Cable Tunnel Fire Modeling And Linear Temperature Sensing Fire Detector Study

With the rapid improvement of China’s modernization, electrical power is applied in industry more and more widely and power transmission security issues aroused great attention. But the cable tunnel fire occurred frequently, which bear long-distance power transmission, and the harsh environment in cable tunnel causes difficult fire fighting, easy resurgence, long-time fighting and big loss.In recent years, fire detection technology continuously improve and new technologies come out one after the other, especially fiber Raman fiber grating fire detection technology and thermal fire detection technology that base on optical fiber sensing technology. Since their outstanding technical advantages, they have displaced traditional fire detection technologies in explosive areas including petroleum and petrochemical and harsh environment including road tunnels. However, due to the complex structure of the cable tunnel and fire causes, existing fiber thermal fire detection technology can not be used directly in the cable tunnel fire detection. Aiming at the issues of the lack of cable tunnel fire early stage model and the lack of design basis for new fire detection technologies in cable tunnel, this paper establish theoretical model for cable tunnel, calculate temperature distribution for different fire scenes, study the response of different linear heat detectors in different fire scenes reproduction experiments, fix theoretical models combining with experiment results to guide the standard establishment for the detector installation, application and acceptance check.Firstly, the theoretical basis, detection mechanism and product specifications of existing fiber Raman and FBG temperature fire alarm systems are studied, which are analyzed and compared in terms of environmental factors and fire detection factors. Then, statistical analyzing existing fire cases, the fire is divided into cable over-heating fire, small-scale fire and large-scale fires and fire scenes reproduction programs are developed. Investigating cable tunnel application environment for fiber temperature sensing fire detection technology, application environments transfer model is established to calculate and analyze the temperature distribution and dynamic trend for different fire scenes. According fire temperature field prediction from heat transfer model and understanding of existing fire detection technologies, experimental program is developed and experimental platform is established in real or rebuild industrial environment. Finally, technical indicators of fire detectors in different fire scenarios simulation are analyzed, comparing temperature field differences between experimental and theoretical models are compared and their causes are analyzed to modified heat transfer model and optimize the experimental program and detector installation or setup parameters. The conclusions are following:1) overheating cable only affects its layer where neighboring cable temperature will rise, but effects to adjacent lower and upper layers is little. Only detector that lay on layer and contact directly could detect the temperature change of the cable and give alarm signal effectively.2) Since heat release rate and thermal radiation of small-scale fire are low, the temperature at fire location increases rapidly and then decreases gradually. Because its affected area is small and occurrence location is uncertain, every installation method has detection blind spots.3) Large-scale fire will cause temperature rapid increasing in the top of tunnel and the increasing rate will reach30℃/min just above the pool fire location. Linear fire detectors can be suspended under the tunnel ceiling. The distance setting between two FBG temperature detection units does not exceed6m, differential temperature alarm function is suitable and heating rate alarm thresholds can be set to5℃/min.The main research results and innovation of this paper is to:1) three typical cable tunnel fire simulation scenarios including cable overheating fire, small-scale fire and large-scale fire and experimental data acquisition system are established in a physical cable tunnel;2) Based on finite element heat conduction analysis, cable tunnel different fires temperature model are established, through simulation and modeling experiments, temperature field distribution and variation of simulation and experimental results are analyzed and installation and using design specifications for optical fiber temperature sensing fire detection system in cable tunnel are proposed;3) through three typical cable tunnel fire simulations establishing a heat transfer model of the early stages fire, according to this model, it can estimate different fire scenarios in the temperature field distribution and variation.