LADWP Electric Station Operator – Circuit Breakers, Disconnects, Transformers Practice Test

Porcelain fragmentation from fault currents happens when the insulating glaze on a porcelain surface is driven into breakdown by the energy of the fault. The HV conductor in equipment like transformers passes through bushings that are made with porcelain to insulate and seal the lead through the enclosure. During a fault, intense current and transient voltages can cause surface discharges (tracking) along the porcelain, especially if the surface is contaminated or moist. This arcing along the surface deposits heat and mechanical stress, causing the porcelain to crack and break apart. The surface involved is the porcelain insulation on the bushing, which is why the bushing is the correct choice. The other components don’t present the same porcelain surface in this context, so they aren’t the source of porcelain fragmentation.