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The underground power cable joint is the weakest part of the power system,which significantly influences the safe operation of power system.From the fire accidents caused by overheating of cable connector,its developing rate is slow,and its lasting time is longer.The on-line monitoring of cable joint can effectively prevent and reduce the cable fire accidents.From the published material,there are many difficulties in online monitoring for power cable joints such as difficulty of power supply for monitoring device,the limitation of data transmission distance,the need for a large number of field constructions etc.Due to these reasons,the current on-line monitoring systems for power cable joints mostly are only suitable for power plants and transformer substations.Current monitoring devices for power cable joints in branch box have problems such as inconvenient installation,complicated maintenance,high cost and other issues,which restrict its application.Based on these factors,in view of the characteristics such as large quantity and wide distribution of power cable joints in urban districts,this thesis preliminary puts forward a type of on-line fault monitoring and early warning system design.Moreover,the distributed measuring system usually used at present is only suitable for a relatively small scope within an enterprise.For the power distribution network in urban or the border district,especially those of laying method of direct burying underground,quantity of joints,long distance and complex wiring,the traditional system appears helpless.By taking in account all above mentioned factors and bottlenecks appeared in the design of on-line monitoring system of power cables,In this thesis,the real-time powercable fault monitoring system has been designed and implemented,which uses analog sensors for temperature and ground current fault detection embedded in the joint,a microcontroller based data processing system which collects the data from analog sensors and sends the cable data after digital conversion to the host though intemet.The web-interface(designed in HTML)displays the real-time measurements on the host PC accessed via IP(Internet Protocol)address of the monitoring system.The system realizes the low-cost,reliable and real-time power cable failure monitoring system for underground power cable system.