CN102252787A - Method for measuring pressure of insulation interface of cable terminal - Google Patents

Abstract

The invention provides a method for measuring the insulation interface pressure of a cable terminal. The method of combining on-site measurement and numerical simulation is adopted to directly measure the spring strain of the spring compression device of the high-voltage cable terminal on site. The force relationship of the tightening device, to achieve the purpose of obtaining the axial pressure of the stress cone through indirect measurement; establish the overall numerical simulation model of the high-voltage cable terminal, check the reliability of the simulation model according to the axial pressure of the rubber stress cone, and finally calculate the numerical simulation according to the mechanical, electrical and thermal load conditions The distribution and change law of the insulation interface pressure at the cable terminal. The method avoids the problem that the interface pressure cannot be directly measured due to the structure of the high-voltage cable terminal, and the method has the characteristics of reliability, effectiveness and convenience.

Description

Method for Measuring the Pressure of Cable Terminal Insulation Interface

technical field

The invention belongs to the technical field of high-voltage power grid testing, and can accurately and reliably measure the distribution and variation law of the insulation interface pressure of a high-voltage cable terminal.

Background technique

交流输电网是目前我国骨干电网。 The power grid is an intermediate link in the transmission and distribution of electric energy. It is mainly composed of transmission lines, substations, distribution stations and distribution lines connected into a network. At present, my country's power grid is mainly based on high-voltage and ultra-high-voltage AC transmission lines. ,

The AC transmission network is currently the backbone power grid in my country.

Among the components of the power grid, the power transmission system undertakes the task of transporting and distributing power to various power-consuming departments, and it also has the greatest impact on the operation of the power system. The power transmission system is mainly composed of three parts: cables, cable accessories and line structures. Cable accessories refer to other components and equipment in the cable line except the cable body, including cable terminals and cable joints. The probability of power system faults in the past shows that the faults of cable accessories account for more than half of the faults in cable operation. Cable terminals are an important part of power transmission and distribution systems. However, due to the complexity of the cable terminal's own structure, manufacture, connection and operating conditions, terminal failures are always unavoidable. The high-voltage cable terminal is a cable accessory used to connect the high-voltage cable with the high-voltage power grid or other electrical equipment. It is installed at the end of the power grid line and plays an important role in the transfer of the entire power grid line. the key link.

The tightness of the contact interface of the internal components of the cable terminal is very important to the stability and reliability of the cable terminal interface. It will directly affect the insulation characteristics of the cable terminal, such as partial discharge, instantaneous breakdown strength and long-term breakdown strength. Rubber prefabricated stress cone high-voltage cable terminals are widely used in engineering, which consists of rubber prefabricated stress cone, copper bracket, epoxy resin sleeve, base, porcelain sleeve, top cover, rain cover, outlet rod, cable insulation and cable core. The technical feature is that the rubber prefabricated stress cone and the epoxy resin sleeve work together as an insulation strengthening component and an electrical stress control component, and at the same time, a spring pressing device is used to press the rubber prefabricated stress cone, and the rubber prefabricated stress cone is pressed against the epoxy resin The inner side of the casing, so that the interface between the rubber prefabricated stress cone, the epoxy resin casing, and the cable insulation is in close contact, and maintains a long-term reliable interface pressure, increasing the reliability of the cable terminal.

The rubber prefabricated stress cone is a key part of the high-voltage cable terminal. The rubber prefabricated stress cone should be in close contact with the epoxy resin sleeve and the cable insulation, and a certain interface stress should be maintained. The size and distribution of the interface stress directly affect the cable terminal. The distribution of the electric field directly affects the electrical performance of the cable terminal. The breakdown electric field strength of the cable terminal increases with the increase of the interface stress, and when the interface stress reaches a certain level, the breakdown strength of the terminal reaches saturation. Where the interface stress is different, the breakdown electric field strength is also different. Before reaching saturation, the smaller the interface stress, the smaller the breakdown electric field intensity, and when the interface stress is uneven, the distribution of the terminal electric field is uneven, and the phenomenon of electric field concentration occurs. Some end faces with small interface stress may be affected by the electric field. breakdown. Therefore, it is very important to understand and master the magnitude and distribution of the interface pressure of the high-voltage cable terminal to ensure the stability and reliability of the cable terminal.

However, since the high-voltage cable terminal is a complex structure composed of various material parts, and the structure is tight, it is very difficult to directly measure the insulation interface pressure, especially the insulation interface pressure during installation and operation. At present, there is no mature Therefore, it is very necessary to have a method of measuring the insulation interface pressure during the installation and operation of the high-voltage cable terminal.

Contents of the invention

In order to overcome the difficulty of directly measuring the insulation interface pressure of the cable terminal, the invention provides a method for measuring the insulation interface pressure of the cable terminal, which is an indirect method for measuring the interface pressure. This method combines actual field measurement with numerical simulation, and finally calculates the insulation interface pressure of the high-voltage cable terminal through the finite element method.

The technical solution adopted by the present invention to solve its technical problems is:

A method for measuring the insulation interface pressure of a cable terminal, which adopts the method of combining on-site measurement and numerical simulation, directly measures the spring strain of the spring compression device of the high-voltage cable terminal on site, according to the rubber stress cone of the high-voltage cable terminal and the spring compression device. The force relationship is used to achieve the purpose of obtaining the axial pressure of the stress cone through indirect measurement; the overall numerical simulation model of the high-voltage cable terminal is established, the reliability of the simulation model is checked according to the axial pressure of the rubber stress cone, and finally the cable terminal is calculated according to the numerical simulation of the mechanical, electrical and thermal load conditions The distribution and change law of insulation interface pressure.

Under the initial installation condition, the specific steps of the on-site measurement of the spring strain are as follows:

1) Install a static digital resistance strain gauge;

2) The strain gauge is connected to the static digital resistance strain gauge by the half-bridge method. In order to eliminate the influence of temperature and other factors on the test, the temperature compensation strain gauge is used in the experiment;

3) Connect the strain gauge to a well-grounded AC power supply for preheating, and calibrate the static strain gauge after the preheating is complete;

4) While tightening the screw nut inside the spring, perform data collection;

5) According to the relationship between the axial pressure on the rubber stress cone of the high-voltage cable terminal and the measured strain, the axial pressure on the rubber stress cone under the initial installation condition is obtained.

Under operating conditions, the specific steps of the on-site strain measurement are as follows:

1) Install a dynamic strain tester;

2) The strain gauge is connected to the dynamic strain tester by the half-bridge method. In order to eliminate the influence of temperature and other factors on the test, the temperature compensation strain gauge is used in the experiment;

3) Connect the strain gauge to a well-grounded AC power supply for preheating, and balance and reset the dynamic strain test system after the preheating is complete;

4) The cable terminal running time and data collection time of each voltage working condition are the same;

5) According to the relationship between the axial pressure on the rubber stress cone at the high-voltage cable terminal and the measured strain, the axial pressure on the rubber stress cone under operating conditions is obtained.

The above numerical simulation method is a finite element method, and its specific steps are as follows:

1) According to the actual structural size of the high-voltage cable terminal, the overall nonlinear finite element simulation model of the high-voltage cable terminal is established;

2) Verify the reliability of the finite element model according to the axial pressure results of the rubber stress cone obtained through indirect measurement;

3) The nonlinear finite element numerical simulation calculation is carried out under the condition of force, electricity and heat load, and the distribution and change law of the insulation interface pressure of the high-voltage cable terminal are obtained.

The beneficial effect of the present invention is that, the combination method of on-site measurement and numerical simulation is adopted, and the simple and feasible on-site test experiment method is used for measurement, and the final result is obtained through numerical calculation, thereby avoiding the interface that cannot be directly measured due to the structure of the high-voltage cable terminal To solve the problem of pressure, this method is reliable, effective and convenient.

Description of drawings

Fig. 1 is a partial structural view of the stress cone of the high-voltage cable terminal of the present invention.

Fig. 2 is a flow chart of the operation of the method of the present invention.

Fig. 3 is the overall numerical simulation model of the cable terminal of the present invention.

Figure 4 is the calculated interface pressure distribution curve between the high-voltage cable terminal stress cone and the cable insulation.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

A method for measuring the insulation interface pressure of a cable terminal, which adopts the method of combining on-site measurement and numerical simulation, directly measures the spring strain of the spring compression device of the high-voltage cable terminal on site, according to the rubber stress cone of the high-voltage cable terminal and the spring compression device. The force relationship is used to achieve the purpose of obtaining the axial pressure of the stress cone through indirect measurement; the overall numerical simulation model of the high-voltage cable terminal is established, the reliability of the simulation model is checked according to the axial pressure of the rubber stress cone, and finally the cable terminal is calculated according to the numerical simulation of the mechanical, electrical and thermal load conditions The distribution and change law of insulation interface pressure.

As shown in Figure 1, the high-voltage cable terminal stress cone includes insulating oil 1, epoxy resin sleeve 2, rubber prefabricated stress cone 3, magnetic sleeve 4, shielding layer 5 and spring support device 6. Stick strain gauges on the spring supporting device 6, and use dynamic and static strain gauges to measure the spring strains during installation and operation respectively.

As shown in Figure 2, under the initial installation condition, the specific steps of the on-site measurement of the spring strain are as follows:

1) Install a static digital resistance strain gauge;

2) The strain gauge is connected to the static digital resistance strain gauge by the half-bridge method. In order to eliminate the influence of temperature and other factors on the test, the temperature compensation strain gauge is used in the experiment;

3) Connect the strain gauge to a well-grounded AC power supply for preheating, and calibrate the static strain gauge after the preheating is complete;

4) While tightening the screw nut inside the spring, perform data collection;

5) According to the relationship between the axial pressure on the rubber stress cone of the high-voltage cable terminal and the measured strain, the axial pressure on the rubber stress cone under the initial installation condition is obtained.

Under operating conditions, the specific steps of the on-site strain measurement are as follows:

1) Install a dynamic strain tester;

2) The strain gauge is connected to the dynamic strain tester by the half-bridge method. In order to eliminate the influence of temperature and other factors on the test, the temperature compensation strain gauge is used in the experiment;

3) Connect the strain gauge to a well-grounded AC power supply for preheating, and balance and reset the dynamic strain test system after the preheating is complete;

4) The cable terminal running time and data collection time of each voltage working condition are the same;

5) According to the relationship between the axial pressure on the rubber stress cone at the high-voltage cable terminal and the measured strain, the axial pressure on the rubber stress cone under operating conditions is obtained.

The implementation principle is: the relationship between the pressure on the rubber stress cone at the end of the high-voltage cable and the measured strain is

                                (a)

(a)

为弹簧丝直径，

为弹簧直径和弹簧丝直径之差，

为弹簧材料的剪切弹性模量。 in, is the pressure on the stress cone, To measure strain,

is the spring wire diameter,

is the difference between the spring diameter and the spring wire diameter,

is the shear modulus of elasticity of the spring material.

The pressure on the rubber stress cone is calculated according to formula (a) to verify the reliability of the numerical simulation model, and the insulation interface pressure of the high-voltage cable terminal is calculated by using the finite element method according to the imposed installation and operation boundary conditions.

The above numerical simulation method is a finite element method, and its specific steps are as follows:

1) According to the actual structural size of the high-voltage cable terminal, the overall nonlinear finite element simulation model of the high-voltage cable terminal is established;

2) Verify the reliability of the finite element model according to the axial pressure results of the rubber stress cone obtained through indirect measurement;

3) The nonlinear finite element numerical simulation calculation is carried out under the condition of force, electricity and heat load, and the distribution and change law of the insulation interface pressure of the high-voltage cable terminal are obtained.

The finite element simulation of the high-voltage cable terminal is carried out as a whole, and the thermal-mechanical coupling field nonlinear finite element solution equation is established according to the material and geometric nonlinearity:

                                (b)

(b)

为位移矩阵，

为整体载荷矩阵。根据高压电缆终端的受力情况，载荷矩阵中包含由电缆温度应变引起的温度载荷和橡胶应力锥受到压力载荷，即： in, is the overall stiffness matrix, which is the element nodal displacement The function,

is the displacement matrix,

is the overall loading matrix. According to the force condition of the high-voltage cable terminal, the load matrix includes the temperature load caused by the cable temperature strain and the pressure load on the rubber stress cone, namely:

(c)

为电缆温度应变引起的载荷矩阵项，

为橡胶应力锥受到压力载荷矩阵。 In the formula, is the gravity and pressure load matrix,

is the load matrix item caused by cable temperature strain,

The rubber stress cone is subjected to the pressure load matrix.

As shown in Figure 3, according to the actual structural size of the high-voltage cable terminal, the overall nonlinear finite element simulation model of the high-voltage cable terminal is established; as shown in Figure 4, the interface pressure distribution curve between the stress cone of the high-voltage cable terminal and the cable insulation is calculated, and the shape The trend approximates a step function curve. The interface pressure is high near the compression side of the stress cone, and the interface pressure is small away from the side. Between 0-60mm, the pressure increases gradually, and the change is relatively gentle; between 60mm-80mm, the pressure value increases rapidly; between 80mm-140mm, the pressure gradually increases, and the change is relatively gentle; after 140mm, The pressure gradually decreases again; a minimum value appears near 210mm; between 210mm-220mm, the pressure value increases rapidly, and reaches the maximum value at 220mm; as the voltage increases, the pressure distribution of the insulation interface changes with the interface position The trend of change is the same, but the fluctuation range of the curve increases, and the interface pressure increases.

Claims (4)

1. A method for measuring the insulation interface pressure of a cable terminal, characterized in that the method of combining on-site measurement and numerical simulation is adopted to directly measure the spring strain of the high-voltage cable terminal spring compression device on site, and according to the rubber stress cone of the high-voltage cable terminal The force relationship with the spring compression device achieves the purpose of obtaining the axial pressure of the stress cone through indirect measurement; the overall numerical simulation model of the high-voltage cable terminal is established, and the reliability of the simulation model is checked according to the axial pressure of the rubber stress cone. The distribution and change law of the insulation interface pressure of the cable terminal are calculated by numerical simulation. 2. A kind of method for measuring cable terminal insulation interface pressure according to claim 1, it is characterized in that, under the initial installation condition, the concrete steps of described on-site measurement spring strain are as follows: 1) Install a static digital resistance strain gauge; 2) The strain gauge is connected to the static digital resistance strain gauge by the half-bridge method. In order to eliminate the influence of temperature and other factors on the test, the temperature compensation strain gauge is used in the experiment; 3) Connect the strain gauge to a well-grounded AC power supply for preheating, and calibrate the static strain gauge after the preheating is complete; 4) While tightening the screw nut inside the spring, perform data collection; 5) According to the relationship between the axial pressure on the rubber stress cone of the high-voltage cable terminal and the measured strain, the axial pressure on the rubber stress cone under the initial installation condition is obtained. 3. A kind of method for measuring cable terminal insulation interface pressure according to claim 1, is characterized in that, under operating conditions, the concrete steps of described on-site strain measurement are as follows: 1) Install a dynamic strain tester; 2) The strain gauge is connected to the dynamic strain tester by the half-bridge method. In order to eliminate the influence of temperature and other factors on the test, the temperature compensation strain gauge is used in the experiment; 3) Connect the strain gauge to a well-grounded AC power supply for preheating, and balance and reset the dynamic strain test system after the preheating is complete; 4) The cable terminal running time and data collection time of each voltage working condition are the same; 5) According to the relationship between the axial pressure on the rubber stress cone at the high-voltage cable terminal and the measured strain, the axial pressure on the rubber stress cone under operating conditions is obtained. 4. a kind of method for measuring cable terminal insulation interface pressure according to claim 1, is characterized in that, described numerical simulation method is finite element method, and its concrete steps are as follows: 1) According to the actual structural size of the high-voltage cable terminal, the overall nonlinear finite element simulation model of the high-voltage cable terminal is established; 2) Verify the reliability of the finite element model according to the axial pressure results of the rubber stress cone obtained through indirect measurement; 3) The nonlinear finite element numerical simulation calculation is carried out under the condition of force, electricity and heat load, and the distribution and change law of the insulation interface pressure of the high-voltage cable terminal are obtained.

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