CN108957183B - Method and device for monitoring direct current magnetic bias of transformer - Google Patents
Method and device for monitoring direct current magnetic bias of transformer Download PDFInfo
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- CN108957183B CN108957183B CN201810730017.0A CN201810730017A CN108957183B CN 108957183 B CN108957183 B CN 108957183B CN 201810730017 A CN201810730017 A CN 201810730017A CN 108957183 B CN108957183 B CN 108957183B
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Abstract
The invention provides a method and a device for monitoring direct current magnetic bias of a transformer, wherein the method comprises the following steps: measuring a mixed current signal at a neutral point of the main transformer which is grounded through a current measuring device, wherein the current measuring device comprises a Hall element which is arranged at the neutral point of the main transformer which is grounded, and the mixed current signal comprises direct current magnetic bias current, magnetic bias response current and power frequency unbalanced current; analyzing the mixed current signal to determine the direct current magnetic bias current and the magnetic bias response current; and determining the magnetic bias response degree of the transformer according to the magnetic bias response current. The scheme can accurately detect and monitor the direct current bias current flowing into the transformer when the direct current system operates in a single-pole ground mode; the magnetic biasing response degree of the transformer after the direct current magnetic biasing current flows into the transformer can be monitored, so that the influence of magnetic biasing on the transformer is evaluated, and whether a suppression measure is taken or not is determined.
Description
Technical Field
The invention relates to the technical field of power transformer application, in particular to a method and a device for monitoring direct current magnetic bias of a transformer.
Background
In recent years, with more and more domestic direct current transmission projects, direct current flowing into the earth and an alternating current transmission system in a single-pole earth operation mode of a direct current transmission project have more and more common coupling relations, and the specific coupling relations are shown in fig. 1. Monitoring shows that in an alternating current transmission substation with a direct current grounding electrode within 100 kilometers, main transformers with direct grounding neutral points are influenced by direct current flowing into the ground to different degrees, the direct current flows into the neutral points of the transformers from the ground, and partial direct current which originally only passes through a ground resistance loop is bypassed through the transformers and an alternating current transmission line network, so that the problem of relatively serious direct current magnetic bias of the transformers is caused.
The dc magnetic bias causes the noise and vibration of the transformer to be increased. From some monitoring data, the vibration and noise of the transformer and the harmonics in the transformer current increase with the increase of the dc current through the transformer neutral, and the magnitude of the dc current in the transformer grounded neutral is related to the dc line power transmission and the dc ground distance in the single-pole ground operation. This phenomenon can be explained by the transformer core saturation magnetization characteristic: the direct current flowing into the winding becomes a part of the exciting current of the transformer, the direct current makes the iron core of the transformer generate magnetic bias, the exciting curve working point of the transformer is changed, a part of the original magnetizing curve working area is moved to the iron core magnetic saturation area, the total exciting current becomes spike wave, the problems of local overheating, insulation aging, load performance reduction and the like of the transformer caused by the spike wave cause great influence on the normal operation of the transformer, and the transformer can be damaged and protected when the spike wave is serious. Meanwhile, the transformer after direct current magnetic biasing can generate considerable broadband harmonic waves, and the operating environment of a power grid is polluted. Although researchers have certain knowledge about the negative effects of the alternating current power grid, according to most of the events of aggravation of noise and vibration of the transformer which occur in the power grid with the direct current transmission converter station, it can be found that the negative effects generated after the direct current magnetic biasing of the transformer are larger than expected, and even the transformer with serious magnetic biasing response can not normally operate.
Therefore, the measurement of the direct current magnetic bias current of the transformer can provide important basis for system operation management, understanding of the direct current magnetic bias condition of the transformer and taking corresponding measures, can effectively perform accurate measurement and provide basis for judging whether to put into a magnetic bias suppression device, and can also accurately and quantitatively analyze the influence degree of the direct current magnetic bias on the transformer. However, in the existing dc magnetic bias measurement technology, it is generally considered that the transformer magnetic bias current is a pure dc current, and in practice, the dc current measured at the neutral point of the main transformer ground is a mixed current, most of which is the excitation current component after the magnetic flux distortion of the transformer controlled by the dc magnetic bias. Therefore, it is inaccurate, unscientific and imprecise to evaluate the influence of the dc magnetic bias on the transformer by using the transformer magnetic bias current as a pure dc current.
Disclosure of Invention
The embodiment of the invention provides a method and a device for monitoring direct current magnetic bias of a transformer, which can accurately detect and monitor direct current magnetic bias current flowing into the transformer instead of being used as pure direct current when a direct current system operates in a monopolar ground mode, and can improve the accuracy by evaluating the influence degree of the direct current magnetic bias on the transformer by adopting the direct current magnetic bias current.
The method for monitoring the direct current magnetic bias of the transformer comprises the following steps:
measuring a mixed current signal at a neutral point of the main transformer ground by a first current measuring device, wherein the first current measuring device comprises a Hall element arranged at the neutral point of the main transformer ground, and the mixed current signal comprises a direct current magnetic bias current, a magnetic bias response current and a power frequency unbalanced current;
analyzing the mixed current signal to determine the direct current magnetic bias current and the magnetic bias response current;
and determining the magnetic bias response degree of the transformer according to the magnetic bias response current.
This transformer direct current magnetic biasing monitoring devices includes:
the current signal measuring module is used for measuring a mixed current signal at a neutral point of the main transformer which is grounded through a first current measuring device, wherein the first current measuring device comprises a Hall element which is arranged at the neutral point of the main transformer which is grounded, and the mixed current signal comprises direct current magnetic bias current, magnetic bias response current and power frequency unbalanced current;
the signal analysis module is used for analyzing the mixed current signal and determining the direct current magnetic bias current and the magnetic bias response current;
and the bias response degree determining module is used for determining the bias response degree of the transformer according to the bias response current.
The embodiment of the invention also provides computer equipment which comprises a memory, a processor and a computer program which is stored on the memory and can be run on the processor, wherein the processor executes the computer program to realize the transformer direct-current magnetic bias monitoring method.
The embodiment of the invention also provides a computer readable storage medium, and the computer readable storage medium stores a computer program for executing the transformer direct current magnetic bias monitoring method.
In the embodiment of the invention, a mixed current signal at the neutral point of the main transformer grounding is measured by a Hall element arranged at the neutral point of the main transformer grounding, the direct current bias current and the bias response current are determined according to the mixed current signal, and the bias response degree of the transformer is determined according to the bias response current. Compared with the prior art that the transformer magnetic biasing current is used as pure direct current, the method and the device evaluate the influence degree of the direct current magnetic biasing on the transformer through the actual direct current magnetic biasing current obtained through calculation and the actual direct current magnetic biasing current obtained through calculation, and can improve the accuracy.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic diagram of a direct current transmission monopole earth operation earth current circulation path in the prior art;
FIG. 2 is a waveform diagram I of a current measurement record of a neutral point of a certain 500kV transformer;
FIG. 3 is a waveform diagram II of a current measurement record of a neutral point of a certain 500kV transformer;
FIG. 4 is a waveform diagram III of a current measurement record of a neutral point of a certain 500kV transformer;
FIG. 5 is a waveform of a neutral current waveform of a transformer with delt wire winding after being biased by DC;
FIG. 6 is a schematic diagram of the DC bias principle of the transformer;
FIG. 7 is a graph of transformer excitation characteristics;
FIG. 8 is a graph of exemplary transformer core BH versus core permeability;
FIG. 9 is a partial enlarged view of a waveform of an idling magnetizing inrush current of a 500kV transformer;
FIG. 10 is a recording plot of the transformer after it has generated a bias response;
FIG. 11 is a recording diagram of a transformer without bias response;
fig. 12 is a flowchart of a method for monitoring dc magnetic bias of a transformer according to an embodiment of the present invention;
FIG. 13 is an equivalent circuit diagram of a transformer;
FIG. 14 is a diagram illustrating a simulated waveform after a bias response occurs in a transformer;
FIG. 15 is a waveform diagram of a current waveform at a neutral point of a 220kV transformer with YN/Yn/D connection;
FIG. 16 is a waveform diagram of current recording at the neutral point of a converter transformer with a certain connection line of Y/Y;
FIG. 17 is a waveform diagram of current recording at the neutral point of a converter transformer with a certain connection line of Y/D;
FIG. 18 is a waveform of the neutral point current recording of an autotransformer with a wiring of AUTO;
FIG. 19 is a graph of the recording of the neutral point current (with the power frequency current component removed);
fig. 20 is a schematic structural diagram of a transformer dc magnetic bias monitoring device according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the prior art, the existing dc magnetic bias measurement technology generally considers that the transformer magnetic bias current is a pure dc current, collects a data point from several seconds to tens of seconds during collection, and considers the data as the magnetic bias current of the transformer.
For example, fig. 2 is a graph showing a trend of a waveform change of a current at a neutral point of a 500kV transformer between 6 points and 8 points in a mountaineer on day 3, 27 in 2016, fig. 3 is a graph showing a trend of a waveform change of a current at a neutral point of a 500kV transformer between 8 points and 9 points in a mountaineer on day 3, 27 in 2016, and fig. 4 is a graph showing a trend of a waveform change of a current at a neutral point of a 500kV transformer between 9 points and 10 points in a mountaineer on day 1 in 4, 4 in 2016, where abscissa of fig. 2 to 4 is N sampling points and ordinate represents a dc bias current sampled at an nth sampling point in a unit a. In actual operation, when a direct current system operates in a single-pole earth mode, a part of direct current is transmitted to an alternating current system through a transformer grounded neutral point, namely flows to a coil through the transformer neutral point near an earth pole, is introduced into a transmission line network from the coil and flows into an earth loop through other transformer neutral points, the part of direct current is generally not large, the value of the direct current introduced by each transformer through the grounded neutral point is from a few amperes to tens of amperes, the direct current distributed to a few amperes of each phase is generated, a large bias direct current flux is generated on a transformer iron core due to the large number of turns of the transformer coil, and the iron core flux of each phase is periodically and intermittently saturated in time sequence after being superposed with a periodic 50hz alternating current excitation flux, so that a pulsating current periodically appears in a certain half wave (positive or negative half wave) on each phase of the transformer, three pulsating currents with a phase difference of 120 degrees appear in a period of the three-phase winding, because the three phases are uniformly deviated to one side of a time axis, and the current is in a direct current property from the direct current measurement point of view.
Fig. 5 is a waveform plot recorded at the neutral point of a transformer with a delt connection winding after being dc biased. When the direct current bias current received by the monitoring transformer is continuously measured by one sampling point of five seconds and ten seconds, due to the time difference caused by the frequency change of the sampling clock and 50hz, the actual sampling value is like a very slowly moving slit, the sampled data is a certain moment of a waveform seen through the slit, and the slit moving speed is the error of a computer clock and the difference speed of the real-time change of the power grid frequency, which is equivalent to that a cycle is moved for tens of minutes, so that the trend waveform measured and monitored through the sliding window is necessarily like the trend change recorded in the three actual fields (fig. 2 to fig. 4). It is not scientific and rigorous to evaluate the degree of influence of dc magnetic biasing on the transformer based on the maximum values recorded by such measurements.
FIG. 6 is a schematic diagram of the DC bias principle of a transformer, wherein (a) shows the overall rise of the magnetic flux waveform after the positive half wave of the transformer is affected by the DC bias; (b) the graph shows that the working point of the iron core excitation characteristic curve of the main transformer enters a saturated or even severely saturated nonlinear section from a linear section below the point A; (c) the diagram shows that the main transformer exciting current waveform affected by the direct current magnetic bias is distorted, the peak value of the exciting current is increased sharply, the waveform is changed from a smooth sine wave to a sharp top wave, and the sharp top wave is the original magnetic bias response current in the coil.
A typical transformer excitation characteristic graph is shown in fig. 7, in which the abscissa represents the excitation voltage coordinate in kV, and the ordinate represents the excitation current amplitude in a. Fig. 7 illustrates a 500kV voltage class transformer as an example, in a normal system operation condition, about a relatively rated voltage 525/v 3-303 kV is taken as an inflection point, as an excitation voltage increases, an excitation current increases sharply, a transformer core is in a saturation state, and an equivalent excitation impedance thereof also decreases sharply in proportion.
Fig. 8 is a graph of magnetic field strength in H on the horizontal axis and magnetic induction in T on the vertical axis for a typical transformer core BH plotted against core permeability. The equivalent excitation impedance of the transformer is completely changed in direct proportion to the magnetic permeability of the iron core, after the iron core of the transformer is superposed with a direct current magnetic flux through a transformer winding due to overvoltage or direct current magnetic bias current, the iron core enters a saturated state, and the equivalent excitation impedance of the iron core is not linear in characteristic but changes along with the saturation degree of the iron core.
After severe direct current magnetic biasing, the change of the exciting current is basically consistent with the half-wave waveform of the current in the corner of a TCR (thyristor controlled reactor), and the difference is that in the initial stage of the current, the saturation degree of a transformer iron core is low, the equivalent exciting resistance is high, the current slowly rises, once the transformer iron core is deeply saturated, the equivalent exciting resistance is severely reduced, the exciting current rises very fast, and the curve becomes steep. As shown in fig. 9, the horizontal axis represents the phase current coordinates of the transformer a in units of a, and the vertical axis represents time in units of s.
From the direct current bias detection and monitoring, and further judging the influence result of the bias on the transformer, the cause-effect relationship between the direct current bias detection and monitoring and the influence result of the bias on the transformer needs to be clarified, and actually, the actually measured neutral point direct current is the average value of pulsating current serving as the bias influence result plus the direct current bias current instead of the pure cause of the result (namely, the direct current with the unchanged magnitude in the true direction flowing into the transformer is distributed in the alternating current system in the single-pole ground loop mode of the direct current transmission system).
In other words, the current of direct current nature measured at the neutral point of the main transformer ground is a mixed current, most of which is the excitation current component after the magnetic flux distortion of the transformer after being subjected to the direct current bias control. For most transformers with Y/D wiring sets, the actual waveforms after the transformer has passed the biasing current and the biasing current has produced an effective biasing response to the transformer are shown in fig. 10.
In addition, for a transformer in which a bias current has flowed but no bias response has occurred, the actual current waveform at the neutral point is as shown in fig. 11, in which the horizontal axis is the neutral point current coordinate in mA and the vertical axis is time in ms. The waveform is a standard ideal direct current plus 50hz power frequency alternating current (the waveform recorded by the channel No. 30 in the figure, the residual zero sequence current of the transformer is lifted off the time axis (the thin line below) under the direct current.
From the above analysis, it can be seen that the current of the dc nature actually measured at the neutral point of the main transformer ground is a mixed current, and most of the mixed current is the excitation current component after the magnetic flux distortion of the transformer is controlled by the dc bias. Based on this, the pure dc current in the prior art is used to evaluate the influence degree of the dc magnetic bias on the transformer, which is inaccurate, and based on this, the present invention provides a method for monitoring the dc magnetic bias of the transformer, as shown in fig. 12, the method includes:
step 1201: measuring a mixed current signal at a neutral point of the main transformer ground by a first current measuring device, wherein the first current measuring device comprises a Hall element arranged at the neutral point of the main transformer ground, and the mixed current signal comprises a direct current magnetic bias current, a magnetic bias response current and a power frequency unbalanced current;
step 1202: analyzing the mixed current signal to determine the direct current magnetic bias current and the magnetic bias response current;
step 1203: and determining the magnetic bias response degree of the transformer according to the magnetic bias response current.
In the embodiment of the present invention, an equivalent circuit diagram of a common three-winding transformer is shown in fig. 13. Since the exciting current is about 0.5% of the rated current when the transformer is in a normal operation state (unsaturated), the exciting impedance of the transformer is reduced by about 100-fold and 200-fold when the transformer is in a saturated state, after the transformer is subjected to direct-current magnetic biasing, the transformer shows that the transformer is unsaturated in a part of time period and is in a saturated state in a part of time period, and the magnetic biasing response current of the transformer is as shown in fig. 14, wherein the horizontal axis is the primary three-phase current coordinate of the transformer, the unit is kA, and the vertical axis is time, the unit is s.
Because the transformer has a plurality of wiring modes, the response characteristics of the transformers with different wiring modes after direct current magnetic biasing are different, and the direct current magnetic biasing response detection measurement and monitoring method of the transformers with different wiring modes is explained by analyzing different practical cases.
The wiring group of the transformer is a representation method of the wiring form of the combination of the primary winding and the secondary winding of the transformer. The method for representing the connection group of the transformer comprises the following steps: capital letters indicate the primary side (or primary side) wiring scheme, and lowercase letters indicate the secondary side (or secondary side) wiring scheme. The common transformer windings have two connections, namely a delta connection (D) and a star connection (Y), and because Y is connected with a neutral line and a neutral line, the neutral line is not added with any symbol representation, and the neutral line is added with a letter n after the letter Y. n represents that the neutral point has an outgoing line. "Yn" represents a connection with a star-shaped neutral line on the primary side.
When the wiring group of the transformer is YN/Yn/D:
FIG. 15 is a waveform of a 220kV transformer neutral point current waveform with YN/Yn/D connection, and a transformer voltage level of 220/110/10kV, wherein the horizontal axis represents a neutral point current coordinate in mA, and the vertical axis represents time in ms. It can be seen from the figure that the transformer neutral point current is formed by superposing a direct magnetic bias current on an unbalanced power frequency alternating current and a small amount of harmonic current (the direct magnetic bias response is not obvious).
The direct current component current in the current is the direct current which is coupled to the transformer substation grounding grid through a ground resistor, flows into a neutral point on the 220kV side of the main transformer and further flows into the ground through a grounding electrode under a part of direct current single-pole ground operation mode of an alternating current system power grid. The current passes through a primary coil of the transformer to form direct current ampere-turn magnetic flux which is superposed on an iron core of the transformer and generates magnetic bias influence on the transformer. The DC current is a bias current.
The bias current analysis method is easy, and the calculation method is as follows:
1) firstly, a filtering algorithm is adopted to filter out 2 to 25 harmonics (namely, the second mixed current) in the mixed current signal, and fundamental wave and magnetic bias direct current components (namely, the first mixed current) are reserved.
2) Calculating direct current magnetic bias current:
firstly, the amplitude average value calculation is performed on the sampled instantaneous value in the first mixed current within a time window, for example, the sampled instantaneous value average value calculation is performed on the real-time sampled waveform of the neutral point current in the above fig. 15 within a calculation window (preset first time window) of 5 power frequency cycles (100 milliseconds). The calculation result is:
wherein Id represents direct current magnetic biasing current, In represents first mixed current, and m represents sampling times In a preset first time window;
3) calculating direct current bias response current:
the direct current bias response current contains harmonic components with a wide frequency spectrum, so that the direct current bias response current is analyzed by adopting Fourier analysis to analyze the content of each harmonic wave below 25 times, and the calculation formula is as follows:
wherein, IkDenotes the kth harmonic current, N ' denotes the number of iterations, N ' is 1,2, … …, N-1, 2 pi i is an imaginary number, i is an imaginary unit, and In ' denotes the second mixed current containing the bias response currents of the harmonics 2 to 25.
And judging and evaluating the influence of the DC magnetic bias on the transformer according to the calculated waveform.
When the wiring group of the transformer is Y/Y:
FIG. 16 is a waveform of current waveform of neutral point of converter transformer with certain connection line as Y/Y. Because the iron core of the converter transformer is influenced by the bias of the direct-current bias current, the magnetic fluxes of the three independent iron cores of the three independent single-phase transformers are sequentially saturated in time sequence according to an angle difference of 120 degrees, and because the time width of saturation and non-saturation of each phase is controlled by the direct-current bias current, the direct-current bias current is superposed with the excitation current of the transformer, the direction of the bias is controlled by the direct-current bias current, and the time when the bias enters a saturation region and exits the saturation region, and the depth of the bias saturation is controlled at the same time, namely the bias response.
Specifically, the characteristic current similar to that of a magnetically controlled reactor appears in the aspect of exciting current, when the bias saturation reaches a threshold value, the magnetic valve is opened instantaneously, the exciting impedance is reduced sharply, the exciting current rises rapidly, and the larger the direct-current bias current is, the longer the magnetic valve is kept opened, so that the wider and larger the pulse width and the current amplitude of the exciting pulsating current in a certain half-wave period are, and the smaller the interruption time width between two adjacent pulsating waves is.
The bias current analysis method for the type is as follows:
1) direct current bias current
For the Y/Y-connected transformer, the current waveform of the neutral point completely reflects the periodic fluctuation change of the bias magnetic influence of the direct-current bias magnetic current on the transformer on a three-phase time sequence, namely the control characteristics on the amplitude and the width of each phase of exciting current pulse, namely the bias magnetic response characteristics. Therefore, the real-time calculation and analysis by utilizing the waveform and the visual analysis of the oscillogram can be carried out relatively directly, and the judgment and judgment can be carried out visually.
Since the dc bias current only affects the saturation increase of the excitation current of a certain half-wave, the dc current component at the pulse break is the dc bias current. The specific implementation method comprises the following steps: the sampling waveform is analyzed in real time in a time window (preset second time window) (for example, 100ms), whether the transformer core is in a saturated state or not and whether the waveform is discontinuous or not can be judged according to the current change rate, and the current average value current value in the time period in the unsaturated state is the direct current injected to the neutral point of the transformer from the outside.
2) DC bias response current
The pulsating current with 120 degrees of phase difference in the corresponding waveform diagram is the direct current magnetic bias response current, and the degree of the transformer influenced by the direct current magnetic bias current can be judged according to the peak value and the opening width of the pulsating current. The specific implementation method comprises the following steps: the sampling waveform is analyzed in real time in a time window (a second time window is preset) (for example, 100ms), whether the transformer core is in a saturation state can be judged according to the current change rate, and the magnetic bias response degree of the transformer can be known by analyzing the harmonic component and the amplitude in the saturation state.
And (III) when the wiring group of the transformer is Y/D:
FIG. 17 is a waveform of current waveform at neutral point of converter transformer with certain connection line as Y/D. Because the converter transformer iron core is influenced by the bias of the direct-current bias current, the magnetic fluxes of the three independent iron cores of the three independent single-phase transformers are sequentially saturated in time sequence according to an angle difference of 120 degrees, the time width of saturation and non-saturation of each phase is controlled by the direct-current bias current, and the direct-current bias current is superposed with the excitation current of the transformers, so that the bias direction is controlled by the direct-current bias current, the time when the bias enters saturation and exits saturation is controlled, and the bias saturation depth is controlled. The magnetic bias response specifically reflects that characteristic current similar to that of a magnetically controlled reactor appears in the aspect of exciting current, when magnetic bias saturation reaches a threshold value, the magnetic valve is opened, the excitation impedance is reduced sharply, the exciting current rises rapidly and increases, the larger the direct-current magnetic bias current is, the longer the magnetic valve is opened, and therefore the wider the pulse width and the current amplitude of the exciting pulsating current in a certain half-wave period are. In addition, because the Delt winding acts as a filter for 3 rd order and multiple of the harmonic, the Delt winding filters most of the third order and multiple of the harmonic in the pulsating current, resulting in a waveform that is different from the current of the Y/Y connection.
The bias current analysis method for the type is as follows:
1) DC bias current calculation
And reducing the neutral point current of the transformer connected with the Y/D wire, and adding 3-order harmonic components with corresponding amplitudes and phases into the neutral point current through the measured third harmonic content in the D winding, wherein the magnetic bias current measurement of the transformer connected with the Y/D wire is the same as that of the Y/Y wire.
The specific implementation method comprises the following steps: and analyzing the sampling waveform in real time in a time window (a preset third time window) (for example, 100ms), adding a third harmonic component with amplitude and phase corresponding to the mixed current signal according to a harmonic proportional relation, so that the current waveform can be restored to the transformer neutral point magnetic bias current of the Y/Y wiring, judging whether the transformer iron core is in a saturated state according to the current change rate of the restored current, and analyzing the current average value in the non-saturated state, namely the direct current externally injected to the transformer neutral point.
2) DC bias response current calculation
The pulsating current with a phase difference of 120 degrees in the corresponding reduced oscillogram is the direct current magnetic bias response current, and the degree of the transformer influenced by the direct current magnetic bias current can be judged according to the peak value and the opening width of the pulsating current. The specific implementation method comprises the following steps: the sampling waveform is analyzed in real time in a time window (a preset third time window) (for example, 100ms), and a third harmonic component corresponding to the amplitude and the phase is added according to the harmonic proportional relation, so that the current waveform can be restored to the transformer neutral point magnetic biasing current of the Y/Y wiring, the restored current waveform is analyzed, whether the transformer iron core is in a saturation state can be judged according to the current change rate, and the magnetic biasing response degree of the transformer can be known by analyzing the harmonic component and the amplitude in the saturation state.
In an embodiment of the present invention, when the transformer is an autotransformer, the method further includes:
measuring direct current and harmonic current passing through the autotransformer by a second current measuring device, wherein the second current measuring device is an alternating current transformer or a photocurrent transformer and is arranged on the high-voltage side or the medium-voltage side of the autotransformer;
and analyzing the mixed current signal, the direct current and the harmonic current to determine the direct magnetic bias current and the magnetic bias response current.
(IV) when the transformer is an autotransformer:
fig. 18 shows a waveform of a neutral point current waveform of an autotransformer whose connection is AUTO, and a transformer voltage level is 525/220/35kV, in which the ordinate represents current coordinates of three phases and a neutral point in a unit of a, and the abscissa represents time in a unit of ms. The third winding is a balanced and reactive compensation winding of angular connection and is connected with a parallel capacitor bank with 5% series reactance. Under the influence of DC bias current, the transformer generates obvious bias response, and neutral point bushing CT measures corresponding bias current with obvious characteristics. Meanwhile, the high-voltage side phase current also has a pulsating current with a considerable magnitude in the negative half-wave current, so that the current waveform is obviously distorted. After filtering out the fundamental wave (fig. 19, the ordinate is the current coordinate after removing the fundamental wave from the phase current, and the unit is a, and the abscissa is time, and the unit is ms), it is clearly shown that after the high-voltage a-phase iron core magnetic flux is affected by the direct-current bias magnetic current magnetic flux, an additional pulsating current is generated in the negative half wave of the excitation current of the a-phase coil, and appears in the a-phase current periodically.
Because the Delt winding is present, the function of the filter is equivalent to a filter with 3 times and multiple of the harmonic wave, when a capacitor bank with 5-6% of reactance rate of a third winding operates, the main transformer impedance and the series impedance can form a good 4-time harmonic wave current filter under the frequency of 4 times of harmonic wave. The Delt winding filters out 3 and multiples of harmonics in a part of the pulsating current, and after 4 harmonics, causes a waveform of the current flowing out of the midpoint to be greatly different from the current conversion of the Y/Y connection. Therefore, the presence or absence of the third winding (angle connection) of the transformer, and the presence or absence of the parallel capacitor bank operation of the third winding, affect the overall dc bias characteristics, and the neutral output current waveform.
For the autotransformer, because the direct current magnetic bias current flows from the neutral point grounding transformer in the medium-voltage side power grid through the autotransformer, the direct current magnetic bias current passes through the autotransformer, is transmitted to other grounding transformers through the direct current resistance loop of the high-voltage power grid, and flows into the ground through the grounding grid. Therefore, the autotransformer is required to monitor and detect not only the neutral point dc magnetic bias condition thereof, but also the dc magnetic bias current condition transmitted between the power grids of different voltage levels through the autotransformer.
The calculation method for the type of bias current analysis is as follows:
since the transformer has the effect of a delta-connected winding and the filtering effect of a parallel capacitor bank, it is not so easy to calculate and analyze the bias dc current therein using only the waveform measured and recorded at the neutral point.
One method comprises the following steps:
the regression method, after the waveform is corrected and regressed to the same waveform as the Y/Y connection, can adopt the calculation and analysis method (II) above.
The second method comprises the following steps:
and (3) filtering 2, 3, 4 and above harmonics by using a filtering algorithm, and reserving fundamental wave and magnetic bias direct current components.
And calculating the bias current and the power frequency current by adopting the calculation method (I).
And then, the measured waveform curve is subjected to calculation processing of subtracting the bias current and the power frequency current, and the influence of the direct current bias on the transformer is judged and evaluated according to the calculated waveform.
Based on the same inventive concept, the embodiment of the invention also provides a transformer direct-current magnetic bias monitoring device, which is described in the following embodiments. Because the principle of solving the problem of the transformer direct-current magnetic bias monitoring device is similar to that of the transformer direct-current magnetic bias monitoring method, the implementation of the transformer direct-current magnetic bias monitoring device can refer to the implementation of the transformer direct-current magnetic bias monitoring method, and repeated parts are not repeated. As used hereinafter, the term "unit" or "module" may be a combination of software and/or hardware that implements a predetermined function. Although the means described in the embodiments below are preferably implemented in software, an implementation in hardware, or a combination of software and hardware is also possible and contemplated.
Fig. 20 is a block diagram of a structure of a dc bias monitoring device of a transformer according to an embodiment of the present invention, as shown in fig. 20, including:
a current signal measuring module 2001, configured to measure, by a first current measuring device, a mixed current signal at a neutral point of a main transformer ground, where the first current measuring device includes a hall element installed at the neutral point of the main transformer ground, and the mixed current signal includes a dc bias current, a bias response current, and a power frequency unbalanced current;
a signal analyzing module 2002, configured to analyze the mixed current signal, and determine the dc magnetic bias current and the magnetic bias response current;
and a bias response degree determining module 2003, configured to determine the bias response degree of the transformer according to the bias response current.
This structure will be explained below.
In the embodiment of the present invention, for a transformer with a winding connection mode of an YN-D type, the signal analysis module 2002 is specifically configured to:
the dc bias current is determined as follows:
filtering the mixed current signal by adopting a filtering algorithm in a preset first time window to obtain a filtered mixed current signal, wherein the filtered mixed current signal comprises a first mixed current containing a fundamental wave and a bias magnetic direct current and a second mixed current containing a bias magnetic response current of 2-order to 25-order harmonic waves;
carrying out amplitude average value calculation on a sampled instantaneous value of a first mixed current containing a fundamental wave and a bias direct current, wherein the average value is the direct bias current;
the bias response current is determined as follows:
fourier analysis is carried out on second mixed current of the magnetic bias response current containing 2-25 harmonics, and the content of each harmonic below 25 in the second mixed current is the magnetic bias response current.
In the embodiment of the present invention, for a transformer with a winding connection mode being Y-Y type, the signal analysis module 2002 is specifically configured to:
the dc bias current is determined as follows:
judging whether the transformer iron core is in a saturated state or not according to the current change rate of the mixed current signal in a preset second time window, wherein when the transformer iron core is in an unsaturated state, the average value of the mixed current signal in a time period in the unsaturated state is the direct-current magnetic bias current;
the bias response current is determined as follows:
and judging whether the transformer iron core is in a saturated state in a preset second time window or not according to the current change rate of the mixed current signal, and analyzing a harmonic component in the mixed current signal in the saturated state at the time period of the saturated state, wherein the harmonic component is the bias response current.
In the embodiment of the present invention, for a transformer with a winding connection mode being Y-D type, the signal analysis module 2002 is specifically configured to:
determining the DC bias current according to the following formula:
analyzing the mixed current signal in a preset third time window, determining a harmonic proportional relation, adding 3-order harmonic components with corresponding amplitude and phase to the mixed current signal according to the harmonic proportional relation to obtain a mixed current reduction signal, judging whether the transformer core is in a saturated state according to the current change rate of the mixed current reduction signal, and when the transformer core is in an unsaturated state, taking the average value of the mixed current signal in a time period in the unsaturated state as the direct-current bias current;
the bias response current is determined as follows:
and analyzing the mixed current signal in a preset third time window, determining a harmonic proportional relation, adding 3-order harmonic component of the amplitude and the phase corresponding to the mixed current signal into the mixed current signal according to the harmonic proportional relation to obtain a mixed current reduction signal, judging whether the transformer core is in a saturated state according to the current change rate of the mixed current reduction signal, and analyzing the harmonic component in the mixed current reduction signal in the saturated state when the transformer core is in the saturated state, wherein the harmonic component is the bias magnetic response current.
In this embodiment of the present invention, when the transformer is an autotransformer, the current signal measuring module 2001 is further configured to: measuring direct current and harmonic current passing through the autotransformer by a second current measuring device, wherein the second current measuring device is an alternating current transformer or a photocurrent transformer and is arranged on the high-voltage side or the medium-voltage side of the autotransformer;
the signal analysis module 2002 is further configured to: and analyzing the mixed current signal, the direct current and the harmonic current to determine the direct magnetic bias current and the magnetic bias response current.
The signal analysis module 2002 is specifically configured to:
filtering the mixed current signal, the direct current and the harmonic current by adopting a filtering algorithm in a preset first time window to obtain a filtered current signal, wherein the filtered current signal comprises a third mixed current containing fundamental wave and bias magnetic direct current and a fourth mixed current containing bias magnetic response current of harmonic wave from 2 times to 25 times;
carrying out amplitude average value calculation on a sampled instantaneous value of a third mixed current which contains a fundamental wave and a bias magnetic direct current to obtain the direct magnetic bias current;
and performing Fourier analysis on a fourth mixed current of the bias response current containing 2 to 25 harmonics, wherein the content of each harmonic below 25 in the fourth mixed current is the bias response current.
The embodiment of the present invention further provides a computer device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements the method when executing the computer program.
The embodiment of the invention also provides a computer readable storage medium, and the computer readable storage medium stores a computer program for executing the method.
In summary, the method and the device for monitoring the dc magnetic bias of the transformer provided by the invention have the following advantages:
1. the invention can accurately detect and monitor the DC magnetic bias current flowing into the transformer when the DC system operates in a single-pole ground mode;
2. the invention can monitor the magnetic bias response degree after the transformer flows in the direct current magnetic bias current, thereby evaluating the influence of the magnetic bias on the transformer and further deciding whether to take inhibiting measures.
3. The invention can accurately distinguish the direct current magnetic biasing current flowing into the transformer and the larger exciting current after the magnetic biasing response of the transformer caused by the direct current magnetic biasing current when the direct current system operates in a single-pole earth mode.
4. The invention aims at the characteristics of different wiring of the transformer, and realizes the measurement of the magnetic biasing current and the monitoring of the magnetic biasing response degree of the transformer in the form of Y/D and Y/Y wiring in a direct current converter station, Y/Y/D three-turn transformer which is common in a high-voltage power grid and the most common AUTO self-coupling wiring in an ultrahigh-voltage power grid.
5. The invention is also applicable to the measurement and detection of the transformer which is not saturated by the smaller direct current flowing into the transformer.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes may be made to the embodiment of the present invention by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A method for monitoring direct current magnetic bias of a transformer is characterized by comprising the following steps:
measuring a mixed current signal at a neutral point of the main transformer ground by a first current measuring device, wherein the first current measuring device comprises a Hall element arranged at the neutral point of the main transformer ground, and the mixed current signal comprises a direct current magnetic bias current, a magnetic bias response current and a power frequency unbalanced current;
analyzing the mixed current signal to determine the direct current magnetic bias current and the magnetic bias response current;
determining the magnetic bias response degree of the transformer according to the magnetic bias response current;
for a transformer with YN-Yn-D type winding connection mode, the direct current bias current is determined according to the following mode:
filtering the mixed current signal by adopting a filtering algorithm in a preset first time window to obtain a filtered mixed current signal, wherein the filtered mixed current signal comprises a first mixed current containing fundamental wave and bias magnetic direct current components and a second mixed current containing bias magnetic response current of 2-order to 25-order harmonic waves;
carrying out amplitude average value calculation on a sampled instantaneous value of a first mixed current containing fundamental wave and bias magnetic direct current components, wherein the average value is direct current bias magnetic current;
the bias response current is determined as follows:
carrying out Fourier analysis on a second mixed current of the bias response current containing 2 to 25 harmonics, wherein the content of each harmonic below 25 times in the second mixed current is the bias response current;
for a transformer with a winding wiring mode of Y-Y type, the direct current bias current is determined according to the following mode:
judging whether the transformer iron core is in a saturated state in a preset second time window or not according to the current change rate of the mixed current signal, wherein the average value of the mixed current signal in the unsaturated state is the direct-current magnetic biasing current in the unsaturated state when the transformer iron core is in the unsaturated state;
the bias response current is determined as follows:
judging whether a transformer iron core is in a saturation state or not according to the current change rate of the mixed current signal in a preset second time window, and analyzing a harmonic component in the mixed current signal in the saturation state when the transformer iron core is in the saturation state, wherein the harmonic component is the bias response current;
for a transformer with a winding wiring mode of Y-D type, the direct current magnetic bias current is determined according to the following formula:
analyzing the mixed current signal in a preset third time window, determining a harmonic proportional relation, adding 3-order harmonic components with corresponding amplitude and phase to the mixed current signal according to the harmonic proportional relation to obtain a mixed current reduction signal, judging whether the transformer core is in a saturated state according to the current change rate of the mixed current reduction signal, and when the transformer core is in an unsaturated state, taking the average value of the mixed current signal in a time period in the unsaturated state as the direct-current bias current;
the bias response current is determined as follows:
and analyzing the mixed current signal in a preset third time window, determining a harmonic proportional relation, adding 3-order harmonic component of the amplitude and the phase corresponding to the mixed current signal into the mixed current signal according to the harmonic proportional relation to obtain a mixed current reduction signal, judging whether the transformer core is in a saturated state according to the current change rate of the mixed current reduction signal, and analyzing the harmonic component in the mixed current reduction signal in the saturated state when the transformer core is in the saturated state, wherein the harmonic component is the bias magnetic response current.
2. The method for monitoring dc bias of a transformer according to claim 1, wherein said dc bias current is determined for a transformer having a winding connection of type YN-D according to the following formula:
wherein Id represents a direct current bias current, In represents a first mixed current containing a fundamental wave and a bias direct current component, and m represents the sampling times In a preset first time window;
the bias response current is determined according to the following formula:
wherein, IkDenotes the kth harmonic current, N ' denotes the number of iterations, N ' is 1,2, … …, N-1, 2 pi i is an imaginary number, i is an imaginary unit, and In ' denotes the second mixed current containing the bias response currents of the harmonics 2 to 25.
3. The method for monitoring dc bias of a transformer according to claim 1, further comprising:
when the transformer is an autotransformer, measuring direct current and harmonic current passing through the autotransformer by a second current measuring device, wherein the second current measuring device is an alternating current transformer or a photocurrent transformer and is arranged on the high-voltage side or the medium-voltage side of the autotransformer;
and analyzing the mixed current signal, the direct current and the harmonic current to determine the direct magnetic bias current and the magnetic bias response current.
4. The method for monitoring dc bias of a transformer according to claim 3, wherein analyzing the combined current signal and the dc current and harmonic current to determine the dc bias current and the bias response current comprises:
filtering the mixed current signal, the direct current and the harmonic current by adopting a filtering algorithm in a preset first time window to obtain a filtered current signal, wherein the filtered current signal comprises a third mixed current containing a fundamental wave and a magnetic bias direct current component and a fourth mixed current containing a magnetic bias response current of harmonic waves from 2 times to 25 times;
carrying out amplitude average value calculation on a sampled instantaneous value of a third mixed current containing fundamental wave and bias magnetic direct current components to obtain the direct current bias magnetic current;
and performing Fourier analysis on a fourth mixed current of the bias response current containing 2 to 25 harmonics, wherein the content of each harmonic below 25 in the fourth mixed current is the bias response current.
5. A transformer direct current magnetic bias monitoring device is characterized by comprising:
the current signal measuring module is used for measuring a mixed current signal at a neutral point of the main transformer which is grounded through a first current measuring device, wherein the first current measuring device comprises a Hall element which is arranged at the neutral point of the main transformer which is grounded, and the mixed current signal comprises direct current magnetic bias current, magnetic bias response current and power frequency unbalanced current;
the signal analysis module is used for analyzing the mixed current signal and determining the direct current magnetic bias current and the magnetic bias response current;
the bias response degree determining module is used for determining the bias response degree of the transformer according to the bias response current;
for a transformer with a winding wiring mode of YN-Yn-D type, the signal analysis module is specifically used for:
the dc bias current is determined as follows:
filtering the mixed current signal by adopting a filtering algorithm in a preset first time window to obtain a filtered mixed current signal, wherein the filtered mixed current signal comprises a first mixed current containing fundamental wave and bias magnetic direct current components and a second mixed current containing bias magnetic response current of 2-order to 25-order harmonic waves;
carrying out amplitude average value calculation on a sampled instantaneous value of a first mixed current containing fundamental wave and bias magnetic direct current components, wherein the average value is the direct current bias magnetic current;
the bias response current is determined as follows:
carrying out Fourier analysis on a second mixed current of the bias response current containing 2 to 25 harmonics, wherein the content of each harmonic below 25 times in the second mixed current is the bias response current;
for a transformer with a winding in a Y-Y type wiring mode, the signal analysis module is specifically configured to:
the dc bias current is determined as follows:
judging whether the transformer iron core is in a saturated state in a preset second time window or not according to the current change rate of the mixed current signal, wherein the average value of the mixed current signal in the unsaturated state is the direct-current magnetic biasing current in the unsaturated state when the transformer iron core is in the unsaturated state;
the bias response current is determined as follows:
judging whether a transformer iron core is in a saturation state or not according to the current change rate of the mixed current signal in a preset second time window, and analyzing a harmonic component in the mixed current signal in the saturation state when the transformer iron core is in the saturation state, wherein the harmonic component is the bias response current;
for a transformer with a winding wiring mode of Y-D type, the signal analysis module is specifically configured to:
determining the DC bias current according to the following formula:
analyzing the mixed current signal in a preset third time window, determining a harmonic proportional relation, adding 3-order harmonic components with corresponding amplitude and phase to the mixed current signal according to the harmonic proportional relation to obtain a mixed current reduction signal, judging whether the transformer core is in a saturated state according to the current change rate of the mixed current reduction signal, and when the transformer core is in an unsaturated state, taking the average value of the mixed current signal in a time period in the unsaturated state as the direct-current bias current;
the bias response current is determined as follows:
and analyzing the mixed current signal in a preset third time window, determining a harmonic proportional relation, adding 3-order harmonic component of the amplitude and the phase corresponding to the mixed current signal into the mixed current signal according to the harmonic proportional relation to obtain a mixed current reduction signal, judging whether the transformer core is in a saturated state according to the current change rate of the mixed current reduction signal, and analyzing the harmonic component in the mixed current reduction signal in the saturated state when the transformer core is in the saturated state, wherein the harmonic component is the bias magnetic response current.
6. The apparatus according to claim 5, wherein when the transformer is an autotransformer, the current signal measuring module is further configured to: measuring direct current and harmonic current passing through the autotransformer by a second current measuring device, wherein the second current measuring device is an alternating current transformer or a photocurrent transformer and is arranged on the high-voltage side or the medium-voltage side of the autotransformer;
the signal analysis module is further configured to: and analyzing the mixed current signal, the direct current and the harmonic current to determine the direct magnetic bias current and the magnetic bias response current.
7. The transformer dc magnetic bias monitoring device according to claim 6, wherein the signal analysis module is specifically configured to:
filtering the mixed current signal, the direct current and the harmonic current by adopting a filtering algorithm in a preset first time window to obtain a filtered current signal, wherein the filtered current signal comprises a third mixed current containing a fundamental wave and a magnetic bias direct current component and a fourth mixed current containing a magnetic bias response current of harmonic waves from 2 times to 25 times;
carrying out amplitude average value calculation on a sampled instantaneous value of a third mixed current containing fundamental wave and bias magnetic direct current components to obtain the direct current bias magnetic current;
and performing Fourier analysis on a fourth mixed current of the bias response current containing 2 to 25 harmonics, wherein the content of each harmonic below 25 in the fourth mixed current is the bias response current.
8. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the method for monitoring dc bias of a transformer according to any one of claims 1 to 4 when executing the computer program.
9. A computer-readable storage medium, wherein the computer-readable storage medium stores a computer program for executing the method for monitoring dc bias of a transformer according to any one of claims 1 to 4.
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| CN109873346B (en) * | 2019-02-01 | 2020-08-18 | 南方电网科学研究院有限责任公司 | DC power transmission common grounding electrode system maintenance method and device |
| CN109884440A (en) * | 2019-04-09 | 2019-06-14 | 国网陕西省电力公司电力科学研究院 | A method of for detecting transformer DC magnetic bias |
| CN110187175A (en) * | 2019-07-08 | 2019-08-30 | 浙江大学台州研究院 | The online Frequency Measurement System of quartz wafer polishing grinding |
| CN111580035B (en) * | 2020-05-27 | 2022-12-09 | 国网江苏省电力有限公司 | Statistical identification method for magnetic saturation of voltage transformer |
| CN111580016A (en) * | 2020-05-28 | 2020-08-25 | 沈阳工业大学 | Transformer direct-current magnetic bias detection device and method through vibration signal analysis |
| CN111751645B (en) * | 2020-06-22 | 2023-05-12 | 北京国网富达科技发展有限责任公司 | Method, device, equipment and system for monitoring DC magnetic bias of transformer |
| CN113009264A (en) * | 2021-03-17 | 2021-06-22 | 中铁第四勘察设计院集团有限公司 | High-speed railway traction substation pavilion direct-current magnetic bias monitoring system and method |
| CN113655417A (en) * | 2021-07-30 | 2021-11-16 | 深圳南云微电子有限公司 | Fluxgate magnetic saturation protection circuit and magnetic saturation detection method |
| CN113671235A (en) * | 2021-08-25 | 2021-11-19 | 国网上海市电力公司 | Transformer neutral point bias current measuring device, method and statistical method |
| CN113866478A (en) * | 2021-09-08 | 2021-12-31 | 深圳供电局有限公司 | Stray current measuring method, device, equipment and system |
| CN114325044B (en) * | 2021-12-21 | 2023-08-01 | 国网上海市电力公司 | Method and system for judging relevance of direct-current magnetic bias of transformer substation and direct-current fluctuation source of rail transit |
| CN116047355B (en) * | 2022-12-28 | 2023-12-05 | 山东理工大学 | Grounding transformer operation condition on-line detection method based on high-voltage side current signal |
| CN117388780A (en) * | 2023-12-11 | 2024-01-12 | 国网江西省电力有限公司电力科学研究院 | Multi-element model-based transformer wide-area direct-current magnetic bias testing method and device |
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| CN103197178B (en) * | 2013-03-21 | 2015-08-05 | 辽宁省电力有限公司电力科学研究院 | Transformer DC magnetic bias on-Line Monitor Device and monitoring method thereof |
| CN103439605A (en) * | 2013-08-28 | 2013-12-11 | 国家电网公司 | Method for detecting transformer direct-current magnetic bias capacity |
| CN104133130A (en) * | 2014-07-11 | 2014-11-05 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Transformer direct-current magnetic bias current calculation method and system based on fault recording data |
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