| The improvement of the development level of the power system has led to the widespread use of power cable tunnels in the power system.Cable tunnels provide convenience for the protection of cables and the operation and maintenance of power systems,but they also bring many problems,such as frequent cable fires caused by various factors that cause insulation defects in power cables.Therefore,cable tunnel fire prevention and early warning technology is playing an increasingly important role in the power system.However,cable tunnels are deeply buried underground and have strong sealing properties.In the event of a fire,the performance of tunnel fire prevention measures is insufficient.In addition,existing early warning technologies are delayed in determining the fire situation,making it difficult to accurately determine the location of the fire and the magnitude of temperature rise,often resulting in significant losses.In order to solve the above problems,this paper starts with the fire spread characteristics of cable tunnel,and explores the longitudinal temperature distribution law and vertical temperature distribution law of cable tunnel fire;Determine the laying conditions and environmental conditions with strong fire resistance performance;Propose fire prevention methods for cable joint compartments,providing new ideas for cable tunnel fire warning technology;According to the law of temperature rise at the top of the tunnel,a method of fire source location and maximum temperature prediction in the cable tunnel based on double exponential function is proposed.This article establishes a 1:1 full-scale cable tunnel fire experimental platform and restores common environmental conditions of underground power cable tunnels.Experimental analysis was conducted on cable tunnel fires under different laying conditions.Through a series of experimental results and data analysis,the conclusions obtained are as follows:(1)The common cable tunnel environment was restored through the 1:1 full size cable tunnel fire experiment platform,and the fire spread characteristics of the cable tunnel were studied.The fire spread characteristics mainly focused on the longitudinal temperature distribution and the vertical direction temperature distribution.The results of exploring the longitudinal temperature distribution of the cable tunnel fire showed that the longitudinal temperature distribution showed an obvious step change,and the temperature of the tunnel ceiling decreased with the increase of the distance from the fire source.Within the same length range,the difference in temperature rise amplitude in the length range closer to the ignition source is more significant.There is an obvious temperature stratification phenomenon in the vertical direction temperature distribution:that is,the vertical direction temperature distribution also presents an obvious step change,and the temperature in the tunnel increases with the increase of the vertical height.(2)Exploring the fire and flame retardant effects of different laying conditions and cable joint compartments in cable tunnels,combined with a series of data on temperature field changes and toxic gas concentration changes in power cable tunnel fire experiments,the results show that in order to suppress the spread of cable fires,the cable laying layer spacing should be selected to be 0.35m to 0.40m in terms of setting tunnel cable interlayer spacing;In terms of setting tunnel ventilation speed,it should be avoided as much as possible to set the ventilation speed under the condition of hump wind speed;When studying the impact of the laying method of fire barriers on the fire resistance and flame retardancy,it can be concluded that the overall fire resistance effect is better when the fire barrier is located above the cable than when the fire barrier is located below the cable;When exploring the impact of cable layout on fire resistance and flame retardancy,the "one" parallel layout method has a significantly better fire resistance effect than the "product" triangular layout method.At the same time,in response to the frequent cable tunnel fire accidents in recent years,a cable joint compartment has been designed on the basis of traditional cable tunnels to optimize fire prevention in the cable joint area inside the cable tunnel.By comparison,it can be concluded that the cable joint compartment uses calcium silicate material as a fire barrier,and the parameter configuration with a aspect ratio of 3:1 is the optimal solution among various schemes to suppress fire spread,reduce post disaster tunnel temperature rise,and reduce post disaster toxic gas concentration.(3)A double exponential function prediction method for the fire source location and internal temperature extreme value of cable tunnel is proposed.The calculation results show that the fire source positioning method in the cable tunnel can better reflect the position of the fire source point.By using this method,the maximum distance deviation between the calculated fire source position and the actual result is 0.071m,the average distance deviation is within 0.058m,and the average accuracy is 98.13%or above.The fire source positioning method in cable tunnels can accurately identify the location of the fire source.A method for predicting the extreme temperature inside a cable tunnel has been proposed,which can effectively predict the maximum temperature inside the cable tunnel.After using this method,the calculated temperature extreme value in the cable tunnel deviates from the actual temperature extreme value by 6.9 ℃,the average temperature deviation is 5.7℃,and the minimum temperature deviation is 4.5℃.The average accuracy is 99.17%.This method is of great significance for mastering the extreme temperature values of fire in cable tunnels.The relevant achievements of this article have important supporting significance for fire prevention and flame retardancy in cable tunnels,accurate warning,determination of fire source location,and can effectively improve the effective grasp of fire information by operation and maintenance personnel in tunnels,and enhance the sensitivity of warning devices in cable tunnels to fire,providing scientific guidance for the stable and safe operation of cable tunnels and even the power system. |
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