Developing a smart monitoring system for leakage currents from insulators on wooden poles
Creators: name: Sokolowski, Peter
Publisher: name: RMIT University
Year: 2024

description: In Australia and many other countries, power distribution lines are carried on wooden poles. These lines suspended on insulators, which are fixed to wooden poles, pass cities as well as bushlands. Under different weather conditions, insulators become contaminated, and in particular, with damp weather, these insulators lose their ability to provide a perfect insulation between the high voltage conductor and the ground (through high impedance objects such as wood). A leakage current, small in magnitude, starts flowing from the high voltage conductor to the ground across the polluted insulator and through the wooden pole. If this phenomenon continues over some time, the currents start heating the wood where there is an abundance of wood-to-metal contact. At a certain stage, it will start smoking and this may lead to a pole fire. The obvious consequences of this are the loss of power to customers, public safety hazards and potential disasters such as bushfires.<br><br>This thesis aims at determining which measure or combination of measures of leakage current are best suited for creating a ‘Leakage Current Health Index’ (LCHI) that can be later used to provide a power system operator with health status for a feeder or system, indicating how urgent a response is needed.<br><br>To achieve this goal, the impedance characteristics of wooden poles altering the leakage current from insulators are investigated to better understand the role of wood in leakage current signatures. The effective impedance of wood used for poles in Victoria, Australia is established for the first time. Examining the impedance properties of typical Copper Chromium Arsenate (CCA) impregnated wood for 66 kV distribution poles shows dangerous conductance properties of wood at this voltage, providing an explanation for these poles catching fire at triple the rate of 22 kV distribution poles. After a systematic investigation of wood used for poles, a typical impedance characteristic is established for a weathered CCA impregnated wooden pole operating at 22 kV under both dry and wet weather conditions.<br><br>Next, the leakage current from a single high voltage insulator is examined for various contamination levels and under different weather conditions. A new nonlinearity measure is established which utilises the Pearson correlation coefficient to measure the degree of leakage current nonlinearity and to build leakage current profiles of a single insulator under different conditions prior to flashover. Several fractal dimensions are also considered for the first time to measure characteristics of the leakage current profile of a single insulator. These measures are able to quantitatively differentiate between various levels of insulator contamination and different weather conditions, showing an enhanced level of nonlinear activity in the stage prior to insulator flashover.<br><br>After developing an understanding of a single insulator, systematic modelling is used to build measure profiles of leakage currents for a simple power line, a lossless power line and a lossy power line. Finally, power utility zone substation data for a pole top fire are examined to verify the validity of the profiles observed utilising the measuring techniques determined suitable for establishing a LCHI.