Quality Analysis of Ceramic Insulators Under Electro Thermal Stresses

Abstract

The insulators used in power transmission and distribution networks are expected to withstand continuous electrical, mechanical and thermal stresses under different environmental factors. These stresses may reduce their performances such as surface resistance, flash over voltage and puncture strength. This reduction in characteristics may cause large leakage current to flow on the insulator which leads to degradation of the insulator. The AC insulators leakage current behaviour was studied under various temperature and applied voltage. The general procedure specified in IEC 61325/1995-03 for accelerated ageing tests under electro thermal stresses such as Electrical body resistance (EBR) measurement and thermal runaway (TRA) test were followed for quality evaluation. In the present work, new cap-and-pin type AC insulators from four different manufacturers were used for the study. Two samples from one manufacturer and three samples from another manufacturer were failed in EBR & TRA tests. After the tests, the failed insulator's defective and good region samples were subjected to Scanning Electron Microscopy, Energy Dispersive Spectroscopy and X-Ray Diffractometry tests. It is observed that the presence of more voids and mullite content reduces the dielectric strength of the ceramic insulator and results in puncture. Hence, it is concluded that the EBR & TRA tests may be useful to identify the poor-quality insulators.