CN102841233B - Secondary current compensation method for current mutual inductors - Google Patents
Secondary current compensation method for current mutual inductors Download PDFInfo
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- CN102841233B CN102841233B CN201210334800.8A CN201210334800A CN102841233B CN 102841233 B CN102841233 B CN 102841233B CN 201210334800 A CN201210334800 A CN 201210334800A CN 102841233 B CN102841233 B CN 102841233B
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Abstract
The invention relates to a secondary current compensation method for current mutual inductors. The method comprises the steps specifically as follows: making a large amount of experiments on current mutual inductors in the same batch to obtain typical input and output curves of the current mutual inductors; conducting segmentation and fitting on the output curve of the current mutual inductors under a given error; calculating a compensation coefficient of each segment; and writing the compensation coefficients into signal collecting software. By adopting the secondary current compensating method for current mutual inductors, the problem of the current mutual inductors in inaccurate detection under large currents can be well solved, and accurate measurement values can be obtained through compensation even in condition of large currents.
Description
Technical field
The present invention relates to a kind of current compensation method, particularly a kind of Current Transformer Secondary current compensation method.
Background technology
Along with the development that modern society produces and lives, digitlization, the intellectuality of traditional switch electrical equipment become inexorable trend.The central processing module that the parameter such as electric current, voltage at Operation of Electric Systems scene all directly can not be digitized controller carries out the acquisition and processing of signal, and measured passage all will be sent into after transformer (as current transformer, voltage transformer etc.) are transformed to corresponding electric quantity signal, after further conditioning, just can deliver to A/D converter become the digital quantity that central processing unit and Controlling model can accept and process.Along with the lifting of processor performance, make electronic loop more and more less for the impact of the precision of signals collecting and the performance of device for switching, therefore, due to the restriction of current transformer nonlinear characteristic, its progress of disease error has become the deciding factor affecting device for switching acting characteristic.
In various electric equipment, instrument and meter, often need the inspection carrying out electric current, and different equipment is not quite similar for the standard of current detecting and scope: common instrument and meter generally only need detect the small electric stream within the scope of rated current; Motor protector only need detect the electric current within rated current 5 times; Electronic overload relay generally only need detect the electric current within 7.2 times; And control and protective switching device, not only will detect 7.2 times of rated current during overload, also will detect 6 ~ 12 times of electric currents of definite time protection, in the product of some specification, highest detection electric current can reach kilo-ampere, is the hundreds of times of lowest detection electric current.
Be limited by the restriction that volume of switch is little, the design size of current transformer is limited, considers the impact of CT saturation characteristic, and the linearity test that will realize electric current within the scope of so large curent change is almost impossible.So when current transformer detects larger current, secondary current often needs the reaction primary current value that certain compensation could be comparatively true and reliable.
Traditional compensation method can be divided into the Passively compensated and large class of active compensation two.Passively compensated method has a variety of, as turn compensation, parallel capacitive compensation etc., but these compensation can only translation error wireless, and the shape of error curve can not be changed, again for the consideration of the factors such as current transformer cost and size, this compensation way is too limited, when particularly current transformer occurs saturated, the effect that this compensation way obtains is very faint.The basic ideas of active compensation are, are extracted or the exciting current of analog current transformer by certain method, then generate the equal exciting curent of summation current transformer by electronic circuit, and are injected in secondary circuit, thus compensate secondary current.But this compensation way also exists shortcoming, as needs increase electronic circuit, and complex structure, debugging inconvenience, realization difficulty etc.
Therefore, if based on the software compensation of current transformer input-output curve, by obtaining the output of ideal Current Transformer Secondary electric current to the segmented compensation of input-output curve.It has, and principle is simple, realization is convenient, without the need to advantages such as peripheral circuits.
Summary of the invention
The object of this invention is to provide a kind of Current Transformer Secondary current compensation method, can when CT saturation, by to the classification of current transformer, the compensation of secondary current, make the output characteristics of current transformer still can meet the requirement of system.
For achieving the above object, the invention provides a kind of secondary current compensation method of current transformer, concrete steps are as follows:
(1) current transformer of same batch is tested, obtain the input-output curve of current transformer;
(2) segmentation and matching are carried out to the curve of output of current transformer;
(3) penalty coefficient of each section is calculated;
(4) by penalty coefficient write signal acquisition software.
In the present invention, step (1) concrete operations are as follows:
1) classify to commaterial or with the current transformer of a collection of processing;
2) by the methods of sampling, 10 current transformers are randomly drawed;
3) primary side of each current transformer is led to respectively to the rated current of different multiples, and the rated voltage of record current transformer secondary side;
4) mean value of Current Transformer Secondary side voltage when asking for the rated current of different current transformer primary side different multiples, and record; Draw the input-output characteristic curve of current transformer, abscissa is the multiple of the rated current of current transformer, and ordinate is secondary side voltage.
In the present invention, step (2) concrete operations are as follows:
1) from the 1st point of the input-output characteristic curve of current transformer, connect and the 3rd L1 that is in line at the 1st, and try to achieve linear equation;
2) the 2nd the straight line L2 parallel with straight line L1 was tried to achieve again;
3) try to achieve further parallel with L1, L2, and to their equidistant straight line L3, with the fitting a straight line of L3 for putting 1,2,3;
4) error of fitting of calculation level 1,2,3, geometrically easily proves, the error of the 1st is maximum, is designated as
, then with given error
relatively;
5) if
, then produce the first paragraph of curve segmentation, then namely now all before straight line L1 distal point point formations one section are the starting point 1 of next segmentation with the distal point of the first segmentation, continue step 1); If
, then think that the point between straight line L1 and straight line L2 is substantially linear, error meets the demands, and continues to perform step 5);
6) connect at the 1st and form new L1 with more lower (the 4th point), and try to achieve this linear equation;
7) calculate between L1 two-end-point and arrive L1 apart from maximum some Q, then cross Q and make the straight line L2 parallel with L1; Be L3 and L1 further, L2 is parallel, and apart from equal, think that L3 is new matched curve;
8) error of fitting of L1 starting point (the 1st point) is calculated
, repeat step 5);
9) until calculated all measured datas, and segmentation is completed.
In the present invention, step (3) concrete operations are as follows:
1) curvilinear equation before calculation compensation;
（1）
Wherein:
for the secondary side voltage of the current transformer of actual measurement;
for the multiple of rated current;
with
for curve coefficients.
2) curvilinear equation of the ideal curve after calculation compensation;
(2)
Wherein:
for the secondary side voltage of ideally current transformer, that is: the output voltage after compensation;
for the multiple of rated current;
for ideal curve coefficient.
3) simultaneous two Solving Equations obtain the correction formula of secondary current, obtain penalty coefficient;
（3）
Wherein,
,
with
can be obtained by program computation based on existing test data.Further order
,
, be called penalty coefficient.Then formula (3) can be rewritten as:
（4）
Wherein:
for the secondary side voltage of ideally current transformer,
for the secondary side voltage of the current transformer of actual measurement,
,
for penalty coefficient.
In the present invention, step (4) concrete operations are as follows:
1) penalty coefficient is write EEPROM, and programming is to signal pickup assembly;
2), when harvester collects electric current, the current segmenting residing for signal is first judged;
3) then to table look-up acquisition penalty coefficient;
4) utilize compensation formula, the signal gathered is revised, obtains new electric current.
Beneficial effect of the present invention: the secondary current compensation method adopting current transformer of the present invention, under can be good at solving big current, indeterminable problem examined by current transformer.The method first carries out piecewise fitting to curve, obtains the compensation formula of each segmentation, and then by the segment information of typical curve, the compensation formula of each section implants the Current calculation program of processing unit with the form of code.When measuring in real time, which section interval is program can be positioned at by automatic discrimination current measurement value, then starts corresponding backoff algorithm and compensates, thus obtain measured value comparatively accurately, when big current, can obtain measured value accurately equally by compensation.
Accompanying drawing explanation
The flow chart block diagram of Fig. 1 this patent compensation method;
Fig. 2 is the input and output virtual value empirical curve of current transformer;
Fig. 3 is current transformer curve segmentation schematic diagram;
Fig. 4 is current transformer curve repeatedly stepwise schematic views;
Fig. 5 is the compensation schematic diagram of matched curve;
Fig. 6 is segmentation and the matching example of curve;
Fig. 7 is the current transformer curve after compensating.
Detailed description of the invention
Below in conjunction with drawings and Examples, the present invention is made comparisons detailed description.
Embodiment 1:
With reference to Fig. 1, this is the concrete steps flow chart block diagram of secondary current compensation method of the present invention.
With reference to Fig. 2, this is the input and output virtual value empirical curve of current transformer.
As shown in the figure, for the ease of the Signal sampling and processing of hardware circuit, secondary current is converted into magnitude of voltage by sampling resistor.
Can clearly find out from figure when detect ER effect must larger time, secondary current curve of output rises and tends towards stability, it is no longer linear that its numerical value and input detect electric current, and along with the further increase of electric current, the error of current detecting can increase the stage being difficult to accept.In order to address this problem, the mode that have employed software compensation is revised secondary current, thus obtains the measurement electric current with actual primary current linearly relationship change.
With reference to Fig. 3 and Fig. 4, it is the piecewise fitting schematic diagram of current transformer curve.
Because curve of output exists serious non-linear, accurate as far as possible matched curve, just first must carry out segment processing to curve, and then distinguish each section of matched curve, finally obtain the fit equation group of this curve.The basic demand of curve segmentation is: under the prerequisite meeting error requirements, the least possible segmentation.Introduce the method for the controlled software automatic segmentation of a kind of error range below, step is as follows:
1) from the 1st point of measured data, connect and the 3rd L1 that is in line at the 1st, and try to achieve linear equation;
2) the 2nd the straight line L2 parallel with straight line L1 was tried to achieve again;
3) try to achieve further parallel with L1, L2, and to their equidistant straight line L3, with the fitting a straight line of L3 for putting 1,2,3;
4) error of fitting of calculation level 1,2,3, geometrically easily proves, the error of the 1st is maximum, is designated as
, then with given error
relatively.
5) if
, then produce the first paragraph of curve segmentation, then namely now all before L1 distal point point formations one section are the starting point 1 of next segmentation with the distal point of the first segmentation, continue step 1); If
, then think that the point between L1 and L2 is substantially linear, error meets the demands, and continues to perform step 5);
6) connect at the 1st and form new L1 with more lower (the 4th point), and try to achieve this linear equation;
7) calculate between L1 two-end-point and arrive L1 apart from maximum some Q, then cross Q and make the straight line L2 parallel with L1; Be L3 and L1 further, L2 is parallel, and apart from equal, think that L3 is new matched curve;
8) error of fitting of L1 starting point (the 1st point) is calculated
, repeat step 5);
9) until calculated all measured datas, and segmentation is completed.
As shown in Figure 3, for being come under given error range to the schematic diagram of measured curve segmentation by the method for linearity error band.Fig. 3 is the schematic diagram of repeatedly segmentation.Can prove, in linearity error band, the error of each point after overcompensation can not higher than the error of fitting compensating each point in front error band.And the higher limit of error of fitting can be artificially given.
With reference to Fig. 5, it is the compensation schematic diagram of matched curve.
After carrying out segmentation and matching according to above-mentioned steps to experimental data, following work will compensate by the curve good to matching exactly.So-called compensation will be revised the functional value in matched curve exactly, and makes revised value meet the error requirements of current measurement.One section after getting matching below in curve is example, describes the method that digital compensation realizes in detail.As shown in Figure 4.
If the equation of the matched curve ab section before compensating is:
（1）
Curve after compensation can be similar to the curve of output thought close to desirable, if linear equation is as follows:
(2)
Simultaneous equations (1) and (2), can obtain the correction formula of secondary current measured value:
（3）
In formula (3),
,
with
can be obtained by program computation based on existing test data.Further order
,
, be called penalty coefficient.Then formula (3) can be rewritten as:
（4）
Formula (4) is the compensation formula of secondary current, when secondary current (being converted into magnitude of voltage) measured value drops on ab interval, revised through formula (4) by this measured value, then revised measured value is close to ideal value, thus can obtain the size of tested primary current exactly.Obviously, the method is equally applicable to the error compensation of other curved section, just each section corresponding
with
be not identical, and the penalty coefficient of each section can be obtained by program computation.
embodiment 2
For the input-output characteristic curve of certain current transformer in Fig. 2.This curve has obtained by having done great many of experiments to the current transformer of same batch of same specification, has typicalness.The scope of testing current is 6A ~ 600A, totally 35 test points.By observation experiment curve and experiment with computing data known, when input current is between 6A ~ 150A, actual curve of output is very close with ideal curve, and namely the inspection of secondary current truly can reflect the size of primary current, therefore without the need to correction.But along with primary current continue to increase from 100A time, due to the saturation effect of current transformer, secondary current can not linearly increase, and causes error to become large, at this moment just needs to revise measurement result.
Given departure
=5%, the curve segmentation obtained by automatic segmentation fit procedure is 4 sections, and fit equation is same is the form of formula (1), and concrete data are as follows:
Table 1 curve segmentation and fitting parameter
| Hop count | 1 | 2 | 3 | 4 |
| a1（V/I） | — | 2.6 | 1.2 | 0.7 |
| b1（mV） | — | 122.1 | 443.7 | 625.6 |
| Primary current scope | 0~102A | 102~208A | 208~402A | 402~603A |
Matched curve as shown in Figure 6.
Penalty coefficient through calculating each section is further as follows:
Table 2 compensating parameter
| Hop count | 1 | 2 | 3 | 4 |
| 1 | 1.5 | 3.3 | 5.6 | |
| 0 | -184.2 | -1450.6 | -3506.1 |
Former data through formula (4), by the data obtained after table 2 parametric compensation as shown in Figure 7.
Get below between the first and last point of each segmentation and first and last point and depart from the characteristic point of fitting a straight line point farthest as error calculation.Easy proof, to drop in each segmentation worst error a little must appear among above 3.As table 3.
Table 3 error calculation
| Primary current (A) | 100.6 | 152.0 | 208.0 | 326.0 | 402.0 | 452.0 | 603.0 |
| Secondary voltage measured value (mV) | 361.0 | 537.0 | 672.0 | 831.0 | 900.0 | 946.0 | 1040 |
| Secondary voltage match value (mV) | 379.0 | 519.0 | 679.6 | 818.4 | 905.6 | 940.4 | 1045.3 |
| Secondary voltage offset (mV) | 380.3 | 621.3 | 782.8 | 1266.8 | 1533.9 | 1791.5 | 2317.9 |
| Secondary voltage ideal value (mV) | 394.7 | 596.3 | 816.0 | 1278.9 | 1577.1 | 1773.2 | 2365.6 |
| Error (%) before compensation | -9.3 | -11.0 | -21.4 | -53.9 | -75.2 | -87.4 | -127.5 |
| Error (%) after compensation | -3.8 | 4.0 | -4.2 | -1.0 | -2.8 | 1.0 | -2.0 |
The data of table 3 show, given departure
=5%, curve is divided into four sections, and each section compensate after worst error be all no more than 5%, with compensate before application condition, be greatly improved by the error after this digital algorithm compensates, well solving current transformer can not the difficult problem of linearity test on a large scale.
Although the present invention describes with reference to the above embodiments; but those of ordinary skill in the art; will be appreciated that above embodiment is only used to the present invention is described; should understand and wherein can make various changes and revise and not depart from the present invention in a broad sense; so not as limitation of the invention; as long as in spirit of the present invention, all the protection domain of claim of the present invention will be fallen into the change of above-described embodiment, distortion.
Claims (2)
1. a secondary current compensation method for current transformer, is characterized in that concrete steps are as follows:
(1) current transformer of same batch is tested, obtain the input-output characteristic curve of current transformer;
(1.1) classify to commaterial or with the current transformer of a collection of processing;
(1.2) by the methods of sampling, 10 current transformers are randomly drawed;
(1.3) primary side of each current transformer is passed to respectively to the rated current of different multiples, and the voltage of record current transformer secondary side;
(1.4) mean value of Current Transformer Secondary side voltage when asking for the rated current of different current transformer primary side different multiples, and record; Draw the input-output characteristic curve of current transformer, abscissa is the multiple of the rated current of current transformer, and ordinate is secondary side voltage;
(2) segmentation and matching are carried out to the input-output characteristic curve of current transformer;
(2.1) from the 1st point of the input-output characteristic curve of current transformer, connect and the 3rd L1 that is in line at the 1st, and try to achieve linear equation;
(2.2) the 2nd the straight line L2 parallel with straight line L1 was tried to achieve again;
(2.3) try to achieve further parallel with L1, L2, and to their equidistant straight line L3, with the fitting a straight line of L3 for putting 1,2,3;
(2.4) error of fitting of calculation level 1,2,3, geometrically easily proves, the error of the 1st is maximum, is designated as
, then with given error
relatively;
(2.5) if
, then produce the first paragraph of curve segmentation, then namely now all before straight line L1 distal point point formations one section are the starting point 1 of next segmentation with the distal point of the first segmentation, continue step (2.1); If
, then think that the point between straight line L1 and straight line L2 is substantially linear, error meets the demands, and continues to perform step (2.6);
(2.6) connect and the more lower L1 that namely the 4th formation is new at the 1st, and try to achieve this linear equation;
(2.7) calculate between L1 two-end-point and arrive L1 apart from maximum some Q, then cross Q and make the straight line L2 parallel with L1; Be L3 and L1 further, L2 is parallel, and apart from equal, think that L3 is new fitting a straight line;
(2.8) the L1 starting point i.e. error of fitting of the 1st is calculated
, repeat step (2.5);
(2.9) until calculated all measured datas, and segmentation is completed;
(3) penalty coefficient of each section is calculated;
(3.1) curvilinear equation before calculation compensation;
（1）
Wherein:
for the secondary side voltage of the current transformer of actual measurement;
for the multiple of rated current;
with
for curve coefficients;
(3.2) curvilinear equation of the ideal curve after calculation compensation;
(2)
Wherein:
for the secondary side voltage of ideally current transformer, that is: the output voltage after compensation;
for the multiple of rated current;
for ideal curve coefficient;
(3.3) simultaneous two Solving Equations obtain the correction formula of secondary current, obtain penalty coefficient;
（3）
Wherein,
,
with
can be obtained by program computation based on existing test data; Further order
,
, be called penalty coefficient; Then formula (3) is rewritten as:
（4）
Wherein:
for the secondary side voltage of ideally current transformer,
for the secondary side voltage of the current transformer of actual measurement,
,
for penalty coefficient;
(4) by penalty coefficient write signal acquisition software.
2. the secondary current compensation method of current transformer according to claim 1, is characterized in that step (4) concrete operations are as follows:
(1) penalty coefficient is write EEPROM, and programming is to signal pickup assembly;
(2), when harvester collects electric current, the current segmenting residing for signal is first judged;
(3) then to table look-up acquisition penalty coefficient;
(4) utilize compensation formula, the signal gathered is revised, obtains new electric current.
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| KR101798689B1 (en) * | 2013-12-05 | 2017-11-16 | 엘에스산전 주식회사 | Power device including current transformer and method for compensating of current trnasformer |
| CN105093160B (en) * | 2015-07-28 | 2018-03-20 | 宁波三星医疗电气股份有限公司 | A kind of electric energy meter error segmented compensation method |
| CN105866721B (en) * | 2016-06-06 | 2018-09-21 | 海盐新跃电器有限公司 | A kind of modification method of electric current split-core type meter gamut |
| CN107817462A (en) * | 2017-09-27 | 2018-03-20 | 苏州万龙电气集团股份有限公司 | A kind of breaker of plastic casing transformer current linear compensation method |
| CN107831352A (en) * | 2017-09-27 | 2018-03-23 | 德力西电气有限公司 | A kind of breaker and current measuring method with ribbon core current transformer |
| CN108680776A (en) * | 2018-05-23 | 2018-10-19 | 浙江中凯科技股份有限公司 | A kind of compensation system and equipment of electric signal |
| CN110138085A (en) * | 2019-05-28 | 2019-08-16 | 珠海博威智能电网有限公司 | A kind of high-precision distribution terminal based on nonlinear compensation algorithm |
| CN112816754B (en) * | 2020-12-22 | 2022-07-12 | 深圳供电局有限公司 | Current compensation method and equipment for current transformer |
| CN113687291A (en) * | 2021-08-24 | 2021-11-23 | 浙江大学 | Secondary side current compensation method and device of current transformer and electronic equipment |
| CN115078820B (en) * | 2022-08-19 | 2022-11-18 | 石家庄科林电气股份有限公司 | Saturation processing method for protection current transformer of low-voltage intelligent circuit breaker |
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