131 / 2018-08-24 23:59:06

Discussion on the Formation and Action Process of Interfacial Stress between the Center Conductor and the Basin Body of the UHV Spacer Used in 1100kV GIS

UHV; GIS spacer; interfacial effects; shear stress

The Ultra High Voltage (UHV) spacer is an important component in gas insulated switchgear (GIS) and gas insulated transmission lines (GIL) and its typical insulation structure exists in power equipment. The spacer consists of a central metal conductor and epoxy insulation composite. When the voltage level of power system rises to 1100kV, the insulation strength requirements of the GIS spacer are also increased. For improving this, the method of size amplification of the low voltage class spacer is usually adopted but the mechanical strength of the spacer will decrease at the same time. In this paper, the failure mode of the UHV spacer after the water pressure failure test is analyzed. In the hydrostatic failure test, the mechanical damage of UHV spacer often initiates from the interface between center conductor and insulation material. The bonding strength of the epoxy resin/alumina composite material and the central metal conductor at room temperature is measured, the value reaches 11.24 MPa, and the standard deviation is 2.85 MPa. In order to find the reason why the mechanical strength of the spacer is low, the stress of UHV spacer during the hydrostatic test must be analyzed. In this paper, by Using finite element software, the stress distribution of the spacer during hydrostatic test has been simulated and calculated. when considering the effect of water pressure on UHV spacer, it is not enough to damage the interface. Therefore, it is estimated that there are other stress contributions at this interface, it is mainly introduced by its production process. In the production process of the spacer, the introduction of stress at the interface mainly is through two ways. On the one hand, during the pouring process of the spacer, the epoxy resin solidifies and shrinks, and stress generates inside it and at the interface of the conductor. On the other hand, after the epoxy resin is cured, it needs to be cooled from the curing temperature to room temperature. Since the coefficient of thermal expansion between the conductor and the epoxy resin does not match, there is a difference in the amount of shrinkage between the two in the process of cooling, so interface stress generates at the interface between the two. After the production of the UHV spacer is completed and dropped to the room temperature, the first principal stress at the interface may reach 26.9 MPa, but it is not enough to cause direct crack of the spacer. The maximum axial and radial shear stresses at the interface may reach 15.8 MPa, which is much larger than the shear strength of 11.24Mpa between the insulation material and the center conductor measured by the standard sample. It can be seen that the shear stress at the interface is the main factor causing large-area peeling at the interface after the hydrostatic test. Therefore, effective measures must be taken to relieve the interfacial stress between the center conductor and the insulation material. Similar to the interfacial stress problem in UHV spacer, it is also present in other power equipment. The research method of this paper can be used to analyze these similar heterogeneous interfacial stress problems, which lays a theoretical foundation for solving the interfacial stress problem in the future.