Abstract: Aging and overloading of high-voltage cables increase fire risks and seriously threaten the safety of power systems. During cable fire spread, melt drip burning can ignite underlying cables, accelerating fire propagation. This study used 110 kV flame-retardant cables as test materials to conduct TG-DSC analysis on the cable sheath and carried out melt drip burning experiments under different spacing conditions. Parameters including droplet mass, cable temperature, droplet flame radiation, and dripping frequency were measured and analyzed. Thermogravimetric results indicate that the pyrolysis process of the flame-retardant sheath mainly consists of two mass loss stages. Pyrolysis begins at approximately 400.0 °C, while melting starts near 420.0 °C. During fire spread in high-voltage cables, the molten sheath drips and burns directly below the cables, forming a more intense three-dimensional fire. Due to the large diameter of high-voltage cables, cracking and detachment of the char layer formed by the flame-retardant material exacerbate dripping combustion. The mass of melt drip residues accounts for about 17%~30% of the total cable mass loss. The distribution of melt drips from high-voltage cables is scattered and highly random. Dripping behavior can be divided into two zones: frequent dripping zone (f ≥ 1) and infrequent dripping zone (0< f <1).

Key words: cable spacing, fire spread, melt drip, dripping frequency