RU2615178C1 - Protection method of steel-aluminium cables of overhead transmission lines from fatigue oscillating damages at the outlet from supporting clip - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in the place of support clip installation to the wire, coaxial to it, the protective element made of aluminium is welded by means of thermite welding, which is the body of revolution, to the outer surface of which the preformed into a spiral steel aluminized wires are welded, the central part of the protective element, mounted in the supporting clip has diameter D₀ equal to (1.4-2) of wire diameter d_p, which along to the length L₀ of cantilever part is reduced upto the wires diameter dp, at that the diameter of the protective element cantilever part D(x) in the places after going out from the supporting clip is determined according to the current coordinate x, measured from the extreme points of the supporting clip from the mathematical expression.

EFFECT: increase of the wire resource stability during its vibration, reduction of the maximum total stress from the wire stretching and its bending in the place of its going out from the supporting clip, in case of the wires swinging, when it is subjected to the significant mechanical overloads.

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Description

The invention relates to the electric power industry and can be used on overhead power lines to protect their wires from fatigue vibration damage, as well as damage caused by dancing wires caused by a combination of wind loads with icy-frost deposits on the wires.

A known method of protecting the wires of overhead power lines from fatigue vibration damage at the outlet of the support clamp, according to which, in the place on the wire where the support clamp is to be mounted, wire tread spirals are wound, on the inner surface of which covering the wire, an abrasive with glue is preliminarily applied [one].

In this technical solution, despite the presence of an abrasive on the inner surface of the tread, due to the sliding of the tread relative to the wire during bending deformation in the place of exit from the support clip caused by vibration, the wire-tread system has insufficiently high stiffness and bending strength, which does not allow for efficient wire protection against fatigue damage.

The closest analogue to the proposed method is a method of protecting the wires of overhead power lines from fatigue vibration damage at the outlet of the supporting clip, including fixing to the wire at the installation site of the supporting clip of the protective element [2].

In the known method, the static force that stretches the wire at the place of its exit from the support clamp is reduced by winding onto the wire at the place of installation of the support clamp, a layer of steel wire preformed in a spiral with an inner diameter of the spiral of (1-1.5) mm less than the diameter wires.

However, the friction force of the surfaces of the wires of the spirals and the wires of the overhead power lines does not prevent the mutual shift of the wire and wires relative to each other when they bend at the exit of the supporting clamp due to vibration of the wire, resulting in a decrease in the bending stiffness and strength of the wire with a spiral wound on it.

Another disadvantage of this method is the low moment of resistance of the wire, protected by a spiral, at the place of its exit from the supporting clip. Therefore, when a significant alternating moment occurs, acting on a wire in a dangerous section in the mode of ice-wind loads (wire dance), the required strength is not provided, which reduces the reliability of overhead power lines.

The objective of the present invention is to prevent damage to the steel-aluminum wires of overhead power lines from fatigue vibrational damage at the outlet of the support clip.

The problem is solved in that in the known method of protecting the wires of overhead power lines from fatigue damage at the outlet of the support clip, which includes securing the protective element to the wire at the installation location of the supporting clip, a protective element made of aluminum is welded by coaxial to it, representing a body of revolution, into the outer surface of which aluminum aluminized steel wires transformed into spirals are welded, the central part of the protective The element mounted in the supporting clip has a diameter D ₀ equal to (1.4-2) the diameter of the wire d _P , which along the length of the cantilever part L ₀ decreases to the diameter of the wire d _P , while the diameter of the cantilever parts of the protective element D (x) in places after exiting the supporting clamp, it is determined, depending on the current x coordinate, counted from the extreme points of the supporting clamp, from the equation

Where

Due to the fact that the aluminum protective element, which is the body of revolution, is welded to the wire, coaxially to it, by means of thermite welding, as a result of fusion of the surface of the steel-aluminum wire between it and the protective element, a solid one-piece connection is formed, eliminating their relative movement during bending deformation of the wire in exit point from the support clip. Due to this hindering the sliding of the protective element relative to the wire, the obtained one-piece connection is much harder and stronger than the connection consisting of the protective element placed on the wire with the possibility of mutual shift, as noted in [3, p. 104].

Welding aluminized wires preformed into spirals into the outer surface of the protective element provided an additional increase in the flexural and tensile strength of the permanent connection of the protective element with the wire.

The implementation of the protective element in the form of a body of revolution, the central part of which is mounted in a supporting clamp, has a diameter D ₀ equal to (1.4-2) the diameter of the wire d _P , significantly increased the resistance moment of the permanent connection and the area of its dangerous section, respectively, in ( 2.7-8) and (2-4) times. This led to a decrease in additional stresses during bending and stretching of the wire at the place of exit from the supporting clamp, in the event of ice-wind loads. The form of the cantilever parts of the protective element shown in the claims closest to the shape of an equal bending resistance pinched from one end of the rod and at the same time provides a smooth transition from the diameter of the protective element D ₀ to the diameter of the wire d _P , which allows for the least material production a protective element to significantly reduce the bending stresses on the wire not only at the outlet of the supporting clip, but also at the outlet of the wire from the protective element itself.

The invention is illustrated by drawings, where in FIG. 1 shows a general view of a protective element welded to an aluminum-steel wire; FIG. 2 shows the shape of the cantilever portion of the security element; FIG. Figure 3 shows the dependence of the bending stress on the cantilever part of the protective element on the x coordinate.

The aluminum protective element 1, which is the body of revolution, is welded to the steel-aluminum wire 2 by means of thermite welding at the place of installation of the supporting clamp 3. The aluminum alumi nated steel wires preformed into spirals are welded into the outer surface of the protective element 1. 4. The pitch of the spirals and the diameter of the wires are chosen from conditions equality tensile strength of the wire 2 and the shielding member 1. The central part of the shielding member 1 to be mounted in the supporting clamp 3 has a diameter D _0, equals d (1,4-2) wire diameter d _n, which allows assembling the wires with an increased due to the protective element diameter in suspension clamp prior or next larger size depending on the size of the possible extreme loads due to sticking of snow, icing or dance of wires.

To a first approximation, a wire with a protective element welded to it at the outlet of the supporting clamp can be represented as a console of circular cross section of length L ₀ , with a rigidly fixed end of a larger cross section, radius R ₀ = D _0/2 , loaded at the free end, radius r = d _P / 2, transverse force F ₀ , which creates a bending moment on the console M _izg , having the greatest value in the place of its fastening (Fig. 2). A constant tension force T is also applied to the free end of the console, the value of which according to [4] should not exceed 13% of the breaking strength of the wire.

The ability of a wire with a protective element to withstand vibrational vibrations without damage is determined primarily by the level of cyclic bending stresses at its exit from the support clip, as well as in the cross section at the output of the wire from the protective element. Based on these conditions, the shape of the cantilever part of the protective element is selected so that in all sections along the length of the cantilever, the bending stresses do not exceed the permissible value of σ _max and, if possible, are the same, in order to make the most complete use of the material of the protective element, while ensuring a smooth transition from diameter D ₀ to the diameter of the wire d _P. For an arbitrary section of the console, spaced at a distance x from the place of its fastening, the condition for ensuring the required strength has the form

where M _ex (x) bending moment, M _ex (x) = F ₀ (L ₀ -x);

W (x) of circular cross section moment of resistance, W (x) = πD ^3/32,

here D = D (x) is the diameter of the steep in the section x, and D (0) = 2R ₀ , D (L ₀ ) = 2r.

The condition for equal bending resistance for the console will be

or

where R = R (x)

We rewrite this equality in the form

Where

A smooth transition from the diameter D _{0 of the} protective element to the diameter of the wire d _{P is} provided when

We seek y≡R ³ in the form

of the following conditions

;1) x = 0,

;

2) x = L ₀ , y = r ³ ;

3) x = L ₀ , y '= 0,

this condition is equivalent to equality (5);

four)

when this condition is met, the deviation of the actual longitudinal profile of the console from the theoretical one, which is a cubic parabola, is ensured, which is due to the need to make a smooth transition from the diameter D _{0 of the} protective element to the diameter of the wire d _P.

,It follows from condition 1) that

,

,from condition 2)

,

, или

.from condition 3)

, or

.

Then

and

In this way

The minimum condition for the integral I (7)

taking into account (10) leads to

or

After calculating the integral (12), we obtain an expression for determining the coefficient e

Substituting in (13) the value of the coefficients β from (4) and from (8) and c from (9), we have

Thus, in equation (6) all the coefficients are determined:

After transformation (6), we obtain an equation for determining the diameters of the cantilever parts of the protective element D (x) in places after exiting the support clip, depending on the current coordinate x, counted from the extreme points of the support clip

Where

The protective element 1 is welded to the wire coaxially to it, at the installation site of the supporting clamp 3 according to the technology of thermite welding [5] as follows.

Steel aluminized wires 4 are wound onto the wire 2, which are helically transformed in the shape of the outer surface of the protective element 1. Then, steel half-molds (iolukokili) are installed on the wire preformed in the spiral 4, the volume of which reproduces the shape of the protective element 1. Steel half-molds are rigidly fixed on the wire 2 by lock devices installed on their end parts, forming a single chill mold. Then, through the sprue hole, the volume between the inner surface of the chill mold and the wire 2 is filled with aluminum powder. Then, on the outer surface of the central part of the chill mold, a layer of termite paste containing pyrotechnic magnesium, iron oxide, and quick-drying nitro-lacquer is applied as a binder. After the termite layer has hardened, it is ignited using a thermal match. When termite burns out as a result of an exothermic reaction, a significant amount of heat is generated and high temperature develops. As a result, the aluminum powder melts inside the chill mold and the surface of wire 2 is melted. Thus, the aluminum protective element is welded to the wire 2, coaxial to it, and the steel aluminized wires 4 preformed into spirals are welded into the outer surface of the protective element 1. At the end of welding, the choked mass of the termite is removed and steel half-chills are removed from the protective element 1.

Evaluation of the effectiveness of the proposed method was carried out when it was used to protect the AC 120/19 wire according to GOST 839-80 from fatigue vibrational stresses.

To the wire with a diameter d _P equal to 15.2 mm, a protective element is welded coaxially to it, the diameter of which at the outlet of the supporting clip D ₀ is 30.4 mm. The length of the cantilever part of the protective element L ₀ is equal to 0.5 of the length of the supporting clip and is 110 mm On the arm portion of the protective element acts _mfd bending moment M due to forced vibrations of AC 120/19 at a flow of its air flow. When exposed to air flow at a speed of V = 1.47 m / s, with a span of 300 m, a stable vibration of the wire is created. The value of the bending moment M _ex under these conditions is 1.912 N⋅m [6].

In FIG. 2 shows a longitudinal section of the cantilever part of the protective element, the profile of which is determined for the indicated values of the values D ₀ , d _P and L ₀ , in accordance with equation (15), while its coefficients have the following values: a = 3511.808 mm ³ , b = -20.952702 mm ² ,

c = -0.380901 mm, e = 0.0028857.

From the FIG. 3 dependences of the bending stress σ _ze on the cantilever part of the protective element on the x coordinate obtained from equation (1), it follows that over its greater length, starting from the exit from the supporting clamp, the condition of equal bending resistance is almost satisfied while ensuring a smooth transition from the diameter D ₀ protective element to the diameter of the wire d _P. The bending stresses at the exit from the supporting clamp σ _p and σ _ze directly for the AC 120/19 wire and for the wire with the protective element welded to it are equal, respectively

;where W _n is the moment of resistance of the wire,

;

W _Ze - the moment of resistance of the wire with a protective element,

after substituting in the formulas (16) and (17) the numerical values of the quantities given in them, we obtain that the stress due to bending at the exit from the supporting clamp σ _p and σ _ze is respectively 5.444 and 0.68 N / mm ² .

According to the Weller curve of safe bending stresses [7], a probabilistic estimate of the number of oscillation cycles to the destruction of the wire at the outlet of the supporting clip in the absence and presence of a protective element was determined, which amounted to 10 ⁹ and 10 ¹⁰ cycles, respectively. Thus, the application of the proposed method allows at least 10 times to increase the resource resistance of the wire during its vibration.

и от изгиба

. Это обусловлено тем, что площадь сечения системы провод с защитным элементом и ее момент сопротивления существенно, соответственно в 4 и 8 раз, превышают указанные величины собственно для провода.Along with increasing the resource durability of the wire, the proposed method allows to prevent accidents of power lines due to mechanical overload of wires in the event of wire dancing caused by a combination of significant wind loads with icy deposits. In the most dangerous section of the wire, at the place of its exit from the supporting clamp, the total voltage arises from the tension of the wire and from its bend. When dancing the wires, the tension of the wire T increases significantly due to the fact that the specific load on the wire from the weight of the wire coated with ice and the wind pressure on the coated ice can several times exceed the load due to the dead weight of the wire (for AC 120/19 more than 5 times [8]). In addition, when exposed to air flow at a speed of up to 30 m / s, there is an increase in the alternating bending moment acting in this section. In this case, the effectiveness of the proposed method of protection against damage to the wires in this case is determined by a significant reduction in the dangerous section of the wire, with the protective element coaxially welded to it, of the maximum stress ah, equal to the sum of the tensile stresses

and from bending

. This is due to the fact that the cross-sectional area of the system wire with a protective element and its resistance moment are significantly, respectively, 4 and 8 times higher than the indicated values for the wire itself.

Information sources

1. RF patent No. 2435265, M. cl. H02G 7/02.

2. RF patent No. 2190288, M. cl. H02G 7/14.

3. Timoshenko S.P. Strength of materials. T 1. M .: Nauka, 1965.364 s.

4. Rules for the installation of electrical installations. M .: CJSC Energoservice, 2000. 607 p.

5. Evseev R.E. Termite welding in electrical installation. M .: From the literature on construction, 1968.127 p.

6. Trofimov S.V. Evaluation of the effectiveness of the tread installed to protect the wire at the outlet of the supporting clamp // Electric stations, 2004. - No. 2. - S. 42-46.

7. Guidelines for typical protection against vibration and vibration of wires and lightning protection cables of overhead power lines with a voltage of 34-750 kV. RD 34.20.182-90. M., 1991. 41 p.

8. Handbook of high voltage electrical networks. M.-L.: Gosenergoizdat, 1962.560 s.

Claims (3)

A method for protecting steel-aluminum wires of overhead power lines from oscillatory fatigue damage at the outlet of the supporting clamp, comprising securing a protective element to the wire at the installation location of the supporting clamp, characterized in that a protective element made of aluminum is welded to the wire coaxially with it, which is body of revolution, into the outer surface of which aluminum aluminized steel wires transformed into spirals are welded, the central part of the protective the element mounted in the supporting clamp has a diameter D ₀ equal to (1.4-2) the diameter of the wire d _P , which along the length of the cantilever part L ₀ decreases to the diameter of the wire d _P , while the diameter of the cantilever parts of the protective element D (x) in places after exiting the supporting clamp, it is determined, depending on the current x coordinate, counted from the extreme points of the supporting clamp, from the equation

, Where

;

;

;

.

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