A method for evaluating insulation interface pressure of high-voltage GIS cable terminals

Abstract

The present invention relates to a method for evaluating the insulation interface pressure of a high-voltage GIS cable terminal, including: using an assembly structure to establish a high-voltage GIS terminal simulation model, analyzing the separation motion at the interface between the stress cone and the epoxy casing; introducing a penalty function method at different insulation structure interfaces of the GIS terminal simulation model, and obtaining the interface pressure changes and interface separation processes at different temperatures through the interface penalty function method; based on a thermo-mechanical stress field coupling calculation model, calculating the interface pressure between the stress cone and the epoxy casing in the terminal caused by the difference in thermal expansion coefficients of different materials, and evaluating the pressure distortion at the contact interface between the stress cone and the epoxy casing in the cable terminal. The present invention is reasonably designed and can evaluate the pressure distortion at the contact interface between the stress cone and the epoxy casing in the cable terminal, and can be widely used in the interface pressure evolution analysis of prefabricated GIS cable terminals at different operating temperatures.

Description

Technical Field

[0001] The invention belongs to the technical field of high-voltage power distribution, and relates to a high-voltage GIS cable terminal, in particular to a method for evaluating the insulation interface pressure of a high-voltage GIS cable terminal. Background Art

[0002] High-voltage GIS cable terminal is a high-voltage power distribution device that uses SF6 gas as an insulating medium and is composed of high-voltage electrical equipment such as circuit breakers and isolating switches. Due to its compact structure, high reliability, and convenient maintenance, high-voltage GIS cable terminal has become the best equipment for power conversion in ultra-high voltage substations and has been widely used in my country's power transmission and transformation projects.

[0003] GIS cable terminal is an indispensable terminal form for GIS combined electrical appliances. It adopts dry design and uses SF6 gas as the external insulation part. It has the advantages of compact structure, simple operation and maintenance, and stable performance. With the emergence of extreme weather in recent years (as low as -40℃), GIS cable terminal failures have occurred frequently. What is obviously different from the past failures is that the time of recent failures is significantly related to the climate temperature. The GIS terminal breakdown accident in cold weather has seriously affected the safe and stable operation of the power grid. After disassembling the faulty terminal, it was found that its fault characteristics were mainly manifested as: there was no obvious discharge channel on the cable body and the inner side of the stress cone, but there were obvious discharge and high-temperature burning marks at the interface between the stress cone and the epoxy casing. It was initially judged that the interface breakdown was caused by the decrease in interface insulation strength. The change in the matching state of the insulation interface (such as interface pressure) is a key factor affecting the overall insulation performance of the terminal. Considering that there is an order of magnitude difference in the thermal expansion coefficients of silicone rubber and epoxy resin, the interface pressure may drop due to thermal expansion mismatch in low temperature environments.

[0004] How to discover the evolution law of the terminal insulation interface pressure under low temperature environment and evaluate the state of the terminal insulation interface at different ambient temperatures is an urgent problem to be solved. The traditional coordination model cannot accurately evaluate the change of the cable terminal insulation interface pressure at different temperatures. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and propose a method for evaluating the insulation interface pressure of a high-voltage GIS cable terminal, which solves the problem that the traditional matching body model cannot accurately evaluate the changes in the insulation interface pressure of the cable terminal at different temperatures, and realizes the evaluation function of the pressure distortion at the contact interface between the stress cone and the epoxy casing in the cable terminal under extreme temperature environments and abnormal temperature changes.

[0006] The present invention solves the technical problem by adopting the following technical solutions:

[0007] A method for evaluating the insulation interface pressure of a high-voltage GIS cable terminal comprises the following steps:

[0008] Separation motion analysis steps at the interface between stress cone and epoxy casing: Use assembly structure to establish a high-voltage GIS terminal simulation model, and analyze the separation motion at the interface between stress cone and epoxy casing;

[0009] Interface pressure change and interface separation steps: Introduce the penalty function method at the interfaces of different insulation structures in the GIS terminal simulation model, and obtain the interface pressure change and interface separation process at different temperatures through the interface penalty function method;

[0010] Steps for evaluating the pressure distortion at the interface between the stress cone and the epoxy casing: Based on the thermal-mechanical stress field coupling calculation model, calculate the pressure at the interface between the stress cone and the epoxy casing in the terminal caused by the difference in thermal expansion coefficients of different materials, and evaluate the pressure distortion at the contact interface between the stress cone and the epoxy casing in the cable terminal.

[0011] Furthermore, the GIS terminal simulation model includes: a cable body, a stress cone, an epoxy casing, a tail pipe and a stress cone support; the stress cone is composed of a stress cone semi-conductive part and a stress cone enhanced insulating part, and the stress cone semi-conductive part serves as a transition zone for the cable outer shielding to play a role in uniform electric field; the stress cone enhanced insulating part and the epoxy casing together constitute the main insulation of the GIS terminal, and a stress cone support is installed at the bottom of the stress cone to provide pressure compensation.

[0012] Furthermore, the analysis method of the high-voltage GIS terminal simulation model is as follows: each component in the GIS cable terminal is set as a separate object, and the domain sets in the separate objects are not connected to each other. When meshing, the vertices and edges of the boundary mesh units are not shared, that is, the two domains are discontinuous, and the physical field in the entire domain generates a consistent pair by contacting the boundary to ensure its own continuity, and then analyze the separation motion at the interface between the stress cone and the epoxy casing.

[0013] Furthermore, the penalty function method is based on the assumption that there is a rigid spring at the contact boundary, the stiffness of the rigid spring is represented by the penalty factor, and the simulation calculation function of the pressure generated at the interface or the interface separation is realized.

[0014] Furthermore, the penalty factor in the penalty function is selected from the Young's modulus of the material, the normal interface pressure T n It is expressed as:

[0015]

[0016] Where d g is the interface gap distance, E is the Young's modulus of the material, and p0 is the initial interface pressure at zero gap.

[0017] Furthermore, the thermo-mechanical stress field coupling calculation model is established by the following method: the thermo-mechanical stress field is coupled by the relative volume change caused by the different thermal expansion of the two materials under the constraint state, and the relative volume change ΔV is expressed as follows:

[0018] ΔV≈ΔT(α1-α2)

[0019] Where α1 and α2 are the thermal expansion coefficients of the two materials, and ΔT is the relative change temperature.

[0020] Furthermore, the constraint state includes the fixed constraint at the epoxy sleeve flange and the body load constraint of the stress cone support, wherein the body load constraint direction is vertically upward, in order to simulate the interface pressure regulation effect of the stress cone support in the actual terminal under low temperature environment, the load size is equivalent to the spring force and is proportional to the spring compression. The body load constraint F is expressed as:

[0021]

[0022] Where F0 is the initial spring force, n is the number of springs, N is the number of effective coils of the spring, k is the stiffness of a single coil spring, and T ref is the reference temperature.

[0023] The advantages and positive effects of the present invention are:

[0024] The invention is reasonably designed. It adopts a high-voltage GIS terminal simulation model with an assembly structure, and solves the problem that the traditional matching body model cannot accurately reflect the pressure at the fitting interface; a penalty function method is introduced at the matching interface to obtain the interface pressure change and the interface separation process at different temperatures; based on the thermal field-stress field coupling calculation, the problem of accurately calculating the interface pressure distortion between the stress cone in the terminal and the epoxy casing caused by the mismatch of thermal expansion coefficients at different ambient temperatures is solved, so that the interface pressure change caused by the difference in thermal expansion coefficients of different materials under extreme temperature environments and abnormal temperature changes is accurately obtained, and the pressure distortion at the contact interface between the stress cone in the cable terminal and the epoxy casing is evaluated, and the invention can be widely used for the interface pressure evolution analysis of prefabricated GIS cable terminals at different operating temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural diagram of a simulation geometric model of the present invention;

[0026] Figure 2 It is the interface temperature field distribution calculation result diagram of the present invention;

[0027] Figure 3 is a diagram of the interface pressure coupling calculation results of the present invention;

[0028] Figure 1Among them, 1-cable body, 2-high voltage electrode, 3-stress cone enhanced insulation part, 4-epoxy casing, 5-tail pipe, 6-semi-conductive shielding layer, 7-cable main insulation, 8-stress cone semi-conductive part, 9-stress cone support. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the accompanying drawings.

[0030] A method for evaluating the insulation interface pressure of a high-voltage GIS cable terminal comprises the following steps:

[0031] 1. Separation motion analysis steps at the interface between stress cone and epoxy casing: Use assembly structure to establish a high-voltage GIS terminal simulation model and analyze the separation motion at the interface between stress cone and epoxy casing.

[0032] This embodiment is described by taking a 110kV high-voltage GIS terminal as an example. Figure 1 As shown, the 110kV high-voltage GIS terminal simulation geometric model includes five components: a cable body (1), a stress cone, an epoxy sleeve (4), a tail pipe (5) and a stress cone support (10). The stress cone is composed of a stress cone semi-conductive part (8) and a stress cone enhanced insulating part (3). The stress cone semi-conductive part (8) serves as a transition zone for the cable outer shielding and plays a role of uniform electric field. The stress cone enhanced insulating part (3) and the epoxy sleeve (4) together constitute the main insulation of the GIS terminal. At the same time, in order to make the interface between the stress cone and the epoxy sleeve (4) closely contact, a stress cone support (10) is usually installed at the bottom of the stress cone to provide pressure compensation.

[0033] The present invention uses an assembly model to set each component in the GIS cable terminal as a separate object. The domain sets in the separate objects are not connected to each other. When meshing, the vertices and edges of the boundary mesh units are not shared, that is, the two domains are discontinuous. The physical field in the entire domain generates a consistent pair by contacting the boundary to ensure its own continuity, so as to realize the separation motion analysis at the interface between the stress cone and the epoxy casing.

[0034] The present invention adopts an assembly modeling method to solve the problem that the traditional matching body model cannot accurately reflect the pressure at the fitting interface.

[0035] 2. Interface pressure change and interface separation steps: The penalty function method is introduced at the interfaces of different insulation structures in the GIS terminal simulation model. The interface pressure change and interface separation process at different temperatures are obtained through the interface penalty function method.

[0036] The penalty function method is based on the assumption that there is a rigid spring at the contact boundary. The stiffness of the rigid spring is represented by the penalty factor, which can realize the simulation calculation function of the pressure generated at the interface or the interface separation.

[0037] In this embodiment, the penalty factor is the Young's modulus of the material, and the normal interface pressure can be expressed as:

[0038]

[0039] Where d g is the interface gap distance, E is the Young's modulus of the material, and p0 is the initial interface pressure at zero gap.

[0040] 3. Steps for evaluating the pressure distortion at the interface between the stress cone and the epoxy casing: Based on the thermal-mechanical stress field coupling calculation model, calculate the interface pressure between the stress cone and the epoxy casing in the terminal caused by the difference in thermal expansion coefficients of different materials, and evaluate the pressure distortion at the contact interface between the stress cone and the epoxy casing in the cable terminal.

[0041] The thermal-mechanical stress field coupling calculation model proposed in the present invention is a full-scale thermal-mechanical stress field coupling calculation model for cable terminals. The thermal-mechanical stress field coupling calculation model is established by the following method: the thermal-mechanical stress field is mainly coupled by the relative volume change caused by the different thermal expansion of the two materials under the constraint state. The relative volume change ΔV is expressed as follows:

[0042] ΔV≈ΔT(α1-α2) (2)

[0043] Where α1 and α2 are the thermal expansion coefficients of the two materials, and ΔT is the relative change temperature.

[0044] The above-mentioned constraint state mainly includes the fixed constraint at the flange of the epoxy sleeve (4) and the body load constraint of the stress cone support (10), wherein the body load constraint direction is vertically upward, in order to simulate the interface pressure regulation effect of the stress cone support in the actual terminal under low temperature environment, the load size is equivalent to the spring force and is proportional to the spring compression. The body load constraint F is expressed as:

[0045]

[0046] Where F0 is the initial spring force, n is the number of springs, N is the number of effective coils of the spring, k is the stiffness of a single coil spring, and T ref is the reference temperature.

[0047] The above method can be used to complete the interface pressure changes caused by differences in thermal expansion coefficients of different materials under extreme temperature environments and abnormal temperature changes, and accurately evaluate the pressure distortion at the contact interface between the stress cone and the epoxy casing in the cable terminal.

[0048] The specific evaluation process of the present invention is described below.

[0049] When evaluating the insulation interface pressure of high-voltage GIS cable terminals, thermal field calculation is required. Thermal field calculation mainly includes three heat transfer modes: heat conduction between solid media, heat convection between gases, and heat radiation from solid media to the gas environment. The thermal equations are expressed by formulas (4)-(6):

[0050] Heat conduction:

[0051]

[0052] Where T is temperature (K), q is heat flux (W / m 2 ), φ heat flow (J), λ material thermal conductivity (W / (m·K))

[0053] Heat convection:

[0054] q=h·Δt (5)

[0055] Where h is the surface convection heat transfer coefficient (W / (m 2 ·K)), Δt Temperature difference between the object and the fluid surface (K)

[0056] Heat radiation:

[0057] Q=εAσ b ΔT 4 (6)

[0058] Where ε is the surface emissivity, A is the effective radiation area (m 2 ),σ b Constant (5.67×10 8 (W / (m 2 ·K))), T is the surface temperature of the object (K). The heat generated at the GIS cable terminal is mainly the Joule heat generated by the current flowing through the cable body (1). According to IEC-60287, the AC resistance of the conductor can be calculated according to formulas (7)-(9):

[0059] R=R0[1+α 20 (T-20)](1+Y s ) (7)

[0060]

[0061]

[0062] Where R0 is the DC resistance of the conductor per unit length at room temperature, R0 = 7.2 × 10-3 (Ω / km), α 20 is the temperature coefficient of resistance of the conductor, α 20 =3.93×10-3(1 / K),Y s is the skin effect coefficient of the conductor, K sis the shape factor of the conductor, K s =1, f is the current frequency, f=50Hz. The outer surface of the epoxy sleeve (4) and the outer surface of the tail pipe (5) are for radiation heat exchange, and the surface emissivities are 0.85 and 0.2 respectively; considering that the interface pressure will affect the interface contact thermal resistance, the contact position between the stress cone (3, 8) and the epoxy sleeve (4) is set as the thermal contact surface, and the shrinkage conductivity model of the gap gas is used for heat transfer calculation.

[0063] In the stress simulation, the interface stress caused by the mismatch of thermal expansion coefficients between the stress cone (3, 8) silicone rubber and the epoxy sleeve (4) is mainly considered. The thermal expansion stress mainly depends on the temperature, elastic modulus and thermal expansion coefficient of the material. In the thermal stress coupling calculation, the epoxy sleeve flange (4) is set as a fixed constraint, and a vertical body load is set at the stress cone support (10). The load size can be expressed as formula (3).

[0064] The temperature field calculation results are as follows: Figure 2 As shown in the figure, the simulation results can obtain the overall temperature characteristics of the terminal, and it can be seen from the simulation results that in a low temperature environment, the simulation model can intuitively obtain the interface temperature distortion. At the same time, the thermal-mechanical stress coupling calculation results are shown in Figure 3 As shown, the simulation results can fully reflect the interface pressure distortion caused by the mismatch of thermal expansion coefficients between the stress cone (3, 8) and the epoxy sleeve (4) in a low temperature environment. It is found that near the high-voltage electrode and the grounding method, the interface pressure drops to almost 0 due to material shrinkage caused by temperature drop, which may cause cracks and air gaps between the stress cone and the epoxy sleeve, threatening the safe and stable operation of the terminal.

[0065] At this point, the geometric and physical modeling of the simulation model is completed. Then, by setting different external ambient temperatures and performing iterative calculations, the calculation results of the terminal insulation interface pressure distribution can be obtained.

[0066] It should be emphasized that the embodiments described in the present invention are illustrative rather than restrictive. Therefore, the present invention includes but is not limited to the embodiments described in the specific implementation manner. Any other implementation manners derived by those skilled in the art based on the technical solution of the present invention also fall within the scope of protection of the present invention.

Claims

1. A method for evaluating the insulation interface pressure of a high-voltage GIS cable terminal, characterized in that: The following steps are involved: Separation motion analysis steps at the interface between stress cone and epoxy casing: Use assembly structure to establish a high-voltage GIS terminal simulation model, and analyze the separation motion at the interface between stress cone and epoxy casing; Interface pressure change and interface separation steps: Introduce the penalty function method at the interfaces of different insulation structures in the GIS terminal simulation model, and obtain the interface pressure change and interface separation process at different temperatures through the interface penalty function method; Steps for evaluating the pressure distortion at the interface between the stress cone and the epoxy casing: Based on the thermo-mechanical stress field coupling calculation model, calculate the pressure at the interface between the stress cone and the epoxy casing in the terminal caused by the difference in thermal expansion coefficients of different materials, and evaluate the pressure distortion at the contact interface between the stress cone and the epoxy casing in the cable terminal; The penalty function method is based on the assumption that there is a rigid spring at the contact boundary, the stiffness of which is represented by a penalty factor, to achieve a simulation calculation function of the pressure generated at the interface or the interface separation situation; The penalty factor in the penalty function is selected from the Young's modulus of the material, the normal interface pressure T n It is expressed as: Where d g is the interfacial gap distance, E is the Young's modulus of the material, and p0 is the initial pressure of the interface at zero gap; The thermo-mechanical stress field coupling calculation model is established by the following method: the thermo-mechanical stress field is coupled by the relative volume change caused by the different thermal expansion of two materials under the constraint state, and the relative volume change ΔV is expressed as follows: ΔV≈ΔT(α1-α2) Where α1 and α2 are the thermal expansion coefficients of the two materials, and ΔT is the relative change temperature.

2. A method for evaluating the insulation interface pressure of a high-voltage GIS cable terminal according to claim 1, characterized in that: The GIS terminal simulation model includes: a cable body, a stress cone, an epoxy casing, a tail pipe and a stress cone support; the stress cone is composed of a stress cone semi-conductive part and a stress cone enhanced insulating part, and the stress cone semi-conductive part serves as a transition zone for the cable outer shielding to play a role in uniform electric field; the stress cone enhanced insulating part and the epoxy casing together constitute the main insulation of the GIS terminal, and a stress cone support is installed at the bottom of the stress cone to provide pressure compensation.

3. A method for evaluating the insulation interface pressure of a high-voltage GIS cable terminal according to claim 1 or 2, characterized in that: The analysis method of the high-voltage GIS terminal simulation model is as follows: each component in the GIS cable terminal is set as a separate object, and the domain sets in the separate objects are not connected to each other. When meshing, the vertices and edges of the boundary mesh units are not shared, that is, the two domains are discontinuous. The physical field in the entire domain generates a consistent pair by contacting the boundary to ensure its own continuity, and then analyze the separation motion at the interface between the stress cone and the epoxy casing.

4. A method for evaluating the insulation interface pressure of a high-voltage GIS cable terminal according to claim 1, characterized in that: The constraint state includes the fixed constraint at the epoxy sleeve flange and the body load constraint of the stress cone support. The body load constraint direction is vertically upward to simulate the interface pressure regulation effect of the stress cone support in the actual terminal under low temperature environment. The load size is equivalent to the spring force and is proportional to the spring compression. The body load constraint F is expressed as: Where F0 is the initial spring force, n is the number of springs, N is the number of effective coils of the spring, k is the stiffness of a single coil spring, and T ref is the reference temperature.

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