Virtual differential current model establishment method and transformer defect detection method and device

Abstract

The invention relates to the technical field of online diagnosis of internal defects of transformers, in particular to a virtual differential current model establishment method, a transformer defect detection method and a transformer defect detection device, and particularly relates to a virtual differential current modeling and defect diagnosis detection method and a virtual differential current modeling and defect diagnosis detection device suitable for transformers of various connection groups. Aiming at the defect that the existing differential current protection cannot perform early warning, differential current is used for diagnosis of early defects of a transformer and early warning of defect deterioration; according to the method, a differential current model is automatically established, the internal defects of the transformer can be found in time by comparing virtual differential current with a set threshold value based on virtual differential current characteristic indexes, and diagnosable defect types include winding turn-to-turn short circuit faults, interphase short circuit faults, winding deformation, winding internal ground short circuit faults and the like. The early warning signal is sent to the operation personnel in time to prompt the operation personnel to timely arrange power failure and maintenance for the transformer in a planned manner, so that unexpected power failure accidents can be effectively avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of on-line diagnosis of internal defects of transformers, in particular to a virtual differential current model establishing method, a transformer defect detection method and device, and more particularly to a virtual differential current modeling and defect diagnosis detection method and device suitable for transformers of various connection groups. BACKGROUND

[0002] When the differential current of a transformer is applied to transformer protection, it is used as a trip signal for transformer faults, and cannot timely discover early defects of the transformer. After the differential protection acts, the consequence is unexpected large-scale power outage. The current method of using differential current as a transformer fault trip signal can only remove the fault after the fault occurs, which is a post-treatment method and cannot timely discover early features of internal defects of the transformer to give a pre-warning.

[0003] In the prior art, Chinese patent CN120652361A discloses a power distribution transformer internal defect diagnosis method and device based on virtual differential current, which proposes the concept of virtual differential current and a set of diagnosis methods based on virtual differential current for internal defects of power distribution transformers. However, the method and its calculation method disclosed in the patent are only limited to Dy connection method of double-winding power distribution transformers, and cannot be applied to double-winding transformers and three-winding transformers of other connection groups. SUMMARY

[0004] The present application provides a virtual differential current model establishing method, a transformer defect detection method and device, which can overcome the deficiency that the prior art cannot be applied to double-winding transformers and three-winding transformers of Yd, Yy, Dd and other connection groups. The technical solution of the present application is as follows: According to a virtual differential current model establishing method of the present application, it comprises, According to the connection group of the transformer, an initial differential current model is established; wherein the initial differential current model has an initial single-phase differential current model corresponding to any phase of the transformer, and the initial single-phase differential current model is used to represent the relationship between the winding voltage at the core column of the corresponding phase and the differential current of the corresponding phase; the measured winding voltage of each winding at each core column of each phase is obtained and substituted into the initial single-phase differential current model of the corresponding phase to obtain the predicted differential current of the corresponding phase; According to the connection group of the transformer, the calculation method of the winding current of each phase of the transformer is determined, the measured winding current of each winding at each core column of each phase is obtained, and the real differential current of each phase of the transformer is obtained in combination with the winding turn ratio; The modulus of the phasor difference between the differential current model and the real differential current is obtained to obtain the virtual differential current of each phase; The model parameters are obtained when the virtual differential current is minimum, and a differential current model is established.

[0005] Preferably, the initial single-phase differential current model adopts a linear model, which is applicable to the double-winding transformer of the Dy connection group, and the double-winding transformer of the Yd, Yy and Dd connection groups, and the three-winding transformer of the Yyy and Ydy connection groups. The initial single-phase differential current model includes a differential current model corresponding to the A phase of the transformer a differential current model corresponding to the B phase of the transformer and a differential current model corresponding to the C phase of the transformer The initial differential current model is characterized by ; Wherein, , and respectively represent the predicted differential current of the A phase, the B phase and the C phase of the transformer at time t, n represents the number of windings at the same core column, 1≤k≤n, if the modeling object is a double-winding transformer, then n=2, if the modeling object is a three-winding transformer, then n=3. represents the measured winding voltage of different windings at the same core column at time t, , and are parameters to be optimized.

[0006] Preferably, the optimization of the initial single-phase differential current model is completed based on a plurality of groups of continuously collected measured winding voltages and measured winding currents.

[0007] Preferably, for the double-winding transformer, when the winding connection form is Y-shaped, the winding current is a line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage; when the winding connection form is D-shaped, the winding current is obtained based on the line current and the loop current in the winding, and the winding voltage is obtained based on the voltage to ground.

[0008] Preferably, for the three-winding transformer, for the Yyy connection group, the winding current is a line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage; for the Ydy connection group, the winding current of the Y-shaped winding connection form is a line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage, the winding current of the D-shaped winding connection form is obtained based on the line current and the loop current in the winding, and the winding voltage is obtained based on the voltage to ground.

[0009] Preferably, for the calculation of the loop current of the Dy, Yd triangle connection transformer, comprising, The loop current in the winding is obtained based on the zero sequence voltage and current of the Y-shaped side winding and the leakage reactance of the D-shaped side winding, i.e., ; Wherein, is the loop current in the D-shaped winding, and is the zero sequence voltage and current of the Y-shaped side winding, is the leakage reactance of the D-shaped side winding.

[0010] Preferably, for the loop current processing of the Dd connection transformer, comprising, when the connection group is Dd, .

[0011] According to the transformer fault diagnosis method of the present application, comprising, obtaining the voltage phase and current phase of each winding of the high-voltage side and low-voltage side of the transformer and the winding turn ratio; obtaining the real differential current based on the current phase and winding turn ratio; obtaining the predicted differential current based on the voltage phase and differential current model; obtaining the virtual differential current based on the real differential current and the predicted differential current; predicting the transformer fault based on the virtual differential current.

[0012] Preferably, the virtual differential current adopts the modulus of the phase difference between the real differential current and the predicted differential current, sets the A-phase threshold value, B-phase threshold value and C-phase threshold value corresponding to the transformer A-phase, transformer B-phase and transformer C-phase respectively, and determines that the transformer is fault-free when the virtual differential current of the transformer A-phase, transformer B-phase and transformer C-phase does not exceed the corresponding threshold value, otherwise it is determined that the transformer has a fault.

[0013] According to the transformer fault diagnosis device of the present application, comprising, the acquisition device is used for obtaining the voltage phase and current phase of each winding of the high-voltage side and low-voltage side of the transformer and the winding turn ratio; the first calculation device is used for obtaining the real differential current based on the current phase and winding turn ratio; the virtual differential current model is used for obtaining the predicted differential current based on the voltage phase; the second calculation device is used for obtaining the virtual differential current based on the real differential current and the predicted differential current; and the output device is used for predicting the transformer fault based on the virtual differential current and outputting.

[0014] Compared with the prior art, the present application has the following advantages: The scheme of the present disclosure uses differential current for the diagnosis of early defects of a transformer and the early warning of defect deterioration, aiming at the defect that the current differential current protection cannot give early warning; by automatically establishing a virtual differential current model, the virtual differential current characteristic index can be used to compare the virtual differential current with a set threshold to timely find internal defects of the transformer; the diagnosable defect types include winding inter-turn short circuit fault, phase-to-phase short circuit, winding deformation, winding internal ground fault and the like; by timely sending an early warning signal to an operator, the operator is prompted to timely arrange power outage and maintenance of the transformer, so that unexpected power outage accidents can be effectively avoided. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A flowchart of a transformer fault diagnosis method of the present disclosure; Figure 2 An embedded deployment mode of a transformer fault diagnosis device of the present disclosure at a double-winding transformer; Figure 3 An embedded deployment mode of a transformer fault diagnosis device of the present disclosure at a three-winding transformer; Figure 4 A deployment schematic diagram of a transformer fault diagnosis device of the present disclosure when applied to a Dy double-winding transformer; Figure 5 An equivalent circuit diagram of a transformer fault diagnosis device of the present disclosure when applied to a Dy double-winding transformer; Figure 6 A deployment schematic diagram of a transformer fault diagnosis device of the present disclosure when applied to a Yd double-winding transformer; Figure 7 An equivalent circuit diagram of a transformer fault diagnosis device of the present disclosure when applied to a Yd double-winding transformer; Figure 8 A deployment schematic diagram of a transformer fault diagnosis device of the present disclosure when applied to a Dd double-winding transformer; Figure 9 An equivalent circuit diagram of a transformer fault diagnosis device of the present disclosure when applied to a Dd double-winding transformer; Figure 10 A deployment schematic diagram of a transformer fault diagnosis device of the present disclosure when applied to a Yy three-winding transformer; Figure 11 An equivalent circuit diagram of a transformer fault diagnosis device of the present disclosure when applied to a Yy three-winding transformer; Figure 12A deployment schematic diagram of a transformer fault diagnosis device of the present disclosure applied to a Yyy double-winding transformer in a connection group; Figure 13 An equivalent circuit diagram of a transformer fault diagnosis device of the present disclosure applied to a Yyy double-winding transformer in a connection group; Figure 14 A deployment schematic diagram of a transformer fault diagnosis device of the present disclosure applied to a Ydy double-winding transformer in a connection group; Figure 15 An equivalent circuit diagram of a transformer fault diagnosis device of the present disclosure applied to a Ydy double-winding transformer in a connection group; DETAILED DESCRIPTION

[0016] For further understanding of the present application, the application will be described in detail with examples. It should be understood that the examples are only used to explain but not to limit the present application.

[0017] The present disclosure proposes a virtual differential current model establishing method, which comprises, According to the transformer connection group, an initial differential current model is established; wherein the initial differential current model has an initial single-phase differential current model corresponding to any phase of the transformer, and the initial single-phase differential current model is used to represent the relationship between the winding voltage at the core column of the corresponding phase and the differential current of the corresponding phase; the measured winding voltage of each winding at each core column of each phase is obtained and substituted into the initial single-phase differential current model of the corresponding phase to obtain the predicted differential current of the corresponding phase; According to the transformer connection group, the calculation method of the winding current of each phase of the transformer is determined, the measured winding current of each winding at each core column of each phase is obtained, and the real differential current of each phase of the transformer is obtained in combination with the winding turn ratio; The virtual differential current of each phase is obtained by calculating the modulus of the phasor difference between the differential current model and the real differential current; The model parameters when the virtual differential current is minimum are obtained by taking the virtual differential current of each phase of the transformer as the optimization target, and the differential current model is established.

[0018] Wherein, the initial single-phase differential current model can adopt, for example, a linear model; the initial single-phase virtual differential current model can have a differential current model corresponding to the A phase of the transformer a differential current model corresponding to the B phase of the transformer and a differential current model corresponding to the C phase of the transformer ; that is, the initial differential current model can be represented as, ; Wherein, , and respectively represent the predicted differential currents of the transformer A-phase, B-phase and C-phase at time t, n represents the number of windings at the same limb, 1≤k≤n, represent the measured winding voltages of different windings at the same limb at time t, and are parameters to be optimized.

[0019] It can be understood that for a three-winding transformer, n=3; for a two-winding transformer, n=2.

[0020] wherein the optimization of the initial single-phase differential current model is completed based on a plurality of groups of continuously collected measured winding voltages and measured winding currents; specifically, when the continuously collected time set is , the optimization target can be expressed as, wherein , and are corresponding measured winding voltages at time , , and are corresponding true differential currents at time .

[0021] wherein the solution to the above optimization target can be realized by using, for example, existing conventional means such as curve fitting or least square method, which is not described or limited herein.

[0022] wherein for a two-winding transformer, it has, . wherein , and represent the measured winding currents of the high-voltage A-phase, B-phase and C-phase windings of the transformer, , and represent the measured winding currents of the low-voltage A-phase, B-phase and C-phase windings of the transformer, and K represents the turns ratio of the high-voltage winding and the low-voltage winding.

[0023] wherein for a three-winding transformer, it has, . wherein , and represent the measured winding currents of the high-voltage A-phase, B-phase and C-phase windings of the transformer, , and ​​represent measured winding currents of high voltage A-phase, B-phase, C-phase windings of the transformer, , and represent measured winding currents of low voltage A-phase, B-phase, C-phase windings of the transformer, represents the turns ratio of the high voltage winding and the medium voltage winding, represents the turns ratio of the high voltage winding and the low voltage winding.

[0024] It can be understood that the turns ratio , and can be set manually based on actual parameters, or can be read from the tap switch of the connected transformer.

[0025] wherein, for a double-winding transformer, when the winding connection form is Y-shaped, the winding current is the line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage; when the winding connection form is D-shaped, the winding current is obtained based on the line current and the loop current in the winding, and the winding voltage is obtained based on the voltage to ground.

[0026] Specifically, when the winding connection form is D-shaped, ; ; wherein, , and are the voltages to ground at the corresponding busbars, , and are the line currents at the corresponding busbars, is the loop current in the winding.

[0027] wherein, when the connection group is Yd or Dy, ; wherein, and are the zero sequence voltage and zero sequence current of the Y-shaped winding, is the leakage reactance of the D-shaped winding; when the connection group is Dd, the loop current cannot be calculated, and is set to .

[0028] It can be understood that, ; ; ; wherein, X is the nominal leakage reactance of the transformer, which can be calculated by the factory parameters of the transformer.

[0029] wherein, for a three-winding transformer, for Yyy connection group, the winding current is the line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage; for Ydy connection group, the winding current of Y-shaped winding connection form is the line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage, and the winding current of D-shaped winding connection form is obtained based on the line current and the loop current in the winding (as above), and the winding voltage is obtained based on the voltage to ground (as above).

[0030] It can be understood that the voltage to ground and the neutral point voltage can be directly measured based on, for example, a voltage transformer, and the line current can be directly measured based on, for example, a current transformer.

[0031] as shown in Figure 1 , another object of the present disclosure is to provide a transformer fault diagnosis method, which comprises, obtaining the voltage phasor and the current phasor of each winding of the high-voltage side and the low-voltage side of the transformer, and the winding turn ratio; based on the current phasor and the winding turn ratio, obtaining the real differential current; based on the voltage phasor and the virtual differential current model, obtaining the predicted differential current; based on the real differential current and the predicted differential current, obtaining the virtual differential current; based on the virtual differential current, predicting the transformer fault.

[0032] wherein, the real differential current can be calculated based on the steps described above, which will not be repeated here.

[0033] wherein, the virtual differential current model can be established based on the method described above, in actual use, it can be determined whether the virtual differential current model needs to be trained or retrained, and when training or retraining is needed, the above-mentioned virtual differential current model establishment method is executed, and then the training or retraining of the virtual differential current model is completed.

[0034] wherein, the virtual differential current can adopt the modulus of the phasor difference between the real differential current and the predicted differential current, that is, ; wherein, represents taking the modulus of a complex number, , and are the virtual differential currents of the A phase, the B phase and the C phase of the transformer at time t, respectively.

[0035] Wherein, A-phase threshold value, B-phase threshold value and C-phase threshold value corresponding to transformer A-phase, B-phase and C-phase respectively can be set, and when virtual differential currents of transformer A-phase, B-phase and C-phase all do not exceed the corresponding threshold value, it is determined that the transformer is fault-free, otherwise it is determined that the transformer has a fault.

[0036] That is, only when and and , it is determined that the transformer is fault-free; wherein, , and are A-phase threshold value, B-phase threshold value and C-phase threshold value respectively.

[0037] Wherein, A-phase threshold value, B-phase threshold value and C-phase threshold value can be the maximum virtual differential current appeared in the training stage of the virtual differential current model, or can be determined based on no-load current percentage and rated current, for example, ; Wherein, no-load current percentage is , and rated current is .

[0038] As shown in Figure 2 and 3 , in addition, the disclosure also proposes a transformer fault diagnosis device, which comprises, a collection device for acquiring voltage phasor and current phasor of each winding of high-voltage side and low-voltage side of the transformer and winding turn ratio; a first calculation device for acquiring real differential current based on the current phasor and the winding turn ratio; a virtual differential current model for acquiring predicted differential current based on the voltage phasor; a second calculation device for acquiring virtual differential current based on the real differential current and the predicted differential current; and an output device for predicting and outputting transformer fault based on the virtual differential current.

[0039] As shown in Figure 4 and Figure 5 , when a transformer fault diagnosis device of the disclosure is applied to a Dy double-winding transformer with a connection group, the collection device can include a current transformer (CT) and a voltage transformer (PT), and it can be understood that if the required measured voltage does not exceed 1000V, it can be directly measured without a voltage transformer (PT); the data read by the collection device can include high-voltage side line voltage and line current , low-voltage side phase voltage and line current ; The first computing device can obtain the winding voltage and the winding current of each winding based on the following formula, ; ; Then, the first computing device can calculate the real differential current, the virtual differential current model can calculate the predicted differential current, and the second computing device can obtain the virtual differential current, and the output device can predict and output the transformer fault based on the virtual differential current.

[0040] When the transformer fault diagnosis device of the present disclosure is applied to a Yd double-winding transformer, Figure 6 Figure 7 , the first computing device can obtain the winding voltage and the winding current of each winding based on the following formula, ; .

[0041] When the transformer fault diagnosis device of the present disclosure is applied to a Dd double-winding transformer, Figure 8 Figure 9 , the first computing device can obtain the winding voltage and the winding current of each winding based on the following formula, ; .

[0042] When the transformer fault diagnosis device of the present disclosure is applied to a Yy double-winding transformer, Figure 10 Figure 11 , the first computing device can obtain the winding voltage and the winding current of each winding based on the following formula, .

[0043] When the transformer fault diagnosis device of the present disclosure is applied to a Yyy triple-winding transformer, Figure 12 Figure 13 , the first computing device can obtain the winding voltage and the winding current of each winding based on the following formula,

[0044]

[0045] . ​​​​​​​​

[0046] See Figure 13 and Figure 14 When the transformer fault diagnosis device of the present disclosure is applied to a Ydy three-winding transformer, The first calculation device can obtain the winding voltage and winding current of each winding based on the following formula, For the Y side, ; For the D side, ; .

[0047] The scheme of the present disclosure aims at the defect that the differential current protection cannot give early warning, and uses the differential current for the diagnosis of early defects of the transformer and the early warning of defect deterioration. Through the automatic establishment of a virtual differential current model, the transformer internal defects can be found in time by comparing the virtual differential current with a set threshold based on the virtual differential current characteristic index. The diagnosable defect types include winding inter-turn short circuit fault, phase-to-phase short circuit, winding deformation, winding internal ground fault, etc. Through the timely early warning signal to the operator, the operator is prompted to arrange power outage and maintenance of the transformer in a planned manner in time, which can effectively avoid unexpected power outage accidents.

[0048] In one specific embodiment of the present disclosure, it can include the following steps.

[0049] S1: read the synchronous phasor of the transformer (voltage phasor and current phasor of each winding) and the tap position.

[0050] The method for reading the synchronous phasor of the transformer given in S1 is compatible with double-winding transformers (S1.1) and three-winding transformers (S1.2); it is suitable for double-winding transformers of different connection groups and three-winding transformers of different connection groups; for transformers with delta connection, a calculation method for internal delta current is given. S1.1 for double-winding transformer

[0051] 1) Input or automatically obtain the transformer tap position, and calculate the current turn ratio ; 2) Read the synchronous phasor and calculate the winding synchronous phasor: High-voltage winding voltage and winding current: ; Low-voltage winding voltage and winding current: .

[0052] The subscript represents the winding, the subscript represents high voltage and low voltage, and the subscript Three-phase of transformer. Voltage on high and low voltage windings wound on the A-phase core limb; Current flowing through high and low voltage windings wound on the A-phase core limb; Voltage on high and low voltage windings wound on the B-phase core limb; Current flowing through high and low voltage windings wound on the B-phase core limb; Voltage on high and low voltage windings wound on the C-phase core limb; Current flowing through high and low voltage windings wound on the C-phase core limb.

[0053] For the transformer described in S1, the possible connection groups are Yd, Dy or Dd. Among them, the Yd connection group includes but is not limited to Yd5, Yd11, etc. The Dy connection group includes but is not limited to Dy5, Dy11, etc. The Dd connection group includes but is not limited to Dd6, Dd12, etc.

[0054] For the transformer of Yd or Dy connection group, the zero sequence current of the star side winding is , and the zero sequence voltage is .

[0055] Taking the transformer of Dy connection group as an example, the winding voltage and winding current of the D side (delta side) cannot be directly measured and need to be indirectly obtained according to the following formula, , is the voltage to ground measured by the bus PT, is the line current measured by the CT, is the circulating current in the delta side winding; the winding current of the wye side (i.e. the low voltage side) is the line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage. In particular, the formula gives the calculation formula for indirectly obtaining the winding current for the example. If the connection group label is different, or the PT connection is different, there are other calculation formulas also within the scope of the present disclosure. Among them, the circulating current in the delta side winding is,

[0056] Among them, and the zero sequence voltage and the zero sequence current of the star side winding; is the leakage reactance of the delta side winding; the zero sequence voltage , and the zero sequence current ; Preferably, the leakage reactance of the delta side can be approximately taken as half of the nominal leakage reactance of the transformer reduced to the high voltage side, that is, .

[0057] For example, for a transformer with Yd connection, the winding voltage and winding current on the d side (delta side) cannot be measured directly, but can be obtained indirectly by the following formula, , is the ground voltage measured by the bus PT, is the line current measured by the CT, is the circulating current in the delta winding; the winding current on the Y side (i.e. the high voltage side) is the line current, and the winding voltage is the measured ground voltage minus the neutral point voltage. Among them, the circulating current in the delta winding,

[0058] wherein, and the star side winding zero sequence voltage and zero sequence current; is the leakage reactance of the delta side winding; the zero sequence voltage , the zero sequence current ; preferably, the leakage reactance of the delta side can be approximately half of the nominal leakage reactance of the transformer reduced to the low voltage side, that is .

[0059] In addition, for a transformer with Dd connection, the circulating current in the delta winding cannot be measured, and it is considered that . S1.2 For three-winding transformers

[0060] 1) Obtain the transformer tap position (automatically read or manually set), calculate the current high voltage and medium voltage winding turns ratio , high voltage and low voltage winding turns ratio .

[0061] 2) Read the synchronous phasor of PT voltage and CT current, and calculate the winding voltage and current synchronous phasor: high voltage winding voltage and winding current: ; medium voltage winding voltage and winding current: ; low voltage winding voltage and winding current: .

[0062] wherein, subscript represents the winding, subscript represents high voltage, medium voltage and low voltage, and subscript represents the three phases of the transformer.

[0063] If the three-winding transformer winding adopts Yyy connection group, the winding current is the line current measured by CT, and the winding voltage is the ground voltage measured by bus PT minus the neutral point voltage.

[0064] If the three-winding transformer winding adopts Ydy connection group, the Y and y winding currents are the line currents measured by CT, and the winding voltage is the ground voltage measured by bus PT minus the neutral point voltage; the d winding voltage and current are obtained according to the calculation method of Yd connection double-winding transformer given in S1.1.

[0065] S2: Calculate the differential current of each phase of the transformer.

[0066] S2 is compatible with transformers of different connection groups, compatible with double-winding transformers and three-winding transformers. S2.1 for double-winding transformer

[0067] Further, the measured differential current of the two windings on the same core column can be obtained: ; S2.2 for three-winding transformer

[0068] Further, the measured differential current of the three windings on the same core column can be obtained: ; S3: Model training. Take the modulus of the virtual differential current (the difference between the model differential current and the measured differential current) as the optimization objective, train the differential current model, and obtain the model parameters.

[0069] The mathematical expression of the virtual current in S3 is compatible with transformers of different connection groups, compatible with double-winding transformers and three-winding transformers. S3.1 is run for a period of time to establish the model differential current : For double-winding transformers, the input-output relationship of the model is: ; For three-winding transformers: ; Model Use the data in the training stage to establish. Use the actual measured differential current, and the virtual differential current obtained by the model : ; Where, represents taking the modulus of a complex number. S3.2 The modeling idea and modeling method of S3 are to, Modeling idea: Find a set of model such that the sequence of model outputs approximates the sequence of measured differential currents .

[0070] Method of modeling: 1) Let the model be represented as: ; where for three-winding transformers = 3; for two-winding transformers ; is the parameter to be solved.

[0071] 2) Let the model training time be T, then the method for solving the parameter is: ; The solution of the optimized model can be selected but not limited to curve fitting or least square method.

[0072] 3) After the parameter is solved, the differential current model is obtained: .

[0073] S4: Defect deterioration judgment. Compare the modulus of the virtual differential current (the difference between the differential current calculated by the model parameters and the measured differential current) with the set threshold value to judge whether the defect of the transformer is deteriorated. If the defect is deteriorated, give an early warning in time.

[0074] The virtual differential current obtained after the model training can be used as a judgment basis: and and

[0075] When the criterion is met, the transformer is fault-free; otherwise, it means that the transformer has a defect. Preferably, may be taken as the maximum value in the training stage, the maximum value in the training stage, the maximum value in the training stage. Preferably, may also be taken as times of the rated current , i.e. times of the rated current.

[0076] ​It is easy to understand that the person skilled in the art can combine, split, recombine, etc. the embodiments of the present application on the basis of one or several embodiments provided by the present application to obtain other embodiments, and these embodiments do not exceed the protection scope of the present application.

[0077] The above describes the present application and its embodiments in a schematic manner, and the description is not restrictive, and the examples shown are only part of the embodiments of the present application, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired thereby, without departing from the purpose of the present application, similar structural modes and embodiments are not created by creative design, and all should belong to the protection scope of the present application.

Claims

1. A method for establishing a virtual differential current model, comprising, establishing an initial differential current model according to a transformer connection group; wherein the initial differential current model has an initial single-phase differential current model corresponding to any phase of the transformer, and the initial single-phase differential current model is used to represent the relationship between the winding voltage at the core column corresponding to the phase and the differential current corresponding to the phase; obtaining the measured winding voltage of each winding at the core column of each phase, and substituting it into the initial single-phase differential current model corresponding to the phase to obtain the predicted differential current corresponding to the phase; determining the calculation method of the winding current of each phase of the transformer according to the transformer connection group, obtaining the measured winding current of each winding at the core column of each phase, and combining the winding turn ratio to obtain the true differential current of each phase of the transformer; obtaining the virtual differential current of each phase by calculating the modulus of the phasor difference between the differential current model and the true differential current; taking the minimum virtual differential current of each phase of the transformer as the optimization target to obtain the model parameters when the virtual differential current reaches the minimum value, and establishing the differential current model.

2. The method of claim 1, wherein: The initial single-phase differential current model adopts a linear model, The initial single-phase differential current model includes a differential current model corresponding to a transformer A phase a differential current model corresponding to a transformer B phase and a differential current model corresponding to a transformer C phase ; The initial differential current model is represented as, ； wherein, , and respectively represent the predicted differential current of transformer phase A, phase B and phase C at time t, n represents the number of windings at the same limb, 1≤k≤n, if the modeling object is a double-winding transformer then n=2, if the modeling object is a three-winding transformer then n=3; represents the measured winding voltage of different windings at the same limb at time t, , and are parameters to be optimized.

3. The method of claim 2, wherein: Based on the continuously collected multiple groups of measured winding voltages and measured winding currents, the optimization of the initial single-phase differential current model is completed.

4. The method of claim 3, wherein: For a double-winding transformer, When the winding connection form is Y-shaped, the winding current is a line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage; When the winding connection form is D-shaped, the winding current is obtained based on the line current and the loop current in the winding, and the winding voltage is obtained based on the voltage to ground.

5. The method of claim 4, wherein: For a three-winding transformer, For a Yyy connection group, the winding current is a line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage; For a Ydy connection group, the winding current of the Y-shaped winding connection form is a line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage. The winding current of the D-shaped winding connection form is obtained based on the line current and the loop current in the winding, and the winding voltage is obtained based on the voltage to ground.

6. The method of claim 5, wherein: For the loop current calculation of the Dy and Yd transformers with a delta connection, it includes, The loop current in the winding is obtained based on the zero sequence voltage and zero sequence current of the Y-shaped side winding and the leakage reactance of the D-shaped side winding, i.e., ； wherein, is the loop current in the D-shaped winding, and is the zero sequence voltage and zero sequence current of the Y-shaped side winding, is the leakage reactance of the D-shaped side winding.

7. The method of claim 6, wherein: The circulating current processing for the Dd connection transformer includes, when the connection group is Dd, . 8.A transformer fault diagnosis method, comprising, obtaining the voltage phasor and current phasor of each winding on the high-voltage side and the low-voltage side of the transformer, and the winding turn ratio; obtaining the true differential current based on the current phasor and the winding turn ratio; obtaining the predicted differential current based on the voltage phasor and the differential current model; obtaining the virtual differential current based on the true differential current and the predicted differential current; predicting the transformer fault based on the virtual differential current.

9. The transformer fault diagnostic method of claim 8, wherein: The virtual differential current adopts the modulus of the phasor difference between the true differential current and the predicted differential current, and sets the A-phase threshold value, the B-phase threshold value and the C-phase threshold value corresponding to the A-phase of the transformer, the B-phase of the transformer and the C-phase of the transformer respectively. When the virtual differential current of the A-phase of the transformer, the B-phase of the transformer and the C-phase of the transformer does not exceed the corresponding threshold value, it is determined that the transformer is fault-free, otherwise it is determined that the transformer has a fault. 10.A transformer fault diagnosis device, comprising, The collection device is used for collecting voltage phasors and current phasors of each winding of a high-voltage side and a low-voltage side of a transformer and a winding turn ratio; The first calculation device is used for obtaining a real differential current based on the current phasors and the winding turn ratio; The virtual differential current model is used for obtaining a predicted differential current based on the voltage phasors; The second calculation device is used for obtaining a virtual differential current based on the real differential current and the predicted differential current; And The output device is used for predicting and outputting a transformer fault based on the virtual differential current.

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