as described above.

[0043] Advantages of the present invention: The present invention constructs a protection criterion based on exciting inductance parameter identification, which can reflect the essential characteristics of transformer faults. Secondly, a branch equation is constructed by instantaneous voltage and current values to solve the exciting inductance, without relying on power frequency quantities. Compared with the transformer differential protection based on power frequency electrical quantities, the present invention is not affected by power source characteristics and has high sensitivity. Thirdly, the protection criterion constructed by the present invention will not malfunction during inrush current, and has high reliability. Finally, the present invention can reliably operate within 12 ms after protection startup. Compared with the traditional ratio restraint differential protection that requires at least 20 ms to operate, the present invention has a faster action speed. Description of the Drawings

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for description in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0045] Figure 1 Schematic diagram of the T-equivalent circuit for constructing the voltage equation of the transformer exciting branch in the present invention;

[0046] Figure 2 Flowchart of the method in the present invention;

[0047] Figure 3 Value of the exciting inductance calculated by the method of the present invention during normal operation of the transformer in the present invention;

[0048] Figure 4 Value of the exciting inductance calculated by the method of the present invention during inrush current of the transformer in the present invention;

[0049] Figure 5 Value of the exciting inductance calculated by the method of the present invention during phase A fault of the transformer in the present invention;

[0050] Figure 6 Average value of the exciting inductance calculated by the method of the present invention during inrush current of the transformer in the present invention;

[0051] Figure 7 Value of the exciting inductance of the fault phase calculated by the method of the present invention during phase A fault of the transformer in the present invention;

[0052] Figure 8 Diagram of the computer device in the present invention; Detailed Embodiments

[0053] To make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given in conjunction with the accompanying drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0054] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0055] Example 1, referring to Figures 1 - 7 This is an embodiment of the present invention, which provides a transformer protection method based on the identification of excitation inductance parameters. The purpose is to provide a transformer protection method that is not affected by the power supply characteristics, does not malfunction during inrush current, and has a fast operation speed.

[0056] Considering the change in the topology of the transformer equivalent circuit, it can reflect the essential characteristics of internal faults in the transformer. The change in the topology of the transformer equivalent circuit is manifested as the change in its equivalent circuit parameters, which is not affected by the power supply characteristics and can reliably reflect the operating state of the transformer. Therefore, the following technical solutions are adopted in this method: a transformer protection method based on the identification of excitation inductance parameters, which includes the following steps in sequence:

[0057] S1: Judge whether the protection is started based on the differential current fault component criterion;

[0058] S2: Construct a voltage equation set of the transformer excitation branch for each sampling point at the protection start time and within 8 - 12 ms after the protection starts based on the T-type equivalent circuit of the transformer;

[0059] S3: Solve the voltage equation set of the transformer excitation branch based on the singular value decomposition method to obtain the calculated value of the transformer excitation inductance at the protection start time and within 8 - 12 ms after the protection starts;

[0060] S4: According to the protection action criterion reflecting the characteristics of the excitation inductance, judge whether there is a fault within the protection area of the transformer. If there is a fault within the area, the protection acts; otherwise, the protection does not act.

[0061] Step S1 is the protection start link, which specifically includes the following steps:

[0062] S11: Sample the currents of each phase on both sides of the transformer with a measuring device and calculate the differential current of each phase:

[0063] i d i(k) = i1(k) + i2(k)

[0064] Where, i1(k) and i2(k) are the instantaneous phase currents on the high - voltage side and low - voltage side of the transformer at the k - th sampling point respectively, and each phase current is converted to the high - voltage side of the transformer for calculation; i d (k) is the differential current of each phase of the transformer obtained by calculation, and the calculated differential current of each phase will be used to judge whether the protection starts in the next step.

[0065] S12: Judge whether the protection starts according to the fault component of the differential current of each phase. The protection start criterion is as follows:

[0066] |i d (k) - i d (k - N sample )| > I dset

[0067] Where, N sample is the number of sampling points in one cycle of the measuring device, i d (k) - i d (k - N sample ) is the fault component of the differential current, and I dset is the setting value of the protection start criterion. This protection start criterion can be described as when the absolute value of the fault component of the differential current between phases is greater than the setting value, the protection starts and enters step S2 for subsequent fault judgment. Otherwise, the protection will not start and step S1 will be repeated.

[0068] The setting principle of the protection start criterion is to ensure reliable non - start during the normal operation of the transformer. The specific setting value of the start criterion can be calculated by the following formula:

[0069]

[0070] Where, K q is the reliability coefficient, which can take values from 1.0 to 2.0; I0 is the effective value of the no - load current of the transformer, which can be measured through the no - load test of the transformer. For transformers with no - load test parameters in the nameplate, it can be directly calculated according to the corresponding nameplate parameters. That is, the peak value of the differential current corresponding to the normal operation of the transformer. Therefore, using the above setting value can ensure that the protection will not start during the normal operation of the transformer.

[0071] Steps S2 - S4 are for fault identification after the protection starts. Step S2 specifically includes the following steps:

[0072] S21: According to Figure 1 the T - type equivalent circuit of the transformer shown, establish the voltage equation of the excitation branch of the transformer as follows:

[0073]

[0074] In the formula, R m is the exciting resistance of the transformer exciting branch, and L m is the exciting inductance of the transformer exciting branch. i1, i2, u1, and u2 are the phase currents and voltages on both sides of the transformer respectively, and they have been converted to the high-voltage side of the transformer. k represents the value at the sampling point k.

[0075] S22: Since there are 2 parameters to be solved in the above formula and it is impossible to directly solve through 1 exciting branch voltage equation. To solve the exciting inductance at the kth sampling point, the exciting branch voltage equations are written respectively according to the sampling information at the kth to k + n sampling points to construct the transformer exciting branch equation set, where n is the number of sampling points corresponding to 2 ms. Let i m = i1 + i2, and after discretization by three-point numerical differentiation, the equation set of continuous sampling points is as follows:

[0076]

[0077] In the formula, ΔT is the time interval between two sampling points of the measuring device. It is considered that the parameters of the exciting branch will not change suddenly in a short time, so the exciting branch resistance and inductance in the equation set both take the values at the sampling point k. To facilitate the solution of the equation set, the transformer exciting branch voltage equation set is rewritten in matrix form as follows:

[0078]

[0079] The corresponding relationship between each matrix in the matrix form equation set and the original exciting branch voltage equation set is described as follows:

[0080]

[0081] S23: For each sampling point at the protection starting moment and within 8 - 12 ms after the protection starts, the exciting branch voltage equation set is formed according to S22:. In the next step, the exciting inductance at each sampling point will be obtained by solving the constructed exciting branch voltage equation set.

[0082] Step S3 is to solve the transformer exciting branch voltage equation set by the singular value decomposition method. The singular value decomposition method is a classic method for solving overdetermined equation sets and has strong numerical stability. It specifically includes the following steps:

[0083] S31: For the coefficient matrix A k X k = B k of the exciting branch voltage equation set at each sampling moment, the singular value decomposition is carried out as follows: k as follows:

[0084] A k= U k Σ k V k T

[0085] Wherein, Σ k The diagonal elements of are the singular values of the coefficient matrix A k and the non - diagonal elements are 0.

[0086] S32: Calculate the pseudo - inverse matrix of Σ k as follows: as follows:

[0087]

[0088] Wherein, ε is the precision threshold for judging non - zero matrix elements, used to avoid the influence of calculation numerical errors. In this method, ε = 1×10 -10 .

[0089] S33: Calculate the solutions of the excitation branch voltage equations at each sampling moment as follows:

[0090]

[0091] The solution X of the excitation branch voltage equations k contains the excitation inductance values at each sampling point. In the next step, the excitation inductance values calculated will be used to judge whether there is an internal fault in the transformer.

[0092] Step S4 specifically includes the following steps:

[0093] S41: Judge whether the calculated excitation inductance of the transformer meets the protection action criterion. The protection action criterion is as follows:

[0094]

[0095] Wherein, L m (0) is the calculated value of the excitation inductance at the protection startup moment, and L m (k) are all the calculated values of the excitation inductance from 8 to 12 ms after the protection startup. This protection criterion can be described as: after the protection starts, when the average value L av of the excitation inductance calculated from 8 to 12 ms is lower than the setting value L mset, it is determined that there is a fault within the zone; otherwise, there is no fault within the zone. The basis for setting this protection action criterion is as follows: When the transformer is operating normally, the iron core is not saturated, and the excitation inductance of the transformer always remains at a relatively large value. When inrush current occurs, the transformer iron core will alternately enter and exit saturation. Therefore, in the inrush current scenario, the excitation inductance of the transformer will also periodically change between a large value and a small value. When an internal fault occurs in the transformer, the equivalent excitation inductance of the excitation branch is numerically equal to the parallel connection of the excitation inductance and the fault inductance, which is much smaller than the excitation inductance during normal operation and will not change periodically. Therefore, it is proposed that when the protection action criterion is met, it indicates that the excitation inductance of the transformer is always in a small value and should be identified as a fault within the zone. By constructing a protection criterion through the excitation inductance parameter that can reflect the essential characteristics of transformer internal faults, this method is not affected by the power supply characteristics and can reliably reflect the operating state of the transformer.

[0096] The setting principle of the protection action criterion is that the protection should not operate reliably under the most severe inrush current condition. The specific setting value of the protection action criterion can be calculated by the following formula:

[0097]

[0098] In the formula, K d is the reliability coefficient, which can take a value of 0.8 - 1.0; L m0 is the value of the excitation inductance when the transformer is operating normally, which can be measured through the no-load test of the transformer. For transformers with no-load test parameters included in the nameplate, it can be directly calculated according to the corresponding nameplate parameters; K b-min is the minimum value of the ratio of the magnetic permeability in the non-saturated state to the magnetic permeability in the saturated state in the magnetization characteristic curve of the transformer, which can be calculated by querying the corresponding magnetic permeability according to the type of silicon steel sheet of the transformer iron core. Since the excitation inductance value and the magnetic permeability are approximately linearly related, the above setting value can reflect the excitation inductance value under the most severe inrush current condition of the transformer. Using this setting value can ensure that the protection does not operate under the most severe inrush current condition.

[0099] S42: If internal faults are identified in at least one phase, the protection operates; otherwise, the protection does not operate.

[0100] As can be seen from the above technical solutions, the beneficial effects of this method are as follows: First, this method constructs a protection criterion based on the identification of excitation inductance parameters, which can reflect the essential characteristics of transformer faults; Second, this method constructs a branch equation through the instantaneous values of voltage and current and solves for the excitation inductance, without relying on power frequency quantities. Compared with the transformer differential protection based on power frequency electrical quantities, this method is not affected by the power supply characteristics and has high sensitivity; Third, the protection criterion constructed by this method will not malfunction during inrush current, and has high reliability; Fourth, this method can operate reliably within 12 ms after the protection is started. Compared with the traditional ratio restraint differential protection that requires at least 20 ms to operate, this method has a faster operation speed.

[0101] Example 2, refer to Figures 1 - 7 , which is the second embodiment of this method. The implementation process of this method is provided with a more detailed implementation manner through calculation and simulation experiments for scientific demonstration in combination with the accompanying drawings.

[0102] Figure 2 It is the flow chart of the transformer protection method for identifying the excitation inductance parameter of this method. Taking a 230 / 11kV - 120MVA two-winding transformer as an example to illustrate the specific implementation scheme of this protection method. It is known that the no-load current of the transformer I0% = 1.04%, and the no-load loss P0% = 0.89%. The type of the silicon steel sheet of the transformer core is DW540 - 50. The sampling frequency of the measuring device is 10kHz. For the convenience of explaining the following setting values, the primary side values are used in the calculation, and in the specific implementation, it can be converted according to the ratio of the specific measuring device. The specific implementation steps are as follows:

[0103] S1: Collect the phase voltage and current on both sides of the transformer through the measuring device, and judge whether the protection starts through the differential current mutation starting criterion |i d (k)-i d (k - N sample )| > I dset . Taking the above transformer as an example, the effective value of the no-load current of the transformer can be calculated according to the known parameters as In the formula, S N , U N are the rated capacity and rated voltage of the transformer respectively. Taking the reliability coefficient K q = 1.2, the setting value of the starting criterion is as follows:

[0104]

[0105] When there is an internal fault or inrush current, the differential current of the transformer increases, and the protection starting criterion is satisfied, and it enters step S2.

[0106] S2: Based on the T-type equivalent circuit of the transformer, construct a voltage equation set of the transformer excitation branch for each sampling point at the protection starting moment and within 8 - 12ms after the protection starts. Its matrix form is as follows:

[0107]

[0108]

[0109] Taking the protection starting moment as an example, the above formula is further explained as follows. At the protection starting moment, k = 0 is taken. Since the sampling frequency is 10 kHz, that is, there are 200 sampling points in one cycle, and ΔT = 0.1 ms is the time interval between two sampling points of the measuring device. For 2 ms, n = 19. Substituting k, ΔT, and n into the above formula gives the excitation branch equation set at the protection starting moment. At each sampling point, ΔT and n in the excitation branch equation set are the same, and the corresponding k can be substituted.

[0110] S3: Solve the transformer excitation branch voltage equation set based on the singular value decomposition method to obtain the calculated value of the transformer excitation inductance at the protection starting moment and within 8 - 12 ms after the protection starts. The specific steps are as follows:

[0111] S31: For the coefficient matrix A k X k = B k of the excitation branch voltage equation set at each sampling moment, k perform singular value decomposition as follows:

[0112] A k = U k Σ k V k T

[0113] S32: Calculate the pseudo-inverse matrix of Σ k as follows: as follows:

[0114]

[0115] S33: Calculate the solutions of the excitation branch voltage equation sets at each sampling moment as follows:

[0116]

[0117] Since X k = [R m (k)L m (k)] T , so by solving the equation set, the excitation inductance L m (0) at the protection starting moment and the transformer excitation inductance within 8 - 12 ms after the protection starts can be obtained. For a 10 kHz sampling frequency, that is, L m (80) - L m (120). Figure 3 The calculated value of the excitation inductance during normal operation of the transformer is given. The calculated value of the excitation inductance is always large under normal operation scenarios; Figure 4 The calculated value of the excitation inductance when the transformer is switched on with no load, thus generating inrush current, is given. The calculated value of the excitation inductance fluctuates between large and small values in inrush current scenarios; Figure 5Give the calculated value of the exciting inductance under the scenario of a 5% turn - to - turn fault in phase A of the transformer. Under the fault scenario, the calculated value of the exciting inductance of the faulty phase is always very small, and the calculated value of the exciting inductance of the non - faulty phase is the same as that during normal operation. It should be noted that to fully display the characteristics of the exciting inductance, the calculated values of the exciting inductance for one power - frequency cycle (20 ms) are shown in the figures. In practical applications, only the exciting inductance at the moment of protection startup and the exciting inductance of the transformer within 8 - 12 ms after protection startup need to be calculated. The results show that the characteristics of the calculated values of the exciting inductance under various operating conditions are consistent with the theory.

[0118] S4: According to the protection action criterion that reflects the characteristics of the exciting inductance, determine whether there is a fault within the protection zone of the transformer. The protection action criterion is as follows:

[0119]

[0120] For a sampling frequency of 10 kHz, L m (k) takes L m (80) - L m (120). Taking the above - mentioned transformer as an example, the theoretical value L of the exciting inductance during normal operation of the transformer m0 can be calculated from the transformer parameters I0% and P0% as follows:

[0121]

[0122] Figure 3 It can be seen from the above that the calculated value of the exciting inductance during normal operation of the transformer is basically stable around 203 H, which is consistent with the theoretical value, indicating that the calculated value of the exciting inductance by the method in this paper is effective. Further, according to the type of the core silicon steel sheet, K b-min = 25. Taking the reliability coefficient K d = 0.85, the setting value of the protection action criterion is calculated as follows:

[0123]

[0124] When the protection action criterion is satisfied, it is judged that there is a fault within the zone. When at least one phase is identified as a fault within the zone, the protection operates; otherwise, the protection does not operate. Figure 6 Give the average value of the exciting inductance under the scenario of inrush current. Due to the periodic change of the exciting inductance during inrush current, the condition that the average value of the exciting inductance is always less than the setting value cannot be met. Therefore, the protection does not operate reliably. Figure 7 Give the average value of the exciting inductance of the faulty phase when a 5% turn - to - turn fault occurs in phase A. When there is a fault within the zone of the transformer, the average value of the exciting inductance of the faulty phase is always a lower value, and the protection action criterion is satisfied, so the protection operates reliably. It can be noted that this method can operate reliably within 12 ms. Compared with the traditional ratio - restraint differential protection that requires at least 20 ms to operate, this method has a faster operation speed.

[0125] Embodiment 3 is an embodiment of the present invention, which provides a transformer protection system based on excitation inductance parameter identification, including:

[0126] A data processing module that calculates the differential current, excitation inductance, etc. in the above steps according to the collected voltage and current data of each phase of the transformer;

[0127] A protection startup module that determines whether to start the subsequent protection action module according to the calculated differential current and the protection startup criterion.

[0128] A protection action module that determines whether the protection acts according to the protection action criterion of the calculated excitation inductance.

[0129] Embodiment 4, referring to Figure 8 , is an embodiment of the present invention. Different from the previous embodiment, when the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that makes a contribution to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0130] The logic and / or steps represented in the flowchart or described in other ways herein, for example, can be considered as a definite sequence list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch instructions from the instruction execution system, apparatus, or device and execute the instructions), or in combination with these instruction execution systems, apparatus, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device.

[0131] More specific examples (non-exhaustive list) of computer-readable media include the following: electrical connections (electronic devices) having one or more wirings, portable computer diskettes (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber devices, and portable compact disc read-only memory (CDROM). Additionally, the computer-readable media can even be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or other suitable processing as necessary, and then stored in a computer memory.

[0132] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having suitable combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

[0133] Importantly, the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A transformer protection method based on excitation inductance parameter identification, characterized in that Including: Judging whether the protection is started based on the differential current fault component of the transformer; Constructing a transformer exciting branch voltage equation set for each sampling point within 8 - 12 ms after the protection start moment based on the T-type equivalent circuit of the transformer; Solving the transformer exciting branch voltage equation set based on the singular value decomposition method to obtain the calculated value of the transformer exciting inductance at the protection start moment and within 8 - 12 ms after the protection start; Judging whether there is a fault within the protection area of the transformer according to the protection action criterion reflecting the characteristics of the exciting inductance. If there is a fault within the area, the protection acts; otherwise, the protection does not act.

2. The transformer protection method based on exciting inductance parameter identification according to claim 1, characterized in that: The criterion for protection start is as follows: |i d (k)-i d (k-N sample )|>I dset where i d is the differential current, k represents the k-th sampling point, N sample is the number of sampling points in one cycle of the measuring device, and I dset is the setting value of the protection starting criterion; When the protection start criterion is satisfied, the protection starts.

3. The transformer protection method based on exciting inductance parameter identification according to claim 2, characterized in that: The calculation method of the setting value of the protection start criterion is as follows: Where K q is the reliability coefficient, which can take values from 1.0 to 2.0; I0 is the effective value of the no-load current of the transformer, which can be measured through the no-load test of the transformer. For transformers with no-load test parameters included in the nameplate, it can be directly calculated according to the corresponding nameplate parameters.

4. The transformer protection method based on exciting inductance parameter identification according to claim 3, characterized in that: The construction of the transformer exciting branch voltage equation set is specifically to construct a matrix of the transformer exciting branch voltage equation set with the exciting inductance parameter to be solved, and the specific form is as follows: In the formula: where \(i_1\), \(i_2\), \(u_1\), and \(u_2\) are the phase currents and terminal voltages at both ends of the transformer respectively, and \(R\) m , \(L\) m are the resistance and inductance of the excitation branch of the transformer respectively, \(k\) represents the \(k\)th sampling point, and \(\Delta T\) is the time interval between sampling points; for each sampling point at the protection starting moment and within 8 - 12 ms after the protection starts, the voltage equation set of the excitation branch is formed according to the above formula.

5. The transformer protection method based on exciting inductance parameter identification according to claim 4, characterized in that: The solution of the transformer exciting branch voltage equation set based on the singular value decomposition method includes: For the excitation branch voltage equation set A at each sampling moment k X k = B k The coefficient matrix A of k is subjected to singular value decomposition as follows: A k = U k Σ k V k T Where, Σ k is the singular value matrix, whose diagonal elements are the singular values of the coefficient matrix A k , and the non-diagonal elements are 0; U k , V k are the left singular vector matrix and the right singular vector matrix corresponding to the singular value matrix, respectively; Calculate Σ k of the pseudo-inverse matrix as follows: In the formula, i and j are matrix subscripts, and ε is the precision threshold for determining non-zero elements of the judgment matrix, which is used to avoid the influence of numerical calculation errors; where ε is selected as ε = 1×10 -8 ; Calculating the solution of the exciting branch voltage equation set at each sampling moment as follows:

6. The transformer protection method based on exciting inductance parameter identification according to claim 5, characterized in that: The protection action criterion is specifically: where L m (0) is the calculated value of the excitation inductance at the protection starting moment, and L m (k) is the calculated values of all excitation inductances from 8 to 12 ms after the protection starts; when the protection criterion is met, it is judged that there is an internal fault, otherwise there is no internal fault; The calculation method of the setting value of the protection action criterion is as follows: Where, K d is the reliability coefficient, which can take values from 0.8 to 1.0; L m0 is the value of the exciting inductance during normal operation of the transformer, which can be measured through the no-load test of the transformer. For transformers with no-load test parameters included in the nameplate, it can be directly calculated according to the corresponding nameplate parameters; K b-min is the minimum value of the ratio of the magnetic permeability in the non-saturated state to that in the saturated state in the magnetization characteristic curve of the transformer, and can be calculated by querying the corresponding magnetic permeability according to the type of silicon steel sheet of the transformer core.

7. A system adopting the transformer protection method based on excitation inductance parameter identification as described in any one of claims 1 to 6, characterized in that, Including: A data processing module that calculates the differential current, exciting inductance, etc. in the above steps according to the collected voltage and current data of each phase of the transformer; A protection start module that determines whether the subsequent protection action module starts according to the calculated differential current and the protection start criterion; A protection action module that determines whether the protection acts according to the protection action criterion of the calculated exciting inductance.

8. A computer device, comprising a memory and a processor, the memory storing a computer program, characterized in that, When the processor executes the computer program, it realizes the steps of the transformer protection method based on exciting inductance parameter identification described in any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it realizes the steps of the transformer protection method based on exciting inductance parameter identification described in any one of claims 1 to 6.

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