Leakage current monitoring of composite long rod insulators

The Queensland Electricity Commission (QEC) has had over 15 years of field experience with various types of composite insulators on 110 kV to 275 kV lines. Most of the insulators were first generation composites installed in a variety of contaminated environments. In the heavily contaminated areas, various forms of damage to the sheath and sheds were observed and a number of insulators flashed over. These failures have also been experienced in other parts of the world. To gain a better knowledge of the deterioration of the composite insulators over time and to evaluate the pollution performance of the various types of polymers, the QEC developed a sensitive high voltage leakage current monitor and set up a test program for testing these insulators. In the test, a double circuit 275 kV tower situated between two cooling towers at the Swanbank Power Station was chosen for trialing of the composite insulators. The main polymer types, ethylene propylene diene monomer (EPDM), ethylene silicon polymer (ESP) and silicon rubber were tested over a 15 month period. This paper discusses the development of the leakage current monitor and results from the monitoring program