Calculation of Structural Parameters of Epoxy Resin Casting Insulated Tubular Bus

Abstract
In order to ensure the quality and operational reliability of the insulated tube bus, it is necessary to account for the structural parameters of the different types of insulated tube bus, said Ren Yi, a researcher at the Power Science Research Institute of Hubei Electric Power Company, etc., in the 2018 issue of the Journal of Electrical Technology.
This paper analyzes the structural design principles and influence factors of the insulated tube bus, and analyzes the electric field strength and temperature field distribution of the bus line segment, elbow part and intermediate connection based on the finite elements method, taking 10kV/4,000A epoxy injection type as an example. At the same time, the influence of the key design quantities such as conductor outer diameter, conductor diameter, number of shields and thickness of insulation on its structural design is studied, and the foundation is laid for its structural
optimization
the
insulation tube bus is widely used in power systems because of its strong load-carrying capacity, high mechanical strength, excellent electrical insulation performance, good environmental adaptability, good thermal conditions and well-arranged, concise structure, small footprint and other advantages, especially in substations, power stations and other large compound currents as a line and contact line to get a large number of applications.
Because the insulation tube bus is relatively late in China, its awareness is not high, the relevant basic research is weak, coupled with the lack of authoritative standards and related guidance documents for such power equipment, so that the domestic insulation tube bus exists a wide variety of products, material selection, structural design and production processes, product quality and stability are uneven and other outstanding problems. Therefore, it is necessary to account for structural parameters for different types of insulated tube bus to ensure the quality of their products.
Foreign insulation tube bus products are mainly epoxy injection class, its application is the earliest, the technology is more mature, product quality control is strong;
pouring insulated tube-type bus body insulation mainly uses insulation, semi-conductive (sticky) electrical wrinkle paper band winding, and by epoxy resin vacuum impregnation, heating curing, forming an integrated solid insulation.
at the end, through the semi-conductive wrinkle paper layering according to a certain size winding the main insulation, forming a capacitive screen structure similar to that in the casing, to control the distribution of electric field strength, reduce the concentration of electric field strength. The pouring insulated tube bus connector is generally in the form of an insulated shield cylinder connected to the external cover in a conductor.
shield also has an insulating barrel structure similar to the capacitive screen structure, the inner screen is connected to the conductor and other potentials, the outer screen is a ground conductor. Both ends are connected to the body seal, as shown in Figure 1.
Figure 1 Indirect head structure in the pouring insulation tube bus
Epoxy impregnated paper insulation is a composite insulation of insulation paper and epoxy resin, conductors, semiconductor layers and insulation paper after heating and curing, the formation of a dense, compact integrated structure, so it has both insulation paper and epoxy good insulation and dielectural properties.
This paper takes 10kV/4,000A pouring type insulation tube bus as an example, details the accounting and selection basis of its conductor section, the determination of the insulation tube bus insulation thickness and other accounting processes, and analyzes the insulation tube bus conductor diameter, outer diameter (wall thickness), shield thickness, insulation thickness and other key design changes to its conductor surface temperature rise, maximum electric field strength, end field strength and other key parameters.
1 Structural design principles for insulated tube bus
1.1 design principles for tube conductors
The pipe diameter and wall thickness design of insulated tube bus conductors should comply with the requirements of the following factors: electrostation requirements, long-term project tolerance rated current; Mechanical strength requirements, mechanical strength of the tube bus structure under electrical power and mechanical force shock, thermal resistance of conductors under different insulation structures and the perpeable operating temperature of conductors and different insulation under defined conditions, combined with the value requirements of "economic current density", the effect of skin-tightening effects on different current levels, and the requirements of mechanical stability during operation of tube bus stiffness and operation.
In the State Grid Corporation enterprise standard Q/GDW11646-2016 specified the electrical stability requirements of the insulated tube bus, in normal operation of the stable temperature of the tube type conductor should not exceed the maximum allowable operating temperature allowed, generally take 90 degrees C;
For mechanical strength requirements, the tube bus can meet the dynamic stability requirements when subjected to mechanical shock or even short-circuit electrical power, that is, the maximum stress of the tube conductor should not exceed the maximum allowable stress;
Therefore, the accounting of tube conductors mainly includes: according to the rated load flow and tube-type conductors in normal operation relative to the surrounding media allowed temperature rise to determine the preliminary design of tube-type conductor cross-section, which mainly involves loss, thermal resistance calculation and the solution of the thermal balance equation;
1.2 Design Principles for Insulation Thickness
Based on many years of design and operation experience of power cables with similar structures to insulated pipe bus products, it is not appropriate to design the insulation bus thickness from the maximum electric field strength formula alone. The design of the insulation tube bus insulation thickness of 10-12 must take into account the type and size of voltage it is subjected to in practice, process limitations, mechanical strength requirements, and the knock-through characteristics of the insulation material used.
For voltage types, including frequency voltage, operating impact overvolt voltage and lightning shock overvolt voltage, for process restrictions, the voltage level is very low insulation tube bus, due to the thickness of the insulation layer is too small, process conditions lead to difficult to meet the design requirements, for mechanical strength, in the actual manufacturing and use of the insulation tube bus, inevitably affected by mechanical force, especially There is stress concentration in the curved part of the insulation material, so the insulation tube bus must have a certain insulation thickness to meet the mechanical requirements, for the insulation material's knock-through characteristics, including the long-term frequency of insulation material knock-through electric field strength and impact knock-through electric field strength, with the increase of voltage level, the insulation material's knock-through characteristics gradually become the main factor determining the thickness of the insulation layer.
2 Example of structural accounting of insulated tube bus
This paper takes 10kV/4,000A epoxy pouring type insulated tube bus as an example, based on the finite meta-method, the electric field strength distribution and temperature distribution of the insulated tube bus are simulated, and the material parameters required for simulation are seen in Table 1.
Table 1 Insulated tube bus material parameters
According to the structural characteristics of the insulated tube bus, its length compared with the outer diameter can be approximated to an infinite length, so the end of the electric field strength and temperature field can be ignored. The simulation study assumes that there is no temperature gradient in the axial direction of the insulated tube bus, i.e. there is only heat flow transfer up the diameter, and the contact resistance of the components of the insulated tube bus is ignored.
3 The influence of the key design quantity on the design of the insulated tube bus structure (slightly)
the change of the guide diameter, outer diameter (wall thickness), shield thickness, insulation thickness and other key design quantities of the insulated tube bus will affect the design principles of the insulated tube bus, such as the effect on the temperature rise of the conductor surface, the maximum electric field strength, the end electric field strength, etc.
Conclusion
This paper mainly accounts for the structure of the insulated tube bus type of epoxy resin pouring type, and analyzes the design principle of its straight segment, elbow part and intermediate connection head, and analyzes the influence of the design amount of the guide body diameter and insulation thickness on the structure performance of the insulation tube bus with 10kV/4 000A as an example. The following conclusions are drawn:
1) at the bend of the insulated tube bus, the strength of the inner electric field is slightly less than that of the outer electric field.
2) The maximum strength of the electric field increases almost linearly with the increase of the number of shields, and the radial part of the maximum electric field strength has the same trend of change, while the axial weight decreases gradually with the increase of the number of shields.