Ampacity Calculation of 27.5kV Single-phase Single-core Cross Linked Polyethylene Power Cables in Electrified Railways

We numerically researched the ampacity of 27.5kV single-phase single-core power cables that were used in traction substation.The operating condition was analyzed based on calculations of the circulation loss and eddy current loss of the cable under single-phase and three-phase conditions respectively by using the finite element modeling(FEM)method.A more accurate ampacity calculating model of the cable for cases with single-phase power supply was established by modifying the degree of freedom of the calculating unit and by coupling the thermal analysis of calculation the temperature distribution.On the basis of the model,according to the actual environment of railway cable,changes in the cable ampacity were analyzed in different grounding connections,cable distances,loop numbers,thermal resistances of surrounding media and environment temperatures.Several conclusions can be drawn as follows:for a cable with sheath layers grounded in two terminals,its circulation loss in single-phase mode is 75% more than that in three-phase mode,while the phase condition has little effect on cables with sheath layers grounded in one terminal;the distances between cables,the thermal resistance of surrounding media,and the environment temperature affect the cable temperature seriously;with the increase of cable loops,the temperature of the cables in the middle of the cable loops rises obviously which will result in an overall ampacity decrease of the cable group.