Shielding efficiency of conductive clothing during live-line maintenance

Nowadays live-line maintenance (LLM) is one of the most common methods to repair and maintain energized elements of the power grid. The main advantage of this technique that it represents a balance between technical and economic factors: no consumer disturbance is needed, there is not any service outage caused and losses can be kept as low as possible. Because of these reasons different live-line methods are becoming more and more popular on all voltage levels. Special techniques are available for low, middle and high voltage grids. On high voltage levels “barehand method” is widely applied worldwide. The main principle of this method is an enclosed metal surface around the worker acting as a Faraday cage. Inside an ideal Faraday-cage electric field is zero from outer source. The efficiency of a clothing mainly depends on the size of holes (so called “Faraday-holes”) on the surface. A proper face mesh can guarantee the safety of the live-line worker. Calculations, simulations and measurements in the High Voltage Laboratory of Budapest University of Technology and Economics have proved that poor, coarse or missing face shield decreases the efficiency by the increase of body current.