A method for early warning of transformer faults

Abstract

The present invention discloses a method for transformer fault early warning, which relates to the technical field of transformers. The present invention includes monitoring the excitation inrush current information of the transformer when it is no-load closed after the transformer is put into operation, and extracting the characteristic quantity of the excitation inrush current information; wherein the excitation inrush current characteristic quantity includes the excitation inrush current decay time Tb, the excitation inrush current peak value Im, the excitation inrush current waveform discontinuity angle Tα, and the excitation inrush current current change rate ΔIb: if the characteristic quantity changes more than the reference value of the transformer before the operation than the threshold value, an early warning is issued. Before the transformer is put into operation, a no-load opening experiment is carried out on the transformer to extract the excitation inrush current characteristic quantity when the transformer is no-load closed as a reference. After the transformer is put into operation, the excitation inrush current data after each closing of the transformer is obtained to form a magnetic inrush current characteristic library. The present invention collects the excitation inrush current, analyzes the excitation inrush current, makes a judgment based on the excitation inrush current characteristic quantity, and issues an early warning if an abnormality occurs.

Description

Technical Field

[0001] The present invention belongs to the technical field of transformers, and in particular relates to a transformer fault early warning method. Background Art

[0002] When a transformer is switched on with no load, it experiences a magnetizing inrush current, which can often exceed the rated current by several times or even 10 times. Although the magnetizing inrush current is short-lived, it can still cause significant damage to the transformer, especially the electrodynamic shock caused by the magnetizing inrush current, which cannot be ignored.

[0003] However, transformer design often considers the impact of short-circuit current, but rarely considers the impact of magnetizing inrush current during no-load closing. Magnetizing inrush current can cause cumulative deformation of transformer windings. When accumulated to a certain level, it can damage the transformer insulation and even cause failure. The potential harm is particularly severe for dry-type transformers. Damage to transformer coils caused by magnetizing inrush current, leading to inter-turn short-circuit failures, is also a common occurrence.

[0004] Current research on magnetizing inrush current focuses on identifying it and distinguishing it from fault current to prevent false tripping of relay protection devices. In other words, if magnetizing inrush current is treated as "useless" and eliminated, important information for transformer monitoring and early warning will be lost. Summary of the Invention

[0005] The purpose of the present invention is to provide a transformer fault early warning method, which collects the excitation inrush current, analyzes the excitation inrush current, makes a judgment based on the characteristic quantity of the excitation inrush current, and issues an early warning if an abnormality occurs.

[0006] To solve the above technical problems, the present invention is achieved through the following technical solutions:

[0007] The present invention is a method for transformer fault early warning, comprising: after the transformer is put into operation, monitoring the excitation inrush current information of the transformer when it is no-load switched on, and extracting the characteristic quantity of the excitation inrush current information;

[0008] The characteristic quantities of the excitation inrush current include the excitation inrush current decay time Tb, the excitation inrush current peak value Im, the excitation inrush current waveform discontinuity angle Tα, and the excitation inrush current current change rate ΔIb:

[0009] If the change in the characteristic value compared to the baseline value of the transformer before commissioning is greater than the threshold, an early warning will be issued.

[0010] Preferably, before the transformer is put into operation, a no-load opening test is carried out on the transformer, and the characteristic quantity of the excitation inrush current when the transformer is no-load closed is extracted as a benchmark.

[0011] Preferably, the decay time Tb of the excitation inrush current is:

[0012] After the transformer is switched on, the moment when the first current peak appears is regarded as the starting time of the excitation inrush current. p The absolute value of dI is always less than set , and the rate of change of two adjacent current peaks If it is always less than dI%, the end time of the magnetizing inrush current is taken as the end time of Tdi. set , dI% can be set by the user. p (N) is the Nth current peak, i p (N+1) is the N+1th current peak value, and N represents the serial number of the current peak value.

[0013] The difference between the end time and the start time is taken as the decay time characteristic value Tb of the excitation inrush current.

[0014] Preferably, the excitation inrush current peak value Ib is:

[0015] After the transformer is closed, the current with the largest absolute value among the first N current peaks is taken as Ib, where N is a positive integer ranging from 1 to 5.

[0016] Preferably, the excitation inrush current waveform interruption angle Tα is:

[0017] After the transformer is switched on, measure the discontinuity time t between the two peaks of the magnetizing inrush current;

[0018] Convert the interruption time t to the interruption angle Tα, where Tα = 360°*t / T;

[0019] The average value of the discontinuity angle of each waveform during the entire excitation inrush current decay time is taken as the discontinuity angle characteristic value;

[0020] Where T is the period of the magnetizing inrush current waveform.

[0021] Preferably, the excitation inrush current change rate ΔIb is:

[0022] After the transformer is switched on, calculate the rate of change of adjacent current peaks in the magnetizing inrush current waveform, △i. i p (N) is the Nth current peak value, i p (N+1) is the N+1th current peak value, and N represents the serial number of the current peak value.

[0023] The average value of the change rate △Ib of each waveform during the entire excitation inrush current decay time is taken as the current change rate characteristic quantity.

[0024] Preferably, before the transformer is put into operation, 3-10 no-load closing tests are carried out to obtain the excitation inrush current data after each closing of the transformer and form an excitation inrush current feature library; after the transformer is put into operation, the excitation inrush current data after each closing of the transformer is obtained; and the excitation inrush current data detected each time is compared with the excitation inrush current feature library;

[0025] If the monitored excitation inrush current data is compared with the corresponding characteristic reference value in the excitation inrush current characteristic library and is greater than the reference value by dB1% or less than the reference value by dB2%, the excitation inrush current is abnormal. The dB1% value ranges from 105% to 200%; the dB2% value ranges from 0% to 95%.

[0026] Preferably, if the excitation inrush current decay time is greater than the decay time characteristic value dB1% or more, the excitation inrush current decay time of this closing operation does not meet the time characteristic value index;

[0027] If the peak value of the magnetizing inrush current is above the characteristic value dB1%, the peak value of the magnetizing inrush current for this closing does not meet the peak characteristic quantity index; dB1% is 105% to 200%;

[0028] If the excitation inrush current waveform discontinuity angle Tα is greater than dB1% of the excitation inrush current reference value or less than dB2% of the excitation inrush current reference value, the excitation waveform discontinuity angle for this closing does not meet the discontinuity angle characteristic quantity index; dB1% ranges from 105% to 200%; dB2% ranges from 0% to 95%;

[0029] If the excitation inrush current change rate △Ib is greater than dB1% of the reference value or less than dB2% of the reference value, the excitation inrush current change rate △Ib of this closing does not meet the excitation inrush current change rate characteristic quantity index. dB1% ranges from 105% to 200%; dB2% ranges from 0% to 95%;

[0030] Preferably, if the peak value of the magnetizing inrush current appears after the Nth cycle, the peak value of the magnetizing inrush current for this closing operation does not meet the peak characteristic quantity index, where N is a positive integer and takes a value of 1 to 5.

[0031] Preferably, if there are two or more indicators that do not meet the characteristic quantity indicators, there are hidden dangers in the transformer coil and an alarm needs to be issued for maintenance.

[0032] The present invention has the following beneficial effects:

[0033] The present invention collects the excitation inrush current and analyzes and compares the excitation inrush current decay time Tb, excitation inrush current peak value Im, excitation inrush current waveform interruption angle Tα, and excitation inrush current current change rate ΔIb data. If an abnormality is found, the user is reminded to repair it in time to prevent the fault from expanding.

[0034] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0036] Figure 1 is the transformer schematic diagram;

[0037] Figure 2 This is a schematic diagram of the transformer excitation inrush current waveform;

[0038] Figure 3 is the transformer excitation inrush current characteristic quantity - excitation inrush current decay time Tb;

[0039] Figure 4 The characteristic quantity of transformer excitation inrush current - excitation inrush current peak value Ib;

[0040] Figure 5 is the characteristic quantity of transformer excitation inrush current - interruption angle Tα; DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0042] See also Figure 1 As shown,

[0043] The primary coil is connected to the power grid, with N1 turns; the secondary coil has N2 turns and is not connected to a load. According to the principles of electromagnetic induction and circuit principles:

[0044] When no-load, the voltage of transformer N1 winding is:

[0045]

[0046] Where N1 is the number of turns of the winding, r1 is the resistance of the winding, and Ф is the cross-linked magnetic flux.

[0047] The N1 winding is connected to the grid, and U1 is the grid voltage, which is:

[0048] U1=U scos(ωt+θ) (Equation 2)

[0049] Where θ is the initial phase angle of the grid voltage, we can get:

[0050]

[0051] The magnetic flux of the coil is generated by the current i passing through the coil, which is defined by the coil self-inductance L, and we can get

[0052]

[0053] but

[0054]

[0055] Substituting (Equation 5) into (Equation 3), we can obtain:

[0056]

[0057] Where L1 is the self-inductance of N1 coil

[0058] Solving the differential equation (6), we can obtain:

[0059]

[0060] in is the time constant of coil N1; is the impedance angle of the N1 coil;

[0061] Φ r is the residual magnetism of the transformer core before closing. When the transformer is closed for the first time, the residual magnetism Φ r It can be 0.

[0062] Φ s is the amplitude of the non-periodic component, which is determined by the initial conditions at the time of closing, that is, t = 0. Without considering the residual magnetism, due to the conservation of flux, the instantaneous flux before and after closing should be 0, and Φ can be calculated based on this s

[0063] It can be seen that when the transformer is closed at no load, the magnetic flux consists of three parts: the decaying non-periodic component Φ s e -τt , periodic component And the original remanence Φ r These magnetic fluxes are superimposed on the transformer core, which may cause the total magnetic flux of the magnetic circuit to exceed the saturation flux designed for the transformer, resulting in magnetic circuit saturation, a sharp drop in magnetic permeability, and a large peak excitation inrush current.

[0064] The excitation current is calculated as follows:

[0065] Taking into account

[0066]

[0067] The calculation formula of transformer coil self-inductance is:

[0068]

[0069] L: inductance of transformer coil

[0070] l: average length of the transformer core magnetic circuit

[0071] N: number of turns of transformer coil

[0072] S: cross-sectional area of ​​transformer core magnetic circuit

[0073] μ: Magnetic permeability of the transformer core

[0074]

[0075] Combine

[0076] It can be seen that the transformer excitation inrush current i is a function related to the magnetic permeability μ of the transformer core, the number of turns N of the transformer coil, the grid frequency f, the grid voltage Us, the transformer coil resistance r, and the closing time t, that is:

[0077] i=f(μ,N,f,U s ,r,t) (Equation 11)

[0078] When the transformer core is saturated, the magnetic permeability μ drops sharply, and the transformer excitation reactance also drops sharply, resulting in a very large excitation inrush current i when closing the circuit breaker.

[0079] Among the above parameters, the magnetic permeability μ of the transformer core, the number of turns N of the transformer coil, the grid frequency f, the grid voltage Us, the transformer coil resistance r and other parameters generally change very little. The most influential factor is the phase angle when closing the circuit breaker, that is, Without considering the influence of residual magnetism, as long as the phase angle at closing is the same, the waveform of the transformer excitation inrush current will not change much.

[0080] If the transformer coil's internal insulation is damaged or deformed, the number of turns N and the resistance r of the transformer coil will change, which in turn will cause a change in the transformer coil's self-inductance L. These changes in parameters will also cause the characteristics of the transformer's no-load closing magnetizing inrush current to change.

[0081] The present invention extracts characteristic quantities from the transformer excitation inrush current waveform, and then infers whether the transformer has potential fault hazards based on changes in the characteristic quantities.

[0082] Specifically, a transformer fault early warning method includes the following steps:

[0083] Before the transformer is put into operation, a no-load opening test is carried out on the transformer, and the characteristic quantity of the excitation inrush current when the transformer is no-load closed is extracted as the benchmark value.

[0084] After the transformer is put into operation, the excitation inrush current information of the transformer when it is closed under no-load conditions is monitored, and the characteristic quantity of the excitation inrush current information is extracted;

[0085] The excitation inrush current characteristic quantities include the excitation inrush current decay time Tb, the excitation inrush current peak value Im, the excitation inrush current waveform discontinuity angle Tα, and the excitation inrush current current change rate ΔIb. The excitation inrush current characteristic quantities are visualized in the form of a plot:

[0086] If the change in the characteristic value compared to the baseline value of the transformer before commissioning is greater than the threshold, an early warning will be issued.

[0087] Decay time Tb of magnetizing inrush current:

[0088] After the transformer is switched on, the moment when the first current peak appears is regarded as the starting time of the excitation inrush current. p The absolute value of dI is always less than set , and the rate of change of two adjacent current peaks If it is always less than dI%, the end time of the magnetizing inrush current is taken as the end time of Tdi. set , dI% can be set by the user. p (N) is the Nth current peak value, i p (N+1) is the N+1th current peak value, and N represents the serial number of the current peak value.

[0089] The difference between the end time and the start time is taken as the decay time characteristic value Tb of the excitation inrush current.

[0090] Among them, the peak value of the excitation inrush current Ib is:

[0091] After the transformer is closed, the current with the largest absolute value among the first N current peaks is taken as Ib, where N is a positive integer, generally ranging from 1 to 5.

[0092] Excitation inrush current waveform interruption angle Tα:

[0093] After the transformer is switched on, the discontinuity time t between the two peaks of the excitation inrush current is measured. The discontinuity time t is converted into a discontinuity angle Tα, where Tα = 360°*t / T. The average discontinuity angle of each waveform during the entire excitation inrush current decay time is used as the discontinuity angle characteristic value.

[0094] Where T is the period of the magnetizing inrush current waveform.

[0095] Excitation inrush current change rate △Ib:

[0096] After the transformer is switched on, calculate the rate of change of adjacent current peaks in the magnetizing inrush current waveform, △i. The average value of the change rate △Ib of each waveform during the entire excitation inrush current decay time is taken as the current change rate characteristic quantity. p (N) is the Nth current peak, i p (N+1) is the N+1th current peak value, and N represents the serial number of the current peak value.

[0097] Additionally:

[0098] Before the transformer is put into operation, 3-10 no-load closing tests are carried out to obtain the excitation inrush current data after each closing of the transformer and form an excitation inrush current feature library. After the transformer is put into operation, the excitation inrush current data after each closing of the transformer is obtained; the excitation inrush current data detected each time is compared with the excitation inrush current feature library.

[0099] The magnetizing inrush current characteristic quantities include the magnetizing inrush current decay time Tb, the magnetizing inrush current peak value Im, the magnetizing inrush current waveform discontinuity angle Tα, and the magnetizing inrush current current change rate ΔIb, which are extracted according to the method described above.

[0100] Compare each subsequent detected excitation inrush current data with the excitation inrush current signature database. If the excitation inrush current data detected is greater than the reference value by 1% dB or less than 2% dB, the excitation inrush current is abnormal. The dB1% value is generally between 105% and 200%, and the dB2% value is generally between 0% and 95%.

[0101] Specifically, if the excitation inrush current decay time is greater than the decay time characteristic value dB1%, the excitation inrush current decay time of this closing does not meet the time characteristic value indicator; dB1% is generally set at 105% to 200%;

[0102] If the peak value of the magnetizing inrush current is above the characteristic value dB1%, the peak value of the magnetizing inrush current for this closing operation does not meet the peak characteristic quantity index. If the peak value of the magnetizing inrush current appears after the Nth cycle, the peak value of the magnetizing inrush current for this closing operation does not meet the peak characteristic quantity index. dB1% is generally 105% to 200%; dB2% is generally 0% to 95%; N is a positive integer, generally 1 to 5.

[0103] If the excitation inrush current waveform discontinuity angle Tα is greater than dB1% of the excitation inrush current reference value or less than dB2% of the excitation inrush current reference value, the excitation waveform discontinuity angle of this closing does not meet the discontinuity angle characteristic quantity index; dB1% is generally 105% to 200%; dB2% is generally 0% to 95%;

[0104] If the magnetizing inrush current change rate △Ib is greater than dB1% of the reference value or less than dB2% of the reference value, the magnetizing inrush current change rate △Ib for this closing does not meet the magnetizing inrush current change rate characteristic quantity indicator. dB1% is generally between 105% and 200%; dB2% is generally between 0% and 95%.

[0105] Preferably, one of the monitored excitation inrush current data may be mismeasured. If the transformer is damaged, other data will also be abnormal. When there are more than two indicators that do not meet the characteristic quantity indicators, there are hidden dangers in the transformer coil and an alarm needs to be issued for maintenance.

[0106] It is worth noting that in the above system embodiment, the various units included are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of the functional units are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of the present invention.

[0107] In addition, a person skilled in the art will understand that all or part of the steps in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a program, and the corresponding program can be stored in a computer-readable storage medium, such as a ROM / RAM, a disk or an optical disk.

[0108] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A transformer fault early warning method, characterized in that: include: After the transformer is put into operation, the excitation inrush current information of the transformer when it is closed under no-load conditions is monitored, and the characteristic quantity of the excitation inrush current information is extracted; The characteristic quantities of the excitation inrush current include the excitation inrush current decay time Tb, the excitation inrush current peak value Im, the excitation inrush current waveform discontinuity angle Tα, and the excitation inrush current current change rate ΔIb: If the characteristic value changes more than the threshold value compared to the transformer's baseline value before commissioning, an early warning will be issued. Specifically: If the excitation inrush current decay time is greater than the decay time characteristic value dB1% or more, the excitation inrush current decay time of this closing circuit breaker does not meet the time characteristic value indicator; If the peak value of the excitation inrush current is more than 2% of the characteristic value, the peak value of the excitation inrush current for this closing does not meet the peak characteristic quantity index; If the excitation inrush current waveform discontinuity angle Tα is greater than dB1% of the excitation inrush current reference value or less than dB2% of the excitation inrush current reference value, the excitation waveform discontinuity angle of this closing does not meet the discontinuity angle characteristic quantity index; If the excitation inrush current change rate △Ib is greater than dB1% of the reference value or less than dB2% of the reference value, the excitation inrush current change rate △Ib of this closing does not meet the excitation inrush current change rate characteristic quantity index; If there are two or more indicators that do not meet the characteristic quantity indicators, there are hidden dangers in the transformer coil and an alarm and maintenance are required.

2. A transformer fault early warning method according to claim 1, characterized in that: Before the transformer is put into operation, a no-load opening test is carried out on the transformer, and the characteristic quantity of the excitation inrush current when the transformer is no-load closed is extracted as a benchmark.

3. A transformer fault early warning method according to claim 2, characterized in that: Decay time Tb of magnetizing inrush current: After the transformer is switched on, the moment when the first current peak appears is regarded as the starting time of the magnetizing inrush current; When the current peak value i p The absolute value of dI is always less than set , and the rate of change of two adjacent current peaks If it is always less than dI%, the moment when Tdi ends is taken as the end time of the magnetizing inrush current. i p (N) is the Nth current peak, i p (N+1) is the N+1th current peak, where N represents the sequence number of the current peak; The difference between the end time and the start time is taken as the decay time characteristic value Tb of the excitation inrush current.

4. A transformer fault early warning method according to claim 2, characterized in that: Peak value of excitation inrush current Ib: After the transformer is closed, the current with the largest absolute value among the first N current peaks is taken as Ib, where N is a positive integer.

5. The transformer fault early warning method according to claim 2, characterized in that: Excitation inrush current waveform interruption angle Tα: After the transformer is switched on, measure the discontinuity time t between the two peaks of the magnetizing inrush current; Convert the interruption time t to the interruption angle Tα, where Tα = 360°*t / T; The average value of the discontinuity angle of each waveform during the entire excitation inrush current decay time is taken as the discontinuity angle characteristic value; Where T is the period of the magnetizing inrush current waveform.

6. The transformer fault early warning method according to claim 2, characterized in that: Excitation inrush current change rate △Ib: After the transformer is switched on, calculate the rate of change of adjacent current peaks in the magnetizing inrush current waveform, △i. The average value of the change rate △Ib of each waveform during the entire excitation inrush current decay time is taken as the current change rate characteristic quantity; Where, (N) is the Nth current peak, i p (N+1) is the N+1th current peak value, and N represents the serial number of the current peak value.

7. A transformer fault early warning method according to any one of claims 1 to 6, characterized in that: Before the transformer is put into operation, 3-10 no-load closing tests are carried out to obtain the excitation inrush current data after each closing of the transformer and form an excitation inrush current feature library; after the transformer is put into operation, the excitation inrush current data after each closing of the transformer is obtained; and the excitation inrush current data detected each time are compared with the excitation inrush current feature library.

8. The transformer fault early warning method according to claim 7, characterized in that: If the peak value of the excitation inrush current appears after the Nth cycle, the peak value of the excitation inrush current for this closing operation does not meet the peak characteristic quantity index.

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