Development The Monitoring Device And Thermal Protection Of The Electric Section Cable Joint Based On PTC

In power systems,system faults and accidents caused by power cables are increasing every year,at the meantime,there were several accidents happened in recent years and those are power cable burned along railways.These accidents make negative influence to the power system stability dramatically.From investigations of those power cable burned accidents,found that the fault position is at the cable joint in most cases.Therefore,running a real-time monitoring on operation states of those power cable joints along railways and inventing over-heat protection devices for those cable joints will reduce the risk of cable burned-out magnificently.At first,this paper introduced the structure of power cables and causes which lead to the burned up of power cables.Then analyzed the influence to the power cable along railways from two aspects,traction currents and traction return currents.Build up the model of the induced voltage caused by the traction current and power cables nearby traction power grids and the electric potential model of traction return currents and power cable grounding poles.From the analysis and those two models,and analysis those influences to the protection layer of double side grounding cables.Then,according to characteristics of the cable joint burned out,developed a cable joint current limiting device which uses the PTC thermistor as the protection component.Moreover,build up a power cable test platform which tells the relationship between the current in the cable and the cable temperature.Get the temperatures of the conductor and the protection layer of the cable to set the overheat-warning threshold value of the cable monitoring device.Finally,develop a cable-joints monitoring device which has an ATmegal280 CPU and use CPRS/GSM network for communication.This monitoring device collects information including cable-joints temperatures,grounding currents,induced voltage at cable-joints and locations from the GPS.This device working on a real-time monitoring of cable-joints operation states and sending out monitoring data at a set time period.A warning massage would be sent out to assigned mobile phone numbers when the device discovers abnormal operation states of cable-joints.The device could help the maintenance team to find the problem location quicker,thus,reducing the risk of the power cable burned out.The prototype device has already been used in Ankang power section of the Xi'an Railway Bureau and its functioning well.