RU2584543C1 - Method of determining optimum number of sections of partitioned insulator - Google Patents

Abstract

FIELD: electronic equipment.

SUBSTANCE: invention relates to production of partitioned through insulators. Method of determining optimum number of sections in through high-voltage vacuum insulator made in form of alternating annular, disc or cylinder elements from insulating material and gaskets from conducting material of specified thickness b, comprises pre-measuring dependence of breakdown voltage at surface of element of insulating material, placed in vacuum of thickness d of said element, plotting a graph of measured dependence, approximating plotted graph of an exponential function type U=kd^α, coefficients k and α in said relationship, using experimental data obtained when dependence of breakdown voltage at surface of element of insulating material from its thickness, calculating optimum thickness and number of sections using certain relationships.

EFFECT: at specified working voltage of insulator by selecting optimal number of sections, reduction of dimensions and reduction of cost of insulator can be achieved.

1 cl, 4 dwg, 2 tbl

Description

The invention relates to electrical engineering, namely to the manufacture of sectioned bushings.

It is known that the breakdown strength of the surface of a dielectric in a vacuum increases with decreasing thickness of the test specimen for electric strength. The indicated position is reflected in the designs of high-voltage insulators used in high-voltage transformers, accelerator technology, etc. [one].

In order to increase the dielectric strength of the insulators, the latter are divided into many sections by conducting gradient rings. In this case, a cylindrical or disk shape of the elements of the sections is used. The height of the sections in these designs of insulators is determined, as a rule, based on a large amount of experimental research, which is associated with a significant expenditure of time and materials spent on the manufacture of the tested samples of insulator sections. In addition, the result obtained during research does not guarantee the creation of a sectional insulator design with optimal dimensions.

A known method of selecting the height of the dielectric ring in a partitioned insulator according to the graph of the dependence of the surface breakdown voltage of the insulating material on the thickness of the test sample [2]. This method consists in the fact that a set of samples of the same insulating material of different thicknesses is tested for electric surface strength in any medium, the dependence of breakdown voltage on the thickness of the sample is built, the point of change of the slope of the curve and the thickness of the insulating ring of the sectioned insulator are determined on this dependence such that it does not exceed the thickness of the sample at which the measured dependence changes its slope.

The known method does not allow to choose for the bushing insulator the specific thickness of the dielectric ring in the section, which would ensure maximum breakdown gradients at a given height of the insulator.

The optimal thickness of the dielectric in sectioned insulators depends on the thickness of the gradient gaskets, the material of the dielectric and the design features of the insulator. Therefore, for each specific design of the bushing, the specific optimal thickness of the sectional ring, and therefore the number of rings in the structure, must be determined.

Closest to the claimed method is a method for determining the optimal number of sections of a partitioned insulator [3].

The prototype method consists in the fact that the average breakdown strength E _{i of the} insulating layer of height H and the average breakdown strength E _{n of a} set of n arbitrary but equal in thickness insulating layers separated by gradient spacers of thickness b are determined in a known manner, and the height of the set should be equal to N then determine the optimal number of sections by the formula

where N is the optimal number of sections in the insulator;

H is the height of the insulator; b is the thickness of the gradient strip;

E _i is the average breakdown strength of a non-partitioned layer of height H;

E _n is the average breakdown strength of an arbitrarily sectioned layer of height H;

n is the number of insulating layers, arbitrary and equal in thickness, in a set of height H.

It should be noted that the choice of the thickness of the gradient ring is dictated by the operating conditions of the entire insulator, its assembly technology. In particular, when determining b, the dielectric strength of the medium surrounding the insulator and the requirements for the mechanical strength of the ring are taken into account.

The disadvantages of the prototype method are as follows.

First, when designing an insulator, it is usually set not its height H, but the operating voltage U, based on the size of which its dimensions are determined. In the prototype method, on the contrary, the height of the insulator H is set based on which the optimal number N of sections in the insulator is determined, but the value of the operating voltage U of the insulator, which is one of its most important characteristics, cannot be determined directly from the prototype method.

Secondly, the prototype method has low accuracy in determining the optimal number of sections in the insulator, which does not allow, for a given height of the insulator H and a given thickness of the gradient strip b, to obtain the maximum possible breakdown voltage for the indicated dimensions of the insulator.

Thirdly, the prototype method is quite complicated and requires for its implementation, especially for insulators with large dimensions, the manufacture of a test bench with an ultra-high voltage source, which is not always possible to implement.

The technical problem posed in the framework of the present invention is to simplify the method and improve the accuracy of determining the optimal number of sections in the insulator, allowing to obtain the minimum dimensions of the insulator, designed for a given operating voltage U.

послеThe problem is solved in that in a method for determining the optimal number of sections in a passage high-voltage vacuum insulator made in the form of alternating ring, disk or cylindrical elements of insulating material and gaskets of conductive material of a given thickness b, the dependence of the breakdown voltage on the surface of an insulating element is previously removed material, placed in vacuum, on the thickness d of the specified element, build a graph of the removed dependence, approximate the plotted step ennoy function of the form U = kd ^α, determine the coefficients k and α in said function using experimental data obtained by removing the dependence of breakdown voltage on the surface of the element of insulating material on its thickness, then calculating the optimal thickness of the insulation element d _opt one section of formula insulator

after

which determines the optimal number of sections n _opt in the insulator, according to the formula

where K _h - safety factor insulator dielectric strength, U _pab - operating voltage, kV.

In FIG. 1 shows the dependence of the breakdown voltage of the surface of pyrex rings on their thickness.

The invention consists in the following. The breakdown voltage of the surface of any dielectric in any medium and, in particular, in vacuum can be quite accurately described in the form of a power function, which has the form

Breakdown voltage for a partitioned insulator having n sections can be rewritten as:

where U ₁ - breakdown voltage of the surface of the insulating element of one section with a thickness of d ₁ ;

To determine the optimal number of sections in a partitioned insulator, we find the maximum value of U _pr To do this, we differentiate expression 2 and equate the value of the derivative to 0.

Transforming the expression (3), we obtain:

From the equation (4) after the conversion we get:

From the expression (5) it follows:

The coefficients k and α in expression (1) for each particular case can be calculated by the least squares method using the experimental values obtained by removing the dependence of the breakdown voltage U on the thickness of the dielectric d.

The optimal thickness d _{opt of the} insulating element of one section of the bushing can be determined by the expression

Substituting expression (6) into expression (7), we obtain

называется коэффициентом запаса электрической прочности изоляции. Коэффициент запаса электрической прочности изолятора задают исходя из условий, в которых должен работать изолятора. Обычно K_з≥1,2.The optimal number of sections n _opt in the bushing, calculated on the operating voltage U _pa , can be determined from the following considerations. Suppose that the designed insulator must work reliably at some voltage U _pa . For reliable operation of the insulator in any installations, the value of the operating voltage U _pa must be significantly less than the breakdown U _pr Attitude $$U_{PR}/U_{R\mathrm{but}b}=K_s\text{(9)}$$

called the safety factor of insulation strength. The safety factor of the insulator is set based on the conditions in which the insulator should work. Typically K _s ≥1.2.

The optimal number of sections n _opt taking into account expressions (1), (2), (6) (8) and (9) can be determined by the expression

Concrete example

According to the claimed method, the optimal number of sections n _{opt of the} bushing of the accelerator of charged particles at the operating voltage U _pa = 1 MV = 1000 kV was _determined . The thickness of the conductive strip (gradient ring) of the insulator b was chosen equal to 3 mm

The dependence of breakdown stresses in vacuum U of the surface of Pyrex rings on their thickness d was previously experimentally removed. The experimental breakdown voltages U of the pyrex rings in vacuum of their thickness d are shown in Table 1 and are shown in FIG. 1 circles.

The graph of the removed dependence is shown in FIG. 1. The dependence of the breakdown voltage U on the thickness of the pyrex ring shown in the graph in FIG. 1 approximated by a power function of the form

The coefficients k and α in expression (12) were determined as follows. To simplify the determination of the coefficients k and α in formula (12), we linearize the equation, for which we prologarithm the indicated expression and obtain

We introduce the notation y = lnU, bo = In k, x = lnd. Taking into account the introduced notation, equation (13) can be written in the form:

The coefficients b ₀ and α in equation (14) using the least squares method can be determined from expressions (15) and (16) taken from [4].

To calculate the numerical values of the coefficients b ₀ and α we use table 2.

Substituting the numerical values in formulas (9) and (10), we obtain

After potentiation, we get:

k = 7.648

The final form of equation (12) after substituting numerical values k = 7.648 and α = 0.4187 into it takes the form:

In FIG. 1 the black squares indicate the calculated voltage values from the pyrex rings, determined by the expression (17). As follows from the figure in FIG. 1, the calculated values of the breakdown voltage from the thickness of the insulator according to formula (17) almost completely coincide with the experimental values, i.e. adequately describe the experiment.

The optimal thickness d _{opt of the} insulating element of one section of the bushing can be determined by the expression (8)

In order for the bushing to reliably withstand U _pa , it is necessary that the breakdown voltage U _pr > U _pa (19). Putting K _s = 1,2, we determine the optimal number of sections n _opt by the expression (11)

The overall height of the insulator, fabricated according to the claimed method H _s, will be equal to

Compare the obtained value of n _opt , determined by the claimed method, with the value of the optimal number of sections n _opt.prot , determined by the prototype method for an insulator designed for an operating voltage of U _pa = 1 MV = 1000 kV. The thickness of the conductive strip (gradient ring) of the insulator b was chosen equal to 3 mm For comparison, we take the numbers from a specific example given in [3].

In FIG. 1 of the prototype method [3] shows an insulator layer of height H (for example, H = 300 mm); in FIG. 2 prototype methods [3] - a set of arbitrary and equal in thickness insulating layers of n (for example, n = 12), total thickness H, the thickness of the separating gradient gaskets is b (for example, b = 3 mm); in FIG. 3 prototype methods [3] - a partitioned insulator with a height of H (for example, H = 300 mm).

The prototype method is as follows. Using the known devices (voltage divider, oscilloscope or kilovoltmeter), the average breakdown strength of the insulating layer 1 with a height H (for example, E _i = 1 kV / cm) is determined (see the prototype method of Fig. 1). Then, the average breakdown strength of a set of arbitrary and equal thickness insulating layers is also measured (see the prototype method of Fig. 2), for example, for a set with a height of H = 300 mm, consisting of twelve pyrex rings separated by gradient spacers 2 with a thickness of b = 3 mm ; E _n = 3.8 kV / cm. The set is located between the high-voltage electrode 3 and the grounded flange 4. The measured E _i , E _n substitute in the formula, which determines the optimal number of sections

If you substitute the numbers following from the prototype method: N = 35;

The optimal thickness of the insulating element d _prot one section of the insulator made by the prototype method will be equal to

We estimate by the formula (17), what voltage U _spr can withstand one section of the insulator, made by the prototype method

The optimal number of sections n _opt.prot in the insulator for a voltage of 1200 kV, calculated by the prototype method, will be equal to

The total height of the insulator H _CR , designed for a voltage of 1200 kV, will be equal to

As follows from the expressions (20) and (21), the height of the insulator, designed for a voltage of 1200 kV, according to the claimed method H _h , is less by 63.12 mm than the height of the insulator made by the prototype method H _pr , designed for the same the voltage is 1200 kV,

Compared with the claimed method, the prototype method has a relative error equal to

Thus, the claimed method in comparison with the prototype method has at least 33.3% high accuracy in determining the optimal number of sections in the insulator, which allows for a given height of the insulator H and a given thickness of the gradient strip b to obtain either the maximum breakdown voltage for these dimensions of the insulator, or for a given operating voltage of the insulator to obtain the minimum height of the insulator. In addition, the claimed method in comparison with the prototype method is quite simple, as it does not require for its implementation, especially for insulators with large dimensions, the manufacture of a test bench with an ultra-high voltage source, which is not always possible to implement. In particular, in the examples considered by the authors for the implementation of the proposed method, it is sufficient that the experimental high-voltage installation allows to obtain a voltage not exceeding 30 ÷ 35 kV, since this voltage is sufficient to remove the dependence of the breakdown voltage on the thickness of the insulating element d, while to implement the method -prototype, it is necessary that the installation was able to operate at voltages of 450 ÷ 500 kV, which is more than an order of magnitude higher than the voltage required to implement the proposed method.

In addition, at a given operating voltage of the insulator by choosing the optimal number of sections according to the claimed method, it is possible to reduce the size and reduce the cost of the insulator compared to the prototype method.

Information sources

1. US patent No. 2082474, publ. 1937.

2. Rakhovsky V.N. The physical basis of electric current in a vacuum. M .: Nauka, 1970, p. 57.

3. A.S. 758266. A method for determining the optimal number of sections of a partitioned insulator. / Smirnov G.V., Kassirov G.M., Plankin Yu.V. - Publ. in BI 23.08.80. No. 31 (prototype).

4. Smirnov G.V., Smirnov D.G. Modeling and optimization of technological processes of RES: Textbook. - Tomsk: Publishing House of Tomsk State University of Control Systems and Radioelectronics, 2007. - P. 66-67.

Claims (1)

The method of determining the optimal number of sections in the passage of a high-voltage vacuum insulator made in the form of alternating ring, disk or cylindrical elements of insulating material and gaskets of conductive material of a given thickness b, characterized in that they first remove the dependence of the breakdown voltage on the surface of the element of insulating material placed in vacuum, on the thickness d of the specified element, build a graph of the removed dependence, approximate the constructed graph of the power function of the first type U = kd ^α , the coefficients k and α are determined in the aforementioned dependence, using experimental data obtained by removing the dependence of the breakdown voltage on the surface of an element of insulating material on its thickness, then calculate the optimal thickness of the insulating element d _{opt of} one section of the insulator according to the formula

And then determine the optimum number of sections n _opt in the insulator, according to the formula

where K _s - the safety factor of the insulator for electric strength, U _pab - operating voltage.

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