Substation area space direction of arrival estimation system of substation discharge source
Technical Field
The invention relates to the technical field of insulation state diagnosis of electrical equipment, in particular to a station domain space direction of arrival estimation system of a substation discharge source.
Background
At present, UHF partial discharge detection developed at home and abroad is generally realized by fixedly mounting a sensor on specific single equipment such as a GIS (gas insulated switchgear), a transformer and the like, and the partial discharge detection and positioning of transformer substation equipment are mainly carried out aiming at the specific equipment. However, any high-voltage power equipment in the transformer substation can generate partial discharge, and for monitoring primary electrical equipment in the whole substation, partial discharge monitoring devices need to be installed on all the equipment, so that the cost is extremely high. A novel movable UHF antenna array is adopted, a movable platform is established, fewer ultrahigh frequency sensor matrixes are utilized, all-around partial discharge inspection and positioning are carried out on high-voltage equipment in a transformer substation, labor cost can be greatly reduced, and transformer substation inspection efficiency is improved.
In order to realize accurate positioning of station domain partial discharge, currently adopted positioning methods comprise an energy attenuation method, a starting time method, a time difference positioning method, an azimuth crossing method and the like. The time difference positioning method is widely applied because the accuracy is high and the accuracy time of the signal sent by the discharge source is not required to be known. After the time difference between the antennas is estimated, the discharging equipment can be positioned by two modes of discharging source coordinates and azimuth estimation. In order to facilitate the movement of the partial discharge detection system in the inspection channel, the size of the antenna array is generally small, the coordinate error of the discharge source obtained under the condition is large, and the position of the discharge source is difficult to determine. Research shows that the azimuth estimation accuracy is still high when the array size is small, and an azimuth calculation method is provided. Further, the relatives derive a spatial direction of arrival (azimuth angle and pitch angle) estimation algorithm, but the algorithm is only suitable for the array arrangement in which two pairs of antennas are perpendicular to each other, and an estimation algorithm suitable for any four-element planar array needs to be provided.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, one purpose of the invention is to provide a station space direction of arrival estimation system for a discharge source of a transformer substation, an antenna array has the advantages of small size, suitability for a narrow inspection channel of the transformer substation and the like, and the coordinates of the discharge source can be accurately calculated through the intersection of estimation results of a plurality of test points, so that the position of discharge equipment is determined.
The station domain space direction-of-arrival estimation system for the discharge source of the transformer substation comprises four omnidirectional antennas located on the same plane, and the direction-of-arrival estimation method comprises the following steps: 1) estimating the time difference between the received signals of each antenna by using an interpolation cross-correlation method; 2) and calculating the azimuth angle and the pitch angle of the discharge source by using a direction of arrival estimation method.
In some embodiments of the present invention, the interpolation cross-correlation method in step 1) first adopts a threshold method to approximately determine the signal start time and the time difference ta12(ii) a Approximately regarding partial signals of the wave front section as direct waves, and extracting signals of 3ns before and after the starting moment as the direct waves; then according to the cross-correlation function cc of the calculated direct wave, for the direct wave band signal y measured by two antennas1(n) and y2(N) (N ≦ N), the cross-correlation function of the two signals is calculated as:
where j represents the time delay of j sample points. Time difference delta of cc peak value corresponding to time delay of direct wave12. Combining a threshold value method to obtain the final time difference t12=ta12-Δ12. When the sampling rate is low, interpolation of the cross-correlation function using a smaller time step can improve the estimation accuracy.
In some embodiments of the present invention, the calculation formula of the discharge power source azimuth angle α and the pitch angle β in step 2) is:
in the formula, subscripts 1, 2, 3 and 4 respectively represent the antenna numbers, phi is the included angle between the antenna pair 1 and 2 and the antenna pair 4 and 3, and D12Distance between antenna 1 and antenna 2, D43Distance, t, between antenna 4 and antenna 312For the time difference between the signals received by the antennas 1 and 2, t43The time difference between the signals received by the antenna 4 and the antenna 3.
In some embodiments of the invention, the interpolation of the cross-correlation function in the correlation method uses a cubic spline method.
In other embodiments of the invention, the extension lines of the antennas 1, 2 and 4, 3 respectively intersect at a point.
The invention discloses a station domain space direction of arrival estimation system of a substation discharge source, which comprises four omnidirectional antennas positioned on the same plane. The direction of arrival estimation comprises the following steps: 1) estimating the time difference between the received signals of each antenna by using an interpolation cross-correlation method; 2) the azimuth angle and the pitch angle of the discharge source are calculated by using the direction of arrival estimation method, and the effects are shown as follows: (1) the azimuth angle and the pitch angle estimated by the direction of arrival are less affected by the time difference error, and the algorithm performance is more stable; (2) when the length of the antenna array is 1m, the estimated azimuth angle and the estimated pitch angle can reach higher accuracy, and the method is more suitable for routing inspection and positioning of small-size antenna arrays and narrow passages of transformer substations; (3) the coordinates of the discharge source can be accurately calculated through the intersection of the estimation results of the plurality of test points, and then the position of the discharge device is determined.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 is a schematic diagram of a method for estimating the direction of arrival of a discharge source according to the present invention;
FIG. 2 is a schematic diagram of three antenna array configurations, rectangular, Y-shaped and diamond-shaped, according to an embodiment of the present invention;
FIG. 3 is a diagram of experimental test azimuthal error distribution.
In the figure: a. the1-an antenna 1, a2-an antenna 2, A3-an antenna 3, A4-an antenna 4, D12Distance between antenna 1 and antenna 2, D43Distance of antenna 4 and antenna 3, angle of azimuth α -angle of elevation β -angle of elevation, angle between antenna pair Φ 1/2 and 4/3.
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.
Examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
As shown in fig. 1, the station space direction of arrival estimation system for a substation discharge source provided by the present invention includes 4 omnidirectional antennas located on the same plane, in which the antennas all adopt an omnidirectional biconical structure. The 4 antennas are arranged according to a certain rule and used for receiving the discharge signals of the whole substation.
Direction-of-arrival estimation first estimates the time difference between the received signals of the antennas using an interpolative cross-correlation method. To avoid becoming as much as possibleThe influence of multipath propagation effect in the power station propagation process is characterized by firstly adopting a threshold value method to approximately determine the signal starting time and the time difference ta12(ii) a The partial signals of the wave front section can be approximately regarded as direct waves, and signals of 3ns before and after the initial moment are extracted as the direct waves. Then according to the cross-correlation function cc of the calculated direct wave, for the direct wave band signal y measured by two antennas1(n) and y2(N) (N is less than or equal to N), and the cross-correlation function of the two signals is calculated according to the formula
Where j represents the time delay of j sample points. Time difference delta of cc peak value corresponding to time delay of direct wave12. Combining a threshold value method to obtain the final time difference t12=ta12-Δ12. When the sampling rate is lower, the estimation precision can be improved by using a smaller time step length to interpolate the cross-correlation function, and the actual measurement result shows that the interpolation performance of the cubic spline method is better, and the method is selected. The adopted signal sampling rate is 2GS/s, the time difference precision is 0.5ns at most, and the time difference precision can be further improved by interpolation in time step of 0.1 ns.
For the various antenna arrays of fig. 2, a direction of arrival calculation method is given. The pairs of antennas 1, 2, 4 and 3 in the rhombus and Y-shaped arrays are mutually vertical, and the azimuth angle and the pitch angle can be directly obtained by the following formula
In the formula, subscripts 1, 2, 3 and 4 respectively represent the antenna numbers, phi is the included angle between the antenna pair 1 and 2 and the antenna pair 4 and 3, and D12Distance between antenna 1 and antenna 2, D43Distance, t, between antenna 4 and antenna 312For the time difference between the signals received by the antennas 1 and 2, t43The time difference between the signals received by the antenna 4 and the antenna 3. If t12>0 and t34<0, the discharge source is in the first quadrant, and so on.
For a rectangular array, any two pairs of intersecting antennas can be selected to estimate the direction of arrival, here, antenna pairs 1, 4 and 3, 2 are taken as examples, and the included angle between the two pairs of antennas is
Φ=2tan-1(b/a) (3)
The distance between the two pairs of antennas is
The included angle between the projection of the discharge source on the xy plane and the antenna pair 1 and 4 can be obtained according to the formula (2). The x axis of the rectangular array is along the connection line of the antenna pair 1 and 2, the included angle between the x axis and the antenna pair 1 and 4 needs to be rotated by a coordinate system to obtain an azimuth angle alpha, and the azimuth angle and the pitch angle are
Alpha is converted to-180 DEG and 180 DEG by following conversion]The range is as follows: if α is>0 and t23>0, then α -180 °; if α is<0 and t14<0, then α +180 °; the rest of the situation is unchanged.
Three typical arrangements of the antenna array as shown in fig. 2 are adopted, a partial discharge simulator is used for simulating partial discharge signals at different azimuth angles, and 4m × 2m different arrays are used for testing the arrival directions of discharge sources. Obtaining the azimuth angle and the pitch angle of the discharge source, and estimating the error eαAs shown in fig. 3. Wherein eαCalculated by the following formula
eα=|αr-αe| (6)
In the formula, alpharIs the actual azimuth angle, αeThe result with the highest probability density in all the signal estimation results is obtained.
In this embodiment, it can be seen from fig. 3 that the azimuth angle estimation accuracy of the rectangular and diamond arrays is high, and the error is less than 4 ° at all azimuth angles; the Y-shaped array has larger estimation error of the azimuth angle, the maximum azimuth angle can reach about 10 degrees, and the directivity is stronger. The azimuth estimation accuracy of the rectangular array is overall highest.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.