All types of Composite insulators with crimped end fittings used on the overhead power lines or substations. The mechanical strength of Composite insulators with crimped end fittings is important.
Abstract:
The purpose of this research has been to design an advanced numerical model that can be used to evaluate the mechanical behavior of Composite insulators with crimped end fittings subjected to axial tensile loads. Two issues have been addressed in this study.
First, examples of insulator failure due to improper crimping have been shown and discussed. Second, comprehensive non-linear two- and three-dimensional finite element simulations of crimped insulator ends have been performed. The effects of uniformly and linearly distributed crimping deformations as well as external tensile loads on mechanical stress in the insulator have been examined. Numerical results have been compared with the experimental data obtained by performing tensile strength tests on crimped insulators supplied by Orient. It has been shown in this research that the type of crimping can significantly affect the mechanical strength of crimped composite insulators.
For the same magnitude of crimping and the friction coefficient at the rod/fitting interface the load/displacement diagrams are strongly dependent on the crimping profiles generated during the manufacturing process. The highest radial and tangential stress concentrations in the composite rods exist due to crimping. However, the stresses are reduced if a crimped composite insulator is subjected to axial tension. At the same time, the normal stresses along the rod are significantly increased when the rod is being pulled out of the fitting.
The concentration of the normal stress along the rod is significantly affected by the magnitudes of applied compression and axial tensile loads as well as the type of compression profile on the rod surface generated during manufacturing. It has been clearly shown in this research that the mechanical behavior of crimped composite insulators can be evaluated by performing finite element computations considering the actual crimping deformations and the geometrical and physical properties of the insulator end.
Composite suspension insulators with crimped end-fittings
Composite suspension insulators are used in overhead transmission lines with line voltages in the range 69kv to 735kv. The insulators consist of unidirectional E-glass reinforce polymer (GRP) rod with two metal end-fittings attached to the rod during assembly. In order to prevent electrical degradation of the GRP rod and the electrical leakage currents, the entire surface of the GRP rod is protected by a layer of rubber alloy with multiple weathersheds. The rubber also protects the rod against corrosive environments which can be present in-service. The primary function of the end-fittings is to provide a mechanical link and to transfer loads from the high voltage conductor to the GRP-rod (at the line end), and from GRP rods to the tower (at the tower end).
In previous designs the fittings were attached to the GR{ rod either by an epoxy adhesive (epoxy cone design) or by metal wedges inserted into the rods inside the fittings (wedge design). However, due to a lower cost of assembly, most insulator manufacturers have adopted the crimped onto end-fittings design. In crimped design, the end-fittings are radially compressed onto to the ends of rods. This results in a purely mechanical bond caused by residual compressive stresses at the interface between the GRP-rod and the end-fitting.
Since composite insulators are relatively new product, few published studies have examined their mechanical performance and design. In this research, non-linear finite element computations have been performed to examined the effect of various crimping conditions on the mechanical strength of crimped composite insulators. internal stresses in the insulator ends have been determined for various crimping conditions, external applied load as well as elastic and elasto-plastic properties of the fitting material.
Composite insulators with crimped end fittings are normally providing mechanical load. This property is affected by fittings materials, such as steel or iron.
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