Analysis and calculation of ampacity of 10kV cables in pipes under transient conditions

It is one of the most important that the cable ampacity correctly under transient conditions is defined to guarantee the safe operation of cable. In this paper, the calculation of cable ampacity is based on the method provided by IEC60287 and IEC60853 standard. An ampacity calculation program for screened 10kV XLPE cables, based on the thermal circuit technique, is developed in MATLAB language. By using a technique based on chord secant method, the calculation of ampacity under transient conditions also becomes available. We can better balance between the running speed and the calculation accuracy by this method when if the calculating step is tm/180 (tm is the cut-off time). As the results show, the longer the cut-off time, the smaller the difference between the calculation result and the ampacity under steady condition. In addition, the initial iteration current, the load current will also influence the transient calculation process. Calculation based on secant method of ampacity under transient conditions meet the engineering demands of real-time, accuracy and easy operating to the utmost extent, and greatly facilitated the engineering and technical personnel.