Virtual differential current model establishment method, transformer defect detection method and device
By establishing a virtual differential current model applicable to transformers with various connection groups, the problem of existing technologies being unable to detect early defects in transformers in a timely manner is solved, enabling the diagnosis and early warning of early defects in transformers and avoiding unexpected power outages.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHUHAI WANPU TECH CO LTD
- Filing Date
- 2025-11-06
- Publication Date
- 2026-05-15
AI Technical Summary
Existing technologies cannot detect early defects in transformers in a timely manner, leading to large-scale power outages after differential protection trips. Furthermore, existing methods are only applicable to double-winding distribution transformers with Dy connection and cannot be applied to transformers with other connection groups.
A virtual differential current model is established for double-winding and three-winding transformers with other connection groups such as Yd, Yy, and Dd. By acquiring the winding voltage and current, an initial differential current model is established, the model parameters are optimized, the virtual differential current is calculated, and a threshold is set for fault determination.
It enables the diagnosis of early defects in transformers and early warning of defect deterioration, avoiding unexpected power outages. It can diagnose faults such as inter-turn short circuits, phase-to-phase short circuits, winding deformation, and internal short circuits to ground in windings, and issue timely warnings to operators.
Smart Images
Figure CN121456550B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of online diagnosis technology for internal defects in transformers. Specifically, it relates to a method for establishing a virtual differential current model, a method and device for detecting transformer defects, and more specifically, a method and device for virtual differential current modeling and defect diagnosis and detection applicable to transformers of various connection groups. Background Technology
[0002] When transformer differential current is used in transformer protection as a trip signal for transformer faults, it cannot detect early transformer defects in a timely manner. The consequence of differential protection tripping is often an unexpected, widespread power outage. Current methods using differential current as a transformer fault trip signal can only isolate the fault after it occurs, representing a reactive approach that cannot detect early signs of internal transformer defects and provide timely warnings.
[0003] In the prior art, Chinese patent CN120652361A discloses a method and device for diagnosing internal defects in distribution transformers based on virtual differential current. It proposes the concept of virtual differential current and a diagnostic method for internal defects in distribution transformers based on virtual differential current. However, the method and calculation method disclosed in this patent are limited to two-winding distribution transformers with Dy connection and cannot be applied to other connection groups of two-winding and three-winding transformers. Summary of the Invention
[0004] This invention provides a method for establishing a virtual differential current model, a method and apparatus for detecting transformer defects, which overcomes the shortcomings of existing technologies that cannot be applied to two-winding transformers and three-winding transformers with other connection groups such as Yd, Yy, and Dd. The technical solution of this invention is as follows:
[0005] According to the virtual differential current model establishment method disclosed herein, it includes,
[0006] Based on the transformer connection group, an initial differential current model is established. The initial differential current model has an initial single-phase differential current model for any phase of the transformer. The initial single-phase differential current model is used to characterize 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 the 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.
[0007] Based on the transformer connection group, determine the calculation method for the winding current of each phase of the transformer, obtain the measured winding current of each winding at each phase core column, and combine it with the winding turns ratio to obtain the actual differential current of each phase of the corresponding transformer.
[0008] The virtual differential current for each phase is obtained by calculating the magnitude of the phasor difference between the differential current model and the actual differential current.
[0009] With the goal of minimizing the virtual differential current of each phase of the transformer, the model parameters when the virtual differential current reaches its minimum value are obtained, and a differential current model is established.
[0010] Preferably, the initial single-phase differential current model adopts a linear model, which is applicable not only to the two-winding transformers of the Dy connection group, but also to the two-winding transformers of the Yd, Yy, and Dd connection groups and the three-winding transformers of the Yyy and Ydy connection groups.
[0011] The initial single-phase differential current model includes the differential current model corresponding to phase A of the transformer. The differential current model corresponding to phase B of the transformer. and the differential current model of the corresponding C phase of the transformer The initial differential current model is characterized as follows:
[0012] ;
[0013] in, , and These represent the predicted differential currents of phases A, B, and C of the corresponding transformer at time t, respectively. n represents the number of windings at the same core column, 1≤k≤n. If the modeling object is a two-winding transformer, then n=2; if the modeling object is a three-winding transformer, then n=3. This represents the measured winding voltage at time t for different windings at the same core post. , and These are the parameters to be optimized.
[0014] Preferably, the initial single-phase differential current model is optimized based on multiple sets of continuously acquired measured winding voltages and measured winding currents.
[0015] Preferably, for a two-winding transformer,
[0016] When the winding connection 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.
[0017] When the winding connection 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.
[0018] Preferably, for a three-winding transformer,
[0019] For the 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.
[0020] For Ydy connection groups, the winding current of the Y-shaped winding connection is the line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage. For the D-shaped winding connection, 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.
[0021] Preferably, the circulating current calculation for transformers with delta connection in Dy and Yd includes,
[0022] The loop current within the winding is obtained based on the zero-sequence voltage and zero-sequence current of the Y-side winding and the leakage reactance of the D-side winding, i.e.
[0023] ;
[0024] in, This refers to the loop current within the D-shaped winding. and The zero-sequence voltage and zero-sequence current of the Y-shaped winding are... This is the leakage reactance of the D-shaped side winding.
[0025] Preferably, the circulating current treatment for a Dd-connected transformer includes, when the connection group is Dd, .
[0026] A transformer fault diagnosis method according to this disclosure includes,
[0027] Obtain the voltage phasors and current phasors of each winding on the high-voltage and low-voltage sides of the transformer, as well as the winding turns ratio;
[0028] The actual differential current is obtained based on the current phasor and the winding turns ratio;
[0029] Based on the voltage phasor and differential current model, the predicted differential current is obtained;
[0030] The virtual differential current is obtained based on the actual differential current and the predicted differential current;
[0031] Transformer faults are predicted based on virtual differential current.
[0032] Preferably, the virtual differential current uses the modulus of the phasor difference between the actual differential current and the predicted differential current, and sets A-phase threshold, B-phase threshold and C-phase threshold respectively corresponding to transformer A-phase, transformer B-phase and transformer C-phase. When the virtual differential current of transformer A-phase, transformer B-phase and transformer C-phase does not exceed the corresponding threshold, the transformer is determined to be fault-free; otherwise, the transformer is determined to be faulty.
[0033] A transformer fault diagnosis device according to the present disclosure includes,
[0034] The data acquisition device is used to acquire the voltage phasors and current phasors of each winding on the high-voltage side and low-voltage side of the transformer, as well as the winding turns ratio.
[0035] The first computing device is used to obtain the actual differential current based on the current phasor and the winding turns ratio;
[0036] A virtual differential current model is used to obtain the predicted differential current based on voltage phasors.
[0037] A second computing device is used to obtain a virtual differential current based on the actual differential current and the predicted differential current; and
[0038] An output device is used to predict and output transformer faults based on virtual differential current.
[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0040] The disclosed solution addresses the current limitation of differential current protection in providing early warnings by using differential current for the diagnosis of early transformer defects and early warning of defect deterioration. By automatically establishing a virtual differential current model, it can promptly detect internal transformer defects based on virtual differential current characteristic indicators and by comparing the virtual differential current with a set threshold. The types of defects that can be diagnosed include: inter-turn short circuit faults, phase-to-phase short circuits, winding deformation, and internal winding-to-ground short circuits, etc. By promptly issuing early warning signals to operators, it prompts them to plan power outages and maintenance of the transformer in a timely manner, effectively preventing unexpected power outages. Attached Figure Description
[0041] Figure 1 This is a flowchart illustrating a transformer fault diagnosis method disclosed herein;
[0042] Figure 2 This disclosure provides an embedded deployment method for a transformer fault diagnosis device in a dual-winding transformer.
[0043] Figure 3 This disclosure provides an embedded deployment method for a transformer fault diagnosis device in a three-winding transformer.
[0044] Figure 4 This is a schematic diagram showing the deployment of a transformer fault diagnosis device disclosed herein when applied to a double-winding transformer with a connection group of Dy.
[0045] Figure 5 This is an equivalent circuit diagram of a transformer fault diagnosis device disclosed herein when applied to a double-winding transformer with a connection group of Dy;
[0046] Figure 6This is a schematic diagram showing the deployment of a transformer fault diagnosis device disclosed herein when applied to a Yd double-winding transformer.
[0047] Figure 7 This is an equivalent circuit diagram of a transformer fault diagnosis device disclosed herein when applied to a Yd double-winding transformer;
[0048] Figure 8 This is a schematic diagram of the deployment of a transformer fault diagnosis device disclosed herein when applied to a double-winding transformer with connection group Dd;
[0049] Figure 9 This is an equivalent circuit diagram of a transformer fault diagnosis device disclosed herein when applied to a double-winding transformer with a connection group of Dd;
[0050] Figure 10 This is a schematic diagram of the deployment of a transformer fault diagnosis device disclosed herein when applied to a Yy three-winding transformer with a connection group of Yy.
[0051] Figure 11 This is an equivalent circuit diagram of a transformer fault diagnosis device disclosed herein when applied to a Yy three-winding transformer;
[0052] Figure 12 This is a schematic diagram illustrating the deployment of a transformer fault diagnosis device disclosed herein when applied to a Yyy double-winding transformer.
[0053] Figure 13 This is an equivalent circuit diagram of a transformer fault diagnosis device disclosed herein when applied to a Yyy double-winding transformer;
[0054] Figure 14 This is a schematic diagram showing the deployment of a transformer fault diagnosis device disclosed herein when applied to a Ydy double-winding transformer;
[0055] Figure 15 This is an equivalent circuit diagram of a transformer fault diagnosis device disclosed herein when applied to a Ydy double-winding transformer; Detailed Implementation
[0056] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.
[0057] This disclosure proposes a method for establishing a virtual differential current model, which includes,
[0058] Based on the transformer connection group, an initial differential current model is established. The initial differential current model has an initial single-phase differential current model for any phase of the transformer. The initial single-phase differential current model is used to characterize 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 the 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.
[0059] Based on the transformer connection group, determine the calculation method for the winding current of each phase of the transformer, obtain the measured winding current of each winding at each phase core column, and combine it with the winding turns ratio to obtain the actual differential current of each phase of the corresponding transformer.
[0060] The virtual differential current for each phase is obtained by calculating the magnitude of the phasor difference between the differential current model and the actual differential current.
[0061] With the goal of minimizing the virtual differential current of each phase of the transformer, the model parameters when the virtual differential current reaches its minimum value are obtained, and a differential current model is established.
[0062] The initial single-phase differential current model can be, for example, a linear model; the initial single-phase virtual differential current model can include the differential current model corresponding to phase A of the transformer. The differential current model corresponding to phase B of the transformer. and the differential current model of the corresponding C phase of the transformer That is, the initial differential current model can be characterized as follows:
[0063] ;
[0064] in, , and These represent the predicted differential currents of phases A, B, and C of the transformer at time t, respectively, where n represents the number of windings at the same core column, and 1 ≤ k ≤ n. This represents the measured winding voltage at time t for different windings at the same core post. , and These are the parameters to be optimized.
[0065] Understandably, for a three-winding transformer, n=3; for a two-winding transformer, n=2.
[0066] Specifically, the initial single-phase differential current model is optimized based on multiple sets of continuously acquired measured winding voltages and currents; more specifically, the time set of continuously acquired data is... When the optimization objective can be expressed as,
[0067] ;
[0068] in, , and For a moment The corresponding measured winding voltage at that time , and For a moment The corresponding actual differential current at that time.
[0069] The above optimization objective can be solved using existing conventional methods such as curve fitting or least squares method, which will not be elaborated or limited in this disclosure.
[0070] Among them, for a two-winding transformer, it has the following characteristics:
[0071] ;
[0072] in, , and This represents the measured winding current of the high-voltage A-phase, B-phase, and C-phase windings of the transformer. , and This represents the measured winding current of the low-voltage A-phase, B-phase, and C-phase windings of the transformer, where K represents the turns ratio of the high-voltage winding to the low-voltage winding.
[0073] Among them, for a three-winding transformer, it has the following characteristics:
[0074] ;
[0075] in, , and This represents the measured winding current of the high-voltage A-phase, B-phase, and C-phase windings of the transformer. , and This represents the measured winding currents of the A-phase, B-phase, and C-phase windings of the transformer's medium-voltage windings. , and This represents the measured winding current of the low-voltage A-phase, B-phase, and C-phase windings of the transformer. This indicates the turns ratio of the high-voltage winding to the medium-voltage winding. This indicates the turns ratio of the high-voltage winding to the low-voltage winding.
[0076] Understandably, the turns ratio , and It can be set manually based on actual parameters, or it can be read from the tap position switch of the connected transformer.
[0077] For dual-winding transformers,
[0078] When the winding connection 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.
[0079] When the winding connection 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.
[0080] Specifically, when the winding connection is D-shaped...
[0081] ;
[0082] ;
[0083] in, , and This represents the voltage to ground at the corresponding busbar. , and This represents the line current at the corresponding busbar. This represents the loop current within the winding.
[0084] in,
[0085] When the join group is Yd or Dy
[0086] ;
[0087] in, and The zero-sequence voltage and zero-sequence current of the Y-shaped winding are... The leakage reactance of the D-shaped side winding;
[0088] When the connection group is Dd, circulation cannot be calculated. (Setting...)
[0089] .
[0090] Understandable
[0091] ;
[0092] ;
[0093] ;
[0094] in, The nominal transformer leakage reactance can be calculated from the transformer's factory parameters.
[0095] For three-winding transformers,
[0096] For the 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.
[0097] For Ydy connection groups, the winding current of the Y-shaped winding connection is the line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage. For the D-shaped winding connection, the winding current 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).
[0098] It is understandable that the voltage to ground and the neutral point voltage can be directly measured using, for example, a voltage transformer, and the line current can be directly measured using, for example, a current transformer.
[0099] Seen in Figure 1 Another objective of this disclosure is to provide a transformer fault diagnosis method, which includes,
[0100] Obtain the voltage phasors and current phasors of each winding on the high-voltage and low-voltage sides of the transformer, as well as the winding turns ratio;
[0101] The actual differential current is obtained based on the current phasor and the winding turns ratio;
[0102] Based on voltage phasors and virtual differential current models, the predicted differential current is obtained;
[0103] The virtual differential current is obtained based on the actual differential current and the predicted differential current;
[0104] Transformer faults are predicted based on virtual differential current.
[0105] The actual differential current can be calculated based on the steps described above, and will not be repeated here.
[0106] The virtual differential current model can be established based on the method described above. In practical use, it can determine whether the virtual differential current model needs to be trained or retrained. When training or retraining is required, the above-mentioned method for establishing a virtual differential current model is executed to complete the training or retraining of the virtual differential current model.
[0107] Among them, the virtual differential current can be expressed as the magnitude of the phasor difference between the actual differential current and the predicted differential current, that is,
[0108] ;
[0109] in, Indicates taking the modulus of a complex number. , and These are the virtual differential currents of phases A, B, and C of the transformer at time t.
[0110] The system can set threshold values for phase A, phase B, and phase C of the transformer, respectively. It can determine that the transformer is fault-free when the virtual differential currents of phases A, B, and C do not exceed the corresponding threshold values, and otherwise determine that the transformer is faulty.
[0111] That is, it is only possible to and and At that time, it was determined that the transformer was not faulty; among them, , and These are the threshold values for phase A, phase B, and phase C, respectively.
[0112] Among them, the threshold values for phase A, phase B, and phase C can be determined by using the maximum virtual differential current that occurs during the training phase of the virtual differential current model, or they can be determined based on the percentage of no-load current and the rated current, for example, as follows:
[0113] ;
[0114] The percentage of no-load current is: Rated current is .
[0115] Seen in Figure 2 and 3 Furthermore, this disclosure also proposes a transformer fault diagnosis device, which includes,
[0116] The data acquisition device is used to acquire the voltage phasors and current phasors of each winding on the high-voltage side and low-voltage side of the transformer, as well as the winding turns ratio.
[0117] The first computing device is used to obtain the actual differential current based on the current phasor and the winding turns ratio;
[0118] A virtual differential current model is used to obtain the predicted differential current based on voltage phasors.
[0119] A second computing device is used to obtain a virtual differential current based on the actual differential current and the predicted differential current; and
[0120] An output device is used to predict and output transformer faults based on virtual differential current.
[0121] Seen in Figure 4 and Figure 5 When the transformer fault diagnosis device of this disclosure is applied to a double-winding transformer with a connection group of Dy,
[0122] The acquisition device can include a current transformer (CT) and a voltage transformer (PT). It is understood that if the required voltage does not exceed 1000V, it can be measured directly without a voltage transformer (PT).
[0123] The data collected by the acquisition device can include high-voltage side line voltage and line current. Low-voltage side phase voltage and line current ;
[0124] The first computing device can obtain the winding voltage and winding current of each winding based on the following formula.
[0125] ;
[0126] ;
[0127] Then, the first computing device can calculate and obtain the actual differential current; at the same time, the virtual differential current model can calculate and obtain the predicted differential current; then, 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.
[0128] Seen in Figure 6 and Figure 7 When the transformer fault diagnosis device of this disclosure is applied to a Yd double-winding transformer,
[0129] The first computing device can obtain the winding voltage and winding current of each winding based on the following formula.
[0130] ;
[0131] .
[0132] Seen in Figure 8 and Figure 9 When the transformer fault diagnosis device of this disclosure is applied to a double-winding transformer with a connection group of Dd,
[0133] The first computing device can obtain the winding voltage and winding current of each winding based on the following formula.
[0134] ;
[0135] .
[0136] Seen in Figure 10 and Figure 11 When the transformer fault diagnosis device of this disclosure is applied to a Yy double-winding transformer,
[0137] The first computing device can obtain the winding voltage and winding current of each winding based on the following formula.
[0138] .
[0139] Seen in Figure 12 and Figure 13 When the transformer fault diagnosis device of this disclosure is applied to a Yyy three-winding transformer,
[0140] The first computing device can obtain the winding voltage and winding current of each winding based on the following formula.
[0141]
[0142]
[0143] .
[0144] Seen in Figure 13 and Figure 14 When the transformer fault diagnosis device of this disclosure is applied to a three-winding transformer with a connection group of Ydy,
[0145] The first computing device can obtain the winding voltage and winding current of each winding based on the following formula.
[0146] For the Y side, ;
[0147] For side D, ;
[0148] .
[0149] The disclosed solution addresses the current limitation of differential current protection in providing early warnings by using differential current for the diagnosis of early transformer defects and early warning of defect deterioration. By automatically establishing a virtual differential current model, it can promptly detect internal transformer defects based on virtual differential current characteristic indicators and by comparing the virtual differential current with a set threshold. The types of defects that can be diagnosed include: inter-turn short circuit faults, phase-to-phase short circuits, winding deformation, and internal winding-to-ground short circuits, etc. By promptly issuing early warning signals to operators, it prompts them to plan power outages and maintenance of the transformer in a timely manner, effectively preventing unexpected power outages.
[0150] In one specific embodiment of this disclosure, it may include the following steps.
[0151] S1: Read the transformer's synchronous phasors (voltage phasors and current phasors of each winding) and tap position.
[0152] The method for reading transformer synchronization phasors given in S1 is compatible with both two-winding transformers (S1.1) and three-winding transformers (S1.2); it is applicable to two-winding transformers with different connection groups, as well as three-winding transformers with different connection groups; for transformers with delta connection, a method for calculating the circulating current inside the delta is given.
[0153] S1.1 for a two-winding transformer
[0154] 1) Input or automatically obtain the transformer tap position and calculate the current turns ratio. ;
[0155] 2) Read the synchronization phasor and calculate the winding synchronization phasor:
[0156] High-voltage winding voltage and winding current: ;
[0157] Low-voltage winding voltage and winding current: .
[0158] Subscript Indicates winding, subscript Indicates high pressure and low pressure, subscript This indicates the three phases of the transformer. The voltage across the high and low voltage windings wound on the A-phase iron core column; This refers to the current flowing through the high and low voltage windings wound on the A-phase iron core column; The voltage across the high and low voltage windings wound on the B-phase iron core column; The current in the high-voltage and low-voltage windings wound on the B-phase iron core column; The voltage across the high and low voltage windings wound on the C-phase iron core column; It represents the current in the high-voltage and low-voltage windings wound on the C-phase iron core column.
[0159] For the transformer described in S1, its 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.; and the Dd connection group includes, but is not limited to, Dd6, Dd12, etc.
[0160] For transformers with Yd or Dy connection groups, let the zero-sequence current of the star-connected winding be... The zero-sequence voltage is .
[0161] Taking a transformer with a Dy connection group as an example, the winding voltage and winding current on the D side (delta side) cannot be directly measured and must be obtained indirectly using the following formula.
[0162] ,
[0163] The voltage to ground measured by the busbar PT. The line current measured by the CT. The circulating current within the delta-connected winding; the winding current on the Y-connected 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. Specifically, the formula provides an indirect calculation method for obtaining the winding current for an example. If the connection group designation is different, or the PT connection is different, other calculation formulas may exist, which also fall within the scope of this disclosure. The circulating current within the delta-connected winding... for,
[0164]
[0165] in, and Zero-sequence voltage and zero-sequence current of the star-connected winding; Leakage reactance of the delta-side winding; zero-sequence voltage Zero-sequence current ;
[0166] Preferably, the leakage reactance on the triangular side It can be approximated as half of the nominal transformer leakage reactance attributed to the high-voltage side, that is... .
[0167] Taking a transformer with a Yd connection group as an example, the winding voltage and winding current on the d side (delta side) cannot be directly measured, but can be obtained indirectly using the following formula:
[0168] ,
[0169] The voltage to ground measured by the busbar PT. The line current measured by the CT. The circulating current is within the delta-connected winding; the winding current on the Y-connected side (i.e., the high-voltage side) is the line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage. The circulating current within the delta-connected winding...
[0170]
[0171] in, and Zero-sequence voltage and zero-sequence current of the star-connected winding; Leakage reactance of the delta-side winding; zero-sequence voltage Zero-sequence current Preferably, the leakage reactance on the triangular side We can approximate it by taking half of the nominal transformer leakage reactance attributed to the low-voltage side, that is... .
[0172] Furthermore, for transformers with a Dd connection, it is impossible to measure the circulating current within the delta winding, which is considered... .
[0173] S1.2 for three-winding transformers
[0174] 1) Obtain the transformer tap position (automatic reading or manual setting), and calculate the current turns ratio of the high-voltage and medium-voltage windings. High-voltage and low-voltage winding turns ratio .
[0175] 2) Read the synchronization phasors of PT voltage and CT current, and calculate the synchronization phasors of winding voltage and current:
[0176] High-voltage winding voltage and winding current: ;
[0177] Medium voltage winding voltage and winding current: ;
[0178] Low-voltage winding voltage and winding current: .
[0179] Among them, subscript Indicates winding, subscript Indicates high pressure, medium pressure, and low pressure; subscript This indicates the three phases of the transformer.
[0180] If the windings of a three-winding transformer are connected in a Yyy configuration, the winding current is the line current measured by the CT, and the winding voltage is the voltage to ground measured by the busbar PT minus the neutral point voltage.
[0181] If the windings of a three-winding transformer adopt the Ydy connection group, then the currents of its Y and y windings are the line currents measured by the CT, and the winding voltages are the voltages to ground measured by the bus PT minus the neutral point voltage; the voltage and current of its d winding are obtained according to the calculation method of the Yd connection two-winding transformer given in S1.1.
[0182] S2: Calculate the differential current of each phase of the transformer.
[0183] S2 is compatible with transformers of different connection groups, including two-winding and three-winding transformers.
[0184] S2.1 for two-winding transformers
[0185] This allows us to obtain the measured differential current between the two windings on the same core column:
[0186] ;
[0187] S2.2 for three-winding transformers
[0188] This allows us to obtain the measured differential current of the three windings on the same core column:
[0189] ;
[0190] S3: Model Training. The differential current model is trained with the optimization objective of minimizing the magnitude of the virtual differential current (the phasor difference between the model's differential current and the measured differential current) to obtain the model parameters.
[0191] The mathematical expression for the virtual current in S3 is compatible with transformers of different connection groups, including both two-winding and three-winding transformers. After a period of trial operation, the differential current of the model in S3.1 is established. :
[0192] For a two-winding transformer, the input-output relationship of the model is as follows:
[0193] ;
[0194] For a three-winding transformer:
[0195] ;
[0196] Model The model is built using data from the training phase. It utilizes actual measured differential current and is developed through a model. The obtained virtual differential current:
[0197] ;
[0198] in, This indicates taking the modulus of a complex number.
[0199] The modeling ideas and methods of S3.2 S3 are as follows:
[0200] The idea behind modeling:
[0201] Find a set of models This makes the sequence output by the model approximate the measured differential current sequence. .
[0202] Modeling methods:
[0203] 1) The model Represented as:
[0204] ;
[0205] in For three-winding transformers =3; for a two-winding transformer ; The parameter to be determined.
[0206] 2) Set the model training time Then obtain the parameters. The method is as follows:
[0207] ;
[0208] The optimization model can be solved by, but is not limited to, curve fitting or least squares method.
[0209] 3) Obtain the parameters Then, the differential current model was obtained. :
[0210] .
[0211] S4: Defect Deterioration Judgment. The magnitude of the virtual differential current (the phasor difference between the differential current calculated through model parameters and the measured differential current) is compared with a set threshold to determine whether the transformer defect has worsened. If the defect worsens, an early warning is issued in a timely manner.
[0212] The virtual differential current obtained after model training can serve as a basis for judgment:
[0213] and and
[0214] If the criterion is met, the transformer is fault-free; otherwise, it means the transformer has a defect. Preferably, Can be taken separately The maximum value during the training phase. The maximum value during the training phase. The maximum value during the training phase. Preferably, Alternatively, it can be based on the percentage of no-load current. Take the rated current of times, that is times.
[0215] It is readily understood that those skilled in the art can combine, split, or reorganize the embodiments provided in this application to obtain other embodiments, all of which do not exceed the protection scope of this application.
[0216] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the embodiments shown are only part of the embodiments of the present invention. The actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.
Claims
1. A method for establishing a virtual differential current model, which includes: An initial differential current model is established based on the transformer connection group; where... 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 adopts a linear model; The initial single-phase differential current model is used to characterize 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 phase core column 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. Based on the transformer connection group, determine the calculation method for the winding current of each phase of the transformer, obtain the measured winding current of each winding at each phase core column, and combine it with the winding turns ratio to obtain the actual differential current of each phase of the corresponding transformer. For a three-winding transformer For the 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 groups, the winding current of the Y-shaped winding connection is the line current, and the winding voltage is the measured voltage to ground minus the neutral point voltage. For the D-shaped winding connection, 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. For circulating current calculations of transformers with delta connection in Dy and Yd, including: The loop current within the winding is obtained based on the zero-sequence voltage and zero-sequence current of the Y-side winding and the leakage reactance of the D-side winding, i.e. ； in, This refers to the loop current within the D-shaped winding. and The zero-sequence voltage and zero-sequence current of the Y-shaped winding are... The leakage reactance of the D-shaped side winding; The circulating current treatment for Dd-connected transformers includes, when the connection group is Dd, ; The virtual differential current for each phase is obtained by calculating the magnitude of the phasor difference between the differential current model and the actual differential current. With the goal of minimizing the virtual differential current of each phase of the transformer, the model parameters when the virtual differential current reaches its minimum value are obtained, and a differential current model is established.
2. The method for establishing a virtual differential current model according to claim 1, characterized in that: The initial single-phase differential current model includes the differential current model corresponding to phase A of the transformer. The differential current model corresponding to phase B of the transformer. and the differential current model of the corresponding C phase of the transformer ; The initial differential current model is characterized as follows: ； in, , and These represent the predicted differential currents of phases A, B, and C of the corresponding transformer at time t, respectively. n represents the number of windings at the same core column, 1≤k≤n. If the modeling object is a two-winding transformer, then n=2; if the modeling object is a three-winding transformer, then n=3. This represents the measured winding voltage at time t for different windings at the same core post. , and These are the parameters to be optimized.
3. The method for establishing a virtual differential current model according to claim 2, characterized in that: Based on multiple sets of continuously acquired measured winding voltages and currents, the initial single-phase differential current model was optimized.
4. The method for establishing a virtual differential current model according to claim 3, characterized in that: For a two-winding transformer When the winding connection 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 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. Transformer fault diagnosis methods, including: Obtain the voltage phasors and current phasors of each winding on the high-voltage and low-voltage sides of the transformer, as well as the winding turns ratio; The actual differential current is obtained based on the current phasor and the winding turns ratio; Based on the voltage phasor and differential current model, the predicted differential current is obtained, wherein the differential current model is established based on the virtual differential current model establishment method according to any one of claims 1-4; The virtual differential current is obtained based on the actual differential current and the predicted differential current; Transformer faults are predicted based on virtual differential current.
6. The transformer fault diagnosis method according to claim 5, characterized in that: The virtual differential current uses the modulus of the phasor difference between the actual differential current and the predicted differential current. Thresholds for phase A, phase B, and phase C are set respectively for phase A, phase B, and phase C of the transformer. The transformer is considered fault-free when the virtual differential currents of phase A, phase B, and phase C of the transformer do not exceed the corresponding thresholds; otherwise, the transformer is considered faulty.
7. A transformer fault diagnosis device, comprising, The data acquisition device is used to acquire the voltage phasors and current phasors of each winding on the high-voltage side and low-voltage side of the transformer, as well as the winding turns ratio. The first computing device is used to obtain the actual differential current based on the current phasor and the winding turns ratio; A virtual differential current model is used to obtain the predicted differential current based on voltage phasors, wherein the virtual differential current model is established based on the virtual differential current model establishment method according to any one of claims 1-4; A second computing device is used to obtain a virtual differential current based on the actual differential current and the predicted differential current; and An output device is used to predict and output transformer faults based on virtual differential current.