Fire Spread Characteristics And Identification Method Of Ignition Point For High Voltage Cable Trench Fire In Substation

With the increasing scale of power grid and the increasing number of substations,higher requirements are put forward for the fire safety of power equipment.Due to construction reasons or environmental factors,the insulation problems of trench cables lead to frequent fire accidents,resulting in serious economic losses.It is difficult to judge the early development of cable fire and the location of ignition point from the outside of the trench because of the strong sealing of the trench environment of high-voltage cable in the substation.Therefore,this paper studies the temperature spread law of cable fire in high-voltage cable trench in substation,and then proposes the identification method of ignition point based on ceiling temperature distribution,which provides a means for cable trench fire monitoring.In this paper,the cable laying mode,the fire cause,the fire prevention measures and the ceiling temperature distribution characteristics has been studied theoretically.Combined with the computational principles of fluid dynamics model and combustion model,the finite element simulation software is used to simulate the temperature change at different levels in the trench,the influence of the power of the ignition point on temperature distribution,and the influence of the distance between the ignition point and the firewall on temperature distribution.And a full-size cable trench fire experiment was established,focusing on the study of the influence of the change of ignition point position on ceiling temperature,and compared with the simulation data,a fire point identification method based on ceiling temperature distribution was proposed.The results and conclusions are as follows:1.A simulation model of high voltage cable trench in substation was established,and the spread characteristics of high voltage cable trench fire in substation was studied from two aspects of smoke diffusion and temperature diffusion.The results show that the diffusion of flue gas in the cable trench slows down first and then accelerates.The variation of ceiling temperature is slightly behind the diffusion of flue gas,and the attenuation law is obvious along the longitudinal direction,while the distribution is nearly uniform in the transverse direction.Therefore,the temperature measured at the center line of the trench ceiling can be used as the characteristic temperature to study the law of fire spread.2.The influence of cable ignition point power and cable ignition point position on temperature distribution law of trench ceiling was studied.The results show that the power of cable ignition point has little influence on the temperature distribution of trench ceiling,but has obvious influence on the temperature value.The overall temperature in trench increases with the increase of power of ignition point.When the distance between the ignition point and the firewall is less than 1.5 m,the "mirror" effect makes the maximum ceiling temperature higher than that far away from the firewall.When the distance between the ignition point and the firewall increases,the effect on the temperature rise of the firewall is weakened,but the time when the firewall position reaches the maximum temperature is not significantly affected.3.The identification method of ignition location based on ceiling temperature distribution was studied,and the results show that:Ignition location and power do not change cable trench attenuation of longitudinal temperature of the ceiling.The dimensionless temperature rise and dimensionless distance can be used to fit the attenuation function of ceiling temperature to reflect the attenuation law of trench ceiling.And then,by fitting and analyzing the measured temperature results,a general function formula suitable for the studied cable trench is obtained.Considering the influence of cable trench length on the calculation of ignition point,a fire point identification method based on ceiling temperature distribution is proposed.The relevant research results of this paper are of great significance for safety personnel to master the fire information in the enclosed cable trench and accurately judge the location of the ignition point,which can effectively improve the cable fire monitoring ability in the high voltage cable trench and provide scientific guidance for the safe,stable and reliable operation of the substation high voltage cable trench.