Experience with electrical testing of aerial devices for use at 69–500 kv

Since 1982 Manitoba Hydro has been making periodic electrical tests on the booms of aerial devices used by live line crews at 69 - 230 kV. In 1992 the test voltages were increased to allow use of the booms at 500 kVdc. At that time the importance of appropriate cleaning and recoating of the booms was emphasized. In 1997 and again in 2002 a FRP hot stick flashed over during live line work from a structure at 500 kVac. The related investigations and testing were initially focused on the FRP hot sticks, but were extended to include the booms of aerial devices. A flashover mechanism termed a “fast flashover” was identified which can occur without prior leakage current and at relative humidity as low as 53% when the FRP surface is stressed with direct voltage of negative polarity. While corrective measures have been identified for the FRP hot sticks, work continues to address the reliability of booms for use at 500 kVdc.