Relationship between Leakage Current and Diameter of Composite Insulators during the Early Period of Tracking Wheel Test

The tracking wheel test described in IEC Technical Report 62730 provides a method for composite insulators to assess their resistance to tracking and erosion in order to reject materials or designs which are inadequate. However, the method is only suitable for long rod insulators and some other insulators with relatively small diameters. Because for large-diameter composite insulators, such as post insulators and cross-arms used in ultrahigh voltage systems, hollow core insulators etc., their surface resistivity is smaller than that for small-diameter ones, therefore leakage current is larger under the same test conditions, which may cause tracking and erosion of large diameter composite insulators to appear earlier, and more serious. In addition, it's rather difficult to make the large…