Development Of A Cable Fireproof Monitoring System For Power Plants

The cable fire has been a perplexing problem that imperils the safety inproduction of power plants. The cable fire fighting measures implemented atpresent are all set up on such a basic principle that cable tunnels are devidedinto several close spaces which are relatively independent of each other. In thisway, cable fire spread is restrained and cables are also pretected against the firecaused by other equipment. However these measures fail to prevent a cable fireradically and effectively. This dissertation aims to make clear the reasons and the characteristics ofcable fires, and to further design a cable fireproof monitoring system for powerplants to forewarn about a latent cable fire. It is shown by statistics that the majority of cable fires are caused by cablejoint faults. A cable joint failure is gradually formed and takes a long time fromoverheat to fire. Before a cable catches a fire, a smell of insulation burning andsmoke usually send out. According to such characteristics, a cable fireproofmonitoring system for power plants is developed which operates in real time todetect both the temperature of cable joints and the smoke spreaded in cabletunnels. In this monitoring system, a digital temperature sensor DS18B20 withsingle line and an ion smoke sensor 1412 are implemented as the detectors oftemperature and smoke respectively. An overall design scheme of the system,distribution-concentration-reconcentration, is advanced based on the actualcable distribution in a power plant. A terminal collecting device with an 89C52MCU being its control core is designed to gather the data from the sensors andtransfer them to a PC for processing and displaying. Each terminal collectingdevice can deal with 8 single lines of temperature sensors and 8 ion smokesensors, and each single line can be used to drive several DS18B20 sensors. - II -The collecting device also has a displaying function to show the real-time datafrom the sensors that it drives, thus it has the ability to operate independently. ARS-485 port is equipped in the collecting device, by which serialcommunication with the PC can be realized. The hardware construction of the terminal collecting device is outlined indetails from the aspects of power circuits, smoke sensor circuits, data samplingcircuits of temperature sensors, displaying circuits, communication circuits andso on. The software design for the terminal collecting device is also set forth.The anti-interferance problems in the monitoring system are seriouslydiscussed. Besides, the main points and the matters needing attention forinstalling the monitoring system are explained. The developed monitoring system went into test operation in HunjiangPower Plant in October 2003. Since then, two cases of cable joint overheat hasbeen found and proper measures to avoid fire hazards have been taken in time.The test run results show that the system is reliable and the expected goal isachieved. Thus we have every reason to believe that a cable fire can be stoppedon the whole by combining implementation of this monitoring system with theconventional cable fire prevention measures.