Design of 33 kV Transformer Bushing Insulator from NR and HDPE

Abstract

This research presents a design of transformer bushing insulation at high-voltage wire connection side. The bushing insulator is made from composite materials between natural rubber (NR) and high-density polyethylene (HDPE). The HDPE has been utilized to increase a weather resistance property of natural rubber, such as ultraviolet resistance, temperature, heat resistance, and so on. The blend ratio of materials depends on NR 60% and HDPE 40%. To study properties of insulator material, it is tested by using ASTM D2240 ASTM D412, ASTM D257-99 and ASTM D149-05 standard. The test results shown that the composite material has a tensile strength equal to 4.28+5.4 MPa, volume resistivity more than 2.14X10[superscript16]cm and surface resistivity about 5.56x10[superscript16] square. This insulation material can be withstanding a maximum AC power frequency voltage about 19.7 kV/mm. In additional to design, the electric field distribution around the bushing insulator is analyzed by using a finite element method (FEM). The highest electric field strength occurs at wire connector and equal to 0.95 kV/mm. Finally, the developed bushing insulator has been installed on 33 kV distribution systems at Saraburi province.