CN106772152B - A kind of measurement method of transformer core remanent magnetism - Google Patents

A kind of measurement method of transformer core remanent magnetism Download PDF

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CN106772152B
CN106772152B CN201611050411.7A CN201611050411A CN106772152B CN 106772152 B CN106772152 B CN 106772152B CN 201611050411 A CN201611050411 A CN 201611050411A CN 106772152 B CN106772152 B CN 106772152B
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magnetization curve
remanent magnetism
transformer
current
point
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CN106772152A (en
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赵丹丹
傅晨钊
林敏�
李红雷
黄华
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State Grid Shanghai Electric Power Co Ltd
East China Power Test and Research Institute Co Ltd
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State Grid Shanghai Electric Power Co Ltd
East China Power Test and Research Institute Co Ltd
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00Arrangements or instruments for measuring magnetic variables
    • G01R33/12Measuring magnetic properties of articles or specimens of solids or fluids

Abstract

The present invention relates to a kind of measurement methods of transformer core remanent magnetism, method includes the following steps: 1) obtaining the magnetization curve of transformer core, which discloses the DC component of no-load current and the relationship of iron core remanent magnetism;2) 380V ac test voltage is loaded in transformer winding, measurement obtains no-load current;3) DC component of the no-load current is obtained;4) iron core remanent magnetism is obtained according to the magnetization curve and DC component.Compared with prior art, the present invention has many advantages, such as simple and feasible, can quantitative determine the remanent magnetism amount of master iron core, instructs the formulation of the demagnetization scheme of master iron core remanent magnetism, assesses erasure effect, provides technical support for main transformer test and operation.

Description

A kind of measurement method of transformer core remanent magnetism
Technical field
The present invention relates to transformer test and operation fields, more particularly, to a kind of measurement side of transformer core remanent magnetism Method.
Background technique
Transformer is by electromagnetic induction effect operation, using magnetic field as coupled field.Transformer core generally selects magnetic conductivity Higher ferromagnetic material, such as silicon steel sheet.The magnetic conductivity of ferromagnetic material be it is nonlinear, numerical value with magnetic field strength variation And change.Why ferromagnetic material has high magnetic property, be due to Ferromagnetic Material there is many very littles, have determining magnetic pole Property and there is the magnetic domain of very hard magnetization intensity, as shown in Figure 1.Under extraneous magnetic fields, magnetic domain has again along outer magnetic field direction It is regularly arranged, so that the magnetic field actually generated is more much bigger than the magnetic field in nonferromagnetic material.
The polarization of magnetic domain needs to undergo a process, therefore in magnetic history, the magnetic induction density B in ferromagnetic material Variation lags behind the variation of external magnetic field strength H, i.e. hysteresis.Under alternation external magnetic field, iron-core magnetic induction intensity B is with outer magnetic The change curve of field intensity H becomes hysteresis loop.Different hysteresis loops can be measured with different Bm values, by all hysteresis loops It is connected on the vertex of I quadrant, obtained magnetization curve is called fundamental magnetization curve, as shown in Figure 2.Due to most of iron The hysteresis loop of magnetic material is all very narrow, therefore, in engineer application, hysteresis loop solution can be replaced to ask with fundamental magnetization curve Topic, error are allowed by engineering.
After transformer is cut off the power, the magnetic linkage retained in the core is known as remanent magnetism.Remanent magnetism will increase when main transformer closes a floodgate Excitation surge current increases the harmonic wave in exciting current, increases transformer power consumption, it is also possible to cause protective relaying maloperation to be made, to main transformer Operation adversely affect, meanwhile, remanent magnetism is also possible to make follow-up test results abnormity.
The way of production of remanent magnetism be mainly D.C. resistance test, remanent magnetism number depend on transformer winding pass through it is straight Galvanic electricity intensity of flow and time.It is directly hindered in test in transformer, to improve measurement accuracy, shortening time of measuring, usually uses high current Test equipment is more than exciting current, makes core sataration, can generate serious remanent magnetism.In addition, can also be produced in no-load transformer separating brake Raw remanent magnetism, but master iron core is all made of soft magnetic materials at present, and remanent magnetism amount is less, and corresponding harm is also smaller.
In order to guarantee the accurate and main transformer operational safety of follow-up test, it is desirable that did D.C. resistance test after to main transformer into Row demagnetization, but erasure effect can not check.In subsequent low-voltage no-load test, it is often different with delivery test often to there is test result The case where cause, cannot really reflect inside transformer state.It needs scene to carry out secondary demagnetization, increases test work load and work Time.In addition, also occurring the influence due to iron core remanent magnetism in super-pressure main transformer closes a floodgate and tests, and leading to main transformer excitation surge current Excessive, the thing of triggering main transformer grave gas protection act occurs.
In summary, important in inhibiting is tested main transformer and be safely operated to the measuring technique of main transformer remanent magnetism amount.Comprehensive mesh Preceding domestic and international present Research is concentrated demagnetization technology for the research of main transformer remanent magnetism at present, the measurement of remanent magnetism is related to less.
Summary of the invention
It is an object of the present invention to overcome the above-mentioned drawbacks of the prior art and provide a kind of simple and feasible changes The measurement method of depressor iron core remanent magnetism.
The purpose of the present invention can be achieved through the following technical solutions:
A kind of measurement method of transformer core remanent magnetism, method includes the following steps:
1) magnetization curve of transformer core is obtained, which discloses the DC component and iron core remanent magnetism of no-load current Relationship;
2) 380V ac test voltage is loaded in transformer winding, measurement obtains no-load current;
3) DC component of the no-load current is obtained;
4) iron core remanent magnetism is obtained according to the magnetization curve and DC component.
The magnetization curve of the transformer core is converted by main transformer no-load characteristic.
When main transformer no-load characteristic is converted to the magnetization curve of transformer core, following hypothesis is set:
A) ignore the magnetic hysteresis and eddy-current loss in iron core;
B) ignore winding resistance;
C) magnetization curve is formed point by point.
During the formation magnetization curve, the current value of each point in magnetization curve is calculated by trapezoidal integration.
In the step 3), by carrying out FFT decomposition to the no-load current, DC component is obtained, and pass through following public affairs Formula obtains DC component per unit value:
In formula, IdcFor the DC component of the no-load current of actual measurement,For DC component per unit value, I0For the specified electricity of main transformer The virtual value of stream.
Compared with prior art, the invention has the following advantages that
(1) present invention proposes that simple and feasible transformer core is surplus by the relationship of research no-load current and iron core remanent magnetism The measurement method of magnetic.
(2) present invention can quantitative determine the remanent magnetism amount of master iron core, to instruct the demagnetization scheme of master iron core remanent magnetism It formulates, assesses erasure effect, provide technical support for main transformer test and operation.
(3) present invention can effectively measure iron core remanent magnetism amount, facilitate the inspection of erasure effect, to improve main transformer The safety of operation.
Detailed description of the invention
Fig. 1 is the magnetic domain schematic diagram in ferromagnetic material, wherein (1a) is schematic diagram before magnetizing, and (1b) is after fully magnetising Schematic diagram;
Fig. 2 is the hysteresis loop and fundamental magnetization curve in ferromagnetic material, wherein (2a) is hysteresis loop, and (2b) is basic Magnetization curve;
Fig. 3 is that iron core magnetizes curve synoptic diagram;
Fig. 4 is to have no-load current schematic diagram in the case of remanent magnetism;
Fig. 5 is the Relationship Comparison schematic diagram of iron core magnetization curve and no-load current DC component and remanent magnetism curve;
Fig. 6 is flow diagram of the invention;
Fig. 7 is no-load transformer current waveform schematic diagram under small voltage, wherein (7a) is that (low pressure is non-linear by Br=-25 Area) when waveform diagram, (7b) be (the low pressure inelastic region) Br=-100 when waveform diagram, (7c) be Br=-495.17 (low pressure is non- Linear zone) when waveform diagram.
Specific embodiment
The present invention is described in detail with specific embodiment below in conjunction with the accompanying drawings.The present embodiment is with technical solution of the present invention Premised on implemented, the detailed implementation method and specific operation process are given, but protection scope of the present invention is not limited to Following embodiments.
The typical fundamental magnetization curve of transformer is as shown in figure 3, can be divided into three parts: low pressure inelastic region, linear zone, height Press inelastic region.In no remanent magnetism, when low-voltage no-load test is carried out at scene, iron core multiplexing is made non-linear in low pressure Area.If there is remanent magnetism in iron core, the test voltage of low-voltage, magnetic induction intensity and residual magnetic induction in iron core are loaded on winding Intensity is superimposed, and the magnetic induction intensity in iron core just will appear biasing, correspondingly, no-load current also will appear direct current biasing, such as Fig. 4 It is shown.Therefore, the DC component in no-load current is the direct reaction of remanent magnetism amount in iron core, measures the zero load electricity under small voltage Stream, can measure iron core remanent magnetism indirectly.
From principle, the DC component in the small no-load current of small voltage abides by the basic of the transformer with iron core remanent magnetism amount Magnetization curve constraint, i.e., iron core remanent magnetism amount and the DC component in no-load current are one-to-one.
To verify this corresponding relationship, by taking certain 110kV main transformer winding as an example, simulation model is established using EMTP, in iron core Upper load 380V sinusoidal voltage calculates the no-load current under different iron core remanent magnetism amounts, and applies Fourier analysis, calculates sky Carry the DC component in electric current.Calculated result is as shown in table 1-2, and in table, a reference value of electric current is the sky under main transformer voltage rating Set current value (1.78A), a reference value of magnetic flux are the magnetic flux (495.17Wb) under voltage rating.Magnetic induction intensity point in iron core Not at low pressure inelastic region, linear zone and high pressure inelastic region, no-load current waveform difference is as shown in Figure 5.
As it can be seen that DC component in no-load current under small voltage it is corresponding with iron core remanent magnetism amount about with the transformer Fundamental magnetization curve is almost the same.
In fact, test and operations staff can only learn main transformer no-load characteristic from Transformer Plant Test report, due to The stray capacitance influences of transformer, there is a certain error with the excitation curve of iron core, but error is in engineering allowed band. In the present invention, iron core fundamental magnetization curve is substituted using main transformer no-load characteristic.
As shown in fig. 6, the measurement method of transformer core remanent magnetism of the invention the following steps are included:
1) main transformer no-load characteristic is obtained, the magnetization curve of transformer core is converted into, which discloses The DC component of no-load current and the relationship of iron core remanent magnetism;
2) 380V ac test voltage is loaded in transformer winding, measurement obtains no-load current;
3) by carrying out FFT decomposition to the no-load current, DC component is obtained;
In this method, DC component is recorded using per unit value form, is obtained by the following formula:
In formula, IdcFor survey main transformer no-load current DC component,Based on it is emptying carry current dc component mark Value, I0For the virtual value of the rated current of main transformer;
4) iron core remanent magnetism is obtained according to the magnetization curve and DC component.
Key using the no-load current measurement measurement of residual magnetism under small voltage is that no-load transformer characteristic is converted into substantially The accuracy of magnetization curve.In conversion process, do it is assumed hereinafter that:
1, ignore the magnetic hysteresis and eddy-current loss in iron core;
2, ignore winding resistance;
3, magnetization curve is formed point by point.
Voltage in electric system can regard ideal voltage source, i.e. standard sine voltage, therefore iron core magnetic flux as are as follows:
(in the formula, urms, ω what is respectively indicated?)
In formula, urmsFor system voltage virtual value, ω is system voltage angular frequency, and the π of ω=2 f, f are system voltage frequency, In China f=50Hz.
CTR current transfer ratio is more complex, and in conversion process, choosing first point is reference point, partially thinks below reference point It is linear region.
Current value of the reference point in magnetization curve sees below formula
In formula, irms,1For electric current conversion in, first point, that is, reference point current effective value.
The equal recursion of remaining each point acquires.Assuming that inFor next value to be asked, and then assume sinusoidal magnetic linkage just in maximum Value reaches φn.Current curve uses Piecewise, and each known point is it has been determined that only final stage is because of inIt is unknown uncertain. Then i is calculated with integration methodnVirtual value:
Using trapezoidal integration, can calculate
In formula, a, b are respectively the constant coefficient of trapezoidal integration, can calculate gained according to main transformer magnetization curve.
Separately have, In=irms,n
The current value i of nth point in magnetization curve can then be found outn, to form magnetization curve point by point.

Claims (2)

1. a kind of measurement method of transformer core remanent magnetism, which is characterized in that method includes the following steps:
1) magnetization curve of transformer core is obtained, which discloses the DC component of no-load current and the pass of iron core remanent magnetism System, the magnetization curve of the transformer core are converted by main transformer no-load characteristic;
2) 380V ac test voltage is loaded in transformer winding, measurement obtains no-load current;
3) DC component of the no-load current is obtained;
4) iron core remanent magnetism is obtained according to the magnetization curve and DC component;
When main transformer no-load characteristic is converted to the magnetization curve of transformer core, following hypothesis is set:
A) ignore the magnetic hysteresis and eddy-current loss in iron core;
B) ignore winding resistance;
C) magnetization curve is formed point by point;
During the formation magnetization curve, the current value of each point in magnetization curve is calculated by trapezoidal integration, specifically, choosing Taking first point is reference point, and current value of the reference point in magnetization curve sees below formula:
In formula, irms,1For electric current conversion in, first point, that is, reference point current effective value;
inFor next value to be asked, i is calculated with integration methodnVirtual value:
Using trapezoidal integration, calculate
In formula, a, b are respectively the constant coefficient of trapezoidal integration;
Pass through In=irms,nFind out the current value i of nth point in magnetization curven, to form magnetization curve point by point.
2. the measurement method of transformer core remanent magnetism according to claim 1, which is characterized in that in the step 3), lead to It crosses and FFT decomposition is carried out to the no-load current, obtain DC component, and DC component per unit value is obtained by following formula:
In formula, IdcFor the DC component of the no-load current of actual measurement,For DC component per unit value, I0For the rated current of main transformer Virtual value.
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CN107910157B (en) * 2017-11-30 2023-12-15 国家电网公司 Universal intelligent main transformer demagnetizing instrument
CN108107384A (en) * 2017-12-18 2018-06-01 国网新疆电力公司检修公司 750kV auto-transformers directly hinder remanent magnetism amount computational methods after experiment
CN109541506A (en) * 2018-10-16 2019-03-29 中国电力科学研究院有限公司 A kind of measurement of power transformer iron core magnetic characteristic and analytical equipment
CN109490729B (en) * 2018-12-07 2020-12-22 国网四川省电力公司电力科学研究院 Residual magnetism assessment method and system based on variable region integration in voltage attenuation process
CN110208725A (en) * 2019-06-19 2019-09-06 国家电网有限公司 A method of judging power transformer iron core, whether there is or not remanent magnetism
CN112068050B (en) * 2020-09-10 2023-10-13 云南电网有限责任公司电力科学研究院 Transformer remanence quantitative evaluation and elimination method
CN113325345B (en) * 2021-06-02 2024-04-09 云南电网有限责任公司电力科学研究院 Device and method for testing residual magnetism of transformer core
CN115032577B (en) * 2022-08-10 2022-11-15 之江实验室 Low-noise residual magnetism detection device and method for annular ferrite material

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