Numerical Simulation Of Cable Combustion Process In Urban Underground Utility Tunnel Under Internal Heat Source

As the lifeline of the city,the emergence of utility tunnel has realized the full utilization of urban underground space and the intensive management of urban pipelines,which achieves the goal of saving resources and protecting the environment in the modernization construction,and provides a new model to solve the contradiction of urban infrastructure construction.However,the large accumulation of fire loads inside the utility tunnel,the narrow and long spatial structure,and the semi-closed conditions lead to serious casualties and property losses once a fire accident occurs.Therefore,the study of cable fire inside the utility tunnel is a very important subject.Based on FDS three-dimensional heat transfer and pyrolysis model,the internal heat source fire process of 15 k V XLPE cable in utility tunnel is modeled and analyzed.As the initial stage of utility tunnel fire,the combustion process of single cable under internal heat sources shows that the under the same conditions,with the increase of heat source power,the fire risk of cable increases;The change of insulation type will affect the cable fire in two aspects: heat dissipation and flammability;Strong thermal conductivity of cable core materials can significantly reduce the rate of heat accumulation inside the cable and reduce the probability of fire;Depending on the judgment basis,the "heat dissipation/preheating" effect of the cable core material will also be different.At any time,blocking the power supply in time can restrain the occurrence and development of the fire to a certain extent and reduce the degree of fire hazard;Appropriate ventilation conditions have a certain ’ quenching ’ effect,but with the deepening of the fault degree,’ quenching ’ wind speed increases gradually.As the development stage of utility tunnel fire,the combustion process of cables in local space under internal heat source conditions shows that the spacing between horizontal and vertical directions can affect the combustion process of multi-layer cables.Reasonable horizontal and vertical spacing can well inhibit the occurrence and development of fire,minimize fire hazards,and increase the response time for emergency rescue;With the increase of horizontal / vertical spacing,the risk of ignition source cable to the surrounding cable gradually decreases,and the diffusion and flammability of cable fire gradually decrease.With the deepening of the fault degree,the influence range of horizontal / vertical high temperature of the ignition source cable increases,but the upward trend is gradually flat.Within the scope of the study,the reasonable horizontal spacing of 15 k V XLPE cables is twice the diameter;the vertical spacing should be the maximum value based on actual conditions.