Process Improvement to Restrain Emergency Heating Defect of Composite Insulator

The rod in the composite insulator is a load-bearing component, and glass-fiber-reinforced plastic (GRP) has always been regarded as the most suitable material. However, the investigation reveals that the performance shortcomings of GRP rods are the main cause of emergency heating defects of 131 new 500-kV ac composite insulators in South China. The finite-element simulation is conducted to understand the potential mechanism of heating. It is demonstrated that the holes with moisture distort the electric field, increasing heating power. A hole with moisture in the GRP rod longer than 500 mm could lead to emergency heating defects with temperature rise exceeding 5 K. For the holes in the GRP rod are formed by adjacent voids, the emergency heating defect is inevitable unless the porosity decreases. The fiber infiltration process of the GRP rods is analyzed on the basis of Darcy’s Law, and an improved process is proposed to reduce porosity. Maintaining the mass fraction of fiber by at least 70% and replacing the damp infiltration fluid in time in the production of GRP rods are necessary to restrain porosity. 300-h water diffusion test with a 50-
$\mu \text{A}$
threshold is an effective evaluation method of the GRP rod performance. This method should be used before putting composite insulators into operation.