Qualification Testing of Insulated Aerial Devices Rated 69 kV and Below

Laboratory and field measurements were made at the American Electric Power System facilities to compare the three methods commonly used in the industry for testing insulation of an aerial lift device rated for live-line maintenance work at 69 kV and below. Charging current was measured into the bucket of an insulated 69 kV aerial lift truck, from the truck body to ground, and from permanently installed electrodes in the insulating boom section. The results from one set of field measurements on a 69 kV transmission line compare the three methods, for which current values were 400 µA, 168 µA and 8 µA, respectively. Of the three methods used, the permanently installed electrodes is the only method that adequately approaches the true leakage current through the boom insulation. Tests also demonstrated that the addition of a shield over the electrode (collector band) increased the measurement resolution by reducing the current reading by about 50%.