CN107992713B - Combined air gap breakdown voltage prediction method - Google Patents
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Abstract
The invention relates to a high voltage and insulation technology, in particular to a combined air gap breakdown voltage prediction method, which comprises the steps of defining an air gap between a high-voltage electrode and a suspension conductor as a first gap, defining an air gap between the suspension conductor and a grounding electrode as a second gap, establishing a three-dimensional model of the combined air gap, calculating electrostatic field distribution by adopting a finite element method, extracting a set of electric field characteristics on the shortest path of the first gap and the second gap from the electrostatic field distribution, taking the set of electric field characteristics as an input parameter of SVR (space vector regression), and determining a breakdown gap and a breakdown voltage value thereof through breakdown voltage one-time prediction; performing electrostatic field secondary calculation, electric field feature set extraction and breakdown voltage secondary prediction according to the potential change condition of the suspended conductor after breakdown, and determining the breakdown voltage value of the breakdown gap; and comparing the two breakdown voltage values, and taking the larger value as the predicted value of the overall breakdown voltage of the combined air gap. The method is beneficial to reducing the test quantity and provides theoretical guidance for the optimization of the combined air gap structure.
Description
Technical Field
The invention belongs to the technical field of high voltage and insulation, and particularly relates to a combined air gap breakdown voltage prediction method.
Background
The combined air gap is a metal conductor with a certain size between the high-voltage electrode and the low-voltage electrode, and the electric field distribution between the original gaps is greatly influenced, so that the high-voltage electrode, the metal conductor and the low-voltage electrode form the combined air gap, and the metal conductor presents a suspension potential. The combined air gap widely exists in power systems, such as a suspended conductor in live-line work of a power transmission line, foreign matters such as bird droppings and the like falling on the power transmission line, birds close to the power transmission line and the like. The rod, the ball and the plate are typical electrodes for researching the air gap discharge characteristics, and the research on the combined air gap formed by the electrodes is helpful for understanding the combined gap discharge mechanism and lays a foundation for researching more complex combined gaps.
Combined air gap insulation breakdown with suspended potential conductors is a complex physical process that involves the mating of two single gap insulation breakdowns. For a combined air gap of different structures, it is uncertain which gap breaks down first. Under the applied voltage, when a certain gap breaks down, the potential of the suspension conductor changes, and the combined gap can be equivalent to a single gap; the other gap breaks down immediately or does not break down at the current voltage, and breakdown occurs after boosting continues.
At present, the Breakdown voltage of the combined air gap is mainly obtained through a discharge test at home and abroad, and due to the problems of high cost and long period of the test research, part of researchers have developed the research on the discharge mechanism of the combined air gap for live working, and have proposed some discharge voltage calculation models, the most representative of which is the Rizk model ("Effect of flowing generating connecting object on critical switching impact of air insulation", IEEE Transactions on Power Delivery, 1995, volume 10, phase 3) and the modification form thereof. The Rizk model is a semi-empirical model obtained based on a discharge mechanism and some simplifying assumptions, has limited applicability, and is difficult to calculate and obtain the breakdown voltage of air gaps of various engineering structure combinations.
Therefore, the combined air gap breakdown voltage prediction research is developed, an effective prediction method is provided, the test workload and the test cost are reduced, a foundation can be laid for developing the combined air gap breakdown voltage prediction of the engineering structure, the combined gap configuration in the practical engineering application is guided, and the method has important engineering significance.
Disclosure of Invention
The invention aims to provide a method for obtaining the breakdown voltage of a combined air gap formed by different high-voltage electrodes, a suspension conductor and a grounding electrode through simulation calculation and intelligent prediction alternative discharge tests.
In order to achieve the purpose, the invention adopts the technical scheme that: a combined air gap breakdown voltage prediction method comprises the following steps:
step 1, defining an air gap between a high-voltage electrode and a suspension conductor as a first gap, defining an air gap between the suspension conductor and a grounding electrode as a second gap, and establishing a three-dimensional model of a combined air gap;
step 2, performing primary calculation on an electrostatic field by adopting a finite element method, extracting a set of electric field characteristics on the shortest path of a first gap and a second gap from a calculation result, taking the set of electric field characteristics as an input parameter of a support vector regression, and determining a breakdown gap and a breakdown voltage value thereof through primary prediction of breakdown voltage;
step 3, performing electrostatic field secondary calculation, electric field feature set extraction and breakdown voltage secondary prediction according to the potential change condition of the suspended conductor after breakdown, and determining the breakdown voltage value of the breakdown gap;
and 4, comparing the breakdown voltage values of the first breakdown gap and the second breakdown gap to obtain the predicted value of the overall breakdown voltage of the combined air gap.
In the above combined air gap breakdown voltage prediction method, the implementation of the voltage prediction method comprises the following steps:
step 2.1, performing primary electrostatic field calculation and electric field feature set extraction, establishing a three-dimensional simulation model of the combined air gap by adopting finite element analysis software, loading high potential on a high-voltage electrode, loading zero potential on a grounding electrode and a cut air boundary, performing potential freedom degree coupling on a suspended conductor, and performing primary electrostatic field calculation; extracting an electric field characteristic set on the shortest path of the first gap and the second gap according to the calculation result, and carrying out normalization processing on each characteristic quantity;
step 2.2, performing one-time breakdown voltage prediction, establishing a prediction model by adopting a support vector regression machine, selecting an air gap with a similar structure and a known breakdown voltage as a training sample according to the structural characteristics of the first gap and the second gap, and training the support vector regression model; respectively inputting the electric field characteristic sets on the shortest paths of the first gap and the second gap into a trained support vector regression model, outputting breakdown voltage predicted values of the first gap and the second gap, comparing the breakdown voltage predicted values, determining the gap which is broken down first, and recording the breakdown voltage predicted value U1；
Step 2.3, performing electrostatic field secondary calculation and electric field feature set extraction, after a certain gap is broken down, regarding the suspended conductor as being equal in potential to the other electrode of the gap, performing electrostatic field secondary calculation according to the potential change condition, loading high potential to a high-voltage electrode, loading zero potential to a grounding electrode and a cut air boundary, if the first gap is broken down first, loading high potential to the suspended conductor, and if the second gap is broken down first, loading zero potential to the suspended conductor; and extracting the shortest path characteristic set of the non-breakdown gap from the secondary calculation result of the electrostatic field, and performing normalization processing on each characteristic quantity.
Step 2.4, secondary prediction of breakdown voltage, namely inputting the electric field characteristic set extracted in the step 2.3 into a support vector regression model, secondarily predicting the breakdown voltage of the gap without breakdown, and recording the predicted value U of the breakdown voltage2Will U is2And U in step 2.21Making a comparison if U1＞U2The predicted value of the breakdown voltage of the combined air gap is U1(ii) a If U is2＞U1It is shown that after the first gap breaks down, the second gap has not broken down yet and the voltage still needs to be raised to U2The combined gap can be completely broken down, and the predicted value of the breakdown voltage is U2。
In the above-described combined air gap breakdown voltage prediction method, the shortest path of the first gap is a straight path having the shortest distance between the high-voltage electrode and the floating conductor, and the shortest path of the second gap is a straight path having the shortest distance between the floating conductor and the ground electrode.
In the method for predicting breakdown voltage of combined air gap, the characteristic set of the electric field includes electric field strength, electric field gradient, electric field square, electric field integral and electric field non-uniformity.
In the combined air gap breakdown voltage prediction method, the voltage prediction method is suitable for various air gap structures containing suspended potential conductors.
The invention has the beneficial effects that: the breakdown voltage of the combined air gap is obtained through prediction by combining electric field simulation calculation and machine learning, so that the test workload is reduced; can provide theoretical guidance for optimizing and combining the air gap structure, has wide applicability and is beneficial to engineering application.
Drawings
FIG. 1 is a flow chart of a combined air gap breakdown voltage prediction according to one embodiment of the present invention;
FIG. 2 is a diagram illustrating an exemplary structure and shortest path of a combined air gap according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a combination gap A according to an embodiment of the present invention;
FIG. 4 is a schematic structural diagram of a combined gap B according to an embodiment of the present invention;
FIG. 5 shows the result of one calculation of the electric field of the combined gap A according to one embodiment of the present invention;
FIG. 6 shows the result of one calculation of the electric field of the combined gap B according to one embodiment of the present invention;
FIG. 7 shows the electric field quadratic calculation of the combined gap A according to one embodiment of the present invention;
FIG. 8 shows the second calculation of the electric field of the combined gap B according to one embodiment of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
The embodiment is realized by adopting the following technical scheme that a combined air gap breakdown voltage prediction method is characterized in that an air gap between a high-voltage electrode and a suspension conductor is defined as a first gap 1, an air gap between the suspension conductor and a grounding electrode is defined as a second gap 2, a three-dimensional model of the combined air gap is established, the electrostatic field distribution of the combined air gap is calculated by adopting a finite element method, an electric field characteristic set on the shortest path of the first gap 1 and the second gap 2 is extracted from a calculation result and is used as an input parameter of a Support Vector Regression (SVR), and the first breakdown gap and a breakdown voltage value thereof are determined through breakdown voltage one-time prediction; performing electrostatic field secondary calculation, electric field feature set extraction and breakdown voltage secondary prediction according to the potential change condition of the suspended conductor after breakdown, and determining the breakdown voltage value of the breakdown gap; and obtaining the predicted value of the overall breakdown voltage of the combined air gap by comparing the breakdown voltage values of the first and the second breakdown gaps.
The specific implementation comprises the following steps:
1. and (4) performing primary calculation of an electric field and extracting characteristics. Establishing a three-dimensional simulation model of the combined air gap by adopting finite element analysis software, loading high potential on a high-voltage electrode, loading zero potential on a ground electrode and an intercepted air boundary, coupling potential freedom degrees of a suspended conductor, and performing primary electrostatic field calculation; and extracting the electric field characteristic set on the shortest path of the first gap 1 and the second gap 2 according to the calculation result, and carrying out normalization processing on each characteristic quantity.
2. The breakdown voltage is predicted once. Establishing a prediction model by adopting a support vector regression machine, selecting an air gap with a similar structure and known breakdown voltage as a training sample according to the structural characteristics of the first gap 1 and the second gap 2, and training an SVR model; respectively inputting the electric field characteristic sets of the first gap 1 and the second gap 2 into the trained SVR model, outputting breakdown voltage predicted values of the first gap 1 and the second gap 2, comparing the sizes of the two, determining the gap which is broken down first, and recording the breakdown voltage predicted value U1。
3. And (4) electric field secondary calculation and feature extraction. After a certain gap is broken down, the suspended conductor and the other electrode of the gap are considered to be equipotential, electric field secondary calculation is carried out according to the potential change condition, high potential is loaded on a high-voltage electrode, zero potential is loaded on a grounded electrode and a cut air boundary, if the gap 1 is broken down first, high potential is loaded on the suspended conductor, and if the gap 2 is broken down first, zero potential is loaded on the suspended conductor. And extracting the shortest path characteristic set of the non-breakdown gap from the electric field secondary calculation result, and carrying out normalization processing on each characteristic quantity.
4. And (5) secondarily predicting the breakdown voltage. Inputting the electric field characteristic set extracted in the step 3 into an SVR model, secondarily predicting the breakdown voltage of the gap without breakdown, and recording the predicted value U of the breakdown voltage2Will U is2And U in step 21Making a comparison if U1＞U2After the breakdown of the first gap, the second gap is broken down immediately, and the predicted value of the breakdown voltage of the combined air gap is U1(ii) a If U is2＞U1After the first gap breaks down, the second gap is not broken down, and the voltage is still required to be increased to U2The combined gap is completely broken down, i.e. the predicted value of breakdown voltage is U2。
The shortest path of the first gap 1 is a straight path having the shortest distance between the high-voltage electrode and the floating conductor, and the shortest path of the second gap 2 is a straight path having the shortest distance between the floating conductor and the ground electrode.
Moreover, the electric field characteristic set includes physical quantities related to an electric field, such as electric field strength, electric field gradient, electric field square, electric field integral, electric field unevenness, and the like.
Moreover, the prediction method is suitable for various air gap structures containing the suspension potential conductor.
In this embodiment, the breakdown voltages of the combined air gaps of the two structures under the action of the positive polarity direct current voltage and the negative polarity direct current voltage are taken as objects, and the breakdown voltages are predicted by the prediction method of this embodiment and compared with the test result.
The two types of combined air gaps in this embodiment are referred to as "The effect of a flowing conductor on The breaking down string of a DC gap at sidewalls" (IEEE Power Engineering Society and Exposion in Africa, 2012), and are denoted as combined gap A and combined gap B, respectively.
Fig. 1 is a flowchart illustrating a breakdown voltage prediction of a combined air gap according to the present embodiment, taking a rod-sphere-plate combined air gap as an example, and fig. 2 is a schematic diagram illustrating a shortest path between a first gap 1 and a second gap 2.
Referring to fig. 1, the present embodiment includes the following steps:
firstly, calculating an electric field once and extracting characteristics.
The schematic structural diagrams of the combined gap A and the combined gap B are respectively shown in fig. 3 and fig. 4, wherein the high-voltage electrode is a 30-degree conical rod, the rod body is 0.5m long, and the diameter is 16 mm; the grounding electrode is a plate electrode with the length of 2.0m, the width of 1.2m and the thickness of 2 mm; the suspended conductor is a brass ball electrode with the diameter of 150mm, and the tail end of the suspended conductor is provided with a section of cylindrical flat-head rod with the length of 100mm and the diameter of 5 mm. The distance from the conical rod to the floating ball electrode is a first gap 1, and the distance from the floating ball electrode to the plate electrode is a gap 2. For the combined gap a, the suspended conductor is upright, as shown in fig. 3, the lengths of the first gap 1 and the second gap 2 are both 25cm, and the positive polarity direct current breakdown voltage test value of the combined gap a is 263.8 kV; as shown in fig. 4, the length of the first gap 1 was 4.375cm, the length of the second gap 2 was 13.125cm, and the negative polarity dc breakdown voltage test value of the combined gap B was 223.9 kV.
And respectively establishing a three-dimensional simulation model of the combined gap A and the combined gap B by adopting finite element analysis software ANSYS, loading unit potential 1V to the conical rod electrode, loading zero potential to the plate electrode and the cut air boundary, coupling the potential freedom degree of the suspension ball electrode, and performing primary electrostatic field calculation. The results of the first calculation of the electrostatic fields of the combined gap a and the combined gap B are shown in fig. 5 and 6, respectively. And extracting the electric field characteristic set on the shortest path of the first gap 1 and the second gap 2 according to the calculation result. For the combined gap A, the shortest path of the first gap 1 is a straight path from the tip of the conical rod to the suspension ball, and the second gap 2 is a straight path from the butt of the suspension ball to the plate electrode; for the combined gap B, the first gap 1 is a straight line path from the tip of the conical rod to the flat head rod at the tail end of the floating ball, and the second gap 2 is a straight line path from the floating ball to the plate electrode.
And for the combined gap A and the combined gap B, extracting a plurality of sampling points on the shortest paths of the first gap 1 and the second gap 2 respectively, extracting the electric field intensity and coordinate information of each sampling point, and calculating corresponding electric field characteristic quantities. The electric field characteristic includes physical quantities related to the electric field, such as electric field strength, electric field gradient, electric field square, electric field non-uniformity, etc., and table 1 shows a typical shortest path electric field characteristic set. Each feature quantity in table 1 obtained by calculation was normalized to the [0, 1] interval.
TABLE 1 electric field characteristics set for shortest path
Secondly, breakdown voltage is predicted once.
And (3) establishing a prediction model by adopting a support vector regression machine, and selecting an air gap with a similar structure and a known breakdown voltage as a training sample according to the structural characteristics of the first gap 1 and the second gap 2. For the combined gap A, a training sample set of the SVR model comprises a rod-plate gap with a rod diameter of 0.4cm and a gap of 8-9 cm and a rod-rod gap with a rod diameter of 0.2-0.4 cm and a distance of 50 cm; for the combined gap B, the training sample set of the SVR model comprises rod-plate gaps with the diameter of 0.4cm and the distance of 4-9 cm, plate-rod gaps with the rod length of 5cm, the diameter of 1-6 cm and the distance of 10cm, and plate-rod gaps with the rod length of 10cm, the diameter of 2-20 cm and the distance of 10 cm. The relevant test data of the above training samples are cited from "Breakwown process of a rod-to-plate gap in an underlying thermal air under dc voltage stress" (IEEE Transactions on Electrical Insulation, Vol. 26, No. 2, 1991), "DC Breakdown voltage characteristics of the rod-rod gap" (HV, No. 2, 1990), and "relationship between DC Breakdown voltage and corona morphology" (HV technique, No. 4, 1984).
And respectively establishing a finite element model of the training sample set to carry out electrostatic field calculation and electric field characteristic set extraction, and further training the SVR model to enable the SVR model to have generalization popularization capability. For the combined gap A and the combined gap B, the electric field characteristic sets of the first gap 1 and the second gap 2 are respectively input into the corresponding SVR models and outputThe breakdown voltage of the gap 1 and the gap 2 is predicted once. According to the one-time prediction result, for the combined gap a, the breakdown voltages of the first gap 1 and the second gap 2 are 221.67kV and 1561.13kV respectively, and the breakdown voltage of the second gap 2 is much larger than that of the first gap 1, so that the first gap 1 is broken down first under the loading voltage. For combined gap B, the breakdown voltages of first gap 1 and second gap 2 were 70.33kV and 608.55kV, respectively, and likewise, the breakdown voltage of second gap 2 was much greater than gap 1, indicating that first gap 1 broke down first. Recording the first gap 1 breakdown voltage one-time prediction results U of the combined gap A and the combined gap B respectively1A221.67kV and U1B＝70.33kV。
Thirdly, electric field secondary calculation and feature extraction.
After the first gap 1 is broken down, the electric arc voltage drop is ignored, the suspended conductor and the high-voltage electrode (conical rod) are considered to be equipotential, electric field secondary calculation is carried out according to the potential change condition, the conical rod and the suspended conductor are loaded with high potential, and zero potential is loaded on the plate electrode and the cut-off air boundary. The results of the electric field secondary calculation of the combined gap a and the combined gap B are shown in fig. 7 and 8, respectively. And extracting the shortest path characteristic set of the non-breakdown gap, namely the second gap 2, from the electric field secondary calculation result, and carrying out normalization processing on each characteristic quantity.
And fourthly, predicting breakdown voltage twice.
Respectively inputting the electric field characteristic set of the second gap 2 extracted in the third step into corresponding SVR models for the combined gap A and the combined gap B, secondarily predicting the breakdown voltage of the second gap 2, and recording the predicted value U of the breakdown voltage2AAnd U2BBased on the prediction, U2A＝254.46kV，U2B＝229.53kV。
Will U2AAnd U2BRespectively with U in the second step1AAnd U1BBy comparison, it can be seen that U2A＞U1A，U2B＞U1BFor the combined gap a and the combined gap B, after the first gap 1 breaks down, the second gap 2 is not broken down, and the voltage is still required to be increased to U2AAnd U2BThe combined gap is completeAnd (4) breakdown.
According to the results, the predicted value of the breakdown voltage of the combined gap A under the action of the positive polarity direct current voltage is 254.46kV, and the relative error is-3.5% compared with the tested value of 263.8 kV; the predicted breakdown voltage of the combined gap B under the action of the negative polarity dc voltage was 229.53kV, and the relative error was 2.5% compared to the test value of 223.9 kV. The error result is small, and the effectiveness of the combined air gap breakdown voltage prediction method provided by the invention is verified.
Therefore, by the prediction method provided by the embodiment, the breakdown voltage of the combined air gap can be predicted by combining electric field simulation calculation and SVR machine learning, so that a discharge test is replaced, the test workload is reduced, and theoretical guidance can be provided for researching a combined gap discharge mechanism and optimizing a combined gap structure.
It should be understood that parts of the specification not set forth in detail are well within the prior art.
Although specific embodiments of the present invention have been described above with reference to the accompanying drawings, it will be appreciated by those skilled in the art that these are merely illustrative and that various changes or modifications may be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is only limited by the appended claims.
Claims (4)
1. A combined air gap breakdown voltage prediction method is characterized by comprising the following steps:
step 1, defining an air gap between a high-voltage electrode and a suspension conductor as a first gap, defining an air gap between the suspension conductor and a grounding electrode as a second gap, and establishing a three-dimensional model of a combined air gap;
step 2, performing primary calculation on an electrostatic field by adopting a finite element method, extracting a set of electric field characteristics on the shortest path of a first gap and a second gap from a calculation result, taking the set of electric field characteristics as an input parameter of a support vector regression, and determining a breakdown gap and a breakdown voltage value thereof through primary prediction of breakdown voltage;
step 3, performing electrostatic field secondary calculation, electric field feature set extraction and breakdown voltage secondary prediction according to the potential change condition of the suspended conductor after breakdown, and determining the breakdown voltage value of the breakdown gap;
step 4, obtaining the predicted value of the overall breakdown voltage of the combined air gap by comparing the breakdown voltage values of the first and the second breakdown gaps;
the implementation of the voltage prediction method comprises the following steps:
step 2.1, performing primary electrostatic field calculation and electric field feature set extraction, establishing a three-dimensional simulation model of the combined air gap by adopting finite element analysis software, loading high potential on a high-voltage electrode, loading zero potential on a grounding electrode and a cut air boundary, performing potential freedom degree coupling on a suspended conductor, and performing primary electrostatic field calculation; extracting an electric field characteristic set on the shortest path of the first gap and the second gap according to the calculation result, and carrying out normalization processing on each characteristic quantity;
step 2.2, performing one-time breakdown voltage prediction, establishing a prediction model by adopting a support vector regression machine, selecting an air gap with a similar structure and a known breakdown voltage as a training sample according to the structural characteristics of the first gap and the second gap, and training the support vector regression model; respectively inputting the electric field characteristic sets on the shortest paths of the first gap and the second gap into a trained support vector regression model, outputting breakdown voltage predicted values of the first gap and the second gap, comparing the breakdown voltage predicted values, determining the gap which is broken down first, and recording the breakdown voltage predicted value U1；
Step 2.3, performing electrostatic field secondary calculation and electric field feature set extraction, after a certain gap is broken down, regarding the suspended conductor as being equal in potential to the other electrode of the gap, performing electrostatic field secondary calculation according to the potential change condition, loading high potential to a high-voltage electrode, loading zero potential to a grounding electrode and a cut air boundary, if the first gap is broken down first, loading high potential to the suspended conductor, and if the second gap is broken down first, loading zero potential to the suspended conductor; extracting the shortest path characteristic set of the non-breakdown gap from the secondary calculation result of the electrostatic field, and carrying out normalization processing on each characteristic quantity,
step 2.4, breakdown voltage secondary prediction, step 2.3Inputting the extracted electric field characteristic set into a support vector regression model, secondarily predicting the breakdown voltage of the gap without breakdown, and recording the predicted value U of the breakdown voltage2Will U is2And U in step 2.21Making a comparison if U1＞U2The predicted value of the breakdown voltage of the combined air gap is U1(ii) a If U is2＞U1It is shown that after the first gap breaks down, the second gap has not broken down yet and the voltage still needs to be raised to U2The combined gap can be completely broken down, and the predicted value of the breakdown voltage is U2。
2. The method of claim 1, wherein the shortest path of the first gap is a straight path having the shortest distance between the high voltage electrode and the floating conductor, and the shortest path of the second gap is a straight path having the shortest distance between the floating conductor and the ground electrode.
3. The method of claim 1, wherein the set of electric field characteristics comprises electric field strength, electric field gradient, electric field square, electric field integral, and electric field non-uniformity.
4. The method of claim 1 wherein the voltage prediction method is applied to various types of air gap structures including floating potential conductors.
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