Effect of the Thickness of Polyethylene Insulation on Flame Spread over Electrical Wire with Cu-core under AC Electric Fields

Effects of applied electric fields on downward and upward flame spreads (DFS and UFS) over polyethylene (PE) insulated electrical wires with Cu-core are investigated by varying the applied voltage (VAC) and frequency (fAC) at various inclination angles (8). With AC electric fields, FSRs are influenced appreciably by complex dynamic behaviors of molten-PE and flame. For the DFSs, the FSR with 8 exhibits increasing, decreasing, and increasing trends. For the UFSs, the FSR with 8 shows an increasing tendency, along with dependencies on VAC and fAC. Further analyses are conducted at 8 = +/- 70 degrees. For the DFSs, the globular molten-PE size, the distance between flame front and globular molten PE, and electrospray influence FSR. For the UFSs, downward flow of molten-PE in some cases increases FSR. While the strong downward flow causes a flame detachment from the main body of the flame and/or a merging phenomenon between molten-PE drops, reducing FSR. A serious of bulged flames due to electrospray increases FSR. These FSR behaviors for DFS and UFS are well characterized with their related physical parameters. Flame extinction occurs only for DFSs with NiCr- and Cu-core. The critical extinction frequency for DFSs is characterized with log (fAC,ext) = a x VAC + b.