Three-dimensional FEM Electrical Field Calculation for FRP Hot Stick during EHV Live-line Work

In February and December 2012, SaskPower experienced two flashovers of "clean" Fiberglass-Reinforced Plastic (FRP) hot stick during cold weather live-line work under steady-state 230 kV ac system conditions. As for SaskPower, Manitoba Hydro had two separate live-line tool flashover events, in 1997 and 2002. Clean-fog tests and non-uniform wetting tests at Hydro-Quebec Research Institute (IREQ), and cold-fog tests at Kinectrics and UQAC were carried out to explain these flashovers. The laboratory tests demonstrated that inadvertent contamination of clean tools at a very light level (similar to 2-3 mu g cm(2)) of Equivalent Salt Deposit Density (ESDD) likely reduced voltage withstand capability of FRP hot sticks, particularly under freezing conditions. The flashover mechanism was identified when surfaces become fully wetted by the environment or surrounding fog. However, the source of moisture in field flashovers well below 0 degrees C, i.e. as low as -19 degrees C, was not identified. This study is based on laboratory tests and on using available pollution flashover models to explain the results. In this paper, the main objective is to determine the potential and electric field distribution along a FRP hot stick under dry condition and non-uniform wetting. A commercial software, COMSOL Multiphysics (TM), based on the finite element method (FEM), was used for the three-dimensional modeling and simulations. The results obtained will be useful to improve knowledge on the determination of discharge initiation conditions based on electric field distributions along a FRP hot stick.